Study On Analysis Method For Grouped Pile Foundation Of Bridge In Slightly Stable Slope Area

As for highway engineering in mountainous areas,sometimes the related bridges are constructed along slightly stable slope.Under these circumstances,the pile foundation of the bridge should bear not only the combined load transmitted from the superstructure to the top of the pile,but also the potential landslide thrust force of the slope.Therefore,in terms of the grouped pile foundation in the slightly stable slope,based on the study of elastic foundation coefficient of local slope stratum in front of loading segment of the stabilizing piles,lateral bearing capacity of stratum surrounding the embedded segment of the piles,as well as embedded depth of the piles,the calculation method of internal forces and displacements of the grouped pile foundation is proposed via theoretical analysis and numerical simulation.The main analysis results are as follows:(1)Based on the two-stage foundation coefficient method of stabilizing piles calculation(loading segment with m method and embedded segment with K method),combined with the upper bound method in plastic limit analysis,and taking the proportion coefficient of foundation coefficient in the infinite condition of the soil mass in front of the loading section as a benchmark,the calculation method of the proportion coefficient of foundation coefficient is determined under the condition that the front side of the stabilizing piles is a finite soil mass,and the foundation system is obtained.Quantitative relationship between proportional coefficient of number and slope of soil in front of loading segment.The proportional coefficient of the foundation coefficient decreases nonlinearly with the increase of the slope of the soil in front of the loading section.(2)Based on the upper bound method of plastic limit analysis,the formula for calculating the lateral ultimate resistance of the stratum in the embedded section of stabilizing piles with inclined sliding surface is deduced.Then,according to the relationship between the embedded depth of the pile determined by the elastic foundation beam method and the lateral resistance of the stratum,the method for calculating the minimum inserted depth of the pile in this case is established.Minimum inserted depth of pile increases nonlinearly with the increase of inclination angle of sliding surface.(3)Aiming at the grouped pile foundation with symmetrical arrangement of 3×3 type,the plane rigid frame model is adopted.Considering the interaction between concentrated load on the top of pile cap and landslide thrust on the side of pile,the power series method is used to deduce the foundation based on the compatibility condition of displacement at the top of each pile and the static equilibrium condition of rigid pile cap.Formulas for calculating displacement,rotation angle,shear force and bending moment of piles.Finally,the internal force and displacement of pile group foundation are determined by superposition method,considering the continuity of internal force and displacement at the interface between loading segment and block,and the relevant expressions are deduced.(4)Combining with an engineering example,the concrete theoretical calculation and analysis are carried out,and the results are compared with those of FLAC3 D numerical simulation.The results show that there is a certain gap between the results of the two methods at the top of the pile,but at the deeper position from the top of the pile,the difference between the results of the two methods is small,and the theoretical results are relatively conservative.The calculation methods of elastic foundation coefficient of local slope stratum,minimum inserted depth of pile and the related grouped pile foundation proposed in the dissertation can provide guidance and reference for practical engineering,which plays an important role in theoretical analysis and engineering application for the structure.