Effects of engineering geological properties of Gachsaran Formation gypsum on karst development (Khuzestan, Ramhormoz)

Karstification develops in gypsum easily due to high solubility. In this paper, determine geological engineering properties of Gachsaran Formation gypsum from Ramhormoz area and has been related with karst development by petrological and rock mechanic studies. ANFIS as combines fuzzy logic and neural networks in the form of neuro-fuzzy method were used for detect type of gypsum. Input data include uniaxial compression strength, tensile strength, durability Index and porosity percentage from 80 laboratory samples. ANFIS was built model that with little knowledge of rock, was able to predict the type of rock. Based on petrographic studies, Gachsaran Formation gypsum with two different textures has been considered, fine grained (alabastrine) and coarse grained (porphyritic) gypsum. The results indicate that texture, especially grain size and shape, is an important parameter controlling the differences in the mechanical properties of the two gypsum types studied. Based on intact rock engineering classification, alabastrine gypsum and porphyritic gypsum classification as DH and EH category respectively. Alabastrine gypsum than porphyritic gypsum has more unconfined compressive strength, tensile strength, solubility and brittle behavior so karstic phenomena such as dissolution sinkhole, karstic wells(jamas), natural roof and caves are more spread in them. Porphyritic gypsum than alabastrine gypsum have more slake durability and less strength so collapse and subsidence sinkholes are more spread also karren and pinnacles are bigger in them.