Experimental And Numerical Simulation On Behavior Of Pre-Stressed High Strength Concrete (PHC) Nodular Pile In Soft Soil Area

In the eastern coastal areas of China,there are large amounts of deep soft soil layers,and the poor engineering properties of soft soil result in low skin friction and base resistance of piles.The bearing capacity of prestressed high-strength concrete(PHC)pipe piles cannot be fully utilized in deep soft soil areas.The PHC nodular pile is a new type of pile,which is developed based on conventional PHC pipe pile.The nodule exist along the PHC nodular shaft can improve its bearing capacity.In recent years,PHC nodular pile has been successfully applied in building and transportation engineering projects in soft soil areas.However,the research on the bearing mechanism and settlement characteristics of PHC nodular pile is limited This paper investigates the engineering applicability of PHC nodular piles in soft soil areas,examines its bearing characteristics and load transfer mechanism,studies factors affecting the bearing capacity of the pile through field static load tests and ABAQUS finite element numerical simulations,and proposes a single pile bearing capacity calculation formula to provide a theoretical basis for the design and application of PHC nodular piles in actual engineering projects.The main conclusions include:(1)Field static load tests comparing the bearing performance of PHC nodular piles and PHC pipe piles reveal that 47 m long 550(600)mm PHC nodular pile in soft soil areas have an ultimate bearing capacity 1.23 times greater than PHC pipe pile with the same outer diameter.The settlement variation of PHC nodular piles is uniform,indicating strong safety in foundation engineering in soft soil areas.(2)A three-dimensional model of PHC nodular pile is established using ABAQUS finite element software,and the pile bearing mechanism was analyzed.During the initial loading stage,the skin friction of the tubular part gradually played a role,with the soil in the inclined lower part of the nodule subjected to compression.This strengthened the skin friction around the pile,eventually reaching the ultimate value.As the relative displacement between the pile and soil continued to increase,the upper soil of the nodule becomes hollow,and the stress reduction phenomenon gradually reduced the skin friction at the end of the tubular part.(3)The bearing characteristics of the nodular part are obtained through numerical simulation analysis: the bearing capacity of the nodular part continuously increases with the increase of applied load,eventually becoming the primary contributor to the pile bearing capacity.When the single pile reached its ultimate bearing capacity,the contribution of the nodular part to the total bearing capacity reaches 60%.Additionally,the bearing capacity of each nodule in the same soil layer increases with the increase of depth.The upper neck of the nodule is affected by the negative skin friction of the surrounding soil,the end of the nodular provides skin friction resistance,and the lower neck of the nodular provides tip resistance,which plays the main role of the total bearing capacity.PHC nodular pile can be known as a friction multi-node end-bearing pile.(3)Nodules effectively improve the ultimate bearing capacity of PHC nodular pile,and the effect is more significant with smaller nodule spacing.The load bearing ratio of the nodule part decreases with increasing nodule spacing in the limit state.Larger nodule height or nodule diameter results in greater ultimate compressive bearing capacity for PHC nodular pile,and the load bearing ratio of the nodule part is about 59% in the limit state.The larger the nodule inclination angle,the smaller the ultimate compressive bearing capacity of the PHC nodular pile,and the load bearing ratio of nodule part has a sharp increase between 26.6 ° and 45 ° of the nodule inclination angle.(4)In actual engineering design,the preferred method to improve the ultimate bearing capacity of PHC nodular pile is to reduce nodule spacing,followed by reducing nodule height,decreasing the nodule inclination angle,or increasing nodule diameter.To improve the engineering economy of PHC nodular pile,the preferred method is to reduce nodule height,followed by reducing nodule spacing or inclination angle.(5)A formula for the vertical bearing capacity of a single PHC nodular pile is proposed,considering the bearing and force characteristics differences of PHC nodular pile.The accuracy of the formula is verified by field static load test results.