Dynamic Prediction Of Deep Foundation Pits Surrounding Surface Subsidence In Soft Soil Area

Based on50foundation pits engineering examples data’s statistics analysis, current construction monitoring data yield is not high. The reason is a common result of the construction technology personnel quality, time, cost, design human factors and foundation pit engineering itself uncertainty factors.Because at present the large-scale subway construction projects are built in Nanjing、Suzhou and Wuxi cities of South Jiangsu Province, and Changzhou subway has also been projected, so in South Jiangsu Province subway construction projects will last for a long time. In order to give some references for the design and construction of metro projects in this region, the existing literature data was collected, based on many metro deep foundation pits of South Jiangsu Province, the deformation rules of about10～20meters metro deep excavations which maintenance structures are diaphram wall or secant piles were obtained by using experience statistics. The position of maximum lateral displacement lies between (0.57h～1.13h) and is about near the excavation surface, the rang of maximum surface settlement lies between (0.62‰h～3.17‰h),and the linear relationship of maximum lateral displacement and the maximum surface settlement were presented. These results were compared with the experience statistic data in Shanghai, related data has similarity and difference between South Jiangsu Province and Shanghai. These conclusions will be contributed to the future construction of subway stations in South Jiangsu Province.Gompertz and Logistic models are growth curves which are like inversely S-shaped, often are used in production and business areas. Gompertz and Logistic derivative models are parabolic and similar with the curves of deep foundation pits. After Gompertz and Logistic models are derivatived and adjusted, δ(x)=ace(b-cx)exp(-e(b-cx)) and δ2(x)=abcexp(-cx)[1+bexp(-cx)]-2of the ground surface settlement formulas of deep foundation pits surrounding are acquired. In order to improve the calculation accuracy, Weighting model δ(x)=w1δ1(x)+w2δ2(x) of subsidence prediction formula of deep foundation pit surrounding surface are concluded. Based on large quantities of measured data, formula parameters value scopes of b, c, w1and w2are got. It shows that the prediction precision is high with five engineering examples. They are simple and practical methods of foundation pit surface subsidence prediction. It shows that the prediction precision is high with the engineering example.Gompertz and Logistic’models don’t need maximum lateral value as prediction conditions.the prediction calculation steps of the formula was given, Parameters are acquired by testing different work conditions and using dichotomy. It changes that present methods for selecting parameters have big discretion, and it is easy for designers to select parameters value, the value of the parameters eliminates human influence factors, is more reasonable. The engineering example shows that the formula is accurate.