Introduction

Seepage is a critical concern in the design and operation of earth dams, as uncontrolled water flow through the dam body or foundation can compromise structural integrity, leading to potential failure. Over the years, various seepage mitigation techniques have been developed and implemented to ensure the safety and stability of earth dams. Among these, the application of geomembranes and cut-off walls has shown promise in reducing seepage rates. However, the effectiveness of these methods can vary significantly depending on site-specific conditions and the design of the dam. This study focuses on evaluating the efficacy of seepage control measures applied at two earth dams in Iran—Shahid Yaghoubi and Maloo dams—located in Khorasan Razavi province. Both dams have experienced seepage issues, prompting the implementation of advanced seepage mitigation strategies. This paper presents a detailed analysis of these strategies, their impact on seepage rates, and the overall implications for dam safety.

Methodology

The research methodology involves the use of GeoStudio 2012 software, specifically the SEEP/W module, to conduct finite element analysis of water flow through the dams under study. The SEEP/W module is well-suited for analyzing both steady-state and transient seepage conditions, allowing for a comprehensive evaluation of the implemented mitigation measures. The study began with the validation of seepage models using actual data recorded from the dams, ensuring that the simulations accurately reflect real-world conditions.

For the Shahid Yaghoubi dam, validation was conducted using seepage data collected by onsite operators, while for the Maloo dam, piezometric pressure data was utilized. The validated models were then used to simulate different scenarios, including the application of a geomembrane layer on the dam's upstream face and the installation of a cut-off wall beneath the clay core. The effectiveness of these interventions was assessed by comparing seepage rates before and after their implementation.

Case Study 1: Shahid Yaghoubi Dam

The Shahid Yaghoubi dam, a rockfill structure with a clay core, has been operational since 1997. Located near Torbat Heydarieh city, the dam plays a critical role in regulating water flow from the Kal-Salar River. Despite its importance, the dam has experienced significant seepage issues, particularly in the downstream drainage gallery. The initial analysis revealed a seepage rate of 0.41 liters per second, with critical hydraulic gradients forming in the downstream drain.

To mitigate these issues, two seepage control measures were proposed and analyzed using the SEEP/W module. The first involved applying a geomembrane layer to the dam's upstream face. The geomembrane, with a permeability coefficient of 5.0×10^-13 m/s, was found to reduce seepage by 15%, effectively eliminating critical hydraulic gradients within the dam. The second measure involved the construction of a cut-off wall beneath the dam core. Three different scenarios were modeled, with the wall positioned at various locations relative to the core. The results indicated that placing the cut-off wall in the downstream part of the core achieved the greatest reduction in seepage, decreasing the flow rate by 35%. However, the critical hydraulic gradient remained unchanged, highlighting the complexity of seepage dynamics within dam structures.

Case Study 2: Maloo Dam

The Maloo dam, an earth dam with a clay core, is located near Torbat Jam city. This dam also faced significant seepage issues, prompting the implementation of both a geomembrane layer and modifications to an existing cut-off wall. The initial seepage analysis revealed a flow rate of 0.36 liters per second, with critical hydraulic gradients identified near the core.

The first mitigation measure involved applying a geomembrane layer to the upstream face of the dam. This intervention reduced seepage by 6%, a modest improvement attributed to the low reservoir levels during the study period. The second measure focused on increasing the height of the existing cut-off wall beneath the dam core by 4 meters. This modification led to a more substantial reduction in seepage, decreasing the flow rate by 25%. The results underscore the importance of tailoring seepage control strategies to the specific conditions of each dam, with structural modifications offering significant potential for improving dam safety.

Conclusions

The study's findings demonstrate the effectiveness of advanced seepage mitigation techniques in reducing water flow through earth dams, thereby enhancing their structural integrity and operational safety. The application of geomembranes and cut-off walls at the Shahid Yaghoubi and Maloo dams resulted in significant reductions in seepage, although the impact varied depending on the specific conditions of each dam. The results highlight the importance of site-specific adaptations in seepage management, with tailored strategies offering the best outcomes for maintaining dam safety.

These case studies contribute valuable insights into the optimization of seepage control measures, emphasizing the need for ongoing monitoring and adaptive management to address the dynamic nature of seepage in earth dams. The research also underscores the critical role of precise instrumentation and reliable data in evaluating the effectiveness of mitigation strategies and ensuring the long-term safety of dam structures.

Overall, this study advances the understanding of seepage dynamics and provides practical guidance for the implementation of seepage control measures in earth dam engineering. The findings have significant implications for the design, construction, and maintenance of earth dams, particularly in regions prone to seepage-related challenges.