软岩大变形小净距隧道施工方案优化研究

发布时间：2018-04-03 14:18

本文选题：软岩大变形　切入点：小净距隧道　出处：《兰州交通大学》2014年硕士论文

【摘要】：国内外对于软岩大变形小净距隧道的围岩变形研究还不多见，，再加上有些已建成的软岩大变形小净距隧道出现衬砌裂纹、地表裂缝、洞门墙开裂及中墙柱开裂等情况，故对此类隧道的力学行为进行理论研究与施工方案探讨。本文以兰渝铁路新城子隧道为背景，应用大型通用有限元分析软件（MIDAS/GTS），对隧道的施工过程进行有限元数值仿真模拟，研究在不同台阶开挖长度和不同左右线隧道掌子面距离条件下，进行隧道变形和支护单元受力模拟分析，综合现场监控量测数据，取得了以下成果：（1）造成新城子隧道发生大变形的主要原因是隧道所处的地应力场是高地应力场，岩体被切割挤压成小块状，另外节理裂隙异常发育，促使岩体的自稳能力低下，围岩表现出位移增大期较长，累积变形总量大的特点。（2）根据现场监测数据整理分析，采用三台阶开挖法软岩大变形小净距隧道的变形时间规律：拱顶沉降变化288mm，上台阶水平收敛值最大，达到354mm；上台阶位移变形急速变化时间为25天；中台阶位移变形急速变化时间为20天；下台阶位移变形急速变化时间为15天。围岩压力增长期为70天；接触压力增长期为50天，从拱部到侧墙，随着空间自上而下变化，其应力最终值逐渐减小；且通过分析得出，长锚杆对于控制围岩净空收敛方面有很好的效果。（3）通过模拟三种工况开挖隧道，对比拱顶沉降、水平收敛及支护应力，画出了他们的位移和应力随施工步的变化曲线图，分析得出：采用工况Ⅰ开挖隧道时，拱顶沉降、水平收敛、各初支单元的受力、钢拱架轴向应力、喷射混凝土应力、二衬混凝土应力及锚杆轴力受力均比采用工况Ⅱ、工况Ⅲ时小。综合考虑变形控制、洞室稳定等方面，认为在新城子隧道所处条件下，采用3m台阶长度较为合理，有利于围岩的自稳，有效发挥围岩的自承能力，且拱顶下沉和水平收敛值较小，初支和二衬单元受力比较均匀，更多的削弱了初支单元和二衬单元受力集中范围，保证洞室本身的稳定性。（4）通过不同左右线掌子面距离的模拟分析结果可以看出，拱顶沉降、水平收敛值随着掌子面距离的增大而减小，且变化速率随着距离增大而减小。工况一、工况二和工况三施工时隧道位移变化较大，且该三种工况施工时隧道位移的变化有较大区别，而工况四和工况五差别不是很大，工况五的变形略大于工况四的变形。通过综合分析左右线隧道掌子面距离的变化对拱顶沉降值和水平收敛值的影响，在本文分析的情况中，左右线隧道掌子面距离为30m或40m时的相对效果较好，拱顶沉降和水平收敛值较前三种工况小，此距离可有效控制拱顶沉降和水平收敛变形，有利于洞室的稳定。
[Abstract]:Both at home and abroad for the large deformation of soft rock tunnel with small spacing deformation studies are still rare, small spacing tunnel lining crack, surface crack of large deformation of soft rock and some have been built, and the column wall portal wall cracking cracking and so on, so that the mechanical behavior of the tunnel in theory and construction study of scheme.
Based on the background of Metro Tunnel on Lanzhou Chongqing railway, the application of finite element analysis software (MIDAS/GTS), finite element numerical simulation for tunnel construction process and research in different excavation step length and different distance line around the tunnel face under the condition of tunnel deformation and support element stress analysis, comprehensive the site monitoring data, the following results have been achieved:
(1) the main reason caused by metro tunnel is large deformation tunnel where the stress field is high stress field, rock cut squeeze into small blocks, and joint abnormalities, prompted the rock stability of surrounding rock is low, showing displacement increases over a long period of time, the total cumulative deformation characteristics.
(2) according to the on-site monitoring data analysis, using three step excavation of large deformation of the small spacing tunnel method in soft rock vault settlement changes 288mm, the step level convergence value of the largest, up to 354mm; the step displacement rapid change time is 25 days; the step displacement rapid change time for 20 days step displacement; rapid change time is 15 days. The surrounding rock pressure of growth for a period of 70 days; the contact pressure increase for a period of 50 days, from the arch to the side wall, with the changes in the stress space from top to bottom, the final value decreases gradually; and the long bolt, have very good effect to control tunnel convergence.
(3) by simulating three kinds of conditions of tunnel excavation, comparison of crown settlement and horizontal convergence supporting stress, draw their displacement and stress with the construction step of change curve shows the condition of tunnel excavation, crown settlement, horizontal convergence, the initial supporting force of single element steel arch, axial stress, shotcrete stress, two lining concrete stress and axial force of the anchor force are compared with the condition II, III. Considering the condition of small deformation control on tunnel stability, that the conditions in the metro tunnel, the 3M step length is more reasonable, is conducive to the surrounding rock stability, effectively play the self-supporting capacity of the rock and the crown settlement and horizontal convergence value is smaller, the initial support and lining two unit force uniform, more weakened the primary support unit and the two unit lining stress concentration range, to ensure the stability of cavern itself.
(4) through different simulation results about distance line tunnel face can be seen, vault settlement, horizontal convergence value decreases with increasing the distance of the tunnel face, and the rate of change with distance increases. The first condition, operating mode two and three during the construction of tunnel displacement changes greatly, and the changes of three kinds of tunnel construction conditions when the displacement is quite different, and the operating mode four and five difference is not large, the deformation condition five is slightly larger than the effect of deformation of four conditions. Through the comprehensive analysis about the changes of the distance line of the tunnel face to the vault sedimentation and horizontal convergence value in this paper, analysis of the situation, about the distance line of tunnel face for the better effect of 30m or 40m relative to the crown settlement and horizontal convergence than before in the three conditions, the distance can effectively control the settlement of vault and horizontal convergence deformation, is conducive to the stability of the cavern.

【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U455.4

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