Estimation methods of the constants for Soil and water characteristic curve at granite slope using field measurement data of water content.

Abstract

In order to predict the initiation of shallow landslide due to rainfall, it is important to establish the method to determine the constants in Soil and water characteristic function (SWCF) , which is the relation between volumetric water content θ and matric potential φ, only from the in-situ observed data of water content or matric suction, without indoor test on undisturbed sample. In this article, some methods were applied and examined using in-situ observed data of Aratani observation slope at Hiroshima.
Firstly, in order to compare the reliability of the trial and error method which inversely solutes the constants in van Genuhten equation using only the measurement data of volumetric water content, and that of in-situ θ-φ method which combines the measured volumetric water content and measured matric potential directly, simulation of the time variation of volumetric water at certain rainfall event were carried out. It revealed that both methods have almost same reliability. Secondly, in order to reflect the variation of SWCF along the vertical depth, not only α, n in van Genuchiten equation, but also θs which corresponds to saturated water volumetric content, should be also identified by in situ θ-φ method for approximating SWCF better especially in a region of low matric potential.