钢管桩基坑支护稳定性模型试验及数值模拟

发布时间：2018-04-08 21:50

本文选题：支护设计　切入点：钢管桩　出处：《中国矿业大学》2017年硕士论文

【摘要】：本文以北京某基坑1-1支护剖面为原型通过理论设计、模型试验、数值模拟研究了钢管桩基坑支护的位移、应力、变形及对基坑稳定性的影响,对钢管桩代替钻孔灌注桩的可行性进行了研究。通过理论计算设计了6种不同直径、壁厚的钢管桩代替钻孔灌注桩进行基坑支护。选用了最大、最小直径的两种钢管桩进行了物理模型试验,试验结果表明大直径管桩单根桩打桩引起的土体水平位移、竖向位移以及作用范围均较大,但在相同支护区域内土体水平位移的累积位移值差别不大。应力监测表明,打桩引起的土体应力变化主要在桩体的下部分,小直径管桩施工造成的土体应力增幅大于大直径管桩。对锤击数的分析表明随着管入土深度的增加大,将大直径管桩打入土体的锤击数增幅大于小直径管桩,但小直径管桩的挤土效应更明显。基坑开挖模拟表明土体的水平位移变化在基坑边缘处最大,大、小两种管桩开挖引起的水平位移开挖模拟值分别为3.23 mm、10.16 mm,现场实测值中最大值约为4 mm。小直径管桩在开挖后期模型箱边缘土体有小部分垮落,大直径的管桩开挖过程中出现了土体的大范围垮落。小直径管桩保持桩后土体的整体性较好,但控制水平位移的能力较差,而大直径管桩在支护时更需要与其他支护结构结合使用。相似模拟的土体沉降趋势与实测沉降值相似,大、小两种管桩支护情况下的最终沉降值分别为-2 mm、-3.48 mm,实测最大值为-2.04 mm,根据模拟值与实测值可将土体的沉降变化分为3个阶段:沉降发展阶段、沉降过渡阶段以及沉降稳定阶段,模型试验中沉降过渡阶持续时间短。数值模拟表明,随着钢管桩直径的增大,桩体的刚度增大,桩后土体的位移、管桩承受的应力水平均变小,但钢管桩直径对基底隆起并无影响。桩后土体位移的数值模拟值、模型试验值、实测值均小于监测报警值,桩身的应力均远小于钢材的强度设计值,表明所设计的钢管桩满足控制土体位移的要求且钢管桩自身安全稳定。以直径1.0 m的钢管桩为例,分析了布置间距对基坑的影响,建议在实际工程中采用2.0D间距布置钢管桩。
[Abstract]:In this paper, the displacement, stress, deformation and the influence on the stability of a steel pipe pile foundation pit are studied by theoretical design, model test and numerical simulation based on the 1-1 supporting section of a foundation pit in Beijing.The feasibility of replacing bored pile with steel pipe pile is studied.Through theoretical calculation, six kinds of steel pipe piles with different diameters and wall thickness are designed to support foundation pit instead of bored piles.Two kinds of steel pipe piles with maximum and minimum diameters are selected for physical model test. The results show that the horizontal displacement, vertical displacement and action range of soil caused by single pile of large diameter pipe pile are large.However, the cumulative displacement of soil in the same supporting area is not different.Stress monitoring shows that the stress variation of soil caused by piling is mainly in the lower part of the pile, and the increase of soil stress caused by the construction of small diameter pipe pile is larger than that of large diameter pipe pile.The analysis of hammer number shows that with the increase of pipe depth, the increase of hammer hit number of large diameter pipe pile is larger than that of small diameter pipe pile, but the squeezing effect of small diameter pipe pile is more obvious.The simulation of excavation shows that the horizontal displacement of soil is the largest at the edge of the foundation pit, and the simulated values of the horizontal displacement caused by the excavation of two kinds of pipe piles are 3.23 mm and 10.16 mm, respectively, and the maximum value of the field measured value is about 4 mm.In the later stage of excavation, a small part of soil collapse occurred at the edge of the model box, and a large scale collapse occurred during the excavation of the large-diameter pipe pile.The small diameter pipe pile keeps the integrity of the soil after the pile, but the ability to control horizontal displacement is poor, while the large diameter pipe pile needs to be used in combination with other supporting structures.The settlement trend of similar simulated soil is similar to the measured settlement value.The final settlement values of the two types of pipe piles are 2.mm -3.48 mm and the measured maximum value is -2.04 mm. According to the simulated values and the measured values, the settlement changes of soil can be divided into three stages: the stage of settlement development, the stage of settlement transition and the stage of settlement stabilization.In the model test, the duration of settlement transition order is short.Numerical simulation shows that with the increase of the diameter of the steel pipe pile, the stiffness of the pile body increases, the displacement of the soil behind the pile and the stress level of the pipe pile become smaller, but the diameter of the steel tube pile has no effect on the uplift of the foundation.The numerical simulation values, model test values and measured values of the soil displacement behind the pile are all smaller than the monitoring alarm values, and the stress of the pile body is far less than the strength design value of the steel.The results show that the designed steel pipe pile can meet the requirement of controlling the displacement of soil and the steel pipe pile itself is safe and stable.Taking the steel pipe pile with diameter of 1.0 m as an example, the influence of layout spacing on foundation pit is analyzed, and it is suggested that the steel pipe pile should be arranged with 2.0D spacing in practical engineering.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.1

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