桩锚支护结构内力演化及受力特性对比研究

发布时间：2018-04-15 03:24

本文选题：深基坑 + 桩锚支护结构　；参考：《兰州理工大学》2013年硕士论文

【摘要】：本文在对西北地区深基坑支护结构设计研究现状的基础上,首先,以西宁火车站综合改造基坑工程为例,对深基坑桩锚支护结构优化设计和基坑降水进行了说明。其次,在该基坑中选择3个典型桩锚支护单元,分别对悬臂排桩、单支点排桩和两支点排桩在基坑开挖和桩头侧向加载、不同工况锚杆拉拔过程中桩的内力和锚杆内力进行监测。结果表明： (1)悬臂阶段3根支护桩外侧桩身应力呈“拉—压—拉”变化,内侧桩身应力呈“压—拉”变化,这与一般认识不同。随着基坑的开挖,同一测点钢筋应力逐渐增大,最大值位置略微下移,应力零点出现的位置随桩长的不同而不同。 (2)单支点阶段随着基坑暴露时间的增加,外露桩身应力增大,桩身钢筋应力峰值出现在开挖面附近区域,开挖面以下桩身应力变化复杂,嵌固段应力零点比悬臂阶段出现的早。冠梁不仅能使支护桩的变形状态不同于上端自由的直立杆件,而且可以有效减小桩身内力。 (3)两支点阶段桩身钢筋应力变化趋于复杂,主要受基坑开挖时间和预应力锚杆的张拉锁定等因素的影响。 (4)锚杆拉拔至220kN时,10.5m以上桩身外侧钢筋受拉,内侧受压；12.0m以下内外侧钢筋均受拉,其中16.0-18.0m以下桩身受力几乎为零,说明支护桩长可以适当优化。锚头位移量为15-20mm,残余变形约3mm。 (5)在此地层条件下,单悬臂桩头内侧加载至210kN时,桩头位移达3.3cm,加载影响深度约8.0m；卸载至0kN时,桩体存在残余应力。 (6)锚杆锁定初期轴力减小量较大,随着时间的增加锚杆轴力略有提高。随着施工的进行,最大轴力值沿杆体向底部位移,说明潜在滑裂面随着锚杆预应力发挥的程度逐步向锚杆尾部移动；0-5.0m锚杆区段轴力降低约10%-15%,15m处基本为零,可以取为临界长度。 (7)对于两道或两道以上桩锚支护,下一道锚杆预加荷载承担了上一道锚杆原来抵抗的部分土压力,使上一道锚杆自由段的轴力减小。可通过超张拉与改进锁定工艺和严格施工管理等手段来弥补,使每根锚杆都发挥应有的作用。 (8)杆体轴力和剪力不是平均分布的,与目前预应力平均分布的假设和计算方法有一定出入。锚杆支护结构不应单纯以其承载力作为设计标准,而需考虑其最大允许变形量作为设计标准。通过对现场试验成果的分析,准确地掌握了基坑开挖过程支护结构内力演化规律,实现了信息化施工；同时,为后续支护设计参数修改提供了依据,指出了目前支挡结构设计中存在的不足及进一步研究的方向。
[Abstract]:Based on the research status of deep foundation pit support structure design in Northwest China, firstly, taking Xining railway station as an example, the optimization design and foundation pit dewatering of deep foundation pit pile and anchor support structure are explained.Secondly, three typical pile and anchor supporting units are selected in the foundation pit. The cantilever piles, single fulcrum piles and two fulcrum piles are loaded laterally in the excavation of the foundation pit and the pile head, respectively.The internal force of the pile and the internal force of the anchor rod are monitored during the drawing process of the anchor rod under different working conditions.The results show that:1) in the cantilever stage, the stress of the outside pile of three supporting piles is changed with "pull-compression-pull", and the stress of the inside pile is "pressure-tension", which is different from the general understanding.With the excavation of foundation pit, the stress of reinforcing bar at the same measuring point increases gradually, and the position of maximum value moves down slightly, and the position of stress zero is different with the length of pile.2) with the increase of foundation pit exposure time, the stress of exposed pile body increases in single fulcrum stage, and the peak stress of reinforcement appears in the area near the excavating surface. The stress change of pile body under excavating surface is complex, and the zero point of stress in fixed block is earlier than that in cantilever stage.The crown beam can not only make the deformation state of the supporting pile different from the vertical member with free upper end, but also effectively reduce the internal force of the pile body.3) the stress variation of reinforcement in pile body tends to be complex in two fulcrum stages, which is mainly affected by the excavation time of foundation pit and the tensioning and locking of prestressed anchor rod.4) when the anchor rod is pulled up to 220kN, the outside steel bar of the pile body above 10.5m is pulled, and the inner side steel bar below 12.0m is pulled, in which the force of the pile body below 16.0-18.0m is almost zero, which shows that the length of the supporting pile can be properly optimized.The displacement of the anchor head is 15-20 mm and the residual deformation is about 3 mm.5) under the condition of here layer, the displacement of pile head reaches 3.3 cm and the loading depth is about 8.0 m when the inside of single cantilever pile head is loaded to 210kN, and there is residual stress in pile body when unloading to 0kN.(6) the axial force decreases greatly at the initial locking stage, and increases slightly with the increase of time.With the development of the construction, the maximum axial force is shifted along the bottom of the bolt body, indicating that the potential slip surface moves gradually to the end of the anchor with the degree of prestressing force of anchor rod. The axial force of the Anchorage section of 0-5.0 m reduces by about 10 ~ 15m and is basically zero, and can be taken as the critical length.For two or more piles and anchors, the next anchor bearing part of the earth pressure of the previous anchor under preload, which reduces the axial force of the free section of the last anchor.It can be made up by means of overtension, improved locking technology and strict construction management, so that each anchor can play its due role.The axial force and shear force of the bar body are not evenly distributed, which is different from the assumption and calculation method of the average distribution of prestress at present.The bearing capacity of bolt supporting structure should not be taken as the design standard, but the maximum allowable deformation should be considered as the design standard.Through the analysis of the field test results, the evolution law of the internal force of the supporting structure during the excavation process of foundation pit is accurately grasped, and the information construction is realized, which provides the basis for the modification of the design parameters of the subsequent support.The deficiency and the direction of further research in the design of retaining structure are pointed out.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU473

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