Study On Cutting Face Stability During Slurry Shield Tunneling In High Water Pressure And Shallow Cover

ABSTRACT:The slurry shield operation is the required constructive measure in underwater tunnel, especially in the cohesive soil ground across river or sea. The key feature of shield tunnel is depending on slurry pressure to maintain cutting face stability. Generally, there is well-established method to set slurry pressure and to choose different slurry based on the performance. However, when consider the high water pressure and shallow cover condition in underwater tunnel, there is no related theory and experience to set slurry pressure and make choice on different slurry performance, which could prevent accidents of slurry gushing and cutting face collapse caused by hydraulic fracture.The large diameter of Yangtze river tunnel, the high water pressure, the thin soil and especially the sharply discontinuous terrain in the stamping notches all make threats to the project. How to maintain the cutting face stability is the key point to the success of passing through. Our previous studies and experiences of slurry pressure all based on even and flat terrain and slurry characteristics to maintain cutting face stability. However, there is no related theory and experience which can be well applied in the section of stamping notches, where the terrain is discontinuous.This study applies previous earth pressure calculating method to analyze and calculate the slurry pressure in the dangerous terrain, which requires the engineer to not only consider the large enough slurry pressure to maintain cutting face, but also prevent the pressure too high to cause accidents. Meanwhile, based on results of indoor test and field test, especially the specific analysis of the position where hydraulic fracturing may happened to, the paper analyze the rational setting method of slurry pressure in risk areaIn addion, FLAC 3D numerical simulation softwarere is adopted to analysis the cutting face stability in the section of stamping notches, by comparison with the above theoretical results, provide the upper and lower limitations of slurry pressure, set value of slurry performance and tunneling parameter for project, which made shield pass through the risk area without any reinforced method. This paper also accumulates precious experiences to later similar project.