Research On Optimization Design Of Foundation Reinforcement For Static Pressure Underpinning Piles Of Existing Multi-storey Buildings

Most of the multi-storey building structures adopt a strip foundation,which has poor structural integrity and is prone to uneven settlement under the influence of external factors.The static pressure-supporting pile foundation reinforcement technology can make full use of the characteristics of the strip foundation,and compensate the foundation bearing capacity by the replacement pile,which can effectively prevent the uneven settlement of the building.The paper aims at the optimization of the existing multi-storey building foundation reinforcement engineering with static pressure-supporting piles under the strip foundation,and the optimization of the bearing capacity of the static-pressure piles and the pile spacing.The main contents are as follows:（1）The design principle of bearing capacity compensation for static pressure-supporting piles of multi-story buildings is studied,and the design equation for bearing capacity compensation of static pressure-supporting piles is established:F_a’=n?R_a≥F_k+G_k-P_o?A_o,which correct the traditional calculation formula for the bearing capacity of existing multi-story building foundations,and to make it more in line with the actual needs of the project.By analyzing the design points of the bearing capacity compensation of static pressure-supporting piles,the content of the optimal design of static pressure-supporting piles is determined:the reasonable prediction of bearing capacity of static-pressed piles and the optimization of pile spacing.（2）The relationship between static pile pressure and single pile bearing capacity is discussed.The nonlinear fitting equation of static pressure pile termination pressure,pile length and single pile bearing capacity is established by using L-M optimization algorithm:Q_uk=1.527L×R_sm÷（2+L）.Prediction method for bearing capacity of static piles.（3）According to the fitting equation of bearing capacity of static piles,the bearing capacity compensation design of static pressure-supporting piles is carried out.The influence of soil compaction effect of static piles under different pile lengths on the horizontal displacement of pile soil is discussed.The recommended value of the minimum pile spacing of the pile is 6d.Then the numerical simulation is used to analyze the bearing performance of the reinforced concrete strip foundation and the upper brick masonry under the support of the understand pressure,and according to the upper part of the multi-storey building The size of the structural load is used to obtain the reasonable range of the spacing of the static piles.（4）Taking the foundation reinforcement project of a multi-storey building with static pressure underpinning in the loess area of Shanxi Province as an example,the optimal design of the static pressure-supported pile foundation reinforcement was carried out from the aspects of reasonable prediction of bearing capacity of static pile and single pile spacing optimization.The feasibility of the optimal design of static pressure underpinning piles is verified from the measured data of single pile bearing capacity,the settlement of static pressure piles,the horizontal displacement of piles and the development of cracks in brick masonry.（5）On the basis of the existing theory and engineering practice of static pressure-supported pile foundation,the paper can improve the foundation reinforcement cost by improving the prediction method of the bearing capacity of the static pile and optimizing the pile spacing.About 8%can provide reference for similar foundation reinforcement of existing buildings.