Finite Element Analysis Of Deep Excavation Pit On The Bearing Behavior Of Uplift Piles Beneath The Basement

In this paper, the stress characteristics of pulling resistant pile of the deepfoundation pit excavation are studied using Cam-Clay model of ABAQUS. Thebottom of pile and single pile at different positions are quantitatively analyzedrespectively by using the two-dimensional axisymmetric model and three-dimensionalmodel, and use three-dimensional finite element model to simulate bearingcharacteristics of the pulling resistant pile group in the sheet strip pit bottom. Themain research work and results are as follows:(1) For the single uplift pile at pit bottom, considering the pile length, pilespacing, the depth of excavation and the width of excavation, and considering that pilegrouting effects on uplift pile bearing capacity. Analysis shows: the length and thediameter of pile can significantly influence the bearing behavior of uplift piles afterexcavation; Excavation depth and width combined effect bearing capacity of upliftpile at pit bottom, When the ratio of excavation width and depth of the excavation isconstant, pile length is the main factor affecting uplift capacity; The pile grouting cansignificantly improve the pile bearing capacity, especially pile length is longer, pilegrouting only improve limit side friction values of the body at the bottom of a certainlength, therefore determine a reasonable length of grouting is necessary.(2) For the three-dimensional model, consider the effect of single pile in differentlocations of pit bottom on pullout characteristics. Analysis shows that isdifferent,which is the ultimate uplift capacity of uplift pile after excavation atdifferent positions of pit bottom, the center pile is smallest, the side pile is next, thecorner pile is the biggest, the excavation area and pile length largely effect thecapacity, the greater area, the gap of center and corner piles is larger, the pile longer,the gap of center and corner piles is smaller. Finally, consider the pile grouting, andfind that grouting has the most obvious effect on the central pile, determine thereasonable length of grouting in each location is also very important.(3)Group pile’s uplift bearing capacity is different from single pile’s, and theuplift bearing capacity of the pile group is different after the excavation is completed,the uplift bearing capacity of three times the pile spacing is minimum, six times thepile spacing is maximum, which is basically close to the pullout bearing capacity value of single pile. The uplift bearing capacity difference of pile groups in differentpile spacing in different position is relatively large, but this kind of difference isconstantly shrinking as the pile spacing increases. From the point of view of the sidefriction resistance development degree, the influence degree of pile group effect ofpile bottom center pile is greater than the side pile, along with the increase of pilespacing, pile group effect is gradually weakened, five times of the pile diameter canbe regarded as the critical pile spacing of the pile group effect. The longer pile lengthis, the greater ultimate pull load on the pile is, with the increase of the length of thepile, the bearing capacity of center pile under the work load first increases and thendecreases, while the side of the pile is always reduced, pile group effect is a majorfactor affecting the force of center pile. Pile grouting can effectively improve the pileuplift bearing capacity, under the same work load, the bearing capacity of the pilebody of side pile or center pile without grouting was greater than that of grouting,butin different position capacity is basically unchanged.