多头夯扩桩在上拔荷载作用下承载理论计算与性能分析

发布时间：2019-04-27 10:50

【摘要】：随着社会快速发展,兴建大量交通设施及高层建筑等必不可少。结构抗拔问题必然随之日益突显,使得抗拔工程的设计、验算等成为工程建设的重要研究内容之一。多头夯扩桩等可大幅提高承载力的桩型应运而生,其技术成熟、工艺科学可靠、污染程度低并且造价经济。但作为一种新桩型,关于多头夯扩桩的抗拔机理等认识程度就目前而言较低。认清多头夯扩桩承载力传递机理,对其理论研究进行进一步完善,对多头夯扩桩的应用和推广将起到促进作用。本文通过阅读、参考并分析国内外相关研究文献,运用理论计算推导、现场原型试验、室内模型试验及数值仿真模拟等多种方法对多头夯扩桩抗拔机理、承载力特性进行了研究。主要有:第一,在参考抗拔桩破坏面形式基础上,假设多头夯扩桩抗拔破裂面形态并且运用极限平衡法分别对多头夯扩长桩(长径比大于或等于20)、多头夯扩短桩(长径比小于20)的极限抗拔承载力进行理论计算公式推导。第二,通过原型试验研究多头夯扩桩极限抗拔承载力、抗拔机理等,由于试验所得数据并未完全满足研究需求,因此分别在黏土、砂土中进行室内模拟试验对等截面桩、单头夯扩桩、多头夯扩桩的抗拔破坏模式、承载力等进行了研究。分析结果表明:多头夯扩桩较单头夯扩桩、等截面桩具有较高的抗拔承载力,且同级荷载下上拔量偏小。当夯扩桩加至极限荷载时,桩周表面土体产生放射圆状裂缝,土体上拔破坏为压缩变形—局部出现塑性区—整体剪切破坏的渐进式破坏模式。根据室内试验所得成果,多头夯扩模型桩破裂面与假设破裂面形式相近,承载力计算值与实测值接近。第三,运用FLAC 3D有限元模拟软件模拟现场原型、室内上拔试验,得到夯扩桩极限抗拔承载力值,并分析了多头夯扩桩荷载传递规律。多头夯扩桩施加上拔荷载,桩身直桩段、桩身扩大头、扩大头间距直桩段、桩底扩大头承载作用依次逐步发挥即扩大头荷载发挥存在一定时间效应。扩大头分担部分荷载且随着上拔荷载值的增大,其承担荷载比随之呈增大的趋势。随后对夯扩桩抗拔破坏模式、承载力主要影响因素进行了研究,并为其设计提供了参考。
[Abstract]:With the rapid development of society, it is necessary to build a large number of transportation facilities and high-rise buildings. The structural anti-pull problem must be more and more prominent, which makes the design and checking calculation of the anti-pull engineering become one of the important research contents of the engineering construction. Pile types, such as multi-head rammed piles, which can greatly improve the bearing capacity have emerged as the times require. The technology is mature, the technology is scientific and reliable, the pollution degree is low and the cost is economical. However, as a new type of pile, the knowledge about the anti-pull mechanism of multi-head rammed expanded pile is low at present. The mechanism of bearing capacity transfer of multi-head rammed expanded pile is clearly understood, and its theoretical research is further improved, which will promote the application and popularization of multi-head rammed expanded pile. Through reading, referencing and analyzing the relevant research literature at home and abroad, this paper applies many methods, such as theoretical calculation and derivation, field prototype test, indoor model test and numerical simulation, to the anti-pull mechanism of multi-head rammed expanded pile. The characteristics of bearing capacity are studied. The main contents are as follows: first, on the basis of reference failure surface form of anti-pull pile, assume the shape of multi-head ramming pile anti-pull crack surface and apply limit equilibrium method to multi-head rammed long pile (the ratio of length to diameter is greater than or equal to 20). The theoretical formula for calculating the ultimate uplift bearing capacity of multi-head rammed short piles (the ratio of length to diameter is less than 20) is derived. Secondly, the ultimate pull-out bearing capacity and pull-out mechanism of multi-head rammed expanded piles are studied through prototype tests. Because the data obtained from the tests do not fully meet the research requirements, the equivalent cross-section piles are tested in laboratory in clay and sand, respectively. The anti-pull failure mode and bearing capacity of single-head rammed expanded pile and multi-head rammed expanded pile are studied. The analysis results show that the multi-head rammed pile has higher uplift bearing capacity than single-headed rammed pile, and the lifting capacity under the same-grade load is smaller than that of the single-head rammed pile. When the rammed pile reaches the limit load, the radial circular cracks occur on the surface of the pile, and the pull-out failure of the soil is a progressive failure mode of compression deformation-local plastic zone-integral shear failure. According to the results of laboratory test, the fracture surface of multi-head ramming model pile is similar to that of assumed fracture surface, and the calculated value of bearing capacity is close to the measured value. Thirdly, the field prototype was simulated by FLAC 3D finite element simulation software, and the ultimate pull-out bearing capacity of rammed expanded pile was obtained by indoor pull-out test, and the load transfer rule of multi-head rammed expanded pile was analyzed. When multi-head rammed pile is used plus pull-out load, there is a certain time effect in which the pile body straight pile section, the pile body enlarged head, the head spacing between the piles, and the pile bottom enlarged the head load function gradually play the role in turn, that is to say, enlarging the head load has a certain time effect. The load ratio of the enlarged head increases with the increase of the up-pull load value and the partial load is shared by the enlarged head. Then, the main influencing factors of the pull-out failure mode and bearing capacity of rammed expanded pile are studied, and the reference for its design is provided.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.1

【参考文献】