Eleven concentrated seepage outlets were identified in the dam toe drainage prism. When the reservoir water level reached 180.0 m, two zones of continuous pressurized water boiling emerged on the dam-facing slope of the toe pond. Based on the geotechnical property parameters of dam materials, a representative dam cross-section was selected for stability simulations via an AutoBank finite element model. Long-term field monitoring datasets, covering downstream seepage outlet positions and measured seepage rates, were adopted to calibrate and optimize the model input parameters. A series of numerical simulations were then performed by integrating various reinforcement countermeasures into the established model, which allowed identification of the optimal risk mitigation and rehabilitation scheme. Practical implementation of this scheme has delivered satisfactory performance and completely eliminated the risk of dam instability. Before reinforcement, seepage failure develops at the upstream dam toe, the contact interface between the downstream embankment and drainage prism, the gravel-foundation dam, and the surface clay blanket over the downstream riverbed under the check flood level, normal pool level, and 180.0 m water level, alongside substantial total downstream seepage discharge. After reinforcement, the dam remains seepage-stable under all these hydraulic conditions. For both pre-reinforcement and post-reinforcement configurations, the upstream and downstream slopes meet sliding stability criteria across five hydraulic scenarios: check flood level, normal pool level, 180.0 m water level, rapid drawdown from check flood level to normal pool level, and rapid drawdown from normal pool level to dead water level, without potential sliding or deformation hazards. Finite element numerical simulation is adopted as the primary analytical technique to assess the overall stability of dams on gravel foundations. This approach precisely captures the coupled seepage-deformation responses and evolutionary patterns of such dams, yielding accurate, dependable calculation results with well-established, viable technical procedures. Comparative numerical simulations of multiple alternatives enable the optimization of risk mitigation and reinforcement strategies for distressed gravel-foundation dams. This method removes the subjectivity plaguing traditional empirical comparison and delivers a theoretically sound analysis framework. The findings extend the theoretical system describing stability evolution of gravel-foundation dams, and offer robust theoretical support and practical benchmarks for stability mechanism research and refined reinforcement design of similar hydraulic projects globally.
The Kulekhani Rockfill Dam at Makawanpur District in Bagmati Province is the Nepal’s one and only large storage hydropower reservoir project that plays a critical role in country’s peak energy generation. The long-term safety assessment of such dam is very crucial because seepage conditions, reservoir operation and rapid drawdown may significantly influence its embankment stability and deformation behavior over time and continuous operations. This study presents an integrated numerical investigation of seepage, slope stability and deformation characteristics of the Rockfill Dam using the GeoStudio software where SEEP/W was used to evaluate seepage behavior and transient pore-water pressure response while SLOPE/W to assess its either slopes’ stability under steady-state and rapid drawdown conditions and SIGMA/W to investigate the deformation characteristics. The results from the analyses indicate that the embankment dam remains stable under normal operating conditions with factors of safety (FOS) of 2.006 and 1.627 for the upstream and downstream slopes respectively. Under rapid drawdown conditions, the factor of safety progressively decreased and reached a minimum value of 1.793 which indicates that rapid drawdown represents the governing loading condition for the safety of dam. The sensitivity analyses over different parameters showed that the friction angle of the rockfill shell is the most influential parameter controlling the slope stability of the dam. Introduction of an upstream stabilizing berm showed improvement in the factor of safety from 1.750 to 1.930, an increase of approximately by 10.3%. The model validation has demonstrated satisfactory agreement between numerical predictions and available design values of the Project. The study confirms that integrated numerical modelling provides an effective framework for evaluating the hydraulic characteristics, stability and deformation performance of rockfill dams. The findings highlight the importance of reservoir operation control and provide practical recommendations for future safety management of Kulekhani Dam and similar type of embankment dams in Nepal or elsewhere.
The foundation of the Karkheh Dam comprises a heterogeneous geological profile of highly permeable conglomerate layers interbedded with relatively impervious mudstones. Following the extreme flood events of March and April 2019, the reservoir first reached its normal water level (NWL) of 220 m above sea level and subsequently rose by approximately 5 m, peaking at 224.82 m on April 5. Although the dam crest is at 234 m, these conditions raised concerns regarding structural stability and potential seepage hazards, particularly during future floods. To mitigate these risks, strict operational measures were implemented to limit the hydraulic gradient within allowable design values, thereby reducing the likelihood of internal erosion and piping in the foundation and abutments. A three-dimensional seepage model of the foundation and abutment system was developed using FEFLOW 3D, incorporating six conglomerate layers at four reservoir levels. The model was calibrated against monitored seepage discharges by adjusting hydraulic conductivity coefficients and validated with piezometric data. The key results included the identification of the uplift pressure distribution beneath the spillway chute and pinpointing the location of maximum uplift pressure, which is critical for implementing new drainage wells. In addition, the analyses determined a threshold reservoir elevation above which the maximum average hydraulic gradient increases to levels that pose a heightened risk of internal erosion in the foundation and abutments. These findings, along with refined permeability parameters and hydraulic gradient distributions, provide deeper insight into the dam’s hydro‑geotechnical response under extreme hydrological loading and support targeted hydraulic safety management.
Riverbank failure offers serious geotechnical and hydraulic dangers to infrastructure, the environment, and the quality of water along fluvial rivers. This study looks at the collapse causes of riverbanks and surrounding embankments over an 8-kilometer stretch of the Euphrates River in Babilon City. An integrated technique integrating field collection, thorough laboratory testing, and the GeoStudio (SEEP/W and SLOPE/W) model was used. Laboratory data demonstrated that high silt and clay concentration (62% silt, 28% clay in embankments; 58% silt, 24% clay in banks) influences soil behavior. Also, the seepage analysis highlighted pore water pressure variations (0.2–1.2 m) and discharge rates (1.76×10⁻⁸ to 1.84×10⁻⁷ m³/sec), which directly influence embankment stability. Slope stability analysis demonstrated a 26% increase in the factor of safety (FS) with higher soil cohesion, emphasizing the importance of cohesive strength in mitigating failure risks. This study bridges the empirical-computational gap by establishing site-specific hydraulic conductivity functions and safety factor sensitivity charts for fine-grained fluvial soils, offering actionable reinforcement strategies (geosynthetic additives and stone riprap). The integration of field data with comprehensive laboratory tests utilizing GeoStudio to determine seepage flow and slope stability under many circumstances is innovative. The work comes to the conclusion that practical insights for riverbank management may be obtained by combining laboratory data with numerical modeling. Periodic monitoring, soil fortification with additives, and stability-enhancing preventive measures like stone rippling or gabions are among the recommendations.
Connections between earth–rockfill and concrete dams are critical components of hybrid-dam seepage-control systems because material-stiffness contrasts and complex foundation conditions can create localized preferential seepage paths. Using HS Reservoir as a case study, this predictive design-stage assessment employed a full-domain three-dimensional model of the dam–foundation–abutment system and a local three-dimensional model of the cutoff-spur-wall connection. The seepage field, hydraulic gradients, and zonal seepage discharges were evaluated under the normal pool, design flood, and check flood levels, together with the responses of the connection interface and right-abutment grout curtain. Across the three baseline scenarios, the impervious core accounted for 82.2–83.6% of the total head difference at the maximum riverbed section, and the reported control-location gradients remained below the corresponding design values. At the check flood level, the modeled 178 and 179 m head contours passed above the local curtain crest at elevation 177.5 m, identifying an over-curtain seepage pathway. From the design flood level to the check flood level, right-abutment discharge increased from 259.86 to 544.49 m3/d (109.5%), while total discharge increased by 28.6%. Flow in the connection zone diverted around and beneath the cutoff spur wall, and the connection-surface gradients increased with reservoir level. These model predictions characterize the three-dimensional seepage response of the connection zone and right-abutment seepage-control system and can inform curtain-crest review, construction quality control, and post-impoundment monitoring.
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