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how to read soil report?
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Posted by dancingsams (My Page) on Thu, Jan 28, 10 at 18:51
| Hi all,
Our pool is built, but not finalled. It is 25' x 50' infinity edge, plus a bulb out at a corner with a shallow swim around and a spa in the center. The pool is sagging and cracking already. The infinity edge is no longer level. The PB has drained the pool, but told us nothing more except that he is examining the soils report.
I have the report in hand and am trying to decipher it. The pool is concrete/gunite w/pebbletec. It was overexcavated (excavated 4 feet below the bottom of the pool, spa & beach access) 4 feet and compacted, with a soils engineer watching, testing (19 density tests) and reporting on the compaction. The resulting surface was moisture conditioned and recompacted to a minimum of 90% of maximum dry density.
The report says the soil is:
brown silty fine to medium sand USCS: SM
Max. Density 126.0
Optimum moisture 10.0
Can anyone tell me what this report means, and what else I should be looking for/considering? Thanks! |
Follow-Up Postings:
RE: how to read soil report?
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| Are you on a hill? Are the cracks vertical or horizontally inclined? Gunite cracks can be fixed. Soils conditions can be corrected. It's apparent the builder knew of potential suitable soils issues, hence the 4' over dig/ soil replacing. When was the soils report requested? Before or during/after the dig? Scott Scott |
RE: how to read soil report?
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| If he was so concerned that he got a soils report prior to the build then he should have gotten a Engineer's letter to rectify the situation. Here in Atlanta when we come across poor soil conditions we will have a engineer give us a letter to tell us how to make the situation optimum. He then will inspect the job after we are done and if we have done our part correctly he will sign off on the job and if it goes bad then it is his insurance that fixes it. I have never heard of 90% being acceptable. The engineers that I have worked with have always insisted on 98%. |
RE: how to read soil report?
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| It might be a good idea to make contact with the engineering firm and make them aware of the problem. Documenting a log of events would be in order. The % compaction varies between soil types and you have to look at the whole report. This is a very good link that might provide some insight and direction. |
Here is a link that might be useful: pool engineering
RE: how to read soil report?
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| Wow - you all are quick - this is very helpful! Scott: The county requires a soils report before the gunite is shot. We had a geotechnical soils engineering firm do the soils report. They required the 4' dig. Yes, this is on a hill. The house is uphill, and house footings are set down inside bedrock. The pool is about 50' feet from the house.
The cracks began vertical. After draining the pool, we have found a few horizontal as well. The ones causing leakage are vertical. renovxpt: The soils type, per the report, is USCS SM (silty sand). I appreciate your link. It will take a while to read everything there! sceadu: What type of engineer are you referring to? The folks doing the tests are geotechnical engineers. Are you thinking of these, or perhaps structural? Also, the PB has a 10 year warranty against leaks. Thanks!
Cindy |
RE: how to read soil report?
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| Can you provide some more detail on the process? Why was it overexcavated? Was the SM soil removed and replaced with something else, or was the SM material the stuff that was placed and compacted? What is the site like? Is the water table high? Did you see the compaction done? What type/size equipment did they use? SM material can be difficult to compact, and the moisture content of the material during compaction is VERY important for getting good a good result. IMO, 90% MDD is not high enough for this application. It will take a LOT more energy applied to the soil to achieve higher levels of compaction, but for this application, I would have expected them to recommend 95 or even 98% Does the engineer work for you, or the PB? |
RE: how to read soil report?
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| We use a civil engineering firm. I have used them for the 15 years that I have been in the industry and haven't had a problem yet. I have dug pools that were in complete swamps. Some places that I would have never guessed that a pool could be built and with their techniques they still stand. You are in California and I have read that they have a completely different set of rules when building a pool than anywhere else in the country. I would hire my own engineer to be sure that you are getting a unbiased oppinion. |
RE: how to read soil report?
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| Can you post pictures of the pool, the build, current conditions and the area around it? Have there been any earth movements? Any drainage issues? I heard that parts of California have experienced some pretty extraordinary rain this year. Did you reuse the soil from the 4' over dig or replace it with something else like 1/8" stone? Renovxpt, when I was at the NESPA show, I took a seminar that featured Ron Lacher discussing this very type of topic. I was pretty impressed. Scott |
RE: how to read soil report?
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| Hi Scott, Pictures? I have tried, and failed, to figure out how to post pictures. I can email them .... Earth movements - not that we can see Drainage issues - we lost about 1 foot of water in the POOL (actual pool and spa, as opposed to surge tank)over a period of 2 weeks. PB said this was normal. According to a "pool expert" from southern Calif, this is indicative of leakage, which may have caused soil problems, and was definitely NOT normal. 4' overexcavation - they reused the existing soil. It is silty sand, and the geotechnical soils engineer (GSE) considered it fine for use. The GSE was hired by our general contractor on the house, which means he works for us, not the PB. Yes, we have had a fair bit of rain. I have been here for over 30 years, and this was not by any means an exceptional event. Back in 1969 we received 6 inches in 1 hour. This was only 6 inches over a full week. The soil and terrain have no trouble with this kind of rain event. We had more trouble with the 60mph winds (that ruined the spa cover by tearing it from it's mooring and tossing it into a tree). Luckily, no major damage for us. Also, we are not in an area subject to mud slides, nor were any fires near us last year. Any other thoughts? Thank you!
Cindy |
RE: how to read soil report?
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| Judging from what happened, I'd say it possible he was wrong. Do you have a Photobucket account? They are free and have a nice and easy to use box with the html code you would copy and paste here. The photos show up then. Those photos are essential. Vertical cracking suggests a bond beam failure due to a loss of support under part of the pool. The house has footings into the bedrock but the soil will support a pool? I presume there is no autofill in the surge basin else I would be confused how you came up with "lost about a foot over a 2 week period". That sounds like a very substantial amount of water to lose, even for a negative edge. How big is the pool? How wide was the negative edge? Did the water spilling form a sheer or did it run down the wall? How long we you running the negative edge per day? Was there much splash? Scott |
RE: how to read soil report?
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| Cindy, We built a large vanishing edge 24X58 in the same soil classification on a very steep slope. There was 8 ft of engineered SM fill under the catch basin and a portion of the pool. The fill came from a different area on the property and was also SM. The geo-engineer warned us that the soil was very suited to compaction but highly erodeable and we took a variety of precautions to control the erosion during construction and prevent future erosion from a catastophic event such as the pool leaking, dumping into the basin or remnants of a hurricane flooding the site. We incorporated a drainaige sytem under and around the pool with washed gravel and fabric to prevent potential subterranean erosion. We also filled the pool shell right after shotcrete and left it full for 10 days as per the advice of the engineer. He said that any settling would occur quickly in that type of soil. I can send you a link to this pool build process if you give me and email address. To post it on this site would violate the advertising agreement. I'm not sure of the best way for you go about resolving this issue as there are alot of players in the game. Most engineering agreements have a lot of disclaimers and fine print. The fact that this has occured prior to completion of the contract seems like it should work in your favor. Considering the size of this problem you might want to consult an attorney. (Ouch, it hurts to say those words) |
RE: how to read soil report?
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| This story is just extremely unfortunate, because things like this are so avoidable. Is the PB stepping up here to resolve the problem? Unless you owe the PB a lot of money, it just smells like this is going to cost you. And that is just unfair. You certainly don't want to think too far ahead, but you might end up chasing the engineer here. And that's OK really, because he probably has the best insurance. As a licensed engineer here in NY, my firm's professional liability policy would no doubt cover this type of thing. I mention the engineer because 90% compaction of a 4 foot fill is just not good enough. SM soil can be very competent material, but it is also difficult to compact, because having the right moisture content is so important to achieving good results. The Contractor really has to install and compact it carefully. In short, a 4' fill compacted at 90% MDD can still consolidate quite a bit, and concrete pools offer very little tolerance for settlement, particularly in a case like this where the fill was not uniform over the pool area. In other words, the differential settlement is what really hurts you here. So who recommended the 90% compaction? The engineer who did the report, or the engineer that inspected the fill? Or were they the same guy? John |
RE: how to read soil report?
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I would look at the structural integrity as Scott suggested. The location of the cracks will give will give insight as to cause.
The soil you describe sounds pretty good for pools. I've built pools in the Lake Lopez and Arroyo Grande area. It's similar to what you describe. You should also check the engineered plan that was used with the pool and see if it is generic or specific to your pool. This makes a big difference for specialty pools with vanishing edges and spas. Some builders use a structural plan that is one size fits all. This doesn't always work for large complicated pools. |
RE: how to read soil report?
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| Hi everyone, I have a bridal shower to head to in a few moments, so I'll get back to everyone tomorrow night. Tomorrow morning I'll take more photos, and try, once again, to get them posted. golfgeek - where are you based? John - one engineer did the report, the recommendations and inspections (19 compaction tests). The PB has not spoken to us in 1 1/2 weeks - we are leaving messages. Thanks again!
Cindy |
RE: how to read soil report?
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| John is right. Insurace might be your best answer to this dilema. Call your homeowners agent for help on how to remediate the situation. Let them worry about dividing up the responsibility. |
RE: how to read soil report?
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| Cindy, anything new with the pix? Scott |
RE: how to read soil report?
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| I use the Lachers for my engineering and I could have sworn when I've had discussions with them before about using fill dirt to back fill pools that they recommend against it. They usually will require piers or over dig and then back fill with slurry or gunite. I could be wrong. If you need an very well known and highly accredited soils engineer for swimming pools in socal., Call Dennis Hannon from Hannon geo technical. Hope this helps. |
RE: how to read soil report?
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| Sorry for the delay - we have been up at the job site, and working with all sorts of contractors (building the house, too). My daughter is helping me insert pictures, which should be up later tonight. The PB finally got back to us. He says their tests show that the concrete/gunite is faulty. He plans to tear out the area that is cracking and rebuild it. This kind of concerns me, since he is only talking about removing a portion of the work. Is it likely that only part of it would be faulty? If so, I will feel much more comfortable with the partial demolition/rebuild. Pics should be up soon.
Thank you! |
RE: how to read soil report?
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| I really want to see the pix. It's possible that the gunite was mixed wrong at the nozzle but so are a number of other potential issues. Gunite comes out of the nozzle at about 300 MPH and packs itself in. Anything that bounces is call rebound and is usually larger aggregate chunks with little cement. It should be discarded for maximum integrity and strength. If the rebar gets coated with rebound, it's not properly encased and the shell loses strength. This can happen when the nozzleman shoots the gunite from the wrong directions and locations in an other than best practice methodology. Another waste material that should be either discarded or if used, must be well compacted, is the trimmings from sculpting of the walls and floors and only in non structural uses. Checking spa walls, benches and steps for soundness is a good idea as these are places it sometimes get used. I'm not saying any particular cause is what resulted in your case. I am just saying some of the things that can happen and result in what you have described. Scott |
RE: how to read soil report?
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| It is highly unlikely that bad gunite is the cause of your problem. bad gunite will not cause differential settlement. You said your infinity edge is not level anymore right? You have a problem with settlement. Do not accept the PB's fix. He's fixing the easiest thing that he can, the cracked concrete. Please post some pictures. The location, size and orientation of the cracks will tell the story. |
RE: how to read soil report?
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| Bump. We want to help make sure your PB is doing things right. We are on your side. He may be too but may be NOT also. It's possible/probable this was preventable.His "repairs" may not be permanent but rather a band aid, granted, a big band aid and band aids are never permanent. The pix are crucial. Scott |
RE: how to read soil report?
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If a standard pool settles 1/4 inch its not the end of the world, On a vanishing edge pool its catastrophic. In addition to poor soil conditions there is a factor which is equally devastating its called rolling. Rolling occurs when static pressure pushes the pool towards the open side (vanishing side). The damn wall of the vanishing edge AKA the weir wall should extend well into the ground and act as a footing, this prevents rolling. Most engineers are not aware of this detail.
If you would like the name of a engineer who specializes in pool construction and forensic consulting please feel free to contact me. Good luck,
Cip |
Here is a link that might be useful: Pools & Landscapes
RE: how to read soil report?
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| Cip, I work with a lot of engineers, and I don't know any that wouldn't know that a dam wall should be keyed into earth. Just fwiw. I'm really disappointed that Cindy didn't post pics. Even if she didn't think we could help her, still it would have been a good opportunity for many people to learn something from an actual case study, including myself... John |
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