Shear strength properties of cut slopes excavated in jointed rock mass

Definisanje parametara čvrstoće na smicanje ispucalih stenskih masa predstavlja jedan od najzahtevnijih zadataka mehanike stena. Geotehnička istraživanja su uglavnom ograničena na rezultate laboratorijskih ispitivanja malih makroskopski homogenih uzoraka, sa kojih se vrši ekstrapolacija rezultata na terensku razmeru. Ispitivanja se mogu vršiti in situ, ali su i ona ograničena veličinom korišćene aparature i mikrolokacijom na kojoj se vrše ispitivanja. Pored toga, moguće je vršiti različita ispitivanja na fizičkim modelima, koja su veoma složena i skupa. Ekstrapolacija podataka sa malog uzorka na terensku razmeru daje mnogo bolje rezultate u mehanici tla, gde se materijal sa zadovoljavajućom tačnošću može smatrati kontinualnim i homogenim. Kod čvrstih stenskih masa, usled prisustva velikog broja pukotina, javlja se problem diskontinualnosti. Zbog ovoga, rezultati dobijeni na intaktnim uzorcima mogu biti od ograničene upotrebljivosti ukoliko se ne poznaju karakteristike ispucalosti stenske mase. Da bi se definisali parametri čvrstoće na smicanje stenske mase potrebno je primeniti neku od postojećih klasifikacija, koja kombinuje karakteristike ispucalosti i parametre intaktnih uzoraka. Ovde se posebno ističe GSI sistem, jedina klasifikacija koja je sastavni deo jednog (Hoek-Brown-ovog) kriterijuma loma. Ona je subjektivna, pa se u disertaciji daje predlog kvantifikacije GSI dijagrama za fliš preko koeficijenta SCR, kojim je definisan kvalitet zidova pukotina. Nakon otvaranja kosina dolazi do promene naponskog stanja i izlaganja stenske mase dejstvu atmosferskih činilaca. Ovi faktori mogu dovesti do omekšanja, tj. snižavanja parametara čvrstoće na smicanje u vremenu. Zbog toga, za razmatranje dugoročne stabilnosti, nije dovoljno definisati parametre samo u trenutku otvaranja kosina, već je potrebno odrediti ih i u nekom trenutku nakon otvaranja kosina...Determination of shear strength parameters of jointed rock mass is one of the most demanding tasks in the field of rock mechanics. Conventional geotechnical investigations are usually restricted to testing visually homogeneous laboratory prepared samples of small size. Results are then extrapolated to the field scale. Tests can also be performed in situ, but then, they are dependent on the size of the equipment and test location. Besides, it is possible to perform studies on physical models, which are very complex and expensive. Direct data extrapolation from small laboratory scale to the field scale is more and less applicable in soil mechanics, whereas material can be reasonably assumed to behave as homogeneous and continuous. Due to presence of large number of joints, rock material is considered discontinuous, thus the results obtained on intact samples could be of limited use unless joint properties are known. In order to define shear strength properties of jointed rock mass, it is necessary to apply some kind of existent classification system which combines intact and joint properties. The emphasis is here given to GSI system, the only classification which is the part of one shear strength (Hoek-Brown) criterion. GSI classification is rather descriptive in its original form, thus an effort is placed on quantifying the GSI chart for flysch by means of SCR coefficient. After the excavation, stress state is altered and the slope face is exposed to weathering process. These factors can lead to slope deterioration and softening i.e. decrease in shear strength with time. In order to properly consider long-term slope stability it is necessary to determine shear strength parameters in different time periods after the excavation of cut. The purpose of this dissertation is to define shear strength properties of heterogeneous jointed flysch and braided river deposits (Permian red sediments), with interchanging siltstone and sandstone lithologies..