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RE: "Hydrovac" for pier construction

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With silty-sandy formation, the wall of the hole may cave-in. You may be able to use a casing to prevent the cave-in. If you want to take advantage of the side friction between soil and concrete, you may have to withdraw the casing as concrete is placed in the hole.

You can use it "under an existing" building as long as there is access to do the work. Since the file size limitation would prevent attachments to this email, I will send some photographs to your personal ID.


Neil Moore <nma(--nospam--at)> wrote:
Is this a procedure where we could excavate small piers up to 10 deep under an existing building?  The existing soil is silty-sand with backfill densities ranging from 68 to  88 percent relative compaction.  Presently the water table is near the surface, but we can pump that down some.

Neil Moore, SE,SECB

At 02:39 PM 5/23/2006, Padmanabhan Rajendran wrote:
Yes. However, auger cast piles are typical for deep foundations. Hydrovac is used where the pier is not more than 10' deep.


Tripp Howard <tripphoward(--nospam--at)> wrote:
Have you considered using auger cast displacement piles?  Berkel and Morris-Shea Bridge both have a version.  Basically the auger has a blocking section on it that pushes the soil coming up the auger flights out into the surrounding soils so there's no waste to haul off or deal with.  Sounds like it would be a great idea for contaminated sites.

"Garner, Robert" <rgarner(--nospam--at)> wrote:
This is not totally relevant but we recently used a hydrovac truck to assist us in removing saturated, runny soils in an exploratory pit alongside the bay.  A backhoe loosened the soils and the hydrovac sucked them out and stored them in the rear tank of the truck.  This was an ordinary vacuum truck like you would use to clean out manholes, etc.  We had a rental Baker water tank on site so the hydrovac could empty its contents into the tank for segragating the water from the soils and later disposal of the soils (contaminated also).  The remaining soils in our pit remained saturated with significant pore water pressure so our little pit would not be good for supporting much.  Those hydrovacs can sure remove a lot of material in a short time, though.  And keep your feet away from that hose - it'll take your boot right off and turn your ankle a quick 90 degrees with a loud "snap"!
Bob Garner, S.E.

From: Padmanabhan Rajendran [ mailto:rakamaka(--nospam--at)]
Sent: Tuesday, May 23, 2006 1:13 PM
To: seaint(--nospam--at)
Subject: "Hydrovac" for pier construction
In the refineries, it is becoming common to use the "hydrovac" technique for creating hole for a concrete pier construction. In essence it is water jetting method with high pressure water jet.  As the hole excavation progresses, a vacuum hose removes the loosened debris. The method is preferred because it is fast, requires minimum labor, does not create a mess and the excavated material,  which is usually defined hazardous, is removed in a compact way for suitable disposal.

Commonly used formulas for determining the vertical and lateral load bearing capacities for the concrete pier assume undisturbed soil. Are there any modified formulas for use with methods similar to "hydrovac"?

Any additional input from list members?



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