Research On Face Stability Control Of River-crossing Tunnel During Chamber Opening Under Pressure In Nanjing Xinjizhou Shoal

With the rapid development of The Yangtze River Economic Belt in China,the construction of the river-crossing passage is developing rapidly.As the first choice of crossing river,the large-scale construction of shield tunnel promotes the wide application of slurry shield.However,the shield cutter is often need to be changed due to abrasion during the process of slurry shield excavation,and the process is often accompanied by great risk of excavation surface instability,resulting in serious casualties and property losses.Therefore,with the actual engineering requirements,based on the water supply corridor project in Nanjing xinjizhou shoal,this paper researches the formation mechanism of filter cake and the stability of excavation surface under the combined support formation of upper air and lower slurry during chamber open.The main work and research results are as follows:(1)The slurry preparation tests are carried out.The influence of sodium bentonite content,sand content and CMC content on slurry quality are considered in the aspects of density,viscosity,colloid rate and p H.The appropriate slurry compositions used in slurry penetration test are preliminarily selected.(2)The filter cake formation tests are carried out with the help of self-made filter cake formation device.The penetration characters of slurry,the maximum bearing capacity of strata are studied,the quality of filter cake and the slurry membrane to effective conversion efficiency of the slurry pressure are discussed,and the applicability of different kinds of slurry in xinjizhou shoal are demonstrated.(3)The airproof capability tests of filter cake are carried out.An air pressure of 100 k Pa is applied to the slurry for by 4h to form filter cake.After it forms,the 100 k Pa osmotic pressure is applied to study the airproof time of filter cake and the failure performance of filter cake.The influencing factors of filter cake’s quality is comprehensively evaluated combined with slurry infiltration test.(4)The influence rules of tunnel burial depth,water head height and internal friction Angle of soil on the excavation surface and surface deformation during the opening of cross-river tunnel are studied by the help of ABAQUS finite element analysis software to determine the reasonable opening opportunity.Based on the water supply corridor project in Nanjing xinjizhou shoal,The influence of different slurry heights on the stability of the excavation surface is analyzed,and the accuracy is verified by theoretical calculation.So that.the control of slurry heights and support pressure of excavation face during the chamber open are guided,and the basis is provided for the chamber open of the xinjizhou shoal water supply corridor project.