| At present,our cities are vigorously developing in the direction of modernization.The deep and large foundation pit project can be seen everywhere in the city,which makes a large number of related scientific researchers gradually deepen the deep and large foundation pit project research.In recent years,the secant pile supporting structure has been used in the construction of the Lanzhou Rail Transit.This new type of foundation pit enclosure structure can be well adapted to the geological conditions of Lanzhou area and its low cost meets the economic conditions of Lanzhou area.Therefore,the research on the secant pile supporting structure not only has scientific research value,but also can meet the requirements of engineering practice.According to the geological environment of Lanzhou area,this paper studies the system of secant pile supporting structure.After the research,the main conclusions are as follows:(1)The secant pile supporting structure under the same length of the supporting pile and the water stop pile is equivalent to an underground continuous wall structure.According to the theory of horizontal load deformation of the support pile,the deformation coordination effect of the crown beam on the support pile and the water stop pile in secant pile supporting structure is considered and derived the deflection curve equation for calculating the displacement of secant pile supporting structure is given.The equation is solved by the finite difference method,a deep and large foundation pit project in Lanzhou is simulated using finite element software.Comparing the calculation results of the finite element with the calculation results of the method in this paper,analyzed the results and concluded that the calculation results are similar to the model results.(2)According to the typical foundation pit engineering project of the system of secant pile supporting structure in Lanzhou,using the Plaxis 3D finite element analysis software which is commonly used in geotechnical engineering research for calculation.The project site pit monitoring results were studied and summarized,the deviations between the monitoring results and the finite element calculation results were systematically analyzed.Through research,it can be concluded that the supporting structure of occlusal piles with prestressed anchor cable is suitable for Lanzhou area;the supporting structure,surrounding soil and adjacent buildings(structures)can interact with each other and there is a cooperative deformation relationship;The water stop pile contributes to the rigidity of the overall supporting structure.(3)The design parameters of the system of secant pile supporting structure candirectly affect the horizontal displacement of the occluded pile.The structural design parameters in the system of secant pile supporting structure are analyzed by the method of control variables,it is concluded that the increase in pile diameter or occlusal amount will make pile body deformation increased;reduced anchor cable spacing can control pile body displacement and reduce changes in pile body horizontal displacement;increased anchor cable prestress or crown beam stiffness can reduce pile body horizontal displacement changes;the influence of pile body horizontal displacement and cable angle of anchor is relatively small.(4)In the construction process of secant pile supporting structure,due to the inclination of the pile body,the deviation of the hole position and,the expansion and contraction of the diameter,the support pile and the water-stop pile will be poorly engaged,which will affect the foundation pit.According to a deep and large foundation pit project in Lanzhou,secant pile supporting structure with pile body deviations is established.The calculation results show that the deviation causes the rigidity of the water stop pile to decrease,the pile body displacement is larger than the adjacent pile body leakage,even affects the stability of the foundation pit.It is proposed to solve this problem by increasing the amount of secant. |
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