Jeramy C. Ashlock

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.

Mechanistic-based comparisons of stabilised base and granular surface layers of low-volume roads

ABSTRACT Granular surface and base layers of low-volume roads (LVRs) are frequently subjected to severe damage that adversely affects safety and requires regular repair and maintenance. Various stabilisation methods have been evaluated for mitigating damage and improving serviceability of LVR systems. However, few well-documented comparisons exist of the field mechanical performance, durability and construction costs of different stabilisation methods under the same set of geological, climate, and traffic conditions. Therefore, the present study was conducted to identify the most effective and economical among several stabilisation methods for repairing or reconstructing granular surface and base layers of LVRs. In this study, a range of promising technologies from a comprehensive literature review was selected and examined using field demonstration sections. A total of nine geomaterials, three chemical stabilisers, and three types of geosynthetics were used to construct various test sections over a 3.22 km stretch of granular-surfaced road. Extensive falling weight deflectometer (FWD) and dynamic cone penetrometer tests were performed to evaluate the multilayered elastic moduli and strengths of the various sections. This paper details the design and construction of each test section, compares the as-constructed mechanistic performance of all test sections, and assesses stiffness changes of several sections one year after construction. To provide a statistical basis for the comparisons, a pairwise multiple-comparison procedure applied for unequal sample sizes and variances and the paired t-test were used to analyse the FWD test results, demonstrating that the performance measures of the various sections were significantly different.

Assessment of Composite Pavement Performance by Survival Analysis

AbstractThe main objective of this paper is to identify the most appropriate rehabilitation method for composite pavements and to evaluate the influence of different factors for the reflective crack development in composite pavement by survival analysis. Four composite pavement rehabilitation methods are evaluated: mill and fill, overlay, heater scarification, and rubblization. Survival analysis is used to evaluate the four methods using three pavement performance indicators: reflective cracking, international roughness index (IRI), and pavement condition index (PCI). Rubblization can significantly retard reflective cracking development compared with the other three methods. No significant difference for PCI is seen in the survival analysis for the four rehabilitation methods. Heater scarification shows the lowest survival probability for both reflective cracking and IRI, whereas overlay results in the poorest overall pavement condition based on PCI. Parametric survival models are employed to further anal...

Applications of the new approach to resonant column testing

For more than 50 years, the resonant column test has been used to measure the shear modulus and damping of soils for shear strains ranging from 10−5 % to 0.5 %. For most soils, the test is non-destructive, and tests may be performed on the same specimen at multiple confining stresses simulating in situ conditions from near surface to great depths. This paper makes use of the transfer function approach for resonant column theory to obtain simple solutions for the test and applies it for two types of resonant column apparatus: the conventional fixed-base free top (including spring top) now referred to as device type 1, and for a new type of resonant column device, device type 2, where a torque transducer is mounted in the bottom platen of the device. Device type 2 uses the torque measured at the base of the specimen and the rotation measured at the top of the specimen to determine the shear modulus and damping. The advantage for taking torque measurements at the base of the specimen is because the torque that is measured is that transmitted by the specimen alone. Calibrations of top platen inertia, stiffness, damping, and torque input are not needed for device type 2. Solution of these equations with complex variables can be done with any number of programming languages. For example, simple, single page, Excel spreadsheets for each device type are provided. The paper concludes with a discussion of issues that need to be addressed before procedures involving non-resonant frequencies can be introduced into ASTM D4015 [ASTM D4015: Standard Test Method for Modulus and Damping of Soils by Fixed-Base Resonant-Column Method, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA, 2007].

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.

Performance-Based Design Method for Gradation and Plasticity of Granular Road Surface Materials

Granular-surfaced roads frequently experience severe surface damage and degradation, which adversely affects traffic safety and significantly increases maintenance costs. The importance of the gradation and plasticity of granular-surfaced road materials have long been recognized. However, very few studies have focused on quantifying the effects of gradation and plasticity on the resulting mechanical performance of granular roadways. In this study, laboratory tests and statistical analyses were conducted to quantify the effects of variations in gradation and plasticity on the mechanical performance of granular road surface materials. A performance-based design method was developed using Fuller’s model to replace the commonly used arbitrary gradation band specifications. To validate the performance of the proposed method, field test sections were constructed then tested through a seasonal freeze–thaw period. Compared with existing gradation band specifications, the laboratory and field test results demonstrated that the proposed method is more closely tied to performance and can be used to develop specifications with more precise targets. To help secondary roads agencies implement the method while also recycling existing surface materials, a gradation optimization program was developed to determine the mixing ratios of existing roadway aggregate and two to three new quarry materials to come closest to the theoretical gradation for optimum performance. A complete set of testing, design, and construction procedures is also recommended to provide more cost-effective solutions to building or reconstructing granular-surfaced roads.

Strain Measures for Transfer Function Approaches to Resonant Column Testing

This paper presents strain measures to accompany a recently developed transfer function approach for resonant column testing of soils using a free-free apparatus. Although a number of past studies have proposed the use of random excitation or transfer functions in various forms, the new approach is unique in that the transfer function does not involve the current or voltage from the electromagnetic drive system. Consequently, the approach eliminates the need for many device-dependent calibrations and properties, including the torque-current calibration factor, stiffness of the torsional spring connecting the active and passive beams, and mass moments of inertia for the active platen and active beam. A brief review is given of the frequency domain transfer function approach for determining the shear modulus and damping of soil and rock, and a new theoretical formulation is presented for the associated strains in the soil specimen in terms of the measured boundary motion. It is demonstrated that higher modes can possess zero arithmetic average strains; therefore, a root-mean-square strain is proposed and derived as an alternative strain metric that will be non-zero for any frequency at which a specimen is undergoing deformation. Excellent agreement is found between experimental data and the newly derived strain measures. The concepts presented herein are valid for use with harmonic or stepped-sine testing as well as broadband random excitation, whereby strains are obtained for a range of frequencies spanning multiple modes of vibration. The approach provides a rigorous theoretical model that accurately describes the physics of the experiment over a broad frequency range spanning multiple modes. Additionally, the modulus and damping can be arbitrary functions of the frequency parameter without a loss of generality in the theoretical formulation, enabling studies of frequency-dependent modulus and damping.

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.