Advancements in active surface wave methods: modeling, testing, and inversion
This study focuses on advancements in three broad aspects of active surface wave methods: modeling, testing, and inversion. Transfer matrix, global matrix, and stiffness matrix methods were employed to comprehensively model layered structures with half-space boundary conditions for soil structures with increasing/anomalous stiffness profiles, or pavement structures with decreasing stiffness profiles and leaky waves. All three methods were programmed in MATLAB as forward algorithms. The finite element method was adopted to simulate surface wave testing for various half-space site structures with absorbing layers using increasing damping technique. An improved experimental dispersion analysis scheme was developed by scanning phase-velocity and intercept-time followed by a power-spectrum analysis to minimize side lobes and increase sharpness of dispersion images. The multichannel simulation with one receiver (MSOR) method was applied to capture the dispersion characteristics of soil sites. The reciprocity principle for surface Rayleigh waves was verified by comparing dispersion images from MSOR and multichannel analysis of surface waves (MASW) testing at the same site with the same testing system. A multichannel surface wave acquisition system was developed to improve the accuracy of measuring high-frequency and high-velocity dispersion data on pavement sites. A minimally-invasive multimodal surface wave (MMSW) method was proposed to measure multi-mode dispersion data of Rayleigh waves by using either embedded receivers at various depths to record surface wave motions generated from moving impacts on the ground surface or using a multichannel seismograph with an array of geophones on the soil surface for measuring surface wave motions caused by Standard Penetration Test hammer blows at various depths in a borehole. Stiffness matrix and finite element simulations of the MMSW method were employed to identify the critical geophone depths for optimum measurement of higher-mode motions. A hybrid genetic-simulated-annealing (GSA) algorithm was applied to solve multiple minimization and non-linear optimization problems to match the theoretical dispersion curves against their experimental counterparts. Results from simulation and real-world studies demonstrate that the advancements made in the three aspects of surface wave methods can improve the accuracy of surface wave testing results with higher resolution of experimental dispersion data, more complete multi-modal dispersion data, and higher certainty of inversion.