Effect of thermal cycles on volumetric behaviour of Bangkok sand

Abstract

The effect of numerous thermal cycles on the volumetric behaviour of saturated Bangkok sand was investigated using a double thermal oedometer test that incorporates a temperature control system. The tests were performed at various vertical stresses (2.007, 3.211 and 4.014 MPa) on a reconstituted sand having different initial densities and an undisturbed sand from a block sample collected from a depth of 32 m in Bangkok. Up to 100 heating–cooling cycles (each involving 28–50–28 °C steps with a frequency of 1 cycle per hour) were performed at a constant vertical stress in each test and the equilibrated settlement was observed in every cycle. The strains induced by thermal cycles were satisfactorily correlated with the number of cycles using a power law. The maximum thermal cycle-induced strain was 0.0037 (equivalent to a change in relative density of 1.7%) in the case of loose reconstituted sand (initial relative density of 30%) after 100 thermal cycles. The undisturbed sample showed a similar strain of 0.0036 (equivalent to a change in relative density of 1.6%), reflecting its low initial relative density of 44%. Both density and stress level have an influence on the rate of change in log strain over log cycle number. An empirical model was developed using multiple linear regression analysis for predicting vertical strain due to thermal cycles, based on the sand’s relative density and vertical stress.