Numerical direct shear tests for outwash deposits with random structure and composition

Abstract

Outwash deposits is a kind of special geological material composed of soil and stone particles. Since the shear behaviors of outwash deposits are mainly dominated by its complicated structure and composition the strength parameters of which are difficult to be determined accurately. In this work, samples of outwash deposits with random structure and composition taking account of the effects of sizes, shapes and distributions of stone blocks were simulated based on the granular discrete element method. The meso-scale parameters of soil and stone particles were first calibrated by comparing numerical predictions with experimental data. Then a series of numerical direct shear tests for the simulated samples were conducted. Results show that the effects of strain hardening of shear stress–displacement curves become increasingly apparent with the increase of stone content. The shear strength of outwash deposits is dominated by the content as well as by the random distribution of stone blocks. There is an approximate linear relationship between the mean value of shear strength and the stone content lying between 30 and 60 $$\%$$ , while a larger fluctuation in shear strength mainly due to the random distribution of stone blocks. Compared with the mean value of shear strength, the maximum fluctuation of internal friction angle reaches up to 4.26 $$^{\circ }$$ while the maximum fluctuation of cohesion approximates up to 1/3 of its mean value. Results also indicate that the improvement of cementation degree between soil particles increases mainly the macro cohesion of outwash deposits but has almost no influence on the macro internal friction angle. And because of a relative higher strength of stone blocks, the shear yield bands of outwash deposits detours significantly around stone blocks and shows numerous local cracks, which frequently accompanies an acute release of strain energy owing to the geometric redistribution of stone blocks. The integration of laboratory investigations and numerical direct shear tests can be an effective approach to determine the statistical mechanic’s parameters of outwash deposits.