For most contractors, “underground” has meant trenches down Main Street, tearing up multiple spaces in parking lots, spoiling the calm and neatness of residential streets to repair or update infrastructure, and then the costly replacing and reshaping of what was removed. I’m not going to talk about trenches in this article, even though they are still necessary ways for improving some projects. There are projects that do involve some digging (how else would you get underground?) but they are more complicated than trenches done with excavators and backhoes.
The largest underground work that receives attention is probably that done when tunnels are built for vehicles and trains. There are famous underground constructions, such as the Simplon Tunnel, London’s Tubes, and the Paris Metro, that have been in place for more than 100 years. If there is a hill or mountain in the way, the resulting tunnels are underground construction. It’s expert work and used to be reckoned as an extremely expensive alternative to drilling and blasting. Today, making tunnels with tunnel boring machines does not seem much more expensive; one key reason is that it is quicker than alternative methods.
The Big Boring Machines
The biggest tunnel boring machines we hear about grind holes in mountains to make room for roads and railway lines. They are superb examples of engineering; think of the tunnel under the English Channel (or La Manche, if you’re French) from England to France. One aspect to remember about these wide tunnels is they are not finished when the boring machine completes its hole. The interiors of tunnels must be lined with the right materials, electrical lines must usually be installed, and safety features to protect those using the underground channels. There is plenty of subcontracting work to be done safely and efficiently once the boring contractors have done their part.
Smaller than the large tunnel boring machines (TBMs) are those that make holes for multiple sewers and waterways. They are bigger than the drills with which most contractors are familiar, but not huge. Another difference worth noting is that some drills can go through the hardest rocks while others are used mostly for softer ground; the designs of the machines are different. Lovat was, for many years, a well-known and respected name in tunnel boring. This company is now Caterpillar Tunneling, and a couple of recent projects will show potential uses for TBMs in North America. The jobs were abroad, but you can envisage them here. The first involved a Cat RME152SE Earth Pressure Balance TBM (diameter of 12.4 feet), and its job was to bore a pipeline tunnel for oil transmission for the 2 miles from one depot to another. The main geology encountered was clay, sandstone, argillite, and clay stone. The tunnel is lined with precast concrete rings of almost 10.6 feet internal diameter. This Caterpillar TBM was launched in February 2011, advanced through 1,312 feet of overburden, and completed the hole on August 1, 2012. The best advance distance for the contractor was 49 feet in one day and 866 feet in one month.
The other project I’ll mention for Caterpillar Tunneling required a larger TBM, one of very nearly 20 feet in diameter, and its purpose was to bore a metro tunnel with a total length of almost a mile. The location is a growing metropolis, a city that has experienced expansion unexpected 20 years ago. The boring took a little less than 14 months, with the alignment running through clay, sandy clay, and loam. The metro tunnel is lined with precast concrete segment rings with an internal diameter of just over 17 feet. There was much groundwater at the site and difficult alignment requirements, but the Cat TBM made its best daily advance of 64 feet and best two weeks’ performance as 590 feet. A second, parallel tunnel will be started this year, and the whole metro project is expected to be completed in 2016.
In Cincinnati, OH, it was a Robbins Double Shield Rockhead (SBU-RHDS) tunnel boring machine that did the boring for seven sewer tunnels for the Clermont County Ohio Water Resources Department. The TBM has a diameter of 72 inches; the contractor was Midwest Mole Inc. The seven sewer tunnels replace an outdated and exposed system that had begun dumping raw sewage into local Shayler Creek. That creek itself had caused trouble for the system, from 1978, when it suffered erosion and put existing pipe at risk. The new sewer system would have to be installed well below the waterway. This meant a great variety of ground conditions, with interbedded layers of shale and limestone that ranged from dry to sticky to wet. To meet the challenge of this mixed ground, the machine was fitted with a mixed-ground cutterhead that could be exchanged for a hard rock cutterhead, based on the ground conditions at each crossing. The mixed ground cutterhead has 6.5-inch single-disc cutters and carbide bits, while the hard rock cutterhead contains 11.5-inch single cutters and abrasion-resistant muck scrapers.
The Robbins Rockhead was provided with a mixed ground cutterhead for excavation in soft, wet limestone and shale.
Expanding or Replacing Infrastructure
All over North America, infrastructure is failing. However many alternative problems may be addressed by politicians as more important, the infrastructure that supports our safe and healthy living is desperate for repairs, expansion, or transplants. Cities that have grown beyond the expectations of the planners of yesterday seem to get new highways and streets (because they are visible?) but the most important health care for those cities may be more closely related to water supply and sewers. This is where the real underground construction may be in the coming decades: water and sewer tunnels big enough to carry the liquids of our civilization. Those tunnels will be bigger than your average trenchless drill can manage. They are, if you like, real construction projects, because they involve more than holes.
For a hospital in California, it was expansion (and the ground on which the expansion infrastructure would be built) that saw work from another Robbins small boring unit (SBU-A). Small, in that its diameter was 30 inches rather several feet. The Tahoe Forest Hospital in Truckee, CA, was designing a new cancer wing and decided that new utility and mechanical lines would be required before the new building could be constructed. To house the bundled utilities, three crossings had to be bored directly below the (active) main hospital. AM-X Construction & Excavation Inc. was the general contractor, and it subcontracted the three parallel 70-foot sections to Silver State Boring Inc. The variable ground conditions and constraints concerning noise for the hospital made Silver State choose a Robbins SBU-A with a mixed ground head. The hospital is built on ground containing large granite boulders, and Silver State did worry that they could be hit during the boring. In the first bore, at 25 feet along, the SBU-A caught the edge of a boulder about 12 feet in diameter. During the second bore, the machine drilled straight through the same boulder. The Robbins machine also powered successfully through additional boulders of 175 MPa (25,000 psi) in the third bore. The boring was done 8 feet below the hospital’s foundation, and the older hospital had many buried utilities that had to be cut and bypassed during the excavation. Robbins had field service technicians at the site before launching to help with setup and crew training.
How do these mixed-ground boring machines work? The Robbins SBU-A has a circular cutting head equipped with a combination of tungsten carbide bits, single-disc cutters, and multirow disc cutters. You can get such an SBU-A with diameters from 24 inches to 72 inches. With it you can excavate a good variety of hard rocks and mixed ground conditions, including dry soils, cobbles, clay, and boulders from 25 to 175 MPa (4,000 to 25,000 psi) UCS. During the earth-boring operation, the SBU-A is welded to an auger boring machine (ABM), which gives both torque and thrust to the cutting head. Drag bits scrape. Muck scrapers scoop that excavated rock into large openings in the cutterhead, to permit a smooth flow of muck from the face to the auger string.
One method of making the tunnels or channels required for underground infrastructure is called pilot-tube-guided auger boring. There have been several successful projects using this technique (which originated in Germany with Bohrtec), and Icon Tunnel Systems has led the way in distribution for this kind of boring for years. In Arlington, WA, Trenchless Construction Services LLC installed more than 3,400 linear feet of 15-inch- and 24-inch-diameter vitrified clay jacking pipe (VRCP) for the installation of gravity sewers on a 16% grade. In Carroll, IA, Rognes Corp. installed more than 3,200 linear feet of 20-inch-diameter VRCP (from Mission Clay Products) with the help of an Icon BM400LS pilot-tube machine (with 150-ton jacking force). In Middletown, DE, Austin & Bednash Construction Inc. installed more than 600 feet of 12-inch-diameter VRCP with similar help from Icon and Mission Clay Products. This project was designed originally as an open-cut excavation with PVC pipe to be installed, but open cut was determined to be not an option under the circumstances, and the method was changed. In Staten Island, NY, open cut was also not an option, and DiFazio Industries installed more than 330 linear feet of 18-inch VRCP. That “open cut not an option” seems likely to be specified with increasing frequency as alternatives are available.
Pilot tube guided auger boring or pilot tube microtunneling is recommended for installing pipe with an outside diameter (OD) of 4 to 55 inches. When you are challenged with a gravity sewer project that demands accurate installation with line and grade precision of 1 inch or better, the pilot-tube auger boring system will provide the accurate results demanded. Icon offers three styles. The company’s small compact units can install up to 40-inch OD pipe in as little as a 6.5-foot round or square shaft. The long frame units can install up to 55-inch OD pipe in as little as an 8-foot-by-13-foot rectangular shaft. The long compact unit can install up to 48-inch OD pipe in as little as a 12-foot round or square shaft. Each of these Bohrtec models from Icon can provide at least 100 tons of jacking force and 50 tons of pullback, with 8,850 foot-pounds of rotational torque through the gear box and up to 36,878 foot-pounds with the largest model.
While it seems likely that the demand for underground construction related to power utilities, water and sewer infrastructure, and new property developments will keep on growing, we should not forget the construction that lies underneath some of our most important and sensitive structures. Airports and railroads spring to mind. Underground Construction Co. Inc., based in California, has done a job for American Airlines. It was the replacement of the hydraulic fueling system at Terminal 4 of Los Angeles International Airport (LAX). The project comprised some 3,000 feet of fuel pipe installation and 23 new hydrant pits. The work was typical of the project…in most ways. American Airlines required that the terminal remained active during construction and that the work be completed in less than a year. The project was broken down into seven phases; in each phase Underground Construction was given two gates to work in. While the contractor was breaking concrete, digging trenches, and installing pipe, the airline operated buses through the work area, picking up passengers for reloading at another location. It was job of safety challenges, with those buses, planes passing within feet of the construction equipment, traffic delays, jet blasts, and loud engines.
The crew completed the first phase ahead of schedule, and every new phase has been completed ahead of schedule and within budget. At every phase, the contractor had to manage the excavation and soil removal (soil contaminated with jet fuel from the existing hydrant system). An onsite environmental consultant tests the soil during all excavation activities and the contaminated soil is hauled away for disposal at a soil treatment facility in Adelanto. It was, to onlookers, an ordinary construction job, but the abnormal dangers and challenges stemmed from its underground location.
A view of a pit used near Cincinnati for infrastructure rehabilitation.
There is no doubt that underground construction presents dangers that can be more imminent than construction work in most of its locations. Workers in road repair and construction are well aware of the dangers of speeding vehicles (often driven, it seems by people who have no idea of the dangers involved) but working underground can bring dangers of a deadlier and, sometimes, unexpected nature. Those same contractors who learned to work with planes roaring around them in the previous paragraph met some other hazards at a project by a busy railroad. Commuter trains traveling at 70 mph find it difficult to stop quickly, and those that travel the route in the peninsula below San Francisco are no exception. Underground Construction Inc, however, had to remove four manholes and place new manholes at lower grades to permit clearance for new streets. The conduits going from manhole to manhole also had to be lowered to allow temporary tracks to be placed while existing tracks are relocated. There were also locations where conflicts with sewer and storm lines required existing telephone duct banks to be lowered for clearance. (The sewer and storm lines have to be at a specific grade, to allow good flow, but that doesn’t bother phones.) What might have a standard job in most places was changed by the ever-present threat of fast trains rumbling by. The contractor had to have a watchman standing by to give warning of the approach of a train. He sounded a horn when the train approached. The workers moved to a safer place. He sounded the horn when the train had passed, and the work could continue. OSHA has regulations about the preparedness and conduct of people working underground. You should be aware of them and make your employees aware, too. The OSHA regulations are freely available and quite easy to read and understand.
The Familiar Underground Equipment
Some people have called trenchless technology the “last mile” solution for moving essential equipment underground, without tearing up roads and streets. Think of the millions of dollars and hours of labor that have been saved by the underground drilling and boring equipment from companies like Vermeer, Ditch Witch, and TT Technologies. If you think those companies design and market only small stuff, you should take a look at their websites today. They have given evidence of continuing commitment to the public they serve, with new products added to their ranges and new techniques explored and approved.
This is the launching pit for a Vermeer AXIS boring system.
Moving away from water and sewers, but still using relatively small diameter drilling bores, the Brownsville, WI-based Michels Corp. has been involved in almost all the underground construction work in the state for 50 years. The company has installed pipes up to 60 inches in diameter, but one of their top customers has been CenterPoint Energy (a natural-gas distributor) and its predecessor companies. About 70% of that work is in the counties that compose the Twin Cities region of Minneapolis and St. Paul. Most of the work, in a working season that is shortened by harsh winters, is rehab and replacement. For road crossings and restoration-sensitive areas, Michels uses piercing tools, each job with a typical 50-foot length. There are many soils in that Minnesota area, and Michels uses TT Technologies tools with heads that can be changed by the crews on the fly. It means the crews can change from a reciprocating head to a solid head quickly and easily, an advantage especially useful in fine granular soils that don’t offer much in terms of tool-ground friction. For such situations, a fixed-head Grundomat can be an excellent option. You’ll notice that most of this top contractor’s work is in rehabilitation and replacement; that could be where most of the underground work will continue to be, as our country updates its infrastructure.
Ditch Witch (The Charles Machine Works) continues to look ahead and, at the end of 2012, acquired Trencor to add to its line of underground construction equipment. One of the most impressive of the equipment from Ditch Witch has been the range of its All Terrain directional drills, which allow the contractor to do simultaneous drilling and steering through rock and rocky soil. The All Terrains have a two-pipe drilling system to allow continuous rotation of the drill bit. Its low volume of drilling fluid required means considerable savings with less waste, less cleanup, and the benefits of less environmental impact. The shaft within a pipe design offers a strong hex-shaped rod that turns inside an outer pipe, while the inner hex shaft operates as a mechanical motor to drive the bit during the bore. One machine in the range, the JT100 All Terrain directional drill has an operating mass of 47,250 pounds, an overall machine length of 368 inches, an overall machine width of 101 inches, and an overall machine height of 110 inches. It provides a thrust force of 70,000 pounds. Such a drill would be excellent for extended-range bores and installations of large-diameter pipe. Ditch Witch adds that the JT100 All Terrain is the only rock drill in its class that lets the operator transfer drill pipe from one box to another (and add or remove the upper pipe box) without additional support equipment. So the pipe box is never empty.
The Ditch Witch JT100 offers a two-pipe drilling system and other features that have made it excellent for those boring projects below streams and rivers.
All readers are probably familiar with the extensive Navigator range of directional drilling equipment from Vermeer Manufacturing, but this company, too, has expanded its offerings for construction equipment of all types, while still specializing in underground construction needs. Several times in this article I have mentioned boring systems that are not the same as those familiar models from Vermeer, Ditch Witch, and TT Technologies. Vermeer offers a system known as the AXIS guided boring system. Designed for the installation of 10-inch to 14-inch pipe, such as used in water and sewer applications, AXIS can install up to 350 feet of both rigid constructed as well as fusible and restrained joint product pipe. Pinpoint accuracy and flexible design are the goals of this equipment. It is a pit-launched guided boring system that requires a fairly low amount of thrust/pullback force compared with other pit-launched methods. As a good method of reducing costs, AXIS does not require the user to construct a structural backstop or shaft within the launch pit. Located outside the launch pit, AXIS comprises a vacuum power unit, a vacuum tank, and a rack power unit. Inside the launch pit, you will have the heart of the AXIS system, a rack, drill casings, drill head, and pipe laser. The drill head has a flat-face cutter which, combined with the laser guidance system, can complete bores with the on-grade accuracy you need. The head can be changed during installation to give the contractor a different cutter for different ground conditions.
Underground construction today is not cut-and-fill, it’s not trenches all the time, and it’s not disrupting everything in the neighborhood.Systems that achieve the required results have been designed by several companies. In fact, it’s clear from researching these companies and their commitment to better, less expensive to run, that the equipment does not stop with any single new product. Their company websites and catalogs are worth investigating. The first piece of homework is probably to decide the size of the hole, tunnel, or channel you require, and then to know how far you need to go. After that, I think you’ll find that the companies manufacturing underground equipment can give you a practical solution.