Maja Oštrić

A complex landslide in the Rječina Valley: results of monitoring 1998-2010

Results of landslide monitoring undertaken between 1998–2010 on the north-eastern slope of the central part of Rjecina Valley in front of Grohovo village (north-eastern coastal part of Adriatic Sea, Croatia) are presented. This is the largest regional active landslide. The slopes around the Rjecina riverbed are formed in siliciclastic sedimentary rocks with flysch characteristics. The bedrock is mostly covered with unstable slope formations. A limestone rock mass is visible on the cliffs around the top of the river valley. The landslide is complex and retrogressive, with 13 sliding bodies. It occurred in December 1996 by displacement of an initial landslide body where movement had been registered in the 19th century. The limestone mega-blocks and separated rocky towers on the top of the slope have also moved, which is an atypical phenomenon of the flysch slopes in the area of Rijeka. After initial sliding ceased, and major movements subsided, monitoring of benchmark movements from 1998 until 2010 determined further maximum displacements on the upper part of the slope, and minimum movement in the lower part. The area of the Rjecina Valley from the Valici Dam to the Pasac Bridge was selected as a pilot area in the framework of the Croatian-Japanese bilateral joint research project. Monitoring results provided the basis of establishing an early warning system for possible landslide occurrence and estimating the degree of landslide risk.

Geotechnical properties in relation to grain-size and mineral composition: The Grohovo landslide case study (Croatia)

The Grohovo landslide is the largest active slope movement along the Croatian coast, situated on the north-eastern slope in the central part of the Rjecina River Valley (north-eastern coastal part of Adriatic Sea, Croatia). Slopes in this valley are formed of siliciclastic rocks (i.e., flysch), while limestone rock mass is visible on the cliffs around the top of the river valley. The slopes are at the limit of a stable equilibrium state, and slope movement phenomena have been recorded since 19th century. Samples for laboratory testing were taken from the flysch bedrock, weathered zone and slope deposits to provide specimens for determination of their mineralogical, physical and geotechnical properties. Correlation between mineralogical and geotechnical properties and their influence on sliding processes are presented in this paper. Clay fraction in samples ranges from 17 % to 38 %. Clay activity of the tested samples is from 0.45 to 0.89, and the residual friction angle varies from 13.0° to 17.7°. These results correspond to the presence of kaolinite and illite groups of clay mineral. Mineral composition and decrease in strength of fine- grained soil materials, due to the increase of pore water pressures, contributes to the slope movements.

Portable Ring Shear Apparatus and Its Application

The paper presents the concept, design and construction of new ring shear apparatus, ICL-1. The new apparatus is, compared to previous ones (DPRI-5, 6, 7), much smaller in dimensions and has higher performances. It can keep undrained condition up to 1 MPa of pore water pressure (up to two times more than in previous versions of apparatus) and load normal stress up to 1 MPa. This makes it suitable for investigation of large- scale and deep seated landslides. Speed control test and undrained cyclic loading tests were performed to show experimental procedures in details. Typical test results are presented to show the efficiency of this ring shear apparatus.

Effects of Parameters in Landslide Simulation Model LS-RAPID on the Dynamic Behaviour of Earthquake-Induced Rapid Landslides

In this study, the effects of parameters in landslide simulation model (LS-RAPID) on the dynamic behaviour of earthquake-induced rapid landslides were examined to demonstrate the importance of each parameter. It was applied to a case study in Suruga Bay, Shizuoka Prefecture in Japan. The topographic data of the slope surface and sliding surface was generated from digital elevation model (DEM). Three different real seismic records were used as the inputs of earthquake i.e. 2008 Iwate-Miyagi Nairiku Inland Earthquake, 2009 Suruga Bay Earthquake, and the latest 2011 Tohoku Earthquake. Results show that landslides can be triggered by strong seismic loading using 2011 Tohoku real seismic records under a certain pore water pressure within LS-RAPID. The key parameters, including shear resistance at the steady state with physical meaning were found to have significant effect on the dynamic behaviour of these earthquake-induced rapid landslides.

TXT-tool 3.081-1.6: Manual for the Undrained Dynamic-Loading Ring-Shear Apparatus

The development of the ring shear device was upgraded since 2010, particularly for the loading system. Previous version of the ring shear apparatus of DPRI series has a long loading frame consists of pillars and beam for the normal stress system. Recently, loading piston through the single central axis was applied for the normal stress in the newest version of ring shear apparatus. There are two version of this new apparatus, called the ICL-1 and the ICL-2. The ICL-1 version was developed since 2010 as a part of SATREPS project for ‘Risk identification and land-use planning for disaster mitigation of landslides and floods in Croatia.’ Meanwhile, the development of the ICL-2 was carried out since 2012 as a part of SATREPS project between Japan and Vietnam for ‘Development of landslide risk assessment technology along transportation arteries in Vietnam’. As for practical purpose, both version of the undrained dynamic-loading ring-shear apparatus were designed in a small dimensions (compare with DPRI series) but with high performances. Thus, shallow landslide as well as deep landslide can be simulated geotechnically using this apparatus. In this paper, the structure, control and loading system of the apparatus are described in detail. The testing procedures and data analysis of ring shear tests are also explained.