Study On Engineering Geological Characteristics Of Expansive Rock And Its Influence On Tunnel Project

This paper is based on the project of "Yunnan water diversion project of soft rock and soil engineering geological characteristics and influence research".This paper mainly studies the engineering geological characteristics of K1 p,a representative of the expansive rock in the project.The engineering geological problems that may appear in the process of the construction of the second section of Dali mountain tunnel are analyzed through the numerical simulation method.It's about 55.70 km through the soft rock and soil stratum of Dali section preliminary.The length accounts for 54.21% of the total line.The total line of the Bandengshan tunnel is about 20.21 km.,which contains the length of about 2313 m of K1 p.The main lithological character in the region is jurassic sandstone,mudstone,cretaceous sandstone and mudstone.In this paper,the mineral composition,physical and mechanical properties of K1 p are known by field investigation of expansive rock strata in Dali II section and laboratory experiments on representative K1 p formations.formation by the section survey to the swelling rock of the Dali? section of the middle diversion line.The supporting process of excavation and support of the tunnel and support after considering expansion force are simulation by FLAC3 D.The influence of various mechanical parameters on the stability of surrounding rock is analyzed by sensitivity function.The main achievements of this paper are as follows:(1)The lithology of K1 p formation can be sure that is silty mudstone by the result of systematic identification of mineral structure and composition.The sample contains a large amount of clay minerals,including high content of medium expansion illite and a small amount of high expansive illite mixed layer.The types and compositions of clay minerals can directly affect the properties of the rock of K1 p,including swelling,disintegration and mechanical properties.The higher the content of clay mineral is,the stronger the swelling and the worse the disintegration resistance,and the lower the strength.(2)Conclusion the physical and mechanical test of K1 p formation is studied includes that the softening coefficient of the formation rock is low,the plasticity is strong,and the disturbance is strong,the uniaxial compressive strength is high,axial compressive strength,compressive strength and shear strength are low,and the uniaxial compressive strength after water saturation decreases sharply,the deformation modulus is small,and it is easy to produce large deformation,long-term compressive strength is low.(3)The conclusion can be drawn from the study of K1 p formation water property is that the formation rock has strong expansibility,easy to produce large deformation,destruction of the supporting structure,it also has a strong disintegration,poor stability,easily damaged in water.(4)The internal friction angle of the surrounding rock has the greatest influence on the stability of the tunnel,and the influence of the other three mechanical parameters on the stability of the tunnel is different.(5)Based on the numerical simulation results show that the construction process of the tunnel,when the tunnel is below the underground water level,water saturation,or whether it is in the excavation or in supporting parts,the displacement of each part is larger than that of the natural state,and the range of plastic failure zone is wider than that of the natural state,and the maximum principal stress value and the minimum principal stress value are smaller than the natural state,the stress concentration area on both sides of the arch waist is transferred to the tunnel.(6)After tunnel support,in the natural state and saturated state,the displacement of each part is obviously controlled,the range of plastic failure is reduced,the distribution of the maximum principal stress and the minimum principal stress is uniform,and the supporting effect is better.(7)The tunnel surrounding rock in water saturated condition,influenced by rock softening and swelling force,all the supporting structure of the moment value were significantly increased,and the more the tunnel to the lower side,the more obvious the increase.The value of the bending moment at the toe of the hole can be increased nearly 10 times compared with that of the natural state,which is a great threat to the support structure.