【作者】 汤旅军；

【导师】 陈云敏； 陈仁朋； 孔令刚；

【作者基本信息】 浙江大学 ， 岩土工程， 2014， 博士

【摘要】 为有效解决城市交通拥堵问题,越来越多的城市开始大规模兴建轨道交通。城市轨道交通的区间隧道大多采用盾构法施工,由于施工中时常遇到工程地质和水文地质状况多变、建(构)筑物及地下管线分布密集等诸多复杂条件,盾构开挖面稳定性问题日益突出。基于实际工程需求,本文对干砂地层、稳态渗流下饱和砂性土地层(如饱和砂质粉土)这两种典型复杂条件下盾构开挖面稳定性问题进行了系统深入地研究。主要工作和研究成果如下：(1)采用离散元法较为深入研究了干砂地层盾构开挖面稳定性问题。发现失稳过程中开挖面支护力随位移增大存在“先减小至极限值而后逐渐增大并趋于残余值”的现象；获得了当隧道埋深比C/D>1时极限支护力受埋深比影响较小的重要结论；揭示了典型埋深下(即C/D=2)开挖面渐进失稳模式；发现了极限状态时,盾构拱顶以上失稳区内存在显著的“土拱”效应,失稳区内土体出现“松动”现象。(2)研制了适用于模拟单相土层(如干砂)开挖面失稳的离心模型试验装置,基于该装置开展了密实干砂地层开挖面失稳离心模型试验。离心试验证实了离散元研究获得的开挖面支护力—位移变化关系的可靠性,发现了极限支护力随埋深比增大先增加而后基本保持不变的规律,借助PIV技术揭示了极限状态时开挖面前方呈现“楔形体—棱柱体”的失稳模式,获得了失稳“棱柱体”高度与隧道埋深有关的重要结论。(3)研制了国内外首套适用于模拟稳态渗流下盾构开挖面失稳的离心模型试验装置,基于该装置开展了国内外首个稳态渗流下饱和砂质粉土地层盾构开挖面失稳离心模型试验。研究发现：稳态渗流下,开挖面失稳过程中有效支护力随位移增大存在“先减小至极限值而后线性增大”的现象；稳态渗流下开挖面极限有效支护力随密封舱与远场水头差增大而线性增大；极限状态时,开挖面前方呈现“楔形体—棱柱体”失稳模式,此时失稳“棱柱体”已经发展到地表,其高度不受隧道埋深比的影响；孔压沿开挖面向远场逐渐增大,当距开挖面水平距离大于0.75D后,孔压几乎保持不变。(4)在本文离散元数值研究及离心模型试验的相关成果基础上,围绕失稳模式和“土拱”效应两方面对经典“楔形体—棱柱体”极限平衡模型(Anagnostou&Kovari1996)进行了修正,建立了适用于计算单相无粘性土层(如干砂)、单相粘性-摩擦型土层、稳态渗流时两相粘性-摩擦型土层等复杂条件下开挖面极限支护力(或极限有效支护力)的修正“楔形体—棱柱体”极限平衡模型。本文修正“楔形体—棱柱体”理论模型的准确性得到了笔者开展的离心模型试验的验证,成功应用于杭州地铁1号线九堡东站—下沙西站区间盾构工程。本文研究有助于提升行业内对复杂条件下开挖面稳定问题的认识,为实际工程中控制盾构开挖面稳定性提供参考。更多还原

【Abstract】 In order to solve the problem of the heavy traffic in the cities, more and more cities begin to construct the urban rail transits. Nowadays, most interval tunnels of the urban rail transits are constructed by the shield machines, due to the complicated constructional conditions such as the severely variable engineering geology and hydrologic geology, the densely distribution of the buildings and underground pipelines, the problem of face stability of the shield tunnel has become increasingly important. Based on the engineering requirement, two typical tunnel face stability problems under complicated constructional conditions were mainly investigated in this thesis, one is for tunneling in the dry sandy stratum, the other is for tunneling in the saturated sandy soils (e.g. the sandy silt stratum) with the steady state seepage.The major works and results of this dissertation are as follows:(1) Relatively in-depth DEM studies on the problem of tunnel face stability in the dry sandy ground was performed. According to the DEM investigations, it is found that during the tunnel face failure, with the increase of the face displacement, the support pressure firstly decreases to the limit support pressure and then increases gradually to a stable value (i.e., the residual support pressure). It is also obtained that when the cover-to-depth ratio C/D is no less than1.0, the limit support pressure is almost not influenced by the C/D value. For one typical buried tunnel (i.e., C/D=2), the failure patterns of the limit state and the residual stated were investigated. In the limit state, it is found that significant soil arching occurs in the upper part of the failure zone (which is above the tunnel crown), meanwhile, the soil becomes loosened in the failure zone.(2) An onboard centrifuge apparatus for investing the problem of tunnel face stability in the single phase soils (e.g. the dry sand) was developed. Based on this apparatus, a series of centrifugal model tests on tunnel face stability in dense sand were performed. The relationships between the support pressure and face displacement revealed by the DEM analysis are confirmed, it is obtained that the limit support pressure increases with the increase of relative depth CID and then remains almost the same. By using the PIV technology, it is found that in the limit state, a "wedge-prism" failure pattern occurs in front of the tunnel face, and it is also found that the relative depth has effects on the height of the failure "prism" in the limit state.(3) A world-first onboard centrifuge apparatus for investing the problem of tunnel face stability under the steady state seepage was developed. Based on this apparatus, a series of world-first centrifugal model tests on tunnel face stability in the saturated sandy silts stratum under the steady state seepage were conducted. During the tunnel face failure, with the increase of face displacement, it is found that the support pressure firstly decreases to the limit effective support pressure and then increases linearly and gradually. The limit effective support pressure increases linearly with the increase of the water head difference in the shield’s chamber and the far ground. In the limit state, a "wedge-prism" failure pattern occurs in front of the tunnel face, while the height of the failure "prism" is not affected by the relative depth of the tunnel (i.e., C/D). It is also found that the pore pressure increases with the horizontal distance to the runnel face, and when the horizontal distance to the tunnel face is no less than0.75D, the pore pressure seems to keep invariant.(4) Based on the investigations via DEM simulations and centrifugal model tests, some modifications on the classical "wedge-prism" limit equilibrium model (Anagnostou&Kovari1996) from the perspectives of the failure pattern and soil arching were conducted to build the improved "wedge-prism" model, which is more suitable for calculating the limit support pressure (or limit effective support pressure) on the conditions of the dry cohesionless soils (e.g., the dry sand), dry cohesive-frictional soils, and two phases cohesive-frictional soils (e.g., the saturated sandy silts) in steady state seepage. The accuracy of the improved wedge-prism model were verified by the results of the centrifugal model tests, and it was successfully applied in the interval tunnels of the line No.1of the Hangzhou metro.This research will obviously improve the engineers’cognitions on the problems of the tunnel face stability under complicated constructional conditions, and also will help to guarantee the face stability of the shield tunnels in the practical engineering.更多还原