The Study Of Negative Skin Friction Of Pile Foundations In Guanzhong's Collapsible Loess

In our country,the acreage of collapsible loess is very large,and with the development of the western region of China,the engineering problems of collapsible loess area become more and more serious.The bearing capacity of the pile foundation is very good,so it is widely used in collapsible loess area.Because of the collapsibility of the collapsible loess,the pile foundation will appear large negative skin friction which can lead to destruction of buildings,so the study of pile's negative skin friction in collapsible loess foundation has important practical significance.Firstly,pile field test in Guanzhong collapsible loess was simulated on based of the modulus' reduction.Then analysed how to design load of pile's top and pile diameter and pile end soil's deformation modulus affect the negative skin friction of single pile.The results show that with the increase of design load on pile's top and the decrease of deformation modulus of pile end soil,the negative friction resistance decreases gradually;based on the result of the field test and numerical analysis,summarize the calculation formula of neutral depth ratio and maximal negative skin friction and depth of maximal negative skin friction of pile foundation in Guanzhong,and use broken line method to calculate the negative skin friction of pile foundation in collapsible loess.Then,though the 2×2 and 3×3 pile model,analysed how pile spacing and pile position and number of piles effect the negative skin friction of pile group,and compared the negative skin friction with the corresponding single pile's.The results show that the negative skin friction decreases with the increase of pile spacing;at different positions the negative frictional of the pile is different,the center pile's negative friction is the least,next is side pile,corner pile's is largest;with the increase of the number of piles,the pile group effect of negative skin friction of pile is more and more obvious,when the number increases to a certain extent,the negative skin friction'spile group effect tends to be stable;the degree of the depth of neutral point and the depth of maximal negative skin friction and the maximal negative skin friction effected by pile group effect is different,maximal negative skin friction is largest,next is the depth of maximal negative skin friction,depth of neutral point is the least;finally,the calculation formula of negative skin friction of pile group in Guanzhong area is given.