| Due to the special structural characteristics of collapsible loess, loess area non-uniform Collapsibilityoften poses a threat to bridge pile foundation or other series of engineering works in loess areas, that evenresult to serious damage. Therefore, how to determine the foundation bearing capacity and pile sidenegative frictional resistance of loess non-uniform collapse area is a key problem in the design of bridgepile foundation which should be solved. This paper is based on the project of bridge pile foundation underthe condition of non-uniform collapse of loess areas in Heyun high speed, shanxi. To study the pile groupmechanical characteristics under the condition of non-uniform collapse a working mechanism of pile sidenegative frictional resistance is set up as the main clue, to determine the bearing capacity of the pile beforeand after immersion and a non-uniform deformation of pile foundation negative friction resistance model isset up as the main aim, of this paper on the basis of summarizing the present situation of research at homeand abroad, making a system to study the non uniform pile load-bearing characteristics of loess collapsearea and mechanical characteristics of pile side negative frictional resistance, using field tests indoor modeltest, theoretical method and numerical simulation. The research results offer theoretical basis for referenceon filling the blank of bridge pile side negative frictional resistance under the condition of non-uniformcollapsibility of a bridge pile group in loess area. Main research results are as follows:1．Conducted field Pile foundation soaking load test, monitoring and analyzing the settlement of pilefoundation, pile axial force and pile side friction, making a comparative study about loess under naturalstate and soaking state, revealed non-uniform collapsibility characteristics of this loess region, summed upthe influence of ground soaking timing problems on pile foundation stress characteristics, summarized therelation between loess collapse and time during and after water immersion, analyze the relationship ofpilefoundation bearing capacity was analysed under three conditions of, natural,immersed and after immersion states, and affirmed the feasibility and effectiveness of pile foundation negative friction resistanceusing controlling variable method of pile foundation soaking test.2．Used a set of self-invent indoor model device, conducted model test of single pile and pile groups,under the condition of soil non-uniform deformation, studied a series of mechanical characteristics of thepile top settlement, the axial force of pile, pile side friction resistance, pile side negative frictionalresistance, discussed the mechanism of the load transfer under the condition of non-uniform deformationof loess, studied the non-uniform deformation of loess influence to the bearing capacity of pile foundation,analyzed different position of the stress characteristics of pile under the condition of loess non-uniform deformation and further studied of the pile group effect of the different pile side soil and different pilespace.3．Conducted Friction properties test of pile-soil interface, explored the influence of pile sidefriction under increased or reduced water in loess, studying the change law of pile side shear strain underincreased or reduced water in loess through changing pile lateral soil water content, affirmed therelationship between the maximum shear stress and relative displacement, put forward the shear transferfunction of bridge pile foundation pile-soil interface in similar regions.4．Based on the mechanism of foundation negative frictional resistance, together with the effectivefactor of negative frictional resistance and the force characteristic of negative friction resistance in the field,ascertain the calculational model of pile and soil of relative displacement, rationalize the locality of neutralpoint and the maximum negative friction resistance, built a calculational model of single pile negativefriction resistance of a parabola shape, and put forward a calculation method and calibration coefficient ofpiles foundation negative friction resistance at the base of single pile foundation negative frictionresistance, compare the theory result with the field test data, further more, compute the down-drag load indifferent number of piles.5．Used the finite element software ADINA, based on the mechanism of collapsible loess, putforward the new method of density model revision to simulate the collapsible loess deformation, used thefigure visualization tool of the software of for data analysis, validate the feasibility of the method ofdensity model revision to simulate the deformation of collapsible loess, combined immersion test of pilefoundation, to get the result of the density coefficient model revision of this loess area, rationalize therelated expressions of settlement in discretional depth after the loess collapsed.6． Based on piles foundations items of Hejin-Yuncheng expressway, use the finite element softwareto get the numerical simulation of piles load test and the force characteristic of piles load immersion test,study the transformation law of the character of bearing capacity, pile caps, displacement of pile and soil,axial force of pile and frictional resistance of pile side, apply the density method of the model revision toresearch piles foundation negative friction resistance under the condition of loess collapsibility, analyze theforce characteristic of piles in different locations, and combine the theory analysis and field test, toestimate the down drag of loess non-uniform collapse area, provide certain reference significance forfuture similar programme. |
