Pass paper

2a) For ground investigation with tunneling in rock (either drill and blast or tunnel boring machine), describe the objective and minimum requirement of the ground investigation program.

Objective and minimum requirement of the ground investigation program should be follows: Identify the geological profile for the preliminary and alignment

design. Identify adverse geological features e.g. fault zone / hard rock zone

for selection of construction method Identify the hydrogeological profile for permanent and temporary

support design. Identify the rock mass properties for the selection of tunnel

construction method, temporary and permanent support design. Identify the sensitive structures (e.g. dams, buildings & bridges) 2b) Describe in less than 400 words why and how a staged ground

investigation program should be conducted.

Pre-construction staged:

Desk studyBefore ground investigation field works commenced, the topographic maps, geological maps, aerial photographs should be examined. Preliminary geological model can be formed and served geological features e.g. fault zone, dyke can be identified which can facilitate the future planning of ground investigation filed works. More attention will be paid on the served geological features. Existing ground investigation report should be noted which provide basic information of forming geological profile and bedrock lithology can be found for preliminary design.

Ground Investigation field works

Vertical BoreholeVertical boreholes should be implemented along the proposed tunnel alignment. The vertical boreholes can provide updated geological profile and collect soil samples (mazier sample) and rock samples (double core barrel) for the laboratory test. Apart from the samples collect for the laboratory test, the following field test can be conducted to find out the soil and rock properties:

Standard penetration test is conduct to find out the stiffness, relative density of soil and rock. Pressuremeter test is carried out to find out the bearing pressure of the soil/ rock.

Piezomenter and standpipe is used to measure the groundwater table, perched water table and confined aquifer.Constant head permeability test is conduct to find out the permeability of each soil stratum.Water absorption test provide the permeability of insitu rock.

Inclined BoreholeInclined boreholes should be carried out to confirm the location of suspected fault zone. The soil/ rock sample at the fault zone should be collected for the laboratory test.

Laboratory testThe following test should be test on soil sample to indentify the soil parameter and classify the soil:Triaxial compression test provide estimation of soil cohesion and its friction angle.Oedometer test provide undrained shear strength parameter.Chemical test provide soil aggressiveness. Index test provide information for soil classification.

For rock sample, the following laboratory test should be carried out:Unconfined compressive strength or point load test should be carried out to find out the compressive strength, Young Modulus and Poisson’s ratio of the rock mass.Punch test, drilling rate index etc would be carried out for facilitating the use TBM.

During Construction:

Horizontal directional drilling should be conducted along the tunnel alignment for better understand the geology of the alignment. Design review can be carried out immediately according to the actual site condition. The rock joint, fault zone and groundwater ingress should be identified to modify the support system according to the actual rock mass classification and Q-value.

2c) There are many factor where geologist would rely on in determining where the geological material is a fault zone or not. List at least 7 factors or key works.

The rock mass in fault zone is different due to thermal alteration. The rock mass in fault zone is highly fractured and weathered. The permeability is high in fault zone. The rock mass is highly sheared. Evidence of piping. Matrix infill is found. Sudden change in rock head level.

3a) What are the advantages of in-situ testing over laboratory testing of geological material for engineering purpose? Please supplement

your arguments by using examples of different in-situ testing techniques and laboratory testing techniques.

(Retrieved from ch.24 of Geoguide 2)Field test are generally desirable where it is considered that the mass characteristics of the ground would differ appreciably from the material characteristics. These difference generally arise from several factors, are the extent to which the laboratory samples are representative to the mass, and the quality of the sample that can be taken.

(Retrieved from ch 21 of Geoguide 2)The samples conducted by the field test would be less disturbed compare with sample collected to carry out laboratory test.In-situ test is always cheaper, quicker response and routine base compare with laboratory test.

Standard penetration test provide the information regarding the soil parameters and foundation condition and the test is simple, quick response and inexpensive, compare with the trial axial test conduct in laboratory

Vane shear test provide the information about undrained shear strength of soil sample. The main advantage is that the test cause little disturbance of the ground that that of unconsolidated undrained test.

Constant head / variable head to determined the in-situ soil permeability which is more reliable than laboratory test, as the sample size is larger and the sample does not disturb.

Impression packer survey provide an assessment of the orientation and aperture of discontinuity on in-situ rock.

(Retrieved from ch 27 of Geoguide 2)Field density test provide information of dry density of in-situ soil and test for control of compaction of embankments.

3b) What are the advantages of laboratory testing over in-stiu testing of geological material for engineering purpose? Please supplement your arguments by using examples of different in-situ testing techniques and laboratory testing techniques.

(Retrieved from Geoguide 2 Table 12 and Table 13)The advantage of laboratory testing are identify and classify the samples with a view of making use of past experience with materials of similar geological age, origin and condition. It can also obtain soil and rock parameters relevant to the technical objective of the investigation.

Triaxial test can provide the design parameter of soil cohesion and friction angles. It is not empirical result but numerical compare with SPT.

Oedometer test provide the amount and the time scale of settlement for consolidation analysis, which take time and unfeasible to test with large in-situ specimen.

Direct shear stress test used to determine the shear strength characteristics of rock discontinuities. The rock mass cannot be sheared on site directly, small samples can facilitate the test.

Uniaxial compression test or point load test provide the rock compression strength, static young’s modulus, where SPT / CPT cannot provide accurate estimation of the mentioned parameter.

4a) Develop a site investigation and laboratory testing plan to acquire the necessary information to design the upgrading slope stabilization work within a reasonable budget. You have to give adequate details to implement the plan, including but not limited to, the number of boreholes, location of boreholes, depth of boreholes, drilling sequence, type of in-situ and laboratory tests to performed, operation parameters for laboratory testing etc.

(Retrived from Table 3 and 4 of GEOGUIDE 2)According to the GEOGUIDE 2, the slope can be classified as Class 1 site, assume the angle of slope is greater than 30 degree.

Site investigation should be carried out by examination of terrestrial photographs, aerial photos and geological map. Topographical, geological and surface drainage survey should be carried out. Borehole location should be 10m to 30m, Mapping of geological features and surface features.

Ground investigation works included vertical boreholes 30m horizontal spacing and 10m vertical spacing each is proposed in stagger pattern to find out the soil stratum underneath and collect soil/ rock sample for laboratory test (~15 nos. of boreholes are required). Slope stripping also proposed to find out the overlaying material at 30m horizontal spacing (~3 nos. of slope stripping). The vertical bore holes can also identify the fault zone and underlain weak material at slope. The boreholes should be terminated at 5m rock head where Grade III or better rock with total core recovery greater than 85%, or toe level of the slope is reached. Piezometer should be installed at the top and bottom of the feature to find out the groundwater level of the slope.

Collect soil by mazier sampler and rock sample by double tube core barrel. The mazier sample collect should be at 3m intervals, so that each sample from each soil stratum can be collect. The top soil can be collected by using U76 tube samplers for laboratory test.

In-situ testSPT is required to find out the soil stiffness of different soil sample, the SPT should be carried out at 2m interval at first 16m and 4m interval for

further depth.

Piezometers are installed at top, middle and bottom of feature (~6nos of piezometer) to determined the ground water level, perched water level and confined aquifer.

Permeability test (e.g. constant head test) is carried out to find out the permeability of various soil stratums. It can identify the confined aquifer.

Impaction packer / TV televiwer is required to identify the rock joint (for rock slope) to find out the adverse wedge.

Laboratory testIndex tests on soil sample to carry out soil classification.Triaxial compression test carried out to find out the soil parameter (e.g. cohesion, friction angle and Young’s modulus) Odeometer test carried out to provide undrain shear strength for the clay material.

4b) Develop a long term monitoring plan to evaluate the engineering performance from time to time. Your have to give details on types of instruments to be installed, locations of the instruments, frequency of measurement etc.

Piezometers are installed at top and bottom of the slope to detect the groundwater.

Tiltmeter is installed on the buildings to monitor the movement of building.

The inclinometer is installed to measure lateral deflection of buildings.

Extensometer installed in the middle, bottom and top of slope to detect the slope movement.

Tips from Prof Kwong

A) Ground investigation field works submission procedure in Schedule Area

According to PNAP 225, ground investigation in the scheduled area is building works and requires approval and consent under the building ordnance.

GI works in schedule area – approval and consentProcedures are in place in Buildings Department for concurrent processing of applications for approval and consent in respect of new ground investigation works in Scheduled Areas. In order to take advantage of the concurrent processing, a site supervision plan together with the ground investigation plans; and cover letter that you wish to take advantage of the concurrent processing option and submit an application for consent after the 32nd day of the submission of plans

for approval.

Schedule Area No.1 Mid levels schedule area (PNAP 85)Ground investigation in the schedule area No.1 requires approval from the BA. As such, ground investigation plans including laboratory test prescribed in Building (Administration) Regulation 8(1)(1) must be submitted to the BA for approval and consent before the works are commenced.

Ground investigation should conform to standards laid down in GEOGUIDE2 and GEOGUIDE 3, which are prepared by GEO. The ground investigation is adequately supervised on site by a suitably experience engineer or engineering geologist according the code of practice for site supervision.

Schedule Area No.2 & 4 of the schedule area (PNAP 161)GI works in schedule area No.2 & 4 require approval of the BA, plans of proposed GI in these area must submitted to BA for approval and consent before the works are commenced.

AP, RSE and RGE are advised to ensure that GI works are carried out in accordance with GEOGUIDE 2 and 3, and supervised in accordance with COP of Site Supervision. Attention should be given to logging the location and size of cavities, the nature of the cavity wall and the infill, together with rock discontinuities.

The depth of drillholes should relate to the depth of marble bedrock and the magnitude of the load to be applied by the structure. If marble is encountered, a minimum penetration of 20m into sound marble rock is recommended in order to reduce the risk of existing cavities not being identified. The use of water as a flushing medium should be controlled as there have been cases where sinkholes were induced by excessive use of flushing water. High quality core samples of the cavity infill can be obtained by using triple-tube core barrels with air foam.

Discussion with the relevant district Chief Geotechnical Engineer of the GEO before a ground investigation proposal is finalized may allow the optimum drillhole layout to be adopted. At least 2 weeks prior notification of the intention to commence ground investigation works in these areas should be given to the relevant district Chief Geotechnical Engineer.

Pending substantial completion of the building works, all cores and samples should be retained on site in good condition for inspection by BD and GEO.

Schedule area No.3 PNAP 77GI works at schedule area No.3 required prior approval and consent form BA. All proposals within the Schedule area No.3 shall be subject to special scrutiny of the Government prior to giving approval and consent

for commencing construction works.

The proposal shall be assessed individually on the impact on existing railway and related structures and the following should be included:Details of exploration and locations of the proposed exploration holes, trial pits, trenches, field testing or instrumentation relative to any railway structures

Proposed depth of bore holes, pits or trenches;

A method statement for sinking borehole, excavation, trial pits and trenches including back-filling, conducting field testing or installing instrumentation

A method statement for checking verticality of borehole located with a distance of 10m on plan of any point of the underground railway structures, should boreholes be sunk to a depth of 3m from the heighest point of the railway structures; and

A method statement for controlling depth of boreholes/drillholes sinking within a distance of 3m on plan of any point of the underground railway structures.

Schedule area No. 5 PNAP 165

GI works at within this area will require approval and consent form BA. The following shall be submitted to BA:

Details of the exploration and location of the proposed exploration holes, field testing or instrumentation relative to sewage tunnes;

Proposed depth of holes, filed testing or instrumentation;

A method statement for sinking holes, conducting field testing or installing instrumentation; and

A method statement for checking the alignment of holes when the minimum distance from a hole to any point less than 50m should be sunk to depth within 3m from the highest point of the sewage tunnel

The vertical and horizontal pressure on any sewage tunnel structure should not be increased or decreased by more than 20kPa or 5% of the total overburden pressure for structure at depth greater than 20m

The ppv of artifical shocks should not exceed 25mm/s by artificial shock generated by detonation of explosive or mechanical blow and should not exceed 15mm/s by percussion drilling/ hammer drilling.

No hole should be sunk or excavated within a distance of 3m form any point of any sewage tunnel.

For the GI plans, the plans should be endorsed by Registered Geotechnical Engineer, and T5 supervision report should be submitted once a month to BD.

B) What kind of geological model / GI should be considered?

In order to retrieve more geological and hydrogeological information for the construction of proposed tunnel, the following ground investigation field works, in-situ tests and laboratory tests are required:

Ground investigation field works Vertical boreholes should be carried out to identify different soil

stratum and rock joint/ fault zone. Vertical boreholes at sea level are preferred, and prior consent from Marine Department would be required. Mazier soil samples can be collected and rock samples can be collected by double tube core-barrel.

Inclined drillholes proposed to collect identify the location of fault zone.

Horizontal directional drilling should be carried out along the alignment of the tunnel. In-situ rock/soil samples can be retrieved. The number of joint sets, the quality of rock and the roughness of joint can be found.

In-situ field test Standard penetration tests are proposed to find out the soil

stiffness. Dilatometer tests are proposed to find out the undrained shear

strength of the marine deposit. Piezometer and standpipe were proposed to find out the ground

water level and confined aquifer. Constant head permeability tests were proposed at different soil

stratum to found out the permeability of different soil for further modeling.

Impression packers or BH televiewr are proposed to find out the rock joint.

Water absorption test measures the water acceptance by in situ rock under pressure.

Laboratory test Tri-axial tests are used to find out the soil parameter of different soil

(e.g. cohesion, soil parameter, young’s modulus). Unconsolidated undrain tests and direct shear test are proposed to

find out the undrain shear strength of marine deposit. Chemical test and fundamental index test are used to define the

soil aggressive and soil classification. Unconfined compression test/ point load test for rock are used to

determine the Young’s Modulus and Poission’s Ratio. Flat jack test are measured in-situ rock stress. Punch tests, Cerchar Scratch test and testing for drilling rate index,

bit wear index and cutter life index test are to be carried out for facilitating the use of TBM

Odeometer tests should be carried out to find out the time scale and settlement of the sample

Geological Model

In order to carry out the analysis to predict the effect of the proposed tunnel on the stability of the existing structures, geological and hyrdogeological information obtained during ground investigation field works and the result retrieved from laboratory tests should be correctly interpreted.

Geological profileAccording to the GIFW and the existing geological information (e.g Geological map, Existing GI report from nearby structure), the geological profile can be formed. The fault zone location can be located.

Soil properties & Rock Mass propertiesThe soil and rock mass parameters should be revised by using the laboratory test results in the new soil sample with considering the existing soil samples. For conservative reasons, the lower bound soil parameter and rock mass parameter should be adopted.

Hydrogeological profileThe design groundwater table should be revised depend on the piezometer reading, the highest groundwater table should be adopted in design assumption. The settlement due to groundwater drawdown can be noticed.

ModelingAfter defining the geological and hydrogeological profile related to the engineering problem, a two dimensional sections and 3D model should be formed find out the critical geological and hydrogelogical problem encounter. The computer programme (e.g. FLAC 2D, Plexis) may be used in illustrated the effect on the pipe-pile wall and surrounding ground during stated excavation. The existing deflection should be catered and modeled during consideration of proposed upgrading works. Thus the computer model would be compatible with the actual site condition.

Engineering Difficulties regarding the geological profile

The fault zone may cause rock/soil ingress and water ingress during tunneling.The rock joint may lead to water ingress during tunneling The settlements of ground due to groundwater draw down, as water flow in the tunnel through rock joint.The marine deposit may be settled due to ground settlement because of consolidation.

The rocks fall due to adverse joint sets