Aquatic Technology Pool & Spa, "Creating Water as Art."™

Aquatic Technology Pool & Spa, "Creating Water as Art."™
Pools as an art form - the way it should be!

Saturday, February 14, 2009

Checks & Balances

Aquatic Technology Pool & Spa
Paolo Benedetti

Geotechnical reports (soils reports) are required for the proper engineering of all swimming pools, spas, water features, and fountains, not just complex infinity edge, vanishing edge, slot overflow, knife edge, or perimeter overflow pools.

Since I have been in this industry, I have advocated the use of separate geo-technical and structural engineering firms. There is a great value and benefit for the consumer when using separate firms... the separation of "church & state." Simply stated, there becomes a series of checks & balances and peer reviews.

While there are a great many quality firms that provide all of these service under one roof, there is always the fear of inter-office politics wreaking havoc on a project. Since the "check & balance" peer review occurs behind the scenes, the validity and thoroughness cannot be guaranteed. This format does offer some advantages, such as less scheduling delays during the planning & design phases.

However, there is one major drawback... in the event of a catastrophic event or structural failure, a "one-stop shop" will "rally the troops & encircle the wagons" to protect their interests. They will be able to shield themselves from liability by destroying memos & inter-office communications. These documents and dialogues transfer openly between the Designer, Structural Engineer, and Soils Engineer, when separate geo-technical & structural engineering firms are employed.

The geo-technical engineer will initial make minimum recommendations for a foundation design, based upon the sites soil conditions. These recommendations are based upon a few small 4-6" diameter holes drilled randomly in the area of the proposed construction. The resulting report will make generalized conclusions based upon these random samplings, and therefore the report cannot possibly forecast every subterranean condition on the site.

The recommendations which are included in the geo-technical report, are forwarded to the Structural Engineering firm. They will rely more upon the soils analysis (coefficient of friction, load bearing values, expansiveness index, etc.), than the Soils Engineer's minimum structural recommendations.

The reason that the Structural Engineer does not rely much on the Soils Engineer's foundation recommendations, is because the load of the structure, seismic stability, computer modeling & stress analysis, and related calculus had not been performed. Most Soils Engineers do not possess the related education to even come close to making valid recommendations.

For instance if the structure is to be supported on friction caissons (aka: piers) , the Structural Engineer will be the one to calculate the surface area of the caisson. These piers rely upon the skin friction of the surface of the caisson against the earth, to resist movement. The surface area must be adequate to provide enough friction to overcome the loads placed upon them. Oftentimes, the minimum diameter specified by a Soils Engineer, is not of sufficient diameter to create the amount of surface area required to create the proper amount of friction. The "coefficient of friction" of the soil is multiplied by the surface area of the caisson, & the size of the caisson is increased, until the resultant value exceeds what is required. Soils with a high coefficient of friction require smaller caissons, while a low coefficient of friction requires larger & deeper caissons. This is why the Structural Engineer's specifications for the diameter & depth of a caisson design seems "like over-kill," when compared to the Soils Engineer's minimum recommendations.

After the Structural Engineering has been completed, the Geo-Technical Firm is sent a copy of the plans for review. They are looking to ensure that the design exceeds their minimum recommendations, drainage issues are addressed, and that the T's are crossed & the I's dotted. It is an informal type of "peer review." They then issue a letter, stating that they have reviewed the engineering plans and find them to be in compliance with their recommendations. This letter always accompanies the engineering plans, structural calculations, and designers layout & detail plans.

We have lost some projects over the years (good riddance), where the Soils Engineer has reported back to the property owners, "this engineering is over kill. You are going to spend a lot more money than you need to, on something that you will never see." The property owners then rely on ignorant statements like that, to "re-engineer" (dumb-down & degrade) the structural engineering. After all, what does the "pool guy" know?!

The problem is, that Soils Engineer did not fathom the weight of a filled concrete structure or the seismic loads (earthquake, landslide, subterranean water migration, avalanches, tidal surges, etc.) or stresses upon the structure. To make comments like that, when they have not performed computer generate 3-D modeling & stress analysis, mathematical calculations, or even possess a degree in structural engineering, is totally unprofessional, irresponsible & unconscionable.

For a contractor who may have the pleasure of bidding on one of our design projects, such comments should be the clients first cue to "turn & run" & "show the guy the door (with a boot in the backside for good measure)."

During construction, the first inspection will be by the Soils Engineer. When the initial site grading [dirt removal for the future build-up of the pool decks (base rock, concrete, & stone veneer), excavated pool, retaining wall footings & foundations] has been completed, the open holes will be inspected. This is to ensure that the soil conditions are not any worse than the small sample borings. Any changes in the design or structural engineering usually occur at this point, and can result in delays, while the engineering is modified & submitted to the regulating governmental agencies for approval.

Once the project has progressed to the point where the structural reinforcing steel is in place, the Structural Engineer will usually inspect the steel placement. They will look at the grade of steel; diameter of the bars; the steel's placement, spacing, and over-laps; and the clearances to the soil, plumbing, and other objects. This can be a physical on-site inspection if the Engineers are local, if they are remote & the client is willing to pay their travel expenses, or can be done through digital photography & emails.

More frequently, projects are being "virtually-reviewed." Not only does it save everyone time & money, but it provides the Engineer with a record of what occurred. If the Engineer wants to see something from a different angle or close-up, that can be requested. It is important that close-ups of the steel bars, showing the indicating marks for the grade & diameter, also be provided. A "scale" should always be provided in the images for reference - a yard stick, tape measure, or surveyors staff are perfect.

This system of checks & balances ensure that there is an on-going series of peer reviews during the project, until "everything is set in concrete." These inspections occur independently of Deputy (Special) Inspectors & Building Inspections.

The benefit:

The property owner is guaranteed that the contractor is maintaining the project's integrity. Do it right or don't do it!

Paolo Benedetti - Aquatic Artist
"Creating water as art."™
Aquatic Technology Pool & Spa