Research On Uplift Bearing Characteristics Of Pile Foundation In Sand

With the rapid development of urbanization,the demand for land resources has increased dramatically,and the development of underground space has become a new trend.In order to solve the anti-floating problem of underground space,setting up anti-pile foundations has become an important measure.This article mainly uses indoor model tests to study the existence characteristics of uplift piles in sand.The main research contents and conclusions are as follows:(1)Carrying out the test of equal section half-mold piles,the results show that the vertical displacement of the soil gradually increases along the pile from top to bottom,the displacement concentration area is at the pile end,and the failure mode of the model pile in the sand It is a cylindrical shear failure.(2)The uplift test of a single pile of equal cross section was carried out,and it was found that as the length-to-diameter ratio of the pile gradually increased,the uplift ultimate bearing capacity of the single pile of equal cross section gradually increased.Under the same uplift load,the uplift displacement with a small aspect ratio is greater than that with a large aspect ratio.The axial force of the pile body gradually decreases from top to bottom.Except for the pile length of 20 cm,the friction resistance of the pile side is "big at both ends and small in the middle".The friction resistance of the other piles increases with the increase of the length-to-diameter ratio.The peak value is concentrated in the middle and lower part of the pile body.(3)The uplift test of the group piles shows that the load-displacement curve of the group piles and the single pile is basically the same,and the uplift displacement will increase with the increase of the pile spacing and the number of piles.Under the conditions of different pile spacing,pile length and pile number,the pile group effect coefficients are all less than 0.6.The distribution law of the axial force of the pile body of the group pile is basically the same as that of the single pile,and they all show the distribution rule of "upper width and lower width".The depth of the peak frictional resistance of the pile is different depending on the distance between the piles.When the length of the pile is short,the frictional resistance of the pile side comes into play first.When the length of the pile is long,the frictional resistance of the pile side is firstly small,then large,and then small.(4)Among the five different methods for calculating the ultimate bearing capacity of single piles,the code method is closest to the test value.In the method of calculating the uplift bearing capacity of group piles,it is found that the size of uplift bearing capacity will be affected by the pile spacing,pile length and number of piles,and also pay attention to the important parameters in the formula,and the way of its value will be affected.Calculation results.The normalized method and the Patra model are used to estimate the ultimate pull-out bearing capacity in each specific case,which is closer to the test value than the regression formula method.