Landslide Mitigation Research Articles

Slovenian national landslide database as a basis for statistical assessment of landslide phenomena in Slovenia

Landslide databases on a national scale are an important tool for good spatial planning and for planning prevention measures or remediation activities. We have developed a modern national landslide database that enabled better landslide occurrence understanding, and will in the future help to assess landslide hazard, risk, potential damage, and enable more efficient landslide mitigation. In the paper landslide database construction steps and their properties are described. Following the collection of the landslide data from various sources and their input into the database the consistency of the database was assessed. Based on the data collected we have assessed basic statistical landslide properties, such as their overall spatial distribution, size and volume and the relation between them, landslide distribution in relation to engineering-geological units and different land-use, and past landslide mitigation activities. Analysis of landslide distribution also indicated areas in Slovenia where no landslide mapping was performed in the past, yet it should be, due to the high landslide susceptibility of these areas. Consequentially future national activities in relation to landslide problems should be governed primarily based on the findings of the database analyses to achieve the highest efficiency.

ホンジュラス共和国を対象とした日本の国際協力による地すべり調査・対策の取り組み

ホンジュラス共和国を対象とした日本の国際協力による地すべり調査・対策の取り組み

Report of the 2nd G-EVER International Symposium and the 1st IUGS and SCJ International Workshop on Natural Hazards and the “Sendai Agreement”

The 2nd G-EVER International Symposium and the 1st IUGS & SCJ International Workshop on Natural Hazards aimed to encourage extensive discussions on the present situation of natural disaster mitigation of earthquake, tsunami, volcanic eruption and landslide in the Asia and Pacific regions. The discussions included (1) prioritization of important researches to make society strong and resilient, (2) development of suitable hazard maps which are essential to society and Asia-Pacific scale hazard assessment activities, and (3) the importance of contributions to solid earth science. There were also discussions on the mitigation processes needed in the next-decade to reduce the risks of natural hazards. The 2nd G-EVER International Symposium and the 1st IUGS & SCJ International Workshop on Natural Hazards was held in Sendai, Tohoku, Japan on Oct. 19-20, 2013 (Fig. 1). The symposium was organized by the G-EVER Consortium, Geological Survey of Japan, AIST, the International Union of Geological Sciences (IUGS) and Science Council of Japan (SCJ). It was co-organized by the Geological Society of Japan and the Coordinating Committee for Geoscience Programmes in East and Southeast Asia (CCOP). Tohoku University, Disaster Prevention Research Institutes (DPRI) of Kyoto University, National Research Institute for Earth Science and Disaster Prevention (NIED), GNS Science, Philippine Institute of Volcanology & Seismology (PHIVOLCS), the Seismological Society of Japan, the Volcanological Society of Japan, Japan Association for Quaternary Research, Japanese Society for Active Fault Studies, Japan Society of Engineering Geology, and Tokyo Geographical Society supported the symposium (Fig. 2). The Asia-Pacific Region is an area with a high risk of catastrophic natural disasters such as earthquakes, tsunamis and volcanic eruptions. In today’s highly globalized economy, when a major disaster occurs, it can create unpredictable turmoil not just in the affected area but also the rest of the world. Countermeasures against these natural disasters are crucial for the sustainable development. We believe that continuous efforts to develop an effective international framework to reduce the risk of natural disasters are very important. It is expected that geological institutions will collaborate and create a system to gather and process information to formulate disaster mitigation measures in the Asia-Pacific Region. This system must be easy to use and freely accessible to the public to meet societal needs. The Sumatra earthquake of December 26, 2004 and Tohoku earthquake of March 11, 2011 clearly show the urgency of developing an information and knowledge system for infrequent natural hazards. We also have to recognize that smaller events could have adverse effect to society. For example, the magnitude of the February 2011 Christchurch earthquake was just 6.3 (ML), but caused major damage to the second largest city of New Zealand and 185 casualties. Volcanic ash ejected from the Eyjafjallajokull eruptions in Iceland on April 2000 caused more than 20,000 airline flight cancellations a day in Europe, resulting to the largest air-traffic shut-down since World War II. The IATA estimated that airline companies lost US$200 million a day during the shut-down. After the 2011 Tohoku earthquake, more efforts for the prevention and reduction of the risks of natural disasters have been made all over the world. The G-EVER Consortium promotes natural disaster risk reduction activities through the collaboration different research institutes worldwide. The consortium’s major activities are the following: 1. Establish a framework for cooperation of research institutes and organizations working on volcanic disaster prevention in the AsiaPacific region.

Landslide risk assessment in a densely populated hilly area

Landslide risk assessments provide essential information to develop loss reduction strategies. However, only very few studies produce risk maps. Lack of temporal data on landslides is one of the reasons. This paper develops a methodology to assess the economic risk of landslides when limited landslide hazard information is available. It provides spatially explicit estimates of future landslide risks in a densely populated low-relief area and applies different spatial probability scenarios. In the study area (710 km2), residential buildings cover 7 % of the area with elements at risk, but are responsible for about 86 % of the total risk. Roads cover 8 % of the area with elements at risk but are responsible for about 14 % of the total risk. The annual landslide risk is approximately 50 million to 80 million euros 2011 values depending on the spatial probability scenario considered. This indicates that landslide mitigation efforts would create considerable benefits. Landslide risk would reduce significantly if better land use zoning would be applied to sterilize landslide-prone terrain as particularly the residential buildings and access roads determine the total risk.

Hydraulic properties of partially saturated rock fractures subjected to mechanical loading

This study presents a methodology for estimating the unsaturated hydraulic properties of rock fractures under deformation conditions. The surface morphology of an artificial granite rock fracture was examined using a high-resolution three-dimensional laser scanner, and the aperture distribution of the fracture was found to follow a Gaussian distribution. By virtue of the aperture distribution function and applying the Young–Laplace equation to local apertures, a novel model was presented to predict the capillary pressure–saturation relationship and the relative hydraulic conductivity of rough-walled rock fractures subjected to normal and shear loading. The proposed model was partially validated against existing laboratory data on the unsaturated hydraulic properties of rock fractures, and can be readily applied to various engineering practices such as transport phenomena in fractures, landslide mitigation, or underground oil storage.

Statistical analysis of landslides caused by the Mw 6.9 Yushu, China, earthquake of April 14, 2010

The April 14, 2010 Yushu, China, earthquake (Mw 6.9) triggered a great number of landslides. At least 2,036 co-seismic landslides, with a total coverage area of 1.194 km2, were delineated by visual interpretation of aerial photographs and satellite images taken following the earthquake, and verified by field inspection. Based on the mapping results, a statistical analysis of the spatial distribution of these landslides is performed using the landslide area percentage (LAP), defined as the percentage of the area affected by the landslides, and landslide number density (LND), defined as the number of landslides per square kilometer. The purpose is to clarify how the landslides correlate the control factors, which are the elevation, slope angle, slope aspect, slope position, distance from drainages, lithology, distance from the surface rupture, and peak ground acceleration (PGA). The results show that both LAP and LND have strongly positive correlations with slope angle and negative correlations with distance from the surface rupture and distance from drainages. The highest LAP and LPD values are in places of elevations from 3,800 to 4,000 m. The slopes producing landslides are mostly facing toward NE, E, and SE. The geological units of Q4 al-pl, N, and T3 kn 1 have the highest concentrations of co-seismic landslides. No apparent correlations are present between LAP and LND values and PGA. On both sides of the surface rupture, the landslide distributions are almost similar except a few exceptions, likely associated with the nature of the strike-slip seismogenic fault for this event. The bivariate statistical analysis shows that, in descending order, the earthquake-triggered landslide impact factors are distance from surface rupture > slope angle > distance from drainages > lithology > PGA. Besides, as the detailed co-seismic landslides inventories related to strike-slip earthquakes are still few compared with that of thrusting-fault earthquakes, this case study would shed new light on the subject. For instance, the landslide spatial distribution on both sides of the strike-slip seismogenic fault is rather different from that of thrusting-fault earthquakes. It reminds us to take different strategies of measures for prevention and mitigation of landslides induced by earthquakes with different mechanisms.

Japanese-Croatian Joint Research Project for Disaster Mitigation of Landslides and Floods (IV)

Japanese-Croatian Joint Research Project for Disaster Mitigation of Landslides and Floods (IV)

Analysis and Evaluation of Slope Stability under Earthquake and Rainstorm Action

Collapse and landslide induced by"5.12" Wenchuan Earthquake generated a large number of loose solid material, which still remained on the mountain. Aftershocks and heavy rain conditions will induce secondary geological disasters, a direct threat to human life and property security and reconstruction results. Based on the landslide of Hanyuan Two Pretty mountain, this paper studied the basic characteristics of landslide before and after earthquake. The finite difference method is adopted to simulate landslide process, and the stress-strain law and failure trend is explored in three conditions including the natural, rainfall and seismic condition. After this, the method of strength reduction is used to analyze slope safety factor in different rainfall conditions. The analytical results are consistent with the macrogeological phenomena before and after earthquake. Research results can provide a reliable basis for the future study of the impact of earthquakes on the landslide and disaster prevention and mitigation.

Cost assessment of losses due to recent reactivation of Kaliasaur landslide on National Highway 58 in Garhwal Himalaya

National Highway (NH) 58 is one of the important and the major lifelines, which connects Uttarakhand state with rest of the country and linked with its socioeconomic progress. Uttarakhand, being one of the major tourist and pilgrimage hubs of the country, highways are preferred to be consistently maintained and trafficable. However, due to frequent landslide occurrences, particularly during monsoon months (July to September), the highway is poorly maintained. There are hundreds of landslides along the NH 58 starting from Rishikesh (the foot of the Garhwal Himalaya) to Badrinath, the holy shrine of India covering a distance of 320 km. Many landslides are historic, 4–5 decades old and recurring every year during monsoon. Kaliasaur landslide (147 km), Pakhi landslide (250 km), Tangni landslide (254 km), Patalganga landslide (256 km), and Lambagarh landslide (302 km) are a few among the critical ones. Kaliasaur landslide that is one of the most critical landslides recurring for over 9 decades at 147 km on National Highway 58 (from Haridwar) has been selected for the study. It has reportedly occurred first time in 1920 and since then recurring at regular intervals, causing huge socioeconomic losses involving both direct and indirect costs. Previous records of any attempt to estimate the direct (rehabilitation cost, cost on prevention and control) or indirect cost (expenses due to detouring, cost of productive time loss, loss of tourism, and loss in business) have not been found. As a result, the accurate economical impact of landslide on society is very roughly estimated. Even if the estimates of indirect losses are roughly estimated, added with some direct losses will provide the basis for developing the right strategies for proper mitigation and management of landslides. In this paper, an effort is made, first time, to examine the effects of Kaliasaur landslide on socioeconomics of the region. Since the direct losses on property damaged could not be estimated due to lack of recorded documentation, this study mainly focuses on the indirect losses on detouring during the damage/blockage of the highway and some significant direct losses such as restoration work, loss of lives, and damage of vehicles.

Japanese-Croatian Joint Research Project for Disaster Mitigation of Landslides and Floods (I)

Japanese-Croatian Joint Research Project for Disaster Mitigation of Landslides and Floods (I)

The Flood-relief Measure in Project on Risk Identification and Land-use Planning for Disaster Mitigation of Landslide and Floods

The Flood-relief Measure in Project on Risk Identification and Land-use Planning for Disaster Mitigation of Landslide and Floods

Landslide temporal analysis and susceptibility assessment as bases for landslide mitigation, Machu Picchu, Peru

Multi-temporal landslide occurrence information acquired through aerial photo interpretation and field mapping was used to assess occurrence frequencies on the slopes around the UNESCO cultural world heritage site of Machu Picchu, Peru. This showed that the coarse time resolution of the historical landslide information may lead to inaccurate interpretations regarding landslide occurrence frequencies in some parts of the study area. In addition, the assumption that the past landslide frequency can be used to describe the future landslide occurrence was not proved in the study area. Thereafter, unique conditional analyses were undertaken to assess landslide susceptibility using a limited number of preparatory factor maps. It showed that large majority of the Inca City is located on least susceptible areas within the region. The results of the susceptibility assessment combined with landslide occurrence frequencies may serve as a basis for the landslide hazard mitigation in the studied area. For these purposes, pixel-based susceptibility maps were generalized into expert-defined landslide management units. These units provide site managers with easily understandable and applicable hence reliable information about future landslide occurrences. An approach describing usage of the resulting susceptibility maps for onsite mitigation purposes was described with respect to the needs of Machu Picchu site managers.

Reinforced concrete shafts for the structural mitigation of large deep-seated landslides: an experience from the Macesnik and the Slano blato landslides (Slovenia)

During the last decade, several rainfall-induced deep-seated large landslides with volumes of the order of 1 million m3 were triggered in various locations in Slovenia (central Europe), each representing a serious threat to the nearby villages and traffic infrastructure and urging to be mitigated. The Macesnik landslide, triggered in 1989, and the Slano blato landslide, triggered in 2000, were the first two large landslides in Slovenia, where a combination of drainage and retaining works consisting of deep reinforced concrete (RC) shafts/wells was successfully used as a mitigation measure. This paper presents the field conditions and a brief history of the two landslides with emphasis on the design approach and method used for the stability analysis and the design of deep RC shafts/wells. In addition, the paper gives an insight into the problems associated with the execution of works and provides data about the behavior of the two landslides after drainage and retaining works were completed. The monitoring data show that the undertaken mitigation measures were efficient to improve the stability of both landslides and significantly reduce the risk.

DEVELOPMENT OF SOCIO-TECHNICAL APPROACH FOR LANDSLIDE MITIGATION AND RISK REDUCTION PROGRAM IN INDONESIA

Intensive efforts for mitigating and reducing the risk of landslides in Indonesia have been conducted since more than 30 years ago. But still, substantial socio-economical losses continuously occur as the results of landslide disasters. Admittedly, the natural conditions plays important role in controlling the susceptibility and triggering the occurrence of landslides. Yet, the human interfere and landuse changing crucially contribute in the triggering process of landslides. Indeed, the increase in societal impacts due to the landslide disasters also strongly related to the landuse changing, driven by the social constrains. Unfortunately, the technical solution for landslide mitigation and risk reduction does not always appropriately address the socio cultural and socio economical aspects of the disaster prone area. That is why, the hybrid socio-technical system is promoted in this study, in which not only the engineering but also social system has to be strongly considered in the mitigation and risk reduction efforts. The proposed technical system was mainly supported by the participatory landslide hazard and risk map as well as the community-based landslide early warning system. Such system was developed by enhancing the local knowledge, through the local participation, and utilizing the local materials. Meanwhile, the social system was established through a series of community empowerment programs and supported by the establishment of local task force for disaster risk reduction at the village. Accordingly, the developed system can be effectively operated, maintained and sustained by the local community. Indeed, the roles of the local task force and the local university are very important to drive and ensure the effectiveness of the landslide mitigation and disaster risk reduction.

Refraction seismics to investigate a creeping hillslope in the Austrian Alps

Assessing the human and economic threat introduced by sliding or creeping masses is of major importance in landslide hazard assessment and mitigation. Especially, in the densely populated alpine region unstable hillslopes represent a major hazard to men and infrastructure. Detailed knowledge, especially, of the dominant site-specific controlling factors such as subsurface architecture and geology is thereby key in assessing slope vulnerability. In order to quantify the geological variations at a creeping hillslope in the Austrian Alps, we have collected six 2D refraction seismic profiles. We propose using a layer-based inversion strategy to reconstruct P-wave velocity models from first arrival times. Considering the geological complexity at such sites, the selected inversion approach eases the interpretability of geological structures given intrinsic optimization for only a discrete, user-defined, number of layers. As the applied layer-based inversion approach fits our travel time data equally well as traditional smooth inversion approaches, it represents a feasible mean to summarize the structural complexity often present at such sites. Analysis of the inversion results illustrates that bedrock topography clearly deviates from a previously assumed planar surface and exhibits distinct variations across the slope extension. Bedrock topography additionally impacts the intermediate geological units and, thus, this information is critical for further analyses such as geomechanical modeling.

Geosynthetics applications for the mitigation of natural disasters and for environmental protection

ABSTRACT: The paper first describes the versatile application of geosynthetics for the mitigation of floods, landslides, rockfalls, debris flows and avalanches. It focuses on dykes or flood protection dams, on geosynthetic-reinforced stabilising fills (up to 130 m height) and barrier dams. Geosynthetic-reinforced floating embankments (up to 70 m height) in creeping slopes and seismic areas show clear advantages over rigid structures (e.g. bridges) not only from a geotechnical point of view but also regarding economy, maintenance and environmental aspects. Environmental protection is predominantly considered by gaining renewable energy from the ground via ‘energy-geosynthetics'. Several other applications are also mentioned. Compaction optimisation and control of geosynthetic–soil structures is recommended by roller-integrated CCC (continuous compaction control), thus improving their behaviour significantly.

Typical landslides and related mechanisms in Ali Mountain highway induced by typhoon Morakot: perspectives from engineering geology

Typhoon Morakot caused serious damage to southern Taiwan. Almost all major mountain highways located in the affected region suffered severe damage from landslides, rock falls, and debris flows. Among these highways, Ali Mountain Highway is one of the most severely affected. Ali Mountain Highway, i.e., T18 route, was constructed in the early 1980s. For the past 30 years of operation, it has suffered substantial damage from different natural hazards. The continued damage–rehabilitation cycle is implemented to maintain the serviceability of this highway. Ali Mountain Highway was seriously damaged by the strike of typhoon Morakot on August 8, 2009. Traffic through this highway was interrupted for over 3 months until temporary rehabilitation was completed. This paper provides a summary of the damage suffered along the Ali Mountain Highway and presents suggestions for mitigation strategies to minimize the likelihood of similar levels of damage during other extreme typhoons such as the typhoon Morakot. The manuscript summarizes extensive field surveys and aerial photo analysis carried out by the authors to investigate the mechanisms of typical slope failures along the Ali Mountain Highway. The engineering geology perspectives are emphasized in the analyses. Geological and hydrogeological features for the sites in this study were found to be the most influential factors dominating the failures. The fault-related weak zones and impermeable layers dominated the global stability of the slopes. In summary, geotechnical engineers should consider carefully the characteristics of geological structures for mitigation and rehabilitation of landslides. Extreme scenarios, such as typhoon Morakot, should also be considered.

A case study of coping strategies and landslides in two villages of Central-Eastern Nepal

Landslides are an increasing problem in Nepal’s Middle Hills due to both natural and human phenomena: mainly increasingly intense monsoon rains and a boom in rural road construction. This problem has largely been neglected due to underreporting of losses and the dispersed nature of landslides. Understanding how populations cope with landslides is a first step toward developing more effective landslide risk management programs. The present research focuses on two villages in Central-Eastern Nepal, both affected by active landslides but with different coping strategies. Research methods are interdisciplinary, based on a geological assessment of landslide risk and a socio-economic study of the villages using household questionnaires, focus group discussions and transect walks. Community risk maps are compared with geological landslide risk maps to better understand and communicate community risk perceptions, priorities and coping strategies. A modified typology of coping strategies is presented, based on previous work by Burton, Kates, and White (1993) that is useful for decision-makers for designing more effective programs for landslide mitigation. Main findings underscore that coping strategies, mainly seeking external assistance and outmigration, are closely linked to access to resources, ethnicity/social status and levels of community organization. Conclusions include the importance of investing in organizational skills, while building on local knowledge about landslide mitigation for reducing landslide risk. There is great potential to increase coping strategies by incorporating skills training on landslide mitigation in existing agricultural outreach and community forest user group training.

An integrated approach for evaluating the effectiveness of landslide risk reduction in unplanned communities in the Caribbean

Despite the recognition of the need for mitigation approaches to landslide risk in developing countries, the delivery of ‘on-the-ground’ measures is rarely undertaken. With respect to other ‘natural’ hazards, it is widely reported that mitigation can pay. However, the lack of such an evidence base in relation to landslides in developing countries hinders advocacy amongst decision makers for expenditure on ex-ante measures. This research addresses these limitations directly by developing and applying an integrated risk assessment and cost–benefit analysis of physical landslide mitigation measures implemented in an unplanned community in the Eastern Caribbean. In order to quantify the level of landslide risk reduction achieved, landslide hazard and vulnerability were modelled (before and after the intervention), and project costs, direct and indirect benefits were monetised. It is shown that the probability of landslide occurrence has been substantially reduced by implementing surface-water drainage measures and that the benefits of the project outweigh the costs by a ratio of 2.7–1. This paper adds to the evidence base that ‘mitigation pays’ with respect to landslide risk in the most vulnerable communities—thus strengthening the argument for ex-ante measures. This integrated project evaluation methodology should be suitable for adoption as part of the community-based landslide mitigation project cycle, and it is hoped that this resource, and the results of this study, will stimulate further such programmes.

Digital photogrammetric analysis and electrical resistivity tomography for investigating the Picerno landslide (Basilicata region, southern Italy)

Digital photogrammetric analysis and Electrical Resistivity Tomography (ERT) techniques were applied to evaluate the volume of material involved in a complex roto-translational slide occurred in the territory of Picerno (Basilicata region, southern Italy). Analytical and digital photogrammetric techniques facilitated a multi-temporal analysis of aerial photos for the years 1997, 2004 and 2006. In order to identify different geomorphologic features (scarps, terraces and trenches) of the landslide and their development, the analytical and digital photo interpretation was performed at the maximum scale of 1:5000. Geological and geomorphological surveys were carried out to verify photo-interpretation results. Digital Elevation Models (DEMs) for 1997, 2004 and 2006 were produced by applying the Grid Adaptive method. The differential DEMs (2006–1997; 2006–2004; 2004–1997) for the most dangerous part of the landslide allowed us to recognize the areas affected either by deposition or erosion and also estimate any altitudinal changes in each geomorphologic unit. To detect the sliding surface and estimate the thickness of the sliding material, several transversal and longitudinal ERT profiles were obtained. The electrical images of subsurface supported by stratigraphical data from boreholes were integrated with the information from the DEMs. The altitudinal changes and the sizes of the source and accumulation areas allowed us to estimate the volume of material involved in the mass movement. The fusion of data from different sensors allows us to gather indications on the surface and subsurface characteristics of the landslide providing useful information for landslide mitigation activities. Such an approach can help both to improve our knowledge and overcome the drawbacks of each methodology.