| The 21 st century is the golden season of tunnel construction,and buried deep,long tunnel,difficult to build is a general phenomenon of tunnel construction in the present and future.This paper analyzes the current situation of railway tunnel construction in our country,and thinks that the main problem that plagued the construction of the tunnel is the design and construction technology of the weak surrounding rock tunnel.These tunnels are often characterized by large deformation of the surrounding rock,design changes a lot,and construction progress is slow and so on.For the time being,although China's tunnel construction technology has reached the world advanced level,but in the geological conditions are extremely complex of the central and western regions,as the geological disasters in tunnel construction have the characteristics of suddenness,variability,complexity,high degree of harm,high risk factor,tunnel construction technology,methods,equipment and management and all kinds of norms still need to make great progress and development.The long tunnel built in Chenglan Railway has the characteristics of deep buried,large cross-section.It is a typical high ground stress soft rock tunnel,which has a serious deformation phenomenon during the construction process.The problem of soft rock deformation has become the main problem engineering geological problems.It is of great practical significance to ensure the smooth construction of the tunnel project by means of identifying the soft rock tunnel deformation mechanism and taking targeted excavation support and other control measures.In this paper,the D5K222+360~D5K222+560 of soft rock large deformation mileage is taken as the research object.In this paper,D5K222+360~D5K222+560 in soft rock large deformation range is taken as the research object.Firstly,the engineering geological conditions of the tunnel area are expounded in detail,and the geostress characteristics,rock mechanics parameters and the surrounding rock level of the tunnel are studied by means of numerical simulation,engineering analogy and quantitative evaluation.Then,based on the field investigation,the large deformation characteristics and failure modes of the soft rock tunnel are analyzed,and the temporal and spatial characteristics of the surrounding rock deformation are analyzed in detail from the monitoring and measurement data.On the basis of the above,the geological deformation mechanism is deeply studied by means of geological analysis.Then,through the numerical simulation technique,the excavation and support scheme of the surrounding rock are optimized and simulated.Finally,the author summarizes the above research results,and elaborates the concrete control measures for the large deformation of the soft rock tunnel.After research,the main results are as follows:(1)The study of the ground stress field in the tunnel area shows that the structural stress level of the tunnel area is between 8~12 Mpa and the direction is near EW.The natural stress field of the soft rock tunnel is about 15 Mpa,which is in great agreement with the tunnel direction.This is extremely detrimental to the stability of the tunnel.(2)The physical and mechanical parameters and strength characteristics of the surrounding rock are obtained by GSI system and back analysis technology.Then,the classification of the surrounding rock of the tunnel is studied,and amended according to groundwater and geostress characteristics.The results show that the large deformation is mainly controlled by the ? grade surrounding rock.(3)According to the results of the deformation and failure phenomena of the weak surrounding rock,the deformation and failure modes of the surrounding rock mainly include collapse,inner wall drum,extrusion,vault subsidence,side wall convergence and bottom drum.After the study of the temporal and spatial effects of large deformation of soft rock,the deformation characteristics of the surrounding rock are obviously different from each other when the step method and the third step excavation are used,and the relationship between the radial deformation release rate and the distance of the surrounding rock is obtained.On the basis of the above,the analysis of the large deformation mechanism of the tunnel shows that the large deformation of the soft rock is formed by the coupling of the strata lithology and its structure,the original geostress,the groundwater environment and the construction technology.The large deformation mechanism can be divided into three categories: stress expansion type,structural deformation type and groundwater softening type.The model mainly includes the plastic flow of soft rock,the shear slip of plastic wedge and the shear slip of structural plane.Finally,the third-level division scheme of the surrounding rock is established,and the ? grade large deformation length 46 m,? large deformation length of 44 m,? large deformation length of 60 m.(4)According to the characteristics of large deformation of soft rock in this project,combined with its geological environment,the optimization scheme of excavation and support of soft rock tunnel with different large deformation level is obtained by numerical simulation.From the numerical simulation results,it is suggested that the reserved deformation of grade ? large deformation is 20 cm~25 cm,the reserved deformation of ? grade large deformation is 30 cm~35 cm,and the reserved deformation of ? grade large deformation is 40 cm~45 cm.(5)The time of the secondary lining should be applied after the surrounding rock deformation is relatively stable,and should be different according to different soft rock deformation level: ? large deformation should be applied about 50 to 70 days after excavation,and about 2.3 times the hole from the face of the palm;? large deformation should be applied about 80 to 100 days,and about 2.6 times the hole from the face of the palm;? large deformation should be applied about 100 to 130 days after excavation,and about 3 times the hole from the face of the palm.(6)Soft rock tunnel large deformation control should take all-round,multi-level,multi-means comprehensive control measures.The control system should include seven aspects: stable of palm face control,construction method control,arch foot stability control,reasonable support structure control,space deformation monitoring and control,support reinforcement control,groundwater control.And the experimental section D5K222+010~D5K222+120 is selected for engineering verification,the result proved that the research results of this paper are effective and practical. |
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