自升式钻井平台桩靴在多层粘土中的穿刺机理分析

发布时间：2018-03-15 00:19

本文选题：耦合欧拉-拉格朗日方法（CEL）　切入点：穿刺　出处：《天津大学》2014年硕士论文　论文类型：学位论文

【摘要】：自升式钻井平台在预压期间容易发生“穿刺”事故，穿刺往往会对平台造成巨大的危害甚至整个平台的倾覆。目前，在实际工程中，关于穿刺是否发生SNAME规范和《海洋场井调查规范》等多采用地基极限承载力公式进行评价。但是，海底地质条件多种多样，这些公式并不完全适用，因此，需要采用试验方法和有限元分析的方法解决穿刺问题。离心模型试验是一种模仿原位应力场的有效的试验方法，它的优势在于通过提高径向离心加速度，在一个缩小的模型箱里模拟桩靴的插入过程，得到与原位试验相同的应力水平，是一种较为精确的模拟方法。根据本课题的需要，分别进行了全模型和半模型离心模型试验。半模型离心模型试验结合PIV粒子图像测速分析技术可以精确的得到桩靴在某一插深位置桩靴周围土体的速度矢量图，，从而得到土体的流动机制和破坏模式。全模型试验得到荷载-插深曲线，通过不同插深位置的承载力分析，对穿刺发生可能性作出判断。由于离心模型试验耗资巨大，不易重复，因此，在离心模型试验的基础上，采用ABAQUS有限元分析平台进行数值模拟。传统的有限元模拟方法在研究桩靴插深之类的大变形问题时，会因为网格变形过大造成计算不收敛，往往得不到计算结果。耦合的欧拉-拉格朗日方法（CEL）方法中地基土采用欧拉网格进行模拟，将刚度大、变形微小的桩靴采用拉氏单元进行模拟。这种方法可以完整的模拟动态的插桩过程，解决计算过程中的大变形问题。采用CEL方法模拟桩靴贯入成层土的过程，并用离心模型试验的结果对有限元分析进行可靠性验证。通过离心模型试验和CEL有限元分析模拟桩靴穿过多层粘土的过程得到以下结论：（1）SNAME推荐的理论计算方法的结果显示中部硬层粘土上表层是可能发生穿刺的地方，两种方法均未考虑硬层粘土对上下两层软粘土承载力的影响。（2）通过PIV技术分析离心模型半模型试验得到的照片得到桩靴贯入三层粘土时不同插深的土体的速度矢量图，说明了桩靴穿过软硬软三层粘土时，当桩靴靠近中部硬粘土层和穿过硬粘土层时均有可能发生穿刺的危险。（3）通过CEL有限元分析得到桩靴穿入成层粘土时土体的塑性区以及塑性区的深度随桩靴插深变化的曲线。多层土承载显现出与一般双层土的插桩明显的不同。硬层的存在对于地基承载力影响的大小和方式与硬层的厚度以及硬层的强度有关。
[Abstract]:During preloading, the jack-up drilling platform is prone to "puncture" accidents, which often cause great harm to the platform and even overturn the whole platform. At present, in actual engineering, As to whether the puncture occurs in SNAME Code and the Ocean Field well Survey Code, the formulas of ultimate bearing capacity of foundation are often used for evaluation. However, there are a variety of submarine geological conditions, and these formulas are not fully applicable, so, The method of test and finite element analysis is needed to solve the puncture problem. Centrifugal model test is an effective method to simulate in-situ stress field. Its advantage is to simulate the insertion process of pile boots in a reduced model box by increasing radial centrifugal acceleration. It is a more accurate simulation method to get the same stress level as the in-situ test. The semi-model centrifuge model test and semi-model centrifuge model test combined with PIV particle image velocimetry analysis technique can accurately obtain the velocity vector diagram of soil around the pile shoe in a certain inserted position. Thus the flow mechanism and failure mode of soil are obtained, and the load-depth curve is obtained by full-model test, and the possibility of puncture is judged by analyzing the bearing capacity of different insertion positions. Because the centrifugal model test is expensive and difficult to repeat, so, based on the centrifuge model test, ABAQUS finite element analysis platform is used for numerical simulation. When the traditional finite element simulation method is used to study the large deformation problems such as pile and boot depth, the calculation will not converge due to the large mesh deformation. In the coupled Euler-Lagrangian method (CEL), the foundation soil is simulated by Euler mesh, and the stiffness is large. The pile boots with small deformation can be simulated by Lagrangian element. This method can simulate the dynamic process of pile insertion and solve the problem of large deformation in the calculation process. CEL method is used to simulate the process of pile boots penetrating into layered soil. The reliability of finite element analysis is verified by the result of centrifugal model test. The following conclusions are obtained by centrifuge model test and CEL finite element analysis to simulate the process of pile boots passing through multilayer clay:. The results of the theoretical calculation method recommended by SNAME show that the upper surface layer of the middle hard clay is the place where the puncture may occur, and neither of the two methods takes into account the influence of the hard layer clay on the bearing capacity of the upper and lower layers of soft clay. (2) the velocity vector diagram of soil with different penetration depth was obtained by using PIV technique to analyze the semi-model test of centrifugal model. The results show that the pile shoe passes through soft and soft clay layers, and the velocity vector diagram of soil with different depth is obtained when the pile shoe penetrates into three layers of clay. When the pile boots are near the middle hard clay layer and through the hard clay layer, there is a danger of puncture. Through CEL finite element analysis, the curves of the plastic zone of soil and the depth of plastic zone varying with the depth of the pile shoe are obtained when the pile boots penetrate into the layered clay. The bearing capacity of the multi-layer soil is obviously different from that of the ordinary double-layer soil. The extent and mode of influence on the bearing capacity of foundation is related to the thickness of hard layer and the strength of hard layer.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P751

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