EVALUATION OFD SOIL-ROCK-CONCRETE INTERFACE PARAMETERS

Abstract

In most cases foundations of structures are built on clay, sand or rock. So the three interface combinations i.e. concrete-rock, concrete-clay and concrete-sand are of practical significance and an evaluation of the frictional coefficient, angle of internal friction and cohesion are necessary for design. Evaluation of interface. shear parameters between concrete and rock, concrete and sand or concrete and clay are essential for ensuring stability of a structure against sliding. These interface parameters form an integral part of the input data for carrying out a soil-structure analysis of structures resting on rock, sand or clay. These parameters may be evaluated experimentally by conducting direct shear tests in the laboratory or in-situ. In this thesis an attempt has been made to evaluate interface parameters like strain dependent frictional coefficient (p), angle of internal friction (cp) and cohesion (c) at concrete-rock, concrete-clay, concrete-sand interfaces. Strain controlled direct shear apparatus was used for conducting the experimental programme. Tests were carried out on a large size shear box that can accommodate a sample size of 200 mm diameter and 100 mm height. The samples were tested at confining pressure ranging from 637 kN/m2 to 3,185 kN/m2, which is in the range of pressures expected under prototype conditions. A maximum shear displacement of 25 mm was allowed during testing. Concrete sample of M60 grade were cast and used for the testing programme. Sand from Solani river and clay from Dhandera village of Hardwar district were used in the testing programme. A basalt rock sample of size 200 mm diameter and 50 mm height was used in the tests. One set of tests was carried out keeping ramp rate (rate of shear displacement) constant at 0.05 mm/sec and varying normal load from 20 kN to 100 kN and another set of tests was conducted keeping normal load constant at 60 kN and varying the ramp rate from 0.05 mm/sec to 1.00 mm/sec. Plots of shear load vs. displacement and shear load vs. time were obtained from these tests for constant normal load as well as constant ramp rate. Values of coefficient of friction (i.) for 5% and 10% strain were determined and from these values plots of '.t' vs. normal load as well as `g' vs. ramp rate for 5% and 10% strain were obtained.