Drilling and sampling sub-contract work for the AAI Coimbatore Geotechnical consultancy project for the Department of Civil Engineering, NIT Trichy

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1.0 Mobilization

2.0 Drilling exploratory holes in the soil.

2.2 The work of drilling in soils shall be carried out in such a manner that penetration tests can be carried out as required and collection of undisturbed samples of 100 mm diameter would be possible. The choice of method of drilling is left to the contractors, but preference shall be given to a method, which permits continuous SPT of the soil layers. The size of boreholes shall not be greater than 150 mm diameter. The boreholes shall be thoroughly cleaned by the contractor as and when required. For removing particles larger than silt size, the contractor may have to use drilling mud of the required consistency and flush the hole with mud at the requisite pressure.

2.3 The clearance between the split spoon sampling tube (SPT) and the boreholes shall be as directed by the Consultant. Usually, holes of very large size would not be preferred. The Contractor shall take reduced levels (RL) and Coordinates the borehole locations with reference to a benchmark approved by the Engineer-in-Charge and shall include the same in his report.

2.4 The drilling operations may be interrupted for collecting UDS or for conducting penetration tests etc. The rate for the drilling work is inclusive of all such interruptions and delays. The casing pipes where used shall not be removed unless directed by the consultant. Even after the removal of the casing, a pipe should be left in the borehole to identify the location.

2.5 The contractor shall ensure that sand-blow conditions do not develop while boring/drilling. A sufficient surcharge of water or drilling mud should be maintained all through the operation.

2.6 The boring and/or drilling for a complete borehole up to the required level shall be paid on per meter depth basis. No additional payment will be given if the same rig or a different type of rig is brought to the location of the hole for completing either bed rock drilling or any other balance activity stipulated in that borehole.

2.7 The groundwater level shall be recorded everyday morning before the start of work.

2.8 On completion of work, the bore hole to be refilled and the top 45 cm shall be concreted with lean cement concrete and finished smoothly.

2.9 Mode of measurement & payment: The total depth of boring in soil or weathered rock or hard rock will be determined by measuring or computing the difference in the elevations of the top of the existing soil surface before construction of the working platform and the deeper of the following:

i) The lower edge of the casing pipe.

ii) Elevation of the lowest point of penetration of the sampling tube spoon or lower tip of the dynamic probing cone, whichever is lower.

iii) Hard rock:- Core Recovery more than 60%

iv) Soft rock:- Core Recovery more than 10 % and

v) Soil: - Values lesser than indicated for soft rock shall be classified as soil.

vi) The payment shall be done per meter of drilling as per actual.

3.0 Conducting Standard Penetration Tests (SPT)

3.2 For Standard Penetration Test, the blow count shall be recorded at intervals of 15 cms for a total penetration of 60 cms. The SPT blow count shall be reckoned as the total number of blows for the second and third penetration increments of 15 cms. In exceptional cases, penetration up to 90 cms may be required. No separate payment would be made for this. In case, blow counts exceed 50 for 15 cm or less penetration then terminate the test and note the penetration for 50 blows. Solid cone tests shall be used where directed by the Consultants In lieu of the SPT without any extra payment for a change of the drive point (from the SPT spoon to the cone.)

3.3 All attempts shall be made to recover the full sample of the standard split spoon sampler. The sampler must have a ball valve at the top of the sampler for minimizing loss of sample, where sample recovery is poor or nil; a representative sample obtained from the sludge pump/bailer shall be preserved.

3.4 Wherever a sample is recovered, the following details shall be noted along with a usual record of blow counts. This must be recorded for very stiff clays.

a) Penetration (meters) and blow counts.

b) Recovery (percentage)

c) Logging of silt/fine sand seam if any.

d) Visual classification of the soil sample.

e) Modulus of Sub-grade reaction of soils (For all types of soil)

The above information shall be recorded for each hole, in the specified format given by the Consultant.

3.5 In the case of stiff to medium clay where a sample is recovered in the form of 'cake' a suitable length of cake shall be wrapped with polythene and further by a layer of bandage cloth.

3.6 Mode measurement & payment: The measurement for this item shall be as per completed tests which have been carried out as per specifications to the satisfaction of the Consulting Engineer. The payment shall be done per number of the completed tests. No payment shall be admissible for tests, which are not as per specifications or are incomplete. The opinion of the Consultant in this respect shall be final and binding on the Contractor. Related drilling is payable under item 2.0.

4.0 Collection of disturbed soil sample in tubes (TDS)/plastic Jars

4.2 The samples shall be collected in non-returnable 50mm diameter 'C' class M.S. Pipe of suitable length not exceeding 75 cms/where soil type ranges between plastic silt to clay. The sample tube should have a level edge at the bottom and holes on top for draining trapped water. The sample should be sealed at both ends of the pipe by a double layer of cotton waste and wax. Every care shall be taken to preserve the natural moisture content. If required, continuous sampling should be carried out to identify the presence of lenses and seams of fine sand.

4.3 While conducting sampling operations in sand or silty sand, the sample is likely to slip out during the extraction of a sample from the borehole or trial pit. A flap valve bailer or auger may be used and representative samples shall be collected without appreciable loss of fines and preserved in screw top plastic jars and containers. 20 Kg. samples shall be collected in bags whenever Proctor tests are required or whenever instructed.

4.4 If the contractor is instructed to use a suitable type of piston sampler for conducting sampling in non-cohesive soil, such sampling would be paid at the rate of undisturbed sampling in soil. The contractor shall include the cost of providing such tubes in his unit rate.

4.5 Wherever the sample is collected in tube, the tube shall have a proper identification mark (bore hole No., depth, location, arrow mark indicating bottom end of the sample tube etc.) Rate for this item shall be per no. of sample collected, and shall include providing necessary equipment.

4.6 Mode of measurement and payment: The payment shall be per number of sample, provided that the samples recovered are accepted by the Consulting Engineer. Any unsatisfactory samples or any sampling work, which is not as per the specification shall not be paid for.

5.0 Collection of Undisturbed sample (UDS)

5.2 The moisture in undisturbed samples shall be carefully preserved by sealing both ends of the sample tube by applying a double cast of cotton waste and paraffin wax.

5.3 If the sample slips out due to the natural condition of soil the contractor shall collect representative sample by using a flap valve bailer or auger without appreciable loss of fines. The representative sample shall be preserved in a screwed top plastic jar (4" 0 x 6 " height). In such event the contractor shall be paid at 50 % of the unit rate quoted for collecting undisturbed sample.

5.4 The sample tube shall have a proper identification mark painted on it (e. g. bore hole No, depth, location arrow mark indicating bottom end of the sample tube etc.).

5.5 The undisturbed sampling tube and method of undisturbed sampling shall be made to prevent the sample from slipping. This provision shall be subject to scrutiny and approval by the consultants.

5.6 Undisturbed block samples in trial pit shall be collected by hand out method. The sample thus collected shall be properly protected and sealed for preserving the natural moisture content as mentioned in Earth Manual vide Designation E-2, page 346 to 349.

5.6 Mode of measurement and payment: The payment shall be per number of samples provided that the samples recovered are accepted by the Consulting Engineer. Any unsatisfactory samples or paid for.

6.0 Collection of soil and water samples for chemical analysis

6.2 The water samples shall be collected in airtight amber glass containers (two containers of one litre capacity each for each sample). The contractor shall store such samples in a covered shed.

6.3 The contractor shall reach the samples to the approved laboratory within ten days of their collection and secure a proper receipt to the consultant.

6.4 The contractor shall allow for sand blow while quoting a unit rate for this item. The unit rate should include the cost of all operations such as flushing and cleaning for advancing the borehole deeper.

6.5 Mode of measurement and payment: The payment shall be per number of sample, provided that the samples recovered are accepted by the Consulting Engineer. Any unsatisfactory samples or any sampling work, which is not as per the specification, shall not be paid for.

7.0 Drilling exploratory holes in rock

7.2 The maximum lengths of drilling in bedrock overlain by over burden shall generally not exceed 5.0 m measured in rock.

7.3 The work shall comply with IS 1982 and/or as directed by the consultant. The format as approved by the consultant shall be used for recording the rock-drilling data. The data shall include rate of drilling, colour of wash water, nature of sediments in the wash water, loss or gain of drilling water, core run length, core recovery & RQD (Rock Quality Designation). The length for payment under this item shall be measured in rock.

7.4 Cores shall be kept in wooden boxes with compartments of the exact size of the rock cores. While placing the core samples in wooden boxes, it should be ensured that the direction and sequence of core placement are not altered. The core run shall be restricted to the length as directed by the consultant and generally not more than 1.5 m. In weak and friable rock core run shall be reduced.

7.5 Core Box:

7.5.1 The core boxes shall be provided by the contractor and should be made of good-quality timber. Each core box shall house samples not more than 6 m (six meter) long. The contractor shall include in his rate the cost of providing such core boxes.

7.5.2 The depth of cores-below ground level shall be indicated at 0.75m, and there about every 1.5 meters interval by writing the depth in inalienable ink on wooden spacers, which shall be inserted in their correct position in the box. Similarly, the exact depth of any change in stratum, and failure to recover the core, etc., shall be recorded.

7.5.3 The labeling of core samples of rock shall be done in accordance with Appendix D of IS 1892.

7.6 The double tube core barrel shall be used.

7.7 An arrangement should be made for the collection of wash water by installing a top socket with a cross pipe at the top of the casing before the start of rock drilling. The side of the casing should be well-packed near and top of the hole to prevent leakage. Wash water should be collected in buckets and allowed to settle. A record of wash water shall be maintained indicating the color, change in color, and type of wash water (i.e. thick slurry, lean slurry, or clean water).

7.8 The number of revolutions per minute for the rock drilling shall be constant throughout the complete drilling operation. The rate of penetration for every 250 mm shall be observed during rock drilling and recorded.

7.9 Whenever the field permeability tests are required to be conducted in the underlying bed rock during the intermediate stages of drilling, the contractor shall fix a suitable M. S. pipe as stipulated in the relevant specifications for conducting field permeability tests in the underlying bed rock.

7.10 The contractor shall carry out stage grouting during the course of drilling, whenever water loss conditions are met with. The contractor shall allow for such stage grouting and delays while quoting the unit rate for drilling in rock. The contractor should separately quote unit rate of grouting on the basis per bag of cement.

7.12 Mode of measurement and payment: The total depth of drilling in rock will be determined by measuring or computing the difference in the elevations where SPT > 50 was encountered and the elevation of the lowest point of the core barrel. The total length of payment shall not be more than the total length of boring in soil and rock minus the length payable as drilling in soil. The payment shall be done per meter of drilling.

8.0 Handling and transporting soil, rock, and water samples to the approved laboratory

8.2 The contractor shall secure a proper receipt for its safe delivery to the approved laboratory and present the receipt to the Engineer of Consultant.

8.3 The samples collected at site shall be stored properly in a covered shed till the time of their dispatch.

8.4 Mode of measurement and payment: The payment towards this Item shall be made on the basis of batches of samples dispatched from site and received in the testing laboratories. The number of batches will be decided by the Consulting Engineer.

9.0 Water table

10.0 Indicative values of CR

In view to differentiate various layers of strata broadly into soil/sand OR Soft/Weathered rock OR Hard rock following indicative values of CR shall be considered.

i) Hard rock:- Core Recovery more than 60%

ii) Soft rock:- Core Recovery more than 10 %

i) Soil: - Values lesser than indicated for soft rock shall be classified as soil.

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