Vol 6, No 5 (2015) > Civil Engineering >

Determination of the Viscosity Value based on the Influence of the Sliding Plane by using a Flume Channel

Budijanto Widjaja, Ignatius Tommy Pratama

 

Abstract:

Mudflow is a type of mass movement with high velocity. It is comprised
mainly of silt and clay-sized particles. Mudflow movement behavior involves
undrained shear strength and viscosity as part of a resistance force that
withstands shear stress as a driving force. Many methods have been developed to
determine the value of viscosity. This study used Vallejo and Scovazzo’s
modification method to determine the viscosity value, and assumed that mudflow
material behaves as a Bingham plastic material. A flume channel was used in
this study to measure the displacement and time required for mud to flow in
order to obtain the mudflow transportation velocity. The measurement was
conducted for four different slope angles and water contents. To compare the
samples, Kaolin soil was used for the pilot project and Parakan Muncang soil
was used as the natural landslide material in order to obtain the viscosity
value throughout this study. This study aims to evaluate the capability of
Vallejo and Scovazzo’s method to determine the viscosity value. We found that
Vallejo and Scovazzo’s method cannot be used in a single slope angle. This
approach requires that the sliding plane angle be adjusted for varying shear
stress magnitudes, and that, consequently, different strain rates for each
shear stress are obtained. The correlation curve between the shear stress and
the strain rate, which corresponds to the Bingham plastic material curve, needs
to be governed. The viscosity value was obtained by calculating the gradient of
the linear tangent line. Furthermore, Vallejo and Scovazzo’s method is
recommended only for tests at a low strain rate level, as a high strain level
would cause difficulties in recording string displacement and mud
transportation time. However, testing mud at a low strain rate level will
obtain a higher value of mud viscosity that is not representative of mudflow
viscosity.

Keywords: Liquid limit; Mudflow; Undrained shear strength; Viscosity; Water content

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