Research On Monitoring Technology And Fuzzy Comprehensive Safety Evaluation Of Deep Foundation Pit Engineering

With the vigorous development of China’s construction industry,deep foundation pit engineering is also developing to a deeper level.In order to ensure the safety of deep foundation pit construction,deep foundation pit monitoring is an indispensable control means.The requirements of Engineering Management on equipment cost,information technology and other aspects are higher and higher.The demand of deep foundation pit monitoring technology is growing,so the research on monitoring technology is imperative.Deep foundation pit and its surrounding environment are complex,and there are fuzzy and uncertain factors,which affect the safety of deep foundation pit.Safety evaluation of deep foundation pit is an effective way to ensure its safety.In this paper,the deep foundation pit monitoring technology is studied and discussed;Taking a deep foundation pit project in Hangzhou as the research object,the deformation of the deep foundation pit and its surrounding environment is monitored in the construction process,and the change law of the monitoring data is analyzed;Based on the monitoring data and inspection results,the fuzzy comprehensive safety evaluation of a deep foundation pit project is carried out.The main conclusions are as follows:(1)In this paper,the support axial force of a deep foundation pit project in Hangzhou is monitored automatically,and the monitoring value and the ambient temperature basically show a synchronous change trend.The accuracy of the automatic monitoring of support axial force is verified by comparing with the manual monitoring results.The research on the influence of the measuring distance of the sliding inclinometer shows that in the measuring section where the slope of the deep horizontal displacement test value changes little,the measuring distance can be appropriately expanded when the measuring result of the double guide wheel track is close to that of the double guide wheel track.Taking 1m as one time of the distance between rods,this paper studies the influence of the distance between fixed inclinometers based on the principle of deep horizontal displacement measurement.The results show that the reasonable choice of the distance between rods can reduce the number of sensors and the cost of equipment.(2)Taking a deep foundation pit project in Hangzhou as the monitoring object.The deep horizontal displacement changes with the excavation,and the displacement value is mainly in the range of-5mm～60mm,and the maximum value is in the range of 10m～12m;The settlement of surrounding soil increases first and then becomes stable with the construction progress;Under the influence of temperature and other factors,the support axial force shows a wave like up and down jumping trend;The variation law of groundwater level is basically the same,showing a downward trend as a whole,and the maximum cumulative value is 656 mm;All the monitoring values meet the requirements of design specifications,and the whole construction process is safe.In the process of inspection,cracks and other phenomena appeared on the ground,and some leakage points were found,which strengthened the on-site management.(3)According to the monitoring items and inspection contents of deep foundation pit,the safety index evaluation system is more comprehensive.Referring to the alarm value and expert evaluation of monitoring items,the grade evaluation interval is divided,the membership degree of monitoring and inspection indexes is determined,and the evaluation matrix and model are established.The foundation pit,surrounding environment,monitoring facilities and the overall situation are comprehensively evaluated,which belong to the safety level of grade IV,grade I,grade II and grade I respectively,and the scores are 52.4,82.4,85 and 66.6respectively,which quantitatively reflects the safety status of deep foundation pit engineering,and has important engineering application value.This paper points out the reasons for the decrease of safety score of deep foundation pit engineering,and puts forward some safety control measures to ensure the safety of deep foundation pit engineering.