单排微型桩加固碎石土滑坡物理模型试验

微型桩因其自身优势被广泛使用,但有关其抗滑机理的理论研究相对较少.首先对模型桩的力学特性进了标定试验,获得其弹塑性工作阶段的弹性模量,分别为0.69×104 MPa和0.04×104 MPa;再通过不同桩间距下单排微型桩加固碎石土滑坡室内模型试验,研究微型桩抗滑机理.试验结果表明:不同桩间距下单排微型桩桩后土压力主要集中在滑面以上1/3桩身范围内;桩间距较小,土拱效应越明显,微型桩抗滑失效的最大临界弯矩越大,微型桩能承受的滑坡推力越大,抗滑效果越好.     

桩基变形分析及水平静载试验探讨

本文通过对拟建风电场项目的3根桩长10m,桩身直径为800mm的机械钻孔混凝土灌注桩试验桩进行单桩水平静载试验,准确测定出该工程的试验桩7#、8#、9#三根单桩水平承载力特征值不小于60KN,7#单桩的桩顶水平最大位移量为3.73mm、8#单桩的桩顶水平最大位移量为2.38mm、9#单桩的桩顶水平最大位移量为1.36mm。为项目下一步的设计提供了依据。     

土质边坡中部与顶部抗滑桩动力响应和边坡变形比较

地震作用及其诱发的变形或滑坡常会使抗滑桩受力发生显著变化,为此,研究了地震作用下不同加固位置的抗滑桩的动力响应和边坡变形情况.试验分析表明:中桩位边坡坡顶变形比高桩位边坡坡顶变形大,但中桩位边坡坡脚堆积变形比高桩位边坡坡脚变形较小;在同样条件下中桩位抗滑桩的静力、动力弯矩小于高桩位抗滑桩相应位置的弯矩;地震结束后由于坡体震动残余变形较大,抗滑桩最终承担着震后残余弯矩,但高桩位抗滑桩的承载能力在震后仍然发挥较大.研究结果表明:高桩位加固位置可以有效发挥抗滑桩的抗弯承载能力,但中桩位可以有效抑制坡底坡脚变形.     

深基坑桩撑、桩锚支护结构的应用实例及其分析

桩撑、桩锚支护结构是深基坑支护工程中常用的支护形式,应用比较广泛。本实例深基坑工程对称两侧由于其工程环境条件分别采用了桩撑、桩锚支护形式,通过对桩撑及桩锚支护结构的设计计算成果、监测成果进行分析对比,可为同类深基坑支护工程的设计及施工提供借鉴和参考。     

CFG桩复合地基作用机理及其在工程中的应用

本文介绍了CFG桩复合地基的作用机理及CFG桩复合地基的设计过程,并通过工程实例介绍了CFG桩复合地基在地基处理工程中的应用,可供工程技术人员参考。     

CFG桩施工中使用长螺旋钻存在问题的刨析

通过工程实例,介绍了长螺旋钻孔在CFG桩施工中存在的由于钻门打不开而造成堵管或爆管,憋钻和卡钻,断桩、缩径和桩身缺陷等事故及采取的防治措施。     

基于桩间土拱效应的微型桩间距的分析

通过FLAC3D软件模拟计算和分析陕南勉县的微型桩治理滑坡工程实例,研究了微型组合抗滑桩在滑坡治理中土拱效应的形成、应力的变化状况,得出最佳距径比。结果显示:微型桩在滑坡下滑主动土压力的作用下,首先在沿滑移方向第1排桩桩间形成应力拱效应,然后随着距径比的增加,依次在第2排、第3排桩上形成应力拱效应,并且前排桩的荷载分担比明显大于后排桩的荷载分担比。当距径比达到一定程度后土体绕过第1桩,形成以第2排桩为拱顶,第3排桩为拱脚的应力拱。由模拟的应力云图得知,距径比3和9时,没有明显的或者不存在应力土拱效应,距径比为5~8时最为理想。     

长螺旋钻机施工CFG桩常见质量问题及应对措施

长螺旋钻机施工CFG桩,即水泥粉煤灰碎石桩,目前以钻孔管内泵压混合料灌注(超流态混凝土压灌)成桩为主要工艺方法,该工法适用于粘性土、粉土、砂土以及对噪声或泥浆污染要求严格的场地。     

流变地层中深基坑围护桩侵限成因及应对措施研究

在流变地层中,由于土体力学性能差,导致土体自稳性能差,出现围护桩侵入结构边线的现象,基坑工程中称之为围护桩侵限。围护桩侵限侵占主体结构空间,影响后续主体结构施工。本文以流变地层中某地下室基坑工程为案例,对该基坑工程中围护桩侵限问题进行了分析研究,总结出流变地层中围护桩侵限原因、预防及处理措施,为类似地层条件下基坑工程提供参考。     

抗滑桩与桩顶弧形连系梁协同作用机理及计算分析

桩顶弧形连系梁通过约束桩顶位移,能够优化桩身的受力状态,且能提高抗滑桩的整体稳定性。与直线型连系梁相比,弧形连系梁的受力性能与拱形结构相似,以受压为主,能够充分发挥混凝土较高的抗压能力,通过抗滑桩及连系梁可将部分滑坡推力传递至滑体两侧稳定岩土体,降低了对滑床岩土体强度及抗滑桩桩身强度的要求。根据抗滑桩与连系梁之间的协同作用及变形协调,利用力法原理,建立柔度方程,求解桩顶与连系梁之间的约束冗力,进而计算连系梁及抗滑桩的内力和位移。通过算例表明,弧形连系梁较直线型连系梁内力分布均匀,与单桩及桩顶受直线型连系梁约束的排桩相比,弧形连系梁对抗滑桩的约束效果明显,而且约束效果随弧形连系梁矢跨比的增加而增强。     

Ground deformation in a viscoelastic medium composed of a layer overlying a half-space: a comparison between point and extended sources

We obtain and compare analytical and numerical solutions for ground displacement caused by an overpressurized magma chamber placed in a linear viscoelastic medium composed of a layer over a half-space. Different parameters such as size, depth and shape of the chamber, crustal rheology and topography are considered and discussed. Numerical solutions for an axisymmetric extended source are computed using a finite element method (FEM). Analytical solutions for a point source are obtained using the dislocation theory and the propagator matrix technique. In both cases, the elastic solutions are used together with the correspondence principle of linear viscoelasticity to obtain the solution in the Laplace transform domain. Viscoelastic solutions in the time domain are derived inverting the Laplace transform using the Prony series method. The differences between the results allow us to constrain the applicability of the point source and the flat surface hypothesis, which are usually implicitly assumed when analytical solutions are derived. The effect of the topography is also considered. The results obtained show that neglecting the topographic effects may, in some cases, introduce an error greater than that implicit in the point-source hypothesis. Therefore, for an adequate modelling and interpretation of the time-dependent displacements, topography must be considered.     

Use of a bubble tiltmeter as a horizontal seismometer

Summary. A bubble tiltmeter has been used as a horizontal seismometer. With the appropriate filters, the bubble system has good response for displacement over the passband of conventional seismometers (from about 10 Hz to 200 s), and for tilt from about 1 Hz to DC. The accuracy of the response is confirmed by comparing the filtered bubble output to conventional seismic instruments. The agreement between the filtered bubble records and broad band ( T ₀= 1 s, T _g= 90 s) and short period ( T ₀= 1 s, T_g= 0.2 s) conventional records is extremely good in every case.
The small size, broad-band response, and lack of moving parts make the bubble ideal as an instrument for remote environments. In particular, the instrument seems ideal for the ocean bottom, land and marine boreholes and planetary missions.     

Working a fraction and making a fraction work: a rough guide for geographers in the academy

Little is known about the issues facing geographers working on fractional appointments in higher education institutions in the UK. This paper draws on a survey of UK geography departments and personal experiences to explore some of that territory for the first time. The purpose is both to set the agenda for institutional policy issues and to provide some immediate points of reflection for staff intending to take up fractional work. We consider the place of fractional working in the dominant discourses around paid work, problems of workload division and the impact on professional standing (including the RAE). We suggest that while personal 'life' reasons for fractional working are often positive, fractional workers in the academy risk professional marginalization.