Model Test And Numerical Simulation Of Earth Pressure With Load-reducing For The High Fill Open Cut Tunnel

Nowadays, as a kind of tunnels, which are constructed by the method of open excavation, the open cut tunnels are widely used in the loess plateau region, where Mountains and plains constitute the main body.The rapid development of transportation promotes the process of urbanization, and at the same time, the urban land become more and more tighter. Reclamation and deep groove fill nowadays become one of the most important ways to create the urban land. Therefore, the engineerings of high fill open cut tunnel increase gradually, and the height of backfilling increase too. While, for most of open cut tunnels, the situation of high backfilling is not taken into consideration at the beginning of the designment. And the increasing earth pressure of backfilling become one of the important factors, which play adverse impact on the regular service of the open cut tunnels.To the problem of earth pressure for high fill open cut tunnels, it belongs to the category of problems of earth pressure for high embankment structures. Currently, for these problems are more mainly concentrated in the culvert(tube), and less for high fill open cut tunnels. The increasing pressure take adverse impact on the safety of the open cut tunnel, which lead to the disease of the structure.Based on the problems above, in this paper, two problems are studied, including what measures should be taken to reduce the earth pressure on the open cut tunnel and how to define the value of the earth pressure. Firstlly, according to the model test under different conditions of off-loading, the variation of the earth pressure at the process of backfilling is studied; Secondly, the finite element analysis model is established, the analysis and the test results verify each other, and further, factors that play influence on the variation of earth pressure on top of the open cut tunnel are analysed; Finally, in accordance with the results of the model test and finite element analysis, formula of earth pressure with load-reducing by reinforcement for the high fill open cut tunnel is derived. The principal conclusions are as follows:(1) According to the measured values of the earth pressure and the settlement of fill under different, And the results show: The earth pressure on the top or foot of open cut tunnel increase nonlinearly at the process of backfilling whether set offloading measures or not; low solidity hole+geogrid can reduce the differential settlement of the soil column internal and external, and different ways correspond different efficiency of load-reducing; Laying geogrid under the condition of the low solidity hole is further conducive to the reducement of the earth pressure on the top of open cut tunnel, and because of the limition of space for the geogrid’s deformation, multilayer is not to more significant degree; The improvement of compression modulus of both sides of embankment is positive to the load-reducement under the measures of low solidity hole+geogrid.To the earth pressure on the top of open cut tunnel, it can be approximately calculated by using γH when the fill in low height;With the increase of the fill height, γH is no longer applicable.(2)The model of finite element analysis is established and the results show that: the soil-arch effect will occur at the process of backfilling, which is conducive to reducing the earth pressure; Among all factors, the low solidity hole can bring the biggest impact on the differential settlement of the soil column internal and external, for this reason, it plays the most significant effect on the errth pressure.(3) Refer to the results of model test and numerical simulation, mechananical calculation model of earth pressure with load-reducing by reinforcement for the high fill open cut tunnel is established under the condition of the existence of the slope. The computational formula of earth pressure on the top of open cut tunnel in different height are put forward, which distinguished by the height of the plane of equal settlement. Take the same example to solve and the result of the computational formula is in good agreement with the result of numerical simulation, which can provide theoretical reference to the design and construction for the load reduction structure of high fill open cut tunnel.