Testing the shear strength of soft rock at different stages of laboratory simulated weathering Determination of the change in strength based on simulation of weathering process in laboratory conditions is described in the paper, using marl samples taken from flysch formations in the region of Dalmatia. The testing has revealed that the proposed weathering simulation in laboratory can be conducted within acceptable time frames. Because of the observed change of shear strength parameters as related to values corresponding to the strength of material described as soil, it is sometimes necessary to use soil testing devices so as to take into account the load range applied in individual types of testing devices.

Soft rocks in various forms of marly materials have an important role in the geological structure of Dalmatia (Croatia) and Budapest region (Hungary). These materials can cause serious problems in design and construction, due to their complex behavior under atmospheric conditions. For the purpose of better understanding soft rocks behavior and their properties, a database with approximately 600 samples collected throughout Dalmatia was made and collated along with 260 samples from the Budapest area. Based on the collected data, 30 regression analyses were performed among 14 material properties, and eight different types of linear and non-linear correlations with high coefficients of determination were selected, which connect the important mechanical properties (uniaxial compressive strength and Young’s modulus) with physical properties of marls (porosity, dry unit weight, and ultrasonic pulse wave velocity). Most of the determined relations show symmetry between the marls from the Dalmatian region and the Budapest region, and the relation between dry unit weight and uniaxial compressive strength asymmetry can be observed between the marls with different origins. Obtained correlations may be used in cases where little or no information on geotechnical parameters is available, or where results need to be verified due to the problems present in soft rock testing.

Steep slopes in soft rock are characterized by their susceptibility to instability (rockfall, rockslide) due to weathering and erosion of the slope surface. This article deals with the problem of adapting to the increasing height of the scree slope. The construction of a retaining wall in a scree slope in front of a slope of soft rock with a steep face, where a very rapid weathering and erosion process of weathered material takes place, and the simultaneous deposition of material in front of the steep slope is a common solution. Changes in the geometry of the slope and the front scree are taken into account, and at the same time, sufficient safety against rockfall must be ensured. The analysis is shown on a specific example of a steep flysch slope near Split, Dalmatia. The retaining wall solutions are compared in terms of function, cost and sustainability. The construction of a single colossal, reinforced concrete retaining wall shows that this solution is not feasible due to the high construction costs and CO₂ emissions of the retaining wall. A model was therefore developed to determine the height of the retaining walls for different construction time intervals and distances from the original rock face. The critical failure modes were investigated for various retaining wall solutions with regard to the highest degree of utilization of the resistance, which also allows the cost-optimized solutions to be determined. By building two or more successive retaining walls at suitable intervals and at an appropriate distance from the original rock face, construction costs and CO₂ emissions can be significantly reduced.