Research On Slurry Infiltration And Excavation Face Stability Of Slurry Shield In Round Gravel Stratum

It is quite significant of urban rail transit system to improve the urban economy and society’s sustainable development as well as mitigate traffic congestion and so on.Along with the rapid development of urban rail transit system,it is increasingly important to improve and study the construction technique of metro tunnel especially the shield method.The crucial segment about the guarantee of safety in shield construction is the excavation face stability especially in the high permeability round gravel stratum,which slurry infiltration to film formation is difficult and the stability of excavation face is hard to keep.Therefore,there is a practical significance to analyse the shield slurry infiltration to film formation and excavation face stability in round gravel stratum.Based on the slurry shild construction in Nanning round gravel stratum,the dissertation researches deeply and systematically not only the engineering geological risk and characteristic of slurry infiltration to film formation of round gravel stratum,but also the stability of excavation face by means of combining theoretical analysis,slurry infiltration test,model test and numerical simulation.The main research contents and contributions of the dissertation are as follows:(1)On the basis of the practical construction situation,the dissertation analyses the construction approaches and difficulties of slurry shield in round gravel stratum.Based on modle test similitude theory,the soil of model test is disposed using laboratory test.(2)On the one hand,depending on the slurry characteristic test,the influence of slurry relative density and viscosity changing with content of clay and carboxymethyl cellulose(CMC)is obtained.On the other hand,by using the slurry permeation test,the laws of unit water filtration caused by slurry penetrant as well as the type and thickness of slurry film changing with slurry relative density and viscosity is studied to ensure a national relative density and range of viscosity about the slurry film in round gravel stratum penetrantation.(3)Based on the principle and objective of shield model test,a shield model test system is designed.The system can realize several function,such as shield driving,cutter drilling soil and slurry circulation with ballast.As a result of the controllability of the shield trust 、 cutter speed and slurry capsule pressure,the system meets the requirements of driving and stability of excavation face in shield model.(4)Four changes of slurry permeation、soil stress、subsidence and failure mode of excavation face are ananlysed by shield driving and excavation face stability model test.At the same time,the area and stage are divided at excavation face unstability situation.(5)Combied with model test results,the contract and analyse is finished about limit support pressure、low of subsidence and low of soil stress on the study of excavation face stability at the slurry shield stability by FLAC3 D software.Another anaylsis is about several factors which have an effect on excavation face stability,such as buried depth of tunnel,soil parameter and overlying water pressure.