剪切-体积应变耦合的孔压增量模型试验

Experimental investigation on a new incremental pore pressure model characterized by shear-volume strain coupling effect

以南京细砂为对象,通过共振柱试验及应变控制的排水/不排水分级和单级加载循环三轴试验的系统性研究,建立了能够描述饱和砂土孔压增长规律的新模型。该模型遵循Martin和Byrne提出的基本理论框架,孔压的增长是由循环剪切作用下体积改变所引起的。提出的孔压模型属于应变控制的孔压增量模型。基于排水循环单级加载试验,通过引入体积门槛剪应变γ_(tv)的概念,以具有代表性的15周体应变(ξ_(vd))15为基准点,归准化体应变发展与循环剪应变之间的关系,建立了三参数的体应变增量模型及其参数标定方法。基于排水和不排水循环单级加载试验结果,揭示了体应变与孔压比之间的内在联系,进而导出回弹模量表达式。通过耦合新的体应变增量模型及回弹模量公式,建立了新的剪应变-体应变耦合的孔压增量模型。验证性试验表明,新的孔压增量模型的预测值与试验结果的吻合度较高。

A new model characterized as describing increase in pore-water pressure in fully saturated fine sand specimens, through experimental studies include a resonant column test, a series of drained/undrained multistage strain-controlled cyclic triaxial(MSCCTX) tests and drained/undrained single-stage strain-controlled cyclic triaxial(SSCCTX) tests on a schistous fine sand named"Nanjing sand", is development in this paper. It follows the theoretical framework of Martin’s semi-theoretical model presented by Martin and Byrne. The increase in pore pressure is caused by the change in volumetric strain under cyclic shear load. Thus, this proposed model is controlled by strain. Based on the drained SSCCTX tests, by introducing the concept of volumetric threshold shear strain(γtv) and a representative volumetric strain in 15 cycles, volumetric strains can be normalized by cyclic shear strains, and then a three-parameter incremental shear-volume strain coupling equation is proposed. Combining experimental results of drained and undrained SSCCTX tests, the relationship between volumetric strain and pore pressure ratio is established. Thus, a new pore water pressure increment model coupling new shear strain-volumetric strain is also established considering volumetric strain increment and elastic rebound modulus. Finally, this new pore pressure model is validated, and the predicted pore pressure ratios in the model match well with those obtained from tests including an undrained SSCCTX test and a stress-controlled cyclic test.