| The Qinling Walcr Transmission Tunnel in HAN JIANG-WEIHE WATER DIVERSION PROJECT passes through the Qinling orogenic belt,spanning the main tectonic units due to its super long length,facing high geostress conditions due to large burial depth,in addition the multi-stage orogenic movanent process of the Qinling orogenic belt,so the tunnel engineering geological environment is very Comlpex.The TBM coastruction tunnel section of North Mountain belongs to the phyllite section with a total length of 16.59km.According to the engineering experience,large deformation of surrounding rock is expected Grasping the geological environment characteristics of the tunnel as a whole,monitoring the surrounding rock convergences and surrounding rock pressure,and analyzing its regularity,is of great significance to determine surrounding rock support mode and timing.This paper has obvious engineering application value.(1)The main results of the study on the large deformation mechanism and support mode of the surrounding rock tunnel and the engineering geology and surrounding rock characteristics of the existing tunnel in the Qinling orogenic belt are reviewed.The main cause of the large deformation of the surrounding rock is the insufficient self-supporting capacity of the surrounding rock or the expansive rock.The rigid-flexible combine support is the main support method.The surrounding rock engineering characteristics of the TBM construction section in north Qinling is the intrinsic reason for the surrounding rock convergence and surrounding rock pressure performance.The traditional engineering geological analysis method is difficult to explain the surrounding rock engineering characteristics,and it is necessary to find new engineering geological analysis ideas.(2)For the first time,the theoretical research results of the Qinling orogenic belt,which is based on the plate tectonics,are applied to the study of the surrounding rock geological environment of the Qinling tunnel.Considering the macroscopic structural characteristics of the surrounding rock of the tunnel,the meso-structural characteristics,the division of metamorphic degree,and whether the development of the flow structure,etc.,based on the theory of structural hierarchy,the surrounding rock of the tunnel is divided into 8 sections,which fundamentally grasps engineering geological conditions of the tunnel.The basic characteristics of the surrounding rock in the TBM construction section of north Qinling are:they belong to the middle-level structure,and the buried depth is large,which belongs to the high stress area.The phyla of the phyllite is perpendicular to the tunnel or intersected at a large angle,which is beneficial to the stability of the surrounding rock.Due to the high strength of phyllite,it is not easy to cause large deformation of surrounding rock.The surrounding rock at local joint development zone or gushing zone,has poor stability and needs to be strengthened or pre-supported.(3)Some typical sections are selected to observe the surrounding rock convergence and surrounding rock pressure,and restore the convergence loss is restored to obtain the full convergence value.The maximum horizontal convergence at the No.5 branch tunnel and the relative settlement values at the vault are 33.84 mm and 19.68 mm,respectively.The maximum values of monitoring pressure at left and right arch waist and vault are 0.31 MPa,0.53 MPa and 0.43 MPa.The maximum value of horizontal convergence and vault relative settlement of the main tunnel of TBM construction at k56+926.5 are 53.68mm and 6.09mm;the maximum horizontal convergence and the vault settlement of main hole within TBM construction at k56+963.62,are 60.01mm and 6.28mm.Compared with the relative displacement specified in the Technical Specifications for Shotcrete(GB50086-2001),the surrounding rock is stable.The engineering analogy method was used to It can be determined that no large deformation occurred in the monitoring section based on the engineering analogy method.The reason of the surrounding rock not undergoing large deformation is that the rock belongs to hard or very hard rock,the rock mass is relatively intact,and the granular mineral content is high.so that the surrounding rock occurs bent failure rather than slip along the structural plane.(4)The surrounding rock failure mode of the TBM construction section at north Qinling is mainly the brittle fracture of the vault,located mainly in the southern tunnel of this section.It shows that the surrounding rock is broken within the thickness of 20?50cm near the vault of the cave wall after the TBM tunneling,and the surrounding rock bend at the arch top with serously falling pieces.The reason is the bending failure phenomenon due to the insufficient tensile strength of the rock near the vault caused by high ground stress.Due to the small size and large number of pieces,it is recommend using steel bars combined with steel arch support technology,and the effect is very good.This paper puts forward the particular implementation method of applying the theory on Qinling orogenic belt,which is based on theory plate tectonics,in the study of surrounding rock-engineering characteristics of the Qinling tunnel.Through the first-order determinants and the second-order determinants,the research scale of the surrounding rock engineering characteristics is approached layer by layer.It has completed the transformation of the theoretical research results of large-dimension,small-scale and low-precision orogenic belts into engineering application scales,which is innovative. |
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