Study On Main Factors Influencing Safety Of Deep Foundation Pit Support Of Guangxi Coastal Area

In recent years,the research on the exploitation and utilization of underground space in coastal areas has become an important issue in urban construction.The foundation pit support project is an important engineering measure for the prevention and control of geological disasters in underground space development.The safety of foundation pit support engineering is a concern for geotechnical engineering circles.Based on the basic environmental geological conditions in the Guangxi coastal area and the deep foundation pit support engineering case,this paper analyzes the basic forms,design principles,common geological hazards and hazards of the commonly used foundation pit support engineering under the geological environment conditions in Guangxi coastal areas.The main influencing factors of AHP system analysis of foundation pit safety engineering are the distribution characteristics of groundwater and soft soil,and the size of foundation pits,support methods,and excavation methods.Based on this,combined with a foundation pit support project example,the groundwater numerical analysis software was used to analyze and study the impact of changes in groundwater flow field on the perimeter of the foundation pit,and proposed measures to prevent and control hazards and safety management of groundwater in deep foundation pit support projects.Safety Stability of Deep Foundation Pit Support Engineering.Through the aforementioned research work,we have obtained the following understandings and achievements:(1)Beihai City pays attention to underground space development in the process of urban construction.According to the Beihai comprehensive regional geological survey report,Beihai City is dominated by the coastal plains.The types of soil are mainly fills,muddy soils,sands,and cohesive soils.The type of groundwater is mainly the upper layer of water,diving,and confined water.The types of foundation pit support structures are mainly pile support structures,cement soil wall support structures,and soil nail wall support structures.(2)According to the case study of 18 foundation pit support projects in Beihai City,the main influencing factors of the safety of the foundation pit in Beihai City were analyzed using the analytic hierarchy process.The degree of influence from large to small was the depth of foundation pit excavation,soil type,and foundation type respectively.Pit support structure,type of groundwater combination,pit size and depth ratio,pit drainage method,foundation pit excavation method.A safety risk assessment method for foundation pits,the Composite Impact Index Method for Foundation Pit Engineering(PEIC),was proposed.(3)The method of precipitation in the coastal areas of Guangxi has a great influence on the stability of foundation pits.Generally,the effect of centralized pumping to lower the water level in the foundation pit is actually worse than the precipitation at the well around the pit.Therefore,the well-point precipitation method is often used.(4)When the foundation pit wells are dewatered to the bottom of the foundation pit,the overall stability factor K_S and anti-overturning stability factor K_d are at a relatively large value,which is beneficial to the safety of the foundation pit.The water level in the foundation pit after well point precipitation should be lower than the bottom 0-1m.