A few items from the EEF:

Niek de Haan 2008; "The shabtis of the Prophet of Amun "Hor""
pp. 49, PDF, 13.6 MB
http://www.shabticollections.com/JPGgeschrinkt/horfinal30-8.pdf

Raynaud et al.; "Geological and Geomorphological study of the
original hill at the base of Fourth Dynasty Egyptian monuments.
Etude géologique et géomorphologique de la colline originelle à la
base des monuments de la quatrième dynastie égyptienne".
PDF 5,6 MB
http://halshs.archives-ouvertes.fr/docs/00/31/95/86/PDF/PyramidsSR.pdf
"Rock foundations of the Kephren and Kheops pyramids are
examined in comparison with other Fourth Dynasty monuments:
the Sphinx, Queen Kentkawes' mastaba and the Abu Rawash
pyramid. This study is based on geological and geomorphological
observations, visual observation, and photomontages. Results,
correlated with those of former studies, demonstrate the existence
of natural hills used as substrata in the construction of the two great
pyramids. The minimum volume of these hills can be estimated at
12% and 23% respectively of the volumes of the Kephren and
Kheops pyramids. The use of worked rock hills appears to be
a characteristic of the construction methods under the Fourth Dynasty."