| With the steady advancement of the “The Belt and Road Initiative” strategy,Yunnan province has become an important foreign port in China,and its construction of railway tunnel has increased dramatically.The topographic and geological conditions in Yunnan Province are complex,and the engineering problems of large deformation in weak rock often occur during tunnel construction,which seriously affects the normal progress of tunnel construction.Based on the large deformation section of carbonaceous slate in the Xingzi Mountain Tunnel of Dali-Lincang Railway,this paper comprehensively uses on-site monitoring,indoor and outdoor tests and numerical simulation to analyze the mechanism of large deformation of carbonaceous slate and proposes deformation control technology based on the pre-core soil reinforcement.The research results can provide useful guidance for the treatment of weak rock tunnels in Yunnan area.The main work and conclusions of the thesis are as follows:(1)Combined with the damage of carbonaceous slate section and the on-site monitoring and measurement data,the large deformation characteristics of the carbonaceous slate section of the Xingzi Mountain Tunnel are analyzed.On this basis,the rock component and the secondary stress of the tunnel were tested by XRD and secondary earth stress test.The test results show that the carbonaceous slate of the Xingzi Mountain Tunnel is mainly composed of muscovite and chlorite which are silicate mineral full of joint fissure,as well as detrital mineral quartz.The expansion of rock mass caused by stress release is obvious.The secondary geostress of the surrounding rock in the vertical direction is in the range of 2MPa~6MPa,and the relationship between the large deformation of the tunnel and the geostress value of the tunnel site is small.(2)According to the analysis of the large deformation characteristics,rock mass properties and geostress of the Xingzi Mountain Tunnel,the mechanism of large deformation of weak rock tunnel dominated by the progressive failure mode of surrounding rock in the carbonaceous slate stratum is proposed.(3)The numerical simulation method is used to optimize the excavation support parameters of carbonaceous slate tunnels.The analysis results provide the basis for the selection of large deformation control points and specific parameters of large deformation control measures.(4)The steel frame test is used to optimize the setting parameters of the longitudinal connecting ribs and reveal the failure mode of steel frame under different setting parameters and propose setting suggestions The test results show that the buckling instability of the component occurs when the longitudinal connector is set at a large distance.When the longitudinal connector is set at a small distance,the component breaks down due to reaching yield strength.In the two failure modes,the ultimate bearing capacity of the steel frame is quite different.The stability of the steel frame is sensitive to the spacing of the longitudinal connectors.The longitudinal connector setting of the steel frame should be centered on reducing the longitudinal connector spacing;When the longitudinal connector is set to a certain range,the reduction of the longitudinal connector setting pitch and the increase of the longitudinal connector setting stiffness are not obvious for the stability improvement of the steel frame.In the case of the same amount of steel,the profiled steel with a large moment of inertia and a double symmetrical cross section should be preferred as the longitudinal connector.(5)Combined with the numerical simulation and component test optimization analysis results,the soft rock tunnel construction control technology with the core soil reinforcement as the core and fully integrated with the New Austrian Method and ADECO-RS is proposed in detail,and the large deformation control effect is verified by field test data.The technical points include strengthening the pre-reinforcement and pre-support of the advanced core soil,increasing the rigidity and strength of the initial support,and limiting the allowable range of the reserved deformation.(6)The on-site monitoring measurement results were compared after the large deformation control measures was done,and the internal force of the glass fiber anchor was tested to analyze the effect of the large deformation control measures.The comparison results show that the large deformation control measures can control the surrounding rock deformation effectively,and the supporting structure is more even and reasonable.The internal force test results of the bolts show that the internal force value of the glass fiber anchors at the measuring point of 2.5m after an 1.2m excavation of the face is 31.7%~78.2% of the ultimate tensile force of the anchor.The material properties of the glass fiber anchors are fully exerted. |
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