Study On The Influence Of Deep Foundation Pit Excavation On Adjacent Subway Station In Powder Soil Layer

With the rapid development of cities,the development of subway in large cities in China has begun to take shape,and the TOD business model is becoming a trend.A large number of foundation pit works adjacent to subway stations also appear.Therefore,it is of great significance to reduce the influence of such foundation pit works on adjacent subway stations.Based on the background of a deep foundation pit near Enping Lake Station on the suburban line of Zhengzhou Metro,a three-dimensional numerical model is established by using the finite element software MIDAS/GTS,compared with the monitoring data,the reliability of the numerical simulation is verified,and the influence of the change of the diameter and embedded depth of the pile on the displacement of the main station and the entrance is simulated.The main conclusions of this paper are as follows:(1)Based on the geological and hydrological conditions of the project,the investigation of the present situation of the Enpinghu station on the suburban line of the existing subway,the national industrial standard and the existing engineering experience,the deformation control indexes of the station are determined,and the supporting methods of the foundation pit are selected,it is concluded that the supporting structure type of row piles + internal bracing is more suitable for this project.(2)Through the analysis of constitutive model selection,the suitable constitutive model of silt is determined.The monitoring value is compared with the simulation value to verify the accuracy of the selected model and the effectiveness of the support type of the project.(3)Through numerical simulation,it is found that the displacement of the main station caused by the excavation of the foundation pit is large,and the displacement of the main station caused by the backfilling process is small,and the horizontal and vertical displacement of the main station increases with the excavation of the foundation pit,and reaches the maximum when the excavation reaches the bottom of the pit,at this time,the maximum horizontal displacement is 1.962 mm.The maximum vertical displacement is-0.898 mm.(4)Through numerical simulation,it is found that the horizontal displacement of the entrance and exit of subway station increases with the excavation until it reaches the maximum when the first support is removed,and the maximum value is 2.77 mm.In the whole foundation pit construction process,the uplift value of subway station entrance and exit adjacent to the foundation pit increases first and then decreases,and the maximum uplift value is 4.934 mm.The settlement value of subway entrance and exit far from the foundation pit also increases first and then decreases,and the maximum settlement value is-1.127 mm.(5)By analyzing the influence of pile diameter of retaining pile on the displacement of main station and entrance and exit,it is found that when the pile diameter of retaining pile increases from 0.4 m to 1.2 m,the maximum horizontal displacement of main station decreases by 39.27%,and the maximum vertical displacement of main station decreases by 38.1%.The maximum horizontal displacement of the entrance and exit decreased by 40.35%,and the maximum vertical displacement of the entrance and exit decreased by 44.36%.(6)By analyzing the influence of pile embedment depth on the displacement of main station and entrance and exit,it is found that when the embedment depth of retaining pile increases from 8 m to 16 m,the maximum horizontal displacement of main station decreases by 43.46%,and the maximum vertical displacement of main station decreases by 36.68%.The maximum horizontal displacement of the entrance and exit decreases by 40.35%,and the maximum vertical displacement of the entrance and exit decreases by 47.33%.