Study On The Influence Of Karst Cave And Its Treatment Measures On The Stability Of Pile Foundation

With the rapid development of China’s economy,there are more and more infrastructure construction projects.Many bridge projects are built in karst areas.Pile foundation has strong adaptability under bad geological conditions or complex engineering environment,high bearing capacity,and strong ability to transfer the load from the superstructure to the lower hard soil,so pile foundation is usually used in bridge engineering construction.Karst cave and its treatment measures have great influence on the stability of bridge pile foundation,but there are few related researches,which can not meet the needs of practical engineering.Based on this,combined with engineering examples,this paper uses finite element software to study the influence of karst caves and their treatment measures on the stability of pile foundation.The main research contents are as follows:(1)The related theories of pile foundation stability analysis are studied,and the calculation model of pile foundation stability is discussed.The soil resistance of pile side is equivalent to soil spring acting on pile side.Considering the influence of soil resistance on the stability of pile foundation,the finite element software was used to simulate the horizontal static load test,and the horizontal displacement of pile top under different levels of horizontal load was calculated.Two calculation methods are proposed to convert the horizontal resistance proportional coefficient of multilayer foundation soil,namely the standard method and the weight function method.(2)Taking pile foundation construction project of Fankou Park Bridge as the research background,numerical simulation is carried out by using finite element software ABAQUS,and the pile-soil model is converted into pile-soil spring model in the modeling process.Common methods of soil spring stiffness calculation are discussed,and the more common " m " method is finally used to calculate the soil spring stiffness.In order to ensure that the soil spring can truly simulate the influence of horizontal force on pile foundation,the reasonable distance and quantity of soil spring are discussed in the modeling process.(3)In the establishment of numerical model,the influence of karst cave on the stability of pile foundation is considered.Two methods are proposed to consider the realization of karst cave in ABAQUS.The first method is to consider the karst cave directly according to the height and position of the karst cave,the stiffness of soil spring placed on the pile side is set to 0.The second method is to reduce the thickness of the soil layer at the location of the cave to some extent,and then calculate the stiffness of the soil spring by using the reduced thickness of the soil layer equivalent to the stiffness of the soil spring with the cave.(4)The stress and deformation of pile body of pile foundation are analyzed under the condition that pile foundation runs through karst cave.Several common karst cave treatment measures in karst area are summarized,and the stability of pile foundation under different karst cave treatment measures is analyzed by numerical simulation,and the effects of different karst cave treatment measures are obtained.The pile-soil spring numerical model is used to study the relationship between the horizontal resistance coefficient of foundation soil " m " and the stability of pile foundation.(5)On the basis of engineering examples,this paper conducts quantitative and qualitative analysis on some main factors that affect the stability of pile foundation in karst area,such as pile diameter,pile elastic modulus,pile weight,cave height,cave number and so on,and further studies the stability of pile foundation in karst area.Through grey correlation analysis of influencing factors of pile foundation stability in karst area,the sensitivity of each influencing factor to pile foundation stability in karst area is analyzed,and the sensitivity of influencing factors to pile foundation stability in karst area is ranked.