SHEAR RESISTANCE OF FISSURED NEOGENE CLAYS

Two types of fissured Neogene clays (SM and WB) were tested in the lab oratory using undisturbed and reconstituted specimens. Although of sim ilar age, the clays differ in their geological history: SM clays were deposited in a marine environment, WB are lacustrine clays with a comp lex tectonic history. The index properties of both clays are similar a nd, accordingly, their strength parameters are mutually close. Test re sults of the more compact and less wet clay (WB) are affected by the s ampling and trimming procedures, especially for 38 mm diameter specime ns. Although the behaviour is similar, the origin of fissures is diffe rent. For the SM clays, weathering is the main cause and fissuring rea ches a depth of about 20 m. WB clays are dissected by macro- and micro fissures originating as the result of tectonic processes and volumetri c changes (effect of the coal formation underneath the investigated ma ssif). Cementation of some samples was found and the transition from c lays through cemented clays to claystones (soft rocks) is speculated.