Study Of Grouting Reinforcement Mechanism On Shallow Buried Small Clear Distance Loess Tunnel And Its Application

With the rapid development of the national economy,China's urbanization process has also developed rapidly.The sharply growing population and the demand for urban infrastructure are also growing.Therefore,more and more urban subways or urban underground tunnels have been put on the construction schedule,but due to many factors such as construction,pipelines,transportation,etc.,they can only be designed as shallow buried small distance.Loess is a loose sediment formed during the Quaternary period and has a special status in engineering soils due to its unique external morphology,material composition and engineering properties.It is widely distributed in China,accounting for 6.6%of China's land area.In addition to the world-famous Loess Plateau region,there are also a large number of loess distribution in eastern China,such as Liaoning,Shandong and Jiangsu.When shallow buried small distance tunnels are built in the loess layer,due to the vertical joints in the loess,the tunnels are easily exposed to ground surface cracks,ground collapses and pipeline ruptures,causing major damage to the surface environment and buildings.Grouting is one of the reliable means to prevent and treat bad geological disasters in shallow buried tunnels.However,due to the special engineering properties of loess,the grouting reinforcement mechanism of loess is still unclear.The existing grouting reinforcement theory is not effective for the disaster control of shallow buried small-thickness loess tunnels.Based on the actual project,this paper identifies the distinctive regional characteristics of the engineering properties of Jinan loess by combining experimental research,theoretical analysis and numerical simulation.The distinctive regional characteristics of the nature of the Jinan loess project is identified.The grouting reinforcement mechanism of loess is revealed.The surface grouting reinforcement mechanism of shallow buried small distance loess tunnel is studied.The instability characteristics of surrounding rock of shallow buried small-thickness loess tunnel under water-immersed and humidified conditions are revealed.The grouting reinforcement effect prediction and evaluation method are established.Finally,a set of shallow burial for complex urban conditions is proposed.Grouting reinforcement technology for small clearance loess tunnel is successfully applied in practical engineering.The main work and innovations of the present thesis are as follows:(1)Through a large number of field tests and laboratory tests,the basic physical and mechanical properties of loess in the tunnel area were clarified,and the strength evolution law of loess under water and humidification conditions was revealed.The basic engineering properties of regional loess were comprehensively obtained.Through investigation and comparison of the engineering characteristics of the loess in the central and western regions,the regional characteristics of the Jinan loess and even the loess in Shandong,represented by loess in the tunnel area,are identified.(2)Aiming at the strong water sensitivity characteristics of loess medium,a new grouting reinforcement test device was developed.Grouting plus solids in triaxial compression test,unconfined compression test and permeability test.The indoor experiment of loess grouting reinforcement was carried out.The effects of dry density,water content,slurry water-cement ratio and grouting pressure on the grouting reinforcement effect of loess were studied.The water-sensitive effect of loess grouting and solid strength performance was revealed.(3)The joint influence mechanism of slurry water-cement ratio and soil moisture content on loess grouting and solid strength performance was investigated.The quantitative index which can describe the water-sensitive effect of loess grouting and solid strength performance was established,and the practical loess grouting project was established.The calculation formula of grouting amount reflects the dynamic mapping relationship between grouting amount,formation moisture content and slurry water-cement ratio,and proposes dynamic grouting control technology for loess layer.(4)Through the physical simulation test,the response law of surrounding rock stability of shallow buried small-thickness loess tunnel to surface grouting reinforcement is studied.Based on the test results,the attenuation mechanism of grouting pressure in the depth direction of the surface grouting process is analyzed.Considering the compressive characteristics of the soil during the grouting process,the stratified comprehensive method is used to establish the ground in the surface grouting process.The displacement calculation method was verified and analyzed by the indoor experimental reading theory method.(5)The numerical simulation is used to reveal the displacement evolution law of shallow buried small-thickness loess tunnel in the process of water immersion and humidification.The displacement creep is used as the criterion of surrounding rock instability,and the critical moisture content of surrounding rock under different buried depth conditions is analyzed.The mapping relationship between critical cohesion force and tunnel depth is evaluated.The improvement effect of different grouting reinforcement effects on tunnel surrounding rock stability is evaluated.The evaluation standard of grouting reinforcement effect is proposed.(6)Based on the research results of grouting reinforcement mechanism of shallow buried small-thickness loess tunnel,the grouting reinforcement technology of shallow buried small-thickness loess tunnel under complex urban conditions is proposed.The research results are grouted and strengthened in the tunnel of Jinan Yuhan Road through the loess section.Successful application in the project can provide some reference for similar projects.