Study on calculation method of multi-layer opposite supports foundation pit considering displacement earth pressure
[Objective]With the increase in excavation depth of foundation pit and the strict requirements of surrounding environ-ment of foundation pit,the internal support system is gradually becoming the most main support form of foundation pits.Therefore the calculation theory of multi-layer opposite supports considering displacement earth pressure and construction process is studied.[Methods]Firstly,the displacement earth pressure model proposed by Zai-Mei is improved,and a composite curve is adopted to fit to the relationship between the displacement with earth pressure,and the displacement earth pressure formula is derived.Sec-ondly,a new simple calculation method for establishing the total stiffness matrix of the finite unit method of the row piles rod sys-tem is proposed based on the bending moment and shear force static equilibrium conditions of the nodes.The method proposed can calculate the bilateral row piles together.Finally relying on engineering examples,the differences between the pile bending moment and shear force calculated by considering the displacement earth pressure and construction process with no considering the displacement earth pressure and construction process given in the Regulations are analyzed.[Results]The results show that the Rankine active earth pressure recommended by the Regulation in the calculation examples of this paper is about 16%to 32%smaller than the displacement earth pressure load of this paper,and it is verified by engineering examples,in which the calcula-tion method of the Regulation is 10%smaller than the maximum bending moment of the monitoring data,and the maximum dis-placement is 14%smaller than that of the monitoring data.The method of this paper is 4%larger than the maximum bending mo-ment and 6%larger than the maximum displacement of the monitoring data.[Conclusion]The results show that there are large differences between the two method,which should be emphasized.For the buttress type supporting pile structure,when both sides of the geological conditions are similar to both sides of the supporting pile to the pit displacement,this displacement is mainly by the compression deformation of the support beams,the displacement is very small,so the earth pressure load acting on the supporting pile is closer to the static earth pressure rather than the norms of the active earth pressure,so it is more than rea-sonable to produce the result of this papers calculations examples.This method is applicable to the calculation and analysis of any layer of the support system.
excavation depth of foundation pitopposite supportsupporting piledisplacement earth pressureconstruction processfinite rodnumerical simulation
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