Ground Modification - Purposely Weakening Soil

[BigH]

Colleagues.

There is going to be a conference in Indonesia and I have been requested to provide a paper for it. I will be writing a paper with Fred Matich, my mentor and former student of Terzaghi! (He is 88 now and planning to give presentations in China later this year.

At the conference I just attended, there were multitudes of articles on ground modification - i.e., strengthening for the purposes of improving bearing, reducing settlement, etc.

However, the paper we are contemplating is for ground modification - WEAKENING the soil for purposes of construction expediency. Oldestguy has an inkling I am sure of this - in the rolling surcharge method of displacement that we both have used. I have a number of papers of Fred's which were written in Canadian journals and not widely disseminated. I want to use these papers - including the blasting of soft clayey silt to remould in order to displace, the intentional failures of submarine slopes to "bury" ships in shipping channels.

I would love to know if any of you have experiences in such techniques that you would be willing to forward to me and to let us use - I don't have to be "site specific" if that would cause problems. One area that I would be interested in would be in potential military usage. I remember years ago that someone discussed the difficulties that the Germans had with tanks in Norway with the quick clays. The first tank would cross okay, the second, would settle a bit and following tanks would basically sink as the soil became a heavy motor oil consistency.

As well, as we draft the paper, if any of you would want to read and provide comments, that would be appreciated. Fred is a gifted writer but other views are of interest to me - as I will be doing most of the writing.

The paper will likely be more "generic" and not heavy on data, etc. - it is to have people think and understand that weakening a soil might, in the right case, be beneficial.

Looking forward to hearing from any of you.

Thanks. bohicafries at gmail

 

[SlideRuleEra]

BigH - A common application of intentional soil weakening that comes to mind is a vibratory pile hammer. I'd expect much study has gone into exactly which vibration frequency and other parameters are needed for optimum results.

Your mention of tanks on quick clay in Norway reminded me of stories circulating at our older coal-fired electric generating stations. In decades past, fly ash straight from the electrostatic precipitator was sluiced to (permanent) holding ponds. As the ponds filled, the ash would be mounded so that large surfaces were above the water line. The surface appeared firm... it was no problem to drive a pickup across it. But due to the microscopic spheres that compose fly ash the material is thixotropic. Stop the pickup (or bulldozer, or welding machine) and shut down the engine... no problem. Leave the engine running in the stationary equipment and a little while later the machine in on a slow motion trip towards the bottom of the pond.

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[oldestguy]

Interesting subject.

When I was with Wisconsin DOT I managed to adopt the peat displacement technique that had been developed in Michigan, probably by Housel. I see now the WDOT has that written into the specs. You can well imagine a new soils engineer to the DOT (first one) getting that done without getting any OK from higher ups. I heard about it from Bob Keyser who came from Michigan and was getting his PHD at UW Madison. The contractor on an Interstate job was just in the process of only excavating the peat and he went for it, since it meant more excavation payment.

I think the Michigan usage was developed by Housel. If you do a search for Michigan DOT and Housel you will get a page giving his info and also their spec fr this procedure.

While it may not fit the subject, you can discuss the pros and cons of jetting fill to settle it. I know of one case where backfill to an attached garage at a residential building didn't do so well. The saturated sand placed too much load against the basement wall and in she went. Contraction said he always has done it that way in the past. My statement was, "bet you don't do it any more".