南宁市某工程大直径灌注桩受荷性状及其受地面荷载影响研究

发布时间：2018-02-23 04:20

本文关键词： 静载试验数值分析极限承载力预测桩-土-桩相互作用群桩效应系数地面超载荷载影响　出处：《广西大学》2014年硕士论文　论文类型：学位论文

【摘要】：为了准确确定南宁市某高架平台工程泥岩粉砂岩地基大直径灌注桩的极限承载力,采用静载试验对该工程两根群桩基桩进行静载试验研究。然后,针对静载试验中试桩未达到破坏时如何准确估算大直径灌注桩的极限承载力问题,采用函数拟合法来预测单桩的荷载沉降性状和极限承载力,并对试桩试验进行数值模拟反演分析,验证数值和计算参数的可靠性,并验证本文提出的指数函数拟合法预测该地基试桩荷载沉降性状的适用性,再扩展到群桩分析。同时,针对大吨位堆载法桩基静载试验中桩侧支墩堆载荷载使试桩提前受荷所带来的影响问题,本文结合实际工程试桩情况,通过对堆载法试桩试验进行数值模拟分析,分析支墩荷载变化对试桩的影响。此外,针对该地基桩施工期间受桩侧桩周地面大规模超高填土荷载作用下也会发生过大变形和桩身开裂问题,采用数值模拟分析法对自由单桩和既有受荷单桩分别受桩侧和桩周大规模地面超载荷载影响展开研究。通过以上研究,可以得出以下结论：(1)对于该类地基中试桩未达到破坏时其极限承载力确定问题,可通过本文提出的指数函数拟合法和数值反分析法来预测其荷载沉降性状和极限承载力；通过2×2无承台群桩基桩和单桩的受荷性状的数值模拟对比分析表明,受荷桩的非线性沉降会引起邻近非受荷桩的弹性沉降,这种复杂的桩-土-桩相互作用降低了小间距群桩基桩的承载力。(2)在堆载法静载试验过程中,在试验加载前桩侧支墩荷载吊装会使试桩提前受荷而发生沉降,但在试验中该部分沉降不被量测；在加载初期,受桩侧堆载卸荷作用影响,堆载法对试桩刚度的夸大作用显著；随着加载至约为试桩极限荷载的一半(即Qu/2)后,其夸大作用开始明显减弱,在接近极限荷载时,其夸大作用不明显,可忽略。从桩侧堆载对试桩的影响来说,堆载法对试桩极限承载力的影响可忽略,大吨位堆载法仍是测试单桩极限承载力的可靠途径。(3)在大规模地面荷载影响下,桩基受到的下拉荷载随着地面荷载增加而增大,但存在峰值,达到峰值之后,下拉荷载反而下降；桩的附加沉降规律均近似随地面荷载增加而呈线性增长；与桩侧地面荷载作用下相比,桩周地面荷载影响下自由单桩和既有受荷桩的附加沉降均分别近似为前者的两倍；与自由单桩相比,在相同的地面荷载作用下,既有受荷桩的附加沉降更大。在桩侧地面荷载影响下,桩基发生侧向变位和挠曲并受到横向弯矩作用。本文研究成果可以为解决大吨位桩基静载试验中试桩未达到破坏时其极限承载力的难以准确确定问题提供参考,为评估堆载法桩基静载试验中桩侧堆载支墩荷载变化对试桩的影响和施工期间及工后桩基桩受地面堆载影响提供理论指导依据,具有重要的理论价值和应用价值。
[Abstract]:In order to accurately determine the ultimate bearing capacity of large diameter cast-in-place piles in mudstone siltstone foundation of an elevated platform project in Nanning City, static load test was used to study the static load of two pile groups. Aiming at the problem of how to estimate the ultimate bearing capacity of large diameter cast-in-place pile accurately when the pile failure is not reached in static load test, the function fitting method is used to predict the load settlement behavior and ultimate bearing capacity of single pile. The reliability of the numerical and computational parameters is verified, and the applicability of the exponential function fitting method proposed in this paper to predict the load-settlement behavior of the pile test foundation is verified, which is extended to the pile group analysis. In view of the influence of pile-side pier load on pile-side pile loading in static load test of pile foundation with large-tonnage surcharge method, combined with the actual engineering pile test situation, this paper carries out numerical simulation and analysis on pile test test by surcharge method. This paper analyzes the influence of load change of supporting pier on test pile. In addition, under the action of large scale and super high fill load on the ground around pile side pile during the construction of the foundation, the deformation and cracking of pile body will also occur. In this paper, numerical simulation analysis is used to study the influence of large scale ground overload on free single pile and existing loaded single pile on the side of pile and around pile respectively. The following conclusions can be drawn: (1) for the determination of ultimate bearing capacity of test pile in this kind of foundation when failure is not reached, the load settlement behavior and ultimate bearing capacity can be predicted by the exponential function fitting method and numerical inverse analysis method proposed in this paper. Through the numerical simulation and comparative analysis of 2 脳 2 uncapped pile group pile foundation and single pile, it is shown that the nonlinear settlement of the loaded pile will cause the elastic settlement of the adjacent unloaded pile. This complex pile-soil-pile interaction reduces the bearing capacity of small spaced pile groups. However, this part of the settlement is not measured in the test. In the early stage of loading, the overstatement effect of the surcharge method on the stiffness of the test pile is obvious under the influence of the unloading action of the pile side, and when the pile is loaded to about half of the ultimate load of the pile test (that is, Qu- / 2), The exaggeration effect begins to weaken obviously. When the load is near the limit load, the exaggeration effect is not obvious and can be ignored. From the influence of pile side load on pile test, the influence of surcharge method on ultimate bearing capacity of pile test can be neglected. Large-tonnage surcharge method is still a reliable way to test the ultimate bearing capacity of a single pile. Under the influence of large-scale ground load, the pull-down load of pile foundation increases with the increase of ground load, but there exists a peak value, after reaching the peak value. The additional settlement of pile increases linearly with the increase of ground load. Under the influence of the ground load around the pile, the additional settlement of the free single pile and the existing loaded pile are approximately twice as much as the former, and compared with the free single pile, under the same ground load, the additional settlement of the free single pile is similar to that of the existing pile under the same ground load. The additional settlement of the existing pile is greater. Under the influence of the ground load on the side of the pile, The lateral displacement and deflection of pile foundation are occurred and subjected to lateral bending moment. The research results in this paper can provide a reference for solving the problem of determining the ultimate bearing capacity of test pile when failure is not reached in the static load test of large-tonnage pile foundation. This paper provides a theoretical basis for evaluating the influence of pile load variation on test pile during construction and after construction in static load test of pile foundation by surcharge method, which has important theoretical value and application value.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU473.1

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