Analytical Methods Of Pile-soil Stress Ratio For Pile-net Composite Foundation Under Embankment Loads

Pile-net composite foundation has got a wide range of applications in transportation,construction,hydraulic engineering and other fields and achieved good reinforcement effects because of its economy and practicality.But due to the complex working mechanism of the pile-net composite foundation,which involves the interaction between the embankment fillings,the nets,the piles and the soils,while the theoretical research on load sharing mechanism of pile-net composite foundation is far behind engineering practice currently,which needs to be further improved.Therefore,the load transfer mechanism is studied in detail against mechanical characterterristics of pile-net composite foundation under embankment loads,and the strengthening mechanism of the core components is also studied thoroughly in this paper.Based on this,new analytical methods of pile-soil stress ratio for pile-net composite foundation are proposed,which are more in line with engineering practice.Firstly,the composite foundation and the upper fillings within the equivalent reinforced range of a single pile are regarded as a typical analysis element in this paper,and the acting mechanism of soil arching effect in embankment fillings is discussed in depth.Aiming at the characterterristics of principal stress axis rotation in the fillings as a result of pile-soil differential settlement,the Mohr's circle is introduced to analyze the influence of principal stress axis rotation on the stress state of the fillings,and the soil arching effect in the embankment is analyzed in combination with the vertical equilibrium conditions of outer soil column and internal-external joint soil column.Based on the theory of circular thin plate on Winkler foundation,the deflection deformation of the reinforced cushion is simulated,and the anti-bending effect of the reinforced cushion is analyzed in combination with boundary and continuous conditions.An analytical method of pile-soil stress ratio for pile-net composite foundation in consideration with the influence of principal stress axis rotation is put forward according to the continuous conditions of stresses and deformations.Then,based on the analysis of the load transfer law of pile-net composite foundation under embankment loads,a concentric arch model is introduced to analyze the soil arching effect in the embankment considering the relationship between pile-soil differential settlement and the mobilized degree of soil arch.The deformed surface of horizontal reinforcements is regarded as the combination of sphere and cylinder according to its deformation characteristics,and the membrane effect which is related to pile-soil differential settlement is analyzed.Considering the pile-soil interaction and their differential settlement,a three-dimensional analysis model of pile-net composite foundation is developed with consideration of the coupling effect among fillings,nets and pile-soil reinforcement area,and then an analysis method of pile-soil stress ratio is put forward.This method can reflect not only the influence of soil arching effect,membrane effect and pile soil interaction on pile-soil stress ratio but also the influence of pile-soil differential settlement on mobilized degree of soil arching effect and membrane effect as well as pile-soil interaction.Finally,three engineering examples are analyzed and calculated respectively by using the above analysis methods,and the results are compared with the measured values and the existing similar methods,which show the feasibility and rationality of the analysis methods of pile-soil stress ratio in this paper.Meanwhile the influence of factors such as pile spacing,width of pile cap,tensile modulus of geosynthetics,compressive modulus of underlying stratum on neutral point position,pile-soil differential settlement,mobilized coefficient of soil arching effect and equivalent vertical force of geosynthetics is analyzed.