Construction Mechanics Behavior Analysis of Pile-strut Supporting Structure of a Subway Deep Foundation Pit

Research purposes: The special red sandstone formation seriously affects the construction safety of deep foundation pit in Lanzhou subway station. Therefore, it is urgent to study the construction mechanical behavior of deep foundation pit in the complex environment of special red sandstone. In this paper, based on the site monitoring results and numerical calculation model, taking the pile-strut supporting structure of Lanzhou Metro Line No. 1 Dongfanghong Square Station deep foundation pit as the engineering background, the law of displacement variation of retaining structures, surrounding buildings and surface subsidence is analyzed comparatively. Research conclusions:(1) The results of numerical simulation and field monitoring by comparative analysis indicate that the results are close and have the same change trend, which shows that the results of the analysis to foundation pit excavation supporting by using the birth and death element method can provide effective guidance for the design and construction of deep foundation pit. (2) The maximum value of horizontal displacement pile tip monitored on site is 10.51 mm and is less than the control value of 30 mm, which indicates that the supporting structure of occlusal pile and steel support can effectively control the displacement of Lanzhou special red sandstone formation foundation pit. (3) As foundation pit excavation and supporting continues, the forward heeling curve of pile body gradually becomes the shape of drum belly and the location where the maximum measured slope value is 10.56 mm is located near 2/3 times the depth of the excavation. (4) With the continuous excavation of foundation pit, the vertical settlement displacement of the surrounding buildings decreases with the further away from the station. (5) The maximum settlement around the foundation pit located 1/3 times the depth of the pit. (6) The research result can provide guidance for the design and construction of subway deep foundation pit of similar special stratum in Lanzhou. © 2019, Editorial Department of Journal of Railway Engineering Society. All right reserved.