Abstract
Natural disasters such as earthquakes or heavy rainfalls thwart the potential stability of weathered slopes which has significant effects on the safety of infrastructure in the vicinity. In the case of developing countries, this situation is inevitable and necessitates to develop a quick and economical technique for the overall progress in the assessment of safety. In dealing with the slope instability problems for such regions, at first it is important to identify the potentially unstable slopes and then decide the mitigation strategies. In this regard, in situ shear strength of weathered geo-material exposed on slopes should be carefully delineated which is a time consuming procedure. Therefore, a relation of in situ shear strength of weathered geo-material to the geophysically measured S-wave velocity is employed in the present study. Field experiments were conducted to evaluate the shear-wave velocity, depth and in situ shear strength of surface weathered layer which included seismic refraction, portable dynamic cone penetration and field direct shear tests. Field studies were conducted in Japan (Yokosuka, Nagano, Izu and Kobe), and Pakistan (Muzaffarabad and Taxila). The investigated sites were recently disturbed by strong earthquakes or heavy rainfalls. By using the depth and in situ shear strength of surface weathered layer stability analysis (infinite slope) was carried out and correlated to S-wave velocity, which suggested that the safety factor of a weathered slope reduces to half during the rainfall event. Moreover a safety assessment matrix (SAM) is presented which by inputting the slope angle and the S-wave velocity of the weathered geo-material on slope surface categorizes the level of safety into, (a) stable, (b) Potentially unstable and, (c) Unstable. The authors envision using SAM for the direct evaluation of potential instability by a continuous monitoring of S-wave velocity and slope angle. Therefore, it is recommended that, monitoring of S-wave velocity of surface weathered layer for risk assessment is a quick and economical technique other than time consuming, local and expansive intrusive methods.
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Acknowledgments
The authors are grateful for the financial support by the MEXT (Ministry of Education, Culture, Science and Sports, Japan) and the colleagues at the Geotechnical Laboratory of the University of Tokyo for the assistance during the field experiments in Japan. Also the authors appreciate the logistic support provided by the personnel of Development Authority Muzaffarabad and Dr. Kamran M Khan of University of Engineering and Technology Taxila during the field visits to Pakistan.
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Qureshi, M.U., Yamada, S., Towhata, I. (2013). A Simplified Technique for Slope Stability Assessment Based on Insitu S-Wave Velocity Measurement. In: Ugai, K., Yagi, H., Wakai, A. (eds) Earthquake-Induced Landslides. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-32238-9_95
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DOI: https://doi.org/10.1007/978-3-642-32238-9_95
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