Detection of water paths within the upper soil layer by measuring the earth temperature distribution

Abstract

Many researchers have pointed out the existence of rapid water flow in the forest soil layer, which can not be explained by Darcy's law. The time of the slope failure estimated from the unsaturated-saturated percolation analysis and stability analysis is likely later than the time of actual failure. One reason for this discrepancy can be due to the assumption that the permeability of the soil layer is uniform. To accurately forecast the time of slope failure, we need to examine the 3-dimensional position of the water paths in the upper soil layers.
In this paper, a procedure is proposed to make clear this 3-dimensional position of water paths through the analysis of temperature distribution in the upper soil layer. The outline of the procedure is as follows : Vertical earth temperature distribution in the holes bored by the simple penetration test is detected with an instrument equipped with 14 thermocouples. Data gained in the aligned holes yield isothermal chart. The disturbance appeared in this isothermal chart should indicate suggestions the existence of the water paths.
The procedure was applied on a slope where the actual water paths were confirmed by excavation. By using this procedure, the 3-dimensional position of water path was grasped with the maximum error of 40 cm.