Cyclic Loading and Unloading Test and Energy Consumption Analysis of Sandstone under Dry-wet Cycle

Abstract

The problem of geological disasters caused by rock damage and metamorphism under dry wet cycle is very serious. Studying damage and deterioration effect of rock under periodic dry wet cycle is necessary, the "desiccation-saturatation-drying" process in laboratory is used to simulate the repeated fluctuation of reservoir water level, which is used to study the influence of dry-wet cycle on the mechanical properties and energy mechanism of sandstone, and carries out conventional uniaxial and triaxial compression tests and variable amplitude cyclic loading and unloading compression tests on sandstone under different dry wet cycles. The test results show that the maximum total strain energy decreases logarithmically with the increase of n in the test of sandstone under different dry wet cycle, and the rock sample has irreparable damage under the repeated and alternating action of "water saturation and water loss"; Under the condition of uniaxial cyclic loading and unloading, the cumulative energy consumption ratio increases in the form of quadratic parabola with r. the closer it is to the peak strength, the faster the growth rate is. The energy consumption ratio near the peak strength is about 0.6, which is significantly higher than that of monotonic compression test (0.1 ~ 0.3); At lower confining pressures, the initial dissipated energy and hysteretic energy of the rock sample increase slowly. With the increase in the number of dry wet cycle, the difference between dissipated energy and hysteretic energy increases gradually, the shear strength of rock sample decreases gradually at the post peak stage, the lateral strain develops rapidly, and the confining pressure does negative work, so that total strain energy after peak loading and unloading is lower than the total strain energy at the peak point; The dissipated energy, hysteretic energy and released elastic strain energy develop unsteadily after the peak, and the slope of the curve is much greater than that before the peak.