compaction standards

[AbbyD]

Could anyone tell me the protocol for building a home with a slab foundation over a former creek? A developer placed fill into a 10' deep trench and built homes on top. I am trying to find out if it was done properly, since all of these homes now are experiencing foundation problems ten years later. Is there a certain standard of compaction that must be met? Are there a required soil density readings that are kept on record? Who generally governs this process--- is it part of city code, or is it internally regulated by the design engineer? Thanks for your help.

 

[civilperson]

This could be really poor judgement on the designer's part, & probably easily critiqued in a court of law. The fill of the creek is a small part of the factors needing consideration. What is the soil type and origin below the creek and in surrounding area? What is the estimated settlement amount and rate? What proceedures and materials were used in the fill operation? What surcharge and time to allow predicted settlement to occur were used? What alternate drainage facilities were constructed to replace the creek? If done correctly, the fill of ten feet can be suitable for subgrade below residential loadings of slab on grade construction.

 

[cvg]

10 years later, you may have difficulty finding much information as it isn't always kept that long. Design engineer (civil engineer) may or may not have the answer for you. If the developer hired a geotechnical engineer during design, then he should have made the recommendations for how to fill the trench. Original plans or specifications should have indicated how the contractor was to do it properly.

The developer and his grading contractor should have done some quality control testing of the fill material and densities during construction. This would have been done by a soils testing firm, supervised by a geotechnical engineer. The testing reports should be on file at the engineer's office and with the developer.

the city or county should have also reviewed the plans, issued a grading permit to the builder and done inspections. contact them and have them review the permit file for the properties.

 

[AbbyD]

Thanks for the reply. The soil type is clay with areas of caliche. The drainage was diverted to underground 66" pipes. I plan to contact the engineering department of my city, and I need to know what kind of questions I should ask. So far, they are only telling me, in general, that it's just fine to build over a filled in creek, but they have not told me how they ensure that it is done properly via on-site inspections or compaction standard specifications, etc. I am assuming that the fill should be dumped and compacted in stages of shallower depth and not all at one time. So, if this is true, is there some kind of code in place that would require a recording or documentation of the compaction and/or soil density readings? Thanks again.

 

[cvg]

again, the requirements for grading and drainage would have been made by the designer, not by the city or county. The city probably does have some minimum requirements governing compaction, but filling a creek and building on the top would require a special design to do properly.

the city performs a review and inspection but it really is up to the designer to give the correct recommendations and to the contractor to do a quality job and the city is only there to make sure some minimum requirements are met.

In general, you are correct that fill is generally placed in shallow layers and compacted. But as indicated by civilperson previously, there are other issues to consider which should have been investigated during the design.

You really need to get an engineer to assist you with your investigation who is familiar with the soils, construction methods and city criteria in your area to help you discover what went wrong.

Also, are you sure the problem is with fill compaction? It could also be a problem with drainage, groundwater, collapsible soils in the subgrade, ground fissures or with the structural design of your building foundation slabs. I'm not sure I would want a concrete slab foundation on this site. Perhaps piles or a post tensioned slab would have been a better choice by the designer and could have handled settlement of the fill better.

 

[AbbyD]

Thanks again for your replies. This developer/home builder is going to build again on a site adjacent to my neighborhood. There exists now a creek/pond/marsh on the site. I have seen the plats for the development, and there will be homes directly on top of where the creek/pond/marsh are now. This is the same homebuilder that developed my neighborhood where all of the homes on top of the former creek are currently experiencing foundation shifts and cracking. I realize that other factors do contribute to foundation problems, but 100% of the homes over the former creek have problems, whereas most of their neighbors don't. I know that there is a way to build a home on this kind of site and do it correctly. But I'm afraid that corners were cut, and the builder just dumped a deep load of fill, rolled it a bit, and built on top of it. I was hoping to find some sort of inspection record of whether or not they followed the design engineers plan, or whether there was even a proper design required. If it is required and required to be inspected, and the inspection is required to be kept on record, then I might be able to see a copy of it and find out just what happened when all of these homes were built, and perhaps more importantly, prevent the same thing from happening to all of the homes that are going to built in the new neighborhood. Thanks so much for your time.

 

[msucog]

my firm typically will not be involved with residential construction due to the reasons you discuss. the contractors are typically worse than usual, the owner only cares about getting the site built since they've got shady clauses in their contracts with homeowners, and since there's little oversight of residential construction by engineers. even here where i live where the county is very strict on having engineers involved with retaining wall design, they have silly clauses saying something to the effect that the wall doesn't need to be engineered as long as it's attached the to the house. so, i recently got myself fired off a project where the retaining walls for and around the residential buildings had 3' wide footings for a 15' tall wall located at the edge of wetlands (in the wetlands). even the grading contractor called me because he was concerned about the design. i told him good luck, to absolutely not deviate from a single statement on the plans and document everything...then declined to get involved with the project again. since he's one of the better grading contractors i've run across, i told him that we possibly could get involved if things get ugly but that we may have some potential conflict of interests since we originally worked for the developer/general contractor. everyone knows the particular engineer is shady and will sign off on anything...as a matter of fact, this same "client" brought this guy in after they didn't have us do some inspections required by the county on the last project. i doubt he realizes he signed off on a building that was supposed to be undercut some 4' (which didn't happen). some projects/clients are not worth the liability...even if they do pay their bills on time.

 

[concretemasonry]

Is this request to provide background for engineering on the new development?

Or is it for a suit against the builder/contractor or to prevent the development of another area that the existing owners see as an asset and do not want to de developed?

Obviously, the engineering of the new site will depend on the site conditions and the previous site requirements may not be applicable. The records and inspection will depend on the design and construction methods employed for the new site/project.

Dick