Khang Dang

A new landslide-induced tsunami simulation model and its application to the 1792 Unzen-Mayuyama landslide-and-tsunami disaster

By combining landslide dynamics research and tsunami research, we present an integrated series of numerical models quantitatively simulating the complete evolution of a landslide-induced tsunami. The integrated model simulating the landslide initiation and motion uses measured landslide dynamic parameters from a high-stress undrained dynamic-loading ring shear apparatus. It provides the numerical data of a landslide mass entering and moving under water to the tsunami simulation model as the trigger of tsunami. The series of landslide and tsunami simulation models were applied to the 1792 Unzen-Mayuyama megaslide and the ensuing tsunami disaster, which is the largest landslide disaster, the largest volcanic disaster, and the largest landslide-induced tsunami disaster to have occurred in Japan. Both the 1792 megaslide and the tsunami portions of the disaster are well documented, making this an excellent test of the reliability and precision of the new simulation model. The simulated tsunami heights at the coasts well match the historical tsunami heights recorded by “Tsunami-Dome-Ishi” (a stone showing the tsunami reaching point) and memorial stone pillars.

The 28 July 2015 rapid landslide at Ha Long City, Quang Ninh, Vietnam

From 26–28 July, heavy rainfall occurred in Quang Ninh province causing flooding, debris flows and landslides. It was the largest disaster triggered by torrential rainfall in Vietnam in 2015. The immediate economic loss in Quang Ninh is estimated to be about VND 2000 billion (US

TXT-tool 4.081-1.1: Mechanism of Large-Scale Deep-Seated Landslides Induced by Rainfall on Gravitationally Deformed Slopes: A Case Study of the Kuridaira Landslide in the Kii Peninsula, Japan

92 million). Seventeen people were reported dead, 1,459 households were evacuated and at least 30 houses were destroyed. Eight of the victims died when a landslide buried three houses at Cao Thang ward, Ha Long City. We undertook field investigation and ring-shear simulations to study the initiation mechanism and behaviour of the landslide. The rainfall-induced pore-water pressures were estimated using the Slope-Infiltration-Distributed Equilibrium (SLIDE) model developed by Sassa et al. (2010) and Liao et al. (2010, 2012). The ring-shear apparatus (ICL-1) was used to simulate the soil failure, formation of sliding surface and steady-state motion of the landslide. Landslide dynamic parameters obtained and estimated from ring-shear tests were used in the integrated simulation model LS-RAPID to simulate landslide motion. The results demonstrate that the LS-RAPID model predicts a similar hazard area to that observed in the field investigation. In addition, the time of landslide occurrence estimated from the rainfall record and the LS-RAPID simulation is close to the time of occurrence reported by local inhabitants.

Simulating the Formation Process of the Akatani Landslide Dam Induced by Rainfall in Kii Peninsula, Japan

In September 2011, heavy rainfall brought by Typhoon Talas triggered 72 large-scale deep-seated landslides in Nara and Wakayama Prefectures, the Kii Peninsula, Japan. Most investigated landslides on the gravitationally deformed slopes were preceded by pre-existing small scarps along or near the head of the slopes. This study seeks to clarify the mechanism of the huge rainfall-induced Kuridaira landslide by simulating the increasing of pore water pressure with undrained high-stress dynamic loading ring shear apparatus. The authors also examined how gravitational deformations of upland slopes contribute to the mass movement under shear deformation. Laboratory experiments were conducted on two samples of the sliding plane taken in a site investigation, namely sandstone-dominated materials and shale materials. The pore water pressure control tests and shear displacement control tests clearly indicated that the rapid landslide was initiated due to high excess pore pressure generation and significantly shear strength reduction in the progress of shear displacement. The critical pore pressure ratio (ru) was about from 0.33 to 0.36 while shear displacement at the starting point of failure (DL) had a threshold value ranging only from 2 to 6 mm. More specifically, the high mobility of the landslide was in tests on shale sample due to a significant loss of shear strength. In addition, the authors observed the landslide occurrence associated with the sliding surface liquefaction behavior for both samples. The evidence of liquefaction phenomena in the tests was in accordance with the findings in the field survey and previous studies.

Analysis of a Deep-Seated Landslide in the Phan Me Coal Mining Dump Site, Thai Nguyen Province, Vietnam

The Akatani landslide triggered by heavy rainfall during Typhoon Talas on 4 September 2011 is one of 72 deep-seated catastrophic rock avalanches in Kii Peninsula, Japan. The landslide is about 900 m in length, 350 m in average width and 66.5 m of maximum depth of the sliding surface. A rapid movement of the landslide was downward the opposite valley and formed a natural reservoir that has a height of about 80 m and a volume of 10.2 million m3. This paper presents preliminary results of the simulation of the formation process of the Akatani landslide dam by using ring shear apparatus incorporated with a computer simulation model LS-Rapid. Ring shear tests on sandstone-rich materials and mudstone-rich materials taken near the sliding surface indicated that a rapid landslide was triggered due to excess pore water pressure generation under shear displacement control tests and pore water pressure control tests. The pore water pressure ratio (ru) due to rainfall was monitored from 0.33 to 0.37 in the ring shear tests on rainfall-induced landslides, approximately. Particularly, the formation process of the Akatani landslide dam and its rapid movement were well simulated by the computer model with physical soil parameters obtained from ring shear experiments. The actual ratio of pore water pressure triggering landslides was 0.35 in the computer simulation model. The results of the Akatani landslide simulation would be helpful to the understanding of failure process of deep-seated landslide induced by rainfall for future disaster mitigation and preparation in the area.

Landslide Dynamics: ISDR-ICL Landslide Interactive Teaching Tools (LITT)Open image in new window

A large landslide occurred at the Pha Me coal mining dump site at 4:20 AM on 15 April 2012, buried a huge area, including tens of houses and seven persons. There was no abnormal weather or seismic activity at the time of the landslide. A joint work between Vietnamese and Japanese experts was carried out to investigate characteristics and reasons of the landslide. The achieved results show that coal mining wastes are disposed of on low hill sites where granitic bedrock was intensively crushed due to tectonic activity. Weathering crusts include rich clays of over 15–20 m in thickness. The landslide has a volume of about 2.5 million m3, with a slip surface cut through weathering soils at a depth of about 10 m. The scarp of the landslide departs at an approximate elevation of 85–100 m. Travel distance is 300–350 m. Sliding materials are primarily mining wastes. However the sliding surface is defined to be situated at the depth of 12–15 m in the residual soils. There are two significant causes of the disaster. Firstly, the waste dump site plays a role as a water-storage layer which keeps residual soils permanently saturated. The second cause of the deep-seated landslide is over-loading of mining wastes. Prior evidences of the landslide such as cracks at the top, heave at the trough of the dump site were recognized a week before, however they were not seriously considered.

TXT-tool 3.081-1.5: Manual for the LS-RAPID Software

The International Consortium on Landslides (ICL) and ICL supporting organizations jointly established the ISDR-ICL Sendai Partnerships 2015–2025 which is the voluntary commitment to the Sendai Framework for Disaster Risk Reduction 2015–2030. As the core activity of the Sendai Partnerships, ICL has created “Landslide Dynamics: ISDR-ICL Landslide Interactive Teaching Tools”, which are always updated and continuously improved, based on responses from users and lessons during their application. This paper describes the aim, outline, the contents of Text tools, PPT tools for lectures and PDF tools including already published reference papers/reports, guidelines, etc. Core parts of two fundamentals of the Teaching Tools, namely 1. Landslide types: description, illustration and photos, and 2. Landslide Dynamics for Risk Assessment are introduced.

TXT-tool 0.081-1.1: Landslide Dynamics for Risk Assessment

This paper highlights the LS RAPID software that has ability to simulate the initiation and motion of landslides. Fundamental equations and concepts in the LS RAPID model are briefly explained. Step by step procedure of the use of this software are presented, which started from setting of the topography, creating the possible sliding surface using the ellipsoidal parameter, delineation of the unstable mass, soil and water parameters input, triggering factors for the inducement of landslides, the conditions for calculation, running the landslide simulation and up to the output settings after the simulation. Several cases of landslides which were analyzed by LS RAPID are described further in the PDF Tool: Manual for the LS-RAPID software.

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

The study of landslide dynamics is a fundamental tool to aid in proactive responses to reduce landslide disaster risk, which has become intensified by the increasing development of mountain slopes due to economic and population growth in many developing countries Landslide risk is also increasing due to extreme rainfalls caused by changing climate in many landslide-prone areas in the world. Natural landslide phenomena would have initially attracted attention through the observation of ground deformation/movement which changed the natural scenery in the mountains and sometimes affected people’s living areas before the era of industrialization. Geological and geomorphic studies started at this stage. Civil engineering works to construct roads, bridges, dams and river banks, and engineering works to mine hard rocks, limestones, coals, valuable metal and minerals developed during the industrialization of human society. They caused artificial geomorphic changes and often triggered landslides. To avoid triggering landslides due to human activities and to stabilize landslide slopes, industry-centered landslide studies were developed. The main tool was slope stability analysis based on soil and rock mechanics. In the post-industrialization period, people-centered disaster risk reduction studies integrating natural sciences, social sciences and engineering to save people’s lives have developed. The initial global scale initiative was the International Decade for Natural Disaster Reduction (IDNDR) from 1st January 1990 to the end of 1999. Peoples are rarely killed by either slow-speed or short-distance landslides. The landslides affecting people’s lives are rapid and long-runout landslides, which they cannot escape from. Landslide studies to assess the velocity and travel distance of landslides must be developed. This is topic is landslide dynamics. This paper describes the core concepts and the important aspects of landslide dynamics as the fundamentals of ISDR-ICL Landslide Teaching Tools, which aim to support landslide risk reduction efforts through reliable landslide risk assessment and the early warning and land-use changes.

TXT-tool 3.081-1.8: A New High-Stress Undrained Ring-Shear Apparatus and Its Application to the 1792 Unzen–Mayuyama Megaslide in Japan

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.