Development of a hybrid soil pressure sensor and its application to soil compaction

A new soil pressure sensor based on a combination of the deflecting membrane and fluid-filled approaches has been developed. The advantages of this combined approach are that issues of sensor compliance are eliminated without reducing the effectiveness of the sensor to be used for dynamic measurements. Calibration and verification testing performed under controlled laboratory conditions illustrate these benefits. The new system was implemented in a full-scale field trial that involved the construction of a compacted engineered fill 1.8 m in height. As each layer of fill was placed and compacted, vertical in-soil pressure and vertical in-soil strain were continuously measured. During the vibratory compaction process both vertical soil pressure and vertical soil strain histories were captured in each layer. The data collected allowed for the determination of fill stiffness for both static and dynamic conditions. The results illustrate the effect of both confining pressure and strain level on fill stiffness. The relationship between compaction pressure and depth is clearly defined.