Wraping gravel with geotextile in drainage
Wraping gravel with geotextile in drainage
(OP)
I have a site that needs an interceptor drain to remove subsurface water from the soil above a proposed septic system leach field. This is to be installed upslope of the proposed leach field.
The soil is sandy loam over weathered sandstone. (About 4' depth to the weathered sandstone)
Should a fabric be used to wrap the gravel in an attempt to keep fines out of the gravel? Could this plug up with fines and then prevent water movement into the gravel and pipe?
The plan had a filter fabric wrapping the gravel but the contractor did not install the fabric. Should this be replaced to match the plan?
3/4" clean drain gravel is used in the trench.
Thanks you for your comments.
The soil is sandy loam over weathered sandstone. (About 4' depth to the weathered sandstone)
Should a fabric be used to wrap the gravel in an attempt to keep fines out of the gravel? Could this plug up with fines and then prevent water movement into the gravel and pipe?
The plan had a filter fabric wrapping the gravel but the contractor did not install the fabric. Should this be replaced to match the plan?
3/4" clean drain gravel is used in the trench.
Thanks you for your comments.





RE: Wraping gravel with geotextile in drainage
Get the contractor to follow the plan.
RE: Wraping gravel with geotextile in drainage
RE: Wraping gravel with geotextile in drainage
RE: Wraping gravel with geotextile in drainage
In some 50 plus yeas of experience I have been involved with many a drain system. I did my grad research on highway sub-drains and learned then the beauty if using washed sand suitable for concrete (concrete sand) as the drainage medium and filter. Inside that trench fill of concrete snd sits a drainage pipe, these days slotted Plastic.
Never has one of these drains failed.
On the other hand I have seen engineers and contractors expounding the use of a filter fabric and gravel. I can't say that I have seen every one of these fail, but I have seen some that failed, generally I believe due to improper installation. It is difficult to do the job right, especially with no supervision on site and that there usually is a rush to get the job done. You already found that out.
If you look at the details in the specs for say a non woven fabric, the opening size still is larger than the "opening size" of concrete sand meeting the ASTM C-33 spec for fine aggregate. So, while you may have some transfer of fines via the fabric, that is not so with the concrete sand.
Finally, it is very difficult to improperly install a drain system done as I describe. Can't say the same for a gravel wrapped gravel system.
RE: Wraping gravel with geotextile in drainage
Dik
RE: Wraping gravel with geotextile in drainage
RE: Wraping gravel with geotextile in drainage
RE: Wraping gravel with geotextile in drainage
One of the members in an old thread made reference to a book by Harry Cedergren which deals with filter design. I've used an old NAFAC manual with good info on filter criteria and design. That is available on the Internet.