| According to the size of tunnel cross-sectional area, the tunnel is defined by International Tunneling Association (ITA) as follows:If the channel is built in the strata and its cross-sectional area is more than2m2, the channel is defined as tunnel. If the cross-sectional area is2-3m2, the tunnel is defined as very-small-section tunnel. If the cross-sectional area is3-1Om2, the tunnel is defined as small section tunnel. If the cross-sectional area is3-10m2, the tunnel is defined as small-section tunnel. If the cross-sectional area is10-50m2, the tunnel is defined as middle-section tunnel. If the cross-sectional area is50-100m2, the tunnel is defined as big-section tunnel. If the cross-sectional area is more than100m2, the tunnel is defined as super-large-section tunnel.With the rapid development of China’s transportation construction, big-section tunnels and underground engineering gradually increase. Especially with the rapid development of passenger dedicated line, a number of very-big-section tunnels has emerged. In order to overcome the aerodynamic problems caused by the high speed train on passenger dedicated line, super-large-section tunnel is basically adopted. The clearance area above the track surface of these tunnels is more than100m2, and the excavation area is more than150m2. Compared with the previous tunnels, the mechanical behavior, the cross-section style, lining structure, construction methods, initial support structure mode and support parameters of super-large tunnels have new requirements. Although, at present, many researchers have devoted themselves to the study on the big-cross-section tunnel, they used simple method in the aspects of mechanical parameters and numerical simulation. Especially for the research of soft surrounding rock mechanical effect of super large cross-section tunnel in construction period, the relevant references are relatively less.Slate is a kind of typical soft rock, which has a relatively wider distribution in Yunan, Guizhou, Hunan province. The dissertation relied on Shanghai-Kunming Passenger Dedicated Line Chang-Kun Hunan Section IX tender Yaojia Tunnel and selected slate stratum as the research object. By ingredient identification and microstructure observation, microscopic structure of soft slate was analyzed. The influence rock bedding plane and moisture capacity had on the mechanical properties of soft slate was studied by laboratory experiment. Water absorption, softening, swellabitity, slaking and softening mechanism were discussed. By uniaxial and triaxial creep test the creep law of soft slate was researched and the slate modified Burgers creep model parameters was determined. The influencing law of the water on the slate creep properties was obtained by creep test under different moisture capacity. Using finite element method, Burgers visco-elastic plasticity model parameters were introduced into ANSYS constitutive model, and stress and deformation situation of excavation and supporting of super large cross section tunnel were analyzed. Based on monitoring and measurement data, surrounding rock deformation law with the change of time and space under different tunnel excavation methods was deeply analyzed, and the relationship between radial displacement releasing rate of surrounding rock and time/space was researched. On the basis of analysis of surrounding rock deformation spatial and temporal effects, construction methods under different surrounding rock levels of Yaojia Tunnel were optimized, the best applying timing of secondary lining was ascertained and the supporting measures to control large deformation of super large cross section tunnel surrounding rock were proposed, which can provide references for the design and construction of similar projects.The work dissertation has completed included the following aspects:1. Research to the mechanical and hydraulic characteristics of soft slate(1)Soft slate mechanical properties were systematically researched. By uniaxial and triaxial compression test in natural state, mechanical parameters of soft slate were obtained. The relationship between uniaxial compressive strength, elastic modulus and the angle between the structural surface occurrence and loading direction was analyzed and the anisotropy and its internal mechanism of soft slate were studied. The variation range of soft slate Poisson’s ratio and the relationship between Poisson’s ratio and the angle of the structural surface occurrence and loading direction were discussed. From the point of experiment the relationship between the triaxial compressive strength, residual strength and confining pressure was researched.(2)By grinding and microscopic detection, the mineral composition and content of soft slate were analyzed. By powder X-ray diffraction and electron microscope, the particle composition and content was obtained. The type of cementation and internal structure were analyzed, which provided the basic data for the research of soft slate hydro-physical characteristic and deformation mechanism.(3)The relationship between the natural water absorption and saturated water absorption of soft slate and variation range of water saturated coefficient were analyzed by water absorption test. The regulation of natural water absorption and water saturated coefficient with the change of time and its influencing factors. Relational expressions between natural water absorption, water saturated coefficient and time were respectively proposed. (4)By soft slate free expansion test, the relationship between the expansion deformation, expansion rate and soaking time was analyzed and the relational expression of soft slate expansion rate with the change of time was established. The relationship between soft slate expansion rate and the angle of structure surface direction and sample axial direction was analyzed.(5)By soft slate expansion test of lateral constraints, the law of soft slate lateral constraint expansion rate with the change of time was discussed. The rational expression between soft slate lateral constraint expansion rate and the time was established. Moreover, soft slate axial expansion rate and free axial expansion rate under the condition of lateral constraints were compared and the relationship between soft slate expansion rate and water absorption rate was analyzed.(6)By expansion pressure test under the condition of unchanged volume, the regulation of expansion pressure with the change of time was discussed and the influencing law of sampling angle on soft slate expansion pressure. The variation range of expansion pressure in the direction parallel and perpendicular to the bedding was obtained. From a quantitative point the relationship between expansion pressure and expansion strain was analyzed and the expansion constitutive relation under the condition of unchanged volume was obtained. Based on theoretical analysis and laboratory tests, the relationship between expansion pressure and water absorption rate was obtained.(7)By soft slate disintegration resistance test, the influence of weathering degree on soft slate disintegration was analyzed and the relationship between disintegration resistance index and dry and wet cycles.(8)By uniaxial compression test under the condition of different moisture content, the relationship between uniaxial compressive strength, elastic modulus and water absorption rate was analyzed. The relational expressions of uniaxial compressive strength and elastic modulus with the change of water absorption rate were given.(9)By triaxial compression test under the condition of different moisture content, the relationships between the triaxial compressive strength, elastic modulus, Poisson’s ratio and water absorption rate under the condition of the same confining pressure were researched. The correlation between triaxial compressive strength and elastic modulus of soft slate was analyzed. Using quadratic function to fit the relationship between triaxial compressive strength and elastic modulus had very good fitting effect. Moreover, the relationship between the confining pressure and failure mode was discussed.(10)From points of physical state in which underground water exists in slate and chemical, physical and mechanical effects water has on rock, the hydro-physical property mechanism of soft slate was analyzed. Interaction mechanism of underground water and soft slate was discussed.2. Research to soft slate creep characteristic(1)By unaxial and triaxial creep tests of soft slate, the basic creep law of soft slate was obtained:(a) The time when slate entered into isokinetic creep stage was different under the condition of different confining and axial pressure. However, commonly, they all entered into isokinetic creep stage in less than5hours.(b) Under the condition of the same confining pressure, with the increasing of stress difference, soft slate creep deformation increased and the creep rate suddenly change. Therefore, the stress difference enhanced the speed of slate entering into isokinetic creep stage.(c) When confining and axial pressure was different, the shape of the creep curve and the duration of every phase were different.(d) Increasing of confining pressure made compressive stress acting on the slate increase but stress difference decrease, which restricted the development of creep deformation. Increasing of axial pressure speeded up the process of creep deformation.(2)Based on summarizing classic creep models, the improved Burgers model was introduced. By creep test and theoretical calculations, soft slate improved Burgers model parameters were ascertained. The influence water had on soft slate creep characteristic was acquired and0.19%(water absorption rate) was determined as boundary value of the influence of water on soft slate creep characteristic through creep tests under the condition of different water content.3. Study on mechanical characteristic of super large cross section soft slate tunnel in construction period(1)By finite element method, we introduced Burgers visco-elastic plasticity model parameters into ANSYS constitutive model and analyzed the stress and deformation status of super large cross section tunnel in the course of excavation and supporting.(2)By numerical simulation we analyzed surrounding rock creep characteristic of super large cross section tunnel and obtained the creep law of surrounding rock. Moreover, we considered tunnel depth and quantitatively analyzed the relationship between surrounding rock vault settlement stability value and depth.(3)Using finite element method, we compared the surrounding rock deformation of considering elastic plasticity and visco-elastic plasticity and analyzed the importance of time for surrounding rock deformation after the excavation.4. Study on the surrounding rock deformation characteristics and controlling technology of super large cross section tunnel based on monitoring and measurement(1)To begin with we recommended monitoring and measurement technology of Yaojia Tunnel and data processing method. In combination with monitoring and measurement data of Yaojia Tunnel, we deeply analyzed the surrounding rock deformation with the change of time in different excavation methods and acquired three different types of surrounding rock deformation-time curves. Moreover, we analyzed the curves in detail and obtained surrounding rock deformation law with the change of time in different stages.(2)We analyzed the relationship between surrounding rock displacement releasing rate and time/space. The research conclusions had important value for determining the best supporting opportunity and construction process, which can effectively guide the construction.(3)Based on monitoring and measurement data, we deeply analyzed the relationship between surrounding rock deformation and the distance from the tunnel working face under the condition of different surrounding rock levels and obtained two different types of surrounding rock deformation-distance from the working face curves(step and single chang type). Moreover, we determined the best applying opportunity of secondary lining and the relationship between surrounding rock radial displacement releasing rate and the distance from the working face.(4)Using the methods of geological and structural mechanics, we analyzed the mechanical mechanism of time-space effect and the influencing factors of surrounding rock deformation of super large cross section tunnel, which included as follows:geological structure, adverse geology, the characteristics of surrounding rock, the weakening effect of underground water, initial stress state of rock mass, the tunnel cross section shape and dimension, tunnel excavation methods, supporting structure, construction process and adjacent construction.(5)Relying on the analysis of surrounding rock deformation time-space effect, we introduced soft rock tunnel supporting principle, optimized construction methods of Yaojia tunnel under the condition of different surrounding rock levels, determined the best applying opportunity of secondary lining and proposed supporting measures of controlling surrounding rock large deformation of super large cross section tunnel, which provided references for the design and construction of similar engineering.Innovations of this dissertation were as follows:(1)By uniaxial and triaxial compression tests under conditions of natural state and different moisture content, we analyzed the influence of underground water and dip angle of structural plane on mechanical characteristics of soft rock, discussed microscopic mechanism of underground water on soft slate, and respectively established the relational expressions between mechanical parameters, dip angle of structural plane and water absorption rate. Moreover, we constructed the relational expressions between triaxial compressive strength and elastic modulus, and discussed the relationship between confining pressure and failure mode of slate. The research results can supplement the research of water and rock interaction effect.(2)Based on summarizing classic creep models, we introduced improved Burgers model. By creep tests and theoretical calculation, we ascertained improved Burgers creep model parameters. The improved Burgers creep constitutive model could describe the first, second and third stage. From the comparison of fitting data and experimental data, the fitting accuracy was very high and the fluctuation of all parameters was low, which showed that the fitting had good reliability. The slate creep characteristic under the condition of different water absorption rate was analyzed and the influence of water on the slate creep characteristic and microscopic mechanism was studied.0.19%(water absorption rate) was defined as the boundary value of the influence of water on slate creep characteristics.(3)Using numerical simulation we compared surrounding rock deformation considering elastic plasticity and visco-elastic plasticity. Moreover, we considered the tunnel depth, analyzed the cause of difference, and obtained the importance of time for surrounding rock deformation after the excavation. The results were of certain reference for the research of tunnel surrounding rock time-space effect.(4)Based on monitoring and measurement data, we deeply analyzed the variation of surrounding rock deformation with the change of time and space, and studied the relationship between surrounding rock radial displacement releasing rate and time/space. The research results had very important values for determining the best supporting time of secondary lining and proposing supporting measures of controlling large deformation. |
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