A Seepage Investigation at Inandik Dam Using Numerical Tools
Dams are critical infrastructure, and ensuring their impermeability and stability is paramount. A published study in Environmental Earth Sciences sheds light on the seepage control measures implemented at the Inandik Dam in Turkey. The research, a comparative investigation using Slide2 and Plaxis 2D software packages, provides valuable insights into the effectiveness of slurry trenches and the role of numerical modeling in dam engineering.
The Challenge: Controlling Seepage During Dam Construction
Constructing a dam requires careful management of water, both on the surface and underground. Cofferdams are temporary structures built upstream and downstream of the dam body to create a dry excavation area. The Inandik Dam project utilized an upstream cofferdam with a clay core earth fill design and a slurry trench to minimize seepage.
The Solution: A Multi-Faceted Approach
The study highlights a multi-faceted approach to ensure impermeability which included:
- Careful Site Investigation: Boreholes were drilled to assess the alluvium and bedrock permeability, with permeability tests conducted in the field and laboratory. Pressurized water tests (Lugeon tests) were performed to estimate the rock mass permeability coefficient.
- Slurry Trench: This involved excavating trenches and filling them with a bentonite slurry, later displaced by plastic concrete. The slurry trench acted as an impermeable barrier, increasing the infiltration length and preventing seepage.
- Plastic Concrete Design: Plastic concrete, designed to reduce seepage in the soil beneath the dam body, had its physical, mechanical, and permeability properties carefully determined.
- Numerical Modeling with Rocscience Slide2 and RS2, and Plaxis 2D: Simulating seepage conditions and quantifying potential impacts on the dam body excavation area.
Numerical Modeling: A Comparative Advantage
The research paper emphasizes a comparative study using Slide2 and RS2 built-in finite element seepage analysis module and Plaxis 2D. The study checked the consistency of seepage calculations made in these programs with seepage measurements performed during the excavation of the dam body after cofferdam construction. This comparison of measured values in the two programs are listed below:
Parameter |
Slide2\RS2 |
Initial Water Level |
+9 m |
Water Level Downstream of Slurry Trench |
-15.50 m |
Water Level in Excavation Pit |
-20 m |
Seepage Amount into Excavation Area (2D) |
1.63×10−4 m3/s1.63×10−4m3/s |
Seepage Amount from Excavation Slope (2D) |
0.00016286 m3/s0.00016286m3/s |
Seepage Amount from Bottom of Excavation (2D) |
2.3723×10−7 m3/s2.3723×10−7m3/s |
Influx into Excavation Pit (150 m Cofferdam Width) |
24.45 liters/sec |
Observed Water Output in Dam Body Excavation Pit |
~20 liters/sec |
The compatibility of the seepage calculations made in the computer environment with seepage measurements performed during the excavation of the dam body confirms the accuracy of the models. After construction and the water loading process was complete, the amount of water leaking into the pit of the dam body excavation was measured to be 20 litres/second.
The Results: Success Through Integrated Design and Analysis
The study demonstrated the effectiveness of the slurry trench method in reducing ground seepage. By comparing the results from different software packages (Slide2, RS2 and Plaxis 2D) and validating them against field data, the authors provided a robust assessment of the cofferdam's performance and the effectiveness of the seepage control measures. The research concludes that the upstream cofferdam and plastic concrete provided the necessary impermeability for the safe construction of the dam body.
Key Takeaways for Geotechnical Engineers
This study reinforces several key principles for geotechnical engineers involved in dam design and construction:
- The Importance of Site Characterization: Thorough site investigations, including permeability testing, are essential for accurate modeling and design.
- The Value of Slurry Trench Technology: When properly designed and constructed, slurry trenches are an effective method for controlling seepage.
- The Power of Numerical Modeling: Programs like Rocscience Slide2 and RS2 allow engineers to simulate complex seepage behavior and optimize designs.
- The Value of Validation: Comparing numerical modeling results with field measurements is crucial for validating the accuracy of the models and building confidence in the design.
By integrating these principles and leveraging the power of software like Slide2 and RS2, geotechnical engineers can ensure the safe and reliable performance of dam structures.
