Numerical analysis of soil pipe effects on hillslope water dynamics |
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| Authors: | Raj H Sharma Heinz Konietzky Ken’ichirou Kosugi |
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| Institution: | (1) Geotechnical Institute, TU Bergakademie Freiberg, Freiberg, Germany;(2) Laboratory of Erosion Control, Department of Forest Science, Kyoto University, Kyoto, Japan |
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| Abstract: | Soil pipes are considered to drain off water from a hillslope and play an important role in the subsurface runoff generation
process, thus reducing the slope failure susceptibility. However, soil pipes are also often detected on the collapsed slope
suggesting that they might act to induce slope instability. To examine how the soil pipes act on pore-water pressure generation
and on a slope failure processes, a numerical model was developed. The model was used to test the response of pore-water pressure
in a hillslope with soil pipes of different cross-sectional areas, lengths, distances from the impermeable bed, roughness,
and hillslope angles. The model was also tested to find the response of open soil pipe if blocked. The study reveals that
pipes reduce pore-water pressure (measured closed to bed) around its upstream end and increase around its downstream end if
compared with no pipe case. Pore-water pressure at downstream end is increased with increase in hillslope angle, pipe cross-sectional
area, pipe length, or depth of soil pipe. Soil pipe, even if it is ended within the hillslope, increases the total discharge
from hillslope. Location of rough soil also affects the discharge and pressure within the hillslope. If the less rough pipe
is close to the source of water, discharge from hillslope matrix is greater regardless of its downstream pipe roughness. Blockage
of small portion of open soil pipe increases the soil pressure around the region but not beyond the case if there is no soil
pipe. However, complete collapse of soil pipe from a point to all along the downstream end of hillslope increases the pore-water
pressure beyond the pressure if there were no soil pipes. Therefore, the position and type of soil pipe collapse might play
an important role in shallow landslide initiation. |
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