【作者】 李文华；

【导师】 赵大军；

【作者基本信息】 吉林大学 ， 地质工程， 2013， 博士

【摘要】 随着城市的不断发展和扩大，城市地下空间被各种既有管线、构筑物(桥梁、建筑)基础、已有地铁等占用,新规划的地铁隧道经常出现两条（或多条）并行、净距小开挖断面又很大的情况。与此同时，施工范围内存在多条断层、地层条件差、地下水丰富复杂等多种不利因素，增加新建双线（多线）隧道施工难度。本文结合长沙地铁2号线的以上特点，参考国内外已有经验，通过数值模拟、现场监测、理论分析，对小净距、双线大断面并行隧道进行关键技术研究，提出了改进的双侧壁导坑施工法，对导坑内撑拆除和二衬时机进行了优化；对比分析了双线隧道大小断面开挖先后顺序、中岩墙加固与否、大断面不同开挖方法以及相邻隧道不同间距等条件下中岩墙稳定性；在围岩稳定与变形监测成果的基础上，对岩柱水平位移、钢拱架应变及内力回归分析，得到较为实用的预测公式。为城市轨道工程、山体隧道工程、地下硐室等掩埋结构物施工提供一定的理论基础和实践经验。本文具体工作和研究内容如下：1.小净距、大断面双线地铁隧道的关键技术问题研究（1）根据项目设计的实际情况，对施工风险进行了分析，并提出了控制措施。在总体施工方案确定的基础上，利用FLAC3D软件对大断面、小净距双线隧道暗挖施工数值模拟，分析了双侧壁导坑（九步、六步）、CRD法三种施工方法的力学行为，提出了六步双侧壁导坑施工方法，优化了施工方案。（2）在双侧壁六步导坑法大断面暗挖施工方案基础上，利用MIDAS软件对双侧壁导坑施工步序、内撑拆除和二衬时机优化方面进行了模拟分析。在步序优化方面，提出了改进的六步导坑法，与目前已有的施工方法相比，本施工方法因先把上部分全部开挖完后再开挖下部分，施工工作面增大，对施工工期的缩短和各施工工序及施工工种的协调施工均有很大优势。可为城市轨道工程、山体隧道工程、地下硐室等掩埋结构物施工提供参考。在拆除导坑内撑和二衬时机优化方面，通过对比拆除支撑前后维护结构的位移及内力对比分析，发现拆除临时支撑时，拱顶位移变化较大，初衬结构的弯矩变化较大，增加很快。当二衬施做完成后，支护结构内力变化幅度减小，结构基本趋于稳定。如果一次性拆除临时支撑且二衬不能及时施做，考虑到释放应力的时间效应，拱顶竖向位移将进一步增大。建议拆除临时支撑时，进行分块、分幅拆除，以减小拱顶沉降和释放应力时间效应带来的不安全因素。如果能保证二衬及时跟进，按照拆除临时支撑和二衬施做间距12m方案，可以满足施工安全要求。2.小净距、大断面双线隧道中岩墙稳定性分析（1）通过对多种工况的施工模拟分析，在开挖大小断面顺序方面，对超小净距双线隧道，应先开挖小断面隧道，后开挖大断面隧道，以减少先开挖大断面隧道影响围岩应力变化较大的区域，从而一定程度的影响了单线隧道开挖土体区域。并且开挖小断面隧道也可通过小洞径的开挖确定设计支护是否合理，地质勘查结果是否准确，为后续开挖大洞径隧道提供参考。（2）对是否进行中岩墙加固进行了模拟分析，对于岩墙，当两个洞室的净距很小，岩墙加固与否对其稳定性影响较大，一般采用的加固措施包括注浆加固和两侧采用对拉锚杆，其中通过大量的现场实例和数值计算分析可知，对拉锚杆对岩墙的稳定十分重要。（3）对双线隧道不同开挖方法进行了模拟分析，大断面按照双侧壁导坑施工方法对中岩墙稳定性优于CRD法，且可保证围岩的稳定性，引起中岩墙变形和塑性区也在规范允许范围内，能保证工程的安全施工。（4）对并行隧道不同的净距情况模拟分析，当净距小于1.0D时，岩墙的净距越小，并行隧道开挖所产生的土体位移、应力和塑性区越大，故对于超小净距隧道，对于岩墙采取注浆加固的措施，并施做对拉锚杆，建议隧道硐室采用多部开挖，边开挖边支护的措施，开挖一步支护一步，防止由于土体释放应力过大从而导致岩墙的失稳破坏。3.车站暗挖区间围岩稳定与变形监测及回归分析对车站暗挖区间进行了围岩稳定与变形监测，对监测成果进行了分析整理。通过对实测双线隧道开挖施工沉降、变形、应力监测结果的回归分析，得到了开挖引起中岩柱水平位移、钢拱架应变、内力的变化规律：（1）对于CRD工法，岩柱水平位移与时间呈多次抛物线变化，距离单洞洞口距离越近，抛物线次数越高，反之，距离单洞洞口距离越远，抛物线次数越低。（2）对于暗挖双侧壁六步导坑-B法施工，钢拱架拱顶、仰拱部位应变与时间符合4次抛物线变化规律。（3）钢拱架拱顶、仰拱部位弯矩与时间呈2次抛物线变化规律。（4）仰拱轴力与时间呈3次抛物线变化规律（5）拱顶轴力与时间呈直线变化更多还原

【Abstract】 With the continuous development and expansion of city.The underground space of urban isoccupied by a variety of pipelines,structures (Bridges and buildings) foundation,subways and soon. The small spacing of two (or more)tunnels and large cross-section exist in the new planningtunnels, while, with multiple faults, poor stratigraphic conditions, abundant underground waterand other unfavorable factors exist in construction range,increased the difficult of new two lane(multi-line) tunnels construction.Based on the above characteristics of Changsha subway line2, Reference the experience ofdomestic and foreign, through numerical simulation analysis, field monitoring and theoretical, toresearch the key technology of parallel tunnel with small spacing and large cross-section, putforward the improved two side-surrounding pilot tunnel method, and optimized the opportunity ofdemolition of heading support inside and second liner timbering, comparative analysis of the rockpillar stability in two lane tunnel section excavation sequence, rock pillar reinforcement or not,the large cross-section of different excavation methods and the adjacent tunnel under theconditions of different spacing, based on the stability of surrounding rock and the deformationmonitoring results,do the regressing analysis for rock pillar horizontal displacement,strain andinternal force of steel arch,get the more useful forecasting formula. Provide a theoretical basis andpractical experience for construction of urban rail projects, mountain tunnel, undergroundchambers and other buried structures.In this paper, the concretework and research are as follows:1. Research the key technology of two-lane subway tunnel with small spacing and largecross-section(1) According to the actual situation of the project design, analyzed the construction risk andproposed control measures. Based on the determined general construction scheme, use theFLAC3D software do numerical simulation for two lane tunnel excavation construction withsmall spacing and large cross-section, analysis mechanical behavior of two side-surrounding pilottunnel method (nine, six-step), CRD construction methods, proposed six-step twoside-surrounding pilot tunnel method to optimize the construction program.(2) Based on large cross-section excavation construction program In the six-step twoside-surrounding pilot tunnel method, use MIDAS software do simulation analysis for sequenceof two side-surrounding pilot tunnel construction and optimize the opportunity of demolition ofheading support inside and second liner timbering. In the sequence optimization, is proposed an improved six-step method to the pit, compare with the current existing construction methods, thismethod of construction first excavate all the upper section then excavate under section which canincrease the face, there are great advantages in shortening the construction schedule andcoordinating construction process. Provide reference for construction of urban rail projects,mountain tunnel, underground chambers and other buried structures. Within optimized theopportunity of demolition of heading support inside and second liner timbering, by comparingand analysising displacements and internal forces before and after removal of the supportstructure found that when removal of temporary support, the displacements of vault changedgreatly, the moment of initial lining structure changed greatly, increased rapidly. When the secondliner is complete, the internal force rangeability of supporting structure decreases, the basicstructure stabilized. If the removal of temporary supports and second liner can not be applied todo, considering the time effect of releasing the stress, the displacements of vault will increasefurther. When removal of temporary support we can divided into blocks,framing to removed, toreduce the insecurity caused by vault settlement and time effect of releasing the stress. If you canguarantee second liner construct timely, in accordance with the12m long between removal oftemporary support and second liner construction can meet construction safety requirements.2.Analysis the rock pillar stability of two-lane tunnel with small spacing and largecross-section.(1) Through the construction of a variety of conditions simulation analysis, the excavationsequence of the ultra small spacing in two-lane tunnel,is the small section tunnel is first, and lastis the large section tunnel,in order to reduce area of large cross-section tunnel surrounding rockstress changes greatly, thus to affected the single tunnel excavation soil zone. and a small sectiontunnel excavation through a small hole diameter can also be designed to support the excavation todetermine whether it is reasonable, geological survey results are accurate or not, can providereference for large diamete tunnel excavation.(2) On whether to proceed with the rock pillar reinforcement were simulated and analyzed,for rock pillar, when the clear distance of two cavern is small, the stability of rock pillarreinforcement can impact a lot, the general use of reinforcement measures including grouting andused cross anchor on both sides, and through a large number of field examples and numericalanalysis shows that cross anchor is very important for the rock pillar stability.(3) Different excavation methods for two-lane tunnel were simulated and analyzed,according to two side-surrounding pilot tunnel method construction method better than CRDmethod in rock pillar stability, and can guarantee the stability of surrounding rock, the rock pillardeformation and plastic District also within the allowable range of standardize,it can ensure the safety of construction.(4) Simulate and Analysis the different clear distance of parallel tunnel, when theclear distance is less than1.0D, the rock pillar clear distance is smaller, soil displacement, stressand plastic zone of parallel tunnel excavation is larger, so for ultra-small spacing tunnel takemeasures to grout for rock pillar and do cross anchor, the tunnel chamber should be do a numberof excavation, excavating and supporting should be carried out simultaneously, to prevent therelease of the soil stress too much causing rock pillar instability failure3.Rock stability,deformation monitoring and regression analysis in underground excavationof the station interval.Monitored rock stability and deformation in underground excavation of the station interval,analyzed monitoring results. Do regression analysis for monitoring results of settlement,deformation, stress in two-lane tunnel, to get the variation of the horizontal displacement, steelarch strain, internal forces caused by the excavation of rock pillar:(1)CRD construction method, Rock pillar horizontal displacement and time were repeatedlyparabola,the closer distance from single hole, the higher the number of parabola, conversely, thefarther the distance from single hole, the lower the number of parabola.(2) Six-step two side-surrounding pilot tunnel method-B, For underground construction, steelarch vault, the strain of parts of the inverted arch and time meet4times parabola change rule.(3) Steel arch vault, inverted arch moment and time meet2times parabola change rule.(4) Inverted arch Axial force and time meet3times parabola change rule.(5) Vault axial force and time change is linear.更多还原