盾构隧道穿越液化地基上浮振动台试验分析

Analysis on Shaking Table Experiment for Shield Tunnel through Liquefied Foundation

随着城市地铁线路不断增加,可能出现盾构隧道穿越液化地层的现象。一旦发生地震,盾构隧道存在上浮破坏的潜在风险。为深入研究盾构隧道周边液化地层的动力响应,针对相同密实度砂土在3种不同峰值加速度作用下开展室内振动台试验,分析土体中超静孔压的发展特性和隧道上浮规律。结果表明:1)砂土液化最先发生在地表及浅层土体处,随着深度增加砂土液化程度逐渐降低,即增加隧道埋深有利于降低隧道液化程度。2)模型试验揭示盾构隧道的上浮机制,即使液化地基未完全液化,当超静孔隙水压力引起的上浮力大于隧道残余上覆有效土压力与隧道重力之和时,隧道将出现上浮。设计时可从消除液化地基和增加隧道重力2个方面入手,提高盾构隧道的抗上浮能力,确保隧道结构在地震时的安全。

As metro lines keep increasing in large cities, shield tunnel crossing liquefied foundation may appear. The potential risk of floating damage exists in shield tunnels once earthquake occurs. In order to study the seismic response of the liquefied stratum around shield tunnel,several shaking table tests were carried out under three different peak accelerations. The developing characteristics of the excess pore pressure as well as the floating laws of the shield tunnel were analyzed. The experimental results indicates that:(1) The liquefied appears at the surface and in the shallow area of the saturated sand firstly, The degree of liquefaction decreased along with the increment of buried depth of the shield tunnel, which means increasing the depth of the tunnel can reduce the liquefaction;(2) The floating mechanism of shield tunnel can be revealed by the model experiment. Even if the foundation is not fully liquefied, the tunnel floating movement appears when the buoyancy caused by the excess pore water pressure is larger than the summation of the residual overburden pressure and tunnel gravity. The anti-floating ability of shield tunnel can be improved by eliminating liquefaction foundation and increasing tunnel weight, which ensure the tunnel safety during the earthquake.