The development of a new apparatus for routine testing of subgrades and pavement foundations is described. Potential applications include pavement design, material selection, and proof testing during construction. The main objectives were to develop a relatively low-cost, lightweight, and portable dynamic testing apparatus that has the capability of producing on-site resilient modulus values. A prototype swinging hammer apparatus (odin) has been built and proving trials have been in progress for 12 months. Odin is designed so that thestress and area of impact can be adjusted to simulate various loading conditions to suit the materials and constructions under test. Under low impact stresses, quasi-elastic (resilient) behavior occurs, followed by plastic deformation and failure at higher stresses. Digital storage of the impact pulse facilitates processing of the signalto determine the maximum resilient deflection. By using double integration techniques and incorporating energy balancing equations, a composite modulus value can be determined, taking into account both peak deceleration and pulse time. The apparatus typically produces animpact pulse of 1 to 3 msec duration, with a transient deflection of 0.5 To 3.0 Mm. Intensive field testing of various materials from soft clay subgrades to capping and subbase layers has yielded reasonable moduli that correlate well with other tests. The ability to testdifferent materials and constructions, along with the capability for data capture and interpretation, indicates widespread potential applications. This paper appears in transportation research record no.1291, Fifth international conference on low-volume roads, may 19-23, 1991, raleigh, north carolina, volume 2.
Abstract