为探明盾构竖井垂直顶升施工上覆地层破坏响应机制,建立了盾构竖井在砂质黏土中垂直顶升的颗粒流足尺模型,在对比相关试验结果验证模型合理性基础上,从细观层次探讨了顶升过程中上覆地层的破坏历程、破坏形态及顶升阻力的变化规律,开展了覆土厚度与顶升速度对土层破坏响应的影响性分析。结果表明:(1)顶升阶段上覆土经历三角形受压区形成→受压区内颗粒黏结破坏→黏结破坏区域扩展→局部剪切滑移破坏→破坏面贯通地表的破坏历程,上覆土层可划分为隆起区、挤密区及裂隙区3个区域;(2)竖井端阻力先后经历显增段和渐降段,顶升至h/16(h为上覆土层厚度)时达到峰值,随后逐渐减小并趋于稳定,竖井侧摩阻力呈现先增大后减小的交替循环过程,呈波动趋势,端阻力显著大于侧摩阻力;(3)覆土厚度较大时最先受到顶升影响的地表区域位于竖井两侧,并非竖井正上方区域;(4)顶升速度较大时上覆土层发生“刺入破坏”,出现较窄的剪切带;(5)顶部破坏范围与覆土厚度呈二次函数增大,与顶升速度呈二次函数递减,端阻力与覆土厚度、顶升速度均呈同向线性关系。
In order to study the response mechanism of the overlying strata during the vertical jacking construction in shield tunneling, a full-scale particle flow model of shield shaft vertical jacking in sandy clay was carried out through discrete element method. The rationality of the discrete element model was verified by comparing relevant experimental results. The failure process, failure forms, and changes in jacking resistance of the overlying strata during the jacking process were explored, and an analysis was conducted on the impact of soil thickness and jacking speed on the failure response of soil. The results show that: (1) During the jacking stage, the overlying soil undergoes five stages including form a triangular compression zone→particle bonding failure within the compression zone→expansion of the bonding failure zone→local shear slip failure→the failure surface penetrating the surface. The overlying soil affected by the jacking can be divided into three regions: uplift zone, compaction zone, and crack zone. (2) The resistance at the end of the shaft experiences a significant increase and a gradual decrease, reaching its peak when it reaches h/16, and then gradually decreases and tends to stabilize. The lateral friction of the vertical shaft shows an alternating cycle of increasing first and then decreasing, showing a fluctuating trend. The end resistance is significantly greater than the side friction. (3) When the soil thickness is large, the surface area first affected by the jacking is located on both sides of the vertical shaft, not directly above the vertical shaft. (4) When the jacking speed is high, the overlying soil undergoes "penetration failure" and a narrow shear band appears. (5) The top failure range increases with the soil thickness as a quadratic function, and decreases with the jacking speed as a quadratic function. The end resistance has a linear relationship with the strata thickness and the jacking speed in the same direction.
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