[en] With its production of several million tons per year the Lyulyakata open pit limestone quarry, located in NE
Bulgaria, is the main raw material supplier for soda ash and cement production in the area. The expansion of
the quarry in-depth and its long-term sustainable development require an assessment of the possible slope
instabilities that are closely controlled by the geological and geomechanical properties of the deposit.
Geomechanically the micrite and bio- to lithoclastic limestones are characterized by unconfined compressive
strength (UCS) and tensile strength (UTS) tests. The UCS of the bio- to lithoclastic limestone ranges between
24 MPa and 28 MPa while its UTS is between 3 and 5 MPa. In contrast, the micrite samples demonstrate UCS
between 98 MPa and 151 MPa. The UTS predominantly varying from 6 MPa to 9 MPa. The moderate strength
of the bio- to lithoclastic limestone is explained by its porosity of over 20 % whereas the micrite limestone
(porosity 8 %) exhibits a high strength due to its better cementation. The Rock Mass Rating (RMR89) analysis
revealed that the massif is classified as Good quality. Only at the near-surface level, due to the impact of the
weathering processes, a Fair quality could be expected.
The high strength value of the dominant in the quarry micrite limestone and the geometry of the typical for it
structural blocks, controlled by lithology and regional geology stress regime, could be used as favorable
features for the sustainable extension of the quarry. Following the orientation of the natural rock mass
fragmentation from the pit slope will contributes to its sustainable further development.
