Journal of the Japan Society of Erosion Control Engineering, Vol.58,No.1,2005
Numerical model relating to pipeflow and its assessment by flume experiments
Daizo TSUTSUMI Toshihiko MIYAZAKI Masaharu FUJITA
Abstract
A pipeflow model was developed to examine preferential flow through soil pipes
within slopes and its influences on slope stability. To assess the new pipeflow
model, flume experiments were conducted and its results were simulated by the
model. Soils were filled into a flume to prepare a comparatively large sloping
soil domain (length = 5.0 m, width = 0.5 m, depth = 0.35 m, and gradient = 20)
and used for the experiments under 3 different conditions, i.e.; no|pipe (Run
1), a pipe from upslope end through downslope end (Run 2), and a pipe whose outlet
located within the soil domain (Run3). Output from the matrix at downslope end,
pipe flow from pipe outlet, and distribution of pore water pressure at bottom
of sloping soil domain responding to artificial rainfall on soil surface (82 mm/hr)
were continuously measured. Artificial soil pipes (O.D. = 2.6 cm) were constructed
of stainless steal mesh and felt so as to reduce flow resistance from soil matrix
to the soil pipe, and placed 2.5 cm above the bottom and the center of the soil
domain. Experimental results demonstrated that pipeflow (Run 2) decreased soil
pore water pressure and made the slope more stable comparing to the no]pipe condition
(Run 1), however backflow from the pipe outlet to the soil matrix (Run 3) increased
the soil pore water pressure at the point and generated surface erosion. Through
the experiments, pore water pressure distributions not only along the soil pipe
direction but also along a direction across the soil pipe were detected; this
finding was usually neglected in similar conventional experimental studies. The
pipeflow model presented in this paper simulated the experimental results of pore
water pressure and flow rates, and its availability was confirmed. Furthermore,
distribution of pore water pressure within the soil domain obtained from the model
calculations were compared to surface morphology after the surface displacement
obtained in the flume experiments. Results demonstrated that the model can calculate
the pore water pressure distribution with high accuracy and may be applicable
to the stability analysis for the actual slope in which preferential pathways
such as soil pipes exist.
Key words:soil pipe, model simulation, pipeflow, matrix flow, slope stability
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