基于离散单元法的一类岩土工程土体破损的细观力学行为研究

Meso-mechanic Behavior of Soil Damage of Geotechnical Engineering Using DEM

将颗粒离散元法应用到盾构隧道端头土体细观力学行为的模拟计算,探讨了砂土地层端头土体滑移破损的宏观现象和细观机理,分析了端头土体滑移破坏形态和位移场的演变,得到了端头土体颗粒内部的孔隙率、配位数及滑动接触数等细观特征.结果表明:端头土体的破损和颗粒位移场是渐进性发展的,起因于洞门土体颗粒的力链初始断裂,最终在土体内部形成明显的非连续位移梯度和剪切滑移面,并在洞门上方形成明显的地表沉降槽.剪切滑移区域内,颗粒细观特征变化明显,孔隙率因剪胀而增大,由初始的0.16左右增大到0.19~0.20;配位数由初始的4.1左右减小到3.0左右;力链因断裂而发生弯曲,方向由柱状逐渐变成环状;颗粒间滑动接触数由初始的0增大到0.20~0.28.说明,剪切滑移面右侧土体处于松动、滑移的非稳定状态,颗粒力链断裂、细小剪切裂纹连接、合并与贯通形成优势剪切滑移面.

Granular matter is a large assemblage of dense packed particles. A granular skeleton frame is linked by grain-to-grain contacts. Loads are usually transmitted through the skeleton frame,and heterogeneous force chains architecture are formed. The formation and evolution of shear band have important bearing to the stability of a granular assembly. In this work,the mesomechanical performances of the end soil in shield tunnels are simulated by using particle DEM.Macroscopic phenomena and meso mechanism of the end soil slipping damage are discussed.Evolutions of failure mode and displacement field of the end soil are analyzed. The mseofeatures of porosity,coordination number and sliding fraction are acquired. The results show that the failure and the displacement field of the end soil are progressive,and the failure is originated from initial breakage of contact force chains of the particles near the hole. At last obvious non-continuous displacement gradient and shear slipping surface are developed. The significant settlement tank is formed on the ground at the top of the hole. In the range of shear slipping,meso-characteristics of the particles change obviously with stepping. The porosity becomes large because of shear dilatation,and it increases from 0. 16 of initial status to 0. 19 ~0. 20. The coordination number decreases from about 4. 1 to about 3. 0. The force chain becomes flexural for its fracture,and the chain direction changes from columnar status to ring status. The sliding fraction of the contacts increases from 0 of initial status to 0. 20 ~ 0. 28. These changes show that the soils on the right of shear surface are in non-stability status of loosening and slipping. Major shear slipping surface in the soil is developed by the fracture of force chain,connection,combination and coalescence of fine cracks.