What are designed to prevent movement of back-fill materials while allowing water to pass through?

Filter fabrics are specifically engineered to allow water to pass through while preventing the movement of soil or back-fill materials. This function is crucial in various construction applications, particularly in the installation of underground storage tanks where maintaining the integrity of the surrounding earth is essential.

The active role of filter fabrics is to serve as a barrier that retains soil particles, reducing the risk of erosion or sedimentation that could compromise the structure of the UST. This characteristic helps to maintain proper drainage and prevents the build-up of water pressure behind the tank, which could lead to instability or failure in the storage system.

In contrast, drainage pipes are designed to carry water away but do not prevent back-fill movement in the way that filter fabrics do. Geodetic nets do not fulfill this particular purpose either. While they may contribute to soil stabilization in certain contexts, their primary function differs. Similarly, separation mats are used for different applications and do not have the dual filtration and stabilization function of filter fabrics. Therefore, filter fabrics are the most appropriate choice for this question, as they effectively fulfill the requirements of allowing water to pass while preventing the displacement of geological materials.