In recent years, pumped storage power stations have developed rapidly, and their construction often faces the problem of mixed utilization of soft and hard rock. Soft rock has poor lithological properties, exhibiting significant breakage during construction. Whether mixtures of soft and hard rock can meet the requirements for dam strength and permeability characteristics requires further investigation. Field rolling compaction tests were conducted on soft and hard rockfill materials for a proposed pumped storage power station in Anhui Province, China, to investigate their physical, mechanical, and permeability characteristics under different compaction parameters. A comprehensive test scheme was designed to compare the compaction outcomes under combined conditions of roller weights (22 t and 26 t), water contents (5% and 10%), lift thicknesses (0.6 m and 0.8 m), and number of rolling passes (6, 8, and 10). A novel tensile direct shear test method was employed to measure the in-situ shear strength indices of the compacted rockfill and to identify the compaction parameters meeting the design requirements. This approach bridged the gap between laboratory tests and field conditions, offering a direct basis for reevaluating dam slope stability. The results showed that under identical compaction parameters, the dry density, permeability coefficient, and shear strength of the mixture containing 50% carbonaceous sericite phyllite were slightly lower than those of the sericite phyllite mixture. The dry density of the mixtures increased with the number of compaction passes, showing a convergent trend. Increasing the roller weight and reducing the lift thickness significantly improved the compaction quality. Regarding particle breakage characteristics, breakage occurred mainly in the surface layer of the lift during compaction, while the rockfill at deeper locations experienced minimal breakage due to the encapsulating effect of finer particles. The sericite phyllite mixture primarily experienced breakage of large particles, whereas the carbonaceous sericite phyllite mixture underwent repeated breakage in the surface layer during compaction, resulting in a powdery texture after compaction. Under a lift thickness of 80 cm, the strength parameters obtained using a 22 t vibratory roller with 10 compaction passes were essentially identical to those obtained using a 26 t vibratory roller with 8 passes. Based on the test results and considering both on-site construction quality and efficiency, it is recommended that for the sericite phyllite mixture, the construction parameters should be a lift thickness of 80 cm, a water content of 10%, and compaction with either a 22 t vibratory roller for 10 passes or a 26 t vibratory roller for 8 passes per lift.

This study focuses on the modification effect of incorporating polypropylene fibers to enhance the mechanical properties of self-compacting hydraulic concrete. It systematically investigates the influence patterns of fiber parameters (length and dosage) and curing time on its compressive strength, failure strain, and microstructural evolution. Experimental programs with varying polypropylene fiber parameters (length and dosage) and curing durations were designed. Multi-scale analysis was carried out through macroscopic mechanical testing and microstructural characterization techniques. At the macro level, standard compressive strength tests and failure strain measurements were conducted to analyze the mechanical response to different parameters. At the micro level, scanning electron microscopy (SEM) and computed tomography (CT) scanning techniques were employed to investigate the synergistic mechanisms between fibers and hydration products. Polypropylene fibers significantly improved the mechanical performance of the concrete through “crack bridging” and “energy dissipation” mechanisms. When the fiber dosage reached 0.8%, the compressive strength increased by up to 80.3% compared to the control group. Both compressive strength and failure strain initially increased and then decreased with increasing fiber content. Short-cut fibers exhibited the best performance due to their superior dispersion uniformity. Microstructural analysis revealed that the fibers and hydration products formed a dense three-dimensional network, effectively delaying the failure process. However, fiber agglomeration occurred when the dosage exceeded the optimal level, which weakened the overall mechanical performance. A self-compacting hydraulic concrete mix design incorporating 0.8% fiber dosage and short-cut fibers can significantly enhance the mechanical performance. The synergistic effect between fibers and hydration products is central to performance improvement, while balancing fiber dosage and dispersion is essential to prevent agglomeration. This research provides a theoretical foundation and practical guidance for improving the mechanical performance of self-compacting hydraulic concrete in hydraulic engineering applications.

In order to solve the problem of large early autogenous shrinkage and high cracking risk of the UHPC, the effects of expansive agent and shrinkage reducing agent on the early autogenous shrinkage of the UHPC were studied. The effects of single expansive agent, single shrinkage reducing agent and their combination on the autogenous shrinkage of the UHPC were tested, and the microstructure of the products was analyzed. The results show that both expansive agent and shrinkage reducing agent can reduce the early autogenous shrinkage of the UHPC, and the shrinkage reducing effect of the combined admixture is more significant than that of the single admixture. When mixed alone, the more the amount of expansive agent is, the better the shrinkage reduction effect is. The optimal dosage is 8%, and the addition of 1.5% shrinkage reducing agent has the best effect on reducing autogenous shrinkage. When the expansive agent is added alone, the pores of the UHPC matrix are filled, the structure is denser, and the ability to resist shrinkage deformation is enhanced; When the shrinkage reducing agent is single-doped, the porosity and pore size of the matrix are smaller than those of the Blank group, and the autogenous shrinkage can be reduced under the appropriate dosage. When the expansive agent and the shrinkage reducing agent are mixed, the size of the AFt crystal is smaller than that of the single-doped expansive agent group but larger than that of the single-doped shrinkage reducing agent group, the structure is denser, indicating that the both of these play a synergistic role in shrinkage reduction.

In order to deeply study the micromechanism of polypropylene steel-like fiber permeable concrete, the CT scanning technology was used to scan the specimens, and a visualization model of the pore structure was established through three-dimensional digital reconstruction technology. Based on the image analysis method, a comparative study was carried out on the morphological evolution characteristics of the internal pore system of the material before and after fiber modification. The results show that the addition of polypropylene steel-like fibers can effectively improve the strength of the specimens, but it will inhibit the water-permeability performance of the specimens. The porosity of each layer of the specimens is stable in the range of 15% and 20%, and the connected pores account for more than 97% of the total pores. In the specimens without added fibers, the number of large pores is small, but their volume proportion is large. After adding fibers, some large pores are transformed into medium-sized pores and the connectivity between pores is inhibited, thus changing the pore structure.

The excavation construction of large underground cavern chambers is prone to induce the relaxation of the surrounding rock unloading. Generally, in-situ testing methods are used to determine the relaxation depth during the construction period, but there is a lack of effective means to estimate the relaxation depth during the survey and design stage. Firstly, the characteristics of surrounding rock unloading relaxation in cavern groups are analyzed, and it is pointed out that the adjustment of the stress field is the direct cause driving the macro-mesoscopic evolution of surrounding rock and the decline of bearing capacity. At present, borehole acoustic testing technology and acoustic change rate indicators are mostly used to identify the surrounding rock relaxation depth. The surrounding rock relaxation depth of underground powerhouse for the built hydropower station is generally within 5 m. Then, a quantitative analysis method for rock mass excavation unloading relaxation is established considering damage and deterioration effects, and quantitative indicators and criteria for the evolution of surrounding rock unloading relaxation are proposed. Finally, the assessment of surrounding rock unloading relaxation is carried out for actual projects. It is found that the proposed method and criteria can further quantitatively analyze the degree of surrounding rock disturbed by excavation on the basis of traditional plastic zone indicators, so as to realize more accurate and targeted cavern support design.

In view of the problem that it is difficult to determine the optimization parameters of rock material yards and mine blasting in water conservancy projects, the traditional methods mainly rely on empirical formulas and experimental adjustments. To solve this issue, this study proposes a parameter optimization method that integrates an improved whale optimization algorithm (GWOA) with back propagation (BP) neural network. A GWOA-BP model was developed with optimization objectives focusing on explosive consumption per unit, borehole spacing, and row spacing. Comparative analysis was performed using measured blasting data of a certain project in Yunnan Province. The results indicate that the GWOA-BP model outperforms the conventional BP model in terms of prediction accuracy and stability, with error metrics significantly reduced. This research offers a novel technical approach for optimizing blasting parameters in simliar projects.

Analyzing the safety of the dam is of vital importance for maintaining their safe operation. Relying on the high asphalt concrete core rockfill dam project of the lower reservoir of a planned pumped storage power station, the mechanical characteristics tests of rockfill materials in transition layer, upstream rockfill area and downstream rockfill area were carried out. The Duncan E-B model and rheological model parameters of rockfill materials were measured. On this basis, the three-dimensional nonlinear stress-deformation finite element calculation of the dam was carried out. The safety of the dam was demonstrated from the aspects of dam body, core wall and cutoff wall. The results show that under the normal water level, the extreme settlement value of the dam is -22.29 cm and the settlement rate is 0.28%. The major and minor principal stresses of the dam are 1.38 MPa and 0.54 MPa, respectively. The extreme values of core wall displacement along the river, dam axial displacement and vertical displacement are 11.55 cm, -3.70 cm/3.63 cm and -21.46 cm, respectively. The extreme value of principal tensile strain is -0.8%. The extreme displacement values of the cutoff wall along the river, the axial direction and the vertical direction of the dam are 1.32 cm, -0.11 cm/0.02 cm and -0.54 cm, respectively. The extreme values of major and minor principal stresses are 6.82 MPa and -1.20 MPa respectively. After rheology and wetting are taken into account, the extreme value of dam settlement is -35.00 cm, and the settlement rate is 0.44%. The extreme values of core displacement along the river, dam axial and vertical displacement are 13.65 cm, -4.97 cm/4.77 cm and -33.01 cm, respectively. The comprehensive analysis results indicate that the distribution and extreme value of stress and deformation of the dam are reasonable, and the tensile strain of asphalt concrete core wall and the tensile stress of concrete wall in dam foundation are not beyond the standard value, so it can be judged that the dam can meet the requirements of safe operation.

To reveal the influence of aftershocks on the failure process of gravity dams, the Jinanqiao gravity dam is chosen to perform the investigation. The impact of reservoir water was simulated by using Westergaard additional mass. The elastoplastic damage model was adopted to simulate the nonlinear characteristics of the concrete material of the dam body, and the nonlinear failure process of the dam body under the action of a single main shock and main aftershocks was calculated. The results show that the failure pattern of the dam body under the main aftershock is consistent with that under the single mainshock. The failure areas are mainly concentrated at the dam heel, the upstream and downstream folded slope, and the downstream dam surface. The aftershock effect will cause the further development of the main earthquake damaged area and significantly increase the cumulative plastic dissipation energy of the dam body. The cumulative plastic dissipation energy caused by aftershocks gradually increases with increase of the PGA. After the PGA reaches 0.45g, the contribution of aftershocks to the cumulative plastic dissipation energy gradually stabilizes at around 30%. In terms of seismic performance, the ultimate seismic bearing capacity of the dam body is in the range of 0.50g and 0.55g under the action of a single main shock, while under the action of the main aftershock, it decreases to 0.40g-0.45g.

Tailings dams are formed through long-term accumulation of tailings, featuring complex stratification and non-uniform permeability coefficients. To obtain representative permeability coefficients that reflect their overall permeability characteristics, a novel inversion method was proposed. Optimal Latin Hypercube Sampling (OLHS) was used to obtain uniformly distributed samples of permeability coefficient combinations for tailings dams. These samples were then input into a finite element model for forward analysis to obtain corresponding samples of water heads at monitoring points. The two sets of samples were combined to form a dataset. A nonlinear mapping relationship from the permeability coefficients to the water heads at monitoring points was established using the Kernel Extreme Learning Machine (KELM). The hyperparameters of the KELM were optimized using an Improved Animated Oat Optimization (IAOO) algorithm, which integrated Latin Hypercube Sampling for population initialization, centroid opposition-based learning, and an adaptive optimal-seeking boundary mechanism. An inversion model for the permeability coefficient of tailings dams based on OLHS-IAOO-KELM was thus established and subsequently applied to a practical engineering case. The permeability coefficient values obtained through the inversion model were reasonable. The relative errors between the calculated water heads from forward seepage analysis and the measured water heads at the seven monitoring points did not exceed 2.08%, meeting the engineering accuracy requirements. Furthermore, the potential distribution of the seepage field in a typical cross-section of the tailings dam conformed to general patterns. Compared with other models, the inversion result of the proposed model exhibited the smallest errors. The proposed model demonstrates high accuracy and robustness, and possesses practical value for the inversion of permeability coefficients in tailings dams.

Computational fluid dynamics (CFD) method was used to numerically simulate the two-phase flow on stepped spillways to investigate the initiation mechanism of self-aeration in stepped spillways and clarify the impact of step length on the self-aeration characteristics of stepped spillways with non-uniform step lengths, including concave, convex, random, and semi-uniform step length configurations. Compared with the traditional uniform steps scheme, the results show that both concave and convex configurations prove unsuitable for rapid initiation of self-aeration, leading to a 6.4% and 7.0% posterior shift in the aeration inception points. Although random step configuration promotes the development of turbulent boundary layers to some extent, the inherent uncertainty in their step length arrangements induces excessive surface fluctuations. The semi-uniform step scheme can significantly move forward the position of the initial aeration point (by 18.8%) while ensuring a relatively stable flow state, which has a broader application prospect.