Weather Constraints
Adverse weather conditions can wreak havoc on a carefully planned liner deployment. Strong winds can make it difficult to unroll and position the liner, while rain can produce wet and slippery surfaces that can seriously impede installation. Attempting to install a liner during heavy rain, for example, can lead to water pooling on the liner surface, increasing the risk of slipping hazards for workers and seriously complicating the seaming process.
The most practical solution is carefully monitoring weather forecasts and planning the installation schedule around anticipated weather patterns. However, since unexpected weather changes are always a possibility, be sure to establish contingency plans. In light rain, temporary covers may provide enough protection to the work area and liner material to continue working. Weighted bags or temporary anchoring systems can also help secure the liner against minor winds during deployment.
However, there are limits to what even the best contingency plans can do. Attempting installation during windy conditions can be hazardous and impractical, for example. Even in moderately high winds, the risk of the liner material being damaged, displaced, or becoming uncontrollable is significantly high, posing safety risks to the installation crew and compromising the quality of the installation.
In such scenarios, postponing the installation until weather conditions improve is advisable. Safety and the integrity of the installation should always be the top priority. Establishing clear guidelines and thresholds for weather conditions beyond which installation should not be attempted is vital. This approach ensures not only the safety of the workforce but also the long-term effectiveness and reliability of the liner once installed.
Steep Slopes
Anchoring the Liner
One of the main difficulties on steep slopes is the risk of the liner material sliding or shifting due to gravity, which can disrupt the alignment of the liner, create wrinkles, or even lead to tearing. One option to prevent this is to anchor the liner at the top of the slope by excavating anchor trenches. These trenches act as anchor points to hold the liner in place against the force of gravity. After it’s positioned, the trenches are backfilled and compacted to ensure a strong hold while the liner is unrolled and deployed.
Deploying the Liner
Conventional liner deployment techniques may not be suitable for steep slopes due to the difficulty in controlling the unrolling and positioning of the liner. Ideally, a custom liner would be fabricated using smaller liner sections to make it more manageable. Additionally, liner sections can be unrolled horizontally across the slope rather than vertically down it to better control its placement. This method reduces the pull of gravity on the liner, making it easier to handle and position accurately.
Seaming Issues
When liners must be joined over uneven terrain or around complex shapes, such as in a contoured earth-fill dam, achieving a high-quality, leakproof seam can be challenging. For example, seaming on a sloped surface can be difficult as the material on the lower end of the slope is pulled down by gravity, making it hard to align the seams accurately.
In such cases, specialized seaming equipment, like a portable wedge welder, must be used to adapt to the dam’s slope and contour. Since wedge welders are designed to be lightweight and maneuverable, they can be used effectively even on sloped surfaces and around irregular shapes. Some other points to keep in mind:
- Employ experienced technicians who can manually adjust the liner and ensure precise alignment is essential.
- For complex shapes, custom-fabricated liner panels designed to fit specific areas can minimize the need for extensive field seaming.
- In all challenging seaming scenarios, conducting thorough testing of the seams, such as air pressure or vacuum testing, ensures their integrity and water-tightness before the liner is put into service.
Water Under the Liner
Water that accumulates under the liner is a common challenge that can compromise the liner’s effectiveness and the overall integrity of the dam structure. Here are some examples of how this issue might be addressed.
Nonwoven Geotextiles: In some cases, such as when soil is moderately wet (but not saturated), installing a layer of geotextile fabric beneath the liner can aid in water management. A nonwoven geotextile layer can help with water filtration and drainage, preventing water from becoming trapped under the liner. They also help stabilize the soil, prevent different soil layers from mixing, and reduce the risk of liner displacement due to soil movement.
Drainage Systems: Appropriate drainage solutions should be implemented before installation to manage more substantial water accumulation. Potential solutions include installing subsurface drainage systems or drainage layers that channel water away from the liner area. If water accumulation is due to rainfall, the problem will be eliminated once the liner is sealed. On the other hand, If water is rising up through the ground, it’s crucial to accurately identify the source and implement targeted measures to manage it effectively.
Groundwater Diversion: If the dam is located in an area with a high water table, groundwater can seep into the installation area. A high water table can be a continuous water source, especially in low-lying or water-rich regions. Besides a drainage system, a groundwater cut-off wall or a series of well points can be installed around the perimeter of the installation area to lower the groundwater level.
Surface Grading and Sloping: Adjusting the grading and sloping of the installation area can help direct surface water away from the liner. Proper surface grading ensures that water flows towards designated drainage points, reducing the risk of accumulation beneath the liner.
Water Removal During Installation: If water accumulates during the installation process, particularly during rainy conditions, it should be actively removed before installation using pumps or other water removal equipment to ensure the installation area remains dry.
Timely Installation and Sealing: Efficient and timely liner installation can reduce the window of exposure to elements like rain. Once the liner is positioned correctly and sealed, it provides a barrier against further water entry.
