Construction Pore Pressures in Three Earth Dams

High construction pore pressures developed in two of the three dams built with the same type of residual soil under similar conditions. The development of pore pressure is due to the combined effect of many factors—moisture content, soil gradation, degree of compaction, rate of construction, and drainage features in a dam. In a fill of the residual soil studied which has high natural moisture content, over-compaction may induce high pore pressure; if the soil contains less than 30% minus 200-sieve sizes, its fill is not likely to develop high pore pressure; the drainage system in the fill would not be effective in reducing pore pressure if the rate of construction is high. The development of temporarily high construction pore pressure in an earth dam presents a major problem in design from the view points of safety and economy which may often require unconventional method of solution.