多运营模式下地铁的超静孔压分布特征与动力累积变形规律

Distribution characteristics of excess pore water pressure and power cumulative settlement regularity of dynamic load under various operation modes of subway

以往地铁隧道沉陷研究主要局限于不排水条件下的洞周土体动强度和液化及累积塑性变形等方面,但对排水条件循环荷载下超静孔压和累积塑性变形研究不足。结合地铁的正常运营状况,针对南京地铁河西段粉砂土工程地质特点,开展排水条件下循环荷载三轴实验。在获得可靠的动参数和动变形基础上,运用GeoStudio有限元软件建立二维地基-隧道有限元模型,对地铁多运营模式下隧道地基土的排水条件循环荷载动力响应非线性分析,得到运行方式和运行速度等因素影响下隧道洞周位移和超静孔压的动力响应性状。结果表明:双向运行时隧道上方的竖向位移响应值小于单向运行时的竖向位移响应值。而洞周超静孔压与之相反;列车运行速度为35 km/h的超静孔压响应值大于60 km/h的响应值,竖向位移无明显差异。列车低速产生的振动频率相对较低,能量衰减越慢,所以产生较大的超静孔压,与实测在规律上相符合。

The subsidence research of tunnel in the past was restricted to the dynamic strength, liquidation and cumulative plastic deformation of the soil around tunnel under the undrained condition. The studies on the excess pore water pressure and the cumulative plastic deformation under cyclic loading under the drain- age conditions were not enough. Combined with the normal operating state of the subway and geological en- gineering characteristics of silty sands in Hexi area of Nanjing, triaxial tests under cyclic loading under the drainage conditions were carried out. On the basis of reliable parameters and dynamic deformation, a two- dimensional finite element model of subsoil-tunnel was established by the GeoStudio finite element soft- ware. Nonlinear analysis of dynamic response of subsoil under cyclic loading under the drainage condition was given. The characteristics of vibration responses of the subsoil displacement and excess pore water pressure were obtained in various operation modes, which were influenced by operational mode and opera- tional speed and other factors. Results showed that the vertical displacement response above the tunnel dur- ing bi-directional running was less than that during one-way running, on the contrary, the response of ex- cess pore water pressure around the hole during bi-directional running was greater than that during one-way running. The response value of excess pore water pressure at the speed of 35 km/h was greater than that at 60 km/h, while the vertical displacement was almost the same. When the train ran slowly, the vibration frequency was relatively low and the energy attenuated more slowly, thus producing a large excess pore wa- ter pressure. It was consistent with the actual measured conditions.