A Bucket of Stone plus a Bucket of Mud = ?
What do you get when you add a bucket of stone to a bucket of mud? According to one explanation I've heard, you just get a bigger bucket of mud. Of course this point of view might be a bit suspect because it came from a geotextile salesman. The point is well taken, however, that adding something to a muddy road often has little effect, and can, in fact, sometimes make matters worse because of increased agitation of an already sticky situation.
I have found, however, that there are times when little else can be done except to add aggregate to a section of road that appears bottomless for a while in the Springtime. WHAT you add and HOW MUCH OF IT is what makes the difference between success and gooey failure.
From years of road maintenance and site development, I've found that the only practical way to treat a mudhole is to add enough coarse aggregate to fill the entire hole, essentially bridging the weak spot with strong supporting material. This material needs to be extremely porous and can consist of rocks or large crushed stone (not peastone), and should contain virtually no sand or fines. The goal is to provide enough of this coarse material so that, once it's in place, each rock or stone touches another, and the mud that was there now just fills the gap between stones. The emergency repair takes on the characteristics of the fill material rather than the mud it has replaced.
Using sand or gravel to fill a mudhole usually has little or no effect because the stuff ends up mixing with the mud, just making more mud and sometimes aggravating the problem as equipment stirs up the site. In a similar manner, adding stone or rock aggregate in an insufficient amount can have little or no effect because it is not able to transfer wheel loads from the surface through the mud to a firm base.
Even if the stone repair does not extend deep enough to completely bridge the mudhole from the surface to a firm base, the interlocking effect of stone aggregate, especially if it is very angular, can often support substantial weight by spreading wheel loads over larger areas in much the same manner as a good geotextile stabilization fabric.
The disadvantage of using much stone to stabilize a road is cost. The only time I use stone for stabilization is for emergency repairs. Once frost has left and a road has become workable, I use geotextile stabilization fabric, with outstanding results. For new road or driveway work I try to get the fabric in place before the site gets muddy, eliminating the need for excessive stone and making my geotextile salesman friend very happy.
Note: I've discussed this "Bucket of Mud" concept with Pete Coughlan of the Maine Local Roads Center who uses a similar statement in his "Drainage, Drainage, Drainage" seminar. Must be something to it!