Over excavation of adverse soils under a gravel road
Over excavation of adverse soils under a gravel road
(OP)
I am building a Fire Truck Access road (gravel) and the cross section is going to be something like 6" of 3/4" minus over 9" of 1-1/2" minus. I am building this road over adverse soils (saturated garbage fill, maybe clayey silty loom?? with zero percolation properties). My solution to this problem is to over excavate and replace with 4" minus. I can, out of the air, come up with a depth (of 4" minus) that will easily account for the adverse soils but I am tired of over designing (spending too much of the clients money). How does one calculate (and / or which soil property is calculated) the amount of over excavation needed for an economical design. It would be nice to have the calculations to go along with a "hunch". Thanks in advance ...
BRB
BRB





RE: Over excavation of adverse soils under a gravel road
So back to your original question-how to justify a design? There probaly is literature & design methodologies for road design in poor/soft/organic subgrades. Don't know of one offhand but probably can get something from geotextile manufacturers. Usually local experience is heavily relied on in these cases. This may not help but does give you a second opinion!
Carl
RE: Over excavation of adverse soils under a gravel road
By all means use good-quality geotextile fabric as recommended by CarlB.
Your aggregate section will probably suffice on the fabric. I no longer have the means to design the section, but over 40 years of experience says you are on the right track.
Also, tell your client that the subbase condition is unique, and that repairs may be needed later on.
RE: Over excavation of adverse soils under a gravel road
I have found that when the lower gravel is 'sandwiched' between the geoproducts, the entire structure will move around but will carry a lot of traffic.
RE: Over excavation of adverse soils under a gravel road
If you want to analyze the geotextile condition, you shoot for the lateral stress in the soil layer equal to the fabric strength (or some safety factor on the strength), andd/or the vertical stress equal or less than the punching strength of the fabric, and again use a trial and error thickness approach to get your answer. You will find that very little rock is actually needed over the geotextile, but we usually add more for peace of mind/national fudge factors, etc. After all that you'll probably find that CarlB, jimbo, and emmgjld have pretty much nailed it based on experience (for which there is no analytical substitute!)