软岩大变形小净距隧道支护结构研究

发布时间：2018-05-11 06:15

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

【摘要】：新建兰渝铁路兰州至广元段属多山地区，该片区内多数隧道穿越地层为高地应力软弱围岩、节理裂隙发育、围岩稳定性差、板岩层厚较小、薄层特性明显，多个隧道在施工过程中发生大变形，严重影响施工安全和施工进度；本文以兰渝铁路新城子隧道为背景，通过现场监控和数值模拟，以不同支护结构（长锚杆、双层初支、双层二衬）对软岩小净距隧道大变形控制效果为主线，分别采用理论分析、现场试验检测、数值模拟等方法对在建新城子隧道小净距段支护结构展开研究，以便为后续更小净距段提供可靠的理论依据和技术支持。研究内容与方法： (1)通过对国内外软岩大变形小净距隧道支护结构研究现状进行总结，本文分析了造成软岩大变形的原因、敏感因素、机理、施工控制关键技术等。 (2)结合工程实际，对隧道在不同支护结构（长锚杆、双层初支、双层二衬）下围岩变形及支护结构受力进行监测，并分析新城子隧道围岩及支护结构变形及受力规律，对比分析了不同支护结构支护效果。 (3)通过MIDAS/GTS软件对不同支护结构下隧道施工过程进行模拟，绘制围岩及支护结构关键部位应力应变随施工推进的变化曲线，推断其随时间和空间变化的规律，并且对推荐的支护结构进行了不同因素的优化对比分析。 (4)通过对比现场实测数据与数值模拟数据围岩中位移和支护结构受力，综合评选变形控制效果，，达到支护结构优化目的。主要研究成果： (1)造成新城子隧道发生大变形的主要原因是隧址所处的地质状况是破碎极破碎带，节理裂隙严重发育、地应力场较高、围岩流变作用明显；围岩及支护结构破坏以水平剪切破坏为主，围岩表现出水平收敛大于竖向沉降，累积变形总量大且周期长的特点。 (2)现场实测分析得到采用三台阶开挖软岩大变形小净距隧道变形随时间变化规律：拱顶位移变形快速变化时间为20～25天；上台位移变形快速变化时间为15～20天；下台位移变形快速变化时间为10～15天。上台阶开挖变形占总变形量的60%~70%，中台阶占总变形量的10%~15%，下台阶占总变形量的5%左右。 (3)通过对不同支护结构下软岩小净距段隧道开挖数值模拟表明：不同支护结构下隧道应力应变变化规律跟实际接近，隧道位移和应力较高的部位都出现在边墙、拱脚处，比较容易失稳，应给予加强；后行洞开挖对先行洞位移和支护结构受力有一定影响，随着掌子面间距的减小影响会越来越严重。 (4)通过对现场监测和数值模拟分析得出：双层初支和双层二衬支护效果良好，但双层二衬第一层二衬受力过大，存在安全隐患，故推荐刚度较大的双层初支，并且双层初支可通过延迟第二层初支施做和施做前辅以锚杆注浆可达到进一步加固围岩，充分发挥其自承能力，减小二衬受力。对于软岩隧道应本着一次支护充分让压，合理释放围岩变形能，充分发挥围岩自稳能力，二次大刚度支护进行补强的原则是科学合理的，即：“先柔后刚、先放后抗、变形留够、因势利导、相互制约、充分改善围岩稳定性”的基本原则。
[Abstract]:The Lanzhou - Guangyuan section of the newly - built Lanzhou - Chongqing Railway belongs to the mountainous area . Most of the tunnel crossing strata in the area are the weak surrounding rock with high ground stress , the joint fissure is developed , the stability of the surrounding rock is poor , the thickness of the plate is small , the characteristics of the thin layer are obvious , and the large deformation of the plurality of tunnels in the construction process seriously affects the construction safety and the construction progress ;
In this paper , based on the Xincheng sub - tunnel of Lanzhou - Chongqing Railway , the control effect of large deformation of soft rock small clear distance tunnel is studied by means of field monitoring and numerical simulation . The main lines are analyzed by theoretical analysis , field test and numerical simulation respectively , so as to provide reliable theoretical basis and technical support for the subsequent smaller net - distance segment .

Study contents and methods :

( 1 ) Through summing up the research status of soft rock large deformation small clear distance tunnel support structure at home and abroad , this paper analyzes the causes , sensitive factors , mechanism and key technology of construction control .

( 2 ) According to the engineering practice , the deformation of the surrounding rock and the stress of the supporting structure of the tunnel under different supporting structures ( long bolt , double - layer initial support and double lining ) are monitored , and the deformation and stress law of surrounding rock and supporting structure of Xincheng sub - tunnel are analyzed , and the supporting effect of different support structures is compared .

( 3 ) To simulate the construction process of tunnel under different support structure through MIDAS / T software , the stress strain of surrounding rock and supporting structure is drawn along with the change curve of construction propulsion , the law of time and space change is inferred , and the optimized contrast analysis of different factors is carried out on the recommended supporting structure .

and ( 4 ) comprehensively evaluating the deformation control effect by comparing the measured data of the field and the numerical simulation data in the surrounding rock of the data simulation data and the stress of the supporting structure , so as to achieve the optimization purpose of the support structure .

Key findings :

( 1 ) The main reason for the large deformation of the new city sub - tunnel is that the geological condition at the tunnel site is the crushing pole crushing zone , the joint fissure is seriously developed , the ground stress field is high , and the rheological effect of the surrounding rock is obvious ;
The failure of surrounding rock and supporting structure is dominated by horizontal shear failure , and the surrounding rock shows that the horizontal convergence is greater than vertical settlement , the total accumulated deformation is large and the period is long .

( 2 ) The field test results show that the deformation of large deformation small clear distance tunnel with three step excavation is changed with time : the rapid change time of displacement deformation of vault is 20 ~ 25 days ;
the rapid change time of the displacement deformation of the upper stage is 15 - 20 days ;
the displacement deformation of the step - down displacement is rapid change time of 10 - 15 days . The upper step excavation deformation accounts for 60 - 70 % of the total deformation amount , the middle step occupies 10 - 15 % of the total deformation amount , and the lower step accounts for about 5 % of the total deformation amount .

( 3 ) The numerical simulation of tunnel excavation of soft rock under different supporting structures shows that the change rule of tunnel stress and strain under different support structures is similar to the actual approach , and the location of tunnel displacement and stress is relatively easy to be unstable and should be strengthened ;
The excavation of the back - row tunnel has some influence on the displacement of the preceding tunnel and the stress of the supporting structure , and the influence of the reduction of the spacing of the palm surface becomes more and more serious .

( 4 ) By analyzing on - site monitoring and numerical simulation , it is concluded that the two - layer primary support and double - layer double lining support have good effect , but the two - layer two - lining first - layer two - layer lining has a large stress and a potential safety hazard , so that the self - bearing capacity of the surrounding rock can be fully exerted , and the stress of the two - layer lining can be reduced .

【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】：U455.7

【参考文献】