堤坝形毛竹土钉排桩基坑支护研究

提出了一种新型的软土基坑支护方法即"堤坝形毛竹土钉排桩基坑支护"。该方法主要是以节能环保型的竹材取代传统高耗能的钢质钉材,以毛竹为基坑侧壁支护排桩,以堤坝形土钉墙替代传统的各排土钉等长或上长下短布置。通过对毛竹力学性能的分析、现场抗拔试验、工程实践及数值模拟,验证该堤坝形毛竹土钉排桩基坑支护理念是正确的,表明毛竹在注浆过程中起到诱导作用可使注浆效果更好、能加深土钉在软土基坑的适用深度、可提高基坑支护的安全系数。     

对两个基坑支护规范有关土钉检测值的探讨

在统计分析比较现行《建筑基坑支护技术规程》、《复合土钉墙基坑支护技术规范》中有关土钉检测值规定的基础上,结合潍坊某土钉墙支护工程实际案例,从安全性、经济性、可靠性3个度量指标角度出发,对验收土钉锚固体与土层粘结抗拔检测值、工作土钉及验收土钉杆体抗拉截面配筋的设计方法和相关规定等方面存在的某种程度的欠合理性进行了理论与实践探讨,并制定了合理性评估标准,最后对如何合理确定验收土钉检测值、工作土钉和验收土钉杆体截面配筋及验收土钉临时自由段的相关设置等提出了新的方法和要求,有效地解决了土钉支护设计人员及检测人员对此检测值的困惑,对验收土钉设计和相应规范标准修订完善具有一定的参考价值。     

土钉及超前桩墙复合支护技术的应用

超前桩墙在软弱土基坑土钉支护中的应用 ,扩展了土钉支护技术的适用范围 ,但国内外对其作用机理的研究甚少。本文通过工程实例的边坡水平位移量测和平面有限元分析 ,对超前桩墙在软弱土基坑土钉支护中所起的作用进行了探讨 ,通过超前桩墙的预支挡解决了分层开挖时软弱土边坡的临时自稳问题 ,并有效地控制了软弱土边坡的坡顶位移和坡面变形破坏。本文的结论可供软弱土基坑复合土钉支护优化设计时参考     

谈土钉墙与锚杆、加筋土墙的比较分析

土钉支护是近年来发展起来的用于土体开挖和边坡稳定的一种新型挡土结构,由于经济、可靠且施工快速简便,已在我国得到迅速推广和应用.在基坑开挖中,土钉支护现已成为桩、墙、撑和锚支护后又一项较为成熟的支护技术.本文对土钉及土钉墙的概念、分类以及其应用领域和适用土层进行了阐述,同时也对土钉墙和锚杆、加筋土墙的作用机理和工作性能进行了比较分析探讨,为土钉墙基坑支护方案的选择提供一定的参考.     

土钉墙在深基坑支护中的应用

介绍了洛阳铲成孔土钉墙与旋喷桩深基础加固方案的对比情况,及采用洛阳铲成孔土钉墙取得的较好经济效益,为在管线密集的深基础地区基坑加固提供了新的思路。     

基于MINDLIN解的土钉墙变形计算方法

 土钉墙变形是影响其安全的关键指标,已有的研究没有给出其变形的合理理论计算方法。提出基于MINDLIN解的土钉墙变形理论计算方法,该方法通过虚拟开挖应力模拟土钉墙开挖状态,基于实测资料假定钉土剪力在潜在滑动面两侧沿土钉方向呈双三角形分布,利用MIDLIN应变解计算虚拟应力和钉土剪力在钉尾和潜在滑动面位置产生的侧向变形,根据钉土剪力在潜在滑动面位置等于0的特点得到钉土相对位移在潜在滑动面位置为0的结论,并利用该结论及土钉力学平衡条件得到钉土剪力计算模型的2个相关参数,最后通过钉尾变形和土钉自身拉伸变形的叠加得到土钉墙任意位置的侧向变形。通过与法国CEBTP大型试验1#墙实测数据的对比分析,初步验证该计算方法的合理性和可行性。     

某基坑边坡事故原因分析及加固处理

结合具体工程,根据整体稳定性和土钉锚杆承载力验算的计算结果,分析了基坑事故的原因,针对该工程的特点,提出经济合理的加固方案和施工措施,以确保基坑和周围建筑物的安全。     

风化岩地区土钉墙支护设计与施工若干问题探讨

结合工程经验与规范中的规定,说明岩体内摩擦角φk的确定方法,并利用单轴应力条件下的摩尔—库伦准则来反算岩体的粘聚力ck,利用该方法确定的岩体工程设计参数进行土钉墙支护方案的设计计算;通过工程实例说明风化岩地区钢管式土钉可打入深度与标准贯入试验锤击数之间的关系,为工程设计人员在确定钢管式土钉设计长度时提供参考;提出土钉墙支护在北方严寒地区应用时考虑到冻胀作用影响下应采取的措施。     

深基坑的土钉支护设计与实践

深基坑逐层开挖,逐层在边坡以较密排列打入土钉钢筋,强化坑边坡土体的受力,并在坡面上设钢筋网,分层喷射混凝土,这就是深基坑支护中的土钉支护方法。这种方法与锚杆支护、加筋土比较,具有特有的优点。     

基坑土钉支护结构受力及变形分析

通过对某基坑土钉内力及土体位移的现场测试 ,分析了土钉支护的内力分布规律和土体位移特征 ,研究了基坑土钉支护的工作性能 ,其结果可为理论研究和相关设计提供资料     

复合地基加固软基方案比选分析研究

以某沿海二级公路建设项目为背景,介绍两种常用的复合地基加固软土地基处理方案。在阐述长螺旋钻孔压灌桩和钉形双向水泥土搅拌桩两种桩体成桩工艺流程和质量控制要点的基础上,对两种桩体在加固软体地基方面的优缺点进行对比分析,最终确定该项目软土地基加固方案为长螺旋钻孔压灌桩。     

土钉支护中土钉力的计算方法

土钉支护机理为加固机制上的锚固机制;土钉支护中土钉力的发生、发展是与施工过程中被支护土体应力释放密切相关的。本文从边坡锚固稳定的思想出发,采用能够较好地反映施工过程的增量计算方法,并根据土体应力的释放效果确定了土钉拉力增量的比例系数,提出了土钉力的合理计算方法。最后,根据本文方法对实际工程进行了计算,并与实测结果进行了对比。     

Direct limit analysis based topology optimization of foundations

Topology optimization of foundation structures is conducted using a direct limit analysis based optimization approach. Originally developed for plastic topology design of 2D superstructures and industrial structures, which are traditionally designed based on elasticity, the direct limit analysis based design method demonstrated strong intrinsic properties that make of it a promising alternative for topology design. Unlike existing methods the one proposed here is fundamentally conceived and developed in the framework of direct plastic limit analysis which is the natural and usual known framework for the analysis and design of geotechnical structures. The method is extended to handle foundation design by providing for the simultaneous presence of two materials: the soil and the reinforcement, governed by Coulomb failure law. Two types of designs are considered, namely, continuous and discrete. The first allows a range of graded densities of reinforcement that may in practice represent the types of mixtures used in soil improvement, such as cementation. In the discrete design the reinforcement consists exclusively of solid structural elements. A series of two dimensional example problems demonstrate the capabilities of the method to generate rational classical designs or uncommon but intuitively sound foundation configurations that could inspire designers to develop novel solutions.     

Pseudo-static/dynamic solutions of required reinforcement force for steep slopes using discretization-based kinematic analysis

This paper presents a procedure for assessing the reinforcement force of geosynthetics required for maintaining dynamic stability of a steep soil slope. Such a procedure is achieved with the use of the discretization technique and kinematic analysis of plasticity theory, i.e. discretization-based kinematic analysis. The discretization technique allows discretization of the analyzed slope into various components and generation of a kinematically admissible failure mechanism based on an associated flow rule. Accordingly, variations in soil properties including soil cohesion, internal friction angle and unit weight are accounted for with ease, while the conventional kinematic analysis fails to consider the changes in soil properties. The spatial–temporal effects of dynamic accelerations represented by primary and shear seismic waves are considered using the pseudo-dynamic approach. In the presence of geosynthetic reinforcement, tensile failure is discussed providing that the geosynthetics are installed with sufficient length. Equating the total rates of work done by external forces to the internal rates of work yields the upper bound solution of required reinforcement force, below which slopes fail. The reinforcement force is sought by optimizing the objective function with regard to independent variables, and presented in a normalized form. Pseudo-static analysis is a special case and hence readily transformed from pseudo-dynamic analysis. Comparisons of the pseudo-static/dynamic solutions calculated in this study are highlighted. Although the pseudo-static approach yields a conservative solution, its ability to give a reasonable result is substantiated for steep slopes. In order to provide a more meaningful solution to a stability analysis, the pseudo-dynamic approach is recommended due to considerations of spatial–temporal effect of earthquake input.     

土钉支护软土边壁(坡) 机理相似模型实验研究

 在描述土钉支护软土边壁(坡) 相似模型试验现象和结果基础上, 对其加固、支护机理作了探讨。分析了土钉弓形受力分布有一个产生、形成、发展和畸变的过程, 并非如C. K. Shen 等人给出的固定弓形形态。同时论述了土钉支护面层的鼓形受力特点, 与软土边壁的流鼓破坏模式密切相关。     

基于增量法的土钉墙支护设计方法研究

对于土钉支护设计,与复杂的计算分析相比,简化设计方法更加实用。在增量法的基础上,提出了一套基于增量法的完整的土钉墙设计方法。土钉支护设计计算所用的荷载建议采用考虑放坡的库仑主动土压力;土钉的内力可采用增量法进行计算,进而求出土钉所需的钢筋直径;建议采用库仑滑动面确定土钉的最大内力作用点,根据已确定的土钉的最大内力和库仑滑动面的位置计算土钉伸入到锚固土体里的长度,从而得到各排土钉的总长度;整体稳定采用《建筑基坑支护技术规程》(JGJ120—99)建议的方法进行验算。提供了一个成功应用基于增量法的土钉墙设计方法进行设计的工程实例,工程实践表明应用该方法进行设计是简便可行的。     

GFRP土钉拉拔特性研究

由于传统土钉材料存在易腐蚀、耐久性差等缺点,近年来以GFRP为代表的新型土钉材料得到了高度重视。针对GFRP土钉受力特性,运用双曲线模型描述其在拉拔过程中剪应力–剪应变关系,采用数值方法求解拉拔控制方程,从而确定轴力、剪应力及位移沿钉长的分布。同时,通过室内GFRP模型土钉的拉拔试验,验证了该模型预测结果的准确性。在此基础上,对土钉直径、土–钉界面抗剪强度、土–钉模量比等参数进行了参数分析,并针对GFRP土钉容许拉拔力的确定提出了按位移控制的思路。     

黏土中土钉墙实例分析和变形评估

土钉墙是一种边开挖边支护的支护方式。其设计、施工过程中包含很多随机、不确定性因素,准确评估它的变形大小是极为困难的。全面介绍了13个黏土中类似基坑工程土钉墙实例,包括它们的工程勘察、设计方案、施工、监测、竣工资料。通过分析这些资料,得出基坑最大水平位移大多小于0.7%倍的开挖深度等的一些结论,并提出软土层影响系数和土钉刚度系数两个概念,用实例数据证实了当软土层影响系数增加或当土钉刚度系数减少时,土钉墙变形有增大的趋势。     

Soil-reinforcement interaction: Stress regime evolution in geosynthetic-reinforced soils

Understanding the stress regime that develops in the vicinity of reinforcements in reinforced soil masses may prove crucial to understanding, quantifying, and modeling the behavior of a reinforced soil structures. This paper presents analyses conducted to describe the evolution of stress and strain fields in a reinforced soil unit cell, which occur as shear stresses are induced at the soil-reinforcement interface. The analyses were carried out based on thorough measurements obtained when conducting soil-reinforcement interaction tests using a new large-scale device developed to specifically assess geosynthetic-reinforced soil behavior considering varying reinforcement vertical spacings. These experiments involved testing a geosynthetic-reinforced mass with three reinforcement layers: an actively tensioned layer and two passively tensioned neighboring layers. Shear stresses from the actively tensioned reinforcement were conveyed to the passively tensioned reinforcement layers through the intermediate soil medium. The experimental measurements considered in the analyses presented herein include tensile strains developed in the reinforcement layers and the displacement field of soil particles adjacent to the reinforcement layers. The analyses provided insights into the lateral confining effect of geosynthetic reinforcements on reinforced soils. It was concluded that the change in the lateral earth pressure increases with increasing reinforcement tensile strain and reinforcement vertical spacing, and it decreases with increasing vertical stress.     

复合土钉墙现场测试及数值模拟分析研究

整理分析了济南西部新城某地下车库基坑的复合土钉墙支护结构现场监测数据,采用有限元软件ABAQUS建立基坑支护结构单元三维模型,模拟了其开挖支护施工过程,动态分析基坑边坡坡顶地表水平位移、沉降变化规律,并与现场监测值进行对比,分析了微型桩与止水帷幕对复合土钉墙的影响。表明由土钉、止水帷幕、微型桩、预应力锚杆与土体相互作用的有限元力学模型能较好模拟复合土钉墙支护施工过程,结果可供同类复合土钉墙设计施工提供参考。