浸水饱和条件下黄土微型桩抗压和抗拔承载力试验

为开展浸水饱和条件下黄土微型桩基础抗压和抗拔承载性能试验,设计了一种桩周土体浸水饱和方案,并在甘肃地区2个湿陷性黄土场地分别完成了浸水饱和与天然含水率状态下微型桩单桩抗压抗拔和群桩抗压对比试验。结果表明:浸水饱和条件下黄土地基微型桩单桩抗压抗拔与群桩抗压荷载–位移曲线均呈"陡变型"变化规律,而天然状态下相应微型桩桩荷载–位移曲线则呈初始弹性段、弹塑性曲线过渡段和破坏直线段的三阶段"缓变型"变化规律。浸水饱和条件与天然状态下黄土抗压微型桩桩端阻力分担桩顶下压荷载的10%~15%,而相应黄土抗拔微型桩呈摩擦桩性状。天然状态下黄土微型桩单桩抗拔极限承载力为抗压极限承载力的66%~87%。当黄土浸水饱和后,相同微型桩单桩下压极限承载力平均下降70%,抗拔极限承载力平均下降50%,相同群桩基础下压极限承载力降低约75%。浸水饱和后黄土微型桩单桩和群桩基础下压极限承载力损失远高于相应基础的上拔极限承载力损失,相关试验研究成果可为今后黄土地区工程建设参考。

黄土抗拔基础承载性能

基于黄土抗拔基础现场试验成果,阐述了黄土平地和斜坡条件下等截面直柱基础和直柱扩底基础抗拔荷载位移特征及其承载机理。结果表明,黄土平地等截面直柱基础和直柱扩底基础抗拔荷载–位移曲线均呈"缓变型"变化规律,L-1-L2两点法可较好反映黄土抗拔基础荷载–位移曲线的初始弹性直线段、弹塑性曲线过渡段和直线破坏段3阶段变化特征。等截面直柱基础抗拔承载力由直柱与周围土体间摩擦阻力提供,直柱扩底基础呈扩大端土体压缩挤密发生弹性变形—基础周围土体塑性区形成、发展、贯通—土体整体剪切破坏的渐进过程,抗拔极限承载力由基础自重、滑动面剪切阻力及滑动面范围内土体重量组成,并可分浅基础和深基础2种破坏模式。上拔荷载作用下,黄土斜坡地形等截面直柱基础和直柱扩底基础下坡侧的柱顶及柱侧周围土体位移均大于上坡侧,抗拔土体的破坏滑裂面形态具有不对称性,地表裂缝主要分布在基础下坡侧。基础顶面均产生沿上拔荷载作用方向的微小偏转,且转角随荷载增加而增加。扩底和增加埋深均可提高黄土斜坡基础抗拔承载性能。

Numerical Analysis of Doublet Wells for Cold Energy Storage on Heat Damage Treatment in Deep Mines

Deep mining is an inevitable tendency in the development of coal industry. There are many heat damage problems with the increase of mining depth. The technology of using doublet wells, together with Heat Exchange Machine Systems (HEMSs), to store cold energy is a key to solve the heat damage problems in deep mines. Based on the geological conditions, thermodynamic and hydraulic parameters of Jiahe Mine, the isotherms in the period of cold energy storage and refrigeration and the volumes of cold water within different temperature ranges of the cold energy storage well were numerically analyzed. The results show that 1) with the same pumped and injected water volumes, the lower the temperature of injected water is, the larger the volume of cold water in the cold energy storage well is. With the larger volume, the effect of cold energy storage is better. 2) the larger the volumes of pumped and reinjected water are, the larger the volume of cold water from the cold energy storage well is. With the larger volume, the effect of refrigeration is better. And 3) without disturbance, the volume and temperature of cold water in the cold energy storage well can keep unchanged or have only a little change for a long time. Therefore the technology of doublet wells for cold energy storage is feasible and the cold energy storage aquifers can meet the requirement of the technology.

钢管插入式基础抗拔承载性能数值模拟

为研究输电线路杆塔三角锚固盘钢管插入式基础在承受上拔荷载时锚固盘的受力性能,使用有限元分析软件对钢管插入式基础进行数值模拟分析,研究了锚固件尺寸、混凝土强度、钢管截面和混凝土柱截面对试件抗拔承载性能的影响。结果表明:使用三角锚固盘能够改善锚固盘与钢管焊接部分的应力集中情况,显著提升钢管插入式基础的抗拔承载能力,且混凝土强度越高优势越明显;在一定范围内增加锚固盘尺寸可以提高基础抗拔承载力,提高初始刚度和延性系数,超出范围则影响不明显,最佳的锚固盘尺寸由基础混凝土强度决定;增加混凝土强度、钢管截面尺寸和混凝土柱截面尺寸都可以提高基础的抗拔承载力和初始刚度,延性系数则随混凝土强度的提高先减小后增大,随钢管截面尺寸的提高而减小。