| Relying on the tunnel of the project,it is located in the complicated geological conditions combined with residual sandy clay and soft and hard rock of moderately weathered granite,and there is a situation of topographic bias and unequal height difference between the left and right lines.The depth of the tunnel is shallow and the surrounding rock receives The force is complicated and the bias is ubiquitous.In addition,the difference between the topographic bias and the unequal height difference between the left and right lines of the small clear distance tunnel during the construction process leads to a more complicated stress distribution and stress deformation of the surrounding rock.Not only is there a lot of difficulties in design,but also The difficulty in deformation and stability control of the tunnel construction has been increased,and carelessness will cause safety accidents such as landslides.Therefore,whether it is possible to ensure safe,reliable,smooth and timely completion of tunnel projects is the key to the construction of small-internet tunnels with unequal elevations.It is particularly urgent to comprehensively understand and master the construction characteristics of shallow-buried,small-spacing tunnels with unequal elevations,and to summarize the deformation laws of surrounding rock and supporting structures during construction.In this paper,the numerical simulation of the construction of Haixin No.2 tunnel is carried out.The appropriate constitutive model is selected.Under the condition that the constitutive model,geotechnical parameters,supporting structure attributes and the construction method of the double-sided guide pits are unchanged,the The following research work:(1)Aiming at the project,four numerical analysis indexes,namely the percentage of asymmetric pressure difference of surrounding rock,the shear safety coefficient of surrounding rock,the safety factor of lining structure and the displacement,were proposed to provide criterion criteria for subsequent theoretical numerical modeling.(2)Studying the topography conditions(surface inclination,depth of burial,different elevation differences)on the stress bias of surrounding rock of unequalelevations and small clear distance tunnels,and obtaining the bias of two holes with different heights and small clear distances from the ground surface The increase in slope increases,and decreases with depth of burial depth and height difference;different surface gradients and elevation differences have a greater influence on the degree of bias of the surrounding rock of the left tunnel(the tunnel with lower elevation of the two tunnels),and the local table slope When the level difference between the two holes is less than 40 m,the stress of the surrounding rock of the two caves is still in a bias state and within the influence of a small clear distance,the local surface level and the net distance remain unchanged at 11.5m,and when the difference between the two holes is ? 40 m,The right hole(higher tunnels at two elevations)has been in a biased state due to shallow buried depth and construction techniques,but the stress asymmetry of the surrounding rock in the left tunnel(the tunnel with two lower elevations)has been less than or equal to 10%.The pressure level is very small,and it is also reflected from the side that when the difference in elevation between the two holes is ?40m,the unequal elevation tunnel is no longer within the range of small clear distance.When designing and constructing such tunnels,it can be seen to simplify the process.As a non-biased tunnel.(3)From the perspective of displacement and safety factor of support structure,the comparative study of different advance support structures for the right tunnel opening is made.The surface of the right tunnel portal section is recommended to be reinforced with mortar bolts and shotcrete.The top of the tunnel is advanced.The pipe shed is reinforced and anti-slide piles are used between the left and right holes.(4)From the displacement,internal forces of supporting structures,and surrounding rock mechanics,a comparative study of the different construction sequences of small clear distance tunnels on the left tunnel opening was carried out,and a small clear distance tunnel section was obtained.The construction sequence of two tunnels in parallel was relatively reasonable.(5)Three-dimensional approximate simulation of a small clear distance tunnel within 100 m of the entrance section is carried out.The four types of steps based on double-sidewalk construction are compared and analyzed from the perspective of horizontal convergence displacement,vertical convergence displacement and groundsettlement.The displacement of the step distance changes,and the guide step for the pit when the two-hole double-sidewalk pit method is used is 5m.(6)Establish the tunnel numerical model of the optimal construction scheme obtained from the study,compare the displacement numerical analysis with the field monitoring measurement data,consider all factors,consider the use of double-sidewalk pit method on the right tunnel of the construction site The left hole uses a three-step method. |
PDF Full Text Request