Research On Load Transfer Behavior And Deformation Rule Of Stiff Pile Composite Ground Under Embankment

Rigid piles have been widely applied in the soft ground improvement of highway engineering in china. The bearing mechanism and deformation rule of rigid pile composite foundation have also been deeply discussed, and abundant achievements have been obtained, Based on these research, this paper aims at analyzing the characteristics of rigid pile composite ground under embankment by field experiments ,numerical simulation and theoretical analysis. The main conclusions of this paper are as follows:(1)The state of rigid pile composite ground is reviewed. Driven effect of non-displacement construction techniques is summarized, many relative studies on bearing capacity and deformation for the kind of pile under embankment are summed up, then the problems that should be further solved and the next research goal are introduced.(2) By the analysis of field experiment during pile driven, the disturbance of rigid pile construction on soils around piles under non-displacement are investigated for single pile and pile group, the observed data show that pile group's driven effect is a comprehensive result of every single pile. Static penetration tests at different time show that the soil strength around pile has a great decline, but gradual elevation with the development of time, pile group's disturbance effect is more notable than the single pile's. With the embankment added and removed, soil strength around pile is enhanced; the characteristics of physics and mechanics get a remarkable improvement.(3) Plane finite element method (FEM) is introduced to investigate bearing mechanism of rigid pile composite ground under embankment. Soil arching effect, membrane effect and pile stress concentration are highlighted, and the role of pile cap in the composite ground is analyzed. by the equivalent treatment area of single pile with pile cap, an equation computing the stress ratio between pile and soil is introduced, the contrast between the parameter analysis and FEM result show such an equation has its rationality.(4) By the means of plane FEM ,the settlement rule of rigid pile composite ground is discussed, the settlement responses of the ground under the different parameters are studied ,these parameters are comprised by every material module, pile cap size, pile distance, pile length and so on, meanwhile ,pile with cap or without are analyzed, the results show that total settlement only has a more or less variety under a lower module of sublayer soil by the change of pile cap or pile distance, In this case, embankment settlement after construction should be mainly controlled by pile length ,when the sublayer has a great module, the adjustment of pile cap , pile distance and pile length all have a significant influence on the total embankment settlement.(5) A primary discussion on the settlement calculation for rigid pile composite ground under embankment is put forward, two calculation methods are analyzed, namely composite module method and the method of subsoil stress around pile. By contrast with field observation and FEM, the result shows that both methods have flexibility, but the latter is better closed to actual result.(6) The observed results from two experiment areas are analyzed, including CFG pile and PTC pile with pile cap, the effect of reinforcement on these areas are evaluated and compared, and the results suggest that the reinforcement effect of PTC pile is better than CFG pile.(7) The methods of calculating bearing capacity for rigid pile composite ground presented in the paper are area ratio method and stress ratio method. By contrast with static load experiment of single pile composite ground for CFG pile, both methods have some precision. In addition, harnessing the result of stress ratio method, an ultimate embankment height can be computed, only if the ultimate bearing capacity of subsoil could be known by static load experiment or area ratio method.