Evaluation of unit weight and strength of sand using electro-mechanical impedance

ABSTRACT: In this study, the EMI (electro-mechanical impedance) of a small piezoelectric sensor was applied for measuring a unit weight and strength of sand. Three different sizes of uncemented Nakdong river sand were filled loosely or densely into a compaction mold. A piezoelectric sensor with 2 cm in diameter was installed into sand for EMI measurement. A small Nakdong river sand was mixed with cement ratios of 4, 8 12, 16% and then compacted into a specimen with 5 cm in diameter and 10 cm in height. The cemented specimen consisted of 6 layers with a sensor at the third layer. The EMI signal for 3 days and unconfined compressive strength at 3rd day was measured. As a unit weight of uncemented sand increased, a resonant frequency increased slightly from 102 to 105 kHz but a conductance at resonant frequency (peak conductance) decreased. For cemented sands, as a curing time and cement ratio increased, the resonant frequency increased significantly from 129 to 266 kHz but the peak conductance decreased. An unconfined compressive strength (UCS) of cemented sands was between 289 and 1,390kPa for different cement ratios. The relationship between UCS and resonant frequency linearly increased but one with peak conductance was in inverse proportion.