砂土地基中轴向荷载作用下静压桩群桩效应的研究

发布时间：2018-10-20 08:55

【摘要】：近些年来，超高层建筑不断兴建，海洋石油钻井平台日益增多，很多建筑物建造在不良地基条件下。桩基础一般以群桩的形式存在，需要承受巨大的上拔力甚至轴向往复荷载，桩基础破坏会影响结构物的正常使用甚至会威胁人们的生命财产安全，，因此对轴向荷载下群桩的受力性能研究非常具有理论价值和实际意义。本文通过室内模型试验和数值模拟两种方法对砂土中静压桩的轴向受力性能进行研究。试验方面：首先进行了五组单桩的抗压、抗拔和循环加载试验，研究了桩的入土深度、桩侧粗糙度和桩身材料对单桩受力性能的影响；然后进行了两种粗糙度五种桩间距共十组2×2群桩试验，主要研究桩间距对群桩效应的影响。数值方面：基于荷载传递法中的位移协调算法，采用本文提出的考虑泊松效应影响的弹塑性t-z模型和双曲线q-z模型，编写MATLAB程序，对试验结果进行模拟验证了所采用t-z模型和q-z模型的适用性。研究结果表明：压力荷载作用下静压桩的桩顶荷载-位移曲线与上拔荷载作用下的荷载-位移曲线差异较大。抗压桩的破坏属于缓进型，抗拔桩的破坏属于突进型。入土深度越大，侧表面越粗糙，桩的抗压和抗拔承载力越大。侧表面粗糙度和入土深度对桩的极限位移影响不大。桩身的材料越刚硬，极限抗压承载力越小，极限位移值越小。循环往复位移作用下，静压桩的桩侧摩阻力和桩端阻力均随循环次数增加出现强化。这种强化是由于桩底和桩侧砂土随循环次数增加不断变密实引起的。单桩和群桩试验均表明：抗拔极限摩阻力ft小于抗压极限摩阻力fc，试验测得ft/fc=0.1-0.17。 2×2群桩在承受压力时，最优桩间距为4D，对应群桩效应系数约为1.23；承受拉力时，最优桩间距在4D-5D之间，对应群桩效应系数约为1.2。当桩间距大于7D时，群桩效应基本可以忽略。本文的模型能够模拟单桩抗压能力随三个参数的变化规律，能够模拟抗拔和抗压摩阻力的不同，能够模拟循环荷载作用下桩顶荷载-位移曲线的滞回特性。此外，利用本模型计算得到ft/fc随桩身弹性模量的变化规律，通过拟合群桩试验结果本文还求得了模型中的群桩效应影响系数。
[Abstract]:In recent years, super-tall buildings have been built, offshore oil drilling platforms are increasing day by day, and many buildings are built under poor foundation conditions. Pile foundation usually exists in the form of pile group, which needs to bear huge uplift force or even axial reciprocating load. The damage of pile foundation will affect the normal use of structure and even threaten the safety of people's life and property. Therefore, it is of great theoretical and practical significance to study the mechanical behavior of pile groups under axial loads. In this paper, the axial behavior of static pile in sand is studied by two methods: model test and numerical simulation. In terms of test: firstly, five groups of single pile were tested under compressive, pull-out and cyclic loading, and the influence of pile depth, pile side roughness and pile body material on the mechanical performance of single pile was studied. Then, two kinds of roughness and five kinds of pile spacing were carried out in 10 groups of 2 脳 2 pile groups. The effect of pile spacing on pile group effect was studied. Numerical value: based on the displacement coordination algorithm in the load transfer method, using the elastoplastic t-z model and hyperbolic q-z model considering the Poisson effect, the MATLAB program is written. The simulation results verify the applicability of the t-z model and the q-z model. The results show that the load-displacement curve of pile top under static pressure is different from that of pile under uplift load. The damage of pressure pile belongs to the type of slow advance, and the damage of anti-drawing pile belongs to the type of penetration. The deeper the soil is, the rougher the side surface is, and the greater the bearing capacity of pile is under compression and drawing. The side surface roughness and the depth of the soil have little effect on the ultimate displacement of the pile. The more rigid the pile body is, the smaller the ultimate compressive capacity is and the smaller the ultimate displacement value is. Under the action of cyclic reciprocating displacement, the pile side friction and pile tip resistance of static pressure pile are strengthened with the increase of cycle times. The reinforcement is caused by the continuous compaction of the pile bottom and the pile side sand with the increase of the cyclic times. The results of single pile and pile group tests show that the ultimate frictional resistance (ft) is smaller than that of the compressive ultimate friction (fc,). The optimum spacing of ft/fc=0.1-0.17. 2 脳 2 piles under pressure is 4D, corresponding to the effect coefficient of pile group is about 1.23, and the effect coefficient of pile group is about 1.23 when the pile is subjected to tensile force. The optimal pile spacing is between 4D-5D and the corresponding effect coefficient of pile group is about 1.2. When the pile spacing is larger than 7 D, the pile group effect can be neglected. The model in this paper can simulate the variation law of single pile's compressive capacity with three parameters, the difference of the resistance of uplift and compressive friction, and the hysteretic behavior of the load-displacement curve of pile top under cyclic load. In addition, the variation law of ft/fc with the elastic modulus of pile body is obtained by using this model, and the influence coefficient of pile group effect in the model is obtained by fitting the results of pile group test.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU473.1

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