The Study Of Safety State Quantification Analysis Method Based On The Measured Data Of Deep Foundation Pit Supporting Structure

With the development of city construction, the increase of population density,high-rise buildings continue to rise, the use of underground space is more and morepopular in recent years, which have made a large number of deep foundation pitemergence. However, deep foundation pit is very uncertain and difficult, accidentsstill occur from time to time. Facts have proved that, monitoring data have obvioussigns before the accident, so this paper study the pit safety quantitative evaluationbased on measured data, in order to achieve dynamic security control of foundationpit construction. In this paper, the pit safety evaluation index, the deformation andstress rule of retaining wall and common support system, and the risk assessmentmethod based on measured data is studied. The main work and conclusions are asfollows:1. This paper summed up the current several reasons for major foundation pitaccidents by statistics large number of accident cases, and studied monitoring dataresponse when accidents occur, at last selected suitable monitoring project as safetyevaluation index by comparing predictability, sensitivity, and feasibility.2. The simplified calculation formula of bored pile ultimate moment was derived,and the relationship between ultimate bending moment and reinforcement ratio ofcommon bored pile were calculated. It introduced the principle of calculating ultimatemoment based on displacement data, and pointed out that the key was the calculationof curvature from displacement curve fitting and bending stiffness of retaining wall. Italso studied practicability of several methods for moment combining with theengineering examples, and evaluated the retaining wall stress safety with the selectedmethod of calculating moment. Then it counted up the displacement monitoring dataof bored pile foundation pit in Qingdao area, and suggested the deformation control standard in stratum combined with soil and rock. Finally, it established the safetyevaluation standard based on deformation and internal force control index.3. It made a discussion about the classification of common foundation pitsupporting system according to materials and structures, and analyzed the failuremode and mechanism of supporting system. Then it summarized and analyzed thevariation of axial force in the construction process, as well as the influence of prepressand overbreak. Next it made the stress analysis of the single span support, double spansteel support, double span concrete support, founded out the key safety control indexof mentioned several kinds of support, and showed the calculation process of eachindex. At last, the support safety evaluation index system was established.4. With brief comparison and analysis of common risk assessment methods, itdecided to use AHP and expert investigation method for safety evaluation offoundation pit. Then it established the safety evaluation index system classifyingclearly of foundation pit based on the study of single factor evaluation index. And itmade a detailed discussion about foundation pit safety evaluation based on measureddata from the aspects of evaluation methods, evaluation process; afterwards it verifiedthe conclusions by applying in practical examples. The fact proved that safetyevaluation based on test data not only made the evaluation results more credible, butalso could achieve the macroscopic safety evaluation of foundation pit.