Abstract
Based on large-scale triaxial tests of sandy gravel materials, the strength and deformation characteristics under loading/unloading conditions are analyzed. At the same time, the applicability of the hyperbolic constitutive model to sandy gravel is studied using experimental data. The results indicate that sandy gravel under low confining pressures (0.2 and 0.4 MPa) shows a weak softening trend; the higher the confining pressure, the more obvious the hardening tendency (0.6 and 0.8 MPa) and the greater the peak strength. During unloading tests, strain softening occurs, and the peak strength increases with increasing confining pressure. During loading tests, dilatancy appears when the confining pressure is low (0.2 MPa). With increasing confining pressure (0.4, 0.6, and 0.8 MPa), the dilatancy trend gradually weakens, and the cumulative volume tric strain increases, which reflects the relevance of the stress paths. Through research, it is found that the hyperbolic constitutive model has good applicability to sandy gravel soils, and the corresponding model parameters are obtained.
Highlights
With the rapid development of rail transit, shield tunnel construction has encountered many severe challenges in sandy gravel strata in China
Alonso et al [14] established a constitutive model of unsaturated soil materials by utilizing the double-stress variables of net stress and matrix suction
The sample size is 30 cm in diameter and 70 cm in height, and the test confining pressure is determined by the actual stress state at the site to be 200, 400, 600, and 800 kPa. e loading/ unloading tests were accomplished by the stress-controlled method, and the shear rate was 0.2 kPa/s. is test primarily studies the strength and deformation characteristics of sandy gravel under triaxial compression and unloading conditions
Summary
With the rapid development of rail transit, shield tunnel construction has encountered many severe challenges in sandy gravel strata in China. The first phase of the Luoyang Urban Rail Transit Line 2 project under construction uses the shield method to cross the sandy gravel stratum, which is important for the ground settlement, seepage damage, and the stability of the excavation surface [1,2,3]. Many constitutive models of saturated/unsaturated soil have been proposed, but there are still many controversies regarding some basic problems [9, 11], such as the selection of state variables of stress and strain and the theoretical framework of hydraulic coupling processes [12, 13]. Bai et al [22] proposed a thermo-hydromechanical constitutive model for geomaterials in view of the concept of particle rearrangement during the thermodynamic process
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