Research On Arching Mechanism Of Jointed Horizontal Rock Mass With Weak Interlayer

The stability evaluation of surrounding rock is one of main problems in the design and construction of tunnel and underground engineering.The joints of the rock mass,the dominant joints occurrence of rock mass,and the spatial relationship between the dominant joints and the tunnel have a significant effect on the stability of surrounding rock for rock tunnel.When the dominant joints of the surrounding rock is close to horizontal in tunnel and the underground engineering,for instance,the bedding of sedimentary rocks is close to horizontal,arch rock fall or collapse is one of the most common form of surrounding rock instability in low stress state.Based on the analysis of the deformation and failure characteristics of the surrounding rock with the dominant joints of the surrounding rock is close to horizontal,the arch formation requirement of the horizontal layered surrounding rock is analyzed by the voussoir beam,and the numerical method is used to analyze the effect of bolt-shotcrete support,moreover,some suggestions for the design and construction optimization of surrounding rock support parameters are put forward in this paper.The main contents of this paper are as follows:(1)The arching mechanism of the horizontal surrounding rock with vertical joint can be described by the voussoir beam under the gravity-dominated stress field,the key factors controlling the stability of the arch rock including the stress at middle and top of equilibrium arch,the stress on the joints at both ends of the rock,the rock compressive strength and joints roughness.(2)The surrounding rock form arch bearing structure after separated with upper strata during tunnel excavation,and there are two kinds of failure forms of arch rock when the tunnel surrounding rock is jointed horizontal rock and joints aperture is small,if the joint roughness is low,the rock will slabs along the joints when the horizontal reaction force at ends can't afford the rock weight,if the horizontal reaction force at both ends can afford the rock weight,the hinge joint will crushing failure when the stress of the surrounding rock is stronger than the compressive strength,and the critical deflection of crushing failure is deduced.(3)The stress of the surrounding rock and the bolt force are studied based on the FLAC3 D,it is considered that the bolt in the range of 90° of the tunnel arch has the greatest effect on the stability of the surrounding rock,and the bolt effect is worse in the range of 90° ~ 120°,the bolt action at the side wall is minimum.The optimization suggestions of bolt length,bolt spacing and shotcrete thickness are put forward on the basis.