Research On Field Observations And Behavior Of Pile Foundation During Deep Excavation

Along with the increasing density of urban buildings in soft soil area, thefoundation pit engineering is becoming deep and large scale. To analysis the impactof the excavation on the deformation of foundation pit and stress of piles beneath thebasement, and summary of pile deformation at different positions are needed to bepredicted in advance, thus providing guidelines for the construction of deepfoundation pit in soft soil area. This dissertation carried out researches on thedeformation of foundation pit and the behavior of pile foundation during excavationin Tianjin Yanlord Riverside Plaza III foundation pit project, by means of fieldobservations, in situ test as well as numerical simulation.First of all, through the analysis of the field test, find that in the excavationprocess, the deformation of retaining structures will not only gradually change alongwith the increase of digging deep, but also are non-uniform distribution because ofstiffness of the support system in foundation pit, in the same digging deep, thedeformation modes of retaining structure are different with position differences. Thesettlement of road around foundation pit is mainly related to the lateral deformation ofthe supporting structure, but also affected by road conditions, by the way, the overallperformance of settlement behind the wall is the groove type.Secondly, conduct a field test monitoring pile internal force, investigate changesof pile force during excavation, and compare the different responses of piles atdifferent locations in the pile excavation process. The results show that: in the processof excavation, piles in different locations are subject to certain degree of tension.When excavation is completed, the maximum axial force is located at1/3pile lengthfrom the lower part of pile.Finally, by the finite element software, the behaviors of pile foundation duringlarge-scale deep excavation are analyzed. The results showed that: with the increaseof the depth of excavation, pile axial force increases, the maximum axial force ofgroup pile is located in the middle of the pile, and different from the position of themaximum of a single pile (pile bottom). At the same depth of excavation, axial forceof pile close to the supporting structure is small, and the axial force of pile located inthe central part of foundation is large. The lateral deformation of retaining structure in foundation pit excavation, make piles close to the retaining structure bending, theoverall performance appears large deformation in the upper part of the pile and smalldeformation in the lower.By adjusting the stiffness of supporting structure, support position, brace stiffnessto control the deformation modes of retaining structures, simulate the effects ofdifferent modes of deformation on soil displacement field in the deep pit excavationprocess. The results show that: deformation of the pit deep soil affected by excavationunloading and extrusion variable of retaining structure, the deformation of soil at edgeof foundation pit is the most obvious.