基于PFC模拟的饱和粉砂强度折减范围研究

Strength reduction range study of saturated silt based on PFC simulation

为验证基于颗粒流程序(particle flow code,PFC)模拟的饱和粉砂土体变形和破坏状态下土力学参数与孔隙度的关系,以呼和浩特市地铁2号线公主府站至呼和浩特站盾构区间前期钻探土样为研究基础,对饱和粉砂进行一系列密度梯度的三轴不固结不排水室内试验,根据换算公式将密度指标转化为孔隙度指标,对孔隙度与内摩擦角之间的关系式以及孔隙度、围压与变形模量之间的定量关系式进行拟合。通过离散元法进行三轴数值模拟试验,监测试件在压剪过程中孔隙度随试件变形的变化规律,从而确定饱和粉砂在弹塑性变形阶段和破坏阶段土体孔隙度与变形模量及内摩擦角之间的关系。结果表明,土体强度随密度的增加而增加,基本呈现线性增加的规律。将孔隙度随土体应变变化的曲线对应到内摩擦角随孔隙度变化的拟合曲线中,可以得到饱和粉砂不同阶段土力学参数的取值范围,明确土体强度折减范围。通过PFC模拟曲线确定不同阶段对应的区段,为完善饱和粉砂强度折减规律分析提供了新的方法。

In order to verify the relationship between soil mechanical parameters and porosity during deformation and damage of satu-rated chalky soil simulated by particle flow code(PFC),triaxial unconsolidated and undrained indoor tests with a series of density gradientsc on the saturated silt were carried out based on the pre-drilling soil samples of the shield interval from Gongzhufu Station to Hohhot Station of Hohhot Metro Line 2.The density indexes were transformed into porosity indexes according to the conversion for-mula.The functional equation porosity and friction angle and quantitative equation amory porosity,envelope pressure and deforma-tion modulus were fitted.The triaxial numerical simulation test was carried out through the discrete element method to monitor the change rule of porosity with the specimen deformation in the process of compression and shear,so as to determine the relationship between the porosity of saturated silt in the elastic-plastic deformation stage and the destruction stage,the deformation modulus and the angle of internal friction.The results show that the strength of the soil body increases linearly with the increase of density.More-over,the curve of porosity change with the strain of the soil body is fitted to the curve of the change of internal friction angle with porosity,so that the range of values of the soil mechanical parameters of saturated silt at different stages are obtained,and discounted range of the strength of the soil body is made clear.This work provides a new method to improve the analysis of the strength reduc-tion law of saturated silt via determining the corresponding zones at different stages through PFC simulation curves.