水泥搅拌桩承载力的确定

水泥搅拌桩的承载力的确定首先应判别是纯摩擦桩还是端承摩擦桩，对于纯摩擦存在着桩的有效桩长。另外，为保证水泥桩承载力的发挥需合理设计水泥土的强度和桩径。     

CFG桩处理风积砂土地基承载性状研究

以CFG桩(cement fly-ash gravel pile)处理榆林地区风积砂土地基为例,用有限差分软件FLAC3D模拟了CFG单桩、复合地基的承载性状,与现场载荷试验吻合较好;分析了不同桩体截面、褥垫层参数及桩长等因素对单桩及复合地基承载性状的影响。结果表明:合理的褥垫层厚度对桩土应力比调节作用显著,CFG桩复合地基存在临界桩长,单桩摩擦桩的性状明显,且现有理论计算结果偏于安全;CFG桩复合地基能有效优化风积砂土的承载力性状,从而使风积砂土承载力提高。     

水泥搅拌桩桩长的确定

本文分析了确定水泥搅拌桩桩长的因素，测算了纯摩擦桩的最小桩长和有效桩长，可供设计参考。     

深厚软土地区小直径纯摩擦长桩承载性状研究

通过温州深厚软土地区小直径纯摩擦长桩的静载荷试验和桩身轴力的测试,探讨了小直径纯摩擦长桩的承载力性状和荷载传递机理,把实测摩阻力与理论值进行比较,指出这类桩从承载力角度看,存在着有效桩长。结合测试数据对桩身压缩变形特性进行了计算和讨论,可供纯摩擦长桩的理论研究和工程设计借鉴。     

夯实水泥土桩承载机理及临界桩长的研究

根据夯实水泥土桩试验所得到桩身应力-应变关系和桩侧摩阻力与桩土相对位移的关系,运用荷载传递法结合Geddes公式对夯实水泥土桩的承载机理进行分析,探讨其临界桩长,分析桩身材料无侧限强度qu、桩侧摩阻力τu、桩的直径d对临界桩长的影响,并在此基础上提出夯实水泥土桩的临界桩长建议值。     

碎石桩单桩和多桩荷载传递方式的实验研究

 在自行设计加工的二维实验设备上,应用杠杆–砝码加载系统和应力环直接测量桩底压力的方法,研究桩长对碎石桩单桩及多桩(三桩)荷载传递方式的影响。碎石桩材料为白色水磨石子(大理岩),平均粒径0.75 cm;桩间土为人工调制的一定含水量的兰州黄土和沙坡头细砂按体积比3∶1混合而成。实验给出了碎石桩的临界桩长效应,即长度小于临界桩长的短桩和大于临界桩长的长桩的荷载传递方式不同,短桩主要靠桩底土体承受顶部荷载,而长桩主要靠桩顶拱结构和桩间土承受顶部荷载,这决定了短桩和长桩不同的破坏模式,即短桩的桩身刺入破坏和长桩的顶端拱结构鼓胀坍塌连带桩间土楔形剪出的破坏。与单桩相比,多桩的顶部压力对其底部压力存在交叉叠加影响,并且多桩及其桩间土之间的相互作用可以有效减小临界桩长,在桩较短时就能使桩顶端的拱结构生成并趋于稳定。研究结果说明,需对短桩和长桩分别建立不同的承载力计算公式。     

水泥土桩复合地基荷载传递及变形的原位试验研究

为了获得桩长、置换率等对水泥土桩复合地基荷载传递及变形的定量影响,在5组4桩群桩和5组9桩群桩复合地基的桩体内埋设应变计,在桩间土体内埋设深层沉降标,实测到4桩群桩和9桩群桩复合地基中桩体轴力分布、桩侧摩阻力分布和桩间土变形分布。发现置换率相同时,承台板宽度大,水泥土桩的荷载临界深度也大,桩侧摩阻力分布深度下移。承台板宽从1.0m增加到1.5m时,荷载临界深度由14倍桩长增加到18倍桩长。变形影响深度约为承台板宽度的(1.8～2.5)倍。最大摩阻力出现在承台下1.5m处,该处的竖向偏应力最大,桩体容易在这里破坏。增加桩长能有效减少沉降。荷载水平达到70%以后,变形影响深度下移不再明显。     

同场地大直径纯摩擦桩和端承摩擦桩对比研究

通过对 4组纯摩擦桩和端承摩擦桩的对比试验 ,对这两种摩擦桩的承载性状 ,特别是荷载分配情况进行了研究     

树根桩单桩临界桩长讨论

树根桩不同于常规的桩基,它的长细比较大(一般大于30),具有很大的表面摩阻力,承载力主要由侧摩阻力承担。因此,在竖向荷载作用下,树根桩必然存在一个临界桩长。本文作者借鉴已有的研究成果,采用佐藤悟提出的荷载传递函数解析法,假定荷载-位移关系为理想的线弹塑性关系,分析了树根桩在竖向荷载作用下的荷载传递特性,并借用Esrig按临界状态原理分析得到的桩土界面上的桩侧阻力经验公式,推导出在竖向荷载作用下,树根桩竖直单桩在匀质土层中的临界桩长计算公式。该方法在树根桩设计时,可为单桩临界桩长的合理确定提供一定的理论依据。     

振冲碎石桩工程质量因素的试验研究

分析了影响振冲碎石桩质量的因素。通过正交试验,分析了桩径、桩长、碎石垫层对振冲碎石桩承载性能的影响,说明了碎石垫层的必要性、小桩径的合理性和有效桩长的经济性。     

以沉降控制为标准的水泥土搅拌桩设计方法的研究

从工作荷载作用下水泥土搅拌桩存在着一个临界桩长这一事实出发，通过大量的理论计算和实测资料分析，提出了以沉降控制为基础的水泥土搅拌桩设计方法。     

用于基坑支护的水泥搅拌桩质量检验方法探讨

本文介绍了现有的水泥搅拌桩质量检测方法,这些方法用于基坑支护中的搅拌桩检测仍有局限性。本文通过某工程两次取芯试验的比较,提出了建立新的搅拌桩质量评价规范的必要性。     

复杂钢管结构电视塔塔柱拼接形式研究

河南省广播电视发射塔为高388m的综合性钢结构电视塔，其外塔柱节点间直线段长度达48m，为了满足热浸锌防腐、运输、吊装等工艺要求，必须对其进行分段，在施工现场进行外塔柱拼接，且拼接节点要求抗弯刚度连续。目前钢柱拼接对H形截面柱可采用高强螺栓抗剪连接和全熔透坡口对接焊，但对于箱形截面柱和管形截面柱采用的都是全熔透坡口对接焊拼接方法。为了不破坏热浸锌防腐蚀层，提高施工质量和施工速度，希望能够采用工厂焊接，现场螺栓法兰连接的施工方法。在以往钢塔设计中，法兰连接作为部分刚性连接，不要求其抗弯刚度的连续性，而只要求其受力性能满足设计荷载要求。采用高强螺栓摩擦型连接的法兰来保证河南省广播电视发射塔外塔柱承载力和抗弯刚度的连续性，并通过构件的缩尺加载试验进行验证，说明了该拼接节点的合理性和施工的可行性。     

Effects of Curing Period and Stress Conditions on the Strength and Deformation Characteristics of Cement-mixed Soil

The effects of long-term curing on the strength and deformation characteristics of compacted cement-mixed soil were evaluated. A series of unconfined compression tests and drained triaxial compression (TC) tests were performed on moist cement-mixed sand compacted at various water contents, w_i, and cured at unconfined conditions for different periods up to more than eight years. TC tests were performed on cement-mixed gravel compacted at the optimum water content. The ageing effects on the compressive strength, q_max, from the present study were compared to those with various types of cement-mixed soils and concretes from the literature. An increase in q_max of cement-mixed soil continues for a very long period, up to several years, unlike ordinary concrete. This result indicates that the compressive strength at 28 days of cement-mixed soil, usually employed as the design strength, may largely underestimate the long-term strength. The increasing rate with time of the initial stiffness at small strains becomes continuously smaller than q_max with time. A large high-stiffness stress zone develops when monotonic loading is restarted at a certain high strain rate after some long sustained loading. This stress size is much larger than the one in the case without ageing effects. By positive interactions between the ageing effect and the inviscid yielding, q_max exhibits a larger extra gain when cured longer at more anisotropic stress states.     

Erforderliche Einspanntiefe von Stahlstützen in Betonfundamenten

Required length of restraint for steel columns in concrete foundations. Steel columns are connected frequently bending resistant to concrete substructures. With this type of construction the required length of restraint must be specified and the load‐carrying capacity of the steel columns within the range of the concrete foundations has to be verified. In the report consistent load‐carrying models are presented, which are considering the ultimate plastic load‐carrying capacity of cross sections and new calculation models according to Eurocode 3 for locals verifications. The verification conditions are formulated for steel columns made of rolled and welded I‐sections, which are stressed by one‐ or two‐axial bending with compression normal force. For columns with rolled sections calculation adds are given, which makes it possible to read off directly the required length of restraint.     

基坑工程中的水泥搅拌桩止水帷幕及其冷缝处理

结合基坑工程实际,介绍了三轴水泥搅拌桩止水帷幕在施工中的搭接方法、施工质量控制要点,阐述了双管高压旋喷桩对于三轴水泥搅拌桩止水帷幕的冷缝处理方法,并通过工程实践,验证了三轴水泥搅拌桩的止水效果以及高压旋喷桩对冷缝处理的可行性。     

深层水泥搅拌桩施工监理

对深层水泥搅拌桩施工前的材料控制、施工过程中的质量控制及成桩质量检验方法等进行了阐述,并提出了在进行深层水泥搅拌桩施工过程中加强质量监督的重要性和必要性,以保证施工质量。     

Effect of Curing Stress and Period on the Mechanical Properties of Cement-Mixed Sand

Cement mixing is one of the popular ground improvement technologies in geotechnical engineering practice. In order to effectively and confidently design cement-mixed soil structures for specific purposes, its stress-strain behavior needs to be well understood. Though there have been many studies on cement-mixed soils using different types of soils, their behaviors have not been generalized yet. As is the case with concrete materials, the hydration of cement in cement-mixed soil continues with time, thereby improving the strength and deformation characteristics of cement-mixed soil over time. In the field, the cementation bonds are formed under stress in case of in-situ soil. However, in the usual testing techniques, cementation bonds under stress has not been a point of consideration in most of the previous studies. This has led to an underestimation of the stress-strain behavior of cement-mixed soil. On the other hand, soils are subjected to confining stress during loading which has also some effect on the strength and deformation characteristics of soil which has not been considered yet in the case of cement-mixed sand. This study investigates the effect of curing stress and period on the strength and deformation characteristics of cement-mixed sand. The effect of confining stress in the triaxial test is also investigated in another series of specimens. A series of consolidated drained (CD) triaxial compression (TC) tests were done along with the small strain cyclic loading and bender element tests during monotonic loading to determine the small strain Young's modulus (E_v) and shear modulus (G_vh) respectively. The effect of the curing period is significant in the peak strength, stiffness, E_v, G_vh and also in the post peak regime. The curing stress also has a significant effect on the peak strength, E_v and G_vh. The confining stress has an effect on the peak strength, stiffness and in the post peak regime. However, the effect is small compared to clean sand.     

水泥搅拌桩各参数敏感性分析

运用敏感性分析方法,结合有限元数值模拟,对水泥土搅拌桩支护结构各参数进行敏感度分析,选取影响桩顶最大水平位移的6个参数,计算在基准值不变的情况下,各参数对桩顶最大水平位移的敏感性,为合理选择水泥土搅拌桩的结构参数提供参考。     

超载软土地基被动加固控制邻近桩基侧向变形分析

当堆载超过强度标准或桩顶位移超过变形控制标准后，就需要采取提高地基稳定性和控制桩基侧向变形的措施。深层搅拌法是一种常用的软土地基加固方法。采用有限元法，模拟深层搅拌法被动加固软土地基与堆载邻近桩基的相互作用，分析、讨论了加固宽度、加固深度、加固体弹性模量等桩基侧向变形的影响，可为地基处理提供一定的理论指导。