Raising an Obelisk: Part 4

On Sunday, August 29, we filled the box with sand and finished the ramp. Granite blocks and gravel buttressed the sand box. Late in the day the obelisk was laid with its center of gravity over the pivot block on the bearing wall. Next day, we rigged the obelisk, tensioned the 3-in. steering ropes and began to lower the stone. Portal captains Wyly and Andy directed two teams made up of students from the Massachusetts College of Art and National Guardsmen from Hanscom Air Force Base. Through the 4x5-ft. portals on either side, the sand was symmetrically removed with hoes to a line of workers who carried the sand away in baskets.

The sand had been preheated to 160 degrees and delivered (still hot) absolutely dry to assure free flow. As sand was removed, the sand remaining inside the box flowed downward toward the portal consistently maintaining an angle of repose of 35 degrees. We used this natural slope to support the weight of the obelisk, and the fluid quality of the flowing sand to gently rotate the obelisk to the turning groove. As the sand flowed out of the sand box, two symmetrical slopes formed a ridge down the center of the box in line with the obelisk, and as the ridge descended, the base of the obelisk came down with it, and the pillar gradually rotated around the pivot block above. We had learned from our models that when sand is removed even one scoop at a time, the obelisk moves in turn. This provided very precise control of the process.

After every five degrees of rotation, Jim Kricker measured the profile of the sand to record the relationship between the angle of repose and the position of the obelisk. By the end of the day we had reached 45 degrees. Mark Lehner observed that this was already greater than any of the previous attempts and things seemed completely under control. Looked like a good time to stop for the day.

On Tuesday, we continued lowering the obelisk, knowing that rotation beyond 45 degrees would entrain rope stretch. The distance from the pivot block above to the turning groove on the pedestal below had been calculated by taking the distance from the base of the obelisk to its center of gravity (14 ft., 1 in.) and then adding an allowance for rope stretch based on our testing plus a generous safety factor. (Overshooting the turning groove cannot be corrected and therefore was not an option.)

The workers on the hoes maintained tremendous control on the symmetry and the sand flow. Every scoop had an effect on how the obelisk moved. The actual placement of the symmetrical hoes in relation to the toe or heel of the obelisk was critical in controlling rotation versus forward slippage as the stone moved closer to the final 75-degree angle. Casual removal of sand could result in disaster. Our obelisk team remained focused and slowly piloted the stone onto the stair-stepped bearing wall at 75 degrees, resting on 20 in. of sand directly above and in line with the turning groove. Coming in 20 in. high meant that we had had far less rope stretch than we anticipated. The sand had carried a greater load than we had expected. Hurrah! We did not overshoot the target.

Now the brake-release method would be put to use. The two brake release teams were led by Al Anderson and Jim Kricker, while Grigg Mullen and I went inside the sand pit (facing page) to remove the final 20-in. cushion of sand between the obelisk and the pedestal stone. Simultaneously, the two ends of each rope were released in small increments, repeated by the next pair of ends until all three sets of ropes had been equally released. This cycle of release was repeated again and again as the sand was removed and the obelisk slid down the 75-degree pitch of the bearing wall until it came to rest in the turning groove. The brake release method was very safe and verified our guided rotation theory.

The next morning, we removed the saddle and the steering ropes from the obelisk and the brake logs. We packed up our tools and went home until our return 10 days later for the final pull. During that period, the sandbox and remaining sand were removed. The obelisk rested safely in the turning groove and against the bearing wall, fully rigged and ready to be raised the last 15 degrees. When we returned, on a beautiful, crisp, clear fall day, nearly 200 eager pullers from the Massachusetts College of Art, Fletcher Quarry, Hanscom Air Force Base and the film company joined the obelisk team to complete our task. We spent the morning on final layout of pulling ropes. Two opposed lateral brake lines led from a central harness at the pyramidium to deadmen at the sides, and two brake lines led aft to the brake logs. Four forward pulling lines gathered into a single braid at the harness. The braid would avoid any twisting caused by unequal line pull.

Our experience in Aswan demonstrated the importance of having a unified pulling force. The creation of such a team reenacts a significant feature of Egyptian building history. Pulling the obelisk to 90 degrees is a delicate operation. At 75 degrees, the obelisk has a high and forward center of gravity. After the initial pull towards upright, the load diminishes rapidly. At 86.5 degrees, the obelisk develops a forward motion. Lack of attention might result in the ultimate disaster. We invited the Guild's Joel McCarty, an expert in on-the-spot group management, to bring his hand-raising experience to direct an on-site pulling school. Using our 6-ft., 300-lb. concrete obelisk, the pullers learned fingertip control and experienced firsthand the physical principles necessary for the job.

The pull would be divided into two parts. The first would bring the obelisk from 75 to 86.5 degrees, to be held there with a propping wedge dropped down between the shaft and the bearing wall. The second pull would bring the obelisk to 90 degrees. Joel organized his trained pullers into four teams of 28 people, each team on one rope, standing (for safety) about 100 feet ahead of the obelisk. Grigg Mullen was nominated Single Voice to direct the 112 pullers. Al Anderson and Jim Kricker, our brake and alignment team, released tension on the rear brake lines simultaneously as the 112 pullers tugged the obelisk off the bearing wall. Laura and I lowered the propping wedge between the bearing wall and the back of the obelisk to hold the space we gained as the obelisk moved higher and higher to the crucial 86.5-degree angle. Single Voice gave the word to release the lines to give the pullers a rest before bringing the stone to vertical. Grigg then surveyed the site, refocused the troops and called the final pull. All 112 pullers pulled as one while the brakemen eased off tension on the rear brake ropes. The obelisk moved with the grace of a magnificent bird and without a single sound gently came to rest on its solid base. Our hand-raising Egyptian-style was now complete. -RICK BROWN

Rick Brown teaches at the Massachusetts College of Art in Boston. His last adventure with NOVA and the Timber Framers Guild unfolded last year at Castle Urquhart in Scotland, where he organized the precision casting of 14,000 pounds of lead to be mounted on the throwing arm of a fixedcounterweight trйbuchet. PBS's "Medieval Siege" will air February 1, 2000, and "Pharaoh's Obelisk" will air February 8.