Farm and Ranch Construction receives calls from property owners almost weekly concerning a Dam Leak in one of their lakes or ponds due to a faulty Dam Core or the lack of a core altogether. One of the most disheartening trials as a landowner is to continually wait for rain to fill up your lake and then once it does rain, to watch it disappear because the Dam Core was not constructed properly or because it doesn’t even exist.
Click here to view the NRCS Handbook for proper pond construction.
For dams that are leaking, we do offer treatment in the form of slurry walls or liners to solve those leaking issues. The downside of any slurry project is the cost. Introducing Bentonite into a project can make it significantly more expensive. The key to making your water resource project more effective in the long term is avoiding this kind of repair with proper construction techniques from the start. Building a dam correctly is accomplished by incorporating a core. Simply defined, the core is the center of the dam structure. The core is the heart of the project and the single most important part of any dam.
Click Here for a Core Illustration
Geologically, at some particular depth, there is an impervious formation under the ground, regardless of where your project is located. Formations lie at different depths throughout the state of Texas. This formation will not allow water to sink any deeper. All underground water moves constantly so when it encounters an impervious formation, it reacts by moving horizontally in a downhill direction on top of the impervious formation.
The first step to digging a good Dam Core is to be sure you have reached the impervious formation depth. At times this means digging underwater, so your equipment operator needs to have experience recognizing different types of soils and feeling the contours of the formation bottom through the vibrations of the excavator. Normally this formation is layered rock, hardened sands and gravel, or clay. Thin layers of less than desirable material can be encountered before reaching the impervious formation. The key to a good Dam Core is using the correct equipment. For many years the only tool available was a bulldozer. While a bulldozer is still necessary for construction, we now have equipment such as excavators, hydraulic hammers, and rock saws that make it possible to build the core correctly.
A Core During the Dig Process – Hamilton County, Tx
Recently Farm & Ranch completed a project near Hamilton County, Texas. At that location we encountered a total of fourteen different layers of soil that we determined weren’t suitable as the impervious formation due to possible leaks. Eventually we made our way down to a Blue Shale foundation that allowed us to build our core.
Once the foundation is established, a key way is excavated. This is usually a one to two foot deep trench into the foundation formation. At this point the core trench and key way are back-filled with a suitable clay material with a low permeability rating. Hopefully the core material is readily available on site. The Dam Core material is compacted by a pad roller or other heavy equipment in eight to twelve inch lifts, up to ninety-five percent proctor. Once ground level is reached, the front and rear slopes of the dam will be built in unison with the Dam Core. The slope material does not need to be as impermeable as the Dam Core material. The process of building in lifts is repeated until the project engineer’s recommended spillway height is achieved. Then another 3 or 4 feet of material is placed on top of the Dam Core to serve as the freeboard.