砂卵石地层土压平衡盾构改良渣土粘弹塑性流变模型研究

Earth pressure balance shield (EPBS) tunneling often finds application in sand and gravel strata, where blocking of pressure chamber and failure of tunnel face frequently occur. The key to the solution of these problems is soil conditioning. Nonetheless, the central issue of soil conditioning is a clear understanding of the mechanical properties of the excavated soil inside the pressure chamber before and after conditioning. In soil conditioning, the excavated soil is turned circularly by the blender to be evenly mixed with the modifying agents, thus gaining some fluidity and plasticity; meanwhile, the horizontal thrust transmitted by the baffle plate is large enough to guarantee stability of tunnel face and to prevent ground subsidence. In this study, a variety of methods, including large-diameter triaxial test, rheological test, model test and numerical modeling, were applied to investigate the laws governing the changes in stress-displacement, strength and rheological parameter of different kinds of sandy gravel; a viscoelastic-plastic rheological model for the excavated soil in the pressure chamber under horizontal thrust and circumferential shear was built; and a numerical modeling was also conducted to verify the model and optimize the parameters.

在土压平衡盾构法施工过程中，常常会遇到砂卵石含量较高的地质环境，容易产生压力舱闭塞、开挖面失稳等技术难题，解决这一难题的关键就是土体改良,就是要弄清楚压力舱内渣土在改良前后的力学特征，即渣土将在搅拌器作用下做环向转动，使改良剂与渣土混合均匀，具备一定的流塑性；同时，还受到挡板传递的很大水平推力作用，以保持开挖面的稳定，防止地面沉降。本课题拟采用大直径三轴试验、流变试验、模型试验、数值建模等方法开展研究工作，拟获得不同类型的砂卵石受力-位移、强度变化、流变参数等规律；拟建立压力舱内渣土在水平推力和环向剪切作用下的粘弹塑性流变模型；通过数值建模的方法对模型进行验证，优化参数。

土压平衡盾构在城市地下空间开发过程中具有无可替代的地位。在砂卵石地层施工中，由于其较差的流塑性常常造成压力舱堵塞、刀具严重磨损、掘进效率低下的技术难题，严重制约着土压平衡盾构的一次长距离安全掘进。成为盾构隧道施工掘进的核心难题之一。通过土体改良对砂卵石土体进行改良重塑是解决上述难题的关键技术。通过对压力舱内改良砂卵石水平推力和环向剪切复杂应力状态的分析，获得压力舱内改良渣土的力学特征；采用大型三轴试验获得不同类型砂卵石土体整体力学特性，通过颗粒流数值方法对砂卵石颗粒与颗粒之间点对点接触和颗粒与改良剂之间粘性接触进行微观作用分析，获得砂卵石土体宏观-微观力学特性；通过大型剪切流变试验，获得砂卵石改良前及不同改良状态下其流变力学特性及流变参数，建立改良砂卵石流变模型，依托流变参数（屈服应力和塑性粘度）量化分析改良砂卵石“理想流塑性状态”的流变学参数指标及其范围，为砂卵石改良状态的定量评价提供科学依据，指导工程实践。