Shibin Lin

A study on issues relating to testing of soils and pavements by surface wave methods

A study on the differences between testing soils and pavements using surface wave methods is presented. The differences in theoretical dispersion curves are illustrated using the transfer matrix method and the stiffness matrix method for soils and pavements, respectively. The Levenberg-Marquardt and simulated annealing methods are applied for inversion of experimental data on soils and a concrete foundation slab, and the relative merits and differences of the two inversion methods are discussed.

Comparison of MASW and MSOR for Surface Wave Testing of Pavements

This paper presents a computational and experimental study on seismic stiffness profiling of layered pavement systems using the multi-channel analysis of surface waves (MASW) and multi-channel simulation with one receiver (MSOR) testing procedures. Development of a new custom-programmed data acquisition system for MASW and MSOR testing using MATLAB software and National Instruments hardware are detailed. A receiver coupling method is presented, which was found to perform the best among several methods examined by the authors. The cross-correlation function is employed to statistically quantify the repeatability of impacts, which is critical for MSOR tests in which multi-channel records are simulated by performing multiple impacts over a range of incremental offsets from a single fixed receiver. Experimental dispersion data from MASW and MSOR tests performed at the same asphalt pavement site with the same testing system are compared, and MASW is found to enable measurement of dispersion data to much higher frequencies using the authors’ methods than MSOR. Inversion results from the MASW and MSOR data at the same asphalt pavement site also are compared, and it is found that MASW is able to provide measurements of the stiffness of the pavement surface layer with reduced variability.

Critical Depths for Higher Modes by Minimally-invasive Multimodal Surface Wave (MMSW) Method: Simulations and Field Test

A Minimally-invasive Multimodal Surface Wave (MMSW) geophysical testing method, which is a hybrid of surface and borehole seismic methods, was developed recently by the authors to measure more extensive multi-mode dispersion data and thus improve the accuracy of inversion profiles. The new MMSW method employs a borehole geophone at selected depths to record seismic waves from different source offsets on the soil surface. Presented in this paper is a procedure for estimating a range of optimum geophone depths to capture a given higher mode by the MMSW method. Stiffness matrix and finite-element-based numerical simulations of the MMSW method are performed to identify the relationships between critical geophone depths and apparent cutoff frequencies of higher modes. Specifically, it is shown for increasing velocity profiles that 1) at a given borehole sensor measurement depth, the apparent cutoff frequencies of higher modes increase with mode number, 2) at a given frequency, the critical geophone depth at which a higher mode will first become dominant increases with mode number, and 3) for a given higher mode, the apparent cutoff frequency decreases as measurement depth increases. A preliminary field test is conducted using a vertical geophone placed at five different depths while impacts are applied to the soil surface from 3.66 to 43.89 m from the borehole, with an impact spacing of 3.66 m. Dispersion images from the five geophone depths are superimposed to produce a dispersion image having three modes with improved clarity relative to the surface-only Multichannel Analysis of Surface Waves (MASW) method. A comparison of the experimental and theoretical apparent cutoff frequencies for higher modes is used to validate the theoretical prediction of critical depths by the stiffness matrix method. Matching of experimental and theoretical apparent cutoff frequencies could provide additional optimization constraints to reduce the uncertainty of final inversion profiles.

Evaluation of three nondestructive testing techniques for quality assessment of asphalt pavements

ABSTRACT This study evaluates three nondestructive testing (NDT) techniques for quality assessment of asphalt pavements. The three NDT techniques examined include an electromagnetic density gauge, a dynamic stiffness gauge, and geophysical surface wave tests for measuring modulus. In-situ NDT tests were carried out for four representative paving projects covering a range of asphalt mixes and traffic loads, and cores were extracted at the centre of each NDT testing location for laboratory measurement of density and modulus. A comprehensive correlation analysis was carried out to examine the performance of each NDT method for quantifying the quality of the asphalt pavements. The in-situ density had a low correlation with the laboratory density and was not sensitive to variations in temperature and asphalt mix type. The in-situ stiffness measured on the asphalt mixtures several hours after paving had a high correlation with the in-situ dynamic modulus and laboratory density, and is therefore recommended as a quantitative property for quality control. Among the three NDT measurements, the in-situ modulus was most sensitive to variations in temperature and asphalt mix type. After correction for temperature effects, the corrected modulus is recommended as a quantitative property for quality assurance.

Comparison Of MASW And MSOR For Surface Wave Testing Of Pavements

This paper presents a computational and experimental study on seismic stiffness profiling of pavements using the multi-channel analysis of surface waves (MASW) and multi-channel simulation with one receiver (MSOR) testing procedures. Development of a new custom-programmed data acquisition system for MASW and MSOR testing using MATLAB software and National Instruments hardware are detailed. Effects of different receiver coupling methods on the test results are examined. The cross-correlation function is employed to statistically quantify the repeatability of impacts, which is critical for MSOR tests in which multi-channel records are simulated by performing multiple impacts over a range of incremental offsets from a single fixed receiver. Experimental dispersion data from MASW and MSOR tests performed at the same site with the same testing system are compared, and MASW is found to enable measurement of dispersion data to much higher frequencies than MSOR. Inversion results from MASW and MSOR data at the same site are compared, and it is found that MASW is able to provide measurements of the stiffness of the surface layer with reduced variability.