大面积堆载下桥梁桩基负摩阻力试验与数值分析

发布时间：2018-01-17 20:31

本文关键词：大面积堆载下桥梁桩基负摩阻力试验与数值分析　出处：《东南大学》2015年硕士论文　论文类型：学位论文

【摘要】：沿海地区主要通过吹填淤泥及泥沙进行围垦,由于吹填区域土质较差,淤泥软弱土层较厚,排水固结时间漫长,灵敏度高,强度低,在后期填土作用下,土体会产生很大的固结沉降,易对临近桥梁基础产生较大的负摩阻力,降低桩基承载力,增加桥梁的沉降。在沿海吹填及软土地区因桩基负摩阻力过大导致严重的工程事故时有发生,造成后期补救措施成本较高。目前,国内外对桩基在沿海吹填地区深厚软土地质条件下负摩阻力研究较少,特别是现场试验相关研究更少。所以,展开吹填区后期填土对桩基承载特性影响的研究,具有非常重要的理论意义和工程实用价值。本文结合台州湾大桥工程建设,在箬横段选取三根桩基进行大面积堆载下桥梁桩基负摩阻力试验,按照堆载方案要求堆载一定的面积和高度,模拟沿海吹填区域后期填上对桥梁桩基负摩阻力的影响,并结合不同理论方法计算进行对比分析。同时采用数值模拟手段,利用岩土通用软件FLAC 3D模拟实际堆载尺寸、模拟不同堆载面积、模拟不同堆载高度,分析不同工况条件下对桥梁桩基负摩阻力的影响。主要内容和结论如下：(1)对台州湾大桥箬横段接线工程三根工程试桩进行平衡堆载,近似模拟后期大面积填土对桥梁桩基的影响。试验在桩中埋设钢筋计,测试出桩身内力,在桩顶及周围地表埋设沉降标,测试桩顶及地表的沉降大小。进行了为期三个月左右的长期观测,现场实测结果表明,堆载高度达到4m高度时,负摩阻力总和达到2687kN左右,中性点深度约为29.5m,且负摩阻力的发展是随时间而变化的,在实际工程中应充分考虑负摩阻力的影响。(2)利用Bjerrum建议方法、公路桥涵地基与基础规范法、美国Garlanger等人建议方法、日本建筑基础构造设计规准及层状土迭代法等理论计算方法计算桩基的负摩阻力,计算结果表明,规范法计算出的总负摩阻力比实测值偏大,Bjerrum建议方法计算结果与实测结果较接近,可作为本地区类似工程桩基负摩阻力设计,而其他方法计算结果与实测结果差异较大。(3)利用FLAC 3D软件模拟后期填土对桥梁桩基的影响,考虑到实际堆载面积及堆载高度有限,本文模拟了不同堆载面积及不同堆载高度范围大小对桥梁桩基的影响。模拟堆载面积影响时,结果表明,当堆载面积较小时,堆载面积增加对桩基负摩阻力增加较明显；当堆载面积较大时,堆载面积增加对桩基沉降影响较显著,桩端沉降也很大,但总负摩阻力增长不明显。与较大面积堆载尺寸比较,现场堆载试验的尺寸面积明显存在局限性,产生的桩基负摩阻力以及中性点深度较小。模拟堆载高度影响时,结果表明,随着堆载高度的增加,桩基负摩阻力总和与桩基沉降出现非线性增长。
[Abstract]:Coastal areas are mainly reclaimed by dredging silt and silt. Because of poor soil quality, thick soft soil layer, long time of drainage consolidation, high sensitivity and low strength, it is under the action of late fill. Soil will produce great consolidation settlement, easy to produce a large negative friction on the adjacent bridge foundation, and reduce the bearing capacity of pile foundation. Increase the settlement of bridges. In coastal fill and soft soil areas, the negative friction of pile foundation caused by serious engineering accidents, resulting in higher cost of remedial measures. At home and abroad, there are few researches on the negative friction resistance of pile foundation under the geological conditions of deep soft soil in coastal filling area, especially in the field test. Therefore, the research on the influence of the later filling on the bearing characteristics of pile foundation is carried out. Combined with the construction of Taizhou Bay Bridge, this paper selects three piles in the transverse section of Ruo to test the negative friction resistance of bridge pile foundation under large area of heaped load. According to the surcharge scheme required a certain area and height of the heaped load, the influence of the late loading on the negative friction of the bridge pile foundation is simulated in the coastal filling area. At the same time, the numerical simulation method is used to simulate the actual surcharge size by using the general software FLAC 3D, and the different surcharge area is simulated. Simulation of different heaped heights and analysis of the influence of different working conditions on the negative friction of bridge pile foundation. The main contents and conclusions are as follows: 1) balanced heaped load of three test piles in the Ruo transverse section of Taizhou Bay Bridge. The influence of large area fill on the bridge pile foundation was simulated approximately. The reinforcement meter was embedded in the pile and the internal force of the pile was tested and the settlement mark was laid on the top of the pile and the surrounding surface. The settlement of pile top and surface is measured. The long-term observation for about three months shows that the total negative friction is about 2687kN when the heap-load height reaches 4m. The depth of neutral point is about 29.5 m, and the development of negative friction is changing with time. The influence of negative friction should be fully considered in practical engineering. The method of foundation and foundation code for highway bridge and culvert, the method suggested by Garlanger et al., and the theoretical calculation method such as the criterion of design of building foundation in Japan and the iterative method of layered soil are used to calculate the negative frictional resistance of pile foundation. The calculation results show that the total negative frictional resistance calculated by the code method is larger than the measured value. The calculated results of Bjerrum's method are close to the measured results and can be used for the design of negative friction resistance of pile foundations in similar projects in this area. However, the difference between the calculated results of other methods and the measured results is quite large. (3) FLAC 3D software is used to simulate the influence of fill on the bridge pile foundation in the later stage, considering the limitation of the actual surcharge area and the height of the heaped load. In this paper, the influence of different surcharge area and different heaped height on bridge pile foundation is simulated. The result shows that when the surcharge area is small, the influence of heaped area on bridge pile foundation is simulated. The increase of surcharge area is more obvious to the negative friction resistance of pile foundation. When the surcharge area is larger, the increase of the surcharge area has a significant effect on the settlement of pile foundation, and the settlement of pile tip is also very large, but the total negative frictional resistance is not obvious. The size area of the field load test is obviously limited, the negative friction of pile foundation and the depth of neutral point are smaller. When the influence of the heaped height is simulated, the results show that with the increase of the heap-load height, the negative friction resistance of pile foundation and the depth of neutral point are smaller. The sum of negative friction resistance of pile foundation and the settlement of pile foundation show nonlinear growth.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U443.15

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