Parry Engineering the Pyramids

1. Auflage 2005
ISBN: 978-0-7524-9513-2
Verlag: The History Press
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 192 Seiten

In Engineering the Pyramids, author Dick Parry - a civil engineer - assesses the design of the pyramids and the likely methods of quarrying, transporting and raising the stones. Basing his ideas on both the archaeological record and the basic principles of engineering - as well as the results from a series of model and full-scale tests - Dr. Parry provides a challenging answer to this mystery of the pyramids. He suggests that ramps were used and the huge stones were transported and raised by rolling them, rather than using highly inefficient sledges beloved of Egyptologists. Engineering the Pyramids provides a rich and accessible account of the design history of the pyramids, the techniques and organisation needed to bring about these heroic feats of effort and engineering and fascinating insights into the reasons behind the pyramid design.

Autoren/Hrsg.

Parry, Dick

Leseproben

TWO

When Djoser’s engineer Imhotep undertook the task of converting the pharaoh’s intended mastaba into a much larger structure, he had no existing example of a mass masonry structure on which to base his design. This was the first massive masonry structure ever to be built. Although in common with all the pyramids, and indeed practically all other ancient Egyptian tombs, the Step Pyramid failed in its purpose of protecting forever both the pharaoh’s remains and the objects accompanying him in his afterlife, Imhotep succeeded magnificently in creating a structure both massive and stable, and one which remains substantially intact to this day. A modern civil engineer, armed with mathematics, mechanics and the laws of physics, plus millennia of building technology as guidance, might well adopt the same solution.

Initially, Imhotep built a four-step structure, but perhaps spurred by its successful completion, he extended it to six steps. This consisted of a 60m high central core of rough stone blocks with planar sides having an angle to the horizontal of about 75°, the core supported by a series of accretion or buttress walls lying against it, also with slope angles of 75°, and terminating at successively lower heights as distance from the core increased. This resulted in a stable structure of a stepped pyramid form, with the tops of the buttress walls, which outwardly slope downwards (presumably to shed water), forming the steps. With this example before them, builders of pyramids immediately succeeding this chose to adopt the same design, but the first two of these, that for Sekhemkhet close to the Step Pyramid and the Layer Pyramid about 7km to the north, were abandoned early in their construction, possibly because of the premature deaths of their intended occupants.

The second pyramid to be completed, or substantially completed, poses two questions. Why was it sited at Meidum, a remote area over 50km south of the capital Memphis, and why was it one of three constructed, or at least completed, for the IV Dynasty pharaoh, Snofru? The answer to the first question is likely to remain a mystery, but the second can be plausibly attributed to its collapse, which Snofru may have taken to be a bad omen, an indication from the gods of their disapproval at his having appropriated the pyramid for himself rather than completing it for his predecessor, Huni, for whom some Egyptologists believe it was originally intended. The damage to the pyramid that immediately followed its partial collapse was probably much less than is visible today, after four and a half millennia of assault by the elements on the weakened structure; and, even more important, after the destruction wrought by the quarrying activities to which Petrie, the ‘Father of Egyptology’, drew attention in his descriptions of the results of his excavations at the site. It is likely that the damage could have been repaired at the time of its occurrence to give a stable, if slightly modified, structure, but Snofru eschewed this course of action in favour of moving 45km north to construct the second pyramid attributed to him, at South Dahshur. In fact, if Mendelssohn, who spent ten years studying the Meidum Pyramid, is correct, the builders had already made considerable headway with the construction of this more northerly pyramid when the Meidum collapse occurred, the overlap in construction ensuring continuity in the utilisation of the workforce.

Imhotep extended the originally intended mastaba for the tomb of Pharaoh Djoser into first a four-step, then a six-step pyramid to create the world’s first major stone structure.

The buttress wall design pioneered by Imhotep in the Step Pyramid – with the height of the inclined walls decreasing with distance away from the core – led inevitably to the pyramid shape. Unfortunately, the interfaces between the walls, such as that shown here, introduced inherent weaknesses into the structure.

The buttress wall design of the Meidum Pyramid followed closely that of its Saqqaran predecessor, its initial seven steps subsequently being increased to eight. A decision made on, or very near to, its completion to add an outer coating layer of stones to give planar sloping faces, and thus produce a true pyramid, went disastrously wrong. It led ultimately to its present-day appearance, clearly visible from the Desert Highway: a massive stepped tower of stone protruding above an apparent mound of sand and rubble, which, in fact, consists mainly of the lower intact portion of the pyramid obscured by the sand and rubble which lie against it. The changes in design late in the seven- and eight-step construction phases introduced serious weaknesses into the structure, which led to the partial collapse. Towards or at the end of these construction phases the outer exposed step faces were smoothed off, either for appearance purposes or to shed water. These became incorporated within the structure as further construction proceeded, giving low-friction interfaces within it that introduced serious weaknesses. The collapse, when it came, may have been caused quite simply by the incumbent weight of the added outer surface layers, or it may have been triggered by a natural event such as an earth tremor or heavy rain. Bands of smoothed stones, originally intended as outer exposed faces, are still clearly visible on the surface of the stone tower.

Meidum Pyramid collapsed because the inherent weaknesses in the buttress wall design made it unable to sustain the weight of the outer surface layer, which was added to give smooth outer faces to the structure.

Buttress wall design for step pyramid and Meidum Pyramid.

The builders of the South Dahshur Pyramid adopted the same basic design with buttress walls as for the Meidum Pyramid, but again changes appear to have been made during construction, the initial structure having a base area smaller than that seen today, with slopes of perhaps 60°. Built over a clay layer rather than solid rock, the pyramid exhibits clear evidence of uneven settlements leading to structural distress, manifest in the cracking and block displacements seen in the tomb chambers and their access passages and manifest, too, in the great cedar beams which the ancient builders inserted to shore up and reinforce the upper burial chamber.

Unable to stop severe movements occurring within the structure of the South Dahshur (Bent) Pyramid, arising from weak foundation strata, the builders hastily finished it off at a flatter angle.

Alarmed by the increasingly obvious signs of movements as construction progressed, and perhaps mindful of the Meidum collapse, the builders extended the base dimensions in order to surround the initial structure with a girdle of stone sloping at a reduced angle of slightly less than 55°. At the lower levels these stones were set with an inward slope, presumably in the belief that this would give added stability, suggesting that the builders were unaware that they had foundation rather than structural problems; when the movements continued they reverted to laying these outer stones horizontally in the higher layers. Eventually, when their various measures to arrest the movements failed, they finished the pyramid off at the lesser slope of 43.5° to reduce further weight additions on the defective structure. It would have been more logical to have finished it as a flat-topped structure, but perhaps the need to achieve a pyramid shape, however flawed, was too entrenched even to contemplate this.

Inward sloping outer casing blocks and smoothed facing of South Dahshur (Bent) Pyramid. Much of the smoother outer facing of this pyramid remains intact.

The depth of concern on the part of Pharaoh Snofru and his advisors when the builders, probably with reluctance and after some delay, confessed to the continuing problems they were having at South Dahshur, can only be imagined, the Meidum Pyramid having already been abandoned after its catastrophic failure. A solution had to be found, and quickly. Great civil engineering structures and works around the world today, including bridges, dams and buildings, owe their success in no small part to lessons learned from past failures. It is greatly to the credit of these ancient builders that they learned the lessons of their mistakes, and those of their predecessors at Meidum and South Dahshur, enabling them to produce a stable design of true pyramid form.

Abandoning the concept of a central core and buttress walls, the builders now adopted a coursed form of construction, building the pyramid up tier by tier, each tier consisting of a single layer of blocks uniform in thickness across the full width of the structure, but with some variation in thickness from layer to layer. Greater care in dressing and placing the blocks reduced the need to fill gaps between blocks, particularly in the interior masonry, with rubble or clay mortar, and with only the occasional gypsum mortar. Apparently exercising understandable caution, the builders adopted the conservative slope angle of 43.5° used to finish off the Bent Pyramid, although the flatter slope angle may also have been adopted to ensure rapid completion of a structure fit to receive the body of the god-king, rather than solely for considerations of stability.

With the successful completion of the North Dahshur Pyramid the builders of the Great Pyramid on the Giza plateau for Snofru’s son, Khufu, returned to their preferred slope angle of 52°. This represents a height to base ratio equivalent to four diameters of a cylinder to its circumference, a characteristic that has prompted some modern writers...