SOIL STIFFNESS GAUGE FOR SOIL COMPACTION CONTROL

Compacted soil is an essential element in the construction of highways, airports, buildings, sewers, and bridges. The Federal Highway Administration's (FHWA) cooperative development of a soil stiffness gauge (SSG) will enable the validation of design models, the development of performance specifications, and contractor process control for compacted soil structures. Until now, engineers have used soil density as a measure of soil compaction, because there was no easy method for measuring soil stiffness. Resting on the soil surface, the SSG produces a vibrating force that is measured by sensors that record the force and displacement-time history of a ring-shaped foot. It is a practical, dynamic equivalent to a plate load test. The device has been "beta-tested" by the FHWA and several state highway agencies. Thousands of soil stiffness measurements have been successfully made at highway embankment sites and pipe backfill sites on sand, clay, and sandy loam soils. When converted to density values using correlation charts, these measurements are within 5% of measurements made with a nuclear density gauge. The new lightweight, portable SSG not only provides a means to measure the desired engineering property, but it is faster, cheaper, safer, and more accurate than current standard methods.