Guoying Li

Concrete-faced rockfill dams (CFRDs) constructed in narrow and steep valleys are strongly influenced by the mechanical interaction between the dam body and abutment bedrock. Under long-term construction and reservoir impoundment, time-dependent frictional slip along the dam–abutment interface may alter deformation transfer within the dam system. This study investigated the Dashixia extra-high CFRD through large-scale contact rheological tests and three-dimensional finite element analysis. A contact rheological model was established from interface tests and incorporated into a full-scale numerical model considering valley topography, staged construction, and reservoir impoundment. The influence of contact rheology on dam deformation, face-slab response, and peripheral-joint behavior was evaluated. The results show that contact rheology has little effect on global dam settlement but significantly increases horizontal displacement and redistributes local deformation near the abutments. Under the normal reservoir water level, the maximum upstream displacement, downstream displacement, and settlement increase by 0.7, 3.4, and 1.5 cm, respectively. Meanwhile, the maximum peripheral-joint settlement increases from 43.7 to 69.8 mm, and the maximum tensile opening increases from 8.7 to 12.8 mm. For the Dashixia CFRD, inclusion of dam–abutment contact rheology increases the predicted maximum peripheral-joint settlement and tensile opening by 59.7% and 47.1%, respectively, highlighting the greater sensitivity of local joint deformation compared with global dam settlement.

As a key structural component of rockfill dams, the load-bearing capacity of large-sized concrete slabs under complex multi-axial stresses is directly related to the long-term safe operation of the dams. This study conducted uniaxial and biaxial lateral compression strength tests on C25 concrete slabs with dimensions of 1500 × 1500 × 150 mm using a large-scale bi-directional loading reaction frame test system, systematically revealing the mechanical properties and failure criteria of large-sized concrete slabs. The results indicate that the biaxial compressive strength of the concrete slabs is significantly greater than the uniaxial compressive strength. The stress–strain curves of the concrete slabs and standard specimens exhibit good consistency before failure. Based on uniaxial compressive strength data, the concrete size effect strength reduction formula proposed by Neville was modified, and a compressive strength prediction formula applicable to large-sized concrete members was established. Further integration with code-specified failure criteria led to the development of a biaxial failure envelope for large-sized concrete slabs, which was validated to agree well with measured data. The research findings can provide reliable experimental evidence and theoretical support for the strength reduction, load-bearing capacity assessment, and revisions of relevant design codes for large hydraulic components such as concrete face slabs in rockfill dams.

Microbially induced carbonate precipitation (MICP) technology is employed to reinforce the surface soil of a dam, aiming to prevent erosion caused by water flow and damage to the dam slope. The relationship between penetration depth, calcium carbonate content, and bonding depth was investigated at eight measuring points on the sand slope surface of a mold under different reinforcement durations. It was observed that as grouting reinforcement times increased, there was a gradual increase in calcium carbonate content but a rapid rise in penetration resistance. Moreover, the bonding depth of sand on the bio-reinforced sand slope increased with higher levels of calcium carbonate content. Microbial grouting reinforcement enhanced soil particle bonding force, requiring water flow to overcome this force for activation of sand particles. Consequently, microbial grouting reinforcement significantly improved shear strength and critical starting flow velocity on sand slope surfaces. The experimental results demonstrated that after MICP surface treatment through spraying, a dense and water-stable hard shell layer composed of bonded calcium carbonate and soil particles formed continuously on sample surfaces, effectively enhancing the strength and erosion resistance of sandy soils. These findings provide reliable evidence for silt slope reinforcement and dam erosion prevention.

Wetting deformation has a significant impact on dam safety, and is one of the leading causes of the long-term deformation of dams. For dams to operate safely, it is crucial to precisely estimate the extent of wetting deformation using a reasonable calculation model. This study describes the wetting deformation behavior of gravelly soil core material observed at a hydropower station using a large-scale triaxial wetting test, and the process, characteristics, and mechanism of the wetting deformation are analyzed. The results show that the direction of the wetting deformation exhibits different behaviors influenced by the stress levels. Compared with the significant changes in the wetting direction observed under low stress levels, the changes in the wetting direction under high stress levels appears to lag behind those in wetting deformation. The source of wetting deformation is thought to be the weakening of a material when it encounters water. Thus, a new calculation model of the wetting deformation of gravelly soil core material is proposed. In this model, the wetting strain ratio is in an exponential relationship with the stress levels, and the new model is used to simulate the triaxial wetting test on the gravelly soil core material; its validity and practicability are further evaluated, providing a new computational approach for analyzing the wetting deformation behavior of dams.

The Lianghekou earth core rockfill dam to be built in China will be the third highest rockfill dam in the world. This study presents the results of a series of direct shear tests between high plastic clay and concrete to study the shear behavior of contact clay-concrete cushion interface of Lianghekou dam. Results showed that water content and normal stress are significant factors affecting the shear behavior of the interface. The higher shear strength is related to lower water content and higher normal stress, and the shear strength can be formulated by the bifold-line type Mohr–Coulomb strength criterion. It is also found that the interface exhibits mainly two kinds of shear failure modes, that is, sliding failure along the concrete surface and shear failure in the clay matrix nearby the interface. Moreover, a nonlinear elastic model is proposed to simulate the shear behavior of the interface, of which parameters can be quickly estimated by water content. The simulation of the model is compared with the experimental results, and the results show that the model is reasonable and practical.

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.

Due to the obvious nonlinear effect caused by the shallow waves, the nonlinear wave loads have a great influence on the buried pipelines in shallow water. In order to ensure their stability, the forces on the pipelines that resulted from nonlinear waves should be considered thoroughly. Based on the Biot consolidation theory and the first-order approximate cnoidal wave theory, analytical solutions of the pore water pressure around the buried pipelines in shallow water caused by waves are firstly derived in this paper. The dynamic response of the seabed around the pipelines under the action of irregular waves is explored in laboratory, and the results are compared with the analytical ones. Experiments show that the maximum value of the pore water pressure is at the upper part of the pipelines, and the value at the bottom of the pipelines is the minimum. The pore water pressure amplitude at the upper half of the seabed that arises from waves has a larger fluctuation, and the amplitude at the lower half remains stable. For the sandy seabed, the pore water pressure at the same depth changes over time, with the fluctuating amplitude, and the theoretical values meet well with the test results.