On Frequent Evaluation of Compacted States and Soil Properties by Soil Stiffness Index Measurements

Abstract

The soil properties including stress-strain properties and hydraulic conductivity of compacted soil (typically under wet or saturated conditions) considered in soil structure design are controlled by not only the dry density, ρd, and soil type, but also the degree of saturation, Sr, at the end of compaction, (Sr)EOC. The degree of compaction (Dc)1Ec = ρd/”[(ρd)max]1Ec by laboratory compaction tests using Standard Proctor (1Ec)”, which is often referred to in compaction control and soil structure design, is controlled also by (Sr)EOC relative to (Sr)opt (i.e., Sr where ρd = (ρd)max is obtained for a given compaction curve) and the field value of compaction energy level, CEL, relative to 1Ec. Based on the above, to achieve the (Sr)EOC = (Sr)opt state irrespective of variations of soil type and CEL at as many as possible places in the field, it is proposed to frequently measure soil stiffness index and keep it in a range between the allowable upper and lower bounds that correspond to the allowable lower and upper bounds of (Sr)EOC specified on both sides of (Sr)opt while maintaining the field CEL value high enough and constant. It is argued that the conventional soil compaction control based on “the lower bound control of soil stiffness index” is basically not as effective as the upper and lower bound control.