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One other issue to consider is, "what might happen to the subgrade during construction?". The general answer is, "nothing good". Possibilities include; (a) the excavation is made using a backhoe bucket with teeth that plow the soil, and the operator levels the subgrade by sweeping sideways...

If your lift station bears at 27 feet, Moisture conditioning won't have any effect on the foundation. You probably should flare the excavation above the depth of seasonal moisture variation (15 feet more or less)and backfill with nonexpansive soil to avoid excessive lateral pressures. If you...

The unit weight of concrete should be about twice that of the bentonite slurry. A milk jug filled with water and about half filled with sand should sink through the bentonite but float on the concrete. A concrete test cylinder with an eyebolt probably will do the same.

Are you sure of your numbers? I may be wrong, but my calcs say your foundation will almost flip over unless you bury it a few feet deep.

If the clay is unsaturated, it can respond as the pore air compresses; it doesn't have to wait for pore water to be expelled. Think of a plate load test or consolidation test on unsaturated clay - I think there would be considerable deflection in a few seconds. I don't have what you need, but...

I agree with OG about the ASTM C-33 sand. It is generally considered to be a universal filter and should keep back the mud you have been seeing. It may be too fine to put directly against the perforated drain, however. Good practice would be to envelop the pipe with concrete gravel, 3/4" max...

Good thought. I guess the trumpet can also provide extra protection for the tendon at the rock/structure contact where water and air can move and the grout column may want to crack. Under what conditions would you provide an unbonded zone?

Thank you, my friends. Your suggestions will be helpful. I think you have confirmed my previous conclusion that there are no readily available detailed guidelines for what I call "passive anchors", generally grouted bars in rock or soil used to support a wall or prevent hydrostatic uplift of a...

jdonville, your explanations were quite clear; thank you. SlideRuleEra, I have searched the FHWA document pretty thoroughly without finding any mention of passive (unstressed)anchors. Can you please point the way? Or do you know of another source? Thanks

What methods and equipment are available for checking the azimuth of holes being drilled for anchors? I have set reference stakes forward and backward, but can't see through the rig. Are there electronic compasses available for mounting on rigs, and if so, can they remain accurate with steel...

Tensioning against the rock surface sounds like a good idea, but I would think it would be hard to protect against corrosion.

My company likes to use passive anchors in soil or rock to restrain hydrostatic uplift or to support some retaining walls. I am familiar with PTI's guideline for design of post-tensioned anchors, but having difficulty finding guidelines for passive anchor design, other than the brief treatment...

As you can see from retired13's examples, developing several hundred tonnes of resistance takes a big structure. If the soil has high cohesion, the passive resistance of the wall per linear foot is 2*C*H +Gamma*H^2*Kp/2. C = cohesion in tonnes per square foot; 3 would be a big number. Gamma...

In my experience, settlement occurring long after construction usually involves water. I have seen a thick fill that had been supporting buildings for 80 years start settling due to a broken roof drain pipe. You might want to check for a leaking water main or poor drainage that causes...

I believe walls should be designed not for what the soil pressure will be under ideal conditions, but for what it might be under conceivable conditions. We have all looked at a vertical cut in cohesive soil and asked ourselves why a wall is needed. Because the soil probably won't stand like...

If rapid response is needed or you want automatic recording and/or transmission, vibrating wire piezometers are a good choice. If not, I prefer open standpipes because they can be checked using falling head tests, serviced by surging and flushing, and may have a longer life. A vibrating wire...

I am not experienced with that type of pile, so this is s guess: Perhaps the concrete or grout pump was shut off too soon so that a vacuum was created below the tip as the extraction was completed. This "sucked" the sides inward in the weakest layer. I can't explain the excess concrete...

A common rule of thumb for gravity retaining walls is to have a base width approximately 0.7 times the height. It can be smaller if the backfill has a high friction angle and is not saturated, but 0.4 seems pretty marginal. A global stability analysis is needed. Then I would consider whether...

I have considered this several times, but never tried it: If you are concerned about loose or weak material left on the bearing surface, consider placing some grout in the bottom and stirring it into the slough with the auger, being sure the auger touches the bottom of the excavated hole. If...

If the crack at the base is open slightly and drainage is poor, the tension steel may corrode and fail with time. I have seen this in a 40-year-old cantilever wall. The drain had failed;the wall was overstressed enough to open the crack, and the water was there.