Research On Surrounding Rock Stability And Construction Technology Of Longquan Temple Tunnel

In the process of tunnel construction, there are many factors that influent natural rock mass because of human construction in the tunnel, and it make natural stress field of mass rock to change, lead into surrounding rock stress around the tunnel to self adjusting and redistribute, and form secondary stress field, meanwhile with surrounding rock stress in the field near tunnel transfer, when the maximum peak stress of the stress field of surrounding is more than their own intensity, it will cause the tunnel engineering rock mass to have continuous deformation deformation and destruction, and local damage may result in the chain reaction of engineering rock mass destruction, in last it cause the surrounding rock structural to damage and become instabilitily, and to imperil tunnel construction, and the normal operation, and economic benefit.The paper based on field investigation and comprehensive analysis of the geological survey for the project, and theory and technique of domestic and foreign advanced tunnel support, through the field observation, analysis engineering geological structure, find out the engineering characteristics of surrounding rock, determine the grading index of rock mass, and useing the design method of theory analysis and numerical calculation construction project and construction procedure of Longquan temple tunnel are optimized, and using the method of advance geological prediction forecast the stability of tunnel in order to perfect and improve the tunnel support design to ensure the tunnel project of the excavation and supporting smooth construction.The main research results of the paper inducts as follows:1) Analyse survey data and study on main factors of stability of Longquan temple tunnel, and through the field the site survey the information of geological conditions, traffic, hydrological and geological structure in the region of the tunnel are acquireed;2) Using the method of quantitative and qualitative analysis the surrounding rock of Longquan temple tunnel is graded and it’s quality evaluation is acquireed, according to the results of analysis, the surrounding rock of Longquan temple is divided into three big levels-Ⅲ, Ⅳ, and V. Among them the Ⅲ is divided into ⅢⅠ and Ⅲ2, the corresponding construction and support respectively are:the whole section blasting+shotcrete support, whole section blasting+control footage and spray support according to the site condition; Level IV is divided into IV1, IV2and IV3, the corresponding construction and supporting respectively are:using two steps excavation+Advanced bolt support, using three steps advance excavation method+advanced small catheter grouting, using three steps excavation method to reserve core soil+advanced small catheter grouting+working face advanced grouting; Grade V is divided into Ⅵ and V2again, the corresponding construction and supporting respectively are: using three steps excavation method to reserve core soil+increase the size of steel arch frame+advanced small catheter grouting (when necessary use double layer)+working face advanced grouting+jet high strength concrete grouting, and using three steps excavation method to reserve core soil+advanced small catheter grouting (double layer)+working face advanced grouting, when it is necessary take the methods of the grouting surrounding and spray steel fiber concrete;3) Using the method of numerical calculation analyze the influencing factor of the stability of tunnel under all kinds of construction in loess section, the result shows that in the space of displacement of surrounding rock:the method of short step seven footwork> CRD method> double wall method, in space of controlling structure strength, double wall method> the method of short steps seven footwork> CRD method, in the arch feet and wall feet of tunnel the moment of structure is bigger, and structure security is low. the tunnel deformation mainly show in the excavation of various parts when using three kinds construction method, after the completion of the tunnel inverted arch in tunnel construction the profile deformation and sinking basic remain unchanged;4) According to the results of research in Longquan temple tunnel to determine the specific solutions, construction procedures and related construction details of Longquan temple tunnel, construction overall scheme as follows:after completing excavation of the mouth of cave site build section drains of celing cave, according to the situation of celing cave strengthen the earth’s surface, excavate earth and rock in entrance to cave; realize tunnel dynamic design and construction by using the forecast result data, take advanced advance support in bad geological areas and fault fracture zone; use the method of open cutting in tunnel portal, use three steps construction method in surrounding rock that grade is V or Ⅳ, use steps construction method in surrounding rock that grade isⅢ or Ⅱ, use drill-blasting construction method in excavating the tunnel, the mark of concrete in process of primary sprayed concrete support is C25;5) Through to the combination approach of making geological sketch of working face, geological radar and TSP early geological forecast research the geological state in the front of working face. Study shown that:rock within130meters ahead working face (DK21+077) is strong weathering altered andesite, rock is broken, and show gravel shape, show loose structure, have many joints and fissures, show flexible plasitic body structure, rock mass is effected by structure, local is soil, easy happen to drop down and collapse. The segments of DK17+538～+569surrounding rock is interbed of hard rock and soft rock, rock mass show broken state, local is1water or weak layers. To strengthen the primary support strength and install anchor feet bolt in this geological postion are suggestrd.