Surface Wave Methods for Near-Surface Site Characterization

Surface Wave Methods for Near-Surface Site Characterization
Author: Sebastiano Foti
Publisher: CRC Press
Total Pages: 492
Release: 2014-08-21
Genre: Technology & Engineering
ISBN: 0415678765

Develop a Greater Understanding of How and Why Surface Wave Testing Works Using examples and case studies directly drawn from the authors’ experience, Surface Wave Methods for Near-Surface Site Characterization addresses both the experimental and theoretical aspects of surface wave propagation in both forward and inverse modeling. This book accents the key facets associated with surface wave testing for near-surface site characterization. It clearly outlines the basic principles, the theoretical framework and the practical implementation of surface wave analysis. In addition, it also describes in detail the equipment and measuring devices, acquisition techniques, signal processing, forward and inverse modeling theories, and testing protocols that form the basis of modern surface wave techniques. Review Examples of Typical Applications for This Geophysical Technique Divided into eight chapters, the book explains surface wave testing principles from data measurement to interpretation. It effectively integrates several examples and case studies illustrating how different ground conditions and geological settings may influence the interpretation of data measurements. The authors accurately describe each phase of testing in addition to the guidelines for correctly performing and interpreting results. They present variants of the test within a consistent framework to facilitate comparisons, and include an in-depth discussion of the uncertainties arising at each stage of surface wave testing. Provides a comprehensive and in-depth treatment of all the steps involved in surface wave testing Discusses surface wave methods and their applications in various geotechnical conditions and geological settings Explains how surface wave measurements can be used to estimate both stiffness and dissipative properties of the ground Addresses the issue of uncertainty, which is often an overlooked problem in surface wave testing Includes examples with comparative analysis using different processing techniques and inversion algorithms Outlines advanced applications of surface wave testing such as joint inversion, underwater investigation, and Love wave analysis Written for geotechnical engineers, engineering seismologists, geophysicists, and researchers, Surface Wave Methods for Near-Surface Site Characterization offers practical guidance, and presents a thorough understanding of the basic concepts.

Advancements in Surface Wave Testing

Advancements in Surface Wave Testing
Author: Siavash Mahvelati
Publisher:
Total Pages: 242
Release: 2019
Genre:
ISBN:

The Multichannel Analysis of Surface Waves (MASW) method has been widely used to evaluate the subsurface in engineering applications since late 1990's. In MASW, surface waves are introduced into the subsurface and recorded by sensors along the ground surface. The characteristics of the propagating surface wave are influenced by the subsurface stratification, the manner in which the surface waves are input into the ground, and the survey parameters to acquire data. Rayleigh waves are typically generated by vertical strikes on a metallic plate which serves as a coupler between the active input source (e.g., a sledgehammer) and the ground surface. It has been suggested that plastic-type base plates can improve the low-frequency energy of Rayleigh waves and therefore, can increase the depth of investigation among other potential improvements. However, very little studies exist in the literature that evaluate the role of base plate material, especially plastic materials. In addition to Rayleigh surface waves, seismic surface waves can also be generated with horizontal impacts (i.e., Love waves) using specialized base plates. In this regard, much less is available in the literature regarding Love waves as sources in MASW testing which means that optimum field survey parameters, the effects of near-field, and the role of seismic source have not been thoroughly investigated yet for Love waves. Given the aforementioned gaps in the literature, two aspects of MASW have been investigated. First, the role of base plate material, specifically plastic-type plates, has been studied. Field data collected from six sites along with the data from laboratory experiments and numerical simulations of hammer-plate impact were studied. The results showed that softer base plates improve the energy transfer by as much 20% and lead to minor improvements, typically one-digit numbers in relative changes, in other signal characteristics such as signal bandwidth and signal-to-noise ratio. These results were corroborated with laboratory testing and numerical models of wave propagation with different base plate materials. The second goal was to improve understanding of Love wave propagation, particularly as related to resolution capabilities from survey parameters. Rayleigh and Love waveforms were collected with multiple active seismic sources at three sites and a systematic comparison was made between the two types of waves. Also, seismic wave propagation was simulated using the research community code SPECFEM2D to further investigate their differences. The results revealed critical new information about the depth of investigation, the effects of bedrock location on near-field effects, and the role of the different survey parameters on Rayleigh and Love wave data. The depth of investigation of Love wave MASW was deeper by about 2-9 m than that of Rayleigh MASW as a result of improved minimum frequency. The minimum source offset to avoid near-field effects was comparable for both Rayleigh and Love waves (0.3-0.4 of maximum wavelength). At closer source offset locations, Rayleigh waves were more affected by near-field effects and showed an additional 10% underestimation of planar phase velocities. Overall, the results from both parts of this study provides new practical insights about some of the unexplored aspects of surface wave testing using MASW.

Oceanographical Engineering

Oceanographical Engineering
Author: Robert L. Wiegel
Publisher: Courier Corporation
Total Pages: 546
Release: 2013-09-03
Genre: Science
ISBN: 048616019X

As is the case with many modern fields of study, oceanographical engineering cuts across the boundaries of several disciplines. Like other scientific endeavors, it aims to understand the nature of the ocean and to make use of this understanding for the benefit of humanity through better ports, safer and more economical operations at sea, and greater use of the oceans' natural resources--food, raw materials, and recreation. This graduate-level text requires a knowledge of fluid mechanics; a background in the motions of sediments in fluids is advisable, as is a concurrent course in structural dynamics. Topics include the theory of periodic waves; tsunamis, storm surges, and harbor oscillations; the effect of structures on waves; waves in shoaling water; tides and sea level changes; currents; shores and shore processes; some characteristics of the oceans' waters; moorings; and other related subjects. Certain portions of the book pertaining to the distribution of temperatures and salinities in the ocean are largely descriptive; other portions, such as the sections on waves, are mathematical. Numerous drawings and photographs supplement the text.

Study of Laboratory and Field Techniques to Measure Shear Wave Parameters - Frequency Effects

Study of Laboratory and Field Techniques to Measure Shear Wave Parameters - Frequency Effects
Author: Hassan Ali
Publisher:
Total Pages: 157
Release: 2015
Genre: Shear waves
ISBN:

Over the last decade, significance of correctly evaluating the dynamic properties of soil has been widely recognized by the research community. Among various parameters, shear wave velocity and damping ratio has been recognized as the key parameter for the soils subjected to dynamic loading. The shear wave velocity is used in the geotechnical assessments for site characterization, ground response analysis, and liquefaction potential. The dynamic properties of the soils can be attained in the lab or in-situ. The dynamic soil properties are dependent on different state parameters, such as, void ratio, confining stress, water content, strain levels, and drainage conditions. Apart from the influence of the above parameters, the dynamic soil parameters are also affected by the frequency and the amplitude of the dynamic load applied to the soil. The in-situ tests compliments the laboratory testing in the evaluation of the dynamic soil parameters. Although, correlations can be used to estimate the in-situ parameters but a direct measurement is necessary. To develop a greater confidence of the results of the in-situ tests, it is helpful to compare the field results to conventional laboratory tests. In the RC testing, the effect of base stiffness has a significant effect on shear modulus and damping values. In literature, only two studies have shown the effect of base fixidity. In this thesis, the issue is addressed by testing sand and clay sample on traditional bench and isolation table. In addition to base fixidity, coupling between the specimen and base platen is also very critical. Radial blades in top and bottom platen are introduced along with porous stone fixed underneath the blades. Aluminum probes are recommended for the calibration of the RC device, however, the effect on shear modulus and damping as function of shear strain is not well studied. Therefore, the stiff probe is tested from low to large strains and effect on damping ratio is studied. Finally, a new BE method is proposed to understand the estimation of shear wave velocity at higher frequencies. Due to the large variation in the interpretation of the BE tests results, there is no standard method for the estimation of the shear wave velocity. In this thesis, a new calibration procedure using state of the art laser vibrometer is used to understand the bending behavior of benders in air and in tip to tip configuration. Shear wave velocity comparison between RC and BE tests is done in usual practice, however, the frequency effects from these two tests are not well stated. In this study, the frequency effects are studied and a new methodology, modified frequency domain method, is introduced and tested on dry specimen. The results of the BE tests match well with the RC test values. MASW is a practiced field test to evaluate the shear wave velocity profile for geomaterials, however, the effect of frequency in the case of an anomaly has not been well understood. Therefore, this study uses numerical simulations and a lab scale model to study these effects. In addition, the effect of actual accelerometers on the measurements is studied for the first time using a high frequency laser vibrometer. The frequency effects in field theory of the MASW and SCPT is also studied to address the actual limitations in the analysis of SCPT data without the consideration of frequency effects. Based on the objective, this research focuses on: (1) the study of the laboratory resonant column and bender element tests, (2) numerical simulations and laboratory surface waves testing, and (3) field testing using surface waves and seismic cone penetration method for the estimation of shear wave parameters with emphasis on the frequency effects. An important aspect of the laboratory testing is the calibration of the equipment. Standard procedures are available for the calibration of the resonant column (RC) device, however, the same is not true for the bender element (BE). In this study, the bender elements are calibrated using three different configurations, tip-to-tip, aluminum rods, and using state-of-art laser vibrometer. The State of art laser vibrometer is used to characterize the bending behavior of the bender elements showing the resonance frequency of 12 kHz and damping of 2 % when vibrating in air. The top and bottom platen of RC device were modified to allow better coupling between the specimen and benders. Radial blades were introduced to account for coupling of stiff clay specimens. Four different soils (sand, stiff clay, mine paste, and leda clay) were tested in this study. The results of the tests, from the RC and the BE tests, were analyzed in the time and the frequency domains. Comparison of the results show, a maximum of 45 $\%$ difference in the velocity obtained from the RC and BE tests. Leda clay tests were done on the modified base platens and the difference in the Vs between the RC and BE is 6% compared to the stiff clay specimen where the difference is 28% To study the difference in the Vs values between the RC and BE, a new modified frequency domain method for BE testing is presented. The method was applied to the sand specimen. The sample is excited with a frequency sweep ranging from 0 to 52 kHz and change in unwrapped phase, between the input excitation and output response, is evaluated outside the range of resonant peaks of the specimen. The Vs values from the two tests match well for the frequency range between 29 and 23 kHz, with overall less than 10 % error for the range of confinement range studied in this thesis. Numerical simulations on homogeneous and non-homogeneous medium showed the change in the phase velocity of the Rayleigh waves (R-waves) due to the presence of a void. To introduce non-homogeneity, voids of various size and depth were used. Nine numerical models were analyzed, change in the phase velocity as a function of frequency was observed. A new methodology was introduced in which the receivers were divided into three sections, before, on-top, and after the void. Results from the dispersion curves show that the change in the phase velocity (function of frequency) is between 3% to 50% for different void width and depth. Multichannel analysis of surface waves (MASW) test method was used as the geophysical testing method. The laboratory tests were conducted using three different configurations on sandbox. Two tests involved use of accelerometers as receivers, however, the input source was different. While the third test consisted of using state of art laser vibrometer as receiver. Using the laser vibrometer, 96 surface responses were recorded compared to 12 using accelerometers. The results from the laboratory MASW test showed the frequency effect on the measurements due to the source used in this method. Coupling of the geophone/transducer in surface wave testing is an important issue. Results from the lab test using laser vibrometer showed that the mass loading effect of accelerometer affects the frequency content of the signal. The field MASW and the SCPT tests were done at the University of Waterloo Columbia Lake Test Site (UW-CLTS). The comparison of shear wave velocity from the field MASW and the SCPT shows the average shear wave velocity profile from the two tests, however, importance in not paid to the frequency of the input signal and main frequency difference between the MASW and SCPT tests. In this study, the frequency spectrum from the MASW and the SCPT tests data were analyzed to understand the change in the shear wave velocity at different depths. From the analysis, the percentage change in shear wave velocity between MASW line 1 and SCPT 1 and 2 is more than 90 % for depths between 0 and 2 m, while it reduces to 10 % for depths between 7 and 13 m.

Application of the Surface Wave Survey Method on Multi-Scale Engineering Problems

Application of the Surface Wave Survey Method on Multi-Scale Engineering Problems
Author: Kaoshan Dai
Publisher:
Total Pages: 10
Release: 2014
Genre: Accelerometer
ISBN:

The geometric dispersion of surface waves offers the feature to infer the properties of a medium. The surface wave survey method is under continuous evolution and its applications include the noninvasive characterization of a medium at a small scale and the earthquake geotechnical survey at a large scale. Despite the significant difference in scales, these applications generally utilize the propagation of the surface waves along the boundary of a layered medium. This paper discusses standard steps involved in surface wave surveys. Two application case studies are conducted and presented in detail. In the small scale laboratory application case, a nondestructive testing (NDT) methodology is proposed for the coating investigation using laser interferometric measurements of surface waves. In the large scale field application, an accelerometer-based passive surface wave survey is designed for earthquake geotechnical engineering site characterization. Finally, recommendations for practical application of surface waves in multi-scale engineering problems are presented.