Natural Geo-Disasters and Resiliency

This article attempts to develop a machine learning based slope hazard assessment method using the case study of the 2011 Niigata-Fukushima heavy rainfall disaster in Japan. The proposed method is constituted of two analysis procedures. The first step is a pointwise hazard assessment by machine learning (Step 1), and the second step is an image analysis (Step 2) to extract collapsed blocks based on the analysis results of pointwise hazard assessment. In Step 1, conventional methods have lacked to capture the accurate topographic information necessary to evaluate the stability of collapsed blocks. Since the topographic information needs to be scaled according to the size of collapsed block, it needs to consider from the microtopography to the macroscopic topography to properly catch the various collapsed blocks. In this article, the moving averages of various topographic indexes are introduced into AI-based slope hazard evaluation and its validity is examined. Furthermore, analyses using overground and underground openness indices were conducted and it was found that slope hazard assessment with very high accuracy is possible. Output of pointwise slope hazard assessment is obtained like a mosaic picture. It is used to evaluate the hazardous area, but difficult to discriminate hazardous collapsible blocks. Therefore, in Step 2, this article attempted to extract dangerous blocks by machine learning of the image outputting the hazard assessment. Case studies showed that collapsible blocks are successfully estimated.

Many disaster investigations after significant earthquakes have indicated that the extent of damage is not simply related to the distance from the epicenter. Serious destruction has been found in the near-fault zones, as significantly affected by the distance from the earthquake fault. This study discussed the effect of ground motions from different fault distances under dynamic triaxial compaction tests. Five real ground motions were applied as observed by stations located at different distances from the earthquake fault caused Taiwan Chi-Chi Earthquake in 1999. This study also considered variable initial radial pressures (100 kPa, 200 kPa, and 400 kPa) and the consolidation ratio. The results indicate that both the maximum strain appearing during the dynamic load test and residual strain by near-field shaking are significantly greater than those in other fault distances. Generally, the closer to the fault, the greater the strain. The difference decreases as the initial confining pressure increases. This trend could be obtained under different consolidation ratios. However, the difference becomes more evident under anisotropic initial confining pressures.

Slope revegetation by seeding works with herbaceous plants is widely employed to prevent road embankment from erosion damage. The Percentage of Vegetational Cover (PVC) is used as an indicator for the quality evaluation of the seeding works. However, the PVC is usually measured manually through visual inspection, and the measurement results of the same subject might not be constant. In the present study, RGB image analysis is applied to objectively measure the PVC to overcome this situation. Then, laboratory flume experiments are conducted to investigate the capability of the PVC obtained by RGB image analysis to predict the decrease of sediment erosion against concentrated flow. Two herbaceous plant species, Centipede Grass and White Clover, are employed in the experiments. The findings of the experiments are as follows: Declining trends of the sediment erosion are observed as the PVC increases or plant growth period becomes longer, and the trends are more correlated with the PVC with RGB image analysis than with plant growth period. The results indicate that RGB image analysis can be a useful and inexpensive tool for inspection of the seeding works with herbaceous plants.

Integral bridges can eliminate economic and structural weaknesses by integrating reinforced concrete abutments and girders. However, owing to thermal expansion and compression of the girders under changing atmospheric temperatures, a bridge can be damaged from increased backfill earth pressure resulting from repeated horizontal displacement of abutments. Therefore, the thermal expansion and compression of bridge girders must be considered when designing integral bridges. Climate change associated with global warming may result in extreme temperature changes. Thus, bridge girders may have a higher thermal expansion and contraction compared to those in previous design assumptions. Therefore, we investigated the possibility of quantitatively evaluating the increasing earth pressure caused by the thermal expansion and contraction of bridge girders. This study entailed simulations of the repeated horizontal displacements of the bridge abutments using an aluminum bar laminate model. We obtained the results of 100 cyclic loading tests, which showed that the maximum value of the earth pressure at the end of the cyclic loading is minimally affected by the position of the amplitude center, and it can be predicted from the load–displacement relationship for non-repeated loading. Therefore, based on the results of the non-repeated load tests, the maximum value of the earth pressure resulting from repeated horizontal displacement of abutment can potentially be incorporated into the design of integral bridges.

Recently, rainfall-induced river levees damages have been increasing remarkably. As the frequency of heavy rainfall events is expected to increase due to climate change, it is crucial to develop proper countermeasures to prevent damage to river levees and embankments. Among various modes of river damage, slip failures due to seepage through embankment fill is omnipresent and are primarily associated with the changes in saturation distribution through the comprising soil profile. Efficiently proposing countermeasures for such a problem requires monitoring and considering the changes in water content and shear strain within the embankment, where generally, the rise in river water level is associated with an increase in the seepage forces. Through this study, a sheet-type sensor to continuously measure the changes in water content, strain, and temperature, both horizontally and vertically, was developed and utilized to understand the mechanism and enhance the resiliency of levees. Furthermore, the sensor measurements are utilized to elaborate on the pre-failure indicators through a model experiment.

This research aims to incorporate the information on plant, topography, hydrology, and geology to assess the landslide potential in a forested slope with a large area. The forested slope with 100 hectares is located at the Duona forest route, Taiwan, and the site's elevation is E.L. 950 m. The study investigates the dominant plant species and planting density in the forest stand measures the spatial distribution of the root system in the soil for the dominant plant species. The study area in the forest is divided into 1,000,000 units (unit size: 1 m × 1 m). The study evaluates the plant root reinforcement in the forested slope and carries out slope stability analyses for each unit (1 m × 1 m) using TRIGRS computer program. The analysis considers plant root reinforcement, soil strength, topography, and hydrological condition. The study presents the spatial distribution of the landslide potential in various scenarios in the study area.

In recent years, many housing retaining walls have been damaged or even collapsed by earthquakes in Japan. Among them, the damage to dry masonry retaining walls was prominent. Although there are reinforcement methods for retaining walls such as the earth nailing or the ground anchors, which are not suitable for housing retaining walls due to inadequate construction space. Other reinforcement method such as the root piles, on the other hand, straight piles and tilting piles are installed into sloping ground from the top of slope bank vertically so as easier to construct in narrow residential areas, hence widely applicable for housing retaining walls. But the problem of root piles is that the construction cost tends to be high for individual houses since many straight piles and tilting piles are used. From this background, we propose a reinforcement method in which only use tilting piles and connect the top of them to the top of the existing retaining wall to reduce construction cost by decreasing the number of reinforcing materials. This report aims to confirm how a distance between a retaining wall and a reinforcing material affects on the earthquake resistance by conducting centrifugal tilting tests using dry masonry retaining walls. The results show that connecting the top of the retaining wall to the top of the reinforcement allows the retaining wall retain higher soil pressure and the influence of reinforcement becomes increasing.

As open-type Sabo dam has gained prominence in recent decades, the role it plays in debris flow hazards has become more apparent. Vertical and tilted forms of open-type Sabo dam generated various consequences in the debris flow hazard of Nashizawa (Japan) in 2014, indicating that the impact of inclination needs deep exploration. To solve this problem, this study employs centrifuge tests, which are uncommon in the field of debris flow, to establish not only the feasibility of utilizing the centrifuge to reproduce debris flow hazards, but also to simulate the behavior of various open-type Sabo dams to catastrophes under the same conditions, aiming to make insights into the different performances through comparing the vertical type (0°) and the tilted type (20 and 40°) from the aspect of impulse derived from impact load, capture rate, and blockage area rate et al. The findings indicate that the vertical open-type Sabo dam has a high capture rate and low impulse during the hazards. On the other hand, the tilted open-type Sabo dam has a lower capture rate and a high risk of missing stones during climbing than the vertical one.

Most of the National Highways in Bhutan pass through mountainous areas and they are extremely fragile. At the point where the highway crosses the valley, protection or drainage facilities have not been sufficiently installed. During the monsoon season, debris flows cause road closes lasting several hours or days had a significant impact on the stability of traffic. JICA Bhutan Office is implementing a project to strengthen the capacity of the Department of Road of Bhutan for slope protection works. In this project, the authors organized the procedures and methods to introduce countermeasure facilities with reference to the countermeasure methods of Japan for debris flows. First, desk study was conducted to identify landslides, slope failure, and other landforms indicating unstable slope, and next step, fieldwork to investigate the volume of unstable sediment and the diameters of numerous boulders. Based on these studies and rainfall observation data, it was expected that the volume of debris flow, peak flow rate, and maximum diameter of boulders in debris flow flowing down from the target valley. With these results, the authors considered about the scale of countermeasures to construct safely against such debris flow, and culverts constructed at the pilot site “Bjee” in Trongsa. At the results of these studies, “Guidelines for Countermeasures against Debris Flows” were developed to mitigate road disasters in Bhutan for sustainable construction works.

As an initial experimental study on the mechanism of destabilization of river piers caused by local scour, the effect of grain size distribution of bed materials on pier destabilization was experimentally evaluated from the viewpoints of river engineering and geotechnical engineering. The results showed that the scour resistance of a non-uniform bed was greater than that of a uniform bed, even if initial mean grain sizes of the two bed materials were almost the same. In addition, the rate of horizontal displacement of the pier toward upstream in the non-uniform bed decreased with time, while the rate increased in the uniform bed. The possible reason for this difference is related to coarsening of the bed surface at the pier nose in the non-uniform materials. Coarsening is assumed to easily dissipate the downflow energy because of larger intergranular gaps. This might have led to reduction of the tractive force acting on the ground immediately below the pier bottom, and thus reduced the rate of horizontal displacement of the pier toward upstream.

Natural slopes and embankments typically have negative pore water pressure. They are generally unsaturated, which increases the shear strength and, as a result, the stability of the slopes. The infiltration of rainwater into the ground during a rainy event causes a decrease in the matric suction, ultimately reducing the soil shear strength and leading to slope failures. Therefore, when analyzing the stability of such slopes, it is critical to assess the strength and deformation characteristics of unsaturated soil. A double-cell triaxial test apparatus was utilized in this study to examine the shear strength and deformation behavior of compacted silty soil due to water infiltration. Laboratory element tests were conducted on samples prepared with an 80% degree of compaction and an optimum water content of 20%. The soil samples were isotropically consolidated under a confining pressure of 500 kPa before being sheared with constant volume under constant water content conditions. Pore water pressure was increased just before the shear process to reduce matric suction and initiate water infiltration. From the test results, it was found that the degree of saturation increased by an average of 42.5%, 66%, and 75.5%, while the maximum shear strength decreased approximately by 16%, 18.5%, and 20.5% when the suction was reduced from 20 to 10 kPa, 5 kPa, and 0 kPa, respectively.

The Richards equation is a classical model that describes flow through unsaturated porous media. Efficient numerical methods and relevant theories are limited by its nonlinearity and degeneracy. We introduce two linearized finite element schemes to solve the Richards equation efficiently. In addition to the linearized finite element scheme based on backward Euler format, we also discuss the multi-level linearized finite element scheme based on the Crank–Nicolson format to improve accuracy. Compared to traditional mesh-based methods, such as the finite difference and the finite element methods, deep learning offers a mesh-free approach by taking advantage of automatic differentiation, which can overcome the limitation in dimension and in complexity of boundary shape, allowing for irregularity. We propose an algorithm to obtain the approximate solution of the Richards equation via deep learning. This method is capable of dealing with the high-dimensional Richards equation with complex boundary conditions.

The authors conducted field permeability tests on numerous river embankments using a Marriott siphon in 30-cm test holes to obtain their saturated permeability coefficients. The results revealed that the field-obtained saturated permeability coefficients were larger than those obtained as a result of the laboratory permeability test conducted on the undisturbed specimens sampled from the same location. Regarding embankments constituted by fine-grained soils, there are cases in which the field-obtained coefficients are several orders of magnitude larger than those obtained under laboratory conditions. These results suggest that the field permeability coefficient obtained by the Marriott siphon with large-diameter test holes evaluates the macroscopic permeability, including in situ heterogeneity and anisotropy. In this study, the results of the field permeability tests at two embankments of the Oda and Kano Rivers are shown. In addition, the results of the laboratory permeability test for the undisturbed specimens sampled at each field site are shown. In each survey, the field permeability coefficients were larger than both the laboratory permeability coefficients and the estimated value from particle size, as in the case of other embankments investigated so far.

Owing to climate change, localized heavy rainfall and typhoons have become increasingly dangerous in recent years, leading to accelerated scour and causing damage to river-crossing bridges supported by shallow foundations. Most studies on bridge scour have mainly aimed to evaluate the ground outflow area from a hydraulic perspective, but only a few have focused on the relationship between such an area and the displacement or residual bearing capacity of the foundation, which is necessary to assess the performance of foundations after flooding events. Our previous study focused on local scour caused by the concentrated removal of ground from the upstream edge of the foundation. This study focuses on internal erosion, where fine soil particles flow out of the layer just beneath the foundation. To evaluate the residual bearing capacity after internal erosion, we conducted vertical loading tests of internally eroded shallow foundations using an aluminum rod ground model from which only the small-diameter aluminum rods were extracted to simulate the phenomenon. The test results showed that: (1) residual settlement occurred immediately after the event causing internal erosion; (2) there was no significant increase in the residual slope angle; and (3) the residual bearing capacity did not decrease during emergency repairs, such as the replenishment of the residual settlement with concrete.

This chapter mainly describes the methodology of how to manage the risk of slope disasters in one of JICA projects in Honduras. Although this is still an ongoing project, the risk management method will clarify the relationship between “self-help”, “public aid”, and “mutual assistance,” especially the ideal form of risk communication for community disaster prevention, and the direction of sustainable evaluation and action against slope disasters.

From June 28 to July 8, 2018, concentrated torrential rains occurred in a wide area nationwide, mainly in western Japan, including Hokkaido and the Chubu region, due to Typhoon No. 7 and the rainy season front, etc., and caused serious sediment disasters, including failure slope failure in Kitakyushu City, Fukuoka Prefecture, located in the northern part of Kyushu region. To protect the lives and property of residents from such slope disasters, we believe it is necessary to clarify the risk level of slope failure and the mechanics of slope failure to construct efficient and effective Slope Disaster Prevention measures. Therefore, this study was conducted on six slopes where failures occurred in July 2018 in the Kitakyushu City area to investigate the topographic and geological conditions that contribute to slope failures in detail through field observations, UAV topographic observations, and surveying. The Kitakyushu area is characterized by a relatively steep mountainous terrain with diverse geological compositions and complex geological structures, and we were able to investigate and study the failure slopes that occurred in several geological units, including granitic and paleo sedimentary rocks. The results showed that the six failures were shallow failures classified as surface failures, and all of them occurred in a strongly weathered zone. Although there were no significant differences in the failure modes due to differences in topography and geology, we were able to elucidate the mechanism of each failure.

The authors performed physical model tests to investigate the reinforcement effect of geocell under moving wheel loads conditions. This is important to evaluate the internal stability of reinforced soil foundations. The relationship between the cyclic number of moving wheel loads, the wheel subsidence, and the foundation's deformation behavior was obtained from the series of tests. The deformation behavior was analyzed using the PIV technique on the cross-section pictures of the foundation. As a result, it was observed that the geocell-reinforcing technique could reduce wheel subsidence of the foundation. The PIV analysis indicated that the soil deformation in the inner geocell was confined. The authors have outlined this study's physical model tests and test results. Additionally, the results of the PIV analysis are shown, and the reinforcing mechanism of the geocell is discussed.

Landslides are among the most devastating natural calamities, causing significant changes in landscape morphology, compromising infrastructure, and posing grave threats to human lives. Developing accurate landslide susceptibility maps (LSMs) that indicate the likelihood of landslide occurrence in specific areas is paramount for effective environmental management, urban planning, and mitigating economic losses. Despite the importance of LSMs, existing research in data mining for landslide susceptibility has predominantly focused on small-scale case studies, typically examining single types of landslides. This paper presents a pioneering data mining approach to generate LSMs for the Chamoli district of Uttarakhand, India, a region with a heterogeneous landscape prone to multiple types of landslides. To address the complexity and scale of the problem, the researchers employed the Random Forest algorithm, a powerful and adaptable machine learning technique, to create both susceptibility and classification maps. A total of 13 causative factors were considered for the purposes of training and validation. The model underwent validation using the AUC-ROC method, yielding an AUC-ROC value of 82.7%. This value signifies that the predictive accuracy of the model is in close agreement with the real distribution of landslides across the study area. This accuracy is crucial for reliable risk assessment and informed decision-making. The innovative application of the Random Forest algorithm for landslide susceptibility mapping in a large and heterogeneous region like Chamoli sets a promising precedent. The findings of the study have significant implications for enhancing landslide risk management strategies in similar regions globally, facilitating proactive measures to safeguard lives and assets in Landslide-prone areas.

Slope failure is a process of landform change triggered by geophysical and meteorological factors, and its causes include heavy or prolonged rainfall, earthquakes, and other disasters. Data from the Synthetic Aperture Radar (SAR) satellite ALOS-2 can identify slope failure immediately after a disaster because it can observe a large area of the ground surface at any time, independent of the weather. In general, the commonly used method for slope failure detection is visual interpretation using postdisaster optical aerial image data or satellite data in Japan, which is time consuming and laborious. Therefore, we introduced the concept of extracting ground surface change areas based on slope unit for quantitative purposes. Furthermore, the division of slope unit is improved. The method's feasibility was verified by detecting the heavy rain disaster in North Kyushu, Japan, in 2017. The results show that the improved slope unit has a higher recall of ground surface changes than the previous method. Under the proposal of this study, the location of slope failure can be detected with high accuracy immediately after a disaster.

Idukki is constantly hit by rainfall-triggered landslides, which lead to loss of precious lives of people apart from other various types of allied losses. Residual soils in tropical regions are mostly found in an unsaturated condition. In unsaturated conditions, soil will have different hydrological and mechanical properties, which are quite often ignored in traditional soil mechanics approach due to either insufficient data or for the reasons of avoiding complex analyses. This paper attempts to analyse the rainfall-induced shallow translational landslide at Idukki district of Kerala state in India by conducting regional modelling with incorporation of unsaturated soil properties prior to the occurrence of the landslide. This landslide was triggered by a heavy rainfall which lasted for several days and it claimed seven people lives besides damaging seven houses. Transient Rainfall Infiltration and Grid-based Regional Slope Stability (TRIGRS) was used to model this event by incorporation of saturated and unsaturated soil properties. Site visits were carried out and several field and laboratory tests were performed for the determination of various saturated and unsaturated geotechnical properties of soil required for the analysis. Seepage and stability analyses were performed to determine the conditions that lead to the failure of the slope. It was observed that the rainfall leads to the gradual reduction in suction in the soil along with the rise in ground water table which caused the shear strength to reduce along the slip surface and hence led to a shallow translational landslide.

Differential interferometric synthetic aperture radar (D-InSAR) techniques are a well-established remote sensing tool used for natural hazard detection and monitoring. The Sentinel-1 satellite mission provides extensive spatial coverage, regular temporal sampling, and accessible data availability, making it an ideal source for D-InSAR analysis. In this study, D-InSAR analysis was performed over the potential slope deformation area in the colluvium deposit at Doi Chang, Chiang Rai province, Thailand, using all Sentinel-1 images acquired between March 2016 and March 2017. The results show that the slope movement in colluvium deposits at Doi Chang was slow during the dry season, but its velocity significantly increased during the rainy season, confirming the slope movement behavior observed during site investigation data. The movement rate was sufficient to cause recurrent damage to infrastructure, such as roads and buildings, resulting in economic loss and public concerns. The D-InSAR results revealed substantial activity and displacement behavior on the spatial–temporal evolution. Furthermore, observations were validated, and their accuracy was confirmed via comparison to ground truth data from borehole inclinometers. The detected displacement time series provides an understanding of the spatial–temporal evolution of the corresponding deformation phenomena.

At present, soil displacement is still occurring continuously in some areas of Bangkok and urban areas. Groundwater level change has affected soil displacement around the central of Thailand. The old building and other buildings located in the Bangkok area have been directly affected when groundwater level changes. According to the regulation of groundwater pumping, the rate of groundwater consumption decreased. The groundwater level was recovered from 1997 until the present, referring to many observation wells in Bangkok. This study focused on the possibility of soil surface displacement during groundwater level recovery to the ground surface. The soil surface displacement prediction in Bangkok was mentioned using a theoretical calculation based on Terzaghi’s consolidation theory. The results were verified by comparing the results to the instrumentation data when the groundwater level increased to the ground surface. The results found that the soil surface displacement rates have rebounded from 0.01 to 0.35 cm/year. Soil surface displacement rates between theoretical calculation and observation data have similar trends.

Each year, numerous disasters occur, challenging the resilience of societies worldwide. The effective management of the intricate disaster recovery process necessitates well-prepared plans, robust response strategies, and adequate resources. The recovery process can vary drastically among communities. However, the existing loss models and recovery frameworks rely on predefined loss and recovery functions, limiting their ability to accurately estimate recovery. Additionally, these predefined models encounter challenges in characterizing the complex recovery process due to analytical limitations and the unique nature of recovery in various communities. This study explores a data-centric approach to quantitatively estimate post-disaster recovery. It introduces a Bayesian Neural Network (BNN) model capable of providing near real-time evaluations of the recovery process. Synthetic data has been generated for two different reconstruction modes: in-situ and reallocated reconstruction, as adopted in two towns following the 2008 Wenchuan, China earthquake. In this context, Yingxiu town represents in-situ reconstruction, while Yongchang town represents reallocated reconstruction. The BNN model allowed for uncertainty characterization during the estimation and forecasting of recovery for two different communities. The recovery curves generated using BNN yielded confident recovery predictions with only 30–40% of the training data. This underscores the potential of the BNN approach as an effective post-disaster recovery estimation tool, particularly when integrated with other resiliency estimation models.

In recent years, the research on the liquefied critical (threshold) void ratio of soil deposit has become a fascinating topic. This paper tries to utilize the current liquefaction evaluation criteria to make theoretical use of the collected soil geological survey data. In this study, the liquefied critical void ratio is discussed in the particle size characteristics of soil through the particle packing model. Utilizing the microscopic study of the critical void ratio of the soil, the particle packing model can be applied to the in-situ soil practically. This study is based on the particle packing model and the liquefied critical void ratio database of in-situ data to carry out numerical regression analysis. This paper conducts a variety of discussions on the soil particle packing model and the in-situ soil to demonstrate the suitability of the model in practical applications. Through the complete database verification and correction, an empirical formula for in-situ critical void ratio suitable in Yilan area is obtained. This paper proposes a set of hypothetical formulas for predicting the critical void ratio in Yilan area, $$e_{i}^{\text{cr}} = 0.5455\left( {1 + 0.47C_{u}^{ - 0.15} } \right)d_{i}^{ - 0.088\rho }$$ e i cr = 0.5455 1 + 0.47 C u - 0.15 d i - 0.088 ρ , to provide an innovative approach of liquefaction judgment. This study makes the estimation of the critical void ratio of soil liquefaction more comprehensive and improves the knowledge of evaluating soil liquefaction. Hopefully, the proposed liquefied critical void ratio can be used to evaluate the soil state to judge the possibility of soil liquefaction for having certain benefits on the local public infrastructure in Yilan area for the future.

In 2016 Kumamoto Earthquake, many retaining walls, such as aged masonry retaining walls collapsed. Many of the existing retaining walls still have high potential for collapse during a future earthquake event in Japan, so that they need to be reinforced. It is necessary to know how those collapsed retaining walls perform during the earthquake loading. However, it is difficult to estimate the seismic capacity of existing retaining walls and appropriate reinforcement method has not yet been established. The Ministry of Land, Infrastructure, Transport and Tourism has been studying on establishing methods for reinforcing existing retaining walls and estimating their seismic resiliency. The purpose of this study is to establish a method for estimating the seismic capacity of existing retaining walls. Linear slip is often used in the stability analysis of retaining walls, but it could be less consistent with the actual situation. Logarithmic spiral slip is considered more realistic than linear slip, but the accuracy is not known due to lack of examples of calculations using it. In this manuscript, therefore, the logarithmic spiral method was used to calculate active earth pressures acting on retaining walls and slip lines to check the accuracy. Calculations were performed under different conditions and results are compared to those obtained by other theories, such as Coulomb’s earth pressure theory. The results showed differences in magnitude of active earth pressures and shape of slip lines. From this, it was found that the logarithmic spiral method is as accurate as or more accurate than Coulomb’s theory.

It is important to grasp the circumstances under which coseismic landslides occur as soon as possible for providing rapid initial response to these disasters. Though many factors are cited as reasons for coseismic landslides, only a few studies have focused on antecedent rainfalls or these have used only point rainfall data without two-dimensional extension, and instances of detailed quantitative evaluation have been low. Therefore, in this study, we estimated the effect of areal antecedent rainfalls on coseismic landslides. The Mid Niigata Prefecture Earthquake in 2004 was targeted for this purpose. We used random forest and classification and regression tree analysis for estimating the major factors that influence, and their effects on coseismic landslides. We found that antecedent rainfall had limited influence on the occurrence of coseismic landslides in this earthquake. However, the impact of antecedent rainfall on large landslides was greater than that on small landslides. In addition, the impact of long-term rainfall may be greater than that of short-term rainfall, at least for large landslides. This suggested that the accuracy of estimation of occurrence of coseismic landslides could be improved by considering the influence of antecedent rainfall.

In Japan, lots of cities are suffering from land subsidence problems, resulting from liquefaction due to its soft ground constitution. Among the various preventive and/or mitigation measures practiced for combating it, the chemical injection method is commonly selected for it with the intention of increasing the strength of the ground. However, the limitation of this technology lies in the scarcity of data on the probable influence and effectiveness of the sprayed chemicals over the long-term period into the surrounding grounds. It is necessary to study in detail to ensure that incidents like chemical accidents do not occur in the future due to the failure in strength over the long-term period. Therefore, the objective of this study will be the evaluation of ultrafine particle grouting materials properties in terms of durability over the long-term period by using the prediction method. The results generated by these prediction methods are verified by comparing them with the test results. In this study, the prediction is made by the Autoregressive integrated moving average (ARIMA) model, machine learning predictive model (MLPM), and state-space representation model (SSRM). For the lower input data amount, the results generated by the ARIMA model can be of higher precision comparatively, but the margin of error is still high. Thus, in order to conclude on the best model, a higher degree of research is required to identify all other influencing parameters and comparative studies of other methods.

In risk assessments of slopes after rainfall, to quantify the amount of fluid outflow from the system, it is essential to obtain the amount of evaporation from the slope surface. The amount of evaporation can be estimated from the general meteorological data and the soil surface temperature using the bulk method (β-method). Evaporation efficiency, an essential parameter of the bulk method, expresses the ease with which evaporation occurs and is dependent on soil moisture and surface soil type. However, the effect of different surface soil types on the soil moisture associated with evaporation efficiency has not yet been quantitatively evaluated using soil parameters. This study discusses the effect of different soil types on the soil moisture dependence on evaporation efficiency based on the results of the laboratory experiments on two types of sandy soil. Results showed that the effect of different soil types can be evaluated by focusing on the range where evaporation efficiency is valued at less than 1.0. Furthermore, the experimental results confirmed that the evaporation efficiency was slightly smaller for samples with higher fine fraction content in the range of shallow soil moisture content. The result showed consistency with the estimations since the higher the fine fraction content, the smaller and more structurally complex the void becomes. These findings suggested that the effect of soil conditions on the soil moisture dependence on evaporation efficiency can be evaluated using the void size distribution.

This research presents a simple technique to detect and classify landslide seismic signals from other seismic noise signals. Research aims to develop non-structural mitigation measures for landslide hazards, including monitoring landside-induced seismicity. The data was collected in real time from an 18-seismometer array situated in North Western Himalayas. The methodology to detect events in the time history record is based on STA/LTA, where managed event was analyzed through Peterson noise model, and finally, an event was considered a potential landslide event if it crossed the maximum noise boundary. The Time–Frequency Analysis (TFA) technique was used to classify the detected events. Based on literature review, Short-time Fourier Transform (STFT), Fourier Synchrosqueezed Transform (FSST), Wavelet Synchrosqueezed Transform (WSST), and Smoothed Pseudo-Wigner-Ville Distribution (WVD) are the best suitable for seismic signal analysis. As a result, in our study region, seismic events can be classified with high-frequency resolution and time localization with WSST; also, we found some frequency bands for dominating frequency with the event source. The results have been verified with actual events records, and all these events happened in recent years.

The Ms6.4 Yangbi earthquake occurred in Yunnan Province, the southwestern part of China. Under the influence of severe seismic motion, slopes were damaged and lots of tensile cracks appeared on the slope surface. Considering the potential further failure of damaged slope in the post-earthquake rainy season after Yangbi earthquake, the stability analysis of damaged slope is necessary to be carried out to evaluate its safety in the following rainy season. Through field investigation including UAV shooting and ERT measurement, the surface topography and subsurface geological condition of the damaged slope are obtained based on DEM and resistivity profile. The numerical mesh model of the damaged slope is built using mesh model reconstruction method with tetrahedron element. By using the result of DEM and ERT to define the geometry of upper gravel soil elements, a mesh model considering the damage characteristic of damaged slope is reconstructed. The stability of the damaged slope was calculated by the strength reduction method. The results show that the deformation is concentrated on the rear edge of the damaged slope, and the upper part above the excavation area of damaged slope may lose stability during the following rainy season. The results of numerical calculation are verified by the phenomenon observed in the investigation after post-earthquake rainy season, indicating the validity of reconstructed mesh model using DEM and ERT.

At 21:26 on April 14, 2016, an earthquake of JMA magnitude 6.5 with its epicenter in the Kumamoto region of Kumamoto Prefecture occurred, with a JMA seismic intensity of 7 observed in Mashiki Town. At 1:25 on April 16, an earthquake of JMA magnitude 7.3 also occurred. Strong tremors occurred over a wide area mainly in Kumamoto Prefecture, including tremors with JMA seismic intensity of 7 observed again in Nishihara Village and Mashiki Town, causing tremendous damage. This series of seismic activity resulted in damage to numerous road structures, including the collapse of Aso-Ohashi located in front of the site of a large-scale slope failure, the destruction of the National Route 57 road, damage to bridges and tunnels on the Prefectural Route 28 Kumamoto-Takamori Line, and the collapse of a bridge spanning Kyushu Expressway. This paper introduces some technical measures to reduce a risk of the loss of function in bridges subjected to the ground deformation induced by an earthquake, with practical examples of restoration projects for three road bridges, namely Tawarayama-Ohashi, Aso-Choyo-Ohashi, and Aso-Ohashi which were damaged by the effect of the ground deformation due to the 2016 Kumamoto earthquake.

Ground improvement is necessary in many flat areas and landfill sites in Japan because these areas have soft ground and are highly susceptible to serious damage such as long-term consolidation settlement and liquefaction. The deep mixing method (DMM) is an in-situ soil treatment in which native soils or fills are blended with cementitious and/or other materials. Ground treated by DMM has higher strength and lower compressibility than untreated ground. However, there are quality problems in this method due to a condition in which a mixture of soil and materials adheres to and rotates along with the stirring blades without performing efficient mixing. Therefore, our purpose is to improve quality of improved columns produced by the mechanical mixing method using vertical rotary shafts and mixing blades. In this study, five cases of small-scale model experiments were conducted with changing in the blade rotation number, the incident angle of agitating blades, and the agitating blade angle. Strength tests were conducted using unconsolidated samples at different depths to investigate strength distribution, and needle penetration tests were also conducted. From the results, the effects of the blade rotation number, the incident angle, and the agitating blade angle on improvement quality were discussed.

A shallow earthquake occurred in the West Sulawesi Province of Sulawesi Island, Indonesia, with a moment magnitude (Mw) of 6.2 on January 15, 2021, at 02.28 local time. The epicenter of the earthquake was in Majene, ~ 32 km from the provincial capital, Mamuju. The earthquake was caused by the tectonic movement of the Makassar Strait Thrust fault, leading to thousands of buildings being damaged and hundreds of people dying in the city of Mamuju. The objective of this study was to investigate the relationship between ground conditions and large seismic amplification that might occur. Therefore, a series of geotechnical investigations were undertaken. Non-linear and equivalent linear site-specific response analyses were also conducted to model the estimated ground response propagated by earthquakes. Our findings suggested that the earthquake generated a large seismic amplification due to the ground conditions in the city. The computed seismic amplifications were 1.4–2.67 in the period of 0.4–2 s, which coincided with the resonant periods of two–five-story buildings in the city. These results would be beneficial in mitigating the seismic hazards in the city, in the near future.

The strongest velocity pulse orientation is a critical factor when considering the near-fault ground motions and their adverse seismic response. The strongest velocity pulse identification methods usually focus on a single orientation and two orthogonal components in the horizontal plane. In this paper, a new identification method of the strongest velocity pulse is proposed that considers three orthogonal components of ground motion, by rotating the ground motion to the orientation that corresponds to the maximum peak ground velocity (PGV) in three orthogonal components. The identification results by this method are compared with the identification results by the wavelet analysis method. The results demonstrate the feasibility and accuracy of the strongest velocity pulse identification method considering the three orthogonal components of ground motion.

In order to predict the mechanical responses of Haikou red clay under over-consolidation and cyclic loading conditions, this paper adopts a unified critical state model considering the over-consolidation and cyclic behaviour (i.e. CASM-kII) for the constitutive modelling. Although the CASM-kII can reasonably characterize the isotropic and hardening behaviours of soils, the dilatancy law of original CASM-kII is modified in this paper to achieve a better agreement with stress-dilatancy relation observed in laboratory test. Through the comparisons of a series of experiment data and simulated results, it is found that the modified CASM-kII can accurately characterize the over-consolidate and cyclic responses of Haikou red clay under different loading conditions.

As a soft measure to prevent sediment disasters, various measurement devices and monitoring systems have been developed through the improvement of ICT technology, and systems that detect signs of collapse and encourage evacuation have been developed based on slope observation data. A major challenge in those systems is what kind of measurement indicates a sign of danger. In this study, instead of predicting collapse based on a geotechnical model from measured data during slope failure, we modeled and analyzed observed data as time-series data to verify whether the signs before collapse can be captured as early as possible. As a method for evaluating slope observation data, we employed a learning method using slope observation data in a normal state during slope stability, and when a pattern of data different from the normal state was detected, we determined that the slope was unstable and issued an alert. A method for detecting anomalies on a slope was verified by using machine learning, in which data are predicted from a time series of slope surface strain data measured in a centrifuge field slope failure experiment, and by using the residuals between the predicted and measured data. As a result, it was confirmed from the time-series change in the number of anomalies detected by the eight installed surface strain sensors that anomalies were detected on the slope before the collapse.

As standards of living rise, so does the amount of waste produced and the need to dispose of it. Landfill is still the most common method of waste disposal. Brownfield sites, especially tailings piles, are well suited for this purpose. Landfills can cause significant damage to their surroundings, so geotechnical and environmental risks must be eliminated. Proper monitoring should be used to prevent this from happening. Local depressions up to 15 m deep have been used in the spoil heap area of a surface coal mine. Due to the nature of the materials in the spoil heap, the approach to geotechnical monitoring of the proposed construction needs to be different from the conventional one. Undoubtedly, the low permeability of spoil heap material is one of the most positive features: In the lower, fully consolidated parts, there are impermeable soils. However, spoil heaps consolidate slowly and can cause uneven deformation, particularly surface settlement. There are associated geotechnical risks of damage to the sealing elements of the landfill. It is therefore appropriate to monitor the deformations of the bottom of the landfill body. Prior to the construction of the landfill, altimeter sensors were installed at the site of interest to measure the relative movements of the landfill floor in relation to the location of the reading unit. A geodetic survey of the site (fixed points around the landfill) can be used to determine the movements of the entire heap. Uneven settlement can be documented from these absolute movement values. Spoil heap materials tend to be unstable; therefore, proper monitoring should be supplemented by numerical methods (stability calculations) to prevent landslides. The geotechnical risks associated with the disposal of waste in landfills under such anthropogenic conditions should be eliminated by unconventional geotechnical monitoring, including the measurement of deformations of the landfill bottom and continuous recalculation of stability.

The cutting slope soil is easily damaged by earthquakes and rainfall owing to excavation disturbance. Soil damage and strength degradation can significantly affect the slope stability. However, research on the evolution process of cutting landslide considering damage accumulation effect is insufficient. Taking the Dayangyun highway under construction affected by the Yangbi earthquake as the study area, field electrical measurements were conducted and slope damage was determined on the basis of evolution law of soil damage under rainfall, which was determined by laboratory test. A discrete element model of the damaged slope was developed, and evolution process of landslide was analyzed with different damage factors. The results indicate that trailing edge crack appears when the damage factor is 0.19. As the damage factor increases from 0.19 to 0.33, the slope body starts to slide along the fissured soil layer. The cutting slope is pushed by the upper slide body, and soil particle displacements increase from 3.5 to 39.0 m.

Uttarakhand is a state in India and is prone to landslides of different types and sizes, predominantly in the monsoon season. In particular, landslides in the Outer Himalayas (Shivaliks) are man-made due to the construction of roadways and highways. Our aim was to ascertain the 3-D displacement of man-made landslides during the tourist season that falls between June and September of each year coinciding with the monsoon season in the region. We selected two epochs, separated by ten days, to study the displacement due to a landslide along the national highway NH-7 in Uttarakhand. The field methodology was the same for both epochs: positioning terrestrial laser scanner (TLS) at equal intervals parallel to the landslide scarp and away from the landslide equal to the road width at each position. The scanning angles were kept 0–360° and − 60° to 90° in horizontal and vertical direction, respectively. For better identification of features within the scan, laser points were collected by the TLS four times at each location within the scan. We collected 10 scans which were subsequently co-registered to create a point cloud of the whole landslide for each of the two epochs. We removed artifacts to clip the point cloud corresponding to the landslide scarp. Finally, we applied the M3C2 method to the two epochs to identify landslide displacements in the x, y, and z directions. Collectively, we were able to show the potential of TLS to study landslide displacements in the Indian Himalayas. This work will be useful in understanding displacement rates of debris outflows in the Himalayas.

Agricultural land use can change hydro-geomorphic conditions and slope stability through vegetation clearance and the modification of slope topography and foundations. To better understand the effect of agricultural land use on landslide susceptibility, it is crucial to examine the spatio-temporal relationships between landslide occurrence and land-use history. This study investigates a recent landslide event in Omishima Island, western Japan. We mapped the distribution of landslides induced by the July 2018 heavy rainfall and land cover types to identify landslides that occurred on artificial slopes. 512 landslides were identified; 282 and 207 landslides occurred in the forest (35.6 km2) and the agricultural land (22.0 km2) areas, respectively. Large-scale landslides (> 1000 m2) were concentrated in agricultural land within low-relief hillslopes. The land cover maps revealed that the agricultural land area rapidly expanded around the early 1970s in this part. Many artificial slopes were constructed by modifying the topography of head hollows in the upstream regions. Large-scale landslides were located on embankments of these artificial slopes; thus, the destabilization of embankment materials is likely to be the primary cause of the landslides. Topographical analysis showed that the gradient at which the landslide occurred (S, m/m) becomes gentler as the upstream drainage area behind the embankment (A, m2) increases. This indicates that the flowing water from upstream significantly decreased the lower limiting angle for landslide initiation. The threshold condition in the form of S = α A−β was estimated using the quantile regression method: S = 0.698 A−0.132 (2nd percentile regression of 19 embankments collapsed due to the landslides). This threshold suggests that the existing embankments include 39 slopes with a higher potential of landslides. Future research should investigate the stability of those slopes in detail, both in terms of drainage and strength of embankment materials.

Non-coaxiality refers to the non-coincidence of the principal stress direction and the principal plastic strain rate. In order to quantitatively investigate the non-coaxial behaviour of clay under cyclic loading, undrained cyclic simple shear tests are conducted on the red clay collected in Heilongtan. The Multi-directional Dynamic Cyclic Simple Shear (MDDCSS) was used to implement this experiment. Both monotonic and cyclic simple shearing are applied to the sample and the corresponding soil behaviours are analysed. Parametric analysis in terms of different moisture content and initial stresses are systematically performed. Conclusions can be drawn that the principal stress direction is advantageous to the principal plastic strain increment direction at the initial stage of shearing, and gradually coincide with the shear progression. In addition, the degree of non-coaxiality gradually reduces with an increase in the stress ratio. These results can provide an experimental basis for constitutive modelling under the principal stress rotation.

In recent years, Japan has experienced a variety of natural disasters, which have become increasingly frequent and severe. In order to reduce the damage caused by natural disasters, it is necessary to take both hardware and software measures. Kikumoto et al. developed the first Gross National Safety index for Natural Disaster, the GNS, in 2015, in which evaluated a risk of against natural disasters can be quantitatively evaluated at prefectural level. However, there is no such general safety index at municipal level. Considering that a more detailed assessment index can help decision and policy makers facilitate implementation of more effective countermeasures, this study aims to develop a GNS for each municipality. In the municipal-version GNS, we were able to obtain more detailed information than the 2015 GNS. Since there are a lot of Disaster-prone areas in Japan but each area has suffered from different kind of Disasters, if the characteristics of the risk in each municipality can be identified from the exposure and vulnerability indices in the GNS, optimal countermeasures can be taken to reduce the damage caused by natural disasters.

Soil properties spatially vary due to the complex geological process in its formation. Recent studies have revealed that soil spatial variability largely influences geo-structure performance, i.e., slope stability. To facilitate the reliable slope design, revealing the spatially varied soil properties in-situ is necessary. However, they may require a large number of geotechnical investigations, i.e., the cone penetration test (CPT). This paper firstly explores the optimal sampling location of a 3D slope by considerng limited pseudo-CPT data. After the identification of the 3D slope failure mechanism, the optimal sampling location for each kind of failure mechanism is investigated by the calculated Euclidean distance using a designed simulation flow. Finally, the uncertainty in the estimation of the failure mechanism is discussed. In the analysis, soil properties (c, tan ϕ, and γ) are treated as random variables, and the limit equilibrium method is used to evaluate the slope stability. The conditional/unconditional simulation is used in tandem with a Monte Carlo simulation framework to evaluate the sampling efficiency together with the failure mechanism of the 3D slope.

The foundations of turbine units are a complex structure. The reliability of turbine units is largely determined by their vibrational state and the nature of compaction of soil bases. In the case of uneven compaction of the soil bases, an unbalanced centrifugal force arises, which is undesirable in practice. With such small values of permissible deviations, there is a need to develop perfect calculation methods in which the real properties of clay soils will be taken into account most fully. To date, with such calculations, the influence of inhomogeneity parameters, the degree of physical nonlinearity, boundary conditions, variability of filtration coefficients, lateral pressure, instantaneous compaction and initial porosity on the nature of vibrational compaction of the soil has not been sufficiently studied. In the existing works taking into account the vibrational creep of the ground frame, the function characterizing the creep deformation is presented as the product of the measure of static creep and the functions of the amplitude of vibrations. The possibility of such a question is limited. The distribution of vibrational waves in ground formations remains in the shadow. A mathematical model of vibrational consolidation of heterogeneous soil is constructed. The constructed model takes into account all these factors. The questions of the existence and uniqueness of the solution of the problem are investigated. The methods of solution are substantiated. The possibility of using the iteration method is proved. Taking the initial conditions of the amplitude and vibration parameters, the problem of wave propagation in the ground is solved. Then, substituting the wave functions in place of the oscillation amplitude functions, the problem of vibration compaction is solved. This approach to the problem, in our opinion, is correct.