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1、 浙江大学博士论文 2005.09 大直径灌注筒桩承载性状研究 大直径灌注筒桩承载性状研究 摘 要 本文采用解析算法，就考虑土芯作用下的筒桩竖向承载力计算、筒桩在竖向与水平 向力同时作用下的性状分析、 双排桩海堤筒桩结构内力与位移计算等三个方面展开了较 为深入细致的研究。主要工作和研究成果如下： 1. 考虑筒桩土芯分担荷载以及筒桩与土芯内摩阻力发挥情况， 采用弹塑性荷载传递 函数推导出了筒桩的竖向荷载沉降关系的解析表达式， 并计算得到任意截面桩身轴力 及内外侧摩阻力的表达式。计算表明：土芯顶端分担的荷载以及筒桩内侧摩阻力随着桩 顶荷载、桩土模量比、筒桩内外径比的变化而变化；在单桩荷载沉降曲线中
2、，l、 sa C 和 a k越大，桩顶极限承载力越大，对应桩顶沉降量也越大。 2. 在现行 m 法假设的基础上导出了筒桩单桩在竖向集中荷载、水平向荷载、桩身 自重以及桩内外侧摩阻力耦合作用下的计算公式，首次把自由段荷载的作用耦合进来。 计算表明：桩身弯矩值和桩身变位随着桩顶轴力P的增大而提高，当基桩自由长度和竖 向荷载较大时，P效应不可忽略；桩身自重以及桩周内外摩阻力对桩身弯矩和桩身 变形的影响很小，数量级在 10-4，计算时可忽略他们其对桩身内力的影响；随着埋入深 度的增大，桩身最大弯矩和桩顶水平变位都增大，但是埋入深度增大一定值，桩身弯矩 和桩身变位趋于稳定； 桩顶水平变位和桩身最大弯矩随
3、着各参数桩顶弯矩或桩顶水 平力、自由长度、桩身弹性模量和自由段荷载等的增大而增大，其中，桩顶水平力对桩 身最大弯矩和桩顶水平变位的影响最大。 3. 介绍了几种筒桩海堤的结构型式， 并应用结构位移法求解了双排桩海堤各桩的等 效桩顶荷载。对桩顶挠度系数、桩顶刚度系数、顶板的位移和转角进行了求解，最后将 作用于筒桩海堤的荷载等效至各桩头。 4. 计算了施工期荷载作用下单桩受力、 海堤施工期短暂作用效应组合以及正常使用 下作用效应的持久组合 3 种工况下的桩身弯矩和桩身水平变位。计算表明：正常使用下 作用效应的持久组合工况下靠陆侧桩身有最大值弯矩； 施工作用效应的短暂组合工况下 靠陆侧桩身弯矩是从桩顶
4、至桩头逐渐衰减的。分析了桩间距 1 B、排间距 2 B的变化对筒桩 海堤荷载传递性状的影响。 大直径灌注筒桩承载性状研究 王哲 关键词： 灌注筒桩；承载性状；荷载传递；自由荷载；解析解；双排桩 大直径灌注筒桩承载性状研究 王哲 LOAD BEARING CHARACTERISTIC STUDIES OF LARGE-DIAMETER TUBULAR PILES USING CAST-IN-PLACE CONCRETE ABSTRACT Construction technics and structure characteristic of large diameter cast-in-sit
5、u tubular piles is different from that of ordinary cast-in-place piles or steel pipe piles, which bring on the particularity of tubular piles bearing characteristic. Using analytical arithmetic, three aspects have been studied that are tubular piles vertical bearing force considering soil cores func
6、tion, tubular piles bearing characteristic under vertical and transverse load, and stress and displacement of double-row-pile sea walls piles. The main original work and results are as follows: 1. With elastic-plastic load transfer function, a set of analytical equations for the axial load-settlemen
7、t curve of cast-in-situ tubular pile have been deduced to determine the vertical bearing capacity of pile according to the settlement of the pile top. The distribution equations of axial force and friction along pile can be gotten. It shows that force soil core beared and friction will change follow
8、ing the pile top load, pile and soil elasticity modulus ratio and piles inner and outer diameter ratio. In single piles load-settlement curve, the longer pile length is or the bigger sa Cand a k is, the bigger the ultimate resistance of the pile is, then the bigger the settlement is. 2. On the basis
9、 of mmethod, coupling formulas have been gotten when single pile is loaded under the load combination of vertical focus load, transverse load, piles self-weight and its inner and outer friction, and free load is concluded in for the first time. It shows that P effect cant be ignored when the free le
10、ngth and vertical load are big, and piles deadweight and its friction have little influence on distortion and bending force along pile. The top transverse distortion and the most bending force have the same current with the top bending force, the top transverse force, free length, piles diameter, et
11、c, in which the top transverse force has the biggest influence on piles most bending force and the top transverse distortion. 3. Several kinds of sea wall structures are introduce in this paper, equivalent pile top load of each pile of double-row-pile sea wall was gotten by the method of structure d
12、isplacement. 大直径灌注筒桩承载性状研究 王哲 First pile top distortion coefficient, top rigid coefficient, tip boards displacement and its corner are calculated, then the loads acting on the tip of the sea wall are equivalent to each pile top. 4. Bending force and transverse distortion along pile are calculated in
13、 three kinds of working conditions, which are single pile under load in construction period, fugacious load domino effect combination in sea wall construction period and permanent load domino effect combination in common using period. It shows that pile has the biggest bending force value under the
14、third working condition, bending force decrease along the pile from the pile top under the second working condition. Influence of changes of pile space between and row space between to load transfer characteristic of sea wall is analyzed. Key Words: Cast-in-place tubular piles；Bearing characteristic
15、；Load transfer；Free load； Analytical solution；Double-row piles 大直径灌注筒桩承载性状研究 王哲 第一章第一章 绪绪 论论 1.1 引 言 大直径现浇混凝土薄壁筒桩又称沉管灌注筒桩（本文后面简称筒桩） ，就目前沉桩 能力及其性状而言， 筒桩适用于饱和软土、 一般粘土、 粉土中。 筒桩的外径D在800 mm 1500 mm，壁厚t在 100 mm250 mm，桩体全部采用现浇的素混凝土或钢筋混凝土 一次成型完成。 筒桩技术为施工机械采用振动沉模、 现场浇筑混凝土的一次性成桩技术， 可快速加固较软弱地基使其满足各类工程设计要求。 这项技
16、术在我国东南沿海软弱粘性 土地区已得到较广范围的应用，已应用于海洋工程（如温州鹿西岛双排桩防浪堤和广州 大亚湾石化工业区双排桩海堤） 、交通道路工程（如杭州绕城高速公路、杭宁高速公路 软基处理） 、工民建工程（如杭州市罗马公寓）和水利工程（如上海浦南东片出海闸导 流堤）等。 在软弱地基处理中， 筒桩在振动成桩过程中大量土不是挤向周围而是被内管套入其 中，并且内管上部有溢出通道，受挤土只是少数，它属于弱挤土桩；并且从混凝土构件 抗弯能力计算可知，断面中心部位混凝土所起的作用也可忽略不计，受力并不需要全断 面，筒桩用合理的材料获取有效的结构效应。筒桩汲取钻孔灌注桩桩径大，桩长可调节 和沉管灌注桩设备简单，施工速度快等优点，又克服钻孔灌注桩泥浆护壁的泥皮减弱了 侧摩阻力，桩端的沉渣减弱了桩端承载力，施工进度慢和沉管灌注桩挤土常导致桩身缩 颈、
