Introduction

This proposal addresses the problem of excavating, and cutting to size, granite monoliths for the half-scale version of Stonehenge planned for the Missouri S&T campus. The proposal will review the requirements in regard fo rock volumes, the current and proposed methods of quarrying granite and the anticipated costs for this venture, if undertaken by the Rock Mechanics and Explosives Research Center (RMERC). The rationale for our doing the work is thereafter appended.

Volume of Rock Required

It is currently anticipated that a one-half scale version of the original Stonehenge structure be created from Missouri granite. This will require the following pieces:

• 10 Triliton limbs each measuring 15 ft X 2 ft X 3-1/2 ft, volume 108.5 cu ft, weight 8.68 tons each
• 5 Triliton caps each measuring 7-5/8 ft X 2 ft X 1-3/4 ft, volume 26.69 cu ft, weight 2,510 lb each
• 30 Sarsen stones each measuring 5-1/8 ft X 1-3/4 ft X 1-3/4 ft, volume 15.7 cu ft, weight 2,510 lb each
• 2 Analema stones each measuring 9 ft X 3 ft X 2 ft, volume 54 cu ft, weight 8,640 lb each

The total volume of rock to be excavated is thus 1800 cu ft of granite for a total weight of 144 tons, approximately.

For the purposes herein addressed the rock must be cut to shape, although it is considered (by this author) that a quasi-rough finish would be more aesthetically pleasing than an exact wire saw or diamond cut finish. Nevertheless, an accuracy of &plusmn1/4 inch is considered important to the rock dimensions. This requires that the rock be considered as "finished" stone as defined by the industry, rather than rough stone. This point is made, since rough stone sells for $5-$8 per cu ft and finished stone, three to four times that amount, provided it can be cut, which brings us to an evaluation of granite slotting technology.

Conventional Slotting

Granite is normally quarried using thermal lances to cut a slot in the solid block. The slot is typically developed on the profile of a 20 X 10 ft or 20 X 40 ft block, to a depth of 10 ft. The underside of this block is then split, using a drill and blast system to create the bottom crack.

This large block is then either split, using small charges or hammer and wedge systems in the quarry, or is moved by derrick to a sawing station. Here the rock is located under large wire saws which draw a carbide paste over the rock, therby slowly cutting through it. These saws slice the rock into slabs to the required thickness for the monuments. They also remove the outer 3 or 4 inches of the block, which has been thermally weakened by the thermic lance (this is rejected.)

The slabs are then loaded onto horizontal conveyors which carry them to the working sheds. (Ths stone is, if acceptable quality, polished on one surface by being rubbed by successive mats carrying increasingly fine grades of carbides.) On each slab imperfect stone is marked and blocks of acceptable stone to a pre-ordered dimension are laid out on the block.

The block is split to the rough shapes in a hydraulic press. Final monument shapes are then either ground on the stone (for smooth sides) or hand-chiselled (for the rough-cut appearance.)

Individual decorations are then carved in the stone using sand-blasting equipment - either automatic for simple letters, or hand-held for intricate floral designs.

I have explained this procedure at some length, since it should indicate the extreme difficulty in cutting blocks, toothe size of the Trilithon monoliths from the solid, without leaving a series of half-collars from the holes required by the "hammer and wedge" or "pre-split blasting" technique. Further, the use of the thermal lance would create a weakened and unattractive face for the rock which should be removed. I do not believe that any of the rock saws using wire could easily cut the 15 ft dimensions of the Trilithon limbs. And the historic method of granite block excavation where vertical holes are drilled on inch apart to the desired depth and the remaining rib then removed by broaching, would, as well as being slow, give an undesirable surface finish.

The only method by which I can conceive of the rocks being cut to size, apart from the method herein suggested, would be to cut the required slots. (These slots would be created at a speed of 7-10 sq ft/hr.) Once the blocks were removed from the solid, then the weakened outer skin could be removed by a specially located diamond saw (the Coggins quarry in Elberton had one - it cost over $100,000 - but it has now, I believe, been abandoned as ineffectual.) To give the required roughened outer surface to the granite would then require hand-finishing with chisels. I believe that the estimate I have received from the Dakota Granite Company of $20/cu ft (for a total rock cost of $36,000, plus shipping of about $6,000), is not unreasonable.

High Pressure Water Jet Slotting

In November of 1978, following experiments at Rolla, a team from the Missouri S&T Rock Mechanics & Explosives research center carried out a demonstration on the use of water jets for cutting granite. This demonstration was carried out at quarries of the Elberton Granite Association in Elberton, Ga. (Figures 1 and 2.)

A water jet lance operating with a dual, balanced nozzle design cut a slot 18 ft long and up to 42 inches deep in this rock, a fine-grained grey granite. The slot was 2 inches wide and an excavation rate of 17 sq ft/hr was achieved at a jet pressure of 17,000 psi. The high pressure water was supplied from the quarry sump, through the portable high pressure pump which the Center operates.

As a result of that test, commercial equipment has been developed and is now available (at a cost of approximately $200,000) toothe granite industry. The University group has, however, virtually all of the necessary components of the system directly to hand. Specifically, we have the pumping unit and the hydraulic power units required to construct the traverse mechanisms. To understand what is required, it is necessary to grasp the procedure we wish to follow (Figures 4 and 5.)

It is intended to excavate a pan of rock approximately 25 ft X 25 ft X 3-1/2 ft from the solid, for the majority of the rock required (apart from the Analema stones.) In order to cut this rock, a single channel girder will form a guide and support rail, along which a rotating water jet lance, fitted with dual 0.049 inch diameter, divergent (at an angle of 30°) nozzles, will travel. The lance will be rotated by an adjacent hydraulic motor, which will simultaneously drive the advance mechanism, to ensure the correct incremental distance between nozzle rotation and advance rate.

Water to power the lance will be supplied, from the quarry sump, through the high pressure portable water jet pump, which the Center has.

At present it is anticipated, for the sake of calculation (based on Elberton experience) that the jet will traverse at 12-1/2 ft/min and that the nozzle will be hand-lowered 1/4 inch after each pass. (This latter feature may (a) be automated, (b) be increased, on latter assessment.) Thus a 42-inch slot will be cut in 336 minutes.

Allowing adequate time for setup of equipment, relocation, maintenance and other down time - an initial estimate is made of 1-1/2 days to cut a single slot in the granite 25 ft long (odd fractions are rounded off.)

It is anticipated that a series of cuts will be made to divide an approximately 25 ft square area as shown in Figure 4. The sequence of cuts projected are shown in Figure 5, and would allow the support of the Trilithon limbs until they are removed from the quarry (by crane.) An additional two slots, cut at the end (for a total of 12) would allow either for a spare or by cutting the blocks in four, give the cap rocks for the Trilithons. It may be better to cut and divide the first block in this manner to (a) give more room for maneuvering the bigger block with less risk of their falling off the ledge, (b) thus it can be arranged that a complete Trilithon (2 limbs and a cap) could be sent up from Graniteville at one time on a low-boy rented from Palmer in St. Louis. This could be done either at weekly intervals, bringing up the rock at the end of the week, or daily at the end of the work at Graniteville.

(It is suggested that Duncan at Pilot Knob might have a crane to load the truck and that Gabrielle be on hand in Rolla to unload and erect the rock as it arrives.)

Figure 1:Water jet slotting of granite, showing jets.	Figure 2:Water jet slotting of granite, showiing Missouri S&T-RMERC portable high pressure unit.
Figure 4:Slot layout in plan view - the slots will be 1-3/4 to 2 in. wide and 42 in. deep.	Figure 5:Face view of the quarrying operation, showing the sequence of cuts projected to protect the Trilithon limbs from damage. Slot 3 will be propped open once it is excavated, and the limb removed before slot 7 is made. The slots will be 1-3/4 to 2 in. wide.

Once the Trilithons have been removed, the Sarsen stones can be cut from the support pieces left on either side of the cavity. (They will actually be 2 ft high but this can be compensated for by burying the rock 3 inches in the ground.)

It is recommended that this procedure be adopted, rather than trying to extract and trim existing boulders and rock to shape, because of the simplicity, and thus speed with which the operation can be carried out. The resulting rock should have the required surface quality that no further treatment will be required once the rock has been excavated. It is further anticipated, in developing these costs, that the exposed bench at the Hayward quarry in Graniteville is used as the source of rock.

Figure 6:Granite showing drill collars left after excavation.	Figure 7: Slot surfaces cut by water jets in granite.

Figure 8:Conventional thermal lance cutting.	Figure 9:Conventional hammer and wedge quarrying (the block is already isolated at the bottom and sides of the block.)
Figure 10:The anticipated site is the ledge on the left of the picture with the metal tray on it.

Why should RMERC do the work?

Apart from the advantages of cost, and that it would be extremely difficult as well as expensive to create the monument blocks any other way, we feel the RMERC has another strong argument.

Water jet technology is the high technoligical innovation in the mining, quarrying, and civil excavation of the 1980's. At this stage it is barely entering commercial practice. The use of our crews and this technology will thus clearly demonstrate the leading position of this University in this area.