Embedded shear wave transducer for estimating stress and modulus of As-constructed unbound aggregate base layer

Resilient modulus is a key property of unbound aggregate layers for construction quality assurance and mechanistic-empirical pavement design. Nondestructive testing methods, such as the falling and lightweight deflectometers, GeoGauge, and seismic techniques, can furnish modulus properties based on the measurement of deflection or seismic waves on the surface of pavement. However, their influence depth or applicability is limited and backcalculation process is required to estimate individual pavement layer moduli. This paper demonstrates the development and field application of a new bender element system as embedded transducer which can estimate the in-situ stress and modulus of aggregate base layers at any desired depth and orientation. An embedded shear wave system (ESWS) using the bender elements was developed for the characterization of a constructed aggregate layer. A power relationship between the shear wave velocity and applied confining pressure was established in laboratory tests to evaluate the average stress state of constructed aggregate layers by using shear wave transducers. The field test results show that the shear modulus of the constructed aggregate layer increases as the moisture in the field evaporates. In addition, the shear modulus estimated under the weight of a super-single tire is greater than that estimated without a load on the surface layer. The ESWS is a promising development for evaluating magnitudes and changes in in-situ stress and modulus according to laboratory calibrated test conditions, and showed a potential for measuring base/subbase modulus at any layer depth during and after construction.