桩埋管参数对渗流下能量桩热-力耦合特性的影响

为获得地下水渗流作用下桩埋管参数对能量桩热-力耦合特性的影响,建立了不同埋管参数的能量桩数值模型,分析了桩埋管数量、埋管布置形式、埋管管径对单位桩深换热量、日换热量、桩截面平均温升、桩身位移增量及桩身附加温度荷载的影响。结果表明：增加埋管数量可以增大能量桩换热量,但也会加剧桩内不同埋管间的热干扰,导致换热性能下降及桩身...     

循环温度场作用下PCC能量桩热力学特性模型试验研究

PCC能量桩是河海大学岩土所开发的一种新型能量桩技术。在常规桩基静载荷模型试验基础上,将PCC能量桩放置在南京典型砂土中,并通过导热管内水体的循环对模型桩体施加温度场,以模拟PCC能量桩在实际运行过程中的承载力特性与受力机制,PCC能量桩先加载至工作荷载（极限荷载的一半）,再施加热-冷循环一次,最后加载至极限荷载,测得不同温度下PCC能量桩的荷载-位移关系曲线、桩身应力-应变关系曲线等变化规律。试验结果表明,能量桩换热过程中,热量更容易从桩体传向土体（即夏季模式的热循环）;热循环及制冷循环都明显改变了桩顶位移值,且往复循环作用下产生的塑性变形不能完全恢复,其积累变形可能危害上部结构安全;桩身受温度场作用产生的热应力相对较大,且不同约束条件下其变化值有所差异;在制冷循环下,桩底部甚至可能产生较大拉应力。     

桩−筏基础中能量桩热−力耦合特性现场试验

能量桩兼具承担上部荷载和传递浅层地温能双重功能,能量桩的换热与承载特性逐渐成为广大工程技术人员关注的重点问题。然而,针对桩?筏基础中能量桩的热?力耦合特性的现场实测资料仍相对较少。提出将桩基完整性检测中的声测管底端连接贯通,作为能量桩的换热管,形成新型能量桩埋管形式;在桩?筏基础中能量桩运行状态下,开展桩?筏基础热力响应特性、能量桩对筏板应力影响的现场试验,实测获得桩身温度、桩身应力及筏板应力变化规律。研究结果表明,该试验条件下,能量桩（1U埋管、有效深度为12.8 m、桩顶埋深为5.5 m）的换热效率约为80～90 W/m;无上部荷载、能量桩加热状态下,筏板上边缘呈现出一定的拉应力,值得工程技术人员关注。     

基于能量守恒的预制桩施工残余应力模拟

预制桩施工阶段形成的残余应力较难由实测获得,其重要影响鲜受关注。从能量守恒原理出发,可模拟沉桩引起的桩身残余应力分布。计算模型采用剪切带理想弹塑性荷载传递关系及残余摩阻力折线型分布假定,以桩身弹性变形能为纽带,对预制桩沉贯和回弹过程进行能量分析,建立了施工全过程的能量平衡方程。参数分析显示,桩长径比与剪切带摩擦性状是影响桩身残余应力的关键因素。该模型能较合理预测某原型试桩的施工残余应力。     

On the understanding of cyclic interaction mechanisms in an energy pile group

Integrating ground heat exchanger elements into concrete piles is now considered as an efficient energy solution for heating/cooling of buildings. In addition to the static load of buildings, the concrete piles also undergo a cycle of thermal deformation. In the case of single energy pile, calculation methods already exist and permit to perform a proper geotechnical design. In the case of energy pile group, the thermo‐mechanical interactions within the group are more complex. Very few experimental results on the energy pile group are available so that numerical analysis can be an interesting way to provide complementary results about their behavior. This paper deals with a numerical analysis including a comparison between a single energy pile and an energy pile group with different boundary conditions at the pile head. In order to take into account the stress reversal induced by the thermal expansions and contractions, a cyclic elastoplastic constitutive model is introduced at the soil–pile interface. The analysis aims to give some insights about the long‐term cyclic interaction mechanisms in the energy pile group. Based on this qualitative study, some guidance can be brought for the design of energy piles in the case where group effects should be considered. Copyright © 2015 John Wiley & Sons, Ltd.     

能源桩传热与承载特性研究现状及展望

能源桩是一种在传递上部结构荷载的同时获取浅层地热能源的新技术,给桩基结构的设计及安全服役提出了新的挑战。从能源桩实际应用的角度,围绕能源桩传热性能和承载性能两个关键科学问题,从4个方面综述目前的研究现状：（1）能源桩的热传递研究;（2）能源桩的结构响应特征;（3）能源桩的承载变形特性;（4）能源桩的荷载传递机制。在此基础上,对当前能源桩传热模型的适用性、热交换作用下能源单桩及群桩的承载特性以及长期运行条件下的承载性能及结构安全性进行了讨论,最后对能源桩工程下一步研究进行了展望。分析成果对于保证结构安全,合理开发浅层地能具有重要意义。     

The interaction factor method for energy pile groups

Prior to this study, no simplified yet rational methods were available for estimating the vertical displacements of energy pile groups subjected to thermal loads. Observing such a challenge, the goal of this study has been threefold: (i) to extend the interaction factor concept from the framework of conventional pile groups to that of energy pile groups, (ii) to present charts for the analysis of the displacement interaction between two identical energy piles over a broad range of design conditions, and (iii) to propose, apply and validate the interaction factor method for the displacement analysis of energy pile groups.     

评估灌注桩极限承载力的概率能量法

本文研究用概率能量方法评估灌注桩极限承载力的可行性,研究所用数据取自南京市区的２００根桩例的ＣＡＰＷＡＰ反分析与静载试验结果。根据能量守恒定律并结合动态桩－土相互作用模型,详细地推导了桩极限承载力计算公式。并对其中的模型参数,Ｊｓ,Ｊｔ,Ｑｓ,Ｑｔ作为随机变量处理,统计分析了它们的平均值,标准差以及概率分布函数。用蒙特卡洛法模拟确定了桩极限承载力的概率分布函数,并进一步提出了计算桩极限承载力超过某一设计值的概率公式。通过计算的桩极限承载力与静载结果的良好可比性,说明了此方法的台理性与准确性。     

Effect of non-linear soil deformation on the interaction among energy piles

This study investigates the effect of non-linear soil deformation on the displacement interaction among energy piles. The work is based on interaction factor analyses of full-scale pile group tests, whose results are compared with experimental evidence. The results presented highlight the tendency of interaction factor analyses that ignore non-linear soil deformation to overestimate the interaction and the displacement of energy pile groups. This outcome, in accordance with previous studies for conventional pile groups subjected to mechanical loads, may be considered in the analysis and design of energy pile groups subjected to thermal (and mechanical) loads through the interaction factor method.     

动测法桩基检测过程中弹性波能量在桩体界面上的反射和透射

本文分别就(1)变阻抗桩(2)变截面桩(3)阻抗截面均有变化的桩阐述了在动测过程中弹性波能量的传输过程,即弹性波能量在截面上的入射、反射和透射的关系及分配特性。     

基于能量桩现场试验的土体综合热导率系数研究

能量桩技术兼具支撑上部荷载和浅层地热能换热器双重功能;作为一种节能减排技术,近年来在国内外获得了一定的发展。然而,目前简单套用基于传统地埋管换热器获得的土体综合热导率系数,无法准确计算能量桩换热效率。依托河南理工大学某低承台3×3能量桩群桩工程应用,开展基于能量桩的土体综合热导率系数测试现场试验和数值模拟研究,分析加热时长、加热功率、流速及桩长等因素对土体综合热导率系数的影响规律,继而探讨能量桩在群桩中的布置形式对土体综合热导率系数的影响规律。研究结果表明,基于传统地源热泵测试所发展起来的土体综合热导率系数线热源分析方法,并不适用于分析基于能量桩现场实测所获得的相关数据;有必要推导一套考虑桩径影响的、适用于能量桩的土体综合热导率系数测试与计算分析方法。     

基于能量法的轴横向荷载作用下单桩受力变形分析

轴向和横向荷载作用下单桩的受力变形分析是桩基研究的重点内容之一。单桩在水平荷载作用下会产生一定的水平位移与弯矩,而此时作用轴向荷载会使得桩体出现一定的压曲与附加弯矩,以致轴横向荷载作用下的单桩受力变形与单独作用水平荷载或轴向荷载的单桩存在较大的区别。故本文基于能量法,首先分别建立轴横向荷载作用下单桩的受力变形能量方程以及桩周土体能量方程,然后考虑桩土变形协调与一定的桩土相互作用,基于最小势能原理得到单桩变形控制微分方程,并采用幂级数法进行求解,最终得到轴横向荷载作用下单桩受力变形分析的幂级数解答。通过编程计算,将本文方法计算结果与试验结果、数值分析结果、规范法计算结果进行对比分析,验证了本文方法的合理性和可行性。在此基础上,基于本文解答进行了影响参数分析,结果表明:桩体长径比、桩土弹性模量比、桩周土模量深度变化系数均对轴横向受荷单桩的桩身水平位移与最大弯矩值有一定的影响,其中桩周土模量深度变化系数以不小于0.6为宜。     

静钻根植能源桩承载特性模型试验研究

为了研究静钻根植能源桩在热?力耦合作用下的承载特性,采用自行设计模型试验系统,测试模型桩在黏?砂双层地基中的热力响应。试验结果表明：桩体温度沿深度变化并不均匀,对桩周土的温度影响半径为3倍桩径;3次冷热循环后桩顶和桩周土表面均产生累积沉降,在桩顶荷载达到单桩极限承载力的25%时,桩顶累积沉降达到桩径的3.12‰,是桩顶无荷载情况下的1.77倍;模型桩附加温度应力沿深度分布均表现为中间大两端小,位移变化零点（附加温度应力最大处）随着桩顶荷载增大（约束增强）而上移,桩顶荷载较小时降温引起桩身局部产生拉应力。因此,静钻根植能源桩的承载特性与温度变化条件、桩顶荷载大小和桩端约束条件密切相关,在工程设计中需要综合考虑以确保运行安全性。     

饱和粉土中相变能源桩热力响应模型试验研究

长期非稳态的桩土热交换使得桩周土温度不断上升,产生热堆积效应,影响桩土换热效率,甚至也可使能源桩系统失效。为此,利用复合相变材料制备了相变混凝土能源桩,并在饱和粉土中开展了相变桩和普通桩热力响应模型试验,对比研究了相变桩的桩周温度分布、桩身应力−应变、桩顶位移和桩身换热效率的变化规律。结果表明：相变桩土热交换方向以径向交换为主,影响区域在2D范围以内,土体温度变化表现出滞后效应;相变桩的桩土温度变化幅度小于普通桩,具有缓解桩周土体热堆积效应的作用;在温度循环过程中,相变桩体累积了不可恢复的塑性应变。经过多次温度循环后,相变桩比普通桩的塑性累积位移更小;在夏季工况相变桩换热功率比普通桩增长约20%,冬季工况两者换热功率基本一致,随着运行时间增加,两者换热效率趋同。     

Thermo-mechanical behavior of energy piles in high plasticity clays

Energy piles make use of constant and moderate ground temperature for efficient thermal control of buildings. However, this use introduces new engineering challenges because the changes of temperature in the foundation pile and ground induce additional deformations and forces in the foundation element and coupled thermo-hydro-mechanical phenomena in the soil. Several published full-scale tests investigated this aspect of energy piles and showed thermally induced deformation and forces in the foundation element. In parallel, significant progress has been made in the understanding of thermal properties of soils and on the effect of cyclic thermal load on ground and foundation behavior. However, the effect of temperature on the creep rate of energy piles has received practically no attention in the past. This paper reports the experimental results of an in situ tension thermo-mechanical test on an energy pile performed in a very stiff high plasticity clay. During the in situ test, the pile was subjected to thermal loading by circulating hot water in fitted pipes, simulating a thermal load in a cooling-dominated climate, at different levels of mechanical loading. The axial strain and temperature in the pile, and the load–displacement of the pile were monitored during the tension test at different locations along the center of the pile and at the pile head, respectively. The data showed that as the temperature increases, the observed creep rate of the energy pile in this high plasticity clay also increases, which will lead to additional time-dependent displacement of the foundation over the life time of the structure. It was also found that the use of geothermal piles causes practically insignificant thermally induced deformation and loads in the pile itself.     

复杂地基反力模式下高承台嵌岩灌注桩的屈曲稳定分析

为探讨桩侧地基土反力对高承台嵌岩灌注桩桩身屈曲稳定的影响,假定地基反力系数呈更为复杂的幂分布,基于弹性地基梁理论建立桩土体系总势能方程,采用最小势能原理,导出了桩身屈曲临界荷载与稳定计算长度的解析解,并据此获得了地基反力系数分布模式、桩身自重及桩侧摩阻力等对桩身屈曲稳定的影响规律。工程应用分析结果表明,考虑地基反力系数为一般幂分布时,桩身屈曲分析结果更趋合理。     

悬臂排桩支护结构空间变形分析

以矩形基坑悬臂排桩支护结构为研究对象,通过分析现场实测数据和数值计算,归纳出了冠梁和支护桩的空间变形模式,建立了整个支护系统的能量表达式。利用最小势能原理,推导了基坑中部桩顶最大位移的解析解,分析了各主要支护参数对该位移的影响。研究结果表明,桩顶最大位移随坡顶超载和桩间距的增大基本呈线性增大趋势;当嵌固深度系数逐渐增大时,桩顶最大位移也逐渐增大,但趋势渐缓;基坑长度对其影响也较大,当基坑长度超过一定数值后,最大位移值趋于稳定。最后利用所得的研究成果对某基坑进行了验证,并与现场实测结果进行了对比,计算结果能够满足工程要求。     

Thermo-hydro-mechanical response of a large piled raft equipped with energy piles: a parametric study

This paper presents the results of a parametric study in which a series of fully coupled, 3-dimensional thermo-hydro-mechanical Finite Element (FE) analyses has been conducted to investigate the effects of the thermal changes imposed by the regular performance of a GSHP system driven by energy piles on a very large piled raft. The FE simulation program has been focused mainly on the evaluation of the following crucial aspects of the energy system design: the assessment of the soil–pile–raft interaction effects during thermal loading conditions; the quantification of the influence of the thermal properties of the soil and of the geometrical layout of the energy piles on the soil–foundation system response, and the evaluation of the influence of the active pile spacing on the thermal performance of the GSHP–energy pile system. The results of the numerical simulations show that the soil–pile–raft interaction effects can be very important. In particular, the presence of a relatively rigid raft in direct contact with the soil is responsible for axial load variations in inactive piles of the same order of those experienced by the thermo-active piles, even when the latter are relatively far and temperature changes in inactive piles are small. As far as the effect of pile spacing is concerned, the numerical simulations show that placing a high number of energy piles in a large piled raft with relatively small pile spacings can lead to a significant reduction of the overall heat exchange from the piles to the soil, thus reducing the thermal efficiency of the system.     

能量桩群桩工作特性简化分析方法研究

采用双曲线模型模拟桩土界面上的力学行为,利用剪切位移法反映剪应力在土层中的传递,考虑群桩之间的相互作用,建立了热?力耦合作用下能量桩群桩基础工作特性的简化分析方法。该方法能反映桩土界面上的非线性、桩顶的约束条件和能量桩位置的影响,可直接计算所有桩的位移和轴力。与现有方法相比,计算得到的双桩相互作用因子更加合理。通过与文献中试验数据的对比表明,若只有局部桩经历温度变化,能量桩运行过程中各桩之间存在差异变形,基础出现倾斜,桩顶荷载发生重分布。所建立方法计算方便,能合理模拟能量桩群桩基础的主要工作特性,可用于大规模能量桩群桩基础的设计计算。     

基于GRLWEAP的桩基可打入性影响因素研究

桩基的可打入性分析对桩的设计十分重要。实际工程中精确的可打入性分析可以避免由于未能将桩打入设计入土深度而导致的截桩和桩头损坏等事故,也能避免在桩的贯入深度已经超过设计贯入深度时仍不能满足设计承载力的情况发生。为精确桩基的可打入性分析,研究了影响桩基可打入性的多种敏感因素,采用正交实验法设计了32组试验,由GRLWEAP软件完成试验,得出打桩分析结果。结合渤海某油田平台工程实例得出桩基可打入性影响因素敏感度规律,即桩基可打入性影响因素敏感度由大到小依次是打桩能量、桩径、地质条件、桩长、垫层厚度、桩壁厚、停锤时间、停锤位置、桩段数量。