Varying soil conditions.  The importance of operator awareness in underground boring

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Operating any underground boring machine requires a keen awareness of what is going on at the drill head that the operator can’t see.  You may think that without sophisticated technology, there is no way an operator can actually know what kind of substrate or obstacle they are dealing with but that’s just not the case.  Long before sophisticated guidance and detection technology came along underground boring operators were boring by using their own senses including common sense.  It’s not to say that there isn’t a role for this technology, there certainly is in many circumstances but for the types of bores that owners of Prairie Dog Boring Equipment do the best technology comes from the operators themselves.

OIP 7 300x168 - Varying soil conditions.  The importance of operator awareness in underground boring

One of the most common problems I hear is that a pilot hole was easy and quick but when the operator started to back ream the machine started bogging down.  Of course, the first question I ask is what the soil conditions are so that I can understand what is going on inside the bore hole.  The next thing I need to know is the experience of the operator.

 

I have written articles on soil conditions dealing with sand and clay, two of the more difficult substrates.  Today I want to focus on the operator.  As mentioned before, I more than occasionally, get feedback that the pilot hole was quick and easy.  Now, you would normally think that this is a good sign but it’s really a red flag and very likely set up the problem on the back ream.  Operators need to understand that when they are boring the pilot hole they need to be keenly aware of feedback from the machine and the pilot bit.  What I mean by this is that they need to be listening to the machine,  they need to be aware of what they are feeling and they need to be paying close attention to the cuttings coming out of the pilot hole.  This requires use of at least 3 senses, sight, hearing, touch and possibly a fourth, smell.(I once drilled into a gas line.  The first sign of a problem was the was the slurry was blown from the hole, the second was the smell of natural gas).  It definitely requires putting all that feed back together into a neat package in their mind that I would call “common sense”.

 

Sound and touch go together.  The operator needs to understand that their machine has limits such as horsepower and what it can easily cut through with the bit being used.  Listening to the machine possibly struggling, especially on a pilot hole, is critical to back reaming success.  I will explain in a minute.  Being able to feel and recognize when the machine encounters different substrates or even obstacles is also crucial to a successful bore.  This is all important information that is needed at the moment but will also be useful on the back ream because the operator will need to know what is coming up drawing from the information he received on the pilot hole.

 

Sight is every bit as important.  The operator needs to pay attention to the color, consistency and quantity of cuttings exiting the hole when boring the pilot.  The most important question is whether there are cuttings actually exiting the hole in sufficient quantity.  If those cuttings aren’t coming out then they are staying in the hole and that WILL cause problems on a back ream and it may cause problems just pulling back copper, HDPE or whatever is being installed.  To illustrate, imagine drilling a hole in wood a piece of wood with a conventional drill bit for the purpose of installing a dowel pin.  That bit has flutes which serve the purpose of removing the wood.  Without flutes the cuttings would just stay in the hole.  Even when we removed the bit the wood chips would remain in the hole making it impossible to install the dowel unless we took additional steps to clear the hole of the chips.  In conventional slick boring we don’t use fluted augers for several reasons.  We use water or water mixed with some kind of drilling mud.  The purpose of the water is to create a slurry that will suspend the particles of the cuttings so that they can run back out of the hole thus creating a clean hole.  This is where the operator has to be paying attention.  He has to have some awareness of the size of the pilot hole he is boring and how much slurry or cuttings should be coming from that size hole.  If there aren’t enough cuttings coming from the hole then it means they are staying in the hole.  They aren’t magically disappearing.  It’s that simple.

 

When the cuttings stay in the hole it’s usually due to boring in reactive clay and a couple of things will happen.  The clay, as it slowly absorbs the water, begins to swell like a sponge and will eventually cause friction and restriction on the bore rods.  This restriction typically will not be noticeable going forward while drilling the pilot hole because the forward motion is creating more space for the cuttings, those that aren’t exiting the hole, to spread out.  However, as soon as pull back or back reaming begins and the drill rods start to move backwards the remaining cuttings in the hole start to back up with the drill rods and will begin packing around the drill rod causing restriction against the rod.  This is the point where I hear the complaint that the machine doesn’t have enough horsepower to turn the back reamer.

 

Imagine if we had 40 feet of drill rod strung out in a shop and it was attached to a machine with a 9hp motor. (don’t attempt this at home or in your own shop by the way)

Now lets put a 10” back reamer on the end of the rod.  Imagine me grabbing that back reamer with my hands and trying to hold on to that back reamer as an operator engaged the clutch.  There is zero chance that I could hold on to it or even slow the engine down as the clutch was engaging.  Zero chance.

 

Now imagine that same 40 feet of drill rod strung out but instead we have twenty men standing on both sides, shoulder to shoulder, squeezing the drill rod, with gloved hands, as tightly as they can.  That’s 40 men trying to restrict the turning of the rod.  Could they?  Sure they could,  they might even be able to bog the engine down to the point of it dying.  This is what is going on inside a bore hole that isn’t properly cleared of the cuttings.  The remaining cuttings are binding, or squeezing the drill rod, preventing it from turning easily.  Now as we start back reaming and the drill rod is moving back toward the machine there is even more opportunity for the swollen clay to “pack” against the drill rod and there is no more water to help flush it because that water is now supposed to be creating a slurry for the back reamer cuttings that will run to the “come out hole” instead of the bore pit.  As the rod turns, in a restricted state, heat is generated which can increase the swelling of the clay, dry it out and thus decreasing any remaining lubricity from the small amount of water that was in the clay.  You can see that the problem of having a pilot hole that isn’t properly cleared of the initial cuttings is quickly compounded.

I mentioned earlier that one of the responses I typically get when asking about the process is that the pilot hole went quick and easy.  I will usually ask how quickly.  How long did it take to bore that 40’ pilot hole?  If the customer is having issues with the back ream the answer to that question is predictable.  It will be something along the lines of “the pilot bit went right through”,  “It only took us 20 minutes to bore the pilot hole”.  It’s at that point that I tell them they simply went too fast and I find myself trying to illustrate the scenario above, grabbing the rods, over the phone in order to explain what boring the pilot hole too fast means to their pull back or back ream and why the machine may be bogging down.

 

At Prairie Dog Boring Equipment, Inc we understand the challenges of varying soil conditions.  We build our machines to be easy to operate but the operator must play a part in a successful bore.  This means that he uses the sense of sight, hearing and touch along with just a little bit of intuition or common sense when operating a boring machine.  Most bores, in reactive clay, can be done with our machines with just water and attention to the cuttings.  Sometimes a drilling fluid can help break down the clay and we have our own specially formulated clay inhibitors for that purpose if they are needed.  They are inexpensive, effective and easy to use just like our machines.  For more information please visit or contact us.  We will be happy to show you how to make your life easier and make even more money with a Prairie Dog Boring Machine.