Residual Shear Strength of Landslide Soils by Presheared Flush Testing for Stability Quantification

Brou Georges Kakou

PhD Candidate,The United Graduate School of Agricultural Science,
Gifu University, Japan

Hideyoshi Shimizu

Professor, Department of Biological Production System,
Gifu University, Japan


Shinichi Nishimura

Associate Professor, Department of Biological Production System,
Gifu University, Japan


In landslide slope stability evaluation, the determination of strength parameters (c and f) is very important. For soil subjected to repetitive sliding, these parameters reduced to their residual values (cr and fr) are used in the calculation of the factor of safety. Currently, among the two types of testing methods that permits to assess these strength parameters, the torsion shear test by means of a ring shear apparatus is widely employed under numerous testing procedures. However, even though engineers have made efforts to minimize errors due to wall friction during the test progression, a considerable number of tests required to determine the shear parameters still extend in time. In this paper, we propose a short and effective procedure to obtain the residual shear parameters in which error due to metal friction is minimized and the shearing time is shortened: the Presheared Flush Test procedure (PFT). The strength parameters resulting from the new Presheared Flush Test Procedure (PFT) on samples from tertiary landslide slope of the Niigata landslide slope drainage tunnel project site are compared to the results obtained by the conventional Flush Test procedure. We also present the results of the quantification of the stability state of the landslide slopes at various groundwater conditions.

KEYWORDS: Landslide, PFT, Ring shear test, Testing procedure, Slope stability


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