深厚软弱堰塞湖相沉积覆盖层上修建高围堰存在沉降变形大、边坡稳定问题突出等问题，目前的研究深度不足以解决实际工程问题。本人在吴梦喜高级工程师的指导下，参与了拉哇上游深厚软弱堰塞湖相沉积覆盖层上所建高围堰工程的分析研究工作。该工作利用MIDAS有限元软件做建模前处理，再基于吴梦喜高工团队研发的LinkFEA软件进行计算分析，对工程进行堰体填筑、基坑开挖全过程的二维渗流应力变形耦合计算，并基于考虑渗流与应力耦合作用的虚功率法分析其边坡稳定安全性，从而得到工程在施工全过程中渗流，位移，应力场以及边坡稳定安全性的动态变化规律。在此基础上，评价围堰地基处理方案的可行性，其分析结果被设计方认可并采用。经过全文总结有以下成果：

(1)土体本构模型参数之间是相互关联，相互影响的非线性关系。本文通过拟合土层三轴试验曲线回归土层参数的方法替代工程设计中直接利用各土类参数加权平均得到土层参数的方法，得到了复杂沉积层的土层参数，为实际围堰工程设计提供了支撑。

(2)土体在有效应力的作用下产生变形导致土体的渗透系数发生变化。本文依据试验所得的固结系数与固结压力的关系，压缩模量与固结压力的关系以及静止侧压力系数，推算出渗透系数与平均应力的关系，从而成功在工程计算分析中考虑渗透系数在时间和空间上的变化。

(3)对碎石桩加固软土堰基的复杂围堰工程进行了细致的模拟，得到了堰基碎石桩处理区域超孔隙水压力的非线性分布特征和动态变化规律。

(4)利用降水管井可以降低覆盖层底部强透水层中的承压水头，在基坑开挖过程中显著提升工程的稳定安全性；碎石桩在堰脚外侧并不具备承压的作用，只发挥排水效应，其效果类似于竖直排水砂井，据此可以判断在基坑开挖边坡区域布置碎石桩并没有固脚的作用。这些具有工程意义的结论可以为之后类似复杂软土地基工程的分析与设计提供参考。

(5)本文关于碎石桩加固深厚软土堰基的复杂围堰工程的计算方法与分析结果得到设计院的认可并采用。

There are some problems in the construction of high cofferdams on the deep soft barrier lacustrine sedimentary overburden, such as large settlement deformation and prominent slope stability problems. The current research depth is not enough to solve the practical engineering problems. Under the guidance of senior engineer Wu Mengxi, I participated in the analysis and research on the high cofferdam built on the deep weak barrier lacustrine sedimentary overburden in the upper reaches of Lawa. In this work, MIDAS finite element software is used for modeling pretreatment, and then based on LinkFEA software, the nonlinear coupling simulation analysis of two-dimensional seepage and stress deformation in the whole process of cofferdam filling and foundation pit excavation is carried out, and the slope stability safety is calculated based on the virtual power method considering the strong coupling effect of seepage and stress, so as to obtain the dynamic variation law of seepage, displacement, stress field and slope stability and safety in the whole construction process. On this basis, the feasibility of the cofferdam foundation treatment scheme is evaluated, and the analysis results are approved and adopted by the designer. The results are as follows:

(1) The parameters of soil constitutive model are non-linear and interrelated. In this paper, the soil parameters of complex sedimentary layer are obtained by fitting triaxial test curve of soil layer, instead of the method of directly using weighted average of soil parameters to get soil parameters in engineering design, which provides support for actual cofferdam engineering design.

(2) The deformation of soil under the action of effective stress leads to the change of permeability coefficient of soil. This paper calculates the relationship between permeability coefficient and average stress according to the relationship between consolidation coefficient and consolidation pressure, compression modulus and consolidation pressure, and static lateral pressure coefficient, and the variation of permeability coefficient in time and space is successfully considered in engineering calculation and analysis.

(3) The complex cofferdam project of soft soil foundation reinforced by gravel pile is simulated in detail, and the nonlinear distribution characteristics and dynamic variation law of excess pore water pressure in the treatment area of gravel pile on weir foundation are obtained.

(4) Using the dewatering pipe well can reduce the confined water head in the strong permeable layer at the bottom of the overburden layer, and significantly improve the stability and safety of the project in the excavation process of the foundation pit; the gravel pile has no bearing effect on the outside of the weir foot, only plays the drainage effect, and its effect is similar to that of the vertical drainage sand well. These conclusions with engineering significance can provide reference for the analysis and design of similar complex soft soil foundation projects.

(5) In this paper, the calculation method and analysis results of the complex cofferdam project of the deep soft soil foundation reinforced by gravel pile are approved and adopted by the design institute.