SPT test will be carryout in accordance with ASTM D-1586 at following intervals (i) 0.00mto15m @1.5m interval (ii) 15m to above @2.0m interval
A manually operated donut hammer weighting 63.5kg will be use and fall height in the hammer drop will be 760mm. SPT will be halt when a maximum of 50 blows counted for penetration not exceeding 450mm. the standard split spoon sample with a ball valve on the top to permit exit of air or water from the sampler during driving and to assist in retaining sample during withdraw. The number of blow required to penetrate the sample 450mm and blows required to drive the sample are recorded for penetration each increment of 150mm i.e three sets of blows are recorded. The SPT N-value is the summation of last two set of blows required to penetrate 300mm (150mm + 150mm). The first set of blow count for penetration of 150mm was recorded as seating blows. However, this number is ignored during compaction of N-value.
Collecting Disturbed Soil Sample:
Soil sample collection from split spoon soil sampler at intervals of 1.5m up to the maximum explored depth of the boreholes. The sample were collected from spilt spoon just after conducting SPT, stored, sealed as disturbed sample transported to laboratory. For testing according to ASTM D-1586.
Collecting undisturbed Soil Sample:
Undisturbed soil sample will be collect from cohesive soil. The sample will collect by using shelby tube sampler 75mm and subsequently sealed to prevent moisture loss and carefully transported to laboratory test according to ASTM D-1587.
Relevant laboratory test will be conduct soil samples to determine physical and engineering properties. Laboratory tests will limited to grain size distribution. Atterberg Limit test and unconfined compression test done on undisturbed cohesive soils.
Particle Size Distribution:
This test method covers the quantitative determination of particle size distribution as well as fineness. The soil washed by No.200 sieve to determine the percentage of fine and coarse particle and sieve analysis done on soil quantity retained on No.200 sieve subsequently. The resulting data was acquired to obtain the particle size distribution and presented in Appendix C of the report. Reference code: ASTM D422-6.
Atterberg Limit Test:
This test method cover the determination of liquid limit, plastic limit and plasticity index of soil. Hand operated Cassagrande apparatus was used to determine liquid limit. The plastic limit was determined using the hand method. Reference code: ASTM 4318.
Unconfined Compression Test:
The unconfined compression test were conducted on all undisturbed soil sample collected using a thin walled Shelby tube sampler and results shown in the appendix. The data acquired was using to determine the unconfined compression strength. Reference code: ASTM D 2166
Natural Moisture Content:
12mm diameter small tube inserted into the disturbed soil sample collected by split sampler sealed both side by wax and sent to laboratory to obtain natural moisture content. It was also determine for the soil samples collected in the Shelby tube.
Direct Shear test of Cohesionless Soil
The soil sample is deformed at a controlled stain rate on a shear plane created by using shear boxes at top and bottom of the specimen under a pre determine normal load. Reference code: ASTM D3080-03
Soil were classified in accordance with ASTM D 2487 “Classification of soil for Engineering Purpose” (Unified Soil Classification System) and ASTM D2488 “Description and Identification of Soil (Visual- Manual)”
EVALUATION OF BEARING CAPACITY AND SOIL RESISTANCE
Evaluation of Skin and Toe Resistance of Pile Foundation:
Ultimate unit skin and toe resistance was computed for each segment of the soil strata based on equation given by M J Tomlinson:
Qs= αc + po*Kstanδ
α= adhesion factor
KS = Coefficient of lateral soil stress
δ= angle of wall friction
Nq = Berezantsev’s bearing capacity factor
po = effective overburden pressure
|Driven piles, large displacement||1-2|
|Driven piles, large displacement||0.75-1.75|
|Bored cast in situ piles||0.7-1|
Terzaghi’s general equations of bearing capacity for shallow footing were used to compute allowable bearing capacity of shallow footing. Hansen’s and Meyerhof’s modified equation were also used for the purpose and summarized and attached in the appendix. Basic equation for bearing capacity is Terzaghi’s bearing capacity equation:
qu= cNc+ γDfNq+ 0.5BγNγ
γ= unit weight of soil
Df = Depth of soil
B= Width of soil
Nc Nq Nγ = Bearing Capacity factors