离岸浅基础在复合加载模式下的承载力特性研究

发布时间：2018-05-01 10:15

本文选题：港口与海洋工程 + 浅基础　；参考：《天津大学》2016年博士论文

【摘要】：由于复杂的自然环境和工作条件,离岸浅基础处于竖向、水平、力矩和扭矩等多种荷载联合作用的复合加载条件下。其破坏模式通常包括竖向整体剪切破坏,滑移破坏和倾覆破坏。在传统的承载力计算理论中,浅基础在复合加载条件下的承载力是通过修正作用于均匀塑性半无限地基上的条形表面基础的竖向承载力而得到的。近些年发展起来的破坏包络面方法克服了传统理论中的诸多不足,能显式地考虑荷载倾斜,荷载偏心,基础形状与埋深,以及地基强度不均匀程度等因素对浅基础承载力的影响。浅基础承载力的破坏包络面理论在离岸浅基础的设计中已获得了广泛的应用,但由于破坏包络面形状的影响因素众多,该理论尚待进一步地完善。基于此,本文首先结合工程实例讨论了破坏包络面理论应用于工程实践需要注意的问题,然后通过建立有限元模型确定了一系列边界条件下的浅基础的破坏包络面方程。本文的研究目的在于完善浅基础的破坏包络面理论,为离岸浅基础的设计优化提供理论指导。本文的主要研究内容和结论如下:(1)基于破坏包络面理论,建立了砂基上四腿平台多基础系统的承载力计算方法,并通过工程实例验证了计算方法的可行性,并对破坏包络面理论在计算荷载安全系数和结合“分项系数”法进行基础设计等方面的应用给出了建议。(2)提出了无拉力土-基础接触面的数值模拟方法。通过与已有研究结果的对比和相关试验的验证,证明了无拉力土-基础接触面可以采用摩擦角接近90°的Coulomb摩擦接触模型模拟。在此基础上,研究了平面V-H-M加载模式下无拉力接触面条形和圆形表面基础的承载力特性。(3)以破坏包络面的形式研究了极复杂荷载条件下无限拉力接触面表面圆形基础和不同宽长比矩形防沉板基础的承载力特性,并在全三维加载条件下,研究了接触面条件对海底防沉板基础承载力的影响。(4)一般情况下,传统方法得到的解都低估了无拉力接触面条件下得出的有限元解。在包含力矩荷载的复合加载情况下,无拉力接触面条件下的破坏包络线会落在无限拉力接触面条件下的破坏包络线的内侧。(5)随着扭矩荷载的增大,H-M破坏包络线成比例地向内收缩,即扭矩荷载能有效地减小包络线的尺寸,但对其形状的影响可忽略不计。所以,可分别根据H-T和M-T间的相互关系,通过减小用于归一化的最大水平和力矩荷载的方式缩小H-M破坏包络线的尺寸,达到考虑扭矩荷载效应的目的。(6)本文提供了所有破坏包络线相对应的破坏包络线方程,并通过计算实例说明如何将所提方程应用于岩土设计。破坏包络线方程能够方便地编入自动计算工具中,快速地生成破坏包络线,辅助港口与海洋工程中浅基础的设计和优化工作。
[Abstract]:Because of the complex natural environment and working conditions, the offshore shallow foundation is under the combination of vertical, horizontal, torque and torque loads. The failure modes usually include vertical whole shear failure, slip failure and overturning failure. In the traditional theory of bearing capacity calculation, the bearing capacity of shallow foundation under composite loading is obtained by modifying the vertical bearing capacity of strip surface foundation acting on uniform plastic semi-infinite foundation. The damage envelope method developed in recent years overcomes many shortcomings in traditional theory and can explicitly consider load tilt, load eccentricity, foundation shape and depth. And the influence of the uneven strength of foundation on the bearing capacity of shallow foundation. The theory of failure envelope of shallow foundation bearing capacity has been widely used in the design of offshore shallow foundation. However, due to many factors affecting the shape of damage envelope, the theory needs to be further improved. Based on this, this paper first discusses the problems needing attention in the application of failure envelope theory in engineering practice with engineering examples, and then establishes a finite element model to determine the damage envelope equation of shallow foundation under a series of boundary conditions. The purpose of this paper is to perfect the theory of damage envelope of shallow foundation and to provide theoretical guidance for the design optimization of offshore shallow foundation. The main contents and conclusions of this paper are as follows: (1) based on the theory of destructive envelope surface, a method for calculating the bearing capacity of a multi-foundation system of four-legged platform on sand foundation is established, and the feasibility of the calculation method is verified by an engineering example. The application of the failure envelope theory to the calculation of load safety factor and to the foundation design with the method of "sub-factor" is also given. A numerical simulation method of tensionless soil-foundation interface is proposed. It is proved that the Coulomb friction contact model with friction angle close to 90 掳can be used to simulate the non-tension soil-foundation contact surface by comparing with the existing research results and verifying the related tests. On this basis, The bearing capacity characteristics of strip and circular surface foundation of tension free contact surface under plane V-H-M loading mode are studied. The surface circular foundation and different widths of infinite tension contact surface under extremely complex loads are studied in the form of failure envelope surface. Bearing capacity characteristics of rectangular anti-sinking plate foundation with length ratio, Under the condition of full three-dimensional loading, the influence of contact surface condition on the bearing capacity of submarine anti-sinking plate foundation is studied. In general, the solutions obtained by the traditional method underestimate the finite element solution obtained under the condition of non-tension contact surface. In the case of a composite load containing a moment load, Under the condition of non-tension contact surface, the failure envelope will fall on the inner side of the failure envelope under the condition of infinite tension contact surface.) with the increase of torque load, the damage envelope line will shrink proportionally inward. The torque load can effectively reduce the size of the envelope, but the influence on the shape of the envelope is negligible. Therefore, according to the relationship between H-T and M-T, the size of H-M damage envelope can be reduced by reducing the maximum horizontal and torque load for normalization. In this paper, all the failure envelope equations corresponding to the failure envelope are provided, and the calculation examples are given to illustrate how to apply the proposed equation to geotechnical design. The damage envelope equation can be easily programmed into the automatic calculation tool to generate the damage envelope quickly, which can assist the design and optimization of shallow foundation in port and ocean engineering.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：U655.54

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