Research On Pile-soil Spacing Effect Of Rigid Long-short Pile Composite Foundation Under Rigid Raft

Under the same settlement, there is a difference in bearing capacity betweensmall raft long-short pile composite foundation and large raft long-short pilecomposite foundation because of the pile-soil spatial effect. This difference makessome problems in theory when using the results of composite foundation (4piles)that under the test of static load to verify the long-short pile composite foundationbearing capacity and settlement. Haveover, for most of the actual project, only thestatic load test of four piles composite foundation or single pile compositefoundation is done limited by the space and loading conditions. In order to solve thecontradiction between theory and reality, the pile-soil spatial effect need to bestudied.This paper based on CFG pile and PHC pipe long-short pile (4piles) compositefoundation under the test of static load. Firstly, through the method of numericalsimulation to discuss the problem of the pile-soil spatial effect, the correlationbetween the pile-soil spatial effect and the capacity of the rigid long-short pilecomposite foundation is studied. This paper has analyzed the changing rule ofload-settlement, pile-soil stress, pile end resistance ratio, pile penetrationdeformation, with different number of piles in rigid long-short pile compositefoundation, and has given the trinomial fitting function. Results have shown that,under the same load level, the more the numbers of piles, the settlement of bearingcounter is larger.With the increase of load value, the differential settlement isgradually increasing under the condition of the same load. The bearing capability oflong-short pile composite foundation is smaller with the amount of piles is largerunder the condition of same settlement. When the size of board becomes bigger orthe amount of piles is bigger, horizontal displacement in the superficial and deep soiland diffusion scope of stress are increasing; the maximal horizontal displacement ispassing to the depth of soil; the stress of top and bottom of long and short piles isdecreasing. The difference of stress among the different models under the conditionof the same settlement with settlement is increasing. For long piles, the stress of thetips is gradually decreasing, in contrast, the short piles is increasing. The ratio of tip resistance is increasing and the upper penetration deformation of long and short pilesin the central place is smaller, while in the corner place the upper penetratedeformation is bigger and the download penetration deformation is smaller for thelong piles.Then, the rule is explained that effect of the length, space of piles and thicknessof bedding cushion on load-settlement, pile-soil stress, ratio of tip resistance andupper penetration deformation, and the influence degree and change rule areevaluated. The research indicates that the effect of pile length on the end and topstress of short piles and upper and download penetration deformation is obvious. Butthe rules of effect of load-settlement and tip stress of piles on the amount of pilescan be ignored. Unde the condition of same settlement, the effect of the change ofpile space on capacity is increasing with the load is increasing. The effect of theamount of piles on soil stress of pile top and ratio tip resistance is obvious and theinfluence is gradually smaller with the amount is bigger, while the effect on thedownload penetration deformation, top and bottom stress of piles and tip resistancewill be ignored. The effect of the thickness of bedding cushion on stress of pile topand bottom is obvious under the same settlement, and the influence is graduallysmaller with the amount is larger. While the factors including load-settlement, soilstress of top and bottom of piles, ratio of stress top to stress bottom, penetrationdeformation of top and bottom piles can be ignored.Lastly, the calculation method about downward penetration deformation of longpiles and underlying stratum additional stress is proposed through combining theBoussinesq and Mindlin. The theory about settlement calculation of rigid long-shortpile under rigid foundation is suggested which is based on the idea of controllingsettlement of long piles and is taking into account spatial effect of pile and soil,upper and downward penetration deformation, compression deformation of cushionin the top of long piles and compression deformation of under soil in the tip of longpiles.