Study On Mud Permeation Film Forming And Stability Of Excavation Face Of Large-diameter Mud Balanced Shield

In the actual construction of mud balanced shield,how to maintain the stability of the excavation face can be said to be a top priority in the whole process.In this paper,relying on the Crossing the Yellow River Tunnel on Jinan Jiluo Road,the stability of the excavation face of the large-diameter mud balanced shield in the permeable sand layer is studied.The article systematically studies the stability mechanism of the excavation face of the mud balanced shield through theoretical analysis,laboratory experiments,and numerical simulation.Analyze and discuss the influence of stratum and mud properties on the film formation of the excavation face,as well as the experiment of the instability characteristics of the excavation face,and combined with numerical simulation for judgment.Finally,the regular patten of instability and the critical supporting force of the excavation face of the mud balanced shield in the sand layer is output.The main contents and results are as follows:(1)Aiming at the mud balanced shield,starting from the basic principle of mud balanced shielding,the mechanism of mud film formation is derived,and the relevant factors affecting the quality of the mud film are studied.The stability mechanism of the excavation face is further analyzed,and the regular patten of instability of the excavation face and the balance relationship between the mud pressure and the excavation face are discussed.(2)By configuring five formations with different permeability coefficients,a mud permeability test was carried out according to the on-site mud ratio to explore the influence of formation properties on the formation of mud film.And through one of the formations,to test the mud film forming effect of different mud ratios.Finally,the experiment summarizes the influence of mud properties on the film formation of the excavation surface,and output appropriate mud ratio for the subsequent excavation face stability experiment.(3)Using the micro mud balanced shield device,combined with the similar theories of the coupled fluid-solid theorem,explore,under different water heads,the variation law of earth pressure,pore water pressure,and surface displacement in front of excavation face during the stage of tunneling,mud penetration and instability of excavation face.And the instability mode of the mud balanced under different heads is obtained.(4)Relying on the Crossing the Yellow River Tunnel on Jinan Jiluo Road,a coupled fluid-solid numerical simulation was performed on the stability of the excavation surface of the slurry shield under the permeable sand.It analyzes changes in pore water pressure,water seepage,ground stress,and excavation face displacement under different support ratios.The critical support pressure ratio for the instability of the excavation face of the slurry shield is obtained.