| The length of the entire line of the Central Yunnan Water Diversion Project is607.20km,of which the Phoenix Mountain Tunnel is 15.73km.The entrance section is mainly Jurassic strata.The rock is generally weak and the lithology is mudstone,silty mudstone,muddy Siltstone and fine sandstone are the main ones.Based on the"Project of Research on Engineering Geological Characteristics of Weak Rock and Soil in Central Yunnan Water Diversion Project and Its Impact on the Project",this paper systematically summarizes the engineering geological conditions of Fenghuangshan Tunnel,and conducts in-situ stress tests on ZK1019 and ZK1039.Through physical and mechanical tests and hydraulic tests,the engineering geological characteristics of the Jurassic soft rock at the entrance of the Fenghuangshan tunnel in central Yunnan were studied.Through field investigation,the rock mass structure types of Fenghuangshan Tunnel are summarized,and the quality of the surrounding rock of the tunnel is evaluated in accordance with"Engineering Rock Mass Classification Standard"?GB T50218-2014?.In order to more accurately guide the construction,the evaluation process will The Type V surrounding rock is further subdivided into Type V1 and Type V2 surrounding rocks.Combining the test parameters and engineering experience of the Dali?and Chuxiong sections,the rock mechanics parameters of the Fenghuangshan tunnel are finally proposed.The three-dimensional geological model was constructed by the rhino software,and the natural conditions were analyzed with the help of FLAC3D.The surrounding rock deformation after the excavation considering the creep effect for 1 month and the creep effect after excavation were considered with 3 different support schemes.Characteristics,the following conclusions are drawn:?1?Feng huang shan Tunnel is mainly divided into soft rock formations mainly composed of mudstone,siltstone,silty mudstone and argillaceous siltstone,and hard layers mainly composed of fine sandstone,siltstone,sandstone and sand mudstone Rocky strata,and a few fault-fracture zones through which a few fault zones pass.In-situ stress test results show that the maximum horizontal principal stress direction of Feng huang shan Tunnel is N22o?28oE,that is,NNE direction,and the lateral compression coefficient??H/?z?of the maximum horizontal principal stress direction ranges from 0.6 to 1.1.?2?Physical and mechanical tests show that the average particle density of mudstone and silty mudstone in Jurassic Tuodian Formation is relatively close;the porosity of mudstone is greater than silty mudstone;mudstone is more sensitive to water than silty mudstone.The mechanical strength of the Jurassic Tuodian soft rock is low.The uniaxial compressive strength of mudstone and silty mudstone under saturated water is 10.25 MPa and 10.39 MPa,respectively.The failure modes are mainly shear failure type,flake exfoliation type and compression-induced cracking type;the cohesion of mudstone obtained by triaxial compression test is 1.72MPa,the internal friction angle is 31.81°,and the cohesion of silty mudstone It is 1.95 MPa and the internal friction angle is 37.04°.?3?The creep effect of the Jurassic Tuodian Formation soft rock is obvious:the initial creep variable of mudstone is about 0.142mm,the final creep variable is about0.31mm,the initial creep variable of silty mudstone is about 0.045mm,the final creep The variable is about 0.105mm;the creep of mudstone under saturated water is larger than silty mudstone.?4?The soft rock of Jurassic Tuodian Group has remarkable hydraulic properties:the softening coefficient of mudstone is about 0.37?0.45,the softening coefficient of silty mudstone is about 0.35?0.42;the average swelling power of mudstone is777.29 KPa,and the average swelling power of silty mudstone is 606.25 KPa;the disintegration resistance indexes of mudstone and silty mudstone after the second and tenth cycles are 0.44,0.54 and 0.09 and 0.23,respectively,showing moderate and strong disintegration.At the same time,the comprehensive analysis believes that the mudstone belongs to water-absorbing expansion and collapse Disintegration mechanism,silty mudstone is a mixed disintegration mechanism.?5?The lower limit of the full weathering of Feng huang shan tunnel is about6.6m,the average of the lower limit of strong weathering is about 19.6m,and the average of the lower limit of weak weathering is about 59.7m.Most of the rock masses in the tunnel are of good quality and belong to weakly weathered to fresh rock masses According to the survey statistics,the rock mass structure types of Feng huang shan Tunnel are divided into four types:thick layered structure,interbedded structure of sand and mudstone,thin layered structure and fragmented body structure;Phoenix is analyzed by BQ method The quality of the surrounding rock was graded,and it was found that most of the cave sections were mainly of?and?1 types of surrounding rocks.In the inlet section and the middle fault fracture zone,they were mainly of?1 and?2 types,and very few sandy sections were of?type surrounding rocks.rock.?6?Analysis of the deformation characteristics of confining pressure after tunnel excavation under natural conditions shows that the displacement after tunnel excavation generally shows a trend of type?2>?1>IV surrounding rock.Among them,the amount of?1 surrounding rock vault subsidence and cave bottom bulging increased by about 12.35%compared with?type surrounding rock;?2surrounding rock vault sinking and bottom bulging volume increased by about 20.76%compared to?1 surrounding rock..This means that the better the quality of the surrounding rock,the smaller the displacement and the range of the plastic zone,and the better the stability of the surrounding rock of the tunnel.?7?Analysis of the deformation characteristics of the surrounding rock after the tunnel was excavated for 1 month under the consideration of the creep effect,and it was found that the displacement amount increased to varying degrees compared with the natural condition;among them,the vault subsidence value of the type?1surrounding rock section increased About 71.41%;the subsidence value of the vault of the?2 surrounding rock segment increases by about 2.95 times,indicating that the creep effect will significantly reduce the stability of the surrounding rock.?8?By comparing and analyzing three different support schemes,it is found that all three support schemes can play a good supporting effect and have a positive effect on the stability of surrounding rocks.Among them,the C support scheme supports the effect The best,you can consider the C support program as a reference in the later construction. |
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