Filter fabric specification

[koodi]

I'm considering specifying some yard drain/basins that are similar to a coffee maker (i.e. water drains through a conical insert with holes in it that can be removed and emptied).

In additon the insert may be fitted with a geotextile fabric. The filter fabric insert, if not permanent, might temporarily be used during grading as part of the BMP'S.

So here's the questions:
What type of nonwoven geotextile would be best?
What type of apparent opening size should the cloth have?
Is the geotextile even worth using?
Are these contraptions worth specifying?

 

[LHA]

Here in PA, USA they are called Inlet Filter Bags (IFBs). They are recommended as temporary BMPs during earth disturbance. They are also required to be removed after the site is stabilized. Here is the site to download our Erosion and Sediment Control Manual , IFBs are on pp 105-106:

http://www.dep.state.pa.us/dep/depu...aterManagement/GeneralInformation/default.htm

IFBs work great, but only if maintained. I would not recommend them for a permanent BMP (which is what your post sounds like you are thinking about doing), even if your regulatory agency allows it. The future owners will almost certainly never clean them, rendering the entire drain useless after a few lawn mowings.

As they are readily available, I would just spec a manufactured product, rather than reinventing one from geotextile. ACF makes them under the name Siltsack. They are at acfenvironmental.com.

 

[koodi]

Yeah, maintenance is the problem with every product on the market.

There will not be any lawn mowings the slope is a little steeper than 1.5:1. The whole thing is a premanufactured unit, with an optional geotextile filter bag that fits in the "strainer."

Since I am an engineer, I would like to make a more informed judgement as to the cost and potential benfit of a geotextile filter fabric. When specifying a geotextile for a drain, I know the apparent opening is usually specified slightly larger than required based on particle size. The fabric will partially clog and will have an actual opening size less than that of the geotextile's spec.

So does anyone have any thoughts on geotextile "strainers".........?

 

[layfieldman]

From koerners book on designing with geosynthetics you should size the opening to have the O95 (opening size of which 95% are larger than) less than 2.5 times the D85 of the soil. This is for non critical flow. If you don't know what the D85 of the soil is then usually the AOS of a material goes down as the thickness goes up and you could try for an educated guess based what's known of the local soil conditions.