Showing papers by "Dong-Soo Kim published in 2001"

Evaluation of the dispersive phase and group velocities using harmonic wavelet transform

Abstract: The evaluation of the dispersive phase and group velocities having sensible physical meaning is of practical importance in various NDT techniques. In this paper, we propose a method based on the harmonic wavelet transform to evaluate dispersive phase and group velocities. To apply the harmonic wavelet transform in the evaluation of dispersive velocity, the meaning of the harmonic wavelet coefficient is interpreted from a different point of view. Based on these concepts, the step-by-step procedure to evaluate the dispersive phase and group velocities was proposed. In the proposed method, both phase and group velocities can be obtained directly from information extracted from data based on the harmonic wavelet transform. To evaluate the validity of the proposed method, numerical simulations of the multi-layered system were performed and the phase and group velocities determined by the proposed method match very well with theoretical velocities showing the good potential of the proposed method.

Alternative method of determining resilient modulus of subgrade soils using a static triaxial test

Abstract: The cyclic test for the determination of resilient modulus ( MR) is often too complex and time-consuming to be applicable on a production basis. Therefore, the development of a simple and reliable alternative MR testing tech- nique is essential for the application in the mechanistic design of a flexible pavement system. Seven disturbed subbase soils were collected from the actual pavement projects for testing. To evaluate the effect of particle size on MR, stan- dard MR tests with various maximum particle sizes and specimen diameters were performed using three subbase soils. The resilient moduli determined from various specimen sizes with the same particle-size distribution were almost iden - tical. However, the value of the slope parameter k2 in the bulk stress model was constant, but the value of k1 increased with a decrease in maximum particle size. The effects of mean effective stress, loading frequency, and number of load- ing cycles on modulus were evaluated from torsional shear (TS), triaxial (TX), and MR tests. The alternative MR testing procedure using the static TX test was proposed considering deformational characteristics of subbase soils. The pre - dicted MR values from the proposed method matched well with those determined by the standard MR test, showing the capability of the proposed method for determining MR.