PETROGRAPHY, DIAGENESIS AND GEOTECHNICAL PROPERTIES OF THE EL-RUFUF FORMATION (THEBES GROUP), EL-KHARGA OASIS, EGYPT

The El-Rufuf Formation (Thebes Group) outcrops widely in Egypt. It is quarried as an ornamental building stone and used as slabs in walls an d floors. It is also important in foundation construction. The geotech nical behaviour of these rocks is commonly related to stratigraphical position, controlled by their petrography and textural and diagenetic features. The El-Rufuf Formation of Naqb Assiut, El-Kharga Oasis, cons ists of 63 m of micritic and neomorphosed limestones which are marry a t the base. Microfacies analysis of these limestones indicates an inne r to middle shelf open marine environment. The most common diagenetic features are neomorphism, silicification, dissolution and stylolites. There are clear relationships between the measured compressive strengt h of rocks and the facies and diagenetic features. Neomorphic sparry l imestone has the lowest compressive strength, while cherty biomicritic limestone shows the highest values. Micritic and biomicritic limeston es show intermediate values. Some anisotropism of compressive strength values is recorded in the stylolitic limestones and in the foliated m arry part of the formation. The present study reveals that the El-Rufu f limestones, according to Deere's (1968) classification, are low to m edium strength rocks with low modulus ratios (DL-CL), while the marry parts of the formation are low strength rocks with low modulus ratios (EL). The rocks of the marry part of the El-Rufuf Formation are unstab le with regard to water and therefore have a zero softness coefficient . (C) 1997 Elsevier Science Limited.