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It's worth considering isolation joints between the rock- and soil-suported portions of the structure. You might also consider overexcavating the rock 6 inches (15 cm) or so and backfilling with gravel or compacted native soil to provide more uniform foundation support.

dgillette, I was not clear. And your comment is mathematically and procedurally correct, but theoretically problematic. Here's what I mean: For a non-cohesive material, the failure envelope defined by the maximum stress values of a series of direct shear tests is presumed to pass through the...

With regard to the OP, your question seems to presume that stress increases uniformly with depth. Certainly a theoretical condition! To DRC and dgillette, I suspect that you're both right, and suggest that the challenge of phi determination is a perpetual boondoggle. We observe that shear...

Just try not to drop the sample on the floor.

Whatever your local code says, I would think twice before subjecting a typical floor slab to a permanent 80+kip load. My reference for allowable slab live loads: TM 5-809-12/AFM 88-3, Chap. 15 If it were my call, I would recommend an isolated footing for boiler support. A six-inch slab...

Yes, expected settlement and related issues should control foundation design. Terzaghi (1938) and quite a few others have commented on this issue. 'Settlement governs' is a common phrasing in the design texts. But how to change codes to reflect this? As a practical matter, I think we'll...

Ron, your lips to God's ears my friend.

Yes, I generally start with the corps/Unified Command docs or local DOT, all available on line. Seems sources like USACE, AASHTO, FHA, are so broadly referenced, you're likely to end up back there sooner or later anyway. If you've picked up a PE Exam guide lately (McGraw Hill), the...

Ron, I am with the local (Palm Beach) office of a regional, but good-sized outfit (+/- 500 employees). The company primarily serves Florida, Metro Atlanta, Gulf coast areas outside of Florida, the Bahamas, etc... It's Hellish, I tell you... :-)

Ron, for example, 1 inch is the minimum thickness for Palm Beach County road sections. When I relocated here from Maryland and saw that 1" thickness-- well, the shock took a while to wear off. : ) We usually spec 1.5 inches bituminous for low volume road sections such as parking lots. The...

I used to follow a similar procedure for calibration of the consolidometer. We would apply the usual incremental consolidation load to a porous stone and 1" hardened steel follower, and read the resulting deformation at each increment. This procedure actually shows deformation *of the machine...

South Florida roads use crushed limestone base. A typical section is 1 inch bituminous, 6 to 8 inches limerock, and 12 inch 'stabilized subgrade' i.e., the native sand with enough limerock mixed in to stabilize it to LBR 40. In this case, LBR = Limerock Bearing Ratio, which is equivalent to...

We had four fragments (from a total cored length of 20 feet) that actually met the 2:1 height/diameter ratio for compressive strength testing. That said, the resulting breaks ranged from 5000 to 7500 psi. The remaining core sections were fractured horizontally at an interval of 2 inches to...

Just occurred to me that 'temporary' is an oft' abused term. Murphy says the wind will howl and the waters rise before your project is complete. :]

I have reported such verbal classifications as 'gravelly sandy loam' or 'sandy loam with gravel,' that sort of thing. The point is that the gravel fraction (above say 10 percent) is not treated as sand for the purpose of classifying the soil on the textural triangle, or subsequent...

OK, we managed to miss the rebar. We collected 4, 5-ft long cores using a 2-inch id double wall core barrel. The resulting cores look just awful. Numerous horizontal separations, discoloration, and I can abrade the surface with my fingernail. Makes me think 'bad tremie job.' Any thoughts?

Hmmmm... 1) If you mean stress change over depth, yes and no. The answer depends in part on settlement that may have occurred following installation of the (drilled or driven?) piles. That would suggest the depth of the neutral plane, below which positive pile shear stress would develop...

NDT suggested a problem. Contractor disagrees...

I believe the USDA standard requires mathematically replacing the gravel material.

OK experts. What is the preferred method for cutting a vertical full depth core from an existing drilled shaft foundation? (cue Syncopated Clock)