| A large area of ultra-deep excavation pit means that the normal soil stress of theside of engineering piles which are excavated in the end are significantly reduced,meanwhile the bottom soil excavation resulted in the generation of a strong rebound,and it causes soil having an pull effect on the pile in great length from the top, but thelower part of the pile will produce down friction to balance the pulling force on theupper part of the pile,which resulted by soil pit rebound, the total length of the pileare in tension. Pit excavation led to the mechanical characteristics of the pilesignificantly different from a shallow excavation. The main research work and theresults of this paper are as follows:(1) Using ABAQUS software and the modified Cam-clay constitutive model, atwo-dimensional axisymmetric finite element model of the test single pile isestablished under three different conditions, the Influence on the pit bottomEngineering piles stiffness made by unloading effect and rebound effect caused by theexcavation is drawn through comparative study. Comparative analysis showed that:caused by soil excavation, unloading effect and rebound effects were reduced limitvertical deformation stiffness and bearing capacity of the bottom of the pile.(2) This paper also establishes the three-dimensional model of single pileconsidering the foundation pit dewatering，for studying and analysing tension of pilecaused by the soil rebound during the excavation of the foundation pit dewatering,and it analyzes the effect of the precipitation on the bottom soil, rebound of the top ofpile and the tension of pile. The results of the analysis show that: the excavation pitdewatering significantly reduce the rebound of bottom soil, total rebound of the topof piles and tension values of piles, considering pit precipitation significantlyimproved vertical deformation stiffness and ultimate bearing capacity of the bottom ofthe pit pile.(3) In this paper, two models of pile groups are established, one is a1/4computing model of rectangular pit, to consider spatial effects of pit bottom unevensettlement of pile groups caused by pit excavation. Especially the differences ofvertical stiffness and the pile bearing capacity of corner piles, side and center of thepile; The other is a long strip of the whole pit model, for exploring and analyzing the causes and effect factors which effect uneven settlement of pile groups. The resultsshowed that: the stiffness of reduce the degree and difference of pile groups are fargreater than the single pile, which led by excavation at different locations; In thefunction of all levels of work load, at pit bottom pile groups overall present dishsettlement trends, and due to the impact and effect of pile group, side friction curve ofpile group is R-shaped distribution; when comparing the results of different lengthconditions, which is found is that uneven settlement of pile groups at pit bottom exista " The most disadvantageous pile length " phenomenon, namely that under the pilelength, the difference of uneven settlement at pit bottom reach the maximum. |
