Geoenvironmental Disasters

Estimating the magnitude and intensity of landslides is a fundamental requirement in quantitatively evaluating the risks involved, and preparing a mitigation strategy. Though the physics-based dynamic model of landslide can predict the travel distance, kinematic velocity, and hazard zone, the effects of erosion and the excess pore water pressure during the dynamic process of landslide are often ignored. In order to study these factors, a physics-based dynamic model of landslide considering erosion and excess pore water pressure is presented in this paper. A high-precision numerical method based on the finite volume method is proposed to solve the model equations. Several numerical tests are performed to verify the numerical method and the model. The effects of erosion and excess pore water pressure on the dynamic process of landslide are also analyzed. The numerical results indicate that the scale and mobility of a landslide are influenced by the effect of erosion and excess pore water pressure. The excess pore water pressure can reduce the resistance to shear stress from the erodible bed and lead to a higher erosion amount and longer moving distance of the landslide. It also affects the degree of erosion and further affects the dynamic process of the landslide. The sensitivity analysis of the parameters that influence excess pore water pressure indicate that these parameters have a significant impact on the evolution of excess pore water pressure, and that the degree of saturation of bed sediment has the highest influence on excess pore water pressure.

The International Workshop on Seismic Design and Assessment for Resilience, Robustness and Sustainability of Slope Engineering was held on 13–15 January 2023 on line, focusing on the theme of “Seismic resilience of slope engineering and the concept of resilience-based seismic design (RBSD) for geological disaster prevention and control”. In this workshop, a number of keynote and invited lectures provided an international exchange platform for researchers, industrial engineers and students to share their research, engineering practice and exchange novel ideas on seismic resilience for slope engineering in a way of online. At the same time, during this workshop, technical committee of the ICGdR-TC1 also took this opportunity to hold a working meeting on cutting-edge and strategic issues, and released the Shanghai Declaration on slope engineering.

The application of quantitative risk assessments is increasing for decision-making in many industries and contexts, with the evaluation of risks against some adopted criteria. In this article, we review risk criteria developed and used for landslide management, in particular criteria associated with risk to life. We show that while this natural hazard is encountered worldwide, the social and regulatory contexts under which evaluation criteria are developed can vary significantly. Thus, the applicability of developed criteria to any specific situation should be assessed before adopting them elsewhere. We describe selected considerations for developing risk evaluation criteria, propose a framework for defining these criteria in Canada, and assess the applicability of previously proposed criteria. Examples of risk criteria development and adoption for new and existing residential developments and for railway employees are presented to illustrate some of these concepts.

High basin of Oum Er Rbia River, which is located in Middle Atlas Mountain region, is prone to landslide problems due to the geological features combined with the climate change and human activities. The present work including inventory mapping was conducted to establish landslide susceptibility map using GIS-based spatial multicriteria approach. Eight landslide-related factors, including land cover, lithology, distance to road, distance to fault, distance to drainage network, elevation, aspect and slope gradient, were selected for the present assessment. Weight for each factor is assigned using Analytic Hierarchy Process (AHP) depending on its influence on the landslide occurrence. The landslide susceptibility map was derived using weighted overlay method and categorized into five susceptible classes namely, very low (VL), low (L), moderate (M), high (H). The results revealed that 30.16% of the study area is at very low risk, 12.66% at low risk, 25.75% of moderate risk, 22.59% of high risk and 9.11% of very high risk area coverage. The very high landslide vulnerability zones are more common within the river valleys on steep side slopes. Most landslides also involve rocks belonging to the Triassic weathered marl and clay-rich formation. Moreover, human activities namely the construction and the expansion of agricultural lands into forests intervene in inducing landslides through altering the slope stability along the river banks. Lastly, effectiveness of these results was checked by computing the area under ROC curve (AUC) that showed a satisfactory result of 76.7%. The landslide susceptibility map of the Oum Er Rbia high basin provides valuable information about present and future landslides, which makes it viable. Such map may be helpful for planners and decision makers for land-use planning and slope management.

It is essential for residents to understand ground disaster and improve disaster prevention awareness, because natural disasters have occurred frequently in recent years. In this study, nondestructive unsaturated seepage behavior was continuously visualized by using MRI (magnetic resonance imaging) with test equipment constructed of non-metal parts. Additionally, the water content of the soil from the MRI image was evaluated, the results of previous experiments were considered and compared. The study revealed from the imaging with MRI that seepage will flow faster in the lower part of the cylinder than in the upper part. A discontinuous water content ratio change of the seepage line part was confirmed from image with the MRI. There was a tendency for air to be trapped on the border of different soil materials in an acrylic cylinder. It was possible for the water content of the sand in the cylinder to be evaluated from the MRI image. The study suggests that complicated unsaturated seepage behavior can be easily visualized. It was suggested that air may be trapped in the different layer border of soil. And these finding will lead to the elucidation of relevance of slope collapse and the piping phenomenon with the rainfall.

The Southeast of Yogyakarta City has had the heaviest damages to buildings in the 2006 of Yogyakarta Earthquake disaster. A moderate to strong earthquake of 6.3 Mw shook the 20 km southeast part of the Yogyakarta City early in the morning at 5:54 local time. On top of extensive damage in Yogyakarta and Central Java, more than 5700 people perished; 37,927 people were injured in the collapse of more than 240,396 residential buildings. Furthermore, the earthquake also affected the infrastructure and local economic activities. The total damages and losses because of the earthquake was 29.1 trillion rupiahs or equal to approximately 3.1 million US dollar. Two main factors that caused the severe damages were a dense population and the lack of seismic design of residential buildings. After reconstruction and rehabilitation, the area where the study was conducted grew into a densely populated area. This urbanistic change is feared to be potentially the lead to a great disaster if an earthquake occurs again. Thus, a comprehensive study about building vulnerability is absolutely needed in study area. Therefore, the main objective of this study has been the provision of a probabilistic model of seismic building vulnerability based on the damage data of the last big earthquake. By considering the relationship between building characteristics, site conditions, and the damage level based on probabilistic analysis, this study can offer a better understanding of earthquake damage estimation for residential building in Java. The main findings of this study were as follows: The most vulnerable building type is the reinforced masonry structure with clay tile roof, it is located between 8.1-10 km of the epicentre and it is built on young Merapi volcanic deposits. On the contrary, the safest building type is the houses which has characteristics of reinforced masonry structure, asbestos or zinc roof type, and being located in Semilir Formation. The results showed that the building damage probability provided a high accuracy of prediction about 75.81%. The results explain the prediction of building vulnerability based on the building damaged of the Yogyakarta earthquake 2006. This study is suitable for preliminary study at the region scale. Thus, the site investigation still needs to be conducted for the future research to determine the safety and vulnerability of residential building.

Landslides are common geological hazard occurring in the mountainous region. The Himalayan belt is prone to landslide disasters, which is directly linked to the prosperity and development of the area. The present study was carried out around the Chamoli-Joshimath area, which is situated in the Northernmost-belt of the Garhwal Himalaya, India. A strategic road connecting Tibet which also links the famous Hindu temples Badrinath and Kedarnath traverses the area. The main purposes of the present study is to delineate the landslide susceptible zones in the area so that it could be helpful towards landslide disaster risk reduction and to highlight the applicability of knowledge based susceptibility mapping method in the Himalayas. The area comprises low-to-high grade metamorphic rocks as well as carbonate rocks such as limestone and dolomite. In the study area, most of the landslides occur along the road and river sections, and in the thrust or fault zones. The landslide zones are strongly controlled by the Main Central Thrust and other faults and the resulting geomorphic condition. Most of the unstable slopes are prone to plane and wedge failures. There are many active and dormant landslides (covered by vegetation) in the area. The active landslides are due to reactivation of pre-existing ones. The predicted landslide susceptible zones are in good agreement with the historical landslide locations, which is good indication that knowledge based landslide susceptibility mapping can be successfully applied in the Himalayas provided the causative factors are thoroughly understood.

On September 28th, 2018, at 18:02 local time (10:02 UTC), a strong earthquake of magnitude Mw = 7.5 struck Central Sulawesi Province, Indonesia. The epicenter was located at 0.256o south latitude and 119.846o east longitude, around 77 km from Palu city, and 20 km below the ground surface. To understand the damage caused by the earthquake, and find a solution to mitigate the geo-disasters in Indonesia, a preliminary investigation on the 2018 Sulawesi earthquake was conducted from 16 to 20 November 2018. This quick report focuses on ground displacements induced by fault movement and large-scale ground flow. During the survey, there is some geotechnical damage were found, such as ground displacement induced by fault movement, liquefaction, landslides, and large-scale ground flow in some certain areas. Large ground displacement was found in some particular areas, such as Kedondong, Pipa Air, Pangeran Diponegoro and Cemara streets in Palu city. The earthquake also triggered large-scale ground flow in some different sites, such as Balaroa and Petobo districts in Palu city and Jono Oge and Sibalaya Villages. The locations of large ground displacements appeared at surface coincide well with the estimated fault line. Therefore the large ground displacements were seems to be induced by the fault movement. Large ground flow caused severe damage to not only human but also houses and buildings. The mechanism of the large ground flow should be clarified in near future.

In the Parangtritis Beach tourism area located in the Southern Mountain of Yogyakarta, karst hills were excavated to build the main accessing road and produce some of long and very steep slopes along the sides of the road. But still, there was none of the slope reinforcement installed along the road. Meanwhile, at several nearby locations within Southern Mountain, rockfall incidents have occurred many times even caused casualties. The potential of rockfall hazard also could be found in the main road of Parangtritis Beach as the study area. The purpose of this study is to determine the rockfall hazard assessment along the main road using Slope Mass Rating (SMR) analysis with the additional parameter of the slope height and the rock block size. The necessary data obtained by direct measurement and laboratory test. Geomechanics analysis, stereographic projection analysis, and hazard parameters weighting were carried out to produce the Rockfall Hazard Zonation Map of the study area. Based on 17 measurement stations, there are 4 (four) rockfall hazard classes in the study area, i.e., very low, low, moderate, and high. The class of very low, which also included road segments without slope, has the largest percentages of 83.83%, followed by the classes of moderate, low, and high with the percentage of 7.16%, 4.28%, and 4,19%, respectively. SMR was assumed as the most significant parameter that influences the rockfall hazard zonation. Historical rockfall points were overlaid over the Rockfall Hazard Zonation Map to validate the predicted hazard zones. Since 91.23% of the rockfall occurred in the moderate and high hazard classes, the zonation map considered reliable to predict future rockfall. This study also identified several landslide potential zones and provides the recommendation of slope reinforcement to be installed in the study area.

In flood prone areas, understanding flood causing factors, assessing the flood induced risks and adopting landscape based mitigation strategies can increase the knowledge, awareness and individual initiatives to protect themselves and their properties using appropriate flood management measures before and during flood events. Dire Dawa city is located in the foothill of southern mountains from where rivers crossing the city are originated. The multidimensional causes of flood hazard and limited landscape based mitigation strategies in the study area have worsen the impacts of flooding. This study was conducted in the Dire Dawa city watershed with the aims of assessing flood causing factors and to propose landscape based flood mitigation strategies. To meet the intended objectives, the study employed the collection of both primary and secondary data. The primary data were collected from 110 households located in flood vulnerable villages. Moreover, the secondary data were collected from the Ethiopian Meteorology Agency, land use map of Dire Dawa city administration and government reports. Rainfall index method and descriptive statistics were used for analysis of primary data. The former was used to check the effect of intense rainfall and flood risk in terms of different duration yearly, monthly, daily and hourly basis, while the latter was used for identification of various factors precipitating flood risks of the study area. The analysis of secondary data employed morphometric analysis so as to identify flood susceptible sub-watersheds. Findings of the study indicated that flood risk in the study area has resulted from multiple factors such as intense rainfall, topography, encroachment to the river banks, institutional problems and aggravating factors resulted from power interruption during heavy rain and regime changes. More importantly, flood risk of the study area was found to be sensitive to hourly variation of rainfall distributions and varies on the location of the sub-watersheds. Following that, flood susceptibility of sub-watershed was ranked based on linear and shape morphometric parameters where higher values of linear and lower values of shape parameters were attributed to high flooding risk. Based on the prioritization of sub-watersheds’ susceptibility to flood risk through morphometric analysis, sub-watershed 5 and 18 were identified as the most flood risk susceptible watersheds demanding urgent landscape-based conservation measures. To this end suitable sites and sustainable water conservation structures are identified across the watersheds. Check dams, terracing, nala bunds, percolation tanks and storage tanks were proposed for different locations across the watershed as effective landscape-based flood risk mitigation strategies. The overall results of the study shows that managing the root causes of flooding at the upper catchments and adopting recommended proposed water conservation structures at proposed site helps to sustainably curb flood induced risks of Dire Dawa city.