Study On The Reasonable Cover Thickness Of Subsea Tunnel

The depth of sub-sea tunnel rock cover plays an important role in the safety and cost to build a tunnel. How to determine the reasonable depth of sub-sea rock cover is still an intractable research subject. These problems mentioned above based on jiaozhou bay sub-sea tunnel were studied in this dissertation.(1) The rock mechanical experiments results indicate that the bedrock of the section studied belong to solid rock, at the same time the bedrock rock mechanics parameters were obtained.(2) On the basis of date collection of built sub-sea tunnel at home and aboard, the experience methods that can determine reasonable depth of sub-sea rock cover were generalized as follows:Norway experience methods of sub-sea tunnel construction, Japanese empirical methods of minimum discharge, domestic empirical formula for underwater coal mining. Through the engineering analogy analysis, preliminary, the range of the LK5+650 section reasonable rock thick was determined from 28 to36.5 meters.(3)Under eleven different rock covers and 2 different boundary conditions, FLAC3D was applied to analysis water inflow. The water inflow was relatively small in impervious conditions meanwhile was relatively large conditions, so the average is taken now. The results show that it presented parabola relation of water discharge versus rock cover thickness. Discharge was smallest when rock cover thickness was 34m combined with engineering analogy methods, the reasonable rock cover thickness was ascertained as 34m to 36.5m.(4)FLAC3D was applied to the wall rock stability simulating analysis under 10 different rock cover thickness. By taking into consideration of principal stress disturbance range, any conditions could meet the requirements, by displacement convergence of surrounding rock, it was reasonable that the rock cover thickness was ascertained as 34m.(5)Based on the 34m of rock cover thickness, this dissertation was further studied seepage-stress coupled analysis. It indicated that the value and size of displacement and principal stress was petty in the affection of seepage flow. The rock cover thickness of 34m was safety.