【作者】 王钢；

【导师】 曹卫平；

【作者基本信息】 西安建筑科技大学 ， 岩土工程， 2017， 硕士

【摘要】 我国湿陷性黄土分布面积大,随着国家西部开发力度的增加,湿陷性黄土地区的工程问题越来越突出。桩基具有良好的承载能力,在湿陷性黄土地区应用非常广泛,由于湿陷性黄土浸水会产生湿陷变形,桩基会出现很大的负摩阻力,严重的情况下会导致建筑物出现破坏,所以研究湿陷性黄土地基中桩基负摩阻力具有重要工程实践意义。本文首先基于模量折减法对关中湿陷性黄土场地桩基现场试验进行了数值模拟,在此基础上分析桩顶设计荷载、桩身长径比、桩端土变形模量对单桩负摩阻力的影响,结果表明随着浸水前桩顶设计荷载的增加、桩端土变形模量的减少,负摩阻力逐渐减小;基于现场试验及数值分析结果,总结得到了适用于关中湿陷性黄土桩基的中性点深度比、负摩阻力最大值、负摩阻力最大值深度的计算公式,提出了通过折线法计算湿陷性黄土桩基负摩阻力。然后,以2×2及3×3群桩模型为例,分析了群桩中桩间距、桩身位置、基桩数量对群桩负摩阻力的影响,并与相应单桩负摩阻力进行了对比。结果显示:基桩负摩阻力随着桩间距的增加而减小;不同位置处基桩的负摩阻力是不同的,中心桩负摩阻力最小,其次是边桩,最后是角桩;随着随着基桩数量的增加,基桩负摩阻力的群桩效应越来越明显,当数量增加到一定程度时负摩阻力群桩效应趋于稳定;基桩中性点深度、负摩阻力最大值、负摩阻力最大值深度受群桩效应影响程度不同,其中受群桩效应影响最小的是中性点深度,其次是负摩阻力最大值深度,负摩阻力最大值的群桩效应最明显;最后给出关中地区群桩负摩阻力计算公式。更多还原

【Abstract】 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.更多还原