Gravel under SOG
Gravel under SOG
(OP)
Hi, is there any criteria for specifying the thickness of gravel under slab-on-grades? I normally recommend 6 in of well graded gravel (similar material to base course for pavements). Sometimes 12 in when the subgrade is weak ( i.e. low CBR). If you have any references it will be appreciated.





RE: Gravel under SOG
http://www.fhwa.dot.gov/infrastructure/50aasho.cfm
RE: Gravel under SOG
RE: Gravel under SOG
http://onlinepubs.trb.org/onlinepubs/circulars/ec1...
RE: Gravel under SOG
RE: Gravel under SOG
Dik
RE: Gravel under SOG
The graded aggregate subbase you propose will have little affect on the slab thickness. As an example, if you assume the aggregate gives you a modulus of subgrade reaction (k) of 225 you can determine the slab thickness. If you have a relatively clean sand subbase, you would assume a k value of 150 to 175, maybe even 200. The slab thickness will not change appreciably.
The graded aggregate can be used to enhance the properties of a low CBR subbase or subgrade, but should be mixed in to do so. If you use the aggregate as a discrete layer below the slab, it will serve as a good capillary break for drainage or water migration mitigation.
RE: Gravel under SOG
Also, this is a different question, but it is related to my original question: what do you think about placing clean gravel (crushed gravel like concrete aggregate, I think it is similar to ASTM C33 no. 6) underneath the slab, say 4" to 8" thick? I understand that it cannot be compacted, but it can be vibrated to interlock the gravel particles. I saw this clean gravel material installed in several projects underneath slab-on-grades and I think that it provides good support for the slab (if it is adequately vibrated).
RE: Gravel under SOG
Caltrans Empirical method for flexible pavement design(based on Hveem method, I believe) uses GE (gravel equivalent) and GF (gravel factor), in addition to TI and R-value (not CBR).
Table 633.1 attached. There is a "credit" for thicker aggregate base (reducing HMA). How is that different than AASHTO? Learn me.
RE: Gravel under SOG
RE: Gravel under SOG
The papers included in EC118 included both rigid pavement (plain concrete) and flexible pavement (asphalt) - lots of material there - I didn't read it all.
So OG and Ron's comment apply solely to concrete slabs for pavement.
RE: Gravel under SOG
RE: Gravel under SOG
RE: Gravel under SOG
RE: Gravel under SOG
RE: Gravel under SOG