Abstract
The factors which change the permeabiliyty (k) of soils was examined on three compacted ino-rganic cohesive soils.
During prolonged percolation the degree of saturation (Sr ) was measured by a back pressure method developed by the auther. On an initial stage, the water percolation induced a rapid increase in Sr and k, but when Sr reached 100% k began to decrease immediately. This phenomenon suggested that there was a factor which decreased k at the beginning of percolation. An intermittent percolation method was adopted to examine the contribution of dispersion and swelling to the reduction of k. k of untreated soil specimen decreased during the period of perc-olation, but it recoverd with the pause of percolation. The reason of this reversibility of k might be attributed to the flocculation of soil particles which had been dispersed by water flow during the percolation period. Whereas the reversibility of k of 0. 5N NaCl-treated specimen was not signifi-cant. The reduction of k of NaCl-treated specimen might be mainly caused by swelling and/or destruction of aggregates. The reduction of k by microorganisms was significant when nutrient matter was dissolved in influent water and the temperature was 21°C, but it was not so in the case of no nutient and/or 1.3°C. The reduction of k which followed consolidation by self weight and/or seepage force was calc-ulated using a new equation of one- dimensional consolidation. The effect of seepage force was superior to that of self weight in the case that simulated the experimental results of puddled soilperformed by Adachi.
