During the (two-years) Project, we plan to investigate two selected sites: one well-developed recent slide site (Horozovina, near Tuzla town, BiH) and one that was active in the past or is likely to be activated in the future (Valjevo, Serbia). Ground methods (seismic and electric) will be used in order to compute full set of elastic parameters and map layer boundaries. Time lapse methodology (6 or more months difference) will be also used, to investigate if any reactivation or slide advancement is happening. The base line survey will be in the dry period, while the repeated survey will be after the rainy period. Considerable field work will require full funding. Time lapse acquisition and processing will engage several experts.
Multichannel Analysis of Surface Waves – MASW (Park, et al, 1999, Geophysics) is a seismic technique to investigate the underground condition by S-wave velocity distribution. It has been used in many engineering applications in recent years. The particular relevance to this Project is provided by Suto (2014, SAGEEP), whereby the MASW survey was successfully applied to assessment of flood damaged roads. This work demonstrated the effectiveness of the MASW survey in mapping weak layers and subsurface voids caused by heavy rainfall. The result was used in remedial design of repairing a road.
Electrical resistivity tomography (ERT). When studying landslides, electrical resistivity tomography (ERT) is a useful method because of the strong contrast in the resistivity between the coarse landslide material and the undisturbed bedrock, despite some ambiguities that could be introduced during the inversion procedure and the limited resolution at depth. This method also helps by revealing the resistivity characteristics of the subsurface, thereby providing valuable information on groundwater distribution and on the geological structure of the subsurface. By conducting ERT in two phases, firstly in dry period and secondly after a rainy period, we should estimate water-table level by using relationship between resistivity and water saturation.
Seismic refraction will be used to infer layer velocities and invert for layer boundaries. Pwave tomography will be computed and combined with refraction interpretation. P-velocity profile will be combined with shear velocity profile inferred from MASW measurements to produce profiles of elastic properties (Young modulus, Poisson's ratio, Lame's constant Lambda, Bulk modulus). These moduli or typical engineering parameters will relate directly to the soil properties, rock strength and quality. Reflection imaging will be used to help interpret layer boundaries and their morphologies as well as fine structures such as faults and fractured zones (Malehmir et. al., 2013: Near Surface Geophysics, 11, 341–350; Journal of Applied Geophysics, 92, 84–102; 2014: Geophysical Journal International, 197, 1693–1704).
Slope stability investigation. In this Project, a geotechnical engineer specialised in landslides will use the data and suggest direction of further investigation and remedial actions. The results will be presented to the local authorities so that they can plan the reconstruction of the damaged infrastructure. The proposed landslide investigation and analysis procedures consist of (1) preliminary investigation, (2) detailed investigation, (3) analyses of landslide mechanism and slope stability, and (4) selection of mitigation measures. In the step (1), collection and review of existing data, detailed site walkover and the topographic study will be undertaken. Based on results of these study, detailed geotechnical investigation including the all core borehole drilling, the geologic structure study, surface deformation study, the groundwater monitoring, and the slip surface investigation will be carried out. Geotechnical laboratory testing such as shear box tests and triaxial tests will be also under taken in step 2, in order to determine the residual strength of geomaterials in the slip surface. The slip surface identified based on these geotechnical studies will be then compared and refined with outcomes of geophysics investigation. Data obtained from preliminary and detailed investigations in the steps (1) and (2) will be then used in the following analyses of landslide mechanism and slope stability in the step (3). Then based on results of all these steps, an appropriate landslide mitigation measure will be selected in the step (4). During the course of these investigations, the short lecture which primarily covers the practical aspects of landslide engineering will be also given to the undergraduate and postgraduate students.