To investigate the strength and deformation characteristics of gravelly sand on the Qinghai-Tibet Plateau under different stress paths, a series of triaxial shear tests was conducted under confining pressures of 50–400 kPa in four types of stress path conditions of conventional triaxial compression (CTC) (drained and undrained), triaxial compression (TC), and reduced triaxial compression (RTC). We can see from the test results that gravelly sand samples show strain hardening and shear contraction under the CTC (drained), TC, and RTC during the shearing process but exhibit strain softening under the CTC (undrained). To explore the microscopic deformation mechanism of gravelly sand, a characteristic angle θ was defined to reflect the relative movement of soil particles. The relationship between principal stress ratio σ₁/σ₃ and characteristic angle θ and that between void ratio e and characteristic angle θ were derived. Subsequently, the relationship expression of stress ratio η (q/p) and void ratio e was established, and the trend of void ratio e with the stress path was studied. To describe the strain hardening and strain softening characteristics of gravelly sand in different stress paths, a new dilatancy equation was obtained by introducing the characteristic state stress ratio M_c into the dilatancy equation of the modified Cam-Clay model based on the state-dependent dilatancy theory. Finally, an elastoplastic constitutive model of gravelly sand was established by applying a nonassociate flow rule. All model parameters can be determined by triaxial shear tests under different stress paths, and the comparison results show that the proposed model can well reflect the mechanical behaviors of gravelly sand under different stress paths.

中文翻译：

---

不同应力路径下砂砾石的力学性能研究

为了研究不同应力路径下青藏高原砾石砂的强度和变形特性，在常规三轴压缩（CTC）的四种应力路径条件下，在50-400 kPa的围压下进行了一系列三轴剪切试验）（排水和不排水），三轴压缩（TC）和降低的三轴压缩（RTC）。从测试结果中我们可以看到，砾石砂样品在剪切过程中在CTC（排水），TC和RTC下显示出应变硬化和剪切收缩，而在CTC（不排水）下显示出应变软化。探索特征角θ的砾石砂微观变形机理定义为反映土壤颗粒的相对运动。主应力比的关系σ ₁ / σ ₃和特性角θ和空隙率之间Ë和特性角θ而得。接着，应力比的关系表达式η（q / p）和空隙率ë成立，和空隙率的趋势ë研究了应力路径。为了描述砾石砂在不同应力路径下的应变硬化和应变软化特性，通过将特征状态应力比M _c引入基于状态相关剪胀性的改进的Cam-Clay模型的剪胀性方程中，得到了一个新的剪胀性方程。理论。最后，通过应用非关联流法则建立了砾石砂的弹塑性本构模型。通过在不同应力路径下的三轴剪切试验可以确定所有模型参数，并且比较结果表明，该模型可以很好地反映不同应力路径下砾石砂的力学行为。