The tombs of Djehuty and Hery (TT11 and TT12) are excavated in a carbonate sedimentary sequence of Eocene age (Ypresiense, 53-46 M.y.), in particular the lower member (Member I) of the Thebes Formation.
The sequence consists of about 38 meter banks or levels, of varying thickness (dm-cm to meters) mainly of massive or nodular limestones. A subdivision into 5 intervals based on the observations made in situ has been made (Fig. 4 y Fig. 5). The limestone is very fine grained and porous (chalk type), consisting predominantly of the remains of calcareous nannoplankton (mainly coccolithophores) and microplankton (mainly foraminifers) with abundant fragments of mollusks. Locally there are slightly dolimitized levels, especially in Section 3. Sections 1 and 3 also show marly levels (higher proportion of phyllosilicates).
Rocks in the funerary complex of the Tomb of Djehuty are porous and have low mechanical strength. This makes them very susceptible to alteration by salt crystallization. The rocks of the tomb are active to retention and transport of solutions. The water inside the rock is full of ions in solution. When the rock dries precipitation of soluble salts occurs (mainly gypsum and halite). The rocks of the tomb have little resistance to the pressure generated by the salt crystallization and, therefore, are not very durable.
The rocks have low stability in its role as a host-rock of the Tombs. The presence of a dense network of fissures intensifies its low mechanical strength. This favors an anisotropic mechanical behavior that causes fracturing in blocks and subsequent collapse.