Study On The Reasonable Supporting Time And Segment Joint Optimization Of Tunnel Pre-cutting Method

As the application of underground space becomes more and more extensive,the requirements for construction safety and ground settlement during construction are getting higher and higher.For this reason,in order to better control the surface settlement,the pre-cutting method can be used.This method has the advantage of greatly reducing the surface settlement and has a small impact on the surrounding soil and the building.In order to improve the pre-strength of the concrete used in the pre-cutting method on site and to improve the overall performance of the segment by changing the segment joint form.This article focuses on the pre-cutting method,using laboratory tests and numerical simulations,to study the pre-strength of the concrete used to cast the pre-cutting segments,and the reasonable stubbing methods at the pre-cutting segment joints.The main research contents and conclusions are as follows:(1)Through the laboratory test,the mix ratio of the compressive strength of the concrete and the workability of the concrete that satisfies 10 hours of curing was determined.With this concrete mix ratio,test the compressive strength of the concrete at different time points of curing,and obtain the compressive strength growth of the concrete in the early stage.In addition,it is concluded that 1.5 ? 2.0 h after pouring the concrete is a reasonable demolishing time,which can provide a reference for site construction;Finally,the actual elastic modulus of concrete measured from the measured data of concrete is about 17.8 GPa,which provides a basis for the selection of concrete parameters for numerical simulation.(2)Determine the joint type as flat joint and tongue-and-groove joint,and use different viscous media.With the help of finite element method,the reasonable boundary conditions are determined by MIDAS / GTS NX software,and the rationality of the numerical model design was verified;Based on the three influencing factors of confining pressure,joint geometry and type of adhesive,175 working conditions are designed for comparative analysis,and the optimal scheme of joint and the suitable viscous medium can be selected under different working conditions are obtained;In addition,the construction method of the tongue-and-groove joint and the epoxy resin adhesive agent can maximize the working performance of the pre-grooved segment and ensure the safety of construction.(3)The lining mold,model loading frame and its monitoring system were designed.The frame and mold size are determined according to the original construction site size,according to a 1: 1 ratio.The most reasonable boundary conditions set in the previous analysis are used to set the constraint form,that is,the combination of the edge angle of 90° ? 90° plus the constraint on the lower side provides a reference for the design of the subsequent model test frame.