2007 Volume 43 Issue 5 Pages 307-311
Observation boreholes for measurement of groundwater potential and movement, water sampling at arbitrary sections were designed and constructed for field test. Casing pipes were attached with sealing belts between the casing pipe and the borehole wall at one meter intervals. Another part of the casing pipe was perforated up to 5% of the surface area. A sonde equipped with five rubber packers was used to seal inside the casing pipe for water pressure measurement and sampling.
Groundwater pressure lower than hydrostatic pressure was measured below the observable water level in the borehole and positive water pressure was measured above the observable water level at a landslide area in Shizuoka Prefecture. Groundwater potential distribution varied after rainfall. Vertical water movement in the borehole was measured accurately using a flow meter sonde. Water flow was concentrated into the flow meter by a packer which stopped a gap between the flow meter and the casing pipe. Changes in the oxidation-reduction potential and electric conductivity of water sampled at different depths with the packers was larger than those sampled without packers. Electrical and temperature logging methods can also be conducted for whole the entire depth. Observation methods that enable measurements or sampling at specified depth are necessary to evaluate groundwater potential and water characteristics in complicated layers of a landslide slope.
