Research On Early Supporting Technology Of Shallow Tunnel In The Broken Rock Sections

Modern tunneling construction technology mainly depends on the New AustrianTunnelling Method,among them anchor and shotcrete supporting is one of the three core inNATM,the interaction of structure and surrounding rock support by anchor and shotcrete hasbeen the difficulty in the stability of the tunnel engineering,the role of structure in surroundingrock support by anchor and shotcrete in mechanism and mechanical properties is the core ofthe interaction between surrounding rock and supporting structure,yet its also has the stiffnessand strength changes over time,shrinkage,creep,and other factors related to time,Time effectof support structure by anchor and shotcrete supporting caused great influence on thestress,deformation,etc.This thesis summarizes previous works and conducts in-depth researchon early supporting technology of shallow tunnel in the broken rock sections.The mainresearch contents and achievements are as follows.(1) It describes the characteristics of surrounding rock under shallow broken geologicalconditions and points out that the shear strength of broken rock is mostly determined by weakstructural plane or weak intercalation;(2) For shallow tunnel in the broken rock sections,cavern excavation could not form afterbearing structure,it’s easy to cause large deformation,instability and failure of surroundingrock,therefore,that should be small duct grouting pre-supporting before excavation.When thetunnel have a certain span,analyses the effect of anchor and shotcrete supporting bycomparing the impact on vertical displacement of vault under different workingconditions,show that for this kind of surrounding rock’ initial supporting,shotcrete supportingon the vault subsidence control,maintain the surrounding rock stability has played a majorrole;With the increase of tunnel buried depth,in the primary supporting,combined support byrockbolt and shotcrete than just sprayed concrete and steel arch support for maintainingstability of surrounding rock has better effect.(3) Proposed the method for determining of characteristic curve of tunnel in shallow broken rock sections,that is tunnel rock initial stress can temporarily set to gravity stress ofsurrounding rock,surrounding rock deformation can be set as the elastic deformation,disregardthe displacement of surrounding rock before tunnel has not yet been digging,and through thetunnel monitoring measurement and other means to obtain the vaults of surrounding rockdisplacement.Thus the displacement value of surrounding rock can be obtained whenshotcrete lining constructing,the released crustal stress,calculate the release rate ofsurrounding rock at this time,can be integrated with the displacement characteristic curve oftunnel surrounding rock and shotcrete lining, that get a convergence-constraint modelrequired in the calculation of the displacement characteristic curve.(4) Analysis the displacement characteristic curve and sprayed concrete internal forces,evaluation of structure rationality of sprayed concrete lining,and by adjusting thedisplacement and the stiffness as the shotcrete lining constructing,determine the reasonabletime and reasonable stiffness of shotcrete lining,optimize the shotcrete lining structure.