INOM EXAMENSARBETE SAMHÄLLSBYGGNAD,AVANCERAD NIVÅ, 30 HP

, STOCKHOLM SVERIGE 2018

Application of Dynamic Grouting to Improve the Grout Spread Using Varying Aperture Long Slot (VALS)

AN EXPERIMENTAL STUDY

ROBABEH HOSSEINI

STEVEN YALTA

KTHSKOLAN FÖR ARKITEKTUR OCH SAMHÄLLSBYGGNAD

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Application of Dynamic Grouting to

Improve the Grout Spread Using

Varying Aperture Long Slot (VALS)

AN EXPERIMENTAL STUDY

ROBABEH HOSSEINI

STEVEN YALTA

KTH ROYAL INSTITUTE OF TECHNOLOGY

S C H O O L O F A R C H I T E C T U R E A N D T H E B U I L T E N V I R O N M E N T

DEGREE PROJECT IN SOIL AND ROCK MECHANICS, SECOND CYCLE

STOCKHOLM, SWEDEN 2018

Application of Dynamic Grouting to Improve

the Grout Spread Using Varying Aperture Long Slot (VALS)

AN EXPERIMENTAL STUDY

Robabeh Hosseini & Steven Yalta

Stockholm, 2018

© Robabeh Hosseini & Steven Yalta, 2018

Master of Science Thesis

KTH Royal Institute of Technology

School of Architecture and the Built Environment

Department of Civil and Architectural Engineering

Division of Soil and Rock Mechanics

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Preface

The research work presented in this Master of Science thesis has been carried out during January-

October 2018 in collaboration between Research Institute of Sweden (RISE) and Division of Soil and

Rock Mechanics, Department of Civil and Architectural Engineering, Royal Institute of Technology

(KTH). The Rock Engineering Research Foundation (BeFo) has financed the research.

The research study has been conducted in close collaboration and under supervision of Dr. Ali Nejad

Ghafar to whom we are very grateful for his precious guidance, support, and patience during the

performance of the laboratory tests and for providing valuable guidance and encouragement at

various difficulties during the progress of this project.

We would also like to express our appreciation to our supervisor Dr. Almir Draganović, one of the

most well-known scientists in the area, for his valuable scientific advices. Special thanks to our

examiner Prof. Stefan Larsson for his support and determined advices. We would also like to thank

Dr. Patrick Fontana for providing us the opportunity to pursue this research project.

Stockholm, October 2018

Robabeh Hosseini & Steven Yalta

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Abstract

In the past centuries, grouting has been one of the most common techniques in geotechnical

engineering to strengthen and seal underground structures. Concerning increasing demands for

tightness and cost efficiency, cement-based grout has been one the most frequent used materials. One

of the first grouting operations is the work done by Charles Bérigny in France back in 1802 in order

to repair a sluice by stabilizing the ground with liquid grout. Several studies have been then conducted

in grouting, which have contributed into successful improvement of the grouting operations. The

investigations have also extended the understanding of the factors such as choice of materials, choice

of equipment, and the applied pressure type and magnitude, etc. that influencing the grout spread in

rock fracture systems.

Among the factors, the applied pressure is one of the most significant ones influencing the spread of

grout during grouting operations. Grouting at static pressure conditions is the most common method

used in field, where in practice the injected grout can only penetrate into the rock fractures wider than

100 µm.

Recent investigations conducted on application of static and dynamic pressure conditions, using

Short Slot and Varying Aperture Long Slot (VALS) in the lab have yielded an overall improvement of

the grout spread under dynamic pressure conditions rather than the conventional static pressure

conditions. However, the efforts conducted are just a beginning, especially in very fine micro factures

smaller than 70 µm

The main objective of this investigation was therefore to improve the spread of grout by dynamic

grouting into fractures smaller than 70 µm effectively, which could not be done with grouting at static

pressure conditions. Furthermore, the aim was to investigate filtration and erosion phenomena/

tendency of grout flow during static and dynamic pressure application using Varying Aperture Long

Slot (VALS) in the lab. The durations of peak and rest periods used in the experiments were 2s/2s and

1s/5.5s, which were equivalent to 0.25 Hz and 0.15 Hz, respectively. The results of dynamic grouting

showed up to 10 times improvement in the volume of passed grout through fracture apertures smaller

than 70 µm.

Keywords

grout penetrability, filtration tendency, varying aperture long slot, sealing, cement-based grout,

dynamic grouting

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Sammanfattning

Injektering är en av de vanligaste metoderna som använts för att förstärka och täta geotekniska

konstruktioner. När det gäller ökande krav på täthet och kostnadseffektivitet har cementbaserade

bruk varit ett populärt förbrukningsmaterial. Injektering användes förmodligen först av Charles

Bérigny i en slussreparation i Frankrike under 1802 där marken stabiliserades med hjälp av flytande

injekteringsmaterial. Flera studier har sedan dess utförts inom injekteringsteknik, vilket har bidragit

till en framgångsrik förbättring av injekteringsoperationer. Dessa undersökningar har också utvidgat

förståelsen av faktorer såsom materialegenskaper, val av utrustning, provprestanda, trycktyp och

storhet som i sin tur påverkar brukets spridningsförmåga i bergets spricksystem.

Forskningen inom bergtätning fokuserar bland annat på att utveckla tillämpningen av statisk och

dynamisk tryck vid injektering. Tillämpning av statiskt tryck är den vanligaste metoden för

injektering ute i arbetsfält, där den injicerade bruket i praktiken endast kan tränga in i bergssprickor

som är större än 100 μm.

De senaste undersökningarna med hjälp av Short Slot och Varying Aperture Long Slot (VALS) har

visat en övergripande förbättring av inträngningen under dynamisk injektering jämfört med de

konventionella statiska. Detta är bara en början och metoden behöver utvecklas mer, särskild för att

åstadkomma bruksspridningen i mycket finare mikrosprickor, exempelvis sprickor mindre än 70 µm.

Syftet med detta arbete var att utveckla injekteringsmetoden där bruket kan tränga i berg med

sprickor mindre än 70 µm. Resultaten på de dynamiska tryckförhållanden visade att

injekteringsbruket trängde bättre i de smala sprickor jämfört med de statiska tryckförhållanden.

Upp till 10 gånger mer mängd av injekteringsbruk passerade sprickor med storlek mindre än 70 µm i

VALS. Vidare har inloppsflödet och filtrerings- och erosionsfenomenen studerats med hjälp av

laboratorieinstrumentet VALS. Varaktigheten av peak- och restperioder som användes i

experimenten var 2s/2s och 1s 5.5s, vilka var ekvivalenta med 0.25 Hz respektive 0.15 Hz.

Nyckelord

bruksinträngningsförmåga, filtrationstendens, VALS, tätning, cementbaserade injekteringsmedel,

dynamisk injektering

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TABLE OF CONTENT

Preface ........................................................................................ i Abstract ..................................................................................... iii Sammanfattning ......................................................................... v

1 Introduction .......................................................................... 1

1.1 Grouting Background ..................................................................... 1 1.2 Scope of work and objectives ........................................................ 2

1.2.1 Limitations ........................................................................... 3

1.2.2 Number of test repetitions ................................................... 3 1.2.3 Geometry ............................................................................ 4 1.2.4 Equipment limitations .......................................................... 4 1.2.5 Limtation in resources ......................................................... 4

2 Research Background ............................................................ 5

2.1 Instruments/methods used for penetrability measurement ............ 5 2.1.1 NES and Nobuto Method .................................................... 5

2.1.2 PenetraCone Method .......................................................... 8 2.1.3 Short Slot ............................................................................ 9

2.1.4 Long Slot ........................................................................... 12 2.1.5 Varying Aperture Long Slot (VALS) .................................. 14

2.2 Pressure type and magnitude ...................................................... 15 2.3 Conceptual model of the mechanism of action in dynamic pressure 18 2.4 Conceptual model of the mechanism of action in static pressure 19

3 Materials and Methods ........................................................ 20

3.1 Grout mix ..................................................................................... 20

3.1.1 Water ................................................................................ 20 3.1.2 Cement ............................................................................. 20

3.1.3 Superplasticizer ................................................................ 21 3.1.4 Mixing and sample preparation ......................................... 22

3.2 Experimental setup ...................................................................... 24 3.2.1 Schematic of experimental setup ...................................... 24

3.2.2 Description of instruments and hardware .......................... 25

3.3 Test plan ...................................................................................... 32 3.4 Procedure .................................................................................... 32 3.5 Applied pressure and evaluation method .................................... 33

3.5.1 Applied pressure ............................................................... 33 3.5.2 The magnitude of the pressure during static and dynamic

pressure applications ........................................................ 33

3.5.3 Evaluation method ............................................................ 34

4 Result and Discussion .......................................................... 36

4.1 Evaluation of total weight of passed grout ................................... 36 4.2 Evaluation of filtration and erosion ............................................... 37

4.2.1 Observation of grout path ................................................. 37 4.2.2 Pressure-time curves ........................................................ 40

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4.3 Evaluation of min-pressure envelope and pressure impulse dissipation ............................................................................................... 42

5 Conclusions ......................................................................... 47

5.1 Future work.................................................................................. 48

6 References ........................................................................ 49

Appendix A ............................................................................... 51

A1: Static test C2 .................................................................................... 51

A2: Dynamic test D3 ............................................................................... 54

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1 Introduction

1.1 Grouting Background

During the last few decades, the demands for improving the performance and longevity of underground

infrastructures have been continuously increasing. This has led to a significant need to seal the

underground infrastructures. Grouting is one of the most well-known methods to achieve the required

conditions such as sufficient sealing in the underground facilities. One of the first grouting operations

in the field was performed by Charles Bérigny in France back in 1802 to repair a sluice by stabilizing the

ground basement with liquid grout (Aarsleff, 2017). Today, cement-based grouting is one of the most

common methods used to decrease the permeability of soil layers and rock masses to tighten and prevent

water ingress into the underground facilities. Preference of the cement-based grouts among other

grouting materials is due to its several economic, environmental and durability advantages. To achieve

the required sealing in subsurface facilities in fractured hard rock, various parameters are involved. One

of those parameters is sufficient grout spread in surrounding areas. Obtaining an adequate penetration

length during the grouting operations is of the highest importance to provide the required sealing with

sufficient durability in soil/sand and rock fractures (Ghafar. A. N., 2017).

A grouting operation in rock fractures consists of several steps. First, boreholes with specific length,

inclination, and spacing are drilled in outer perimeter of tunnel-face. The drilled boreholes are then

grouted in designated order. Depending on spread of the grout into fractures, a water-tight zone is

created around the tunnel (Mentesidis 2015). This procedure is continued further along with an

excavation. This technique, which is known as pre-grouting, can be seen in Figure 1. When the pre-

grouting and excavations are completed, in case of local leakage higher than a specific limit, a post-

grouting operation might be needed to prevent the remaining local water ingress.

Pressure type and its magnitude has been a common factor of discussion when dealing with grouting

evaluation in rock fractures. Several researches investigated influence of pressure on grout spread,

filtration and erosion processes in rock fractures. The influence of pressure on grouting has been studied

by application of static and dynamic pressure conditions. The aim has been to improve the grout spread

into fractured rock by avoiding building or by erosion of filter-cakes (Draganović and Stille, 2014, 2011;

Ghafar. A. N., 2017; Nobuto et al., 2008; Pusch et al., 1985). Pusch et al. (1985) demonstrated that the

influence of dynamic pressure is a key factor on improving grout spread. Pusch et al. (1985) and

Mohammed et al. (2015) conducted experiments using high-frequency oscillating dynamic pressure

impulses, showing improvement of the grout penetrability caused by reduction in grout viscosity.

Borgesson and Jansson (1990) examined grouting using oscillating pressure. Fractures with 100 µm

were grouted through static pressure at 20 bar by superimposing a high-frequency oscillating pressure.

The tests done by them showed satisfactory result where they exposed that the oscillations reduced the

viscosity of the grout and facilitated its penetration. Furthermore, test results done by Nobuto et al.

(2008) revealed that clogging phenomenon could be prevented by gradually increasing the injection

pressure during grouting. Moreover, according to Mohammad et al. (2015), a deeper and faster grout

penetrability happens under dynamic pressure conditions than under static pressure. He studied grout

spread in aperture sizes of 100-500 μm.

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In some previous studies of dynamic grouting with high frequencies, the focus has been on rheology of

the grout as the main governing parameter to consider (Mohammad et. al., 2015; Borgesson and Jansson

1990; Pusch et al., 1985). In grouting, the rheology is not the only parameter to consider but yet the

fundamental issues are filtration and spread. I order to study the filtration and the grout spread, some

previous laboratory experiments were performed using parallel steel plates without constrictions

(Nobuto et.al. 2008; Sandberg 1997) and with constrictions (Draganović and Stille, 2014, 2011; Ghafar

et. al. 2017a; Ghafar et. al., 2016a). However, the grout flow and the filtration process in the slot

geometry should be more realistic to simulate a real fracture in rock with various constrictions

(Draganović and Stille, 2014, 2011). Ghafar et al. (2017a) performed grouting tests by application of low

frequency rectangular pressure impulse in a longer slot with different constrictions, where he expected

less dissipation of the impulses and significant improved spread in fractures < 70 µm.

Figure 1. Pre-grouting operation in the face of tunnel (Swedish Transport Administration, 2015).

1.2 Scope of work and objectives

In order to improve the grout penetrability into fractured hard rock, different methods have been

developed and investigated in previous studies. In previous studies the researchers have used constant

pressure and they just succeeded to do the grouting successfully through fractures mostly larger than

100 µm. The investigations for dynamic grouting have also been limited where they have rarely

succeeded to penetrate through apertures smaller than 70 µm.

In present study, the goal is to improve the previous achievements and to successfully inject grout

through apertures smaller than 70 µm by applying low-frequency dynamic pressure impulses (Figure

33).

This research thesis is an experimental study where the improvement of grout spread into micro-fissures

(i.e. < 70 µm) were studied. A low-frequency dynamic pressure impulse was applied to have a better

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control of filtration regarding to the chosen materials, instrument set-up. Also, the improvement of the

spread of cement-based grout into rock fractures and the dissipation of the dynamic pressure impulses

were analyzed. To replicate filtration in a real rock fracture, an artificial fracture model made of steel so-

called Varying Aperture Long Slot (VALS) 4 m length and with varying aperture of 230-10 µm developed

by Ghafar et al. (2016b) was used (Figure 24). By having a more realistic artificial slot and fully

controlled conditions, the filtration processes were analyzed. The selected peak/rest periods in dynamic

tests were 2s/2s and 1s/5.5s (Figure 33). The next step was to evaluate the filtration and erosion

processes.

The objectives of this study can be summarized as follows:

To improve the grout spread in fractures < 70 µm by applying low-frequency dynamic pressure

impulses compared to grouting with static pressure conditions.

Evaluation of the influence of low-frequency dynamic pressure impulse using Varying Aperture

Long Slot (VALS) in a closed system with pressurized gas as pressure source.

Investigation and application of different peak/rest periods to evaluate the filtration/erosion

and grout spread caused by these selected peak/rest periods.

To Reduce the discharge of the grout and increase the amount of injected grout into the VALS

To improve the volume of passed grout through aperture sizes of 40-70 µm in VALS using the

selected peak and rest periods.

Minimise dissipation of the pressure impulses along artificial fractures in VALS.

Analysing the obtained data gathered in Catman Software to have a better understanding of the

filtration and erosion processes that occur within the VALS in both dynamic and static test

groups.

Analysing the filtration and erosion processes through observations of the remained grout’s path

in the VALS after each experiment.

1.2.1 Limitations

Throughout this study, there are a couple of limitations. The most significant of which are as follows:

1.2.2 Number of test repetitions

The first limitation that should be considered is the number of test repetitions. Although the results

appeared to be sufficient, more repetitions of the experiments could provide more data to obtain greater

confidence in the reliability of the conclusions.

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1.2.3 Geometry

The next important limitation in this investigation is related to the geometry of the slot. The VALS, which

is a replication of a fracture in rock has many differences with a real fracture in rock considering its

dimensions. First, the channels in the slot have been built with fixed dimensions and smooth surfaces

compared to a real fracture in rock. Another limitation is the fact that the distribution of the apertures

in reality differs from the aperture distribution in VALS. Moreover, due to the specific geometry and

design of the VALS, it is not possible to study the grout flow apart from 1D (one-dimensional) flow

condition. This should be also taken into account, since in reality the grout flow is not only in 1D.

1.2.4 Equipment limitations

Due to the specific design of the test setup in this study, all the experiments were conducted in a closed

system. In order to obtain the desired dynamic variation in pressure, certain amount of grout must be

discharged from the slot (in a backflow) during each cycle to drop the pressure within the slot as quick

as possible. The loss of grout in each cycle led to insufficient volume of grout available in tank to inject

through the slot. Accordingly, each experiment was eventually stopped due to complete discharge and

insufficient volume of grout in the grout tank. In order to fix this issue in the next stage of the project,

one suggestion is to use a larger grout tank with an agitating system (to prevent settlement of the

grouting materials inside the tank during the grouting process). The other suggestion could be to use a

pump and a larger grout tank (e.g. 10 l) in an open system. In this way, the discharge of the grout from

the slot in each cycle can be returned back to the grout tank. Furthermore, in this study we only used

three pressure sensors to register the variation in pressure along the slot. Using more pressure sensors

would definitely be advantageous to obtain a better understanding of the filtration and erosion tendency

along the slot.

1.2.5 Limtation in resources

The main issue concerning the available resources related to dynamic grouting is that only limited

investigations have been conducted in the area from which, some of the available reports and

publications are in Japanese. This made them almost impossible to use due to the difficulties in

translation.

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2 Research Background

To achieve enough grout penetrability in soil and rock, many researchers have conducted studies using

different methods with various instruments. The existing equipment/methods developed for

measurement of grout penetrability to the best of our knowledge are as follows:

1. Sand Column

2. Pressure Chamber and Filter Press

3. Filter Pump

4. Penetrability meter

5. NES and Nobuto Method

6. PenetraCone

7. Short Slot

8. Long Slot

9. Varying Aperture Long Slot (VALS)

Some of the methods mentioned above, e.g. Sand Column and Pressure Chamber are utilized for

measurement of grout penetrability in porous materials such as soil and sand than a real fractured rock.

Moreover, the values measured by a Sand column, Pressure Chamber and Filter Pump cannot be

correlated to the penetrability of a fracture in rock (Draganović and Stille, 2011). The main objective of

this study is to improve the grout spread into fractured hard rock using dynamic pressure conditions,

the latter five methods are described as follows:

2.1 Instruments/methods used for penetrability measurement

2.1.1 NES and Nobuto Method

NES method developed by Sandberg (1997) was a method to investigate the grout penetrability in rock

fractures/cracks. Figure 2 shows a general depiction of the test setup used in the NES method. The test

setup was designed to measure the weight of the grout penetrated through a given slot using a data-

logger.

The slot was a replication of a short fracture/crack in rock made of two steel parallel plates bolted

together and connected to a grout tank. The grout tank itself was suspended from a digital scale to

monitor the grout weight over time. The apparatus included a high-pressure gas tank to provide the

required pressure to inject the grout into the slot. The grout tank was connected to the slot through a

borehole with a diameter of 25 mm. Thus, the plug-building/arching occurred at connection between

the bore-hole and the slot. The pressure applied during the experiments was constant pressure of 20 bar

and the slot’s aperture size differ from 50 µm and larger.

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Figure 2. The NES set-up (Sandberg, 1997).

Sandberg (1997) tested cements with three different particle sizes to study and compare their

penetrability. Figure 3 shows the results of the penetration tests of different grouts and water through a

50 µm slot. The grouts consisted of 0.66 % superplasticizer and 25 % silica fume of the cement weight

with a w/c ratio of 3.0. The results showed, at 20 bar pressure, variation in cement particle size

influences the grout penetrability significantly

Nobuto et al. (2008) used a modified configuration of the NES apparatus (Figure 4). The field mixing,

agitating, and injecting equipment were incorporated into the test setup. During each experiment, a

stepwise pressure increase (from 10 to 50 bar) was applied in order to improve the grout penetrability

through the slot (Nobuto et al., 2008).

Figure 3. Penetration of three different grouts compared with penetration of water measured by NES method.

From Sandberg (1997).

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Figure 4. General depiction of the test setup used by Nobuto et al. (2008).

In Nobuto’s setup, the steel parallel plates had four outflow channels (Figure 5). The mechanism of

filtration and clogging under application of stepwise pressure increments proposed by Nobuto et al.

(2008) is shown in Figure 6. The cement particles build bridges/arches at the entrance of the channels.

The built bridges/arches are then collapsed due to the gradual increase in pressure and the grout flows

again through the slot. The results showed significant improvement in grout penetrability under

application of stepwise pressure increments.

Steel plate

with channel

Figure 5. The slot with four outflow channels. (Nobuto et al. 2008).

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Figure 6. The proposed mechanism of filtration and clogging according to Nobuto et.al. (2008).

2.1.2 PenetraCone Method

PenetraCone is another laboratory and field measurement device for grout penetrability, developed by

Axelsson and Gustafson (2010). The device consists of two conical cylinders, an outer and an inner cone

with a gap in between (Figure 7). By turning the inner cylinder, the gap between cones can be adjusted

and the aperture size can be varied continuously (b1 > b2) while the grout flows through.

The inner cylinder is threaded and consists of a straight hollow section, where the grout inlet sits as

shown in Figure 7. According to Axelsson et al. (2009), by gradually decreasing the outlet width, the

grout stream changes from continuous flow to almost stop and then a dripping point is achieved.

A dial indicator gauge connected to the inner cone is used to measure the actual gap between the cones.

The test is completed when a total flow stop is reached.

As suggested by Axelsson and Gustafson (2010), while measuring with PenetraCone, the aperture size

when the continuous grout flow changes to drip is called bfilter and the aperture size when the grout flow

stops is called bstop.

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Figure 7: Illustration of PentraCone (upper) and cross section drawing (lower).The dimensions are in

millimeters as seen in Axelsson and Gustafson (2010).

2.1.3 Short Slot

Draganović and Stille (2011) developed another instrument/method for measuring grout penetrability

called Short Slot, which was essentially built based on the configuration of the NES Method. In this

method, the authors tried to replicate a fracture constriction in hard rock by creation a slot between two

parallel plates with constrictions. The main difference between the two methods is the existence of the

constrictions in the Short Slot. As seen in Figure 8, the channels of the Short Slot lead to two

constrictions before the outlet. The other significant difference between them is that in Short Slot the

filtration happens at the constriction within the slot/fracture but in NES method at connection between

the borehole and a fracture (at the entrance of the slot).

The experimental setup in Short Slot was similar to the NES Method. The Short Slot was made of two

steel parallel plates bolted together (see Figure 9, Pictures 2 and 3). The slot was connected directly to a

grout container (Figure 9, Picture 1) with 2.6 l capacity, which was suspended from a digital load cell to

measure the weight of the grout in the grout tank over time. The grout tank itself was connected to a

high-pressure gas tank to provide the required pressure during the grouting process. A pressure gauge

was also connected to the grout tank to register the pressure in tank during the experiments. Picture 5

in Figure 9 shows a schematic view of the cross section of the slot.

By using Short Slot, Draganović and Stille (2011) studied the filtration phenomenon that controls the

grout penetrability. Figure 10 illustrates a schematic depiction of a partially built plug in the Short Slot

before the constriction. To break away the filtration masses (i.e. the filter cakes) and improve the

penetrability, the applied pressure was increased during the experiment. Consequently, some parts of

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Figure 8: Slot constriction's sections (upper) and arching in the vicinity of the narrowing (lower). From

Draganović and Stille (2011).

the unstable filter cakes were eroded and as a result, the slot was partially open again for more grout

flow. The Short Slot was built with seven various aperture sizes (20, 30, 50, 75, 100, 200 and 300 µm).

To evaluate grout penetrability using a Short Slot, two parameters of bmin and bcrit, developed by Eriksson

and Stille (2003), were used in this study. By definition, bmin is the minimum fracture aperture that a

specific grout can penetrate at all and bcrit is the minimum fracture aperture that a specific grout can

penetrate without filtration. Later on, another parameter called k value was introduced by Eklund and

Stille (2008) which is the ratio between the aperture of a groutable fracture and d95 of the cement used

(d95 is a particle size that 95 % by weight of all the cement particles are smaller than that).

According to Eriksson and Stille (2003) and Eriksson et al. (2000), the principle behind these

parameters is to evaluate the minimum and critical aperture size of the grout. As shown in Figure 11, the

bmin is defined as the point at which the amount of the passed grout starts to increase and represent an

aperture limit under which no grout can enter an opening. The bcritical is the value where 100% of the

maximum volume passes the filter zone and represents an upper limit over which an infinite amount of

grout can pass. Between these two points, a finite volume of grout can pass through, and is restricted

due to filter cake occurrence.

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Figure 9: The pictures and a sketch of the Short Slot used to measure grout penetrability from Draganović and

Stille (2011).

Figure 10: Plug building at the constriction. The view corresponds to section B-B in Figure 9. From Draganović

and Stille (2011).

Figure 11: Illustration of the minimum and critical aperture according to Eriksson et al. (2000), (left) and

Eriksson and Stille (2003) (right).

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2.1.4 Long Slot

Long slot is another equipment/method of measurement of grout penetrability developed by Draganović

and Stille (2014). The aim was to examine the influence of pressure on grout penetrability during the

grouting in a longer artificial fracture than in the Short Slot, and to monitor the filtration process at the

constriction using the pressure gradient as an indication of filtration. The geometry of the Long Slot is

more similar to the geometry of a real fracture in rock compared to that of the Short Slot. The instrument

is made of two steel parallel plates placed over each other to form a slot. The Long Slot is 4 m length and

100 mm width. The first 2 m of the slot had an aperture size of 0.5 mm, which is increased to 1 mm along

a length of 30 mm, leading to a constriction of 75 µm, as seen in Figure 12 a.

To measure pressures during penetration, four pressure sensors were installed along the test setup. As

shown in Figure 12 a, the pressure sensors are located at the grout container, before and after the

constriction, and immediately before the outlet. Similar to the Short Slot, the pressure source was a high-

pressure gas tank providing an applied pressure of ≤ 20 bar. In this study, increase in pressure before

the constriction and simultaneously reduction in pressure after the constriction was an indication of

filtration. On the contrary, reduction in pressure before the constriction and increase in pressure after

that was an indication of erosion.

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Figure 12: Long Slot longitudinal cross section (a), plug-building in time at the constriction during grouting (b),

the pressure curves along the slot without plug-building/filtration (c), and with plug-building/filtration (d), from

Draganović and Stille (2014).

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2.1.5 Varying Aperture Long Slot (VALS)

Another instrument for measuring grout penetrability properties was developed by Ghafar et al. (2016b).

This laboratory apparatus, so-called Varying Aperture Long Slot (VALS), was designed to investigate

grout filtration processes and grout penetrability into rock fractures by using a more representative

replication of a real fracture in hard rock. The equipment was designed in such way that it could be used

to operate at both dynamic and static pressure conditions up to 20 bars. The VALS is made of steel and

four-meter long. The aperture sizes varied from 230-10 µm, with chambers of 500 µm placed between

every two constrictions.

The design of VALS made it possible to examine different grout samples composed of a wide range of

cement and additives/admixtures with different water-to-solid ratios. To install the pressure sensors for

registering the pressure variation along the slot over time, 23 holes were made at the top plate of the

slot, before and after each constriction (Figure 13). The pressure sensor holes were covered by steel caps

when no pressure transducers were in use. There was an entry hole of 30 mm diameter located in the

first chamber together with 11 outlet holes (located in the other chambers) along the bottom plate. All of

the outlet holes could also be used as an inlet depending on the test setup. For a detailed description,

see section 3.2: Experimental setup.

Figure 13: Schematic depiction of the test apparatus: 1. gas container, 2. pressure regulator, 3.

load cell, 4. grout tank, 5. pressure transducers, 6. DAQ. From Ghafar A. N. et al., (2017b).

15

2.2 Pressure type and magnitude

The applied pressure type and magnitude have significant influences on grout penetrability. The

experiments conducted by Sandberg (1997) using NES method illustrated that a high pressure of 20 bar

can considerably increase penetrability of a grout made of very fined-grained cements with a d95 of 12

µm and the w/c ratio of 3.0. Eriksson et al. (2000) used the NES method in experiments with different

magnitudes of pressure and grout samples with various w/c ratios of 1.0 and 0.8. The results showed

that by increasing the applied pressure in the slot with 100 µm aperture the grout penetrability was

increased, while in the slot with 75 µm aperture size, there was no considerable improvement in grout

penetrability. The NES method was also used by Hjertström (2001) in order to investigate the influence

of different pressures (2, 5, and 20 bar) on grout penetrability. The latter showed that a pressure of 20

bar improves the grout penetrability significantly without building filter cakes, unlike the pressure of 2

and 5 bar, which showed considerable filtration due to arching/bridging of the cement particles.

According to Nobuto et al. (2008), the filtration of cement particles can be reduced by applying constant

pressure increments. They performed several tests with an experimental configuration similar to the

NES method, except for the pressure control system and the field mixing, agitating, and injecting

equipment. In their experiments, grout samples with w/c ratio of 1.6, using cement with d95 of 16 µm,

and a slot with aperture size of 50 were used. The results obtained by increasing gradually the pressure

from 10 to 50 bar are presented in Figure 14.

As seen in Figure 14, the highest grout flow was obtained at 750 s from the beginning of the test, where

the applied pressure reached 50 bar (5 MP). Then after a couple of fluctuations that happened due to

erosion of the produced filter cakes, the grout flow tended to zero due to accumulation of filtration.

Nobuto et al. (2008) concluded that stepwise pressure increments result in a higher penetration volume

than the static pressure.

Draganović and Stille (2011) used different magnitudes of pressure to test the grout penetrability in

Short Slot (Figure 15). They applied three different pressures of 4, 7, and 15 bar in their experiments

using a grout sample made of INJ30 with d95 of 30 µm and w/c ratio of 0.6. They illustrated that using

higher pressure, the grout filtration tendency during the grouting process is reduced.

Figure 14: Penetration volume against time with increasing pressure from 10 to 50 bars. From

Nobuto et al. (2008).

16

Mohammed et al. (2015) also studied dynamic grouting and showed some improvements in grout

penetrability compared to that in static pressure application. The tests were performed using 100-500

µm slots (see Figure 16). The results showed that the influence of dynamic pressure on grout

penetrability was considerable for the 250-500 µm slots. However, using 100 µm slot, the improvement

in grout penetrability at dynamic pressure condition was insignificant.

The Short Slot was used by Ghafar et al. (2016a) to study grout penetrability. The dynamic tests were

performed with peak/rest periods of 4s/8s and 2s/2s. The slot’s sizes were 43 um and 30 µm. Low-

frequency rectangular pressure impulse was used to fulfil the required condition for improving the

efficiency of dynamic grouting in comparison to oscillating, ramp shape. The selection of the peak/rest

periods and magnitude of the pressures were the main parameters to control the filtration and improve

the grout spread in dynamic grouting. Firstly, the assumed mechanism of action was assessed for

maximizing the erosion of the filter cakes due to the change of the flow pattern. The proposed

mechanism of action was the major pressure variation (between 15 and 9 bar). In case of major pressure

variation, the flow type changed from turbulent (peak period) to laminar (rest period) and this process

was repeated successively. This variation of flow type results in a significant change of the flow pattern

which increases the erosion of the filter cakes (Figure 17).

Figure 15: Penetrability tests performed on a grout sample made of INJ30 with w/c of 0.6 using a slot

with 50 µm aperture at grouting pressures of 4, 7 and 15 bar. From Draganović and Stille (2011).

Figure 16: Results of grout penetrability tests at static and dynamic pressure conditions using

100-500 μm slots presented by Mohammed et al. (2015).

17

Some static tests were conducted to examine the filtration process and it showed that after 4 s the

filtration process was observed considerably. Therefore, the peak period was selected with 4 s to avoid

filtration and 8 s to obtain the required low-pressure during the rest period. When the dynamic test was

performed with 4s/8 s peak/rest period, the filtration process occurred during the peak period which let

the accumulation of the cement particles increase gradually. On the other hand, 80 % of the pressure

drop occurred during the first 2 s of the rest period. To obtain a better control of the filtration processes,

the peak/ rest period of 2/2s was selected.

To understand better the application of low rectangular pressure impulse and compare the results from

dynamic and static tests, four evaluation methods were used:

Total weight of passed grout: A simple method used to quantify the differences of passed

grout. The observation of filtration and erosion processes are not possible.

The weight-time measurement: A method with the aim of monitoring the filtration

during the experiment. The main drawback was the unclear distinction between the

filtration and erosion processes.

Min-pressure envelope: All the minimum pressures in each cycle were connected

linearly to visualize both filtration and erosion during the experiment. This method

cannot quantify the influence of filtration and erosion.

CMRF (Cycle Mean Flow Rate): This evaluation method quantifies the filtration and

erosion processes in each cycle.

The obtained results from the dynamic tests showed an improvement of the grout spread in 43 µm slot.

The improvement of dynamic tests was two times more than the static tests but the distinction between

the two peak/rest periods of 2/2s and 4/8s was unclear. However, the analysis of the CMRF showed a

better control of filtration in the tests with the peak/rest period of 2/2s. In addition, the grout tank was

empty in a shorter time.

The dynamic test conducted in 30 µm slot with 4s/8s and 2s/2s peak/rest periods showed 2.6 and 11

times larger amount of passed grout compared to static tests, respectively. It is a clear sign of the

efficiency of the low rectangular pressure impulse on improving the grout spread. As mentioned above,

the filtration could be controlled better with a 2/2s peak/rest period.

The VALS was used by Ghafar et al. (2017a) to replicate a more realistic fractured rock and improve the

grout spread in fractured rock. The dynamic tests were conducted with the peak/rest periods of 2s/2s,

with maximum pressure of 15 bar. The selections of the peak/rest periods and magnitude of the pressure

were due to the improvement of the grout spread at Short Slot with 30 µm and 43 µm Ghafar et al.

(2016a). In this study the mechanism of action was the erosion of filter cakes due to the change of flow

pattern. In VALS, the flow type is laminar during the peak/rest periods in comparison with the Short

Slot. It is caused by the friction between the grout and slot inside the VALS, resulting in dissipation of

the pressure.

18

The obtained results showed that after at 2.0 m and 2.7 m lengths of the VALS, 46 % and 25 % of the

initial applied amplitude remained. It is an indication of the potential of low-frequency rectangular

pressure impulses. It is an indication of the potential of low-frequency rectangular pressure impulses.

The sufficient remaining amplitude of the pressure extended the penetration length. This was due to

counterbalancing between the filtration and erosion of the cement particles at the constrictions.

2.3 Conceptual model of the mechanism of action in dynamic pressure

In this study, the mechanism of action is based on the erosion of the cement particles due to the change

of flow pattern. According to Ghafar et al. (2016a), the test performed in the Short Slot, showed an

improvement of the grout spread by applying the mayor pressure variation (15-<9 bar) due to the change

of the flow type in consecutive cycles. The flow type changed from turbulent to laminar, resulting in a

change of the flow pattern during the rest period. This significant change in the flow pattern increases

the probability of erosion of any unstable filter cake, since the laminar flow has a deeply penetration

which makes it possible to avoid the accumulation of the cement particles in corners , see Figure 17.

Figure 17: Major pressure variation (15- <9 bar) taken from Ghafar et. al. (2016a).

The mechanism of action in the present study has some differences. The VALS is longer than Short slot,

therefore, the flow type always remains laminar with a variation in the flow pattern during the peak/rest

periods. During the peak period, due to the high pressure and flow velocity, the streamlines are not

anticipated to increase the potential of the erosion of any unstable filter cake. On the other hand, the

streamlines are expected to increase the potential of erosion of any unstable filter cake, due to the low

pressure and flow velocity during the rest period, see Figure 18.

19

Figure 18: Mechanism of action in VALS during application of low-frequency dynamic pressure impulses.

2.4 Conceptual model of the mechanism of action in static pressure

The assumed mechanism of action in application of static pressure conditions in the VALS is presented

in Figure 19. The accumulation of the cement particles increases gradually. See illustration of flow width

streamlines from step 1 to step 5 until full filtration is reached at the constrictions along the VALS. In

addition, during grouting at static pressure conditions, due to building of filter cakes, the grout flow

decreases stepwise until the flow-stop is reached.

Figure 19: Mechanism of action in VALS during application of static grouting.

20

3 Materials and Methods

3.1 Grout mix

The grout used in this study was prepared based on a commonly used recipe in Swedish grouting

industry. It consisted of:

Cement: Injektering 30 (from Cementa AB) with d95 of 30 µm

Superplasticizer: iFlow-1 (from Sika AB) with 0.5 % concentration to the cement weight

Water-to-cement ratio (w/c) of 0.8

The amount of each material used in the grout mix are presented in Table 1:

Table 1: Grout mix components

Component Water INJ30 Cement Sika iFlow-1

Weight [grams] 2400 3000 15

3.1.1 Water

The water used in each grout mix was tap water.

3.1.2 Cement

The cement used in all grout mixes in this study was Injektering 30 with d95 of 30 µm produced by

Cementa AB. INJ30 is manufactured using the same clinker as Anläggningscement in a fine grinding

process (Cementa AB, 2014).

The cement was delivered in 20 kg sacks (Figure 20), which were completely enclosed in plastic and

placed on a dry pallet to reduce the potential of damage caused by damp air and direct contact with

moisture. The cement should not be stored for a period longer than six months (Cementa AB, 2014). The

cement was directly supplied from Cementa’s plant in Degerhamn to the laboratory and was used within

a couple of weeks.

INJ30 has flow and filtering characteristics at temperatures between 20 ℃ and 8 ℃. The cement’s

properties comply with the requirements of SS-EN 197-1 and SS 13 42 03, and the quality and production

processes are in accordance with SS-EN ISO 9002.

Other properties of INJ30 are sulphate resistance of SR 3 type cement according to EN 197-1, since it

contains 2 % tricalcium aluminate (C3A); a low alkali content of approximately 0.5 %, which reduces

reactions with alkali-reactive aggregates, and low chromate content. Since Injektering 30 is sulphate-

resistant and has low alkali and the crushed dolomite is inert, it does not harden very quickly, as stated

by Axelsson and Gustafson (2010). Nevertheless, persons hypersensitive to chrome should avoid all

contact with cement INJ30. Table 2 lists the characteristics and properties of INJ30.

21

Figure 20: Package of Injektering 30, delivered from Cementa AB.

Table 2: INJ30 characteristics and properties

Setting time [min] 100

BET specific surface area [𝑚2

𝑘𝑔] * 1300

Injection characteristics

Flow and filtering At temperatures of 20 °C and 8 °C

Physical properties

Compact density [𝑘𝑔

𝑚3] Approx. 3100 - 3200

Bulk density [𝑘𝑔

𝑚3] Approx. 800 – 1500

Chemical properties†

𝑀𝑔𝑂 Max. 5.0 % by weight

𝑆𝑂3 Max. 3.5 % by weight

Chlorides 𝐶𝑙 Max. 0.1 % by weight

3.1.3 Superplasticizer

An emollient additive is an effective dispersing admixture for avoiding flocculation of the grout particles.

The superplasticizer used in this study is iFlow-1 from Sika AB. Its main functions are to prevent

flocculation between fine cement particles. To reach optimum disperse ability using iFlow-1, the

Preface | 21

* Determined by BET method (Cementa AB, 2014) † Chemical composition can vary in detail (Cementa AB, 2014)

22

maximum concentration recommended by the manufacturer was 0.5 % by the cement weight that used

in all grout mixes.

Sika iFlow-1 is a light brown liquid packaged in 5 kg plastic cans. It must not be used more than 9 months

after the date of production. It must be stored in a frost-free environment, unopened in the original

packaging. The density and dry content must be considered at the time of dosage and a dosage of

approximately 0.3-0.5 % by weight of cement is recommended. The impact of iFlow-1 may vary

depending on the type of cement used. Overdose may cause retardation. Technical data, characteristics

and properties of the product are presented in Table 3.

Table 3: iFlow-1 characteristics and properties

Density [kg/dm3] 1.09 ± 0,02

pH Value 5 ± 1

Total Chloride Ion Content % w/w <0.10 %

Equivalent Sodium Oxide as % Na2O <1.0 %

Corrosion Behaviour Not relevant when used as instructed

Dry content 40 ± 1 %

Viscosity Fluid

Dosage Approx. 0.3-0.5 % by weight of cement

3.1.4 Mixing and sample preparation

To prepare the grout mix in each experiment, first the required amount of each component was

measured by using scales with proper accuracy, see Figure 23a. The scaled cement (Figure 23d) was

then slowly added to the required water (Figure 23c) in a steel bucket. The steel bucket was cleaned

properly and wetted in order to reduce the water suction by the bucket’s inside surface. A hand-mixer

(Figure 21a) was afterwards used to carefully premix, for almost 1 minute, these two components. Then

a VMA rotor-stator lab mixer with 10.000 rpm (Figure 21b) was used to disperse the cement particles

for a period of 4 minutes. A control unit (Figure 21c) was coupled to the rotor-stator mixer to maintain

the required speed. The superplasticizer (Figure 23b) was added to the cement-water-mixture after 2

minutes of mixing process. Figure 22 shows the mixing moment by VMA rotor-stator lab mixer, after

the addition of superplasticizer iFlow-1, the size of the air bubbles was reduced to very small bubbles

and the noise of the mixer changed from load to soft sound.

23

The following apparatuses are used in the mixing process:

Figure 21:The apparatus used in the mixing process. a) Hand-mixer b) Rotor-Stator adapted to a dissolver

DISPERMAT (VMA – GETZMANN®) c) Control unit (DISPERMAT®) installed at ca 10000 rpm.

Figure 22 shows the process of grout mixing in VMA rotor-stator, before and after adding

superplasticizer.

Figure 22: a) Before the addition of superplasticizer (left). b) After the addition of superplasticizer (right). As

seen, the size of bubbles is significantly reduced.

a)

b) c)

a) b)

24

Figure 23 shows zeroing the scale and scaling of the grout components.

Figure 23: a) Example of zeroing the scale including the weight of the pot. b) Approx. 15g superplasticizer. c)

2400g water. d) 3000g cement.

3.2 Experimental setup

3.2.1 Schematic of experimental setup

The test apparatus used in this study consisted of a nitrogen gas tank (200 bar) to provide the pressure

required during each experiment. The gas tank was connected to a pressure regulator to provide and

maintain a static pressure at 15 bar. The gas tank was then connected to a grout tank that was suspended

a) b)

c) d)

25

from a S-shaped load cell. The load cell (RSCC C3/50 kg from HBM) was used to register the weight of

the injected grout over time.

As shown in Figure 24, valve Vp was located between the grout tank and the pressure regulator to control

the nitrogen gas flow to the grout tank. Valves Vi and Vf were located on the top and the side of the grout

tank. Valve Vi was used to fill the grout tank, while valve Vf was used to release the pressure in the grout

tank after each experiment.

The grout tank was then connected to VALS to study the grout penetrability at dynamic and static

pressure conditions. The VALS itself was equipped with three pressure sensors, which were located

before the constrictions of 230 µm, 50 µm and 40 µm in order to record the pressure variation over time.

All the sensors (the load cell and the pressure sensors) were connected to a QuantumX MX440A, a data

acquisition system, which converts all the obtained analog signals into digital values for processing. In

order to visualize and control each experiment, Catman software from HMB was used during the test

procedure.

Figure 24: Schematic depiction of the experimental setup. 1) Gas tank, 2) Pressure regulator, 3) Load cell, 4)

Grout tank, 5) Pressure transducer, 6) DAQ, 7) Pneumatic actuators and solenoid vales. 8) Timer/Relay.

3.2.2 Description of instruments and hardware

3.2.2.1 Varying Aperture Long Slot (VALS)

In present study, to measure the grout penetrability at static and dynamic pressure conditions, the

varying aperture long slot (VALS) developed by Ghafar et al. (2016b) was used. The setup represents an

artificial fracture made of steel, with 10 cm width, 4 m length, 11 varying constrictions (apertures) of

230-10 µm, and chambers of 500 µm before each constriction (Figure 24). The VALS is composed of

26

four longitudinal supports, a top plate and a bottom plate. These parts are bolted together on a bench

before each experiment (Figure 25).

The top plate has one hole in each chamber and constriction (23 holes), in order to place and install the

pressure transducers. The pressure can thus be registered to monitor the filtration and erosion processes

over time. All of these holes are sealed with caps when no pressure transducer is installed. The bottom

plate has 12 holes that are placed under each chamber. The first hole is considered as the main inlet

(with a dimension of 30 mm) and the other 11 holes as outlet. A ball-valve is installed at each hole

underneath each chamber to control the flow (open/close), see Figure 24 and Figure 25.

It should be noted that the VALS was designed in a way that the maximum deflection of the plates under

internal pressure of 15 bar to become less than a certain limit to avoid any grout leakage during the

experiment. Hence, a 30 mm thick steel plate with 70 mm free load span (maximum deflection of 0.21

µm for ends clamped support conditions and 1.04 µm for ends pinned support conditions) was selected

to use as the top and bottom plates. Two other materials were tested for this purpose: Plexiglas XT (i.e.

that which is manufactured by extrusion) and Polycarbonate (with the aim of observing inside the VALS

during the experiment) but they were not appropriate for the project because the materials could not

withstand the high-pressure condition of the experiments.

After production of the VALS, using a laser CNC (Coordinate Measuring Machine) from Mitutoyo, the

exact size of the chambers and constrictions were examined.

3.2.2.2 Nitrogen gas tank and pressure regulator

The gas tank (N2 Nitrogen) with an initial pressure of 200 bar provided the required pressure throughout

each test. Since the required pressure in our experiments was 15 bar, a pressure regulator was connected

Figure 25: Varying Aperture Long Slot (VALS).

27

to the gas tank to reduce the pressure from 200 bar to 15 bar and keep it constant during the experiment

(Figure 26).

3.2.2.3 Load cell

The function of the load cell used in our test setup was to register the weight of the injected grout

over time. The device used was an S-shaped load cell, RSCC C3/50kg from HBM (Figure 27). The grout

tank was suspended from a stable metallic structure through the load cell (

Figure 28). In order to record the data, the load cell was connected to a computer through a data

acquisition system (DAQ)

a)

b)

Figure 26: a) Nitrogen gas tank b) Pressure regulator.

28

Figure 28: Different illustrations of the grout tank.

Figure 27: Illustration of the load cell, its position and the connection cable (HBM, 2018a).

29

3.2.2.4 Pressure transducers

Three pressure transducers (i.e. P15RVA1/200 bar from HBM) were used during the experiments in this

study (Figure 29). They were located at the beginning of the VALS and before the constrictions of 50 µm

and 40 µm. In this way, the pressure was recorded at the selected locations in order to study the filtration

and erosion phenomena while the experiments were running. The results were transmitted to the

computer through their respective DAQ channels.

30

3.2.2.5 DAQ System

The QuantumX MX440A from HBM (Figure 30) was the data acquisition system (DAQ) that was used

in our test setup. The DAQ transforms the acquired analogue signals into digital values, which will be

analyzed in a later phase. It had four channels and contained Ethernet communication protocol. The

load cell and the pressure transducers were connected to the DAQ to acquire, translate and transmit

pressure-time and weight-time data to the computer.

Figure 30: Quantumx Data acquisition system (HBM, 2018b).

3.2.2.6 The valve system providing the dynamic pressure

The double pneumatic actuators used in this setup were JAG30DA from JAG (Figure 31). The solenoid

valves used were SNMF from ACG and the timers were DCB01 from CARLO GAVAZZI (Figure 31). The

timers were used to configure a peak and rest period, while the pneumatic actuators and solenoid valves

were to open/close the grout flow into the VALS. The combination of all these components converted

the constant pressure into a dynamic pressure.

In order to obtain the lowest possible pressure during the rest period, the solenoid valve controls

(open/close) the pressurized air that was the source of power for the double pneumatic actuators. The

solenoid valves themselves work with electricity that is provided from the timers/relays (Figure 32).

During one cycle (peak/rest period) the actuators rotate two ball-valves that open/close the grouting

flow into the VALS (Figure 31 and Figure 32). These two ball-valves work together in such a way to

reduce sufficiently the pressure inside the VALS in the shortest possible time to achieve the least loss of

the grout during rest period. Firstly, the ball-valve 1 is opened to let the grout flow inside the VALS and

then immediately the ball-valve 1 is closed to stop the grout flow. After a few seconds while ball-valve 1

is closed, the ball-valve 2 is opened/closed to obtain the maximum pressure drop inside the VALS in the

shortest possible time, (see Figure 33). See section 3.5.2 for more details.

Figure 29: Pressure transducer for measuring pressure and their position in the system.

31

Figure 31: 1) Pneumatic actuators JAG30DA from JAG, 2) Solenoid valves SNMF from ACG, 3) Timers/Relays

DCB01 from CARLO GAVAZZI.

Figure 32: Schematic setup of improved dynamic system.

32

3.3 Test plan

The tests performed in this study were divided into two groups (Table 4). In the first test group, Static

(i.e. C1, C2 and C3), a static pressure of 15 bar was applied to the grout throughout each experiment

using the same conditions in order to check the repeatability of the tests. The obtained results were then

compared with the second group, Dynamic (i.e. D1, D2 and D3). This test group was performed under

application of dynamic pressure with two peak/rest periods and a maximum pressure of 15 bar. The

selected peak/rest periods were 2s/2s and 1s/5.5s. The purpose of selecting the latter configuration was

to control/reduce the discharge of the grout out of the system in each cycle (when the internal pressure

of the slot was dropped by opening ball-valve 2 as presented in the previous section) to increase the

possibility of continuing the tests before the grout tank was completely empty. The results obtained

from both groups were compared using different evaluation methods.

Table 4: Test plan.

Test group Name of test Test number Pressure type Peak /rest period[s]

Static

C1 1 Static -

C2 1 Static -

C3 1 Static -

Dynamic

D1 1 Dynamic 2s/2s

D2 1 Dynamic 1s/5.5s

D3 1 Dynamic 1s/5.5s

3.4 Procedure

Before each experiment starts, the Catman Easy Software should be opened, the load cell and the

pressure transducers must be set to zero in order to avoid any errors when reading the obtained results.

The pressure regulator must be adjusted in a way to obtain an applied pressure of 15 bar during each

test. Then, the materials are weighted based on the chosen grout recipe using a proper scale with

sufficient accuracy at ambient temperature (20±2°C).

After mixing the materials, the grout tank is immediately filled with the prepared grout to avoid changes

in the rheological properties of the grout due to the hydration. Then the grout tank is pressurized to 15

bar by opening valve Vp (Figure 24).

When the pressure is stabilized in the grout tank, the test is started by opening the inlet valve and

activating the pneumatic actuators. The pneumatic actuators are calibrated in order to achieve the

desired static or dynamic pressure in each test. At the beginning of each test, all the valves along the slot

are closed except V4 (see Figure 24) since valve number 4 (which is between aperture sizes 40 and 30

µm) is opened as outflow. When the flow-stop is reached in V4 (full filtration along the VALS), the next

valve is opened (V5) and the time of the first and last outcoming grout-drop is written down in each

consecutive valve (i.e. 4, 5, 6, 7, 8).

While the test is running, the pressure is recorded in different locations, depending on where the

pressure transducers are placed. At the same time, the weight of the grout is registered. The amount of

grout that comes out from each valve is weighed and registered. At the end of the test, all the information

recorded by Catman Easy software is saved. Finally, the whole system is dismantled for observation of

the filtration occurred within the slot and cleaning.

33

3.5 Applied pressure and evaluation method

3.5.1 Applied pressure

The focus of this study was application of dynamic pressure and evaluation of its effects on grout

penetrability. The main parameters defined before the experiments were as follows:

1. The magnitude of the pressure during static and dynamic pressure applications

2. The peak and rest times

3.5.2 The magnitude of the pressure during static and dynamic pressure applications

In the experiments conducted at constant pressure conditions, the magnitude of the applied pressure

was 15 bar. In the experiments conducted at dynamic pressure condition, the maximum magnitude of

the applied pressure was 15 bar and the minimum value was close to zero.

The selection of 15 bar pressure was on the basis of the tests performed by Draganović and Stille (2011)

using Short Slot at 15 bar pressure that resulted in a better grout penetrability compared to the tests

performed at lower pressures and the fact that it was much closer to the applied pressure in the field.

3.5.2.1 Selection of the peak and rest periods during the dynamic pressure application

In order to compare the results obtained in this study with the results of the tests performed by Ghafar

et al. (2017a) using the VALS, the same dynamic pressure configuration was primarily selected with the

peak and rest period of 2s/2s, respectively. At the beginning, some preliminary tests were conducted

with air and water to check if all the component of the test setup were working properly. After the tests

with 2s/2s peak/rest periods, we realized that considerable amount of grout was still discharging

through the pressure release hose (Figure 32) in each cycle. Therefore, we developed the dynamic setup

and added two more timers (three timers in total) to configure the opening and closing times of the

valves in a way to reduce the corresponding discharge of the grout in each cycle. The best results

considering the amount of the discharged grout (the lower the better) in each cycle and the magnitude

of the pressure during the rest period was obtained using 1s/5.5s peak/rest periods, see Figure 33.

During the selected peak/rest period of 1s/5.5 s, the double pneumatic actuators worked in such a way

that ball-valve 1 controlled (open/close) the grouting flow and kept it flowing for 1 s (the total time of

peak period). Ball-valve 1 was closed for 5.5 s (the total time of rest period). While the ball-valve 1 was

closed, the pressure was decreasing slowly inside the VALS and to obtain a faster pressure drop, the ball-

valve 2 was opened during 3.5 s of the rest period. In order to reach the least loss of the grout and to

obtain a pressure drop closer to zero, the ball-valve 2 was opened only for 0.1 s of the rest period. During

1.9 s of the rest period the ball-valve 1 and 2 were closed in order to stop the grout flow into the VALS. A

new cycle began by opening the ball-valve 1 again, see Figure 33.

34

Figure 33: Illustration of the low-frequency dynamic pressure impulses with the selected peak/rest time 1s/5.5s

with delayed pressure drop.

3.5.3 Evaluation method

3.5.3.1 Total weight of passed grout

This is the simplest way to study penetrability of a grout through different constrictions. After reaching

the flow stop in each constriction due to the filtration, when the respective valve is open, the time and

the total weight of the passed grout through that constriction are recorded. The weighed grout and the

recorded times from different tests are then compared in order to find the pressure condition with the

best grout penetrability. One limitation of this method is to study when the filtration and erosion

processes occur due to the lack of observation of these processes inside the slot during the experiments.

3.5.3.2 Filtration and erosion

Filtration and erosion is a method of evaluation that was used to assess the performed tests in both static

and dynamic conditions. The pressure-time curves from the three pressures sensor that were placed in

different position was studied by observing theirs path.

An increase of pressure in P2 is due to the filtration process occurs after pressure sensor P2, resulting in

a lower pressure in P3. However, the pressure sensor shows a higher pressure if the filtration process

occurs after its position along the VALS. If the filtration occurs before is position, a lower pressured is

obtained.

The erosion releases the unstable filter cakes, showing a downward trend along the pressure-time curves.

In this study, a drastic downward trend is also due to a valve is opened in order to locate the position of

full filtration (flow-stop) through obtaining the grout flow again. The erosion was analyzed when the

VALS was opened, some pictures were taken to compare the results from the performed tests with static

and dynamic pressure conditions (Figure 36 and Figure 37).

3.5.3.3 Minimum pressure envelope

The minimum pressure envelope is a method of evaluation that was used by Ghafar et al. (2016a) in

dynamic tests to observe the filtration and erosion processes that occur inside the short slot. During the

performed tests, a min pressure was obtained in each cycle (peak/rest period). The minimum pressure

35

values were connected linearly and consecutively in order to analyze the pressure-drop P. Increase and

decrease in constriction size due to the erosion and filtration lead to increase and decrease of P. A

decrease in constriction opening area results to a decrease in P due to agglomeration of cement

particles (filtration). An increase in constriction opening area results to an increase in P due to release

of cement particles (erosion). Thereby, filtration can be described as any positive (upward) trend

through the min-pressure envelope. Erosion can be described as any negative (downward) trend, see

Figure 34.

Figure 34: Illustration of the min-pressure envelope, filtration and erosion in Short Slot (Ghafar et al., 2016a).

It should be noted that this evaluation method in the VALS has some differences that are expected to be

seen when the obtained results will be analyzed. The VALS has different dimensions than the Short Slot.

The VALS’s length gives a dissipation of the pressure due to the friction between the injected grout and

the surface of the slot. During flow, due to friction, the pressure curves (P2 and P3) would show the same

path and the pressure sensor that is closer to the inlet (P1) would show a higher pressure. This occur if

there is no filtration between the pressure sensors (Figure 35). In addition, the linearly connected

minimum pressures are obtained before opening ball-valve 2 which results to an immediate pressure

drop inside the VALS, see Figure 35.

Figure 35: Min-pressure envelopes in VALS.

36

4 Result and Discussion

4.1 Evaluation of total weight of passed grout

Experimental results were obtained from the performed tests by applying static and dynamic pressure

conditions; the results are presented in Table 5. Each test group contains three performed tests.

Table 5: Table of test results.

Test

Group

Test

No.

Peak/Rest

Period

[s]

Initial

Weight

[kg]

Weight of Passed Grout [g]/time[s] Grout

Loss

[kg]

Validity

𝑉4

(40𝜇𝑚)

𝑉5

(50𝜇𝑚)

𝑉6

(60𝜇𝑚)

𝑉7

(70𝜇𝑚)

𝑉8

(100𝜇𝑚)

Static

Pressure

C1 − 4.550 114

258∗/326∗

2750

236/1900

0

1901/−

0

−/−

928

2257/2314

− Not

Valid

C2 − 4.507 84

270/283

60

284/334

0

335/423

0

423/470

3752

470/822

− Valid

C3 − 4.657 0

−/183

0

184/367

44

368/551

16

552/646

3772

647/1384

− Valid

Dynamic

Pressure

D1 2/2 4.402

81

80/196

394

197/335

0

−/−

0

−/−

0

−/−

3.840

Not

Valid

D2 1/5.5 4.563 0

−/63

120

64/296

880

297/1072

0

−/−

0

−/−

2.810 Valid

D3 1/5.5 4.414 0

−/143

76

144/256

964

257/660

0

−/−

0

−/−

3.244 Valid

* First grout-drop coming out /Last grout-drop coming out [s]

Table 6: Results comparison of grout penetrated through 40-70 µm.

Test Group

Test No.

Peak/Rest Period

[s]

Weight of Passed Grout [g]

Improvement

Sum

(40 − 70𝜇𝑚)

Average

(40 − 70𝜇𝑚)

Static Pressure C2 − 144 102 −

C3 − 60

Dynamic Pressure D2 1/5.5 1000 1020 10

D3 1/5.5 1040

During performance of static test group, the grouting material took longer time to flow out through the

VALS. Throughout all the static tests, most of the grouting material had passed through the VALS,

mainly through the apertures larger than 70 µm and the grout tank was empty at the end. However,

except in test C1, the filtration caused flow stop at the constrictions of 40-70 µm, as seen in Table 5.

37

The dynamic test group were more time efficient and it took less time for the first grout drop to flow out

(see Table 5), although a large amount of the grout was discharged through the release hose during the

rest period. The grouting material was discharged because of the pressure drop during the rest period.

The discharged grouts are mentioned as grout loss in Table 5. As seen in the same table, the average

amount of the grout loss in each experiment is approximately up to 74 % of the initial grout. This is due

to the limitation of our test setup which in our suggestion for future work has to be improved in order to

show the effectiveness of the method. As can be seen in Table 6, the average amount of passed grout

through the constriction of 40-70 µm in application of dynamic grouting (i.e. 1020 g) was up to 10 times

more than in grouting at static pressure conditions (i.e. 102 g). This improvement could be a result of

the erosion of the unstable filter cakes at the constrictions through the VALS caused by changes of the

flow pattern or also a result of a lower filtration due to change of flow direction by varying pressure .

Looking at the first static test result (C1) in Table 5, more than half of the grout ran out from valve V5,

which was due to a small channel remained within the filtration area inside the VALS. It’s probably

because of the deviation of the size of the aperture in some areas of the slot from the design value which

again is related to the limitation of the equipment. Therefore, this test is not used in comparison of the

grout passed through the apertures of 40-70 µm associated with the two other static tests. Another test

which has not been taken into account in this evaluation is dynamic test D1. This test which was

conducted using 2s/2s peak/rest period is also disregarded since almost 87 % of the grout was

discharged through the pressure release hose. The first grout-drop from the outlet valve (V4) occurred

at 270 s and lasted up to 283 s. The weight of passed grout through V4 during 13s and V5 over 50 s was

84 g and 60 g, respectively.

The next two static pressure tests (C2 and C3) showed similar amounts of grout passed through aperture

sizes of 40-70 µm. In D3, V5 was kept open almost 232 s and 120 g grout came out. 880g grout passed

through the aperture size 60 µm.

By making a comparison between the static pressure conditions of tests C2 and C3, as well as the

dynamic pressure conditions of tests D2 and D3, an improvement of 10 times in the volume of passed

grout through apertures ≤ 70 μm is achieved. Table 6 shows the improvement on grout spread obtained

using low-frequency dynamic pressure impulses (1s/5.5s) compared to static pressure conditions in

apertures sizes < 70 µm.

4.2 Evaluation of filtration and erosion

4.2.1 Observation of grout path

Filtration and erosion processes were firstly acknowledged by observing the grout path left inside the

VALS at the end of performed static and dynamic tests. By opening the VALS and comparing a specific

aperture size along the slot (50 µm) for both static and dynamic test, significant differences in the grout

flow configurations are seen. In static test results (Figure 36), the chamber before 50 µm, except some

small areas, is totally filtered and the grout flow is almost prevented in construction 50 µm due to

accumulation of filtration and clogging. The test performed by dynamic grouting resulted to a more

eroded and less filtered areas and the grout flow passed through the constriction 50 µm (Figure 37).

Furthermore, the grout front has managed to penetrate a longer distance along the slot and passed

through constriction size of 40 µm in dynamic grouting compared to static pressure conditions. For more

38

pictures, see Appendix A. Figure 36 shows the grout path left by performed static test at the constriction

size 50 µm and the chamber before and after it.

Grout Flow

Filter Cakes

Grout front

Grout Flow

Figure 36: Observation of filtration and erosion areas after application of static conditions at 50 µm inside the VALS.

39

Figure 37 Figure 36 shows the grout path left by performed dynamic test at the constriction sizes 50-40

µm and the chambers before and after them.

Figure 37: Observation of filtration and erosion areas after application of dynamic grouting/conditions at 50-40 µm

inside the VALS.

Grout front

Filter Cakes

Grout Flow

Grout Flow

Grout Flow

40

4.2.2 Pressure-time curves

Another way of identifying the filtration and erosion processes was by studying the obtained pressure-

time measurements in Catman Software. Figure 38 shows the obtained results from test C1. This graph

indicates variation of pressure over time in three locations with some upward and downward trends,

which are indication of filtration and erosion. The resulting graph in test C1 illustrates random filtration

and erosion processes during the test.

In test C1, it took almost two seconds for the grout to reach the first pressure sensor P1. The grout flow

reached the second pressure sensor P2, and the third pressure sensor P3, at 14 s and 30 s, respectively,

see Figure 38.

Another interesting fact about the pressure curves of P2 and P3 is that after the pressure curves reached

maximum pressure level, a gap between these two curves appeared. This gap can be explained by two

main phenomena: filtration and erosion, which occur between these pressure sensors (P2 and P3), and/or

friction between the grout and the surface of the slot.

Figure 38: Development of static pressure conditions along the VALS registered by P1, P2 and P3 in test C1. a)

Test result C1, total time. b) Test result C1, up to 350s.

Erosion

Filtration

V5 opened at 328 s

Erosion Filtration

14s 30s

a)

b)

41

The pressure-time curves followed the same path from 14 s to 326 s. This means that no considerable

filtration occurred between the positions of P2 and P3 inside the VALS (Figure 38). If filtration appears

between P2 and P3, the pressure-time curves should not follow the same path. On the contrary: the

pressure-time curves would show completely adverse paths, with the pressure curve from P2 rising

upwards and the pressure curve from P3 moving downwards due to flocculation in front of the 50 µm

constriction. Any filtration and erosion which represented by this pressure variation happened before

P2, probably at V6 and V7. However, the only supported reason for the existing gap between the graphs

of P2 and P3 is friction. At 328 s, approximately a complete filtration has occurred at 40 µm (flow stop in

V4) constriction, therefore V5 is opened (Figure 38).

As seen in test results C2 (Figure 39), the highest pressure registered by P1 was almost 15 bar, which is

the same as the pressure level calibrated in the gas tank. Immediately after opening V5, the pressure-

time curves (P2 and P3) shows a downward trend, as seen in Figure 39. Not any downward trend in this

pressure-time measurement is an indication of erosion. The pressure reduction in graph C2 right before

284 s is because a valve closer to the beginning of the slot is opened. Therefore, there is shorter length,

less friction and since the pressure at each outlet is considered zero, the pressure at P2 after opening

valve V5 gets close to zero but not zero. And the pressure-drop at both P2 and P3 from 140 to 220s is

therefore not due to the erosion, it was probably due to the filtration before P2 at 60 and 70 µm apertures.

The results of (zero grout flow) from V6 and V7 is verifying that (Table 5).

After flow stop in V6 and V7, V8 was opened at 470 s and the remaining grout material passed through

the VALS with 3752 g (see Table 5 and Figure 39). From the beginning of the test and up to 284 s (as

seen in Figure 39a) the pressure sensors P2 and P3 maintained the same movement, which was based

on the phenomena of filtration and erosion happening long before the grout reached V5. There is a big

gap in the curve lines of test C2 compared to test C1, between P1 and the other two pressure sensors (P2

and P3). This gap is an indication of an early filtration and the main reason might be poor grout

penetrability in V4 and V5, which are placed far away. The gap between P2 and P3, as seen in Figure 39,

was due to friction.

42

Figure 39: Development of static pressure conditions along the VALS registered by P1, P2 and P3 in test C2. a)

Test result C2, total time. b) Test result C2, up to 350s.

4.3 Evaluation of min-pressure envelope and pressure impulse dissipation

All dynamic tests were performed by applying low-frequency dynamic impulses. Results from the first

dynamic test D1 are presented in Figure 40. The result of test D1 reveals a similar result to the test

carried out by A. N. Ghafar et al., (2017). The results obtained from this test showed up to 31 % and 22

% of the initial applied amplitude remained at 2.36 and 2.7 m from the slot’s beginning, respectively

Filtration

Erosion

270 s

V8 opened at 470 s

V5 opened at 284 s

a)

b)

43

Figure 40: Development of dynamic impulses along the VALS registered by P1, P2 and P3 in test D1 (2s/2s

peak/rest period). a) Test result D1, total time. b) Test result D1, from 170 to 230 s.

Another approach to evaluation of the results obtained from dynamic pressure tests is using minimum

pressure envelope. This evaluation method is based on measuring pressure over time, accompanied by

a min pressure envelope intended to visualize both the filtration and erosion processes during the

experiments (Ghafar et al., 2016). Results from the second dynamic test D2, are illustrated in Figure 41

and Figure 42. By studying the min pressure envelope, both the filtration and erosion processes along

the experiment can be visualized (Figure 41b and Figure 42a).

The results obtained from tests with 1s/5.5s peak/rest period showed up to 30 % of the initial applied

amplitude remained at 2.36 m from the slot’s beginning, see Figure 41a. The pressure curve registered

by P2 demonstrates random filtration and erosion Figure 41b. This phenomenon occurs due to an

opened channel existing in the slot. Since this channel is kept open for a longer time, the grout

penetrability is improved, and more grout is injected into the system. In Figure 41a, the pressure sensor

P3 starts at almost 1 bar and does not increase much. An explanation could be that the filtration between

V5 and V6 stopped the grout flow in the slot and caused the pressure to remain low. After passing 64 s

without any grout coming out, V5 was opened and P3 drop to zero.

Peak perioder

Rest perioder V5 opened at 197s

22% remaining

amplitude after 2.7 m

32% remaining

amplitude after 2.36

m

a)

b)

44

Figure 42b shows results from performed dynamic test D2 from 270-300 s. The selected peak/rest

period is clearly registered which means that the applied pressure has been working efficiently.

Figure 41: Development of dynamic pressure impulses along the VALS registered by P1, P2 and P3 in test D2 (1s/5.5s

peak/rest period). a) Test result D2, total time. b) Test result D2, from 100 to 300 s.

V6 opened at 297s

30% remaining amplitude after 2.36m

V5 opened at 64s

a)

b)

45

Figure 42: Development of dynamic pressure impulses along the VALS registered by P1 in test D2 (1s/5.5s

peak/rest period). a) Test result D2, from 100 to 300 s. b) Test result D2, from 270 to 300 s.

Results from the dynamic test D3 are illustrated in Figure 43. Test D3 was also performed with 1s/5.5s

peak/rest period in VALS. The pressure graphs registered by pressure sensors P2 and P3 follow the same

path from 120 s until V5 is opened, however, the rest/peak period is not clear as in test D2. Even so, what

is clear is that the filtration in the aperture sizes of 50 and 60 µm occurred after 145 s, since the registered

graphs by P2 and P3 show the same flow configuration.

The test D3 was evaluated by using the min pressure envelope, see Figure 43 These min-pressure

envelopes can be divided in five different periods: 125 – 150s; 150- 170s; 170-220s; 220-230s; and 230-

257s (Figure 43a). The first period shows the minimum pressure points of each cycle increasing which

indicates that filtration has occurred. This is a strong sign of flow-stop at the constriction 40 µm,

therefore V5 was opened. In the second period, random filtration and erosion occurred. In the third

period the graph shows relatively stable pressure development. In the fourth period, the minimum

points of each cycle decreased instead, which means erosion has occurred. This reveals a sign of

improved grout spread and followed by the last period with filtration. Figure 43b shows test results D3

Rest period Peak period Ball-valve 1

opened

Ball-valve 1

closed

Ball-valve 2

opened

Ball-valve 2

closed

Ball-valve 1 & 2

closed

a)

b)

46

from 100-170 µm and as it is shown with the filtration line in the graph registered by P3 a full filtration

is reached, thereby V5 is opened.

V5 opened

Erosion

Filtration

a)

Filtration

V5 opened

Figure 43: Development of dynamic pressure impulses along the VALS registered by P2 and P3 in test D3 (1s/5.5s peak/rest

period). a) Test result D3, total time. b) Test result D3, from 100 to 170 s.

47

5 Conclusions

The present experimental study was conducted to investigate and improve grout spread into fractured

hard rock by applying low-frequency dynamic pressure impulses using Varying Aperture Long Slot,

“VALS” (Ghafar. A. N., 2017). Two types of pressure (static and dynamic) were tested in order to compare

and examine the acquired results. The chosen materials for grout mixture were a fine cement material

of Sika Injektering 30, tap water, and superplasticizer Sika iFlow-1 with 0.5 % content. The w/c ratio was

0.8. The performed tests were divided into two test groups, static and dynamic. The dynamic test group

contained three tests where the first test was performed with a peak/rest time of 2s/2s, and the second

and third tests were performed with a peak/rest time of 1s/5.5s.

The notable findings from this study are drawn as follows:

In general, application of low-frequency dynamic pressure had an impact on improving grout

spread compared to the application of constant pressure through the artificial fractures in

VALS.

The results of the selected peak and rest periods, i.e. 2s/2s and 1s/5.5s, revealed that cycle

periods regulate the filtration and improved the grout penetrability effectively.

The results obtained from tests with 1s/5.5s peak/rest period showed less grout loss (61%).

compared to test results of 2s/2s peak/period (80%). The choice of a longer rest period gave

a sufficient result, thereby, the amount of injected grout into the VALS was improved up to

more than two times.

Using application of low-frequency dynamic pressure impulses with 1s/5.5s peak/rest period

in VALS, the total grout volume passed through aperture sizes of 40-70 µm was improved up

to 10 times compared to static pressure condition.

The mechanism of action under application of dynamic grouting showed an improvement of

grout spread. This could be caused by erosion of the filter cakes due to the change of the flow

pattern.

The remaining amplitude of the pressure-impulses in test 2s/2s peak/rest was up to 32% and

22% of the initial applied amplitude at 2.36 and 2.7 m from the slot’s beginning.

The remaining amplitude of the pressure-impulses in test 1s/5.5s peak/rest was up to 30%

of the initial applied amplitude at 2.36 m from the slot’s beginning.

Successful observation of filtration and erosion was achieved: the graphs showed a clear

change of the curves’ shape between filtration and erosion. By dismantling the VALS, a better

48

understanding of filtration and erosion occurring in the chambers and constrictions was

attained.

5.1 Future work

In the present approach, a closed system has been used. With this particular limitation, the dissipated

grout volume during the rest times in the dynamic tests was too high. This could be avoided by

developing the closed system into an open system, using a bigger grout tank and installing a pump to

prevent grout loss. Another suggestion for future researchers in this field is to consider the roughness of

rock in the next designed apparatus replication. In this way, one could avoid the smoothness of the steel

plates and any unwanted influence on test accuracy.

49

6 References

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51

Appendix A

A1: Static test C2

Figure 44, Figure 45 and Figure 46 shows the pictures of the grout path left after performed static test

C2.

.

1 2

3 4

5 6

Figure 44: Observation of filtration and erosion areas after application of static conditions inside the VALS,

from 230-130 µm.

52

7 8

9 10

11 12

Figure 45: Observation of filtration and erosion areas after application of static conditions inside the VALS, from

100-60 µm.

53

Figure 46: Observation of filtration and erosion areas after application of static conditions inside the VALS,

from 50-30 µm.

13 14

15 16

17 18

54

A2: Dynamic test D3

Figure 47, Figure 48 and Figure 49 shows the pictures of the grout path left after performed static test

D3.

Figure 47: Observation of filtration and erosion areas after application of dynamic grouting/conditions at 230-100 µm

inside the VALS.

1 2

3 4

5 6

55

7 8

9 10

11 12

Figure 48: Observation of filtration and erosion areas after application of dynamic grouting/conditions at 100-50 µm

inside the VALS.

56

13

Figure 49: Observation of filtration and erosion areas after application of dynamic grouting/conditions at

40 µm inside the VALS.

57

58

59

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