In this paper, based on two series of laboratory compaction tests with resistivity measurement, the relationships between the resistivity and physical properties of the soil and the selection of the optimum compaction control index are discussed. Discussed also is a procedure for correcting the reference value of the resistivity for the change of water content. It has been found that the air porosity or the volume water content is a reliable compaction control index. A procedure for correcting the reference value of the resistivity for the change of water content is presented. This procedure is based on relationships between the resistivity and the air porosity or the volume water content.

INTRODUCTION

The degree of compaction of an embankment can be controlled by:

  1. the quality specifications,

  2. the construction method, or

  3. a combination of the quality specifications and the construction method.

In the quality specifications approach, which is the most widely adopted approach, the degree of compaction can be evaluated in terms of any of the following four physical quantities:

  • The ratio between the field dry density and the maximum dry density as determined by the compaction test in the laboratory.

  • The air porosity which is the ratio of the volume of air to the total volume of the soil, or the void ratio.

  • The degree of saturation

  • The strength and deformation characteristics of the soil.

In the practice of embankment construction in Japan, there are different/several specifications of compaction control (on the control items and their reference values) for different materials and for the main locations in the embankments. In most of these specifications, the degree of compaction for cohesionless soils is evaluated in terms of the density ratio, while that for cohesive soils is evaluated in terms of the air porosity along with the water content, the thickness of soil layer, the thickness of spread soil layer and other parameters (Editing Committee for Soil Testing Methods 1990; Editing Committee for Soil Compaction and Control 1991; Fujii 2000).

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