Study On The Stability Control Technology Of The Deep Open-Cut Foundation PIT In Cobble Stratum

With the acceleration of urbanization in the country, rail transport has become a symbol of urban modernization. The Airport Road tunnel project of Chengdu-Mianyang-Leshan Passenger Line Airport Road that belongs to the category of rail transportation. It is located in urban district and it mainly crossed cobble stratum. However, most the structure of cobble stratum are loose, and theirs distribution were not even. The engineering properties of the cobble stratum is essential different from the sand or the cohesive soil, it has strong discrete character and permeability. Meanwhile, for the complex features of excavation system, how to make a standardized of foundation pit structure of cobble stratum is an urgent need to solve the problem. Therefore, this paper conducted the following research areas to the long deep open-cut pit which has complex geological conditions, many supporting structure types, and complex surrounding environment:(1) According to the discrete character of cobble stratum, using granular discrete element numerical method, studied the earth pressure distribution of cobble stratum foundation pit when the wall move with basic modes-translation(T), rotation about base(RB), rotation about top(RT), and compare numerical simulation results which were fitted with the Rankine earth pressure and get the reduction coefficient of earth pressure cobble foundation pit with different displacement mode.(2) According to fifty-three cobble stratum pits which were researched, it summarized the main types of the supporting structure of cobble foundation pit,and it proved the failure and collapse evolution process of cobble stratum foundation pit without any support measures. It recommended structure form on conditions of cobble stratum foundation pit with different depths. Meanwhile, according to the actual project overview, it established a discrete element model of cobble stratum foundation pit. And it analyzed lateral displacement of the structure pile, surface subsidence, internal forces of the supporting structure and envelope and shaft power of the horizontal support, then these results were compared with the actual measured data, and it explored the stability of cobble stratum foundation pit.(3) According to the actual situation of the construction site, through numerical simulation, it explored the time of the deep foundation pit which erected the cross support.(4) According to the groundwater conditions of the site, through numerical simulation, it cleared the influence of hydrodynamic effects on the stability of the deep foundation in sandy cobble formations, and proposed the corresponding control measures.