Saturated soils.

[wolfhnd]

My geo tech wants me to include a special provision in a contract telling the contractor not to work on a slide if the soil is saturated. He offers no ideas on how the contractor is to know when the soils are saturated. I could use embankment control stakes but if it's moving I'm in trouble anyway. What do I require to measure saturation 20' under a roadbed?

 

[Ginger]

I don't have any experience in this field ,BUT, the method you need will have to be non-destructive and rapidly carried out. So, how about a soil electrical resistivity test. You would need to calibrate the soil by carrying out tests on saturated and partially saturated examples. The install the kit in the field and monitor the resistivity. At the moisture content rises, the resistivity should fall.

Just an idea ............. What do others think? Andy Machon

 

[cvg]

have the contractor install monitoring wells or piezometers and check the water level in the wells on a frequent basis.

or measure movement using:
slope indicators (inclinometers)
settlement/heave measurement devices
stress meters or strain gauges

to prevent saturation, the water must be diverted from the site. Best to prevent the saturation in the first place.

 

[jheidt2543]

Just a question, but why should the contractor be doing the monitoring? The Owner picked the site and it is the Geotech. Co. that is setting the criteria. The soils engineer has the equipment and expertise, they should be doing the monitoring and advising when the conditions are such that the contractor should stop work. Of course, that might mean taking on some responsibilty for the criteria they set!

I might be taking CVG's comment too far, but let's not keep dumping on the contractor. Everyone on a construction project has duties AND responsibilities. If we ALL lived up to our own, instead of trying to shift them to someone else, construction would be more of a TEAM effort.

 

[wolfhnd]

The site is a state highway, I'm the designer and we do not have the resources to monitor the saturation within the highway dept. This may seem as silly to you as it does to me but we just lost a general election to up the gas tax. Management is not likely to aprove more paper clips let alone a new geotech guy . Can one of you guys send me the specs for piezometers and I can sneak them into the contract. I have specs for mointoring wells but the site is on the side of a hill and I don't think they will work.

It seems that after I rejected the first two options from the soils engineer that it's now my problem to deal with and be responsible for. His idea was to build a bypass through a 50' rock bluff and bypass the traffic until the road could be rebuilt. I have about $600,000 to spend I'm guessing that would cover the bypass . It's a crazy world and the poorer the department gets the crazier it's getting.

P.S. If I knew where the water was coming from maybe I could divert it. Limited budgets mean limited borings.

 

[jheidt2543]

wolfhnd,

I have to admit that after reading you latest post, a different light is shed on your question. My first reaction was to suggest writing into the specifications the requirement that the contractor hire a geotechnical firm to do the required monitoring. That way the costs of the monitoring become part of the construction cost rather than the design cost, just as you suggest.

But then I wondered how do YOU decide what the parameters of the monitoring are going to be without first having a geotechical firm tell you? (Bye the way, from what you said in your first post, I would change geotechs!) If that is the case, just leave the whole thing back in the design phase. The monitoring effort should be part of the ongoing project inspection costs and you preserve the "arms length" relationship between design and construction.

This may seem harsh, but I am always skeptical of an Owner who has enough money to do the construction phase, but not enough money to do the complete design or construction inspection phases. In the end, it ALWAYS costs someone more than it should when things are done skimpy.

One last suggestion, can you put in dewatering wells or a cutoff wall to dewater the area?

 

[cvg]

it seems that this may be a way for your "geotech" to cover himself in case of a slide. there must be a reason for his concern that the area may be saturated. I am guessing that he found high water levels in his boring(s). If so, it seems that some areas would be saturated depending on the depth of the water and the depth of excavation. As stated, the site needs to be dewatered. Do you have a dewatering spec in the contract? Are you going to show the Contractor the boring logs with the high water levels? a good contractor will include the cost of dewatering and monitoring in his bid. a poor contractor may hope for the best and lowball to get the work. expect a change order or at worst, a lawsuit when the slope fails! Pray that nobody gets injured. I advise that you step back and determine your potential risk and liability before proceeding with this project.

 

[wolfhnd]

We never include the boring data in the plans for liability reasons .

The boring showed saturated soils, not free water, at varying depths. The embankment runs along a hill side so a pore pressure type well would not acurately display the level of saturation or the present of flowing water.

If dewatering is pratical let me know what I need to read. If it is not too technical I can work it out for myself.

This is very important to me and I really appreciate your help. If anyone has specs that I could use please attach them to an email (msword format )

 

[jheidt2543]

This is another of my hangups, if the Owner/Designer uses the soil borings to design the project, then they should be included in the specifications so the contractor can build the project. How is he going to work out a dewatering method without soil borings? It is costly and unfair to require each bidder to perform soil borings prior to bidding the job. In my opinion, that is the Owner's and Designer's responsibility. The more complete and through the plans and specifications, the more complete and competitive are the bids. In fact, one way to judge a good set of plans and specs. is how tight the bid prices are. The wider the variation between bids, the poorer the plans.

 

It is the geotech's resposbility to give possible suggestions to stabilize the slope. If he can not, change another one.

From practical points of view, dewatering and monitoring well should work if your base is not too deep and there is not any adjencent structure. That should not be too expensive because it does not need complicated equipment.

If that does not work, you may have to use some kind of retaining structures and dewatering system.

The contractor should make a test excavation first to see what happened.

 

[22222222]

Hi Wolfhnd.

I think is quite easy. Take one boring mashine on site and perform STP test every one meter depends on your site(say 10 meters). From split spoon samples get the labo test on saturation and other GP properties of your soil.Labo should know what to do.
Saturation S=Vw/Vv * 100(%)
Vw- volume of water
Vv-volume of voids

Saturated soil is between 95-100%. If the area is landslide you have to take the core also to distinguish failure plane.Be aware of liquefaction problems related to earthquake!!!