Research On The Safety Index System And Risk Assessment Of Structures Adjacent To Deep Foundation Pits

Nowadays,urban land resources are becoming more and more tense.High-rise buildings are increasing day by day,and building foundation pits are also developing in a larger and deeper direction.The surrounding environment of deep foundation pit projects in these cities is often complicated,and there are often various existing structures,such as subway tunnels,high-rise buildings,municipal pipelines,urban roads,and viaducts,which make the construction of deep foundation pits face many disadvantages.Therefore,it is significant to establish a safety index system for adjacent structures in deep foundation pits and to make safety risk assessments on adjacent structures on this basis.A series of researches have been conducted on the index system and risk assessment model of the structures adjacent to the deep foundation pit,and the engineering example verification has been carried out on the basis of the deep foundation pit project of Shanghai Xujiahui Project.The safety index system of structures adjacent to deep foundation pits includes three first-level indexes including the condition of the structures,geological conditions,and foundation pit excavation conditions.Among them,the condition of the structures considers five types of structures such as tunnels,buildings,underground pipelines,pavements,and bridges,including a total of 16 second-level indicators,while geological conditions and foundation pit excavation conditions include 4 second-level indicators respectively.On this basis,the evaluation standards for the safety levels of the above-mentioned second-level indicators are determined,which provides a systematic index system for the safety evaluation of structures adjacent to deep foundation pits.In the study on the determination of the evaluation index weights of structures adjacent to deep foundation pits,firstly,the rough set theory method is determined as the objective weight determination method in this study.The principle steps of the rough set weight determination method are described in detail:(1)Collect and sort large quantities of engineering data;(2)Discrete the engineering data,and establish a decision information table;(3)Perform knowledge reduction processing on the decision information table;(4)Calculate the importance ratio of each condition attribute,and finally normalize it to get the objective weight based on ROSETTA software.Then according to the above steps,the objective weight values of the indicators of tunnels,buildings,underground pipelines,urban roads and bridges are obtained.In the research on the risk assessment model of structures adjacent to deep foundation pits,three risk assessment methods used in this study are analyzed and compared,so as to adopt the set pair analysis theory evaluation method as the continuity risk evaluation method of the structures adjacent to the foundation pit.On this basis,the safety index system of the structures adjacent to the foundation pit and the objective weight of each structure indicators are substituted.Based on the set pair analysis theory and the connection number calculation formula,the total index connection number are solved.Then the normalization process is performed to obtain the precision evaluation scores of various adjacent structures.Finally,the safety status of the structure is judged according to the safety score sheet of the adjacent structures.In this way,a risk assessment model for structures adjacent to deep foundation pits is established,covering five types of structures such as urban tunnels,buildings,underground pipelines,pavements and bridges.Finally,the safety index system of structures adjacent to deep foundation pits,the objective weight of the structures and the risk evaluation model are applied to the deep foundation pit of the Shanghai Xujiahui Center Project,and the engineering overview,the adjacent environment,the foundation pit excavation and support conditions,the soil and hydrological conditions are described so as to determine that the adjacent structures that need to be considered in this project are tunnels and buildings.Then substitute the above-mentioned data into the risk evaluation model to determine the applicability of the evaluation model.The results show that the safety score of the adjacent tunnel is 50.4,and the score of the adjacent buildings is 63.5,both of which are in good condition and belong to the B grade.In addition,the accuracy and credibility of the risk evaluation model are verified.The results show that the risk evaluation score is basically consistent with the actual safety status change trend of the adjacent tunnels,so this risk evaluation model has a high degree of accuracy.