Research On The Interaction Law And Deformation Control’s Key Technologies For Adjacent Deep Excavation Zones In Soft Soil Areas

With the development of society,underground space is constantly being expanded.In the process of promotion,foundation pit engineering has played an important role.The demand for buildings is increasing,and the building area is becoming larger,resulting in the emergence of many adjacent foundation pits or groups of foundation pits that are closer to each other in cities.Due to the mutual influence of adjacent excavation of foundation pits,changes in soil between pits can greatly increase the safety risk of foundation pits.While excavation of foundation pits in different projects can cause mutual influence and harm,engineering disputes can also occur.Therefore,it is of great significance to explore the laws and control measures of the mutual influence between adjacent foundation pits,shared ground walls(piles),and adjacent foundation pit excavation,for the construction of adjacent foundation pits and the mastery of deformation laws during adjacent foundation pit excavation.Therefore,the main work and achievements of this article are as follows:(1)Taking the Shaoxing TOD project as an example.Analyzed the changes in monitoring data such as horizontal displacement,surface settlement,and support axial force of adjacent foundation pit retaining structures at different locations and excavation periods.From this,it can be concluded that the excavation of the latter foundation pit has a reducing effect on the horizontal displacement and support axial force of the adjacent retaining structure of the first excavation foundation pit;There is a trend of increasing surface settlement of soil between pits and changing its morphology.(2)Taking the alumni headquarters of Zhejiang University as an example.The change of axial force of adjacent foundation pit excavation support is analyzed,and the feasibility of calculating axial force by equivalent beam method is verified with the measured data validation.The results indicate that the equivalent beam method has certain applicability for concrete supports;For the combination of concrete and steel support,there is a significant error in calculating the steel support.Studying the influence of adjacent foundation pit excavation on the horizontal displacement of the deep soil of the previous foundation pit,it is concluded that the continuous increase in the excavation depth of the latter foundation pit will cause the horizontal displacement of the deep soil of the previous foundation pit to continue to increase.The closer the location to the adjacent foundation pit common ground connecting wall is,the greater the impact of the excavation of the later foundation pit on the horizontal displacement of the deep soil of the excavated foundation pit.(3)Based on the measured engineering data,establish a finite element model using Plaxis 3D software.A study was conducted on the foundation pit with the same width of the shared ground connecting wall,and the mutual influence and range of influence between the horizontal displacement of the retaining structure and the surface settlement outside the pit were analyzed.Obtained: The excavation of the shared wall foundation pit will result in an increase of 0.08%H～0.084%H in the maximum horizontal displacement of the previous foundation pit’s outer wall,with an impact range of 0～2.76 H along the outer wall direction from the shared wall;The maximum increase in surface settlement outside the external wall pit is0.074%H～0.08%H,with an impact range of 0～2.9H along the external wall direction.(4)Analyzing the changes in horizontal displacement and surface settlement between two foundation pit retaining structures under different spacing distances,it is concluded that when the spacing between the two foundation pits is 1.32 H,the horizontal displacement of adjacent side retaining structures is almost completely affected by the excavation of the foundation pit.When the spacing is small,the sandwich soil near the edge of the foundation pit is affected by the excavation of the next foundation pit,and the surface settlement increases due to the superposition effect compared to the single excavation.When the superposition effect exceeds1.98 H,the superposition effect near the edge of the foundation pit disappears.At an interval of 3.3H,the superposition effect of soil surface settlement between pits disappears,and the curve of surface settlement change is similar to that when the foundation pit is excavated separately.By adding a diaphragm wall between two foundation pits and studying measures to reduce the mutual excavation impact of adjacent foundation pits,it is concluded that for adjacent foundation pits with a spacing of 10 m,adding a 0.6m thick diaphragm wall between the two foundation pits can reduce the impact of adjacent foundation pit excavation by 18.4%,and a 0.8m thick diaphragm wall can reduce the impact by 20%.The difference between the two is not significant,and using a 0.6m thick diaphragm wall is more economical.This article summarizes the general rules and mutual influence range of adjacent foundation pit excavation of shared ground connecting walls.The law of mutual influence between adjacent foundation pits with different spacing was obtained,and the safe spacing of adjacent foundation pits was determined.Studied the reduction of mutual influence between adjacent foundation pit excavation caused by the insertion of diaphragm walls at the sandwich soil of adjacent foundation pits,as well as the relatively economical selection scheme.It has certain significance for studying the excavation of adjacent foundation pits with different spacing and the excavation of foundation pits with shared ground walls.