By David Tisherman
One would like to think that if there was anything all watershapers were good at doing, it would be digging holes.
As with many other watershaping activities, however, it is apparent that some are better at it than others and that the excavation portion of a project either does a good job of setting the stage for great things to follow – or involves errors that can project themselves all the way through to the finished product.
In my view, getting things right at this stage is as important as any other step in the design, engineering or construction process and is actually the culmination of all the hard work that has gone before, whether it’s in giving homeowners an accurate sense of what’s going to happen in the backyard; working with soil and geological conditions to determine the type of structures, equipment and workforce you’ll need; and being ready for the level of on-site management and oversight that will be required to ensure the best possible results.
In other words, there’s much more going on here than the mere digging of a hole of a certain shape and size.
In my work, I see two distinct types of excavations – those we might call “conventional,” meaning the excavation of a vessel that will be completely in the ground, and “unconventional,” which is about those situations where, for example, we’re excavating a hillside for elaborate substructures including piles and grade beams. Much of what I’ll discuss this time applies to both types of digging, but I will get more specific about hillside excavations next month.
As with all aspects of watershape construction, excavation requires careful planning and supervision. When you consider just how intrusive the process is, doing the job correctly on the most basic level means making certain that you’re only breaking up that part of the yard that should be destroyed and removed.
Access is a key concern as well, because it will determine to a large extent what type of equipment you’ll be using. As a rule, bigger and more powerful is always better, because big machines work quickly and thereby offer a measure of cost efficiency. Site access, however, will always determine what kind of machinery you’ll be able to move into position.
|Access will determine what sort of equipment you’ll be able to use in excavating any watershape. In some cases, actually using that access means overcoming obstacles in the form of decks, steps or low walls, which we’ve accomplished here by covering them in dirt to create ramps suitable for passage of lightweight machines.|
You also need to consider what damage the process will cause to the area around the excavation site. If, for example, you have great access and can bring in a large, steel-tread earthmover to get the job done with great efficiency, you can pretty well assume that anything it passes over directly – including driveways and walkways – will be damaged or destroyed.
You can, of course, shield a driveway with a run of two-by-four planks or bury it under a layer of dirt and get a big machine across the surface safely. In these cases, I minimize the risk by having the earthmover make the trip just twice: I move it in and let it do the digging and bring it out afterward, but all the runs to the street with the spoils and debris are made by Bobcats and other lightweight machines.
If by chance you do have great (and destroyable) access, however, I’d suggest bringing in the biggest machine you can find. Then, once in the yard with a machine of whatever size, it’s imperative that you are absolutely clear with everyone what is to be dug up and removed and what is to stay – both structures and plants.
This bit of clarity is especially and obviously important when it comes to specimen or mature trees, but I must say that I sometimes run into clients who have amazing fondness for common, dispensable trees they might have planted or about which they have happy memories. These are issues that must be discussed ahead of time.
This is also why, well before the excavators arrive, we clearly mark every tree in the affected area as to whether it will be dug up and boxed for relocation or removed altogether. When removing trees, I always bring in a service to cut them down ahead of time to a five- or six-foot stump: With that done, it’s easy for a big machine to extract the trunk and root system.
Finally, the day before the equipment shows up, we do a site survey and make sure the work area is cleared of movable pots, patio furnishings and anything else the homeowners might want to save. We also give them the opportunity to get rid of things they don’t want to keep: We don’t encourage anyone to have us clean out a garage for them, but we’re happy to cart away old patio furniture and broken pots.
And we never, ever leave this clean-up step to the day of the excavation: That process is chaotic enough without conducting an impromptu session of musical chairs.
Before we bend a single blade of grass, we make a big point of contacting Dig Alert (or whatever agency performs such services where we’re working) to be sure we have the best possible chance of avoiding contact with any and all electrical, gas, water or sewer lines, septic tanks or leach-field systems.
The potential damage to be done in hitting these below-grade utilities can be astronomically costly. More important, it can be dangerous as well, and under the wrong circumstances somebody could be seriously injured or even killed. And nothing matches the sheer unpleasantness of hitting a sewer line: This is a situation that makes life utterly miserable for homeowners, neighbors and workers alike.
|On occasion, access is so limited that the only option is to bring in crews to excavate the space by hand. Its back-breaking, time-consuming work, but it can be done as the situation requires.|
Another consideration is what you’re going to do with the spoils. In California, for example, spoils and related demolition materials can only be dumped in certain areas by trucks taking certain predetermined routes. With some planning, this is seldom a big deal, but you do have to know precisely how much material you will be removing (or bringing in) to map out all movements and arrange for the right number of trucks to meet the need.
By law (in California at least), all trucks carrying away spoils must also be covered so loose material won’t be scattered over local streets and highways or onto parked cars.
|Sometimes it all works out and it’s possible to get big excavating rigs onto a site. That was important in this project from many years ago: We encountered a granite so hard that it actually broke one of the breaking tools. We needed every ounce of this big machine’s power to get the job done.|
Our greatest area of procedural care, however, comes in forming for the excavation. This is a subject I’ve covered at length in these pages, and it’s important to note that working with reliable and accurate forms begins before excavation, not after. I say this knowing that it is almost an afterthought on many job sites, but it’s my firm belief that good, low-tolerance construction begins with good, low-tolerance excavation – a process that can be greatly aided by deployment of good excavation forms.
Good forming, of course, requires accurate layouts. This is why, before we start digging anything, I personally articulate the layout of the pool with spray paint, carefully following the plan and always indicating details such as skimmer locations, the widths of bond beams and the dimensions of any cantilevered structures.
As with all my forms, those we install to guide excavation are made with two-by-fours and proper stakes with kickers every 24 inches. And we always use fresh lumber: Recycling is a wonderful concept, but using wood that has been exposed to wet/dry conditions and the sun doesn’t tend to be terribly straight. And where we use bender board, we always double it up: It’s flimsy stuff, and when confronted with the jarring pressure and vibration of the excavation process, I want to be extra certain it won’t move or flex.
As the forms are being built, we repeatedly measure, check and recheck to be sure we’re putting everything in the right place, both within the property and with respect to basic measurements and dimensions. We do so knowing that it’s easy to fix mistakes at this point – and a monumental hassle later on.
Excavation forming is one of those areas where I am sometimes appalled by what I see others doing in the field. I have, for instance, seen “forms” made with PVC pipe as stakes, making me wonder how tough is it to send someone to a building-supply center to get a bundle of proper stakes. I’ve also seen bender board wired to stakes, making me wonder how much the savings on the cost of nails must mean to the bottom line. And I’ve seen all sorts of scrap used to make up flimsy forms that are supported with stakes set at three- or even four-foot intervals.
To me, this is the top of a very slippery slope: Those who are willing to cut corners on as direct a process as excavation forming are often those who will take a “close enough” attitude when it comes to dimensions. And that will have to do for these charlatans, because the unstable forms they use are often several inches out of position relative to plan and they’ve already lost control of not only the excavation, but also of the ultimate shape of the watershape – and the digging hasn’t even started yet!
|In every case, the goal is always to complete the excavation stage with a hole in the ground that sets things up perfectly for the project’s subsequent construction phases.|
To me, “almost right” is never acceptable, and abuses of the term “plus or minus” should be banished from industry practice. None of us should accept being off in an excavation by anything beyond the slimmest fractions of inches. And it doesn’t matter what level of work you’re doing: There’s just no excuse for missing the dimensions by as many as six inches. Now is the time, before the digging begins, to take responsibility and make certain everything is correct.
Care at this stage is important for every project, but it is crucial with custom work, where every excavation is different and you can’t fall back on routine to get the job done. Even for similar types of vessels, the conditions of the site can present major differences – starting all the way back where we began this list of considerations with site access and the equipment we’ll be able to use as a result of that access.
For residential spaces where access tends to be limited, Bobcats and other small machines are often used because they require just a couple feet of passing width. But they are limited in power and digging capacity (and therefore take longer to get the job done), so I always look for ways to maximize access so I can bring bigger equipment to a site.
It always helps to know what’s available for these purposes. The major suppliers (Bobcat, Caterpillar and many others) seem to release new and more capable models every day. I take the time to keep up and know the dimensions of different models so I can arrange to have the best-possible equipment brought in.
As a final consideration, you need to decide whether a ramp down into the dig is the best option. Oftentimes, using a backhoe with good reach is a better way to get the job done, and here as elsewhere, bigger is almost always better.
When the big day comes, the process of actually digging the hole should be straightforward enough for completion by any experienced machine operator. In my experience, problems arise only when the necessary preliminary steps haven’t been taken – or where reliable on-site supervision and oversight is either inadequate or absent.
In the run-up to the dig, we routinely run through a checklist of all applicable OSHA guidelines and safety rules. I’ve heard lots of people express annoyance with these regulations, but they serve to protect my crews. For the nearly 30 years I’ve been a watershaper, I’ve always done what’s been required, and nobody has ever been hurt – a record that makes me particularly proud but one that should be a matter of course for all contractors.
Laws of Salvage
Before excavation begins, it’s important for clients to understand the rules about what happens when you run into something unexpected below ground. Yes, soils testing and a Dig Alert report will help you work your around many problems, but you can never be absolutely certain what’s out there until you dig into it.
I often raise the subject of the unexpected with clients by asking them a simple question: “If we find a treasure chest filled with gold bullion or jewels as we dig, who owns it?” Invariably, they say, “We do, of course,” and the law is on their side. This is where I point out that if we hit a big boulder or run into something else completely unexpected, they own that, too, as well as the costs associated with dealing with the problem.
Removing a giant boulder or some other subsurface stone structure is an occasional need and often requires regrouping and determining the next steps because big rocks can be a nightmare. And sometimes you’ll encounter other problems that weren’t revealed in the soils or geology reports. In all such cases, it’s important to have someone on site who is savvy enough to recognize, for example, how differences in the appearance and texture of the soil may effect the structures you’re planning on building.
If there’s nobody on site who’s on the lookout for deviant soil conditions, the entire job might go on and become subject to structural failure – an unfortunate but entirely common occurrence in the watershaping business.
And there’s more to consider by way of the unexpected. Several years back, for example, I was on site in the Hollywood Hills when the excavator unearthed what looked like human bones. I’m not a forensic scientist and didn’t know for certain what we were seeing – and that’s my point: Recognizing that I was looking at something potentially important, I stopped the job and contacted the police. As it turned out, they were human remains and the police slammed the project to a halt for six months while they investigated.
I’ve also heard of situations in which ancient artifacts or the walls and foundations of long-lost structures have been unearthed. That doesn’t happen too often in our young country, but it’s a situation in which it’s enormously important to stop what you’re doing and contact the appropriate authorities.
Don’t feel compelled to stick to your schedule or fear a work stoppage: Just consider instead the consequences of destroying an ancient burial ground, for example, or a possible crime scene. There’s no swimming pool project in the world that would be worth assuming that kind of risk!-- D.T.
Allow me to make two practical points before I set this discussion aside until next month: First, the earth should, in most cases, be considered as no more than a form for the concrete, and all of it should be removed from the confines of the vessel rather than used to define any parts of the structure itself. Unless otherwise specified by an engineer (for a feature such as a big thermal ledge, for example), this means that interior structures such as steps and benches should not be carved from or in any way formed by the soil.
Second, it is always better to excavate the entire site (including grades for decks) at the start of the construction process (before the pool is built) than it is to come back and do so later. All too often, I’ve seen pools being built where the hole is dug without anything having been done around the vessel – this despite the fact that it’s far easier and more economical to use a Bobcat to cut the grade for a deck than it is for a crew to do so manually later on.
This is also important because you need to control relative elevations in light of the materials being used. If the hole isn’t deep enough, for example, a situation may arise in which the coping and decking around a pool may be set in such a way that water hitting the deck will drain back toward the home – not a desirable detail.
Of course, this is another case where planning and complete knowledge of how the process should unfold from first penetration of the surface to application of the last finish detail is critical. In that light, it’s safe to say that digging a watershape is about much more than the hole itself.
Next time: excavations and drilling on sloping sites.