Measurement of granular fill compaction using low frequency vibration testing

This paper describes the use of an instrumented impact hammer test for density measurement in a granular soil (Specification for Highway Works Type 1 fill) whilst monitoring the performance of vibro-tamper compaction. A 3-D finite element model was also used as a predictor. The effect of varying key material properties was studied. An increase in the soil's modulus of elasticity resulted in higher natural frequencies. An impact hammer, fitted with a force transducer, was used to excite the soil whose response was measured by accelerometer and analysed in both time and frequency domains. The change in natural frequencies of the modes of soil vibration was observed after the first pass; this effect reduced with compaction. Shear wave velocities were used to calculate a low strain modulus of elasticity and a correlation was established with the modulus of elasticity derived from Clegg hammer impact values. The same type of tests were applied to understand the field attenuation characteristics of Type 1 fill. There was a slight decrease in the maximum amplitude of the shear waves with increasing compaction; high attentuation of shear waves was also noted.