Study Of Active Pile Horizontal Arch Effect Based On Photoelastic Experiment

In recent years,with the rapid increase of large span bridges and high-rise buildings in China,pile foundations are widely used as foundation forms in engineering construction due to their high bearing capacity and structural simplicity.In the design concept of bearing capacity of such structures,as the horizontal load is much smaller than the vertical load,the displacement of the soil in front of the group pile foundation and the possible passive earth pressure are often ignored,which is not in line with the engineering reality.Therefore,this paper discusses in detail the soil arch effect produced by the row pile under horizontal load and analyses it in depth.This paper mainly focuses on the formation and evolution process of single and double row piles and the influence of various factors on the horizontal arch effect of row piles,and carries out photoelastic model tests and numerical simulation studies.Among them,the main influencing factors selected are depth,pile spacing,row spacing and pile laying method.The main results and conclusions were obtained as follows.(1)Independent development of large-size photoelastic experimental apparatus to reduce the interference of boundary effects on the test;in order to eliminate the residual stress inside the polycarbonate disc particles,after a series of annealing pre-experiments,the annealing curve suitable for this test particle was obtained,and by calibrating the colour squared gradient<G~2>of the annealed polycarbonate particles,the obtained colour gradient fitting curve was embedded into Matlab programming software,which facilitated the extraction of the force chain in the photoelastic image at a later stage,as well as the acquisition of a rose cloud map of the contact distribution of the force chain.(2)For single-row piles,the influence of depth and pile spacing parameters on the soil arch effect formed by single-row piles and the change law of arch effect under horizontal load of single-row piles are analysed.The results show that:the horizontal arch effect of single-row piles undergoes a process of development-stabilization-destruction in the formation process,the direction of the large main stress in the arch-forming area before the pile gradually deflects from the x-direction to the y-direction with the displacement of the pile body;the soil arch effect does not appear in the shallow soil layer,with the increase of depth,the soil arch effect gradually increases,the soil arch vector height gradually decreases with the increase of depth,the arc of the soil arch formed gradually with the increase of depth Smooth,from deep arch shape to shallow arch shape,and finally to smooth shape;as the pile spacing increases,the horizontal arch effect in front of the pile gradually weakened,when the pile spacing increases to a certain critical value,the soil arch effect will completely disappear,the pile operation mechanism in a single row of piles can be approximated as a single pile.(3)For double-row piles,the effects of depth,pile spacing,row spacing and pile laying method on the horizontal arch effect of double-row piles and the formation and evolution law of the horizontal arch effect of double-row piles were analysed.The results show that:when the double-row piles act on the soil in front of the piles,there is a difference in the role played by the front and rear rows of piles,the front row of piles forms the soil arch first than the rear row of piles,and the soil arch strength is much stronger than the rear row of piles,the presence or absence of the rear row of piles has little effect on the front row of piles;the horizontal arch effect in front of the front row of piles increases with the increase of depth,the enhancement trend will be slowed down and will not increase without limit,the shape of the soil arch of the front row of piles basically remains the same with the increase of depth,the horizontal arch effect in front of the rear row of piles The horizontal arch effect of the front row piles is gradually weakened with the increase of the pile spacing,the increase of the pile spacing of the front row piles leads to the weakening of the shading effect of the front row piles and the increase of the slip of the particles,which provides better arching conditions for the back row piles and increases the force chain in front of the back row piles;with the increase of the row spacing,the synergistic effect of the front row piles and the back row piles is gradually With the increase of row spacing,the synergistic effect of front row piles and back row piles is gradually weakened,the load on front row piles increases with the increase of row spacing,while the load on back row piles remains the same;the horizontal arch effect of plum piles in the formation stage is similar to that of single row piles,while the operation mechanism of back row piles is different from that of double row piles in rectangular arrangement;with the increase of row spacing of plum piles,there is obvious soil arch effect on front row piles,while the synergistic effect of back row piles is weaker with the increase of row spacing,and the soil arch As the spacing of the plum piles increases,the soil arch effect of the front piles is weakened and the load on the rear piles increases with the increase of the pile spacing.