上覆土软质岩等截面嵌岩桩抗拔承载特性研究

发布时间：2018-05-20 18:47

本文选题：嵌岩抗拔桩 + 上覆土软质岩　；参考：《西南交通大学》2017年硕士论文

【摘要】：高耸的输电线路铁塔承受的荷载十分复杂,不仅受到上部结构传来的竖向荷载,还需要承受非常大的上拔力,因此输电线路工程实际中常常选用抗拔桩作为基础。西部山区的地层特点:覆盖土层主要为粘土,较薄约0～2m,局部可达4m;基岩主要为软岩,以砂岩、泥岩、砾岩为主。通常把桩嵌入岩层能够一定程度提高抗拔承载力,然而目前对上覆土软岩等截面嵌岩抗拔桩的破坏机理问题研究较少,所以输电线路工程中"上土下岩"桩端嵌入基岩的桩基础上拔承载力设计计算偏于保守,导致基础工程量偏大。本文依托昭化—广元牵引站220kV线路工程和路平—富乐500kV双回线路新建工程,采用离心模型试验、现场试验和数值模拟,研究上覆土软岩等截面嵌岩桩抗拔承载特性,主要的研究内容和结论如下:(1)离心模型试验结果表明上覆土软质岩嵌岩桩抗拔破坏时桩周岩体破坏模式有圆柱型和复合型两种。当嵌岩段桩岩界面摩擦粘结良好时,桩的破坏呈现出复合型破坏模式.,当嵌岩段桩岩界面摩擦粘结较弱时,桩的破坏呈现出圆柱型破坏模式。(2)上覆土等截面嵌岩抗拔桩达到极限状态后,上拔位移变形迅速增大,荷载—位移曲线会出现明显的拐点,表现为突变型。(3)当嵌入软质岩深度不小于1m且上覆土的厚度不大于嵌岩深度时,上覆土极限抗拔力不大于嵌岩桩极限抗拔的10%。上覆土软质岩等截面嵌岩桩极限抗拔承载力随嵌岩深度呈线性增大。软质岩强度对桩侧阻力的大小影响很大,较软岩的桩侧摩阻力约为软岩的桩侧摩阻力2～5倍。上覆土层等截面嵌岩桩极限抗拔承载力随着岩基强度增大而增大。(4)上覆土软质岩等截面嵌岩桩受上拔荷载作用下岩土分界面位置桩侧阻力会迅速增大,在嵌入软质岩0.5～1.5m范围左右到达峰值。随着上拔荷载继续增大,上部软质岩桩侧阻力发挥发生一定程度的减弱,下部软质岩桩侧阻力继续增大,峰值逐渐往下部移动。达到极限上拔力时,桩侧阻力最大值发生在嵌入软质岩2～3m范围。(5)采用《建筑桩基技术规范》按照碎石土计算现场试验软质岩嵌岩桩的极限抗拔承载力,得到的规范计算结果与现场试验结果相差很大,现场试验结果高于规范计算值的12.7%～467.8%。若采用《德国桩基规范》(DIN4014)来计算软质岩嵌岩抗拔桩的极限抗拔承载力,其计算值与本次试验结果吻合更好。(6)数值模拟结果表明,现场试验上覆土软质岩等截面嵌岩桩达到极限抗拔状态后桩周土体发生内部剪切破坏,嵌入软质岩段沿软质岩与桩身表面发生界面破坏,桩从岩层中被拔出。
[Abstract]:The load on the towering transmission line tower is very complex, which is not only subjected to the vertical load from the superstructure, but also needs to bear a very large uplift force, so the anti-drawing pile is often used as the foundation in the transmission line engineering. The stratigraphic characteristics of the western mountainous area are as follows: the overlying soil layer is mainly clay, the thickness is about 0 ~ 2 m, the local area is up to 4 m, and the bedrock is mainly soft rock, mainly composed of sandstone, mudstone and conglomerate. Usually the pile embedded in rock layer can improve the uplift bearing capacity to a certain extent, however, there are few researches on the failure mechanism of rock socketed pile with soft rock section. Therefore, the design and calculation of the uplift bearing capacity of the pile foundation embedded in the bedrock at the end of the pile end in the transmission line project is conservative, which leads to the large amount of foundation engineering. Based on the 220kV line project of Zhaohua-Guangyuan traction station and the new project of Luping Fulle 500kV double-circuit line, this paper studies the uplift bearing characteristics of rock socketed piles with equal cross-section of overlying soft rock by centrifugal model test, field test and numerical simulation. The main research contents and conclusions are as follows: (1) the results of centrifugal model test show that there are two types of rock mass failure modes around piles: cylindrical type and composite type during uplift failure of soft rock socketed pile with overlying soil. When the pile-rock interface friction bond is good, the pile failure presents a composite failure mode, and when the pile-rock interface friction bond is weak in the rock socketed segment, The failure of the pile shows a cylindrical failure mode. (2) after the pile reaches the limit state, the uplift displacement increases rapidly, and the load-displacement curve will appear obvious inflection point. When the depth of embedded soft rock is not less than 1m and the thickness of overlying soil is less than that of embedded rock, the ultimate uplift resistance of overlying soil is less than 10% of the ultimate uplift resistance of rock-socketed pile. The ultimate uplift bearing capacity of rock socketed piles with the same cross section of overlying soft rock increases linearly with the depth of rock socketed. The strength of soft rock has a great influence on pile side resistance, and the pile side friction of soft rock is about 2 or 5 times that of soft rock. The ultimate uplift bearing capacity of rock socketed piles with equal cross-section of overlying soil increases with the increase of the strength of rock foundation. (4) under the action of uplift load, the pile side resistance at the interface of rock and soil will increase rapidly under the action of uplift load on soft rock socketed pile with soft rock overlying soil. The peak value is reached in the range of 0.5 ~ 1.5 m of embedded soft rock. With the increasing of uplift load, the lateral resistance of the upper soft rock pile decreases to a certain extent, and the side resistance of the lower soft rock pile continues to increase, and the peak value gradually moves to the lower part. When the ultimate uplift force is reached, the maximum of pile side resistance occurs in the range of 23m embedded soft rock. The Technical Specification for Building pile Foundation is adopted to calculate the ultimate uplift bearing capacity of soft rock socketed pile in situ test according to the gravel soil. The result of the standard calculation is quite different from that of the field test, and the result of the field test is higher than that of the calculated value of the code, which is 12.7% and 467.8%. If the German Specification for pile Foundation (DIN4014) is used to calculate the ultimate uplift bearing capacity of soft rock socketed pile, the calculated value is in better agreement with the test results. In the field test, when the rock socketed pile with equal cross section of overlying soft rock reaches the state of ultimate pull-out, the internal shear failure occurs in the soil around the pile, the interfacial failure occurs along the interface between the soft rock and the pile body in the embedded soft rock section, and the pile is pulled out from the rock stratum.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM75

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