Influence of weathering processes on the shear strength of siltstones from a flysch rock mass along the northern Adriatic coast of Croatia

Bulletin of Engineering Geology and the Environment - Weathering processes cause significant changes in the engineering properties of rocks. Slope instability in flysch rock formations along the...     

Complex landslide in the Rječina valley (Croatia): origin and sliding mechanism

This paper discusses the development of the Grohovo landslide on the north-eastern slope of the Rječina valley, the largest active landslide along the Croatian part of the Adriatic Sea coast. This complex retrogressive landslide was reactivated in December 1996. Thirteen separate slide bodies have been identified. The slide surface is considered to be on the upper flysch bedrock. Monitoring indicated that the magnitude of displacements was very different in time and space. The maximum movements were recorded on the upper part of the slope. The limestone mega-block and separated rocky blocks on top of the slope have also moved, which is not a typical phenomenon of the flysch slopes in the area of Rijeka.      

Impact of the wetting process on the hydro-mechanical behavior of unsaturated residual soil from flysch rock mass: preliminary results

Slope instabilities in the form of shallow and deep-seated landslides in flysch formations throughout Europe typically occur after prolonged periods of heavy rainfall. The Rječina River Valley, Croatia, is characterized by the presence of flysch material in the lower part of the Valley, where numerous historical and recent landslides have occurred. The weathering process and climate conditions result in a complex engineering geological profile of flysch slopes in the Valley, with unsaturated residual soil covering the slopes. To investigate the behavior of residual soil existing on the flysch slope under increasing water content due to the rainfall infiltration process, undisturbed soil samples collected at natural water content were tested in the modified direct shear apparatus. Under imposed stress conditions, samples of low hydraulic conductivity were subjected to a prolonged wetting process simulating the rainfall infiltration process in the field. The obtained results suggest that a gradual decrease of matric suction and an increase of water content resulted in an increase of displacement rates under constant shear stress, which was interpreted as a failure of samples in partially saturated conditions. A unique shear strength envelope expressed in terms of Bishop’s effective stress equation was found to be able to predict stress conditions at the slip surface at the time of failure, while the relationship between measured matric suction and water content closely matched with the main wetting curve. Although the testing results did not point out any special characteristics of residual soil from flysch rock mass behavior, the data about hydro-mechanical behavior of unsaturated residual soil from flysch rock mass, as well as similar fine-grained soils, are very rare and presented results would be valuable for further research. The presented testing procedure and obtained results are useful for studies of rainfall-induced landslides triggered in fine-grained soil materials in zones above the phreatic line, such as shallow landslides occurring in natural flysch slopes or in physical landslide models built in laboratories.

     

Decentralized planning and control for UAV–UGV cooperative teams

In this paper we study a symbiotic aerial vehicle-ground vehicle robotic team where unmanned aerial vehicles (UAVs) are used for aerial manipulation tasks, while unmanned ground vehicles (UGVs) aid and assist them. UGV can provide a UAV with a safe landing area and transport it across large distances, while UAV can provide an additional degree of freedom for the UGV, enabling it to negotiate obstacles. We propose an overall system control framework that includes high-accuracy motion planning for each individual robot and ad-hoc decentralized mission planning for complex missions. Experimental results obtained in a mockup arena for parcel transportation scenario show that the system is able to plan and execute missions in various environments and that the obtained plans result in lower energy consumption.