What are the required dimensions for a gravel diaphragm trench, and what must be placed between the gravel and the underlying soil trench?

What are the required dimensions for a gravel diaphragm trench, and what must be placed between the gravel and the underlying soil trench?

• A. 3' width, 2' depth, filter fabric
• B. 2' width, 1' depth, gypsum
• C. 2' width, 1' depth, geotextile
• D. 2' width, 1' depth, filter fabric

Answer: (D)

Gravel diaphragm trenches are kept compact and protected from sediment by using a separator fabric. The standard size is two feet wide and one foot deep, which provides enough surface area for infiltration without being oversized. Placing a layer of filter fabric between the gravel and the underlying soil prevents fine soil from migrating into the gravel voids, which could clog the trench and reduce its effectiveness. Gypsum isn’t used in this context, and while geotextile can serve as a separator, the specification here calls for filter fabric. So the combination of two feet by one foot and a layer of filter fabric between the gravel and the native soil best fits the required design.

Gravel diaphragm trenches are kept compact and protected from sediment by using a separator fabric. The standard size is two feet wide and one foot deep, which provides enough surface area for infiltration without being oversized. Placing a layer of filter fabric between the gravel and the underlying soil prevents fine soil from migrating into the gravel voids, which could clog the trench and reduce its effectiveness. Gypsum isn’t used in this context, and while geotextile can serve as a separator, the specification here calls for filter fabric. So the combination of two feet by one foot and a layer of filter fabric between the gravel and the native soil best fits the required design.