Comparative Study On Construction Methods Of Weak Surrounding Rock Tunnels

The weak surrounding rock has the following engineering geological features such as low strength,poor capacity and bonding force,water softening,relatively weak rock structure and easily lead to slumps,etc.The author mainly combines the Chenjiadian tunnel project.The main structure of tunnel is located in IV and V grade weak surrounding rocks.In combination with the actual engineering geological conditions,four tunnel construction methods for weak surrounding rock are selected: bench cut method,CD method,CRD method,both side drift method.and study on the four tunnel construction methods of weak surrounding rock.It provides a certain reference for the construction of similar soft rock tunnel.The major research made in this dissertation are shown as follows:(1)The factors of affecting the stability of weak surrounding rock tunnel are analyzed,including:structure characteristic of rock mass,the mechanical properties of rock,the condition of groundwater and the construction methods of weak surrounding rock tunnel,etc.Thus,four construction methods for weak surrounding rock tunnels have been selected:bench cut method,CD method,CRD method,both side drift method.And four methods are qualitatively compared from the aspects of difficulty,cost,schedule and applicable conditions during construction.Qualitatively,both side drift method is difficult to construct,high in cost but excellent in control of deformation of the surrounding rock,and has advantages in the case of strict control of surface and dome deformation requirements.(2)Based on the actual engineering,FLAC3 D is used to simulate the excavation of four construction methods in weak surrounding rock tunnel.The displacement of surrounding rock,the deformation of surface and tunnel domes,the distribution of plastic zone are obtained.At the same time,the influence of seepage effect in simulated excavation is analyzed.And the displacement of surrounding rock,the deformation of surface and tunnel domes,and the distribution of plastic zone are analyzed respectively in the condition of seepage effect or not in each construction method.Quantitative results:whether the seepage is considered,the displacement value of the surrounding rock,the deformation of the surface and dome,and the distribution range of the plastic zone obtained from the both side drift method simulation are the smallest.(3)With the seepage effect,the displacement of surrounding rock,the final deformation of the monitoring points at the surface and tunnel domes,and the distribution of plastic region for each construction method are analyzed comprehensively.Combining with the actual engineering geological conditions,an optimal construction plan is put forward: both side drift method.