Abstract
This report presents the methods of quantitative assessment for the function decrease of ground drainage facilities with the progress of time after completion of them by using data of pore water pressure and drain water volume which change depending on time series.
For development of the methods, we used data which were observed at Sarukuyoji Landslide area. Two methods are considered in this study. At the tension zone where has sliding mass of high permeability, the method involves estimating the value of rain sensitive pore water pressure and drain water from horizontal drainage boring by using equation (2), (3), and comparing to this with the value of the reference period. At the compression zone water has sliding mass of low permeability, the method is to evaluate yearly changes of the observed data of pore water pressure just before the snowfoll.
