Effective Unit Weight of Soil in Lateral Load Software
Effective Unit Weight of Soil in Lateral Load Software
(OP)
I normally see an effective unit weight of sandy soil below water table in range of 45 to 65 pcf for input of LPILE, GROUP, or COM624P. My understanding is that effective unit weight is basically a saturated unit weight minus water unit weight (i.e. submerged unit weight).
However, the geotechnical report of the current project I'm working on reports sand effective unit weights of 110 to 120 pcf, although these soil layers are all below water table. Is it possible that effective unit weight can be that high? I found that these values are not conservative to use.
However, the geotechnical report of the current project I'm working on reports sand effective unit weights of 110 to 120 pcf, although these soil layers are all below water table. Is it possible that effective unit weight can be that high? I found that these values are not conservative to use.





RE: Effective Unit Weight of Soil in Lateral Load Software
f-d
¡papá gordo ain’t no madre flaca!
RE: Effective Unit Weight of Soil in Lateral Load Software
RE: Effective Unit Weight of Soil in Lateral Load Software
In my opinion, above the water table, a moist or total unit weight of 110 to 120 pcf for sands seems okay. This also seems reasonable for a properly compacted sandy fill material. Below the water table, I would subtract 62.4 pcf from the above values for an "effective" unit weight.
I hope this helps.
RE: Effective Unit Weight of Soil in Lateral Load Software
In piling for the horizontal loads,the horizontal sugrade reaction plays therole and for submerged (below water table)horizontal subgrade reaction is much lower than the dry sand subgrade reaction value.
Check Professsor Tarzeghi paper published in ICE Geotechnique and discussion by Professor Rowe.
HTS
RE: Effective Unit Weight of Soil in Lateral Load Software
I agree with Mickney - likely the geotech didn't change the effective unit weight or should have called it TOTAL unit weight. Contact the author for clarification.
Jeff
RE: Effective Unit Weight of Soil in Lateral Load Software
Our final submittal was before my post, so we wouldn't have a chance to ask the question to the geotechnical engineer. However, we did use their values subtracted by water unit weight since they are more conservative.
Next time I'll make sure to ask them.
k2p