Keigo Koizumi

Hydrogeological survey and satellite remote sensing in the Dunhuang area

Mogao Grottos are located at the eastern foot of the Mingsha Mountain, 25 km southeast of Dunhuang City. The caves were excavated into the cliff on the west bank of the Daquan River. The wall paintings in the caves are subject to the severe deterioration generated by recrystallization of salt. It relates with the movement of water/moisture in rock formation. Through the satellite image analysis and geological survey, it has been clarified that the movement of ground water is governed by the fault system. The geographical nature is specified by the aggressive tectonic movement from the south.

Slope Disaster Monitoring System Using Battery-Operated Wireless Sensor Network

This paper develops a slope disaster monitoring system using distributed sensors. The sensor node has wireless communication and tilt detection capabilities. Each sensor node communicates to each other and sends the corrected data to a base station, which can send an alert message to administrators in case of emergency. The developed slope disaster monitoring system is installed on a slope along the Chugoku Expressway. This first experimental study showed a significant potential of the developed distributed sensor network for detecting slope failures, but it also clarify that the wireless communication capability is sensibly influenced by relative geometric alignments of each sensor nodes. The second experimental study has begun along the Maiduru-Wakasa expressway. Since the geometric alignments are modified, we are having an improved wireless communication correspondence.

IDENTIFICATION OF SLOPES WITH HIGHER RISK TO SLOPE FAILURES BASED ON INFORMATION PROCESSING TECHNIQUES

In recent times, the sediment disasters, such as slope failures, debris flows, and landslides, caused by typhoons or cloudbursts have occurred in Japan. The progression of global warming will increase the scale of typhoons and cloudbursts striking the Japanese Islands, and there is a concern that the frequency of sediment disasters may increase. Therefore, it is important to identify slopes with a higher risk to sediment disasters to prevent future disasters. In this study, a method based on artificial neural networks and mathematical statistics was used to identify such slopes. In the proposed method, the self-organizing map (SOM), cluster analysis, and Hayashi’s second method of quantification are combined. The proposed method was applied to the data gathered from periodical inspections of road slopes. In the results, slopes with a higher risk to slope failure were identified and ranked according to their risk.

Probabilistic management of slope disaster detection systems for reduced energy consumption

Distributed networked sensor systems have a potential applicability for developing a slope disaster monitoring system. A low energy consumption property and an eventual long running life are an important issue in this type of outdoor application. This paper proposes a probabilistic strategy to turn on/off each sensor node that could reduce an entire amount of consuming energy over the network. Effectiveness of the proposed probability assignment strategy is evaluated through both numerical and hardware experiments.

Open image in new windowUnderstanding of Landslide Movement at Bumi Waluya Railway Station, Garut, Indonesia

Mitigation of a slow-moving landslide hazard requires a good knowledge of the landslide movements. This paper presents results of geophysical investigation and slope movement monitoring to understand the characteristics of an active landslide above a railway station in Garut, Indonesia. For this purpose, a series of resistivity surveys was then conducted using a dipole-dipole method to map the hydrological condition of the landslide area, and geotechnical monitoring was conducted to characterize the movement. Based on the N–S resistivity profiles, highly saturated zones, indicated by low resistivity values, exist in soil layers at a depth greater than 7.5 m. The saturated zone also develops in the near-surface soil layer in the landslide body. The slope movement monitoring records suggest that the landslide consists of several landslide segments with different rates of movement and deep sliding zone. Based on this current study, the characteristics of landslide movement is very site specific and is mainly associated with localized hydrological conditions. Because the surface water infiltration from the irrigation ditches and rice fields controls the landslide reactivation, a better surface water and sub-surface water management is, therefore, necessary to reduce the landslide risks to the railway infrastructures.

Microtremor Measurements at Mogao Grottoes, Dunhuang, China for Preliminary Dynamic Characterization for Performance During Earthquake

Mogao Grottoes, Dunhuang, China, is a world heritage of UNESCO created in steep cliff with 50–60 m in height. Micro-tremor measurements and seismic refraction surveys have been carried out as a preliminary study to obtain dynamic characteristics. The site surface geology consists of young sediment of conglomerate in Pleistocene period above granite rock. A velocity sensor with a natural period of 0.5 s was used to monitor the micro-tremors at several points on the top terrace of the cliff and the lower plain in front of the cliff. Two survey lines of some 40 m for refraction survey were performed along which P and S waves were monitored. The velocities obtained from the both refraction lines are in the range of 500–700 m/s. and 1.6–4.0 km/s. for S and P waves respectively. The monitored micro-tremors were in less than a few m kines and the intensities of the motions were changed with time. Particle motions at the most observed sites shows the perpendicular direction to the cliff of EW is the predominant direction irrespective the intensity of the motions. Predominant period of spectral ratio of SW to UD direction shows about 2 s at the top terrace of the cliff and 1 s at the lower plain in front of the cliff. The thickness of the top surface layer of conglomerates is estimated about 125–180 m below the lower plain and 250 m or more. Another characteristic period was found at a period of 0.3–0.4 s. that might be caused by cliff-edge vibration.

Probabilistic Management of Slope Disaster Detection Systems for Reduced Energy Consumption and its Convergence Property

Abstract Distributed networked sensor systems have a potential applicability for developing a slope disaster monitoring system. A low energy consumption property and an eventual long running life are an important issue in this type of outdoor application. This paper proposes a probabilistic strategy to turn on/off each sensor node that could reduce an entire amount of consuming energy over the network. Effectiveness of the proposed probability assignment strategy is evaluated through numerical experiments, and convergence property is also investigated.

Decision Criteria of Slope Hazards by Multi-step Monitoring using a WSN

Expressways link every city in Japan and serve as a main lifeline in emergencies response. However, slope disasters in recent years of expressways may occur without warning due to unexpected heavy rain. This paper proposes decision criteria for slope hazards using a multi-point and multi-step monitoring system. A sensor module with a mesh networking protocol is developed. A compact battery pack gives the module an operating life of more than three years. The installation position of sensors is decided by the safety factor for the stability of a half-infinite slope. Decision criteria for slope hazards caused by heavy rain are proposed based on laboratory test results. The laboratory results agree well with field experiment results.