摘要
为探究砂卵石地层中盾构开挖工作面失稳现象的机理,采用 CDEM (continuum-based discrete elementmethod)可变形块体离散元方法,建立准连续介质模型,对砂卵石土三轴压缩试验开展数值模拟,以分析其细观力学特性;基于“颗粒流动”、“土拱效应”、“超挖出土”等特点,通过平面三角块体离散元建立模拟砂卵石地层盾构开挖面超挖出土的二维动态离散元模型,研究土拱效应、空洞区发展等开挖面失稳的渐进演化机制.研究结果表明:砂卵石土三轴压缩试验宏观应力应变曲线可分为线弹性阶段、弹塑性阶段、理想塑性阶段;卵石作为粗粒相颗粒存在骨架增强作用,砂卵石接触界面对宏观强度具有弱化作用;通过以土拱效应为标定准则的 HopperFlow 标定试验可有效得到不同尺度平面三角形离散单元摩擦角的转换关系;土拱效应显著存在于开挖面前方并随着开挖面超挖出土渐进发展,达到极限状态后逐渐破坏消散;空洞区始于螺旋输送机底部,随超挖出土逐步向上方和前方扩展,最终在击穿承载土拱后到达地表,形成“水滴状”空洞区;从不同角度提出了三类超挖量的控制标准.
The instability mechanism of shield tunnel excavation working face in a sandy cobble stratum was explored,and the CDEM (continuum-based discrete element method) was adopted to establish a quasi-continuous numerical model. Triaxial compression tests of sand-cobble soil were carried out numerically to analyse its macro–mesoscopic mechanical characteristics. Based on the features of “particle flow”,“soil arch effect”, and “over-excavation”,a 2D dynamic discrete element model was established to simulate the tunnel working face over-excavation with plane triangular blocks. The progressive instability mechanisms of the tunnel face (such as soil arch effect and cavity zone) were studied. The results show that the macroscopic stress-strain curve of the sandy cobble soil triaxial compression test can be divided into linear elastic,elastoplastic,and ideal plastic stages. The cobble enhances the soil structure as coarse granular particles. The contact surface of the cobble and sand weakens the macroscopic strength. The Hopper flow calibration test with the soil arching effect as the calibration criterion can effectively obtain the friction angle transformation relationships of discrete plane triangles of different scales. The arching effect is notably ahead of the face, develops gradually with overexcavation, and finally dissipates gradually after reaching the limit state. Void regions start from the bottom of the screw conveyor,develop forward and upward gradually with over-excavation and finally cut through the loadbearing arch, reaching the ground surface and forming water-drop shaped void regions. Three types of control standards for over-excavation are proposed based on different strategies.
作者
薛亚东
张森
李兴
葛嘉诚
XUE Yadong;ZHANG Sen;LI Xing;GE Jiacheng(Key Laboratory of Geotechnical and Underground Engineering of Education Ministry, Tongji University, Shanghai200092,China;College of Civil Engineering,Tongii University,Shanghai 200092,China)
出处
《西南交通大学学报》
EI
CSCD
北大核心
2019年第3期499-506,586,共9页
Journal of Southwest Jiaotong University
基金
国家自然科学基金资助项目(41072206)
关键词
隧道工程
数值模拟
砂卵石地层
盾构开挖面稳定性
土拱效应
tunnel engineering
numerical simulation
sandy cobble stratum
stability of shield tunnel excavation face
soil arching effect
