Tectonic Deformation Characteristics Of The Heihe Section In The Middle Section Of The Qinling Tectonic Belt And Its Influence On The Water Conveyance Tunnel For Hanjing River To Weihe River Water Transfer Project

The middle part of the Qinling tectonic belt is located at the narrowest part of the Qinling orogenic belt.It is sandwiched between the Luonan-Luanchuan fault zone and the Mianlue suture zone.The main body is composed of multiple tectonic stratigraphic units.The belt is bounded,and the interior of each block also presents a plurality of rock-strip collage features,which show the characteristics of the rock mass in different tectonic environments in different eras.The long-term complex evolution history and the superposition of different tectonic processes make the Qinling tectonic belt tectonic deformation extremely complex,especially the multi-phase tectonic movement since the Mesozoic and Cenozoic,which has a decisive influence on the current tectonic features of the Qinling Mountains.In recent years,the construction of a number of large-scale projects has crossed the middle part of the Qinling Mountains,especially the water conveyance tunnel for Hanjing River to Weihe River Water Transfer Project,which traversed the entire middle part of the Qinling Mountains.The structural deformation,especially the brittle deformation,has a great impact on the construction and maintenance of the project.Combined with the water conveyance tunnel for Hanjing River to Weihe River Water Transfer Project,from the perspective of regional geology,the tectonic deformation characteristics of the middle part of the Qinling tectonic belt and the evolution law since the Mesozoic and Cenozoic are studied in detail,and the engineering mechanics characteristics of the surrounding rock are analyzed from the perspective of structure and microstructure.It will provide scientific basis for future construction,construction and maintenance.The Heihe section is a classic section that traverses the Qinling orogenic belt and preserves a large number of rock deformation records,providing a good geological basis for studying the intracontinental tectonic deformation evolution of the Qinling tectonic belt.Moreover,the Heihe section is conveniently located along the 108 National Highway.It is a favorable area for studying structural deformation in the Qinling area.Therefore,this thesis has carried out detailed research on the tectonic deformation records of the Heihe section in the middle section of the Qinling tectonic belt,especially the tectonic deformation developed since the Mesozoic and Cenozoic.Combined with some previous research results,the following understandings have been made:?1?There are five different tectonic stress fields in the middle part of the Qinling area since the Mesozoic and Cenozoic,which are summarized as follows:the near-NS compression stress field in the late Indosinian.The NE-SW direction to the compressive stress field and the NWW-SEE direction to the compressive stress field and the near NW-SE to the compressive stress field in the late Yanshanian period.The NW-SE to the tensile stress field during the Himalayan period.?2?The specific evolution process of the Qinling Mountains since the Mesozoic and Cenozoic can be divided into four stages:the first stage,the late Triassic?T₃?plate collision and compression deformation stage.In the middle part of the Qinling Mountains,the strong north-south thrust is shortened.In the second stage,the early Yanshanian period?J₁-J₂?is the intracontinental orogenic extension stage.At this stage,a large number of magma surged,and many post-collision granitoids formed in the southern Qinling and South Qinling areas,and a series of block faults and braided continental fault basins?Huicheng basin,the Shangzhou Mesozoic fault basin,etc.?were formed along the early main fault zone in the Qinling tectonic belt;In the third stage,the Qinling tectonic belt of the late Yanshanian period?J₃-K₁?was once again transferred to the extrusion deformation stage.Influenced by the superposition of multi-block convergence,the middle part of the Qinling tectonic belt has both the NE-SW-oriented squeeze tectonic stress field and the NW-SE-oriented squeeze tectonic stress field.Moreover,affected by the extrusion of NE-SW,around 123¹00 Ma,the internal block of the Qinling tectonic belt has a strong extrusion-slip-slip activity along the previously formed large-scale fault zone;the fourth stage,the Himalayan period?K₂-Q?Uplifting and stretching stage.The middle part of the Qinling tectonic belt is in the NW-SE extensional stress field.There are a large number of extensional normal faults and tensile fractures in the study area,and the rapid uplift event causes a series of near-level unloading joints in the granite body.?3?The middle section of the Qinling tectonic belt can be divided into five sections according to the characteristics of surrounding rock,which are:1)structural morphological developmental sections,mainly concentrated in the Kuanping Group,Erlangping Group and Danfeng Group.The tangential dip is generally larger than 60°,the shear strength of surrounding rock in some high geostress sections is greatly reduced,which may lead to sliding dislocations along the morphological plane of the surrounding rock.2)The gneiss section of the Qinling Group has a high degree of metamorphic amphibolite facies.The brittle structure is not developed,and the rock strength is high,which leads to a high probability of rockburst in this section.3)the weak surrounding rock section,the Luohansi rock group and the Liuling group phyllite are developed,the tectonic deformation is strong,and the mylonization is serious.The mineral composition is mainly chlorite,sericite,etc.,and it is easy to peel off along the flaky surface.The surrounding rock has a certain rheological effect,and the plastic deformation of the surrounding rock may occur.4)In the granite joint development section,the integrity and coherence of the rock mass are greatly damaged under the divisional constraints of joints in different directions.There will be a block phenomenon.Moreover,most of the shear joints have a dip angle of more than 70°,which is easy to cause water inrush in the tunnel.5)and fault fracture zone.There are many faults in the North Qinling Mountains,and most of them are continuously distributed in the NWW-SEE or EW direction.The material of the fracture zone is composed of fault gravel,breccia,mylonite,fractured rock,etc.When passing through the fault zone,engineering accidents such as water inrush and surrounding rock instability may occur.?4?In the late Yanshanian period?J₃-K₁?,the superposition of multi-block convergence has a great influence on the tectonic deformation characteristics of the middle part of the Qinling Mountains.A large number of folds,thrust faults and conjugate shear joints are developed.The main structural traces are mostly near NW-SE or NWW-SEE,which is an important period for the formation of the present tectonic pattern in the middle part of the Qinling Mountains.The main structural deformations affecting engineering properties are formed at this stage.