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Long Son Petrochemicals Co., Ltd

LSP COMPLEX PROJECT

ITB PACKAGE A1 OLEFINS PLANT Rev. 0

Annex B Technical Design Information

Attachment B7.1.1-01 : Geotechnical designreport

Page: 1 of 102ITB No : OL1-1Y22-0001

____________________________________________________________________________________________

Confidential: This document is confidential and must not be copied or reproduced except with the express

permission of Long Son Petrochemicals Co., Ltd.

PART II

Annex B Technical Design Information

Attachment B7.1.1-01 : Geotechnical design report


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Geotechnical Design Report

Long Son Petrochemical Complex Project for Phase 1 Land Development

MAA Geotechnics Co., Ltd. 1

Table of Contents

Table of Contents 1

List of Tables 2

List of Figures 3

List of Appendices 5

1. Introduction 6

1.1 General 6

1.2 Scope of Work 6

1.3 Definitions, Design Criteria, Constraints and Assumptions 7

2. Subsurface Ground Conditions 9

2.1 Introduction 9

2.2 General Physical Soil Properties 9

2.3 Strength Characteristics 10

2.4 Rock Type and Properties 10

2.5 Subsoil Conditions 10

2.6 Selection of Geotechnical Design Parameters 12

2.7 Groundwater Conditions 12

3. Ground Modification Methods and Foundation Design 13

3.1 Introduction 13

3.2 Ground Modification Methods 13

3.2.1 Excavation and Replacement 13

3.2.2 Dynamic Compaction 14

3.2.3 Dynamic Replacement 16

3.2.4 High Energy Impact Compaction 16

3.2.5 Other Method- Rapid Impact Compaction (RIC) 17

3.3 Recommendations on Ground Treatment Methods 17

3.4 Choice of Type of Foundations 18

3.5 Shallow Foundation Design 19

3.5.1 Bearing Capacity of Shallow Foundation 19

3.5.2 Settlement of Foundation 20

3.5.3 Tank and Heavy Equipment Foundation 21


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3.5.4 Medium Structures 21

3.5.5 Other Structures 21

4. Earthworks and Site Preparation 22

4.1 Introduction 22

4.2 Proposed Plant Elevations 22

4.3 Seasonal Weather Conditions 22

4.4 Earthworks 23

4.5 Clearing, Grubbing and Top Soil Removal 23

4.6 Soil Excavation 24

4.7 Water Jetting 24

4.8 Rock Excavation 24

4.8.1 Mechanical Excavators, Ripping and Impact Breakers 25

4.8.2 Rock Blasting 26

4.8.3 Gap Filling with Concrete 26

4.9 Structural Fill 26

4.10 Normal (Non-Structural) Fill 27

4.11 Sources of Fill Materials 27

4.12 Sounding Test Methods 284.13 Filling in Phase 2 Land Development 29

4.14 Flood Protection System 29

4.15 Drainage Control 29

4.16 Access to Construction Areas 29

4.17 Temporary and Permanent Cut and Fill Slopes 30

4.18 Trial Section of Dynamic Compaction or Dynamic Replacement 30

5. Summary, Recommendations and Conclusions 31

6. References 33

List of Tables

Table 1 Summary of Field and Laboratory Testing in Phase 1 Area 34

Table 2 Recommended Design Soil Parameters for Zone 1 35

Table 3 Recommended Design Soil Parameters for Zone 2 36

Table 4 Comparison among Various Ground Modification Methods 37


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Figure 46 Proposed Area for Clay Filling 97

Figure 47 Proposed Temporary Earth Dike for Flood Protection 98

Figure 48 Example on Slope Stability Analysis 99

Figure 49 Possible Trial Excavation/Blasting and Dynamic Compaction Locations 100

List of Appendices

A Estimated Settlements of Shallow Foundation A-1 to A-10

B Estimated Bill of Quantities B-1 to B-19


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1. INTRODUCTION

1.1

General

The proposed Long Son Petrochemical Complex in Vietnam with a total area of 390

hectares will be built to the south of Ho Chi Minh at Long Son District adjacent to Ganhrai Bayas shown in Figure 1. The complex will be constructed in two (2) phases with almost equal areas.

The satellite photo in Figure 1 indicated that significant portion of the site is occupied by

aquaculture farms as well as canals or water passages. Some hills are found to the north and

northeastern boundaries of the site, and the remaining area is almost flat.

During the past two years, significant engineering works have been conducted to examine the

viability of the project, including the selection of the project site with execution of soil

investigations in both onshore and offshore. The owner,Long Son Petrochemical Co., Ltd., had

approachedMAA Geotechnics Co., Ltd. to evaluate the geotechnical conditions of the onshore

area along with preparation of design document for site preparation in the land development.

A tentative layout plan of the complex in Phase 1 land development was provided byLong Son Petrochemical Co., Ltd., with an approximate occupied area of 170 hectares as

illustrated in Figure 2. The proposed facilities can be divided into twelve (12) blocks, including

the processing plants, tank farms, power plant, warehouses and various buildings etc. An

additional block (Block No. 13) from Phase 2 with an area of 21 hectares is included in this

package because of similar ground modification requirements. It should be emphasized that an

effective layout of the complex depends on various crucial factors, including functionality of the

facilities, effectiveness of the operation, safety measures, logistics of the operation, topography

of the site and subsoil conditions etc.

In most petrochemical projects, there is always a great uncertainty in the construction

time of civil works, especially on the ground preparation including ground treatment and

foundation works. If the ground treatment is needed for the site, then selection of the ground

treatment method may be critical in controlling the overall construction time. In general, the cost

of ground treatment and the foundation may not be significant compared with the total

investment, but these works can have severe impact on the construction time if they were not

properly accounted for. A good understanding on the geological or subsoil conditions of the

project site is essential for appropriate planning of the ground preparation and foundation works.

Thus, a geotechnical interpretative report was prepared providing the findings from the

geological survey of the site as well as the interpretation of the geotechnical data gathered from

all available soil investigation programs.

This design report concentrates on the design aspect of Phase 1 land development,

highlighting the selection of ground modifications as well as the subsequent foundation designfor supporting the petrochemical structures.

1.2

Scope of Work

The scope of work for the geotechnical design for Phase 1 land development can be

summarized as follows:

Summarize geotechnical data. Relevant geotechnical data from the geotechnicalinterpretative report for Phase 1 development are extracted from the geotechnical

interpretative report. The subsoil conditions and soil profiles are also highlighted.


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Propose appropriate ground modifications. For Phase 1 area with poor overlain soils,either residual soils or sedimentary soft clay with shallow bedrock depth, the ground

modifications will be needed to improve the subsoils to a stage that the shallow

foundation becomes viable. This is the most critical factor in the selection of ground

modifications.

Optimize plant elevations of each block. Since Phase 1 development is situated mainly

on hilly ground, optimizing the plant elevation of each block with minimum earthwork

(such as cut and fill) is essential. In addition, the treated subsoil should also be able to

provide adequate the bearing capacity for the structures.

Propose suitable types of foundation. If appropriate ground modification is used,shallow foundation, such as mats or footings, can be applied with much lower foundation

cost compared with pile foundation.

Evaluate seismic conditions. Because of recent seismic activities in Southeast Asia, thepetrochemical industry is more aware of the importance of this hazardous factor, seismic

study is usually required. This has been summarized in the geotechnical interpretativereport.

Outline foreseeable earthwork construction issues. From the subsoil conditions,possible methods of ground modifications along with suitable foundations are outlined in

this report. Merits and limitations of each method are also discussed.

1.3 Definitions, Design Criteria, Constraints and Assumptions

Definitions

Some relevant terminologies used in this report are defined as follows:

Zone: The term, zone, is used to describe an area with similar geological features. For

this project, two (2) main zones are identified based the geological and geotechnical data

collected.

Phase: The term, phase, is used for project development plan only. Phase 1 landdevelopment will occupy an area of around 170 hectares with twelve (12) blocks of

facilities. Additional block (Block No. 13) from Phase 2 is included because of similar

ground treatment required.

Block: The term, block, is used to describe an area with individual function or facility.For example, in Phase 1, Block No. 12 is reserved for tank farms only.

Design Criteria

The design criteria for the earthwork in Phase 1 include the plant elevations, the long-

term or residual settlement of the ground and the bearing capacities of the foundation.

The minimum plant elevation will be set at +2.9 m NDL; this is based on the

hydrological study made as well as designed elevations of nearby facilities.

The residual settlement of the ground is always a concern for long term maintenance and

operation, thereforeLong Son Petrochemicalhad specified a settlement rate of no greater than

2.5 cm per year and less than 20 cm in 50 years of operation. In the residual soil zone, this

criterion is achievable without any ground improvement or modification since the subsoil isrelatively firm, but it will not be stiff enough for supporting structures economically. But in the


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sedimentary clay area, it will be required to improve or to replace the soft clay for minimizing

the residual settlement.

When shallow foundation is used, then a design of load 30 ton/m2is expected for the tank

area in Block No. 12. A lower design load of 15 ton/m2 is assumed for other facilities. In

general, a factor of safety of 3 will be adopted for shallow or mat foundation. The foundation

settlement will be limited to 25 mm for general structures.

If pile foundation is adopted, then a factor of safety of 2.5 will be applied, and the

foundation settlement will be controlled by this factor of safety to within acceptable range for

general structures.

Constraints

The design constraints for the site preparation include:

Optimum earthwork. Since the area for Phase 1 land development is around 170

hectares, it will require vast amount of earth-moving. Therefore, optimizing theearthwork is a key task in the site preparation, minimizing the impact of earth

transportation, especially on imported fill and on disposal of unsuitable material.

Construction schedule. Long Son Petrochemical project will have a rather tightconstruction schedule. It is expected to complete major earthwork of the site preparation

in a year.

Land leasing schedule of Phase 1 and Phase 2. The land leasing for Phase 1 and Phase

2 may not be completed at the same time, depending on the requirements in the land

usage during construction and after construction.

Blasting safety distance. Due to presence of granitic rock outcrop as well as shallowbedrock, rock blasting is inevitable. For safety reasons, the blasting safety distance will

have to follow local laws and regulations. The blasting will be very critical along the

property line area since the safety limit may go beyond the property line.

Assumptions

Because of various uncertainties in the project development, the following assumptions

have been made in developing the design concept:

Leasing of land. The land leasing of Phase 1 and Phase 2 will have to be made together.

Hauling of imported fill. There is no restricted in hauling the fill to the site.

Restriction in rock blasting within the site. When rock blasting is required within thesite, only the laws and regulations on blasting are applied.

Schedule of earthwork. It is assumed that the schedule of earthwork will be around oneyear.

Foundation footprints. To minimize the cost of ground modification, the layout of thefoundations should be made available before ground modifications; otherwise the entire

area will have to be improved. It is assumed that 100% of the area will be improved in

the cost analysis at this moment since the footprints of the foundation are not present. It

is possible to reduce the improvement area when the foundation locations are finalized.


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2. SUBSURFACE GROUND CONDITIONS

2.1 Introduction

The recent soil investigation work carried out by Portcoast Consultant Corporation

under Long Son Petrochemical Co., Ltd. was conducted in (2) stages, namely during October2008 to January 2009 and April to May 2009. A total of forty-eight (48) boreholes and twenty-

nine (29) field vane shear tests were performed. The field exploration consisted of soil drilling

as well as rock coring, along with some in-situ soil testing, such as SPT tests and field vane shear

tests. The collected soil samples from the boreholes were later sent to the laboratory for further

testing in determining their engineering properties, such as physical properties, strength and

consolidation characteristics.

Previous drilling works conducted in Long Son Petrochemical Complex boundary

consisted of six (6) boreholes in the petrochemical complex investigation and seventeen (17)

boreholes in Refinery No. 3 investigation. The available data included soil boring logs along

laboratory test results from the petrochemical complex investigation, but no laboratory data were

available from the refinery investigation. Summary of the field and laboratory tests performed in

Phase 1 area is given in Table 1.

2.2 General Physical Soil Properties

Figure 3 presents the relationship of natural water content versus total unit weight for all

available soil samples. The results of sedimentary soft clay deposits with high water content

indicated that the degree of saturation varied between 90% and 100%. For the residual soil, the

results indicated that the natural water content ranges from 10% to 40%, with large variation in

the degree of saturation possibly due to unsaturated condition for soil samples above the

groundwater table. The low degree of saturation may also cause by some water loss in the soilsample during sampling and storing process. The total unit weights of some soil samples

appeared to be relatively low (less than 1.8 ton/m3) based on the phase relationship, indicating

some errors in the measurements. It is possible that either the sample dimensions or the sample

weights were measured incorrectly.

Figure 4 shows the Atterberg limits of the soil samples on the plasticity chart. The liquid

limit has exceeded 120% for some soft clay samples, but lower value of around 20% is found on

the very stiff clay. The results also showed that the most data points lie close to or slightly above

the A-line. If the soils tested are from a specific geological setting, then the plasticity of the soils

will be somewhat parallel to the A-line on the plasticity chart.

The profiles of physical and strength properties of the residual soils (Zone 1) are plottedagainst depth as shown in Figure 5. The residual soils have water content of 10 % to 20 % with

plasticity index of 10 % to 15 %. The unit weight ranges from 1.8 to 2.1 ton/m3. The fine

content of the residual soil ranges between 15 % and 40 % as shown in Figure 6, and the soils are

dominated by coarse to medium sands.

For Zone 2 area with sedimentary clay deposit, Figure 7 shows the profiles of water

content, liquid limit, unit weight, fine content, undrained shear strength and SPT N value with

elevation for various soft clay thickness sections. The average water content of the upper soft

clay is around 90-100 %. The liquidity index appeared to be around unity indicating that the soft

soil was either sensitive or low in strength.


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2.3 Strength Characteristics

The SPT N profiles for Zone 1 residual soils are plotted in Figure 8, indicating that some

loose material was found in the upper 2 m of soils, followed by greater SPT N values for deeper

residual soils.

A series of field vane tests were performed in Zone 2 sedimentary clay deposit area downto 30 m deep at one location. The test results of field vane shear test including undisturbed and

remolded strength, sensitivity, and corrected undrained shear strength are presented in Figure 9.

The undrained shear strength from the unconfined compression test and the corrected field vane

shear strength were also plotted against elevation as shown in Figure 7, indicating low strength

in soft clay. There were several points with values of undrained shear strength less than 1 ton/m2

at depths of 0 to 6 m. In general, the undrained shear strength of the sedimentary clay increases

with increasing depth.

2.4 Rock Type and Properties

Strength properties of the rock samples including unconfined compressive strength and

modulus along with their densities and RQD (rock quality designation) are presented in Figure

10. Most rock samples have density ranging between 2.5 and 2.65 ton/m3. The unconfined

compressive strength varies significantly from 2 to 189 MPa with modulus of 1 to 25 GPa

depending on the degree of weathering. The variation in the unconfined compressive strength of

granitic rock samples is presented in Figure 11, with most values greater than 25 MPa.

2.5 Subsoil Conditions

From the geological formation along with the geotechnical data collected, the project site

can be divided into two (2) distinct zones. The hilly area with residual soil cover will bedesignated as Zone 1, and the lower coastal plains with sedimentary clay deposits will be

designated as Zone 2. Zone 1 covers an area of 155 hectares, and Zone 2 occupies an area of

235 hectares.

For Phase 1 development of the complex, it will cover most of Zone 1 area along with

some portions of Zone 2 area (defined as Zone 2B) with shallow soft clay deposit. The

combined area will be around 170 hectares.

The subsoil conditions from ground surface down to the rock layer can be divided into a

few distinct layers as shown in Figures 12a through 12f with values of undrained shear strength

and SPT N shown next to the boreholes. The general properties of the soil layers are described

as follows:

Geological Zone 1: Residual Soil

a) Very Loose to Loose Silty SAND:

The upper soil layer of the residual soil area consists of yellowish gray, very loose to

loose silty SAND. This layer is a result of weathering process and surface erosion. The thickness

of this layer varies from 1 to 3 m with greater thickness in the southwest direction. The SPT N

value ranges from 2 to 10 with natural water content of 8 % to 22 %. The fine content of this

layer is between 15 % and 44 % except at Borehole No.L-18 with higher fine content. For

Borehole No. L-18 located in the area between the residual soil and marine sedimentary soil, the

fine content of upper soil varies from 53% to 95%.


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b)

Medium Dense to Very Dense Clayey/Silty SAND:

Below the very loose to loose silty sand is a layer of medium dense to very dense

clayey/silty SAND with yellowish gray and bluish gray in color. The thickness of this layer

ranges from 1 to 3.5 m. The fine content varies from 15 to 40 % with SPT blow count of 11 to

50, and the natural water content is between 10 % and 20 %. This layer is originated from the

granitic rock below through weathering.

c) Granitic Rock:

The granitic rock is found below the medium dense to very dense silty and clayey sand

down to the end of the boreholes. The top of the rock was found from depths of 1 to 6.5 m

below ground surface. The average elevation of bedrock appeared to increase from southwest to

northeast direction similar to the general topography. The unconfined compressive strength of

the rock samples tested varied from 10 and 114 MPa depending on the degree of weathering, and

the rock strength distribution is shown in Figure 11.

Geological Zone 2: Sedimentary Clay

a) Very Soft to Soft CLAY:

The first layer of this zone consists of gray to dark gray and bluish gray, very soft to soft

CLAY which is found from the ground surface of lower flat ground area at elevations of 1.5 to

+2.0 m NDL. The thickness of this layer varies significantly from 3 to 35 m with deepest to the

west because of the topography and the geology of this site. The natural water content ranges

from 60 % to 120 % with liquid limit of 45 % to 120 %. This soft clay layer will give rise to

ground settlement after filling, and it will also initiate negative skin friction on piles if the fill is

placed over it.

b)

Medium Stiff to Very Stiff CLAY:A layer of stiff to very stiff clay is found below the soft clay in some boreholes,

especially in the southwestern area with significant variation in thickness. The thickness of this

soil layer varies from 2 m to over 15 m with greater thickness at the southwest corner. The SPT

N value varies from 7 to 36 with natural water content of 19 % to 50 %.

c)

Medium Dense to Very Dense Clayey/Silty SAND:

This layer consists ofmedium dense to very dense clayey/silty SAND with yellowish gray

and bluish gray in color. The thickness of the sand varies from 0.5 m to 6 m over the entire site

except in some boreholes. The fine content ranges from 9 to 45 % with the average natural water

content of 20 %. This layer is formed from the weathering of the granitic rock.

d) Granitic Rock:

The granitic bedrock is found from depths of 3.5 m to over 30 m in the southwest area.

Rock outcrops were found in the interface areas between Zone 1 and Zone 2 with locations

highlighted in Figure 13. From the appearance of the rock outcrops within the site, these rock

exposures may imply undulation of the bedrock in the entire bedrock formation as illustrated in

Figure 14 . The unconfined compressive strength of the rock samples tested varied from 2 and

189 MPa depending on the degree of weathering.

Figures 15 through 17 show the elevation contours of the ground surface, bottom level of

soft/loose soil and top level of the bedrock.


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2.6 Selection of Geotechnical Design Parameters

The design curves of physical properties and strength parameters are given in Figure 5

and Figure 7 for residual soils and sedimentary clay deposit, respectively. Summary of these

selected parameters are tabulated in Tables 2 and 3.

2.7 Groundwater Conditions

From the soil investigation performed, the groundwater tables were measured in some

boreholes after completion of the boring. The measured groundwater table varied from 0.2 m to

2 m below the ground surface. For the flat ground area, the average groundwater level was

around +0.5 m NDL. The high groundwater table is particularly critical in the ground

densification by the dynamic compaction technique.

For sloping ground, the groundwater table will follow the topography to a certain extent.

It is advisable to continue the groundwater measurements even after the soil investigation period,

so that the seasonal fluctuation in the groundwater table can be determined.


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3. GROUND MODIFICATION METHODS AND FOUNDATION DESIGN

3.1 Introduction

From the subsoil conditions, the proposed petrochemical complex will be located in areas

with residual soils and soft clay deposit with various thickness as shown in Figure 18. The upperloose or soft soil layer will lead to the excessive settlement and instability; therefore ground

improvement cannot be avoided before construction of the facilities. The treatment on the

residual soil will be somewhat different from the soft clay, soil replacement or densification will

be the most appropriate method for the residual soil area.

For the soft clay area, there are several methods of improving the properties of soft clay

to reduce the future settlement or to improve the stability. It should be kept in mind that most of

the ground improvement methods can be rather costly compared with conventional earthwork,

therefore the use of any ground improvement would depend greatly on both technical and

financial aspects of the project. For subsoils requiring consolidation ground treatment, such as

prefabricated vertical drains etc., the improved ground will be designed to carry loads from the

fills and light structures or traffic loads, high permanent load intensity structural loads (with

loads greater than 30 ton/m2) would require additional load support mechanism, such as piles

etc.).

Based on the subsoil conditions encountered in Phase 1 development, pile foundation

would not a feasible option because of cost and suitability. Shallow foundation will be a better

alternative along with the applications of appropriate ground modification techniques, such as

soil replacement, ground densifications (dynamic compaction or dynamic replacement) etc. In

the soft clay area, soil replacement will be the most economical solution because of limited soft

clay thickness.

For flood control, the facilities should have plant elevation of no less than +2.9 m NDL,

implying that it will be necessary to raise the low lying areas (especially in Zone 2) with

appropriate fill up to the foundation level so that shallow foundation can be applied directly.

3.2 Ground Modification Methods

Phase 1 land development covers the entire Zone 1 residual soil area along with part of

Zone 2 area with sedimentary clay of less than 5 m deep. With limited thickness of loose

residual soil and sedimentary clay, soil replacement and ground densification (for residual soil

area only) techniques will be the best solutions for Phase 1 development. The following sections

briefly describe these ground improvement methods with comparisons given in Table 4.

3.2.1 Excavation and Replacement

Apart from improving the compressible soils by consolidation through PVDs and vacuum,

soil replacement can be an attractive option as illustrated in Figure 19. The principle of the soil

replacement is to remove the compressible soils down to required depths, and to replace with

suitable compacted fill. The depth of excavation will be governed by the long-term settlement of

the remaining compressible soils and the overall stability of the excavated pit. It will not be

economical and practical to replace the soft compressible soils if the replacement depth is too

deep because of the vast quantity in replacement and excavation.

There are several major advantages of adopting this method, including:

Ease of construction. The soil replacement predominately involves earthwork with


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excavation, fill placement and compaction etc., which can be handled by the local

earthwork contractor with appropriate construction equipment. But dewatering should be

planned if there is a possibility of water flowing into the excavated pit.

Construction control. The client or clients representatives can also supervise and

control the earthwork as in any other conventional earthwork.

Excavation and filling time. The excavation and filling time can be adjusted depending

on the capacity of the construction equipment and manpower. To accelerate the

construction, it is possible to increase the construction equipment and manpower.

Reuse of excavated soils.The excavated soils can be used as an earth fill or surchargematerial. Therefore, it may not be necessary to dispose the excavated soil outside the

project boundary.

Cost consideration. With no special construction techniques and construction materials,the construction cost of the soil replacement would be the most attractive option.

The main obstacle in applying this method in this project is the uncertainty in estimatingthe amount of boulders and excavation of the undulated bedrock. The undulation of the rock is

apparent in the low-lying area with rock outcrops as highlighted in Figure 13. To achieve a good

soil base for the shallow foundation, weak and unsuitable (high fine content) natural soils will

have to be removed entirely with replacement by proper structural fill. Removal of the weak

soils in pockets between rocks would be a challenging task, and some rock leveling (by ripping,

breaking or blasting) would be required to overcome this problem. Rock excavation or rock

removal would be the most critical task in the replacement process, because of uncertainty in

rock excavation time and issues associated with rock blasting etc. At this moment, it is rather

difficult to predict the degree of rock undulation based on the information available, thereforetrial excavations are proposed to reduce this uncertainty.

Another possible option will be to remove the soils and the loose boulders, followed bysome rock cutting down to 50 cm below the foundation level only. Then the crushed rock is

dumped with some compaction by roller compactors. Additional compaction by dynamic

compaction can be used if the crushed rock did not meet the specifications. This method will

reduce the rock cutting to minimum, but trials should be performed to evaluate the

performance of this option.

Nevertheless, soil replacement is the most cost effective method for Phase 1 development,

especially in Zone 2 with shallow sedimentary clay deposits along with high design loads (in

tank farm area).

3.2.2 Dynamic Compaction

Dynamic compaction is the process of densifying soils to relatively great depths by

applying energy at the ground surface with illustration shown in Figure 20. The soils are

densified at the prevailing water content when the energy is applied. It involves repeated

dropping of large steel tampers by means of crawler cranes in pre-determined 3 to 7.5 m on-

center grids. Tampers typically range from 6 to 20 ton, with drop heights of about 12 to 24

m. The repeated application of the high energy impact causes deep compaction in a soil

mass. Densification occurs by rearrangement of the soil particles (loose sands, silts, etc.) or

collapse of voids within the soil mass (old landfills, sinkholes, etc.). The thickness of deposits

being densified generally range between 3 and 10 m.


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Depending upon the particular site characteristics and structural requirements, an area

treatment may be performed, or the individual footing locations may be compacted. Footing

treatment by dynamic compaction is very cost-competitive when compared to other foundation

systems. Foundation costs can often be reduced significantly in comparison with deep

foundations. With an area treatment, dynamic compaction tends to serve as large-scale deep

proof-testing, with additional tamping being performed in softer areas, thus creating moreuniform subsoil conditions.

The successful application of a dynamic compaction program requires a carefully-

controlled application of impact stresses to the ground, using a predetermined grid pattern. The

craters that are created by the tampers may be up to 2 m in depth and are backfilled by either

dumping fill into the craters or by pushing the craters in with a bulldozer. Multiple phases of

energy application may be required, depending upon the level of improvement required, the

depth of the water table, the soil types, etc. Following completion of the "high-energy" tamping,

a low-energy or "ironing" phase is generally performed to densify the crater backfill and the

disturbed soil between the craters. The ironing phase consists of dropping the tamper from a

height of 3 to 6 m on nearly overlapping centers.One of the most important considerations regarding the applicability of dynamic

compaction is the type of soil being densified. In general, dynamic compaction is most

beneficial on granular materials. Granular materials enable excess pore water pressures that

develop during the densification process to dissipate rapidly. On the other hand, a category of

materials not conducive to dynamic compaction include impervious soils (either natural or fill)

that are saturated. Improvements cannot be made with saturated soils unless the water content of

the soil is lowered. For example, the permeability of clay soils is generally so low that excess

pore water pressure generated during dynamic compaction cannot dissipate in a timely manner.

Therefore, unless escape routes for excess water can be created then dynamic compaction

would not practical for these types of materials. Lastly, the category of soils ranging between

granular materials and saturated clay are classified as semi-pervious. This particular categoryincludes silts, clayey silts or sandy silts. Generally, dynamic compaction will be effective in

these soils. However, since drainage is obviously much slower than in more granular soils,

many phases of energy application are necessary. Water table levels within approximately 2 m

below the level of dynamic compaction often cause problems. During impacting, crater depths

are frequently in the order of 0.6 to 1.2 m, and high pore water pressures generated in the soil

mass generally cause the groundwater table to rise. This could result in water filling into the

craters. Additional drops could cause intermixing of the soil and water with subsequent

softening of the upper portion of the soil mass. If the water table is within 2 m of the ground

surface, the following measures can be taken:

Lowering the ground water table by dewatering ditches or dewatering wells.

Raising the ground surface by placing fill.

The depth of soil improvement depends on the energy per drop, which can be estimated

by the following equation:

WHnD=

Where D = depth of improvement (m)

n = empirical value varies from around 0.3 to 1, depending on the soil type

W = tamper weight (ton)


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H = drop height (m)

The degree of soil improvement depends primarily on the total energy applied to the soils,

i.e., the more energy input into the soil, the greater the degree of improvement. The degree of

improvement is generally expressed in terms of relative density or density as determined by

some in-situ tests.

The dynamic compaction is an attractive method for densifying the loose residual soils to

a degree which can be used as base for the shallow foundation. This method minimizes the

amount of earthwork, in terms of cut and fill, by densifying the in-situ natural soils. To achieve

a satisfactory result, the soils to be improved should be granular, that is sandy soils with low

fines, and the groundwater level should also be sufficiently low in the required improvement area.

Figure 21 shows the range of the gradation curves of the residual soils compared with the soil

group chart used in dynamic compaction work. Most of the residual soil data fall in the previous

and semi-previous soil range. If dynamic compaction is proved to be ineffective for the semi-

pervious soils encountered, then alternative method, such as dynamic replacement, can be

introduced, which uses the same equipment as in the dynamic compaction. The dynamicreplacement method is described in later section.

Another critical factor in the dynamic compaction is the control of the groundwater level.

High groundwater table was found in the hilly area of Zone 1 during the soil investigation stage

with groundwater table at 0.7 to 2 m below the ground surface. It is possible to reduce the

groundwater table in the hilly area by providing adequate trenches or ditches around a particular

block with proper drainage down the hill under gravity instead of pumping or dewatering.

Dewatering by pumping wells can be applied if further reduction in the water level is needed

during dynamic compaction. For some bocks, the plant elevations are also higher than the

original ground level, then the performance of the dynamic compaction should be more visible.

3.2.3 Dynamic Replacement

Dynamic replacement is used to form granular columns with diameters of 2 m to 2.5 m to

depths of up to 8 m. Replacement columns are formed by driving the coarse material into the

soil with 15 to 30 ton pounders, dropped from heights of 10 to 40 m. The column is refilled with

granular material, which is compacted. The process as shown in Figure 22 repeats until the

desired depth and column volume are achieved. These large diameter granular columns have a

very high modulus of deformation therefore reducing post-construction settlements. They also

help to increase the stability against global failure when used under embankments due to their

high shear strength and friction angle.

Since the equipment used is similar to the dynamic compaction, this method can be used

as an alternative to the dynamic compaction for less pervious soils (semi-pervious soils as

described before). The additional granular filling into the crater will further enhance the

properties of the subsoils.

3.2.4 High Energy Impact Compaction

High energy impact compaction (HEIC) is a procedure of compacting in-situ materials at

depth with example shown in Figure 23. The HEIC application is used to improve the

engineering properties of soils, both above and below the groundwater level. Soil strength isincreased, and compressibility and settlements are decreased as a result of the HEIC process.


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Basically, HEIC provides repeated high energy impacts at the ground surface by rotating at

speed the Cam shaped and Pentagonal steel drums of 10 to 14 ton from drop heights ranging

from 150mm to 230mm.

In addition to strengthening the existing in-place materials, HEIC, like proof rolling,

exposes pockets of soft material or materials that are unsuitable for compaction. These areas,when identified during HEIC, may either require additional treatment or undercutting and

replacement with suitable materials. The degree of soil improvement depends to a large degree

upon the total amount of energy applied to the soil, i.e., the more energy input to the soil,

generally the greater the degree of improvement. Induced settlement is typically five to ten

percent of the thickness of the material being treated which can be noticed immediately.

Strength and compressibility, as measured by in-situ tests, are typically improved by a factor of

two to six.

The depth of influence is related to the HEIC drum weight and the rotational drop height,

with possible improvement depths of 2 m to 4 m being commonly recorded by cone penetration

tests, dynamic probes and heavy zone load testing. The depth of influence is dependant on anumber of factors including the soil type and stratigraphic features, efficiency or energy loss of

the HEIC process on soft surfaces, the contact pressure of the HEIC drum face, and the moisture

content of the materials.

This method may be suitable for very shallow compaction in Zone 1 area. It may be used

along with the dynamic compaction as a secondary compaction scheme. There are rather limited

publications on the effectiveness of the high energy impact compaction method; it is unclear how

much improvement one could achieve for the residual soils encountered at this site. It should be

noted that HEIC equipment can easily attached to a conventional earthwork equipment,

therefore it may be worthwhile to conduct a trial at this site for compacting the shallowresidual soils since the cost will be rather insignificant.

3.2.5 Other Method - Rapid Impact Compaction (RIC)

Rapid impact compaction (RIC) is similar to the dynamic compaction in which both

methods utilize a falling weight to compact the ground. The RIC consists of an excavator-

mounted hydraulic pile-driving hammer striking a circular plate that rests on the ground. A

hammer is hydraulically raised to a maximum height and then allowed to free-fall, resulting in a

maximum energy per blow delivered to the plate. The tamper typically strikes the plate at a rate

of 30 to 40 blows per minute and generally 10 to 30 blows are applied per compaction location.

This method may be more suitable for densifying the soils in a small confined area, such asfooting foundations etc.

3.3 Recommendations on Ground Treatment Methods

From the geological conditions, the site can be divided into two (2) regions according to

the ground improvement and foundation requirements. The first region covers Zone 1 area and

the shallow soft clay deposit (< 5m) area of Zone 2, which will be utilized for Phase 1 land

development as shown in Figure 2. The second region covering the deep soft clay deposit of

Zone 2 will be developed later under Phase 2 land development program.

For Phase 1 land development area, 85% of this land is covered with 1-4 m residual soilsand the remaining area is deposited with around 5 m of soft clay. With consideration of the


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combined cost of the ground improvement and the foundations for the structures, densification

by dynamic compaction on the residual soils appears to be the most economical option for Zone

1 area with residual soils. The main advantages of this method are low improvement cost and

fast construction, minimum environment impact etc., but the main uncertainty lies in the

effectiveness on improving the residual soils (with high fine content) to achieve a maximum

allowable bearing capacity of around 15 ton/m2

for the non-tank areas. Trial sections arerecommended to evaluate the effectiveness of the method. As described before, if the dynamic

compaction fails to improve the semi-pervious soils to required level, dynamic replacement shall

be introduced.

For Zone 2 area with soft clay deposit of less than 5 m, the most suitable ground

modification method will be the soil replacement. It should be noted that the soil bearing will be

controlled by the fill or replacement material. From the material survey conducted by the Client,

it appeared that crushed rock from nearby quarries can be the best structural fill in terms of cost

and engineering properties. If crushed rock is used to fill the ground, allowable soil bearing of

over 30 ton/m2 (for supporting the large tanks and heavy equipment) is possible. It should be

noted that the crushed rock is easier to compact and place than the sandy fill. Summary of theproposed ground modification methods for each block is given in Table 5.

From the optimization of cut and fill, the soil replacement will involve substantial rock

excavation. The rock excavation will be the main controlling factor in the earthwork since it will

involve rock blasting which requires proper coordination and safety measures.

3.4 Choice of Type of Foundations

The foundations for supported structures are typically divided into two (2) types, namely

shallow foundation and deep (or pile) foundation. The choice of particular type of foundation

depends upon the properties of the soil, the presence of groundwater at the site, the magnitude ofthe imposed loads, and the project characteristics etc. One has to choose the type of foundation,

which is not merely safe but also economical.

With the subsoil condition encountered along with proposed ground modification

techniques for Phase 1 land development, the selection of foundation becomes obvious. Shallow

foundation will be the most economical solution after the ground has been improved by

densification or by replacement with good structural fill.

At this stage, it is assumed that the required allowable soil bearing will be 15 ton/m2for

area improved by the densification method (either dynamic compaction or dynamic replacement).

In soil replacement area, 30 ton/m2of soil bearing will be possible with good structural fill.

Figure 24 shows an illustration for the area improved by dynamic compaction followedby construction of the shallow foundation. An allowable bearing capacity of 15 ton/m2should

be able to achieve, but the critical issue will be related to the differential settlement with the

presence of undulated bedrock if no rock excavation is made below the foundation level. Further

discussion is made in the next section. If the undulated bedrock is leveled followed by filling

with structural fill as shown in Figure 24, then differential settlement of the shallow foundation

may not be critical. This would apply to the areas with full soil replacement and rock excavation.

3.5 Shallow Foundation Design

With the selected ground modification techniques, shallow foundation will be applied.For areas with soil densification, the improved soil should have a SPT N of no less than 25 or a


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cone resistance of greater than 10 MPa if the allowable soil bearing is set at 15 ton/m2. The

improved area should take the foundation width and the thickness of the soil below the

foundation level into consideration. This is to ensure that the soils in the potential bearing

capacity failure zones have been improved; otherwise the bearing capacity should be

recalculated according to the actual improved and non-improved areas.

For soil replacement with good structural fill, the replaced material should have a SPT N

value of no less than 40 or a cone resistance of over 18 MPa to achieve an allowable soil bearing

of greater than 30 ton/m2. For the soil replacement area in Zone 2 area, all soft sedimentary clay

will be fully removed and replaced, therefore it will be no issue on failure planes passing through

soils with different degrees of improvement.

In shallow foundation design, the foundation should meet both stability and settlement

criteria. For stability or bearing capacity, a factor of safety of 3 is applied in the bearing capacity

calculation. With this factor of safety, the expected settlement will be limited, typically in the

range of 25 mm, unless there is low permeability compressible soil layer below the foundation.

The next sections described the methods of estimating the bearing capacity and the short

term settlement of shallow foundations.

3.5.1 Bearing Capacity of Shallow Foundation

To estimate the factor of safety, two (2) different methods were used; namely from direct

correlation with SPT N value and from estimation using the bearing capacity equation.

One of the most commonly methods for determining the allowable soil bearing capacity

is from the standard penetration test (SPT) N value because of its availability in the soil boring.

The relationship among the allowable bearing capacity for 25 mm settlement limit, the footing

width and the SPT N value is presented in Figure 25. For example, if a footing width is 2.4 m

with SPT N value of 12, the allowable bearing capacity with 25 mm settlement limit is around 19

ton/m2. If one assumes that the factor of safety under this condition is 3, then the ultimate

bearing capacity will be 57 ton/m2. This simple method is used for estimating the factor of

safety.

Apart from using the SPT correlation for estimating the factor of safety, the ultimate

bearing capacity is also estimated based on the plasticity theory, which is known as the bearing

capacity equation (Figure 26). The ultimate bearing capacity, qult , of a shallow footing, with a

depth ofD, from the surface and with a width of Band lengthL, is given by Terzaghi (1967) as,

qult= c Ncsc + D Nq + 0.5 B N

s

where c = cohesion

Nc, Nqand N= Bearing capacity factors

= Total unit weight

Shape factors:

sc= 1 + 0.30 B/L ............ (0 conditions)

sc= [1 + 0.30 B/L] [1 + 0.3 (D/B)0.25

] (= 0 conditions, saturated clays)

s= 1 - 0.2 (B/L) ... (B/L = footing width to length ratio)

s= 0.6 ... (circular footing)


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The effective unit weight of the soil should be used in the bearing-capacity equations for

computing the ultimate capacity. When the water table is below the wedge zone [depth

approximately, H = 0.5B tan(45+/2)], the water table effects can be ignored for computing the

bearing capacity. One can compute the average effective weight eof the soil in the weight zoneas:

2

w2wet2

wwe )dH(

HH

d)dH2( +=

when H = 0.5B tan(45+/2)dw = depth to water table below base of footing

wet= wet unit weight of soil in depth dw

= submerged unit weight below water table = sat- w

Based on the bearing capacity equation, the ultimate bearing capacity was estimated for

varying sizes of footing and SPT N values with results shown in Figure 27 and tabulated in

Tables 6a and 6b. It should be noted that in the shallow foundation design, the groundwater

table is assumed to be at ground level as the worst situation, but it does not necessarily representthe actual groundwater condition at the site.

3.5.2 Settlement of Foundation

Since most of cohesive soils will be removed in the ground modification process,

settlement in granular soil will take place during the initial application of foundation loads. A 25

mm maximum limit of settlement in buildings or structures is generally adopted on the premise

that if the maximum settlement is restricted to this amount, the differential settlements among the

footings of a given structure would be within tolerable limits. Following placement of the

structural fill, it is anticipated that for the majority of foundations for pipe racks, equipmentsupport structures, building foundations etc., where the foundation width is less than 3 m with

foundation loads of less than 15 ton/m2, the 25mm settlement criteria should be met. For

foundations, where the load is greater or the foundation dimensions are such that the existing

soils are influenced by the loads, then settlements of greater than 25mm may occur. In these

cases, consideration needs to be given to the allowable differential settlement for the structures,

ensuring that they are within limits of shallow foundations. A site specific ground investigation

will be required to confirm the final design criteria.

For granular soils, the immediate settlement by the applied load will dominate the total

settlement, and the settlement or compression of the soil is assumed to be linear with stress

change, having the following form:

= it

i

i

i

i

iii H

E

+=

)1(

)21)(1(

where is the change in vertical stress, and the load distribution of circularloading, such as a tank foundation is presented in Figure 28.

H is the thickness of compressible soil;

is the Poisson ratio; and

E is the Youngs modulus,


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From the weather information gathered, the main earthwork should be executed during

the dry season to avoid any problem associated with water. Proper drainage and dewatering

system should also be considered during rainy season.

4.4 Earthworks

For the two (2) methods of ground modifications, the main difference in the earthwork

will be in the soil and rock excavation. At present, Zone 1 area is covered with medium size

trees and tropical vegetation, along with some residential houses and small cultivated areas next

to the houses. A rice field area is located in the lower end of the hilly area where a natural

stream originated from the northeastern area crosses this field, providing natural water to the rice

field area. In Zone 2 with soft sedimentary clay, this area is used primarily as salt farms. There

are some large canals in areas close to the sea for fishing boats, but smaller canals are used for

carrying the seawater to the salt farm areas. Along the shoreline, rows of mangroves are present,

minimizing the effect of coastal erosion to some extent. In some areas, the mangroves have been

damaged, exposing the inner area to direct waves from the sea.

The earthwork will involve clearing the vegetation and existing houses in Zone 1 withminor clearing in Zone 2 area. The follow-up work will depend on the ground modification

techniques in each area.

In the soil replacement area, the weak soils will be removed down to hard soil stratum or

bedrock before rock excavation is carried out by ripping, breaking or blasting to required

founding level. The excavated area will then be filled with good structural fill up to the

foundation level, and the foundations of the structures can be constructed accordingly before

covering the area with additional 1 m to 1.5 m of normal or general fill. The filling of normal fill

will depend on the readiness of the foundation works as well as available stockpile area for the

normal fill (which will be the excavated residual soil from Zone 1). The possible sequence of

work is illustrated in Figure 32.In the densification area by dynamic compaction or dynamic replacement, the ground

will be first stripped down to the residual soil level, followed by some additional excavation to

the level close to the foundation level which is around 0.5 m below the proposed plant level.

Then dynamic compaction will be applied to the areas requiring densifications, i.e., following the

footprints of the foundation if the layout of the facilities is available, otherwise the entire area

will be densified. As mentioned before, the effectiveness of the dynamic compaction will

depend on the depth of groundwater table and the soil type encountered. The groundwater table

should be lowered as much as possible through deep trenches around the area to be improved

with water flowing out under gravity to lower ground. If the soil encountered contained too

much fines where dynamic compaction proves to be ineffective, then it may be necessary to

change the method of improvement to dynamic replacement with the addition of granular fill in

the crater zone. After the compaction, additional crushed rock or structural fill will be placed

and compacted up to the required foundation level. The filling of the normal fill above the

foundation should be done after completion of foundation if possible. The typical sequence of

dynamic compaction is shown in Figure 33.

The schematic of the ground modification process with both methods is illustrated in

Figure 34. Figure 35 shows the possible sequence of construction which can begin from the

northern side in the higher ground area and from the southeastern end in the low-lying area.

The next sections describe each step of the construction process in more detail.


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4.5 Clearing, Grubbing and Topsoil Removal

In Zone 1 area, significant amount of vegetation as well as existing houses will have to be

removed. Grubbing, clearing and topsoil removal can be achieved by utilizing machineries. The

vegetation will have to be removed from the site, but the topsoil free from large stones with low

organic contents can be used as fill in Zone 2 area of Phase 2 development. It is assumed that 30

cm of topsoil will be removed from Zone 1. Since Phase 2 ground improvement work will

involve consolidation by prefabricated vertical drains, the topsoil as fill will eventually be

consolidated by the surcharge placed above. As long as the topsoil is free from large stones

which will obstruct the vertical drain installation, it can be reused as fill with no off-site disposal.

The clearing and stripping will be performed in blocks starting from the northern ends.

Proper drainage should be provided to minimize soil erosion.

4.6 Soil Excavation

For Zone 2 area with sedimentary clay deposit, soil excavation is inevitable since it

would be more economical to remove the 5-m thick soft clay and replace with suitable fill when

considering the overall foundation cost.

For Zone 1 with residual soils, some small areas of Block Nos. 2, 4a, 10 and 11, will have

to adopt soil replacement method with the remaining improved by dynamic compaction. In

dynamic compaction area, soil excavation will be carried out down to the foundation level before

applying the dynamic compaction.

The soil excavation will include soil removal as well as removal of smaller boulders with

size of less than 0.7m3. Appropriate excavators should be used for different subsoil conditions.

Long arm excavators may have to be used for excavation in the soft sedimentary clay deposit

area, whereas short arm excavators may be used in the upper hilly area.

The soil excavation should be terminated with down to the bedrock level or down to the

hard soil stratum which is the decomposed granitic rock with SPT N value of over 50 as

encountered in some boreholes. This hard stratum will have sufficient resistance and high

stiffness to meet the design requirements for shallow foundation.

4.7 Water Jetting

In Zone 2 area with soft clay deposit overlying the bedrock, water jetting can be adopted

to remove the soft clay in areas where the mechanical excavation proved to be difficult. The

flushed material would have to be pumped out from the excavation zone to other areas (for

example in other part of Zone 2 area) for sedimentation. The water jetting will ensure less

contamination on the rocks to be excavated, in other words, better quality of crushed rock can be

recovered from subsequent crushing of the excavated rock if needed.

4.8 Rock Excavation

Due to the geological formation with undulated bedrock, it is anticipated that significant

rock excavation will be needed, especially in the soil replacement area, to achieve a reasonably

leveled ground before structural filling. Furthermore, some additional rock excavation will be

needed in some areas or blocks to achieve the required plant elevation. Figure 36 shows the

proposed ground modification methods in each area, and the areas with additional cutting intothe bedrock are also highlighted. Ideally, the bedrock in those areas should be leveled to a


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certain extent so that the structural fill can be placed in uniform layer. But smooth rock level is

impractical and costly, therefore it is proposed to have a tolerance of rock excavation level of 25cm is shown in Figure 37. To overcome any non-uniformity, a 50 cm layer of crushed rock

(rock bedding) will be introduced to level the uneven excavated rock surface with some

compaction before placing the structural fill. It should be noted that the tolerance of the rock

level can be adjusted after trial excavation is made with appropriate measurements to confirm thehomogeneity of the lower bedding layer. This rock bedding layer is only used for leveling of the

uneven excavated rock surface.

It should be emphasized that rock excavation in these areas would have to be performed

at earliest possible time since it would involve rock blasting with safety measures. Delay in any

rock blasting of a particular block will hamper the earthwork in adjacent work. Therefore, it is

important to have a proper execution plan on the rock excavation.

The design concept of the earthwork has also considered reusing all excavated rock, that

is, the excavated rock can be crushed on site and used as rock bedding and structural fill.

Therefore, there will be a need to provide rock crushing plants within the site to carry out this

task. The contractor should provide a plan on the capacity of the crushing plants based on thepossible rate of rock excavation. It should be noted that estimation on the required working

capacity is beyond the current scope, because it will involve conducting surveys on the

contractors capabilities in that region.

4.8.1 Mechanical Excavators, Ripping and Impact Breakers

If the rock is sufficient weathered, it would be possible to excavate or to rip the

weathered rock or weak rocks when closely jointed as shown in Figure 38, otherwise impact

breaking or blasting will be needed.

The tractor-mounted excavating equipment (mechanical excavators) allows economicexcavation without the help of explosives not only through soils, but also into many of the softer

or more broken rock formations. The mechanical excavators will probably be used to remove

the loose boulders and weak weathered rock.

A ripper usually consists of one or more teeth, called shanks,pulled through soil or rock

to loosen it for excavation. Normally, in moderate to difficult materials, single-shank ripping

gives optimum production and is easier on the operator and the machine. One shank centers the

load and mounting assembly and allows full force to be exerted at a single point. Twin shanks,

however, can be more effective in softer, more easily fractured materials that are going to be

loaded by scraper. Ripping directions are dictated by the extent, shape, and depth of the area to

be ripped and by the dip directions of rock jointing. Even harder rocks when closely jointed orbedded, can be removed by heavy rippers, at least down to the limit of weathering and surficial

stress relief. But for the intact granitic bedrock, it would be impossible to rip. Therefore the

rippers may not be an effective tool for this ground condition.

The impact breakers or pneumatic jack hammer are common for breaking up road

pavements, and they can also be used for breaking up the rocks. Boom-mounted pneumatic or

hydraulic picks (Figure 39) are popular, versatile and powerful enough to break hard rocks.

These equipment are widely used at the nearby quarries for breaking up large pieces of intact

rocks from blasting. The main advantages in comparison with blasting include no loss of time

waiting for fumes to clear and reduction in overbreak. This method may be needed when

blasting is not allowed, especially when the surrounding areas are being constructed. Future

trenching for laying of underground utilities may require such method of rock excavation.


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4.8.2 Rock Blasting

For removal of rock in large area, rock blasting will be the most cost effective method.

Large undulated rock outcrops and bedrock will have to remove through rock blasting. The

method of rock blasting is illustrated in Figure 40.

The rock blasting will have to be carried out by specialists with appropriate permits. Theplanning and execution of this work are beyond the scope of this report since it would involve

the substantial inputs from local blasting companies who have the appropriate experiences in

executing the type of work, especially in rock quarries with similar requirements. Vietnamese

safety regulations shall be strictly followed, including the permits, handling and storage of

explosives, safety blasting distance, safety fencing etc.

A good reference on rock blasting is given in the manual of Systematic Drilling and

Blasting for Surface Excavations prepared by US Army Corps of Engineers.

4.8.3 Gap Filling with Concrete

Due to the nature of the granitic bedrock, it is very likely that some wide rock joints will

be filled with soils, and it would not be practical to remove all soils in the joints. In this case, the

soils in the joints can be removed down to the width of the joints with filling by cement mortar

as shown in Figure 41.

4.9 Structural Fill

Once the excavated depth has reached in the soil replacement method with rock bedding

if needed in the exposed rock surface, then the ground will be raised up to the foundation level

with appropriate structural fill. The best structural fill will be gravelly soil with low fines (refer

to Table 10, DM7), because it can provide high resistance and high stiffness, giving high bearingcapacity and low deformation. Crushed rock with appropriate grain size distribution will be the

best material. Sandy coarse soils with low fines (


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CBR: Minimum 30 % CBR (AASHTO T193) at 95% of maximum dry density in

Modified Proctor Compaction (AASHTO T180).

The structural fill shall be spread in lifts of thickness not exceeding 200 mm, moisture

conditioned to its optimum moisture content, and compacted to a dry density no less than 95% of

the maximum dry density as obtained by Modified Proctor compaction test.

4.10 Normal (Non-Structural) Fill

Normal or non-structural fill will be used in areas above the foundation level. The

normal fill shall consist of sandy soil with low plasticity index of less than 20%. The materials

may consist of reused material, residual soils from the excavation, fine crushed rock produced

from rock crushing or imported from offsite borrow pits. The materials should be free from

detrimental quantities of debris, muck, peat, roots, grass, topsoil, leaves, humus, sewage and

other organic material, clods, and lumps or balls of clay.

Normal fill shall be placed in layers not exceeding 300 mm and each layer shall be

compacted to a dry density of at least 90% of the maximum Modified Proctor density in

accordance with ASTM D1557.

At this moment, it is unclear whether the excavated residual soils as normal fill can be

stockpiled in other areas before the completion of the structure foundations, this is to avoid re-

excavation of this material in the foundation work if it was placed in the earthwork contract. It

will depend on the schedule of the earthwork and the plant construction.

4.11 Sources of Fill Materials

In the design of earthwork and ground modifications, emphasis has been made on

optimizing the materials required through balancing of cut and fill, reusing of all excavatedmaterials (topsoil, soft clay, residual soils and excavated rock) etc. The design is made to control

the total cost of earthwork to a minimum as well as to minimize any hauling of materials to and

from the site which may cause traffic disruptions and environmental pollutions to local

communities.

Disposal of Unsuitable Materials

The only disposal off-site will be vegetation, including trees and grasses etc. The woods

from the cut trees will probably be used for general fuels, woodworks etc. The grassing may

have to be disposed through burning or decomposed by natural means. Apart from the unwanted

vegetation, all other natural soils within the site will be reused as fills.

Normal Fill

In the preliminary material survey carried out by Long Son Petrochemical team, fine

sandy soil from dredging as well as crushed rock are available in nearby areas. Samples of the

fine sandy soil were tested with the gradation curve shown in Figure 43. This fine sandy soil

will be acceptable as normal fill only since it may not produce high resistance due to the lack of

coarser grains. This material is available in large quantity, and there will be no problem in

supplying of this material to the site.

Any residual soil excavated from the site can also be reused as normal fill. Significant

amount of residual soils will be excavated in Zone 1 area. These excavated soils can be

stockpiled temporarily and reused as normal fill above foundation level at a later stage.


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Poor quality crushed rock from rock crushing within the site or off-site can also be used

as normal fill provided it has met the specifications.

Structural Fill and Rock Bedding

Granitic or diotitic rocks are found in nearby area, and several rock quarries are located atthe foothills of these rocky mountains. The expected rock properties are summarized in Table 11.

These quarries produce crushed rocks with different grain sizes for various applications. The

available crushed rock will be able to meet the specifications of structural fill. From the initial

survey, the crushed rock will not cost more than the coarse sand from other sources, therefore the

crushed rock from these nearby quarries can be used as the structural fill if needed, and the

quarries have sufficient capacities to produce the crushed rock for this project.

Since significant rock excavation will be done to achieve the site preparation

requirements, the excavated rock can be crushed within the site as structural fill. In rock

crushing, different grain sizes will be produced. Good quality crushed rock with acceptable

gradation can be used as structural fill which is assumed to be around 50% of the total crushedmaterial, and the remaining can be used as normal fill. It is important to designate a certain area

for the setting up the crushed plants, and the plants should have sufficient capacity in meeting the

demand of crushed rock during site preparation.

It is possible to reduce the fine content of the excavated residual soil in meeting the

specifications of structural fill through soil washing. The washing can produce a material with

less than 5% fines. Since around 25% of the fines will be removed from the washing process, it

will be necessary to provide area for sedimentation to retain the fine materials. This method may

not be practical, in terms of cost and construction control. For present design, all excavated

residual soils will be used as normal fill, and additional normal fill will have to be imported as

well, therefore modifying the residual soil will have no benefit.

4.12 Sounding Test Methods

To verify the quality and uniformity of compacted fill by dynamic compaction or by soil

replacement, standard penetration test (SPT) or cone penetration test (CPT) is proposed. If the

SPT is used, then the minimum SPT N value should be 40 in the tank area and 25 in other areas

at depth interval of 1m down to at least 1.5 times the foundation width unless the bedrock is

reached. For CPT test, the cone resistance shall be at least 18 MPa in the tank area (Block No.

12) and 10 MPa in other areas. The test shall be conducted with cone of at least 10 ton capacity

and sufficient reaction. Both the mechanical or electrical cones (refer to Figures 44 and 45) can

be used.

The main advantage of conducting CPT tests is its testing speed and better resistance

profiling. Since the testing depth will range from 1 m to 7 m only, the testing time will be rather

short. It should be kept in mind that it may be difficult to push the cone into the gravelly soils,

such as the crushed rock. In such case, large diameter cone (with area of 15 cm2) shall be used.

The SPT tests will be performed in boreholes which will take much longer to prepare, and casing

may be needed in gravelly structural fill layer. The merit of using SPT is its availability in local

market.

The frequency of tests will depend on the sizes and the types of the structure foundations,

since no foundation footprint is available, it is assumed that at least one (1) test should be carried

out in every 2,500 m2. Further verification will be needed during the construction of thestructure foundations.


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4.13 Filling in Phase 2 Land Development

For the excavated sedimentary clay in Zone 2 and topsoil in Zone 1 of Phase 1

development, the clayey material can be used for general filling in remaining Zone 2 area of

Phase 2 development. The total excavated clay will be around 1.7 million cubic meters, which

will be sufficient to raise the general ground elevation of Phase 2 by around 1.2 m. This filling

will reduce the amount of fill required in Phase 2 area, but it will increase the cost of the

prefabricated vertical drains slightly due to raising of the ground. It should be noted that the

excavated sedimentary clay from Phase 1 should be filled in layers spread over the entire Phase 2

area for better drying to reduce its water content, otherwise it may be too soft for subsequent

filling. The area for filling is shown in Figure 46.

The topsoil from Zone 1 will also be filled in remaining Zone 2 area of Phase 2. This

topsoil will probably have engineering properties no worse than the excavated sedimentary clay

or existing soft clay in Zone 2 area, therefore there is no reason of not using this material as

general backfill in Phase 2 work unless the organic content is high.

4.14 Flood Protection System

To excavate the soil in low-lying area of Zone 2, a temporary earth dike will be needed

for preventing the inclusion of the seawater from Phase 2 area. An earth dike running north-

south direction will be needed at the beginning stage with location shown in Figure 47.

Suggested dimensions of dike are also shown in the same figure, and it may be constructed with

the excavated sedimentary clay after some drying to achieve an acceptable degree of compaction.

The top of the dike shall be maintained at an elevation of +3.0 m NDL since it will act as a flood

protection barrier during site preparation as well as plant construction. The design of the

temporary dike is not included in this report; the contractor should propose the earth dike

according to the availability of the fill materials and additional erosion protection if required. Awater-gate may be necessary to discharge the water from the site during low tide.

4.15 Drainage Control

Because of excavation below the groundwater table in areas close to the sea with tidal

influence, dewatering and drainage systems should be properly planned. Sump pits and pumps

will be needed to control the water level in the excavation pits. The contractor should provide

sufficient pumps to control the water in the pits. In higher ground areas, proper drainage should

be provided to collect and divert the surface water to designated area and ditches, and this will

reduce soil erosion to a certain extent.

4.16 Access to Construction Areas

For site preparation and other construction works, it is necessary to provide a common

access road to the site. The Client or contractor should provide access to the north and southeast

corner if possible. Since during the site preparation, construction traffic will be significant, it is

vital to maintain the access roads properly to reduce any loss in the construction time as well as

to improve traffic safety.


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4.17 Temporary and Permanent Cut and Fill Slopes

For cut slopes in excavation pits of Zone 2 area, it is recommended to maintain a side

slope of at least 1: 3 (vertical : horizontal) during construction. For permanent or temporary

slopes in Zone 1 area, a slope of 1:2 (vertical : horizontal) is recommended. The results of slope

stability analysis are presented in Figure 48. It should be noted that the permanent side slope of

each block shall be proposed by the EPC plant contractors.

4.18 Trial Sections of Dynamic Compaction or Dynamic Replacement

The effectiveness of dynamic compaction will depend on the fine content of the soils and

the groundwater table apart from the equipment and compaction procedure etc. Since the

dynamic compaction will be applied to the residual soil areas, it is recommended to conduct

some trial sections for determining the effectiveness of the method. Some adjustments to the

compaction procedure can be made accordingly after the trials. As mentioned before, if the

dynamic compaction is not effective, then the method can be modified to dynamic replacement

instead with addition gravel fills.

In the soil replacement area, trial sections should also be conducted at the initial stage for

better estimate on the working capacities required. The trial excavation will include soil

excavation down to the bedrock, followed by rock removal etc., and different methods of rock

excavation can be applied to assess the effectiveness as well as the productivity. The main

uncertainty in the soil replacement lies in the degree of difficulty in the rock excavation which

cannot be evaluated at current stage based on the soil investigation data only.

Possible trial locations for dynamic compaction and excavation are given in Figure 49.


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earthwork contractors before bidding stage, so that the earthwork construction

schedule can be planned accordingly.

Proposed foundation type. The choice of foundation types depend on the subsoilconditions and the adopted ground modification methods. In Zone 1 and shallow soft

clay area of Zone 2, the ground modification methods by soil replacement and

dynamic compaction will ensure the use of shallow foundation, which is either mat or

footing. There will be a significant savings on the foundation work, but the cost of

earthwork will be higher with longer site preparation period.

Material utilization. In the design of earthwork and ground modifications, allexcavated materials from the site will be reused either within Phase 1 project area or

Phase 2 project area as general fill. Minimum importation of fill material is made to

reduce the construction cost as well as to reduce the environment impact to the

surrounding areas and communities. Due to the necessity of raising some plant

elevations, some fills will have to be imported to the site.

Quality control tests in ground modifications. The standard penetration tests (SPT)or cone penetration tests (CPT) are proposed as the quality control tests for verifying

the properties of the improved ground. The CPT test will be the most suitable testing

method because of its speed and simple testing procedure if there is no problem with

pushing the cone into gravelly soils. Otherwise, the SPT tests can be adopted since

they are more widely used in Vietnam.

Flood protection and drainage systems. A3.8 km long temporary earth dike will be

constructed as a tidal barrier for Phase 1 earthwork since some excavation will be

carried out in low-lying areas with excavation below the mean sea level. A water-gate

will be needed to discharge the water within Phase 1 area during low tide under

gravity. This dike will require proper maintenance in keeping the dike crest at the

elevation of +3.0 m NDL, which is the design flood level of the complex.


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6. REFERENCES

1.

Annual Book of ASTM Standards. Soil and Rock; Dimension Stone; Geosynthetics. Vol.

4.08, 1991.

2.

Bowles, J. E. (1996), Foundation Analysis and Design, 4th edition, McGraw-Hill, USA.3. John A. Franklin, Maurice B. Dusseault, Rock Engineering, 1989 Publisher: McGraw

Hill, No. of Pages: 601.

4. Manfred R. Hausmann, Engineering Principles of Ground Modification, 5th Edition,

1990 Publisher: McGraw Hill, No. of Pages: 632.

5. NAVFAC DM-7.1, Soil Mechanics, Department of Navy Facilities Engineering

Command, Alexandria, Virginia.

6. NAVFAC DM-7.2, Foundation and Earth Structures, Department of Navy Facilities

Engineering Command, Alexandria, Virginia.

7.

Nichols, Herbert L. and Day, David A., Moving the Earth, 5th Edition, 2005 Publisher:McGraw Hill.

8. Poulos and Davis (1973), Elastic Solutions for Soil and Rock Mechanics.

9. Process Industry Practices Civil, PIP CVS2100 Site Preparation, Excavation and backfill

Specification, April 2007.

10. Unified Facilities Criteria, Geotechnical Engineering Procedures for Foundation Design

of Buildings and Structures, UFC 3-220-01N, August 2005.

11. Unified Facilities Criteria, Backfill for Subsurface Structures, UFC 3-220-01N, January

2004.

12.

US Army Corps of Engineers, Systematic Drilling and Blasting for Surface Excavation,

EM 1110-2-3800, March 1972.

13. US Army Corps of Engineers, Construction Control for Earth and Rock-fill Dams, EM

1110-2-1911, September 1995.

14. US Army Corps of Engineers, General Design and Construction Considerations for

Earth and Rock-Fill Dams, EM 1110-2-2300, July 2004.

15. US. Department of Transport, Geotechnical Engineering Circular No.1 Dynamic

Compaction, Federal Highway administration, Report No. FHWA-SA-95-037, October

1995.

16.

Soil Investigation Report on Feasibility Stage for South Vietnam Petroche

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