Study Of The Structural And Mechanical Performance Of Underwater Shield-bored High Speed Railway Tunnels And The Boring And Docking Technologies

Abstract:For the sake of environment protection and sustainable development, underwater tunnels must be the favorable solution for transportation corridors to cross seas and rivers in China. Shiziyang tunnel on Guangzhou-Shenzhen-Hong Kong high speed railway is the first underwater super-long railway tunnel in China. The designed train-running speed of the tunnel is 350km/h. Shiziyang tunnel is also the first underwater tunnel in China that has been constructed by shield-docking method. The construction concept and methods of Shiziyang have great reference significance for the construction of future tunnels crossing seas and rivers in China. Therefore, the study on Shiziyang tunnel does not only have great theory significance, but also have great social and economic significance.In this dissertation, the structural and mechanical performance of underwater shield-bored high speed railway tunnels and the boring and docking technologies are studied in detail, with Shiziyang tunnel on Guangzhou-Shenzhen-Hong Kong railway as an example. The major contents and achievements of the study are as follows:(1) The methods for the design of the segment structures are studied systematically. First, the values of the design parameters in the conventional segment structure design models are summarized and the disadvantages are analyzed; secondly, modified beam-joint models are determined to be adopted as the segment structure design method, numerical simulation calculations are made, the structural joints of the segments and the segments themselves are verified, by means of numerous in-situ tests, to be under compressing state, and concepts such as the reduction of the loads on the segment structures and the design countermeasures to improve the economical efficiency of the tunnel are proposed.(2)Tunnels with segment lining have an assembled structure. In case any changes occur to the resistance of the media surrounding the assembled segments, the assembled structure is liable to become an instable outward-expanding structure, which may cause the tunnel to lose its stability. By means of modified beam-joint model method, the potential failure properties of the assembled segment lining are analyzed, the solution to install the secondary lining for underwater shield-bored tunnels so as to ensure the stability of the tunnel structures are expounded and the necessity to install the secondary lining is presented. (3) The ground surface settlement induced in the construction of Shiziyang tunnel is analyzed and the rules of the ground surface settlement in the longitudinal and transverse directions are obtained as a result of numerous monitoring data; the horizontal displacement of various strata in the course of the tunnel construction is analyzed and the corresponding horizontal displacement rules are summarized. Furthermore, conclusion is drawn that except for the overall lifting of the shield-bored tunnel, almost no relative displacement occurs to the tunnel and that there are no direct relations between the ground surface heaving/settlement and the tunnel structure deformation. Therefore, it is recommended that it is unnecessary to monitor the deformation of the shield-bored tunnel structure itself in the future.(4) The geological conditions of Shiziyang tunnel are heterogeneous both in transverse direction and in longitudinal direction, which imposes great technological difficulty for the boring and control of the shield. The metal phase and wearing rules of the cutting tools are studied by means of tests on the strata abrasiveness and strata compositions and effective cutting tool wearing rule equations are proposed. The technology to replace the cutting tools under 0.67MPa water pressure is studied, the cutting tool replacement technology under reduced pressure and limited slurry releasing is proposed, and design optimizations are made to the cutting tools of the shield for Shiziyang tunnel on basis of the assessment on the boring effect of the shield in different tunnel sections.(5) The engineering geological conditions and hydro-geological conditions of the potential shield docking positions of Shiziyang tunnel are studied in detail. Appropriate inside-tunnel control survey accuracy is determined by estimating the influence of the docking position on the break-through accuracy. It is determined, by means of centrifugal tests and numerical simulation analysis, that the preserved docking width that can ensure the stability of the tunnel at the docking position shall not be less than 2.5m, however, under the pressure-maintaining condition,0.5m docking width can also ensure the safety. In the tunneling, the docking is made as follows:When the distance between the two shields is 20-30m, one of the shield stops its boring while maintaining the pressure in its excavation chamber, the other shield continues its boring to dock with the shield that has stopped its boring. Under the protection of the shield shell, the components within the scope of the shield shell are dismantled, the outer rings of the cutter heads of the two shields are welded together to form the tunnel structure, which is followed by the installation of the reinforced concrete lining. In this way, safe, accurate and efficient docking has been accomplished, with the plan error being less than 30mm and the horizontal error being less than 20mm. The successful docking of the shields in Shiziyang tunnel provides valuable experience for the docking of shields in boring of other underwater tunnels in the future.The major construction technologies adopted for Shiziyang tunnel on Guangzhou-Shenzhen-Hong Kong high speed railway are studied and analyzed in the dissertation, with the hope that the study results can provide reference for the construction of sea-crossing tunnels to be built in China in the future.