For hundreds, if not thousands of years, we’ve been excavating the ground the same way: by coming into contact with it. We engage the ground to move it. All earth moving systems to date have been high-contact systems. This means that all existing excavation methods rely on thrust force, torque and mechanical advantage to effectively move the ground. The harder the ground conditions, the more thrust force and torque you need to move it.
For wide diameter tunneling machines, you have enough internal real estate to include large, powerful components that can crush through most any hard geology. Large tunnel boring machines (TBM) can bore through anything really (albeit somewhat slowly). Here's a cool video on how Chinese TBMs are put to work:
The problem is when you need to bore tunnels below 60”-72” diameter, typically called trenchless tunnels, where every component on your machine is slightly smaller and weaker than the large TBMs. When you are boring small diameter tunnels, you also have to downsize everything else: the bearings, the augers, the cutting disks. And so we simply don’t get enough thrust force out of conventional machines to effectively bore through hard rock. Sure, sometimes a skilled and experienced operator might be able to muscle through it. But it’s a pain in the ass and it’s risky. Also, almost all conventional methods tap out at 24K PSI rock. Boring through 44K Sioux Quartzite at 30” diameters is simply *not* done with any trenchless method.
And furthermore, if you were a contractor with equipment that cost you millions of dollars, and you were facing a job with hard abrasive rock, would you risk your expensive machinery? Probably not…at least not for a reasonable rate, that is.
If we're going to bury utilities at scale, we need to rethink how we excavate the ground fundamentally. For hard rock jobs, we need to develop a method that is impervious to the changes in rock hardness and we need to develop a way to bore through any hard, intact rock…we never want to have to do bore samples again and choose a method that we think is going to work because the geotech report came back and told us that the hardest rock we’re going to encounter is 24K PSI but when we get into the bore, we get our multi-million dollar machine stuck in 35K PSI rock.
Put simply, we need to remove thrust force and torque from the excavation equation when it comes to hard rock trenchless boring. We needed to make a method that was agnostic to hardness or abrasivity.
Because we can excavate without coming into contact with the rock, we have removed thrust force from the excavation equation. This means that if you know you're going through hard rock, you no longer have to hope that your bore sample analysis was correct; our cutter head doesn't care how hard or abrasive the rock is - in fact, she prefers hard, abrasive rock.
When you downsize the cutter head to under 72 inches diameter, you can't find machines with enough thrust force to excavate all ground types the same way you do with larger diameter TBMs. And even at the TBM size, the cutterhead must be designed to meet the expected geological conditions. Remember the year and a half delay caused when 57-ft’ diameter Bertha in Seattle hit a 6 inch iron drainage pipe? Machines that bore tunnels below 72 inches in diameter are called trenchless machines and, like their larger TBM siblings, use geology specific cutter heads, thrust force and torque in the same manner.
There's further segmentation when determining which machine to use when tunneling below 72” in diameter. The geology, bore profile, installation pipe, and the length of the bore all effect the type and size of machine used. If you want to bore a utility tunnel, you have 5 'methods' at your disposal, which you will choose based on the specifications of the job:
Each of these trenchless machines are segmented by thrust force–or how much energy they thrust into the ground to move it–and the torque applied to a cutterhead to engage the ground. If you go to the websites of Vermeer, Toro, American Auger, etc, you'll see that they segment their product lines by thrust force. They'll sell a 20,000 lb thrust force machine with a sweet spot in soft soil and [small diameter]. They'll sell a 500,000 lb thrust force machines that are good for short bores in soft rock. You can buy a 1M-lb HDD Maxi Rig from Toro / DitchWitch for $2M, and it'll get through geologies up to 15K PSI rock, which is like a soft limestone. But once you get over 28K PSI, you really don’t bore through it using a trenchless machine. It’s simply not worth the financial risk of taking on the project.
Another way to think about the manufacturers of trenchless machines is that they've built a bunch of 1-trick ponies, each designed with a narrow service window. This has had massive multi-billion-dollar implications on how, where and when we underground or install new utilities, especially in the US and other large markets for undergrounding utilities.
So we thought, let’s try something different. By removing thrust force and torque from the equation, and instead using cutting edge technology applied to a method called thermal spallation, it allows us to excavate without any of the limitations of mechanical advantage you encounter with conventional methods. In 2021, after a few years of R&D, we invented a totally new way to excavate hard geologies with our non-contact cutterhead.
Our method thermally shocks rock intro fragments that are then easily transported via our novel spoils removal system. This contactless method ultimately means that there is no cutterhead being forced into a bore path to engage the ground. In other words, thrust force is only needed to move the install pipe, not push the cutterhead against a nearly immovable force. And it also means there is no torque required to turn the cutterhead against the face of the tunnel. The implications of this method are far-reaching; there’s no risk of wind up resulting in a safer work environment; there are no cutting tools, teeth, or discs to replace reducing–operating costs and allowing for a consistent excavation rate for the entire length of the bore; there is no worry of a cutterhead getting stuck in gelology too difficult to bore; and since the heat source is on an articulating arm, it’s smaller than the carrier pipe and can be easily removed during the bore.
What we’re doing is something that’s never been done in the modern tunneling world, and will have a profound influence on the current utility market by drastically changing both how we get through previously impenetrable rock in the trenchless size range,and allowing us to consider undergrounding utilities in areas we previously avoided. So here’s to the first significant innovation in the trenchless excavation industry in years!
