应力方向旋转对粘土小应变刚度特性影响的试验及本构模型研究

Tunnel and excavation in the urban area always close to the exist road or tunnel, soil strain is in the small scale during excavation in general, and the stress state was complex. The determination of small strain stiffness parameter is important for analyzing the environmental influence caused by underground excavation and tunneling, while both stress history and stress path have significant influence on the small strain stiffness. In this project, we first get the typical soil stress path from a three-dimensional finite-elemental study which focus on the systematically research of principle stress rotation and its influence factors. And a GDS triaxial apparatus with a bender element is used to do the shear wave velocity test at different direction for intact and reconstituted clay and study the anisotropy of the clay small strain stiffness quantitatively. Then ZJU-HCA will be used to do the small strain stiffness test with typical stress path for both intact and reconstituted clay to simulate the behavior of clay during ground excavation coupling with traffic loading. The influence of the stress direction will be analyzed. Finally, a small strain constitutive model considering the effect of the stress rotation is built. In-site dates will also be collected as a support and comparison to analyze the effect of stress rotation and small strain stiffness anisotropy.

城市隧道、基坑的开挖往往紧邻或穿越既有道路、隧道等，开挖引起周围土体应变一般在较小范围内，且受力状态非常复杂。准确分析开挖对周围环境影响需要合理确定土体小应变刚度参数，其受应力历史，应力路径等的影响显著。本项目采用三维数值模拟对城市粘土地基开挖耦合交通荷载下地基土体应力方向旋转变化规律及影响因素进行系统研究，得到土体单元典型应力路径。采用弯曲元技术测定饱和粘土沿不同方向的剪切波速，研究饱和粘土小应变刚度各向异性及影响因素，提出粘土小应变刚度各向异性定量描述方法。再利用空心圆柱扭剪仪对饱和原状和重塑粘土开展模拟地基开挖耦合交通荷载引起典型应力方向旋转路径下的小应变刚度试验研究，分析应力方向旋转对粘土小应变刚度特性的影响规律、机理。最终基于试验研究成果建立考虑应力方向旋转效应影响的粘土小应变刚度模型，收集实测数据对模型进行验证和修正，分析忽略应力方向旋转及小应变刚度各向异性特性的影响。

近年来随着我国城市化进程的快速推进，各大城市都在开展大量的隧道、基坑等大型地基开挖工程的，城市隧道、基坑的开挖往往紧邻或穿越既有建筑、道路、隧道等，开挖引起周围土体应变受力状态非常复杂。准确分析开挖对周围环境可有效支撑实际工程设计施工方案的安全、经济、有效。土体小应变刚度是准确分析开挖工程环境影响的重要参数，其受应力历史，应力路径等的影响显著。针对以上问题，本项目采用三维数值模拟对城市粘土地基开挖耦合交通荷载下地基土体应力方向旋转变化规律及影响因素进行系统研究，得到土体单元典型应力路径。采用弯曲元技术测定饱和粘土沿不同方向的剪切波速，研究饱和粘土小应变刚度各向异性及影响因素，提出粘土小应变刚度各向异性定量描述方法。再利用空心圆柱扭剪仪对饱和原状和重塑粘土开展模拟地基开挖耦合交通荷载引起典型应力方向旋转路径下的小应变刚度试验研究，分析应力方向旋转对粘土小应变刚度特性的影响规律、机理。最终基于试验研究成果建立考虑应力方向旋转效应影响的粘土小应变刚度模型，收集实测数据对模型进行验证和修正，分析忽略应力方向旋转及小应变刚度各向异性特性的影响。结合实际工程对工程实测数据进行了分析研究。