The Adam-Pirie Quarry is the source of Rock of Ages’ dark gray granite.
This first in a two-part article on Vermont’s granite industry, the latest in a monthly series, is provided courtesy of the Vermont Granite Museum. Its origin springs from my and my wife’s decision to design and erect our monument before our deaths and differs from previous historical articles in that it describes the current operations at Rock of Ages. The story of our monument is told from design to quarrying to finishing to setting in the cemetery.
By Paul Wood
Our monument is of blue-gray (Round Seal) granite from the Rock of Ages’ Adam-Pirie Quarry — a “mother lode” of granite with an apparently inexhaustible future supply.
The monument is a double tablet with double exaggerated serpentine top. The exaggerated serpentine (with a 5-inch drop) resembles 19th-century slate and marble tablets. The monument measures 60 inches tall (with 18 inches below ground) by 44 inches wide by 6 inches deep.
The tablet is steeled (dusted) on all surfaces. There are two shape-carved lamps of knowledge (the symbol of enlightenment and the guiding light of scientific inquiry that dispels the darkness of ignorance) centered under each serpentine top.
The lettering is cut in Classic Roman font on the front of the tablet and consists of full names and full dates of birth. The full dates of death will be added below the dates of birth.
Since selecting a monument is a once- or twice-in-a-lifetime event, most people need guidance in designing a monument even though they may have seen a monument they like in a cemetery. We were fortunate to have the help and guidance of Steven Benoit, Rock of Ages’ memorial studio manager.
There are many options — type of granite, monument shape and size, finishes, symbols and ornamentation, text (names, dates, verse, etc.), text fonts and sizes, and placement of the lettering and ornamentation. Pre-need customers like us (those who purchase a monument for themselves) make up about 20 percent of ROA’s customer base. We wanted to select a monument design that represented our taste and hoped to spare our children this task at a probably difficult time for them.
ROA uses two computer-aided design programs — RockCAD (ROA designed) and Monu-Cad — to help customers visualize monument designs as they evolve.
There are about 50 letter fonts available in the design software. Although we thought the Classic Roman font worked the best for our names, there are a number of other popular fonts, including Modified Roman (Classic Roman redesigned so all the letters have equal value), Condensed Roman (good for small lettering and tight spaces), and Vermarco (a san-serif font with a condensed value). Sometimes a softer font with more script-like flow is used for a verse.
A draftsman prepares a full-size drawing including lettering and decorative carvings. In our case, the draftsman was guided by a photo of a hand-carved lamp on my wife’s parent’s monument. The full-size drawing was mailed to us for our approval and signature.
Barre is blessed with virtually unlimited deposits of gray granite that in the 20th century became the world’s standard monumental gray granite by which all others were judged.
Although some granites weather poorly and stain deeply, Barre grays carve well, are durable to the elements, do not stain easily, and are cleanable.
There are three grades of granite quarried in Barre based on color and consistency of grain: light gray, medium gray, dark blue-gray.
Barre medium and light gray granite is quarried at the Smith Quarry. Blue gray, from the Adam-Pirie Quarry, is the darkest, has the finest grain, polishes the best, and is the best for shape carving. Medium gray costs about 10 percent more than light gray and dark blue-gray costs about 10 percent more than medium gray.
ROA-branded Barre medium and dark blue-gray granite is warranted against cracking, checking, discoloring or fading — backed by a trust fund managed independently from ROA. Light gray is mostly used for markers and non-monumental applications.
Other non-Barre ROA granites that are popular for monuments are American Black (Pennsylvania) and Laurentian Pink (Canada). Some of the non-Barre granites can cost up to twice that of the Barre gray granite due to the low recovery rate of these granites. The recovery rates are approximately 6 to 8 percent for American Black compared with 15 to 20 percent for Barre gray granites.
Recently more stone has needed to be quarried at the Adam-Pirie Quarry since the recovery rate has dropped, and as a result drilling has become a bottleneck. The quarry has gone to two shifts because of the limited work area for high quality stone.
In 1882, James K. Pirie and George Lamson established the firm of Lamson & Pirie and purchased 12 acres of land in Williamstown from a farmer by the name of W.S. Flint. The land was strewn with large granite boulders, giving hints of the extensive granite deposit below that was developed into a quarry and passed into the sole ownership of Pirie in 1902.
This was Barre’s darkest and most expensive granite with a high percentage of feldspar. Its uniform texture, excellent polish, and durability made Pirie granite highly sought after for monuments. In 1955, the Pirie family sold the quarry to ROA.
The Pirie Quarry is now closed — not running out of granite but, rather, the remaining deeper granite could not be quarried economically. In 1974, ROA opened the Adam-Pirie Quarry in Williamstown adjacent to the old Pirie Quarry with virtually identical granite. Butch MacRitchie is currently the supervisor at the Adam-Pirie Quarry.
Quarrying technologies at ROA are constantly changing and improving. The following is an overview of the technologies currently in use at the Adam-Pirie Quarry. (The ROA quarries at Woodbury and Bethel are similar in operation.)
The most important quarry equipment consists of slot drills, lift hole drills, double deep hole drills, down-the-hole hammer (DTH) drills, wire saws, inflatable water and air bags, front-end (wheel) loaders, and a 250-ton steel boom derrick used to move equipment and to lift granite from sumps (new development areas).
The pneumatic slot, lift hole, and double deep hole drills were manufactured by Tamrock of Tampere, Finland. ROA uses water to mitigate airborne drilling dust and wire sawing needs water to both flush away the cuttings and to keep down the dust. The required water is pumped from the adjacent, now-flooded old Pirie Quarry.
Currently, both the Adam-Pirie and the Smith Quarries are supplied by large efficient stationary reciprocating (piston) compressors located in the old central compressor house. There are some energy losses in long pipes from the compressor house but there is the compensating benefit that the pipes form a large reservoir of compressed air.
Since the large stationary compressors are expensive to operate, the plan is to use small screw-type electric compressors in the near future and if more capacity is needed, the less-efficient portable diesel-powered compressors will also be used.
Rotary screw compressors employ two meshing helical screws, known as rotors, to compress the gas. The smaller capacity of screw-type compressor is more in line with the reduced compressed air needs (only a single pneumatic drill may be operating at one time) due to the increased usage of wire saws.
Quarrying at the Adam-Pirie Quarry is primarily carried out with diamond wire saws. A very large block called the “bench” — about 40 feet by 30 feet by 20 feet high — is the first to be released from the quarry wall by wire sawing.
For stone that’s tight (that is, has no seams, beds or fractures running through it) and won’t fall apart, the back, side and bottom are wire sawn to release the block. At the Adam-Pirie Quarry, slot drills and lift hole drills (with 1 and 7/8-inch diameter drill bits) are used to bore the vertical and horizontal wire saw pilot holes, respectively.
Only three pilot holes are required to release each bench, joining at right angles at a common point at the lower rear of the bench: (1) a horizontal hole along the bottom of the bench’s back, (2) a horizontal hole along the bottom of the bench’s attached side, and (3) a vertical hole along the back of the bench’s attached side.
Holes (1) and (2) are used for sawing the bottom, (1) and (3) for the back, and (2) and (3) for the side. First, a string tied to a cork (or ear plug) is flushed through the pilot holes with water and then the string is used to pull through the saw wire. The wire is formed into a loop and reeved around a pulley driven by a motor mounted on a track.
To keep the wire under constant tension, a set of gears moves the motor back along the track an adjustable distance from the stone for every revolution of the wire loop. For the horizontal undercut, wedges are used to prevent the wire from binding up.
With the DTH drill, purchased from Marini Quarries Group of Villadossola, Italy and other manufacturers, the drill hammer actually follows the bit into the hole. The drill consists of a hammer at the end of a hollow 2½ to 3-inch steel tube with a slowly rotating carbide button bit that is slightly larger in diameter than the tube.
The drill is powered both pneumatically and hydraulically. With ordinary drills, holes more than 25 to 30 feet deep tend to wander due to the bending of the drill shafts and looseness of the couplings, whereas the DTH drill is much more accurate allowing a pair of pilot holes to accurately meet at their bottoms. Holes that don’t perfectly meet leave sharp edges that can cut the fishing string or damage the saw wire.
Holes can be up to 40 to 60 feet deep. Some of these drills are self-contained and mounted on tracks and so they can be driven right up to the location to be drilled. The Adam-Pirie Quarry started to use the DTH drill in 2012 and is using both the DTH drill and standard drills for pilot holes.
The bench, weighing about 2,000 tons, is too large to move and must be further subdivided by wire sawing along the bench’s hardway lines — the direction of most difficult cutting or splitting.
Pilot holes are drilled horizontally along the hardway at about 5-foot intervals along the bottom of the bench, and then either vertical pilot holes are drilled along the side of the bench to meet these holes or water bags are used in the side channel to slide the entire bench out several inches to make the ends of the horizontal holes accessible for fishing through the saw wire.
The water bags are thin enough that they can fit into channels made by a wire saw. The bench is then wire sawn into eight large slabs measuring approximately 30 feet by 20 feet by 5 fet. Since wire saw channels are only ¾ inch wide as compared to 3 to 4 inches wide for the older drill or burner technology, wire sawing saves a lot of stone — about a quarter cubic foot of granite for every square foot of stone sawn. Also, the smoother sawn surfaces allow more accurate quality inspections by the stone grader.
Water bags consist of two thin steel plates welded together around the edges with a small valve in one corner. The bag is inflated by water pushed through a pressure (power) washer.
Water bags are recycled as scrap after a single use since the steel is permanently deformed. Because of the valve, water bags can only go part way into a channel. A water bag is normally placed at the top of a wire saw cut and another at the bottom to prevent a slab from breaking in half.
Each of these slabs is laid over, a process called “tipping the line,” “laying over the line,” or “turning the cut,” starting at the front of the bench and working toward the back. Padding is used to cushion the fall of the slab. Water bags can push stone a maximum of about 4 or 5 inches which usually is not enough to tip the line.
If the line is not too high, a front-end loader with a toothed tipping boom is used to pull the line over. If the line is too high, then air bags with a longer expansion capability (up to two feet) are used to tip the line. Air bags are made of a rubberized fabric-like material and are inflated with 100 psi compressed air. Air bags can be used multiple times until they sustain a leak caused by a cut.
The large slabs can be split with traditional plug drills and feathers and wedges since the splitting is along the easier rift and lift directions. A grader/inspector lays out the slab — avoiding discoloration, swirls, beds, and other stone defects — to recover the maximum amount of stone possible, up to eight saw blocks if all the stone can be used.
The lower a quarry’s recovery rate, the longer it takes to lay out a slab. Each saw block measures about 5 feet by 5 feet by 10 feet (about 20 tons) and is managed by a front-end loader.
Hence, there is no need for explosives except for the infrequent breaking of the hardway lines of a keyway (the first bench removed from a long step-shaped wall), after which quarrying can move horizontally in both directions along the step without explosives.
Explosives are also required for the rare cutting of a sump — a swimming pool-shaped hole cut so quarrying can spread out horizontally from a new lower layer. The reduction in the use of explosives has advantages in both cost and safety. The wire saw has made this possible by its ability to saw the bottom of blocks which had previously been detached by explosives.
The Adam-Pirie Quarry was the first in Barre to be reconfigured into a drive-in quarry in which a network of roads was built to allow mobile cranes, front-end loaders and trucks to access the bottom of the quarry.
The front-end loaders go right up to the working quarry face and haul saw blocks to a block yard at the edge of the quarry. Waste piles of small broken up material are hauled away in bucket loaders and back dragged into an area away from the active quarrying.
Each saw block is uniquely numbered as to its quarry location and size. As blocks are needed or sold, they are loaded by front-end loader onto flatbed trucks and transported to the ROA finishing plant or the customer.
Paul Wood writes on behalf of the Vermont Granite Museum in Barre.MORE IN Central VermontMONTPELIER — Vermont’s Teacher of the Year, a Capital City teacher, was honored by the president ... Full Story
- Most Popular
- Most Emailed