The Importance of Filters in Dam Construction and Maintenance

Given the importance of dams in agriculture, industrial processes, and human consumption worldwide, there’s no surprise that dam construction is a form of art.

When it comes to dam construction, one of the most important aspects to consider is particle retention lab testing of filters for dams and their design. Filters for dams are utilized to prevent internal soil movement, as well as to control drainage. They can be placed at different locations during construction or added later to reduce risks, such as seepage.

Let’s not forget that seepage can be extremely problematic when it carries materials with it and can lead to erosion, damage to concrete structures, and accidents. Alarmingly, data shows that 50% of dam failures are due to seepage.

Therefore, refined design principles and lab testing of filters are needed to improve dam construction and maintenance across Australia and the rest of the world.

Filters and Drains for Dams

Filters for dams are mandatory structures used to hold soil material particles in place; they can be employed to provide drainage as well. Interestingly enough, the importance of filters in dams has been known for centuries, with dam engineers improving their design and effectiveness on a regular basis.

Now, filter zones in dams are constructed with safe materials. They are effectively incorporated in dams to act as a protective measure to reduce risks and dam maintenance costs. By choosing an effective impervious fill material, experts can reduce risks and hold particles in place. When it comes to granular filters, for instance, graded or crushed earth materials can be highly effective.

Here we should clarify the difference between drains and filters. Some filters can be made of a single material that can act as a filter as well as a drain. On the other hand, depending on the stage, we can talk about first-stage filters that protect the base soil of the dam, and second-stage materials used to provide drainage. In cases when both stages are present in the dam construction process, it’s reasonable to use the term filter-drain.

Types of Filters for Dams

While there is a variety of filters for dams, depending on their design and orientation, filters can be divided into four major groups:

Class 1: Drainage filters used to remove seepage. As these filters are designed to remove particles and provide drainage, they should consist of uniformly graded materials, in two stages. Toe drains are considered drainage filters.
Class 2: Protective filters used to reduce erosion and pore pressure. Chimneys and blankets, for example, can be classified as Class 2 filters.
Class 3: Inverted or choke filters used to support the base material used in your dam. We should note these filters can be used to repair sinkholes in dams.
Class IV: Seismic crack stoppers used to protect against cracks and other problems that dam owners may face.

Lab Testing of Filters for Dams

To ensure safety and facilitate dam construction, particle retention lab testing of filters becomes vital. Lab testing of filters for dams is one of the most reliable methods to provide reliable data. In fact, filters have been a focus of research and simulating conditions within a dam for years.

Analysis of geotechnical parameters, geological mapping of natural formations and dams, as well as field exploration, are all crucial factors in particle retention design and testing.

Here we should note a historic approach to analyse errors can be considered as well, but blending and mixing of materials can occur during excavation and lead to further errors.

Types of Lab Testing of Filters for Dams

As stated above, the importance of particle retention testing is vital. One of the most important parameters to consider is gradation or particle size distribution, along with soil plasticity.

Some of the most popular tests for particle retention testing are the No Erosion Filter Test (with its D15b boundary); the Continuing Erosion Filter Test; and the Rate of Erosion Test. On the other hand, some of the most effective tests for material quality lab testing include the following: Sampling; Test for Clay Lumps; Soundness Test; Test for Plasticity of Fines; Sand Equivalent Test; Petrographic Analysis; Vaughan Test for Cohesion; and Compressive Strength Test.

Note that base soils carrying over 15% fines require in-depth analysis. Both the Crumb test (ASTM D 6572) and the Standard Test Method for Dispersive Characteristics of Clay Soil by Double Hydrometer (ASTM D 4221) can be used. For higher accuracy, it may become necessary to perform chemical testing.

Particle Retention Testing and Design for Dam Filters: Additional Considerations

Apart from conducting lab testing of filters for dams, experts should consider the actual design of the filters. As there’s a wide range of filters, graphical representations and computational analyses become essential.

To provide an example, one of the first step experts should take is to plot the gradation curves of the base soil materials of your dam and determine the presence of any dispersive clay content. Factors, such as D15F sizes, critical hydraulic gradient, minimum thickness, permeability, and hazard classifications, should all be considered. Once this is done, additional filter testing and readjustments might be needed.

When it comes to costs, experts and clients should find a balance between quality and costs to ensure dam safety and effectiveness.