Experimental Study And Discrete Element Simulation On The Effect Of Calcareous Nodules On Soil Shear Strength

The large amount of calcareous nodules distributed in the cohesive soil layer of the Huaibei Plain causes the material composition,structure and properties of the soil to be different from other soils.The quantitative change caused by the large amount of calcareous nodules eventually formed Cohesive soil containing calcareous nodules,a kind of regional special soil.At present,the studies on the mechanical properties of Cohesive soil with calcareous nodules mainly focuse on the qualitative change caused by massive nodules,mechanical properties of soil under the influence of a large number of calcareous nodules,but rarely focuse on how a single nodule affects the nature of the soil.Based on this,the paper uses triaxial compression test and discrete element numerical simulation to study the effect of single or small amount of nodules on the mechanical properties of soil.In this test,the original calcareous nodules with a particle size of 0.4Lc was used to prepare samples with different positions and numbers of nodules in 18%,21%and 24%moisture content,and triaxial compression test(UU)was carried out under under three different confining pressures.By analyzing the typical failure mode of the sample,it is found that the soil deformation near the nodules is small,and the nodules have control action on the failure mode of the sample.Then the stress-strain relationship of the sample is studied,and the influence of the microstructural elements-the number and position of nodules,moisture content,confining pressure on the stress-strain curve of the sample is mainly analyzed.On the basis of laboratory experiments,this paper used PFC~3DD software to build a numerical model,carry out numerical simulation by discrete element method.By analyzing the numerical simulation results,the influence of calcareous nodules on stress field and displacement field between particles at the microscopic scale is obtained.Based on this,the mechanism of the nodules affecting the shear strength of sample was discussed.The Duncan-Chang model based on soil structural damage is introduced at the end of the article and its applicability to the constitutive relationship of Cohesive soil containing calcareous nodules is discussed.The study shows that:During the compression process,stress concentration occurs around the calcareous nodules,which hinders the movement of the fine particles,takes on more shear stress,acts as a skeleton,and enhances the overall strength of the sample;as the number of nodules increases,the role of the skeleton increases,and the nodule at the center of the sample plays the strongest role.This study will help to understand the impact of nodules on the properties of soil engineering,and draw lessons from other studies on the properties of coarse-grained soils,such as earth-rock aggregate,etc.