Study On Stress And Deformation Of Surrounding Rock Of An Extra-large Section Tunnel With Variable Slope Surface

In railway construction in China,most of the tunnels need to pass through the mountainous areas with complex geological and topographic conditions.In such may generate large deformation of surrounding rock in tunnel construction process,if the lack of understanding of the deformation mechanism and deformation law,forced deformation characteristics of surrounding rock area is not enough importance or improper disposal measures,or to take the tunnel surrounding rock control technology not mature enough,easy to cause the construction safety accident,will also be a running tunnel of the main causes of defect arise,even lead to overall overturning tunnel.According to this a series of problem,this paper a three line overload in stake to central China railway tunnel as an example,the use of theoretical analysis,numerical simulation and the method of real-time data monitoring delves into the variable slope under the condition of heavy section of shallow buried large bias tunnel surrounding rock mechanical characteristics,deformation,the relationship between supporting structure and surrounding rock,the deformation control and structural safety evaluation and so on,has made the following main results:(1)By using the theory of limit equilibrium analysis to solve the shallow bias tunnel surrounding rock pressure,delves into the variable slope under the influence of heavy section of shallow bias tunnel surrounding rock mechanical model and theoretical calculation method,the lateral pressure coefficient is revised on the level of tunnel surrounding rock from the correction,make the calculation result more accurate and close to the actual;The different effects of varying slope degree and comprehensive slope on the surrounding rock pressure of tunnel are analyzed,and the correlation curve of the horizontal side pressure coefficient with the change of the modified value of the coefficient is explored.When the modified value of the tunnel horizontal lateral pressure coefficient increases,the horizontal lateral pressure coefficient increases and the tunnel horizontal lateral pressure increases.When the slope and the number of slope changing points of the tunnel change obviously,the stress of tunnel surrounding rock changes obviously.(2)The stress state of surrounding rock during the construction period is analyzed by numerical simulation,and the spatial distribution pattern of surrounding rock stress is determined,which shows that the vertical stress and horizontal stress increase with the increase of excavation step sequence,and the influence range is gradually expanded.The deformation characteristics of surrounding rock under the condition of numerical simulation and field measurement by the three-step temporary invert method are analyzed.The four stages of the time-effect deformation-time characteristic curve of surrounding rock,the expression form of the space effect of surrounding rock and the vertical deformation law of the characteristic position of the tunnel section are obtained.The vertical deformation of surrounding rock increases with the increase of excavation area,and the deformation curve is linear distribution and quadratic distribution,respectively.Moreover,the deformation of the tunnel with extra large section is more complex than that of the tunnel with large section,and the deformation increases obviously.(3)Contrast analysis of the preliminary support of the tunnel advance guard measures and not impose measures under the stress of surrounding rock deformation characteristics,applying advanced protection measures after plummeted by 45%,the vertical deformation of rock mass,the vertical stress reduces about 21% of the initial supporting pressure decreased by 11% or so,illustrates the complex large preliminary support of the applied measures to control the deformation of tunnel surrounding rock deformation effect is obvious.Aiming at the large deformation area of the tunnel,the reasonable deformation control countermeasures are put forward,which can provide reference for similar tunnel construction design.(4)Based on the excavation of tunnel with variable slope surface,the safety evaluation of tunnel supporting structure is made.It is concluded that the actual construction of tunnel supporting structure specification requirements safety coefficient is greater than the minimum safety factor and reliability of tunnel section: Shallow buried side arch foot >Deep buried side arch waist > Shallow buried side under the arch waist > Deep buried side arch feet > Inverted arch > Shallow buried side arch waist > vault > Deep buried side under the arch waist,tunnel supporting structure bearing system meet the requirements,tunnel structure safety.