Study On Relaxation Effect Of Vertical Soil Pressure For Shield Tunnel

The 21st century is the century in which the underground space will be greatly developed and utilized. Shield tunnelling construction method, as an environment protected, low perturbed, high-efficient and fast method in urban tunnelling construction, which will get an high-speed development and become as one of the major technologies applied in the underground space excavation, has a broad development prospect in our country. The investment of segment generally accounting for 30-40% of the total project investment in shield tunnelling construction, is an important factor that influences the construction economic and the structure security, so it is of great significance to design the shield lining safely, economically and reasonably.The key problem of the shield tunnel lining design is to confirm the soil pressure on the lining reasonably. It is the basic demand to design the lining structure safely and economically. The vertical soil pressure influences the horizontal soil pressure and the sub-grade reaction's confirmation and it is difficult to calculate the vertical soil pressure accurately. The vertical soil pressure has a connection not only with the complicated mechanics characteristic of soil, but also with the displacement caused by the shield construction. So, evaluating stratum's relaxation effect accurately is the key to confirm the vertical soil pressure, but there are also arguments for appraising to the relaxation effect of vertical soil pressure in shield tunnelling at present. The limit minimum load of the vertical soil pressure is called relaxation soil pressure. When the counterforce provided by the slice is greater than this load, the stratum can remain stable. The main purposes of this paper are clarifying the vertical soil pressure's relaxation effect in shield tunneling, which is the precondition to appraise the vertical soil pressure's relaxation effect in shield tunneling reasonably and then confirming the relaxation soil pressure.On the foundations of the indoor baffle drop experiment study and the two-dimensional particle flow code simulation, in this paper, researches were done about the relaxation effect of vertical soil pressure in shield tunneling and the relaxation soil pressure as follow:(1) The indoor baffle drop experiment was designed, and the variety regularities of the sand's weight on the baffle and the sand's stress in the box with the drop of the baffle in different compactness and different burial depth were studied.(2) The influence on the biaxial test stress-strain curve in the particle flow code when mesomechanical parameters in two-dimensional particle flow code change was studied. The mesomechanical parameters of sand simulated by particle flow code were confirmed by...