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STANDARD PENETRATION TEST |
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The scope of the work to carry out sub-soil investigation at the proposed locations consists of boring, conducting in-situ tests, collecting disturbed and undisturbed soil samples from the bore holes, and conducting relevant laboratory tests as specified. The purpose of the work is to ascertain the sub-soil profile, index and engineering properties of the soils and evaluation of allowable bearing capacity values for shallow as well as Deep foundations (Piles & Wells etc. etc.) . |
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The work is carried out conforming to relevant Indian Standards. |
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The extent of investigation is:- |
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(i) To carry out field investigations involving boring/drilling sampling and in-situ tests. |
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(ii) Conducting Standard Penetration Test (SPT) at suitable intervals. |
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(iii) Collection of disturbed and undisturbed soil samples and water sample for laboratory testing. |
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(iv) Laboratory tests on disturbed/undisturbed soil samples: |
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(a) Determination of all relevant Index properties eg. Density, moisture content, Specific Gravity, Void Ratio/Porosity, Grain size analysis (Sieve as well as wet analysis), Atterberg Limits, sensitivity etc. etc.) |
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(b) Determination of Engineering Properties |
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(i) Shear Strength parameter through Direct Shear tests. |
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(ii) Effective Shear strength Paraeters through Triaxial Shear tests |
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(iii) Undrained Shear Strength through unconfined compression tests. |
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(iv) Compressibility Characteristics through consolidation tests. |
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(v) Shrinkage and Swelling Characteristics through free swell and Swelling pressure tests. |
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(vi) Chemical analysis of soil and water samples for pH, sulphate and Choloride contents. |
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DYNAMIC CONE PENETRATION TEST (DCPT) |
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In this test, a standard cone 50 mm in diameter and having an apex angle of 60°, attached to a string of drill rods is driven directly into the ground under the blows of 65.0 kg hammer falling from a height of 75 cm. The number of blows for 30 cm penetration is termed the penetration resistance and is designated as Ncd. |
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This test provides the variability of soil profile i.e. it helps to unearth loose/ soft pockets of soil if met at the approach site. |
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This test has been successfully used to ascertain th ebearin gcapacity of Boulder-Cobbles-Gravel-Soil matrixes met at site like Baddi, Parwanoo, Nalagarh and all Hilly terrains of H.P |
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DRILLING IN BED ROCK |
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Drilling into fresh/weathered rock strata is carried out using double tube core barrel of NX size and diamond bits with water or bentonite slurry as drilling fluid run by a hydraulic feed machine. Minimum diameter of cores is 54.0 mm unless otherwise instructed by the Engineer-in-charge |
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The time required to drill through a certain depth, amount of core recovery, rock Quality Designation (RQD), physical condition length of pieces of core, joints, colour water residue, loss of water during drilling, hydraulic pressure weather evidence of disturbance and other effects are carefully noticed and entered in the drilling log. |
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For guidance relevant IS Standards are referred for proper storage of core samples |
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Laboratory tests on rock samples |
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(a) Bulk and Dry density |
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(b) Porosity |
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(c) Water Absorption |
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(d) Specific Gravity |
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(e) Uniaxial Compressive Strength |
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EARTH RESISTIVITY TEST |
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The resistivity measurements are taken at five points-four in the corner and one in the center of the site to represent the entire site. Measurements are taken as per IS :3043-1987 using a high sensitivity digital resistivity meter employing Wenner’s four-electrode configuration (Fig – 1). The electrodes are spaced equvi-distance. Measured D.C. current is passed through the two outer electrodes (current electrodes C1 and C2) and potential drop across two inner electrodes (potential electrodes P1 and P2) is noted. Two sets of measurements i.e. in direct and reverse flow of current are taken at each electrode separation. The electrode separation is increased progressively to obtain resistivity values of deeper layers. |
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PLATE LOAD TEST |
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Following the procedures as laid down in relevant BIS codes, plate load tests are performed to determine the following. |
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(i) Evaluation of bearing capacity of soils for shallow foundation. |
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(ii) Evaluation of Dynamic elastic constants for Machine foundations. |
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(iii) Evaluation of modulus of subgrade reaction for design of Raft foundations and rigid pavements. |
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ROAD WORK |
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Geotechnical investigations are carried out for the determination of sub-grade characteristic of the road samples at subgrade level conforming to IRC-37-2001”Guidelines for the Design of Flexible pavements” . The laboratory tests are carried out and analysed for the following |
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(i) In situ density and moisture content. |
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(ii) Grain size distribution |
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(iii) Specific Gravity |
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(iv) Natural Moisture Content |
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(v) Bulk Density and dry density |
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(vi) Liquid Limit & Plastic Limit |
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(vii) Maximum dry density at optimum moisture content (OMC) by standard as well as modified Proctor Compaciton tests. |
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(viii) Soaked and unsoaked CBR Values. |
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