Zhongzhi Fu

Earth–rock dams provide cost-effective flood control and water storage through the utilization of locally available materials, making them essential infrastructure for regional safety, agricultural development, and sustainability. Electrical resistivity methods offer an efficient, non-destructive means to detect internal defects and potential hazards within dam bodies, thereby supporting dam safety assessment and service life extension. In this review, we focus on sand and clay, the most commonly used materials in earth–rock dams. We summarize the main methods and instruments for measuring soil resistivity and comparatively analyze the applicability and limitations of different approaches. Emphasis is placed on the key factors influencing soil resistivity, and recent progress in modeling the resistivity of soil materials is reviewed. The results show that soil resistivity parameters can effectively characterize physical and mechanical properties, structural features, and moisture migration behavior, providing an important basis for soil property evaluation. However, current studies are largely based on macroscopic experiments, with limited investigation of microscopic mechanisms and a lack of unified testing standards, leading to discrepancies between theoretical models and measured data. In this review, we aim to provide a theoretical reference for research and engineering applications of resistivity characteristics in earth–rock dam materials.

The liquefaction of saturated sand-gravel material samples from the Xinjiang valley were investigated under cyclic loading. A series of large-scale dynamic triaxial tests were used to determine the dynamic characteristics of the sand-gravel sample under different confining pressures, consolidation stress ratios, and stress levels. A suitable pore water pressure growth model is proposed for the sand-gravel and sand materials. The number of cycles required to cause liquefaction was an important parameter in the dynamic pore water pressure growth model. A method to determine the number of cycles was proposed and verified by a large number of experimental data. The presentation of the pore water pressure simulation results demonstrates that the proposed pore water pressure growth model accurately characterizes the dynamic pore water pressure development in sand-gravel under cyclic loading and is also applicable to sand. The proposed pore water pressure growth model can be used to study the anti-liquefaction characteristics of foundation and dam materials of high earth-rock dams and high sand-gravel dams on deep overburdens.

The 247-m DaShiXia (DSX) concrete-faced sand-gravel dam (CFSGD) is currently the highest structure of its type under construction in the world. By reviewing the specific conditions of this dam and common problems that have occurred in other comparable cases, this paper analyzes the technical issues that undermine the safety of the dam. Measures for controlling dam deformation and seepage, improving its aseismic performance, and reinforcing its concrete slabs are explained with the aid of experimental and numerical results and previous experience. The results of the analysis demonstrate that the deformation of the dam under static and dynamic loads is within the range of existing successful cases, thus providing fundamental confidence that the design is feasible. The use of L-shaped drainage within the dam is emphasized because of the vulnerability of sand and gravel material to seepage erosion, uncertainties in the results obtained from laboratory seepage tests, and the need to lower the phreatic surface. Numerical results show that the acceleration response is strong within the upper 4/5 part of the dam, which leads to confined aseismic measures within this particular portion. Reinforcing schemes for concrete-faced slabs and their joints are outlined, and some special design features, including the use of a high toe retaining wall, a stepwise toe plinth, and a deep empty tunnel in this dam, are also explained. The measures adopted are expected to result in acceptable performance of the dam and its impermeable system.

Conventional earth pressure theories are generally applicable to soils with a linear strength envelope. Preferred granular backfill, however, usually exhibits a decreasing peak friction angle with an increasing normal effective stress. In this study, the slice-based limit equilibrium method is used to evaluate the active earth pressure applied by soils that exhibit nonlinear strength behaviour. The force and moment equilibrium equations for a differential soil slice are introduced, and the boundary conditions for the active earth pressure problems are specified. The mathematical nature of the active earth pressure is explored. It is found that the active earth pressure corresponds to a stationary point on a saddle surface. Seeking the active earth pressure is equivalent to identifying the maximum from a series of local minima. By introducing a combination of two functions for the inter-slice force angle distribution, the local minimisation process for each possible failure surface is implemented by varying the combination factor within its valid range. The proposed solution strategy is compared with existing methods and reasonable agreement is obtained. The influences of the inter-slice force angle distribution on the resultant active earth pressure and its position of application are also studied by using three different combination functions.

Constructing the impervious system of an Earth Core Rockfill Dam (ECRD) usually needs a large volume of clay that may exhaust a huge area of farmland. One way to reduce the volume of clay to be filled is to use natural clay-gravel mixtures (CGM) or to add an appropriate percent of gravel materials into the clay and use the artificial clay-gravel mixtures as the impervious core materials. Using clay-gravel mixtures can also effectively increase the modulus of the core and reduce the differential settlement between the core and its adjacent rockfill shoulders, and thus alleviate the risk of occurrence of potential cracks within the core wall. The impermeability behavior of the compacted clay-gravel mixtures, however, has to be careful investigated and verified. In this chapter, four cases in using clay-gravel mixtures in constructing high ECRDs in China are reviewed, with attention focused on the engineering properties of clay-gravel mixtures and the construction and field quality control aspects of ECRDs using clay-gravel mixtures.

A high concrete gravity retaining wall is usually built at the toe of concrete face rockfill dams to accommodate the toe plinth, to avoid adverse natural conditions or excessive excavation. However, earth pressure on the back of the wall is generally neglected due to lack of information on the distribution and evolution of earth pressure during dam construction and reservoir impounding. In this study, two historic cases are reviewed, and a series of plane strain finite element method simulations are performed with an elastoplastic constitutive model for the retained rockfill. The distribution and variation of the normal and shear stresses along the wall–rockfill interface during construction and impounding are studied, and the influence of the interface friction angle is investigated. The evolution of the total normal and shear forces, as well as their application positions, are also analyzed based on the obtained numerical results. Simplifying the dam above the top of the wall as an evenly distributed surface pressure, an empirical formula is proposed to enable evaluation of earth pressure at rest for design purposes. The involved earth pressure coefficient, equivalent dam height, and correcting factor are suggested based on the numerical results. Earth pressures under empty and full reservoir conditions, as well as some favorable design features, are also suggested.