ارزيابي ژيومكانيكي واحدهاي رسوبي سازند آغاجاري در پهنه زاگرس

Geomechanical evaluation of sedimentary rocks units of Aghajari formation in Zagros zone

Recent sediments of Aghajari formation are dominating parts of south and southwest of Iran. This has led to the fact that many of the important developing projects are located on this formation. Therefore a thorough understanding of geomechanical characteristics of various units of this formation could profit such projects at various stages of implementation. Furthermore, these studies would support formation of a geotechnical and geomechanical data bank that can be used in preliminary studies of engineering structures and preparing large scale engineering geological maps of the region. To undertake the proposed research systematically, the Zagros range was divided in three district of northwest, central and southeast. Then the geomechanical characterizations of Aghajari units were undertaken based on the results of rock mechanics laboratory tests and the information acquired from the executed projects in the region. Beside this, durability test of every unit of this formation also was carried out to evaluate the weatherability. The analyses of the test results yielded a comprehensive set of coefficients to evaluate the various mechanical strengths from some simple inexpensive laboratory tests, and the geomechnical behaviors of these rocks are studied. The strength conversion factors have been presented implicitly. The detailed triaxial tests revealed the principal stress response of the total set of the representative samples with respect to various confining pressures. Meanwhile, shear strength parameters c and 9 were determined and the transition condition from brittle to ductile behavior evaluated. An assessment of the results inferred that the rock units of Aghajari formation in central part of the study area have higher strength parameters compared to two other adjacent units. This conclusion may lead to this hypothesis that due to confinement in two strike slip faults restriction, Kazerun and Hendijan faults, these rocks have undergone the diagenetic process more rapidly and intensely. The detail of the undertaken studies is presented in the paper.