Research On Ultimate Carrying Capacity Of Single Pile Considering The Effect Of Soil Compaction During Pile Driving

At present, researches on static pile are mainly focused on machines for pile-compaction, pile driving resistance and feasibility, relation between pile driving force and bearing capacity. There are few improvements in the effect of soil compaction during pile driving of static pile and ultimate carrying capacity of single pile increasing with time passing which is induced by the effect of soil compaction during pile driving. On the basis of this, following research is mainly carried out in this paper.Firstly, a finite element analysis on pile-driven influence in saturated sands is carried out in this paper with Crisp program compiled by Cambridge University. Two constitutive relations (linear elastic model and ideal elastic-plastic model) and two pile-driven process's simulation modes (stress boundary conditions method of cylindrical cavity expansion theory, displacement boundary conditions method of cylindrical cavity expansion theory) are adopted and combined respectively to compute. Moreover, this paper discusses the differences of pile-driven influence such as excess pore water pressure, increment of radial effective stress, land upheaval and radial displacement of sands around the pile, which are caused by three kind of combinations of different constitutive relations and pile-driven process simulation modes (linear elastic model, constant E along depth, stress boundary conditions method of cylindrical cavity expansion theory; linear elastic model, E increasing linearly along depth, displacement boundary conditions method of cylindrical cavity expansion theory; ideal elastic-plastic model, E and Cu both increasing linearly along depth, displacement boundary conditions method of cylindrical cavity expansion theory ), and a constitute relation and a pile-driven process's simulation mode suitable for saturated sands are found out.Secondly, triaxial tests of saturated sands are made using GDS stress path triaxial testing system in this paper. State of stress of soil adjacent to pile after pile has been driven is simulated on GDS triaxial apparatus, and samples are made consolidate. Axial stress is increased as radial stress keeps constant until shear failure occurs. Soil parameters such as G, E,τ_f,φ and relative density D_r,which are the parameters of consolidated sand soil adjacent to pile ,are gained from the test results and their radial and axial distributions are also analyzed.Thirdly, load transfer method is improved. Using the theory of shear -displacement and transfer matrix, the transfer matrix of piles, which can reflect thereduction of parameters of soils adjacent to pile along radial direction, in layered soils according to the principle of layer by layer analysis is derived in this paper. What's more, according to pull for pile from soils adjacent to pile and different state of each layer in failure, the process of testing pile is divided into five parts and bearing capacity of pile is got by analyzing the relationship between load and settlement on the top of pile in each part and drawing P-S curve of the top of pile.Lastly, ultimate carrying capacity of single pile in no consideration of the change of parameters of soils adjacent to pile and before consolidation is solved and compared respectively with that after consolidation in order to analyze respectively the influence of soil compaction, compaction failure of soil induced by pile and consolidation of soil adjacent to pile on ultimate carrying capacity.