Numerical Simulation For The Subway Shaft Construction In Changchun

The subway shaft engineering is an important part of the subway construction. Most subway shaft near the main road, the surrounding environment is very complex, and the working surface is small, thus the construction technology requirements are high and many uncertain factors will be faced with in the process of shaft excavation. With the increasing intensity of urban construction, the construction of adjacent buildings is more and more common. Similar to the open pit excavation, shaft excavation will disturb the surrounding environment inevitably, and change the initial formation of stress field and seepage field, which will cause the displacement and deformation of rock mass, settlement, tilt and even cracking of the adjacent buildings and the surrounding ground, and some economic loss, even to endanger the safety of buildings and the surrounding personnel. Therefore, it is significant to study the neighborhood deformation and safety control due to subway shaft construction.In order to comprehend the response of the surrounding area when the subway shaft under construction, Changchun subway line No. 1 free road station shaft engineering was looked as the background, the settlement of the shaft around the site and adjacent buildings were simulated by using Midas finite element software. The results were verified with the field monitoring data. Then, the hanging wall of a well shaft law construction process around the ground surface deformation characteristics and mechanism was investigated, and the isolation effect of the engineering pile was analyzed. The main results are as follows:1. With the wall hanging upside down method of shaft construction, lock ring beam structure was constructed before excavation. At the beginning of excavation, soil stress release cause shaft bottom rebound uplift, drive supporting structure, and lead to the surface slightly uplift phenomenon.2. In addition to undertake the settlement caused by the ground excavation disturbance and soil loss, the locking ring beam structure also bear the shaft lining early borehole gravity caused by the settlement. So, the vertical displacement cumulative settlement amount at the top of the locking ring is larger, the surface settlement close to the shaft is relatively large.3. The horizontal deformation of the lining and the bottom hole uplift deformation are the main reasons of the surrounding strata deformation and movement caused by the excavation of the shaft. As the depth increases, the maximum shear strain increases and the effective plastic zone becomes larger.4. The isolation pile can be look as a cantilever pile fixed to the soil mass. The balance of force between two sides of the retaining piles will be broken due to the excavation of subway shaft, and the additional force will emerge. When the excavating depth less than the length of the retaining piles, the additional force will be delivered to the lower force bearing layer and the deformation of upper foundation will be blocked, then, the effect of the excavation of subway shaft on cumulative settlement and differential settlement will be decreased. With the increasing in the excavating depth of subway shaft, the embedded depth of cantilever pile is reduced, and the blocking effect will be weakened. Finally, when the excavating depth exceeds the length of the retaining piles, the blocking effect of the lower bearing layer disappear, and the differential settlement will increase significantly.