Steep, and hardly accessible jointed rhyolite tuff cliff faces surround a Castle in NE-Hungary, at village of Sirok. The assessment of cliff stability required the recording of cliff geometry. Traditional surveying was not possible therefore cliff faces were 3D modelled by GNSS supported terrestrial laser scanner and UAV The onsite engineering geological analyses included the identification of major lithotypes, joint- and fault systems. For the slope stability analyses field documentation of strength parameters (Schmidt hammer rebound values) and laboratory analyses of rhyolite tuff samples were also made. Mass parameters (densities), ultrasonic pulse velocity, water absorption, uniaxial compressive strength, tensile strength and modulus of elasticity were measured in dry and water saturated samples under laboratory conditions. Strength parameters were calculated by using Rocscience RockLab software, in addition to GSI values. The global cliff face stability was calculated by using the obtained slope geometries and applying Rocscience Phase 2 software. The stability of smaller sections of cliff faces was evaluated by using joint system data obtained in the field and calculated by Dips software. Both wedge failure and planar slip surfaces were analysed. The complex engineering geological and geodetic survey allows the identification of potentially hazardous cliff faces and the design of cliff face stabilisation (i.e. rock bolts, supporting structures). The present paper demonstrates the applicability of terrestrial laser scanner and drones in slope stability assessment, especially when hardly accessible cliff faces are present.

Recently, terrestrial laser scanning (TLS) has been used in the slope stability analyses (Assali 2014, Franconi 2014). It has been demonstrated that TLS is a useful tool in slope geometry detection. However, at hardly accessible cliff faces it is not possible to apply the TLS from ground. Additional methods are necessary to obtain 3D model of the slope and to generate a digital terrain model. One possible option is the use of unmanned aerial vehicles (UAM). The current paper brings an example where not only TLS but a combination of TLS with UAM was used to create a surface model.