Foundation on Compacted Select Fill
Foundation on Compacted Select Fill
(OP)
We are in the process of designing a crane footing (10ft. square)on controlled fill (20 ft of fill with footing embedment of 5 to 10ft). My primary concern is settlement since the applied loads are in the range of 2 tsf and bearing should not be an issue. I ran an analysis assuming a sandy soil compacted to both 90% and 95% modified proctor yielding a relative density of 50% and 75% respectively and an assumed modulus of 365 and 626 tsf respectively as well. Using Schmetmann I calculated acceptable settlments of about 0.5in to 1.29in. and was going to recommend that the fill (up to 20 ft thick) be plaaced in 8in. lifts to 95% (about 0.5in).
Is this reasonable, are the construction recommendations reasonable, any comments would be greatly appreciated.
Is this reasonable, are the construction recommendations reasonable, any comments would be greatly appreciated.





RE: Foundation on Compacted Select Fill
RE: Foundation on Compacted Select Fill
RE: Foundation on Compacted Select Fill
RE: Foundation on Compacted Select Fill
Immediate settlements are of greater importance for sands and silts, so the maximum crane loads are of greater importance for these soils. What are you using for fill? "Sandy soil" isn't very descriptive -
By the way, your DR values look too low to me - I would expect values of 65-70% and 80-90%. I didn't check the modulus values, though.
Have you thought about using a crane "load test" to force the immediate settlements to occur in a controlled manner? This can be done while the crane is very low to the ground. Be sure and measure the settlements; pay for the surveyor yourself if necessary. It's a great opportunity to learn! I'll bet that your present estimates are too high by a factor of at least 3...
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: Foundation on Compacted Select Fill
The fill materials are known as "select fill", the exact gradation can vary although materials passing the #200 sieve must be less than 12%, passing the #4 30-100% and no particles greater than 4".
About 80% of the load will be placed on the foundations before the crane is in operation so in reality I'm only concerned with the immediate settlements that the lifts will induce (the crane will be shimmed level on its frame after it is installed). Based on this my estimates are very conservative and the functioning crane will not induce much of the predicted settlment during its service life.
The relative density estimates were taken from a statement in Holtz Kovacs "An Intro to Geotech Eng" that stated a 1% change in relative compaction equals a 5% change in relative density (pg 142). Can you recommend another reference or method to correlate compaction to density?
The relative density was then correlated to a description (medium to dense for 50% and dense to very dense for 75%) as per Bowles. Finally a modulus was estimated based on these descriptions as per Bowles.
RE: Foundation on Compacted Select Fill
How are you getting from stress increase (Schmertmann) to change in relative compaction?
Be sure and plug the surveying into the crane test procedure. Include a shot at each corner of the foundation. If your client wants to know why this is necessary, tell him that foundation tilt is a crucial performance issue, and the only way to effectively measure it is to shoot the four corners. He'll bite. You will need shots before, at 25%, 50%, 75% and 100% of maximum load, and post-loading.
And please post your measurement results in this thread. We would also appreciate statistics on the compaction of the fill as well as the gradation and description of the material actually used for this project. That way, we can all learn a bit from your project, myself included. Think of it as a tangible "thank you" -
Please see FAQ731-376 by VPL for tips on how to make the best use of Eng-Tips Fora.
RE: Foundation on Compacted Select Fill