Study On Seepage-stress-damage/Crack Coupling Theory And Method For Hydraulic Tunnel

With the large-scale development and utilization of underground space, the tunnel has been widely used in many industries, such as transportation, mining, petroleum, water conservancy and so on. However, the sudden and unexpected great water inflow and instability of surrounding rock during the process of tunnel excavation often happens which may affect the construction safety and induce the destruction of the tunnel structure and the ecological environment. The lining structure is influenced by water pressure and the constraint of surrounding rock. And the deformation and crack characteristics of lining have great difference with ordinary concrete structure under the coupling effect of seepage field, stress field and damage field. Therefore, it is necessary to make a systematic research of the evolution regulation of seepage field during the excavation and operation period and the lining damage and crack extension mechanism and the variation characteristics of the reinforcement stress under high internal water pressure, which provide the theoretical foundation for the design and construction of the stability of tunnel surrounding rock and operation safety. The main research content is stated as follow:(1)After the hydraulic tunnel excavation, the conformal mapping is adopted to deduce the analytic formula of the seepage inflow based on summarization of various analytical methods both at home and abroad. The analytic results are compared with the numerical results. And it is found that the tunnel excavation-induced groundwater level drawdown has great influence on the seepage inflow during the numerical calculation and the traditional analytic methods which assume a constant groundwater elevation throughout tunnel excavation would lead to greater results. When the seepage field reaches a steady state after tunnel excavation, the height of lowered water level is closely related to the tunnel radius and initial water level. An analytic formula for lowered water level height is proposed according to the numerical results. Based on the widely used formula of Goodman and considering the effect of initial water level and lowered water level, an analytic formula for tunnel inflow is put forward and applies to different conditions, such as various ground surface inclination, tunnel radius and initial water level height.(2)According to the dynamic tunnelling characteristics of TBM, the construction process of tunnel excavation, segments support and pea gravel grouting is simulated by adopting the dynamic hydraulic boundary condition along with time. An equivalent coupled model is proposed which can reflect the change of the permeability of segment lining under the high internal and external water pressure during the water filling and drainage process. The model is developed by the secondary development in the finite element software ABAQUS. The simulation analysis of deep-buried TBM tunnel during the whole process of the tunnelling, segment lining support, water filling operation and drainage maintenance is carried out. The results show that there are significant temporal and spatial effects in the evolution regulation of seepage field. Before the monitor section excavated or supported, the pore water pressure has changed which presents obvious spatial effects. The pore water pressure changes sharply within the length of 5?D (the Tunnel perimeter) near the monitor section. Then the seepage field tends to be stable after excavation for length of 10?D or lining support for length of 87iD, which mainly embodies the characteristics of temporal effects and achieves stability.(3)Based on the elastic-plastic damage constitutive model of rock mass and taking the excavation-induced damage of surrounding rock under tensile and shear stress into account, the seepage-stress-damage coupling model of surrounding rock is established. The coupling model is embedded into ABAQUS software through the second development of USDFLD subroutine. The process of tunnel excavation is simulated by using the coupling model. The results verify that the model can reflect the damage evolution process of surrounding rock and the effect of seepage-stress-damage coupling. After considering the coupling of seepage field and stress field, the deformation of surrounding rock is greater than the results without coupling because of the stress release during excavation and effect of drainage consolidation, while the plastic strain is smaller and the distribution of plastic zone is more even. The permeability of damage rock at waist of tunnel increases greatly after considering the rock damage coupling effect.(4)Based on the damage crack constitutive model of concrete and the theory of previous tunnel, the seepage-stress-crack coupling model of lining concrete is established. This model considers the influence of lining crack on the seepage field under high internal water pressure by introducing a mutation coefficient to reflect the change of permeability of lining cracked. This model also takes the limited cooperation between lining and surrounding rock into account by setting a surface to surface contact element between them. The results show that the working mechanism of fluid-structure interaction during the process of water filling in hydraulic tunnel can be reflected in this model. Under the high internal water pressure, the lining cracks and the distribution rule of cracks appear to be less in quality and wide in width. There is not new cracks appeared in the lining as the internal water pressure increasing. The permeability of lining at cracks increases sharply and the internal water flows through the cracks. The increasing water pressure between the lining and surrounding rock leads to the trend of separation. After separating from each other, the lining and surrounding rock would bear the water pressure within their own scope and show the limited cooperation. With the internal water pressure increasing, the stress of reinforcement will not increase indefinitely. After the lining cracked, the reinforcement stress increases with lower amplitude and even rebound. The value of reinforcement stress stays at low level.