Research On Bearing Capacity Efficiency Factors Of Plies And Soil Between Piles In Rigid Long-short-pile Composite Foundation

Rigid long-short-pile composite foundation is a new type of foundationtreatment form which appears in recent years and it is used more and more widely inmulti-high story buildings and in the treatment of high-fill roadbed. Meanwhile, it hasbeen written into the2012version “Technical code for treatment of buildingfoundations” formally. However, in the formula to calculate the vertical characteristicvalue of bearing capacity, in order to know the contribution of rigid long piles, rigidshort piles and soil between piles to the bearing capacity of composite foundation, thebearing capacity efficiency factors of single pile and soil between piles should becalculated. Based on engineering experience, the national code can only giveempirical value range. When it is used in engineering practice, local engineeringexperience should be taken into account, so the difficulty of using bearing capacityefficiency factors significant increases. As a result, the applications of such kindengineering practices are limited.In this paper, the main research focuses on the bearing capacity efficiencyfactors of long piles, short piles and soil between piles. Firstly the extended definitionof bearing capacity efficiency factor is given, then using the3D numerical simulation,based on the principle that the bearing capacity is judged by the foundation settlement,the influences of pile length, pile diameter, pile distance, cushion modulus andcushion thickness on the bearing capacity efficiency factors of single rigid short piles,long piles and soil between piles are analyzed. Eventually, based on the results ofsimulation, the equations set which could calculate the bearing capacity efficiencyfactors of piles and soil can be acquired. The conclusions acquired in this paper are asbelow:(1) When the length of long pile does not change, the variation of short pilelength has little influence on the efficiency factors of long piles and short piles. Withthe increase of pile diameter, cushion modulus and with the decrease of cushionthickness, the bearing capacity efficiency factors of piles increases. Also, the bearing capacity efficiency factors of long piles increases and the short piles decrease with theincrease of pile distance.(2) When the length of long pile does not change, the bearing capacityefficiency factors of soil between piles increases with the increase of short pile length,pile distance and cushion thickness, decreases due to the increase of cushion modulusand changes little with the variation of pile diameter.(3) In the loading phase, the bearing capacity efficiency factors of pilesincreases with the increase of foundation settlement while the corresponding data ofsoil between piles changes little.(4) Based on the numerical simulation conclusions, the simplified distributionform of pile lateral friction and single pile calculation unit are proposed. Eventually, aequation set which can calculate the bearing capacity efficiency factors of piles andsoil in rigid long-short pile foundation is given.