EFFECT OF VIBRATION CHARACTERISTICS ON SHEAR STRENGTH OF CLAY

Abstract

An evaluation of shear strength parameters is considered to be an important step in ensuring the stability of a structure against possible shearing and sliding. During an earthquake, an upward propagation of shear waves takes place .through the earth's crust. As a result, all soil elements within the zone of influence of the earthquake are subjected to repeated applications and reversal of shear stresses. The magnitude of induced shear stresses depends on the magnitude of the earthquake acceleration. In this thesis, an attempt has been made to study the shear strength of silty clay under different combinations of normal load and shear load with varying strain rate and frequency. Tests were performed for both static and dynamic loading conditions, to study the static and dynamic shear strength of the remoulded silty clay. Static tests were conducted under strain controlled conditions (i) for a constant ramp rate with different normal loads and (ii) for different ramp rates with a constant normal load. In the static tests, the maximum displacement was kept at 25 mm. Dynamic loading tests were conducted under stress controlled condition for different combinations of normal load, shear load and frequency. The different combinations studied: (i) keeping constant shear load and frequency while different normal loads were applied, (ii) normal load and frequency were kept constant and different shear loads were applied and (iii) keeping constant normal and shear load, the frequencies were varied. The results of the study show that static shear modulus increases as normal load and ramp rate increases. Dynamic shear modulus decreases as shear strain and number of loading cycles increases. Also it has been observed that dynamic shear modulus increases with increasing normal stress and shear stress, but it decreases with increasing frequency keeping other parameters constant, for a given number of loading cycles.