To the depression of the apothem during the construction must be added the one caused by the weight of the pyramid. The modulus of elasticity of the blocks is about 60 GPa and the compression of those is negligible, less than 5 mm under the center of the pyramid; on the other hand, the surface of contact between two rows is surely contaminated by sand which give a heterogeneous support of a few mm thickness. The crushing from 1 to 2 mm under each of the 180 joints is sufficient to cause a depression of more than 200 mm in the center of the pyramid where the load is the largest and thus amplify the depth of the apothem on each face.
This crushing appears in three dimensions, the maximum is located in the center at the bottom of the pyramid to decrease, layer by layer, while going up to the top. At a same level, between two layers, crushing decreases from the center towards outside, it is thus larger in the middle of the sides directed according to cardinal points, with the apothems, than at the corners. Crushing mentioned previously made so that each flat surface between the layers forms a basin which imposes at the same time a vertical rotation and a slip towards outside on the overlying blocks. This rotation is visible with the horizontal joints on the faces of the intact facings, as on the Khafre’s pyramid.
The joints crushing, in the case of prevented block rotation or in the case of a too tightened adjustment, could very well have caused a progressive shearing, a rolling subjacent of the facing, starting from the base, in the center on sides where the vertical constraint is most important and the average distance from the center. The corners, as for them, more distant and less charged, would have sheared less quickly. This shearing would have then extended to the top while reducing its progression with the reduction of vertical load to finish along the corners, less requested. It is perhaps the reason for which the Khafre’s pyramid preserved its facing at the higher part, although damaged.
This rolling would have progressively delaminated the facing, deteriorated the finish and disturbed the ascending draft which would have become diffuse; at the same time, the pyramid would have lost its first vocation to become a monument.
Dessin : Dany Lavoie