Proceedings of DFI-India 2019: 9th Conference on Deep Foundation Technologies for Infrastructure Development in India, (DFI)
Importance of Collecting Soil Samples in Hard Strata for Soil Classification and Determination of Shear Strength Parameter
Kuppala Venkata Sivannarayana, Parvathy V. Raj and N. Manikantan
This paper presents case studies of three railway bridges across river Saraswati, Umardasi and Pushpavati pertaining to the difficulties faced in sample collection and classification of soil strata with field SPT ‘N’>100. These bridges in the state of Gujarat were designed as a part of package 3R by the Dedicated Freight Corridor Corporation of India Limited. Pile foundation was proposed at all the three bridge locations. The soil investigation was done in two stages: Stage I and Stage II. The stage I soil investigation consists of drilling borehole up to 50m depth by rotary drilling at each structure support location. It was observed that SPT ‘N’ is greater than 100 below 10-15m depth of investigation at all the borehole locations. The classification of soil with field SPT ‘N’>100 was done using the disturbed sample collected in the SPT spoon sampler. The soil profile in all three structure locations was uniform and consists of silty sand (SM/SP-SM) followed by silt clay (CI/CH). Stage II investigation was carried with an attempt to collect undisturbed sample in strata with SPT ‘N’>100 using mazier sampler for laboratory testing and hence validate the index and shear strength parameters considered for pile design during stage I investigation. On collecting and classifying the soil strata with SPT ‘N’>100, the soil classification got changed from silty clay (CL/CI/CH) to clayey sand (SC). A comparative study between stage I and stage II investigation with respect to soil classification and shear strength parameters is presented in the paper.
|article #3303; publication #1059 (India2019)|