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目的:盾构隧道在成层土中掘进时,地下水渗流容易引起盾构开挖面失稳破坏。本文提出考虑地下水渗流的机动场模型,探讨成层土中地下水渗流规律,研究渗流对开挖面稳定性的影响,并提出渗流条件下成层土中盾构支护压力的计算方法。创新点:1.提出考虑地下水渗流盾构开挖面失稳机动场的模型;2.建立成层土中地下水渗流模型;3.推导考虑地下水渗流的盾构开挖面极限支护压力上限解。方法:1.根据已有工程案例,对渗流条件下成层土中盾构开挖面失稳进行受力分析(图5),并提出开挖面失稳机动场模型(图6);2.通过上限分析,推导得到盾构开挖面失稳极限支护压力计算公式(公式29);3.对成层土中地下水渗流进行数值模拟,并采用理论模型(图15)对渗流规律进行表征;4.研究极限支护压力对地下水渗流因素的敏感性。结论:1.地下水渗流在失稳土体内部产生渗流力作用,在盾构开挖面上也对支护压力产生抵消作用。2.提出成层土中考虑地下水渗流的失稳机动场模型,并推导出极限支护压力上限解;3.在盾构土舱未进行渗透性改良的条件下,成层土中地下水渗流在1200 s内达到稳定,其中,穿越层渗流方向主要为水平向,而覆土层中主要为竖向渗流;4.考虑渗流影响,本文上限解预测的支护压力值更为合理。
OBJECTIVE: When shield tunneling is carried out in stratified soil, groundwater seepage easily causes instability of shield tunneling surface. In this paper, the groundwater seepage model considering the groundwater seepage is discussed. The groundwater seepage law in layered soil is discussed. The influence of seepage on the stability of the excavation surface is studied. The calculation method of shield support pressure in layered soil is presented. The innovation points: 1. Propose the model considering groundwater seepage shield excavation surface instability; 2. Establish groundwater seepage model in layered soil; 3. Derive the upper limit solution of shield support surface considering seepage of groundwater . According to the existing engineering cases, the mechanical analysis of instability of shield tunneling in layered soils under seepage conditions (Fig. 5) Through the upper limit analysis, the calculation formula of buckling limit of shield excavation surface is deduced (formula 29); 3. Numerical simulation of groundwater seepage in stratified soil and the seepage law is carried out by theoretical model (Figure 15) Characterization; 4. Study the limit support pressure on groundwater seepage factor sensitivity. The conclusions are as follows: 1. The groundwater seepage flow produces the seepage force inside the unstable soil, and also counteracts the support pressure on the shield excavation surface. 2. Proposed the instability mechanism field model considering the seepage of groundwater in layered soils and deduced the upper limit solution of the limit support pressure. 3. Under the condition that the permeability of the shield is not improved, the groundwater seepage in the layered soil Within 1200 s, the seepage direction is mainly horizontal while the overburden is mainly vertical seepage.4. Considering the influence of seepage, the upper limit solution of the proposed support pressure is more reasonable.