Checks and Balances
By Paolo Benedetti
Through the years, I've seen plentiful discussions of the fact that geotechnical (or soils) reports are required for proper watershape engineering. And it's not just about complex vanishing-edge or perimeter-overflow pools: It's about all swimming pools, spas, fountains and waterfeatures. Let's consider that case closed.
But who exactly should do the work? Quite often, I come across full-service, one-stop shops that will not only conduct the soils survey but will also take care of the structural engineering once that preliminary information is in hand. For my part, however, I have always been an advocate for keeping these functions separate.
That may seem cumbersome and generally costs a bit more, but to me, I find value in the checks and balances that result from keeping these functions separate.
Church and State
I emphasize that this is a personal preference: There are many quality firms that provide all of the required services under one roof. What I have always feared, however, is the possibility that interoffice dynamics might get in the way of what my clients really need.
To me, it's like the separation of church and state. If the generation and review of reports both happen in the same shop, isn't there always the possibility that assumptions (whether deliberate or inadvertent) will be made? Can the validity of the observations and thoroughness of the process be guaranteed? However subtle these issues may be (and no matter how much simpler it may be to schedule activities with one firm rather than two), I don't think the benefits outweigh the risks.
And here's the rub: In the event of a catastrophic event or a structural failure, the one-stop shop is likely to circle the wagons to protect its interests. And because everything is internal, a less-than-forthcoming firm might, in a truly bad situation, shield itself by disposing of relevant memos and interoffice communications.
That may seem paranoid, but by using two firms, I rest assured that these key documents, dialogues and exchanges are all matters of record among the soils engineer, the structural engineer and my own firm. I can't help thinking that this distribution of information makes the whole process a bit sharper simply by virtue of the fact that it's out in the open and everyone is fully accountable.
Inside the Report
From the designer/builder's perspective, it's important to know what to expect from these reports - and to know, for example, that the soils engineer will establish no more than minimum recommendations for a foundation's design as determined by the site's soil conditions.
These recommendations are based upon a few four- to six-inch-diameter holes drilled randomly in the area of the proposed construction. The resulting report will reach generalized conclusions based upon these samplings - meaning the report cannot possibly forecast every subterranean condition that might be present on the site.
These recommendations are included in a geotechnical report that is sent to the structural engineer, who spends more time looking at the soils analysis (coefficients of friction, load-bearing values and expansiveness indices, for instance) than at any structural recommendations the soils engineer might offer.
Why? Well, it's because the soils engineer has not studied the load of the proposed structure or its seismic stability; hasn't conducted any computer modeling or stress analysis; and hasn't had a need to do any of the calculations pertinent to the structure that might be included on the studied area of soil. All of that is simply beyond the soils engineer's purview and expertise.
Once the structural engineer's report is ready, a copy is sent to the soils engineer for review. The basic purpose of this step is to make certain the proposed structures exceed the minimum requirements defined in the soils report; that drainage issues have been addressed; and that all of the various t's and i's have been crossed and dotted.
This review results in a letter stating that the structural engineering plans have been reviewed and found to be in compliance. (This document then accompanies the engineering plans, the structural calculations and the designer's layouts and detail plans.)
In the Field
Once construction begins, there are occasions when the soils and structural engineers need to come back to the site to check on our progress.
The first one on site will be the soils engineer, who will come in once initial site grading (that is, dirt removal for decks, the pool and retaining wall footings and foundations) is complete and it's possible to inspect the open holes. This examination is meant to ensure that the soil conditions in the construction area are no worse than was indicated by the sample borings.
If any changes to the design or structural engineering are to be made, this is when they will usually come up, resulting in delays while the structural engineering is modified and submitted to the regulating authorities for approval.
Once the project has progressed to the point where the reinforcing steel is in place, the structural engineer is called in to check the grade of the steel; rebar diameters, placement, spacing and overlaps; and clearances to soil, plumbing and other objects. If the engineers are local, this can be an on-site inspection; if not, we'll take copious digital images and transmit them to the engineer's office via e-mail.
(These "virtual reviews" are becoming more and more common. Not only do they save everyone time and money, but they also provide the engineer with a full record of what is occurring. Getting these photographs right takes some practice: When you're just starting out, the engineer will often ask you to retake shots from different angles or to include a yardstick or tape measure to reflect scale. Once you've done this a few times, it's all pretty straightforward.)
When this last inspection is complete, we're on our own with the project and carry it through to conclusion and final inspection by the governing jurisdiction. To me, having had the soils and structural engineering conducted out of house by two separate firms is by far the best way to go: You have to love those checks and balances!