Seismic stability of urban tunnels in shallow depth

为了解应力释放对新奥法隧道抗震稳定性的影响，本文通过在干燥石英砂中模拟半圆形铝隧道和在胶结模型地基中模拟半圆形铝隧道，在离心机上进行了主动剪切试验。结果表明：1)在砂土地基中，作用在隧道顶板上的土压力与太沙基松动土压力相近，小于太沙基松动土压力的理论计算值：ρ_r=ρ_v+ρ_h/2-ρ_v-ρ_h/2Cos2θ2)在应力释放的胶结砂土地基中，隧道衬砌的弯矩分布与太沙基松动土压力作用下梁结构弹性计算的计算值相近。然而，在不释放应力的情况下，隧道衬砌的弯矩分布与采用…对梁结构进行弹性计算时的计算值基本一致3)在砂土地基情况下，作用在隧道衬砌上的土压力接近于理论计算分布。4)在砂土地基中，弯矩分布没有变化，在胶结地基中，随着应力的释放，第一次剪切后隧道的弯矩分布增大。这说明松散砂土地基和水泥砂软土地基由于地基拱度效应而产生的土压力增量机理不同，在水泥砂土地基中，应力释放对因剪切引起的弯矩增量也有影响。与其他情况相比，允许应力释放情况下弯矩分布增量较大。但是，在考虑初始值的绝对值中，地震过程中的弯矩相对较小。较少

This paper presented some results of active type shear tests in a centrifuge by modeling a semi-circular aluminum tunnel in dry silica sand and in cemented model ground to understand the effects of stress releasing on seismic stability of NATM tunnel. According to the results, the following findings were obtained.1) Before shearing, in the sand ground the earth pressure acting on the tunnel crown was close to Terzaghi's loosening earth pressure and smaller than the theoretical calculated overburden pressure by the following equation.ρ_r=ρ_v+ρ_h/2-ρ_v-ρ_h/2cos2θ2) Before shearing, in the cemented sand ground with stress releasing the bending moment distribution of the tunnel lining was similar to the calculated values by elastic calculations of beam structure applied Terzaghi's loosening earth pressure, however in the case of no stress releasing the bending moment distribution of the tunnel lining was similar to the calculated values by elastic calculations of beam structure applied the … More oretically calculated overburden pressure.3) Looseness of the ground over the tunnel had deteriorated by shearing in cases of sand ground, and the earth pressure acting on the tunnel lining close to theoretically calculated distribution.4) Whereas in the sand ground and the bending moment distribution shows no change, in the cemented ground with stress releasing the bending moment distribution of the tunnel increase after first shearing. This indicates that there are different mechanisms of earth pressure increments due to arching effect of the ground dissipate between sand ground as non-consolidated ground and cemented sand as cemented soft ground.In the cemented sand ground, stress releasing also affects to the increment of bending moment due to shearing. Increment of bending moment distribution of allowed stress releasing case is larger compared with the other cases. However, in absolute values considered with initial value, bending moment during earthquakes is relatively smaller than the other cases. Less