Study On Deformation And Seepage Characteristics Of Deep Foundation Pit Excavation Under Inclined Interlayer Near River

With the development of economy and the vigorous construction of infrastructure by the country,foundation pit engineering in various regions is developing towards a deeper and larger trend,which also puts forward higher requirements for foundation pit support and water stop.At present,the research on groundwater and deformation control in the foundation pit mainly focuses on the horizontal stratum,while there are few studies on the seepage and deformation laws after precipitation and pressure relief and how to reasonably optimize the water stop scheme in the inclined sand-mudstone interbedding stratum under the condition of lateral recharge near the river.Based on the deep foundation pit project of Anning Sewage Treatment Plant in Lanzhou City,this paper preliminarily discusses the laws of pore water pressure and surface deformation around the foundation pit after precipitation in the sand-mudstone inclined interbedding stratum through indoor model test and numerical simulation.At the same time,the rationality of the model is verified by the finite element software,and the whole process of the actual foundation pit support is restored and simulated,and the differences between the horizontal interbedding and the inclined interbedding are compared.On this basis,aiming at the problems of water gushing and deformation during the excavation of the actual riverside inclined interbedded deep foundation pit,a new optimized water stop scheme is proposed.Through numerical simulation,the deformation of the support structure,the seepage of groundwater in the foundation pit and the surrounding surface subsidence are discussed,with or without zoning conditions.The main contents are as follows:(1)Taking the deep foundation pit project of Lanzhou Sewage Treatment Plant as the background,the actual site modeling is restored and compared with the horizontal interbedding stratum model.The results show that the load of adjacent buildings has a negative effect on the deformation of the supporting structure and the surrounding ground settlement during the excavation of the deep foundation pit in the inclined stratum.Among them,the total water level curve in the inclined rock stratum shows a stepwise growth due to the influence of the rock stratum trend and dip angle.With the increase of the excavation depth of the foundation pit,the regional water seepage in the inclined interbedding is more serious than that in the horizontal rock stratum,which increases the difficulty of the foundation pit excavation under this special geological condition.(2)According to the particularity of the actual inclined interbed,the indoor model test was carried out to preliminarily discuss the seepage and deformation law after precipitation and pressure relief,and the proportional numerical model was established to verify the reliability of the overall trend by transient seepage.The results show that under the condition of constant head recharge of inclined interbed,the rate of pore pressure reduction at the same depth in the process of pressure relief shows an unbalanced change rule that the deep aquifer is greater than the shallow aquifer.In the process of reinjection,with the passage of seepage time,the pore pressure values at all places tend to be close to the position water head,which is similar to the pore pressure values of horizontal strata,and ultimately only related to the depth of a single variable.(3)In view of the local water seepage problem during the excavation of the deep foundation pit in the inclined interbedding near the river in the actual site,it is proposed to use the natural weak permeability of the inclined aquiclude to carry out the zonal precipitation of the foundation pit.The differences between partitioned and non-partitioned operating conditions are compared and analyzed.The results are as follows: In the process of zonal precipitation in the foundation pit,the diaphragm and the natural inclined water-resisting layer effectively cut off the hydraulic connection inside and outside the foundation pit,making the groundwater level curve at the bottom of the foundation pit show a "trapezoidal serrated" change trend,which plays a limited role in the support structure and the deformation around the foundation pit.At the same time,it ensures the dry operation in the excavation face and increases the overall stability of the foundation pit.