Discussion On Calculation Method Of Bearing Capacity Of Rigid Pile Composite Foundation Based On Pile-soil Deformation Coordination

Rigid pile composite foundations are widely used because they can make full use of the bearing capacity of natural foundations,and have the advantages of less settlement and reliable bearing capacity.At present,the bearing capacity of the rigid pile composite foundation is generally estimated by the formula recommended by the code from the composite bearing capacity of the pile and the soil between the piles.For settlement calculation of rigid pile composite foundation,equivalent compression modulus is mostly used,and then empirical coefficient is used for correction.In engineering practice,there are still some unresolved problems that are worthy of study.For example,for determing the characteristic value of the bearing capacity of the soil between the piles in the layered foundation,there is no effective solution currently.For some hard soil or sand foundation,it is found that the bearing capacity of natural foundation considering depth and width correction is higher than that of composite foundation.Composite foundations with end bearing piles are used in some projects,which are different from friction piles required by the code.What impact will this have? These problems have caused confusion in practical engineering applications.In this thesis,based on the principle of the coordination of pile-soil deformation of the rigid pile composite foundation,the composite foundation is simplified as the resistance of the pile and the foundation soil according to the settlement and deformation coordination.It is considered that the bearing capacity of the composite foundation is the combination of the pile and soil resistance.The load-settlement curve of the composite foundation is calculated from this,and then the load-settlement curve of the composite foundation is used to determine the bearing capacity of the composite foundation considering the requirements of strength safety and deformation control,so as to solve the current calculation problem of the bearing capacity of the rigid pile composite foundation.The specific work is as follows:(1)For the problem of the bearing capacity of the soil between the piles in the layered composite foundation,the bearing capacity of each layer of soil in the layered foundation is different.It is difficult to take the bearing capacity of a layer of soil as the bearing capacity of the soil between the piles.In this thesis,the deformation coordination method is used to determine the resistance of the multi-layer foundation through the settlement of the composite foundation.The resistance is used as the bearing capacity of the multi-layer foundation,which can more reasonably solve the problem of the bearing capacity of the soil between the piles in the layered foundation.(2)For a case of hard soil composite foundation,the pile-soil deformation coordination method is used to comprehensively determine and evaluate the bearing capacity of the composite foundation based on strength safety and deformation control,and the results are compared with the standard method.The analysis results show that,for some hard soil foundations,the rigid pile composite foundation bearing capacity can be determined according to the settlement and strength requirements of the pile-soil deformation coordination method to avoid the situation where the natural foundation bearing capacity is higher than the composite foundation bearing capacity.(3)On the basis of the above research,the settlement curves are calculated and compared with theoretical calculation method,which reflects the bearing capacity characteristics of the two types of composite foundation differences.When end bearing piles are used for composite foundations,the soil settlement between the piles is smaller,and the bearing capacity of the soil is not fully exerted.The end bearing piles will share too much upper load.It is recommended to use friction pile composite foundations under general circumstances and the ability to adjust the load sharing of the pile and soil is more effective.(4)For the rigid pile composite foundation with high bearing capacity design requirements,based on the bearing capacity of the cushion layer,the reasonable control value of pile-soil stress ratio is proposed to ensure the safety of bearing capacity of composite foundation,which can provide certain reference for related engineering design.(5)Through two practical engineering case verification,the method in this theis can consider the principle of pile-soil deformation coordination and pile-soil load sharing.The calculation results are in accordance with the measured data,which verifies the feasibility and practicability of the method and this method is well used to evaluate the bearing properties of composite foundation under the actual foundation.