Study On Judgement And Control Of Risk Of Metro Foundation Pit Excavation Under Complex Environment

In recent years,although the deep foundation pit project risk management system had been continuously improved,different levels of subway construction risks occurred from time to time.It was due to the diversity of geological conditions,the complexity of the surrounding environment and the ambiguity of the deformation mechanism.Especially for the area of Zhangzhuang Road,Dikou Road and Beiyuan Street in Jinan City,it was urban development old town of Jinan Citym whose terrain was relatively low.The Qianfoshan fault zone and the Cultural Bridge fault zone were well developed and the geological conditions were extremely complex in the area above.The silty clay being formed by the backfill had characteristic of low bearing capacity and the weak force between the soil particles,which increased the risk of excavation of deep foundation pits.In addition,the area belongs to the old urban development area of Jinan City,long construction age is relatively,relatively weak basic form of the structural form and complexity of municipal pipeline installations undoubtedly must increase the risk level of excavation and construction of subway pits.Improper handling might easily lead to cracking and tilting of adjacent buildings and municipal pipelines,and even serious collapse and fracture risks.Therefore,it was very difficult to carry out deep risk assessment and control of deep foundation pit excavation in complex geology and surrounding environment.And it had a huge engineering significance.This project was analyzed by Baohua Street Station of the Jinan rail transit R2 line: Firstly,The project geology,hydro-geology,and surrounding environmental risks were mainly described.The risk classification criteria were proposed and the risk level is divided.On this basis,a comprehensive evaluation of the construction risk of subway foundation pits was conducted in the method of level-fuzzy evaluation.The assessment results showed that the risks were high.Additionally,Taking the risk of excavation of foundation pits being caused by engineering geology and hydro-geology and the technical characteristics and applicable scope of underground continuous walls,bored bite piles,bored piles and high pressure jet grouting piles,and SMW construction piles into account,the design project was put forward.Then,the design project was optimized in method of the grey relational theory.Finally,the design scheme selection was verified through field tests,pile inspection,and post-excavation verification.Furthermore,we described in detail the inadequacies of the additional stress method in calculating the deformation of building structure and pipeline during excavation of foundation pits,and dialectically analyzed the rationality of additional displacement methods.And based on this method,the deformation of adjacent buildings and municipal pipelines of Baohua Street Station was forecasted and analyzed.Considering the warning of deformation of long distance passenger transport center and heat iron pipes,the deformation control technology of "adding support stiffness + new recharging measures + new grouting was proposed,which effectively controlled deformation and ensured the safety of the project.