Rig Access Can be Half the Job for Geotechnical, Environmental Drilling
You’re a home owner, and you want to build an addition on the back of your house. You need a geotechnical investigation done to determine the design of your foundation and footings. What do you do? You can’t get a CME 75 in your backyard, and even a 45 won’t make it through the gate, and then across the nice wooden deck surrounding your pool and up a few steps to your interlocking brick patio. Drilling the holes in front of the house is pointless. The engineers need to get their samples and blow counts from within the footprint of the new addition. Most engineering companies know at least one drilling company that has a small rig for such a situation. Sometimes that “rig” is a couple guys with strong backs, a 70-pound chunk of steel, some rods and a split spoon. Other times, it’s a tripod design, a small portable auger rig on wheels that’s hauled around by hand, or in a more ideal situation it’s a small track-mounted rig that’s narrow enough and nimble enough to maneuver through the gate, and around a corner past the gardens, and powerful enough to make your day easier. Like any other geotechnical project, you still drill to the specified depth, drop your hammer and continue on to the next interval, until the hole is completed and you can move on to the next one or you’re finished for the day.
Sounds pretty simple doesn’t it? Just like any other drilling project, but with smaller equipment.
If only it was that easy. Sure, with a smaller, less powerful machine you’ve got smaller, lighter weight tooling. You’re not going to be dealing with five-foot NW rods, eight-inch I.D. hollow stems and 48-inch pipe wrenches, but that lighter-weight tooling in many cases still has to be carried to the borehole. Add to that a foot of snow on the ground, uneven terrain, and slippery slopes due to snow, ice, mud and rain, and suddenly you’ve got a situation where you can spend as much time moving to and from holes as you do drilling them, and using up a lot of your energy in the process.
Now let’s have a scenario for environmental drilling. We’re in the basement of a strip mall. There is, or was, a dry cleaner in the building somewhere and, as a result, there is contamination under the floor. A truck-mounted rig can do holes and install wells outside, but what about inside? There are small direct-push machines that in many circumstances can make short work of the task at hand but, because they are smaller and lighter weight, they can’t always make it to the required depths. Tooling size can be an issue as well. Obviously, smaller tooling will be able to penetrate to deeper depths, but isn’t large enough to install a two-inch well, which seems to be the industry standard for monitoring wells. Larger tooling of an appropriate size to properly install a two-inch well is much more difficult, if not impossible, to drive to depth in highly compacted soil with such a small machine.
In this case augering might be the solution. But how do you get a small auger drill into a basement? If you’re lucky, you can winch it down the stairs if you’ve got a straight shot from the door to the stairs or a solid mounting point inside the building. If there is an elevator available of sufficient size to accommodate the biggest pieces, that’s another option. Or, if the machine isn’t too complex, you can disassemble it and bring it down in pieces. The last choice, however, can be quite time consuming and the client may not be willing to pay for it. But then, if they want the job done, they may have to bite the bullet and pay for the disassembly and reassembly time. In my experience, drilling inside is always more time consuming than outside, especially in places like basements or the bottom of a parking garage. It can take numerous trips and a few hours of work just getting ready to drill. First, there is getting the drill down to the bottom and reassembling it, if necessary, followed by augers, rods, split spoons, concrete coring equipment, well supplies, shovels, brooms—everything you would need for a job on the outside and more.
If you’re working in a parking garage, an extra truck will help with moving equipment and supplies, assuming the truck isn’t too big to fit (it happens). But in a basement, you’re doing this by hand.
So now, you’ve finished sampling and you’re ready to install a well. The soil conditions were good enough that you were able to complete the job with solid-stem augers. But you’ve got limited overhead clearance. I hope you remembered to bring five-foot well pipe and screen! Finally, the well is installed, flush mounted and finished with concrete. You used up two 50-pound bags of bentonite and another 50-pound bag of sand installing the well. But now you’ve got that much weight or more in cuttings to remove plus some concrete cores. The drums are upstairs and outside. Bucket by bucket, you climb the stairs to dump the materials outside, until they’re all gone. Then, it’s time to bring all your equipment and leftover supplies back out. Suddenly, all of this smaller, light-weight tooling is feeling a lot heavier. Finished? Not quite. You’ve got to leave the place as clean as you found it. Out come the broom, mop and bucket. Finally, you’re really finished. <br><br>
Unforeseen Circumstances And Job Pricing
In ideal soil conditions, a smaller drill can have production rates similar to a bigger rig up to certain depths. In my experience, that’s about 15 feet. After that, the taller towers, stronger winches and higher weight make it obvious which rigs are better suited for deeper depths. Unfortunately, this isn’t always obvious to clients. If they’re used to hiring full-sized truck- and track-mounted rigs, they could potentially be in for a nasty surprise.
Even people familiar with your machines can still be taken by surprise on a job. A few years ago we were working at a chemical storage facility with a client who hired us frequently and was very familiar with regard to the limitations of our equipment. Because of the very hard and rocky soil, the job was going slowly and, on a good day, we were installing one well between 15 and 20 feet with hollows. Not to mention, there were other unexpected delays. The fire alarm would go off at least once a week while we were drilling. Everyone on the property had to leave, and gather across the road for a head count. Nothing like random fire drills to add some excitement to a job! While working within certain distances from a filling area, we were required to shut down work while a tanker truck was being filled with volatile chemicals. This would sometimes cause work stoppages of an hour or more. It’s certainly understandable, however. It would be much cheaper to have us sit for an hour or two, than it would be to pay for injuries and damage that may have been sustained if a problem occurred and some stray vapors had ignited. On that particular job, delays of this sort happened frequently and, because of this, the budget was exceeded by a considerable amount. Fortunately, our client and our client’s client were very understanding given the nature of some of the delays.
Another story that comes to mind definitely falls into the unforeseen circumstances category. We had been working for a few weeks in the ditches along a secondary highway and were staged just around the corner on a side road, a few hundred feet down from where we were going to be drilling. It was the last day of drilling before Christmas. The roads were clear and dry and the sun was shining, but there was still a lot of snow on the ground. We had traffic control waiting to start setting up as soon as the clock hit 9 a.m., a boom truck to lift us over the guardrail and lower us down a hill and the consultant—all of us ready to work. The clock hit 9 a.m., and traffic control took off down the road to start putting up signs. They went around the bend and disappeared.
My helper, the consultant and I were discussing the day’s plan of action and having our daily safety meeting. When we looked over in the direction of where we were going to be drilling, to our surprise, we saw a car upside down in the ditch, less than 100 feet from the borehole location. People had stopped and were calling 911. Others were trying to assist the driver. Within a few minutes the police had arrived, and closed the highway, followed by an ambulance and fire trucks. Understandably so, because of the police investigation, we weren’t permitted to work that day. It wasn’t until after the Christmas break that we drilled that last hole and completed the job.
So, we’ve seen how limited-access rigs work out in the field. In the next installment, we’ll talk about the most important aspect of any drilling job: safety.