PZT-Based Soil Compactness Measuring Sheet Using Electromechanical Impedance

Compaction is a crucial process in road construction and the compactness is an important parameter in determining the road foundation quality. Traditional compaction monitoring methods are based on different principles. The major principle of these techniques is detecting the water content and bulk density of the soil, and then calculating the dry density and the compactness. The disadvantages are laborious, low accuracy, low efficiency and costly for large scale measurement. These drawbacks may limit their application in certain aspects. In this paper, a novel electromechanical impedance (EMI) based compactness measuring sheet (CMS) for soil compactness monitoring was proposed. The proposed CMS was fabricated by attaching a circular piezoceramic patch onto a circular sheet with a larger size. Eight round CMSs with a diameter of 150 mm, 100 mm, 80 mm, 50 mm were fabricated in this experimental study. Among them, four CMSs were embedded into soil and subjected to compression tests to simulate the increased soil compaction. In this study, the conductance signatures of the proposed CMS were collected and analyzed during the increasing soil compaction process. Experimental results demonstrated that all the peak magnitudes in the conductance signatures in the selected frequency range of 160 kHz to 310 kHz were reduced with the increase of soil compaction. It showed that some specific frequencies shifted to the right side during the compaction process. The variations in the conductance signatures were then quantified with the aid of three statistical metrics. These metrics include root mean square deviation (RMSD), mean absolute percentage deviation (MAPD), and correlation coefficient deviation (CCD). Through calculation, all these metrics increase with the increase of soil compaction, which can be employed as indicators in the soil compaction process. To obtain more insight into CMS electromechanical system, the finite element analysis were also performed to study the EMI response. The simulation results well verified the experimental results. This preliminary study has verified that the proposed EMI based CMS is feasible and effective in monitoring soil compactness and shows a promising application prospect.