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Measuring Shear Wave Velocity Using Bender Elements
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Book Synopsis Measuring Shear Wave Velocity Using Bender Elements by : EC. Leong
Download or read book Measuring Shear Wave Velocity Using Bender Elements written by EC. Leong and published by . This book was released on 2005 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of bender element to measure shear wave velocity is popular due to its simplicity. However, there are still some uncertainties in the interpretation of the bender element test. In this paper, the use of bender elements in the determination of shear wave velocities of dry, unsaturated, and saturated soil specimens is examined with respect to the characteristics of the bender elements, waveform, magnitude, and frequency of the applied voltage to the transmitter bender element and method of travel time determination. The interpretation of the bender element test can be improved if two performance criteria are adopted: (1) a signal-to-noise ratio of at least 4 dB for the receiver signal, and (2) a wave path length to wavelength ratio of at least 3.33. Procedures to estimate the strain level associated with the shear wave velocity measurement using bender element are also described.
Book Synopsis Shear Wave Velocity Measurement in the Centrifuge Using Bender Elements by : Waleed El-Sekelly
Download or read book Shear Wave Velocity Measurement in the Centrifuge Using Bender Elements written by Waleed El-Sekelly and published by . This book was released on 2014 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Shear wave velocity is an important parameter for the design of geotechnical systems, particularly in seismically active areas. The availability of a reliable method for measuring shear wave velocity in centrifuge soil models is necessary in order to fully characterize the soil. The paper describes enhanced bender elements system developed at Rensselaer Polytechnic Institute. The fabrication process of bender elements in the laboratory is described in this paper. Also, the estimation of the shear wave velocity using the first arrival method is explained along with a study of near field presence in the results. To confirm the validity of the system, four centrifuge experiments were conducted on dry and saturated Ottawa F#55 sand. A comparison is performed between dry and saturated soil having the same relative density. Also, the effect of the direction of polarization of the shear wave is studied in the paper. The results are then compared to theoretical values estimated based on the literature and are found to match reasonably well; thus confirming the accuracy of the new system.
Book Synopsis Discussion "Measuring Shear Wave Velocity Using Bender Elements" by Leong, E. C., Yeo, S. H., and Rahardjo, H. by : J-S Lee
Download or read book Discussion "Measuring Shear Wave Velocity Using Bender Elements" by Leong, E. C., Yeo, S. H., and Rahardjo, H. written by J-S Lee and published by . This book was released on 2006 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Evaluation of Shear Wave Velocity from Bender Elements Using Cross-correlation by : David Airey
Download or read book Evaluation of Shear Wave Velocity from Bender Elements Using Cross-correlation written by David Airey and published by . This book was released on 2013 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of bender elements to determine shear wave velocity, and hence shear modulus, is becoming increasingly popular, with commercial systems now available. The most common method of interpretation is to make use of first arrival; however, automation of this procedure has been impossible for the wide range of velocities, sample sizes, stress levels, etc. encountered in soil and weak rock testing. A method for automating the velocity measurement was proposed by Mohsin and Airey in 2003 and relied on the use of cross-correlation. Since that time, many papers have been published on the method of interpretation, and these have often dismissed cross-correlation out of hand or have suggested that it does not work. These criticisms are based on either the fallacy that the input and output waves must look similar in order for the method to work or the selection of the wrong peak in the cross-correlation. We have been using the technique in the laboratory routinely for several years and have found that it can provide results that are at least as good as those obtained via other methods for soils varying from soft clay to silty gravel and well-cemented sand and at stress levels from 10 kPa to 2000 kPa. The greatest advantage of the technique is that it removes much of the subjectivity from the analysis, and in our opinion it is the only viable currently proposed method that is suitable for automation, and thus for standardization. This paper provides details of the procedure, pulse type and frequency, and calibration and discusses issues that affect the development of a standard. Results for a range of soil types, stress levels, and shear wave velocities are presented to demonstrate the reliability of the technique.
Book Synopsis Bender Elements and Bending Disks for Measurement of Shear and Compression Wave Velocities in Large Fully and Partially Saturated Sand Specimens by : E. Eseller-Bayat
Download or read book Bender Elements and Bending Disks for Measurement of Shear and Compression Wave Velocities in Large Fully and Partially Saturated Sand Specimens written by E. Eseller-Bayat and published by . This book was released on 2013 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bender element and bending disk setups were designed and implemented in a liquefaction box that accommodated a large sand specimen (190 mm × 300 mm × 490 mm). The box was manufactured for testing fully and partially saturated sand specimens under cyclic and earthquake excitation. Special housings for bender elements (31.8 mm × 12.7 mm × 0.51 mm) were manufactured to allow insertion of the elements through the side walls of the box. The bender elements were used to measure shear wave velocities in multiple directions to ascertain the uniformity of a sand specimen prepared in the liquefaction box. Large bending disks (31.8 mm × 0.41 mm) in special housings were utilized to measure compression wave velocities with the aim of investigating the presence and effect of the degree of partial saturation in specimens. The housings for bender elements and bending disks were designed to minimize the boundary effects of the Plexiglas walls of the liquefaction box. This paper provides details of the experimental setup and the designs of the bender element and bending disk housings. Sample test results of shear and compression wave measurements are also included to demonstrate successful application of the test setup. The experimental setup described is well suited for utilizing bender elements and bending disks for shear and compression wave velocity measurements in fully and partially saturated large sand specimens.
Book Synopsis Continuous Monitoring of Bender Element Shear Wave Velocities During Triaxial Testing by : Mark A. Styler
Download or read book Continuous Monitoring of Bender Element Shear Wave Velocities During Triaxial Testing written by Mark A. Styler and published by . This book was released on 2014 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bender element testing is used to measure shear wave velocities (VS) across soil specimens in the laboratory. Conventional bender element testing is carried out at a few discrete points during an experiment. This paper presents a method which uses bender elements to monitor VS continuously throughout a triaxial test. The method is based on monitoring the change in phase angle between a continuous trigger signal and a received signal. It allows the phase velocity at multiple selected frequencies to be monitored throughout a test. The method is described in detail and its use is illustrated for triaxial tests on loose specimens of Fraser River sand prepared by water pluviation. The variation of shear wave velocity is demonstrated during consolidation, ageing, and shearing to failure along a conventional stress path. Potential difficulties of interpretation are presented and discussed. In addition, the potential for continuous excitation of the specimen to alter the test results is considered and dismissed based on a comparison of samples tested without benders and with continuous benders at a range of excitation voltages. The proposed method for continuously monitoring bender element shear wave velocities does not use special or unique equipment. It results in a continuous VS from a trigger and receiver element installed on opposite ends of a triaxial specimen. This method provides a measure of VS during dynamic phases of an experiment that have not previously been observed. For example, this paper includes measures of VS at the onset of creep, the onset of shearing, and over the phase transformation from contractive to dilative behaviour. The relationship between fundamental soil behaviour and VS can now be more easily explored.
Book Synopsis Measurement of Shear Wave Velocity of Soil Specimen Prepared by Different Methods Using Resonant Column Device and Bender Elements by : Omar Osama El-Shafee
Download or read book Measurement of Shear Wave Velocity of Soil Specimen Prepared by Different Methods Using Resonant Column Device and Bender Elements written by Omar Osama El-Shafee and published by . This book was released on 2011 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Laboratory Investigation Into the Effect of Particle Sizes on Shear Wave Parameters Using Bender Elements Test Results by : Abolhasan Sharifi
Download or read book Laboratory Investigation Into the Effect of Particle Sizes on Shear Wave Parameters Using Bender Elements Test Results written by Abolhasan Sharifi and published by . This book was released on 2020 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Evaluating the influences of soil particle size on the dynamic behavior of soils during wave propagation has been an important issue in geotechnical engineering. Heretofore, the effects of particle size on shear wave velocities in soils have been examined using various experimental techniques. Most research in this regard so far have been carried out over a limited range of particle sizes, and the results have indicated contrasting effects of particle size on shear wave velocity ( Vs ). However, there has not been a comprehensive and unambiguous outcome describing the influences of particle size on Vs in soils. This research aims to experimentally investigate the effects of a wider range of particle sizes on Vs , wave shape, and frequency content of the shear waves transmitted in soil specimens. To this aim, a bender element apparatus embedded in a triaxial cell were used to minutely measure shear wave parameters of ten groups of local dry sandy soils, R1 ( d 50=0.225 mm) to R10 ( d 50=7.14 mm) samples. Moreover, dry tamping methods were employed to provide comparable samples at a similar initial void ratio of 0.8. Various amounts of frequency (5-12 kHz) and various confining pressures (50-500 kPa) were conducted on the identically prepared clean sand samples. Based on the results, it was observed that, for samples with mean particle sizes between 0.225 mm (R1) and 1.290 mm (R6), the Vs increased with the particle diameter, but for samples with mean particle sizes between 1.290 mm (R6) and 7.140 mm (R10), an increment in the particle diameter caused the Vs to decrease. It can be inferred that particle size influences the shape of the received signals such that the frequency content of the received signals, in both fine- and coarse-grained soils, are quite similar; however, medium-sized soils have a higher frequency content and a higher Vs , as well.
Book Synopsis Vibrations of Soils and Foundations by : Frank Edwin Richart
Download or read book Vibrations of Soils and Foundations written by Frank Edwin Richart and published by Prentice Hall. This book was released on 1970 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt: For graduate students in soil dynamics with a background in statics and elementary dynamics.
Book Synopsis Automatic Shear Wave Velocity Estimation in Bender Element Testing by : M. Finas
Download or read book Automatic Shear Wave Velocity Estimation in Bender Element Testing written by M. Finas and published by . This book was released on 2016 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dynamic properties of soils, such as shear wave velocity and damping, are some of critical parameters in the design of civil infrastructures subjected to vibrations from earthquakes and machine foundations. Bender element (BE) testing is used in the laboratory to determine shear wave velocity; however, there is no standard procedure for the interpretation of the results. The main limitation in BE testing is the correct estimation of the shear wave arrival time leading to uncertainty in the values of shear wave velocity. In this paper, three different automatic methods for the shear wave arrival time detection were tested. From these methods, a new procedure was proposed for the automatic determination of the shear wave arrival time using the Akaike information criterion. The method is tested on a series of bender element measurements giving less than 5 % error when the results were compared with the standard method for a signal-to-noise ratio higher than four.
Book Synopsis A Hybrid Bender Element-Ultrasonic System for Measurement of Wave Velocity in Soils by : Z. Cheng
Download or read book A Hybrid Bender Element-Ultrasonic System for Measurement of Wave Velocity in Soils written by Z. Cheng and published by . This book was released on 2014 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent years, the determination of the small strain modulus of soils from laboratory measurement of the elastic wave velocity has become more common. Piezoelectric elements are used in these tests, with two types of configurations: fixed to the back face of a platen as an ultrasonic transducer, or as a bimorph that slightly protrudes out of the platen. A survey of the literature shows that bender/extender elements are more widely used than ultrasonic transducers in soil tests. However, bender/extender elements are invasive in nature. Besides introducing some degree of specimen disturbance, they need to be sufficiently robust for insertion into the soil specimen, and they also need to be properly waterproofed to avoid short-circuiting. Ultrasonic transducers can solve the above-mentioned problems. However, the detection of shear waves can be challenging in soils, as reported in the literature. The objectives of this paper are to examine the difficulties of shear wave detection by ultrasonic transducers and to propose a hybrid bender element-ultrasonic system that partially alleviates the problems associated with bender/extender elements while still providing reliable shear wave velocity measurement. The hybrid system used was calibrated with standard materials, and tests were conducted on sand and kaolin specimens. Relative to bender/extender elements and ultrasonic transducers, the hybrid system showed better performance in determining wave velocities in soil tests, especially for shear waves.
Book Synopsis Recent Advances in Instrumentation, Data Acquisition, and Testing in Soil Dynamics by : Shoba Krishna Bhatia
Download or read book Recent Advances in Instrumentation, Data Acquisition, and Testing in Soil Dynamics written by Shoba Krishna Bhatia and published by American Society of Civil Engineers. This book was released on 1991 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: Examines the recent rapid expansion in the abilities of electronics for data acquisition and analysis. These changes were especially welcome in three areas of soil dynamics: surface wave investigations, in-situ liquefaction instrumentation and testing, and laboratory wave velocity tests.
Book Synopsis Fabrication, Operation, and Health Monitoring of Bender Elements for Aggressive Environments by : Brina M. Montoya
Download or read book Fabrication, Operation, and Health Monitoring of Bender Elements for Aggressive Environments written by Brina M. Montoya and published by . This book was released on 2012 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bender elements are commonly used to monitor the shear wave velocity of soils in various tests, including triaxial, consolidation, and centrifuge tests. When used in aggressive soil environments, electromagnetic crosstalk can distort the received bender element signal, preventing accurate shear wave velocity measurements. Aggressive soil environments are defined herein as conductive soils with high relative permittivity. Under these conditions, the electrical source is transmitted from source to receiver bender, dominating any received shear wave signal propagating through the soil. Careful attention must be paid to reducing the transmission of the electromagnetic signal, particularly in aggressive soil environments. When the waterproof coating of a bender element degrades and the inner and outer electrodes become electrically connected in a saturated environment, the bender element will no longer operate. However, when the waterproofing material is degraded so that only a single electrode on the source element is exposed, electric current can enter the pore fluid and affect the received signal. Further, even if the waterproofing coating is intact, electromagnetic crosstalk from the induced electrical field generated by the transmitting bender element can still affect the received signal when the conductivity of the pore fluid is high. Bender elements can be constructed so as to greatly reduce the electromagnetic crosstalk, and simple tests can be performed to help ensure that the bender element system is not susceptible to crosstalk. The objective here is to present details and practical guidelines regarding the fabrication, operation, and health monitoring of bender elements that will help ensure clear shear wave velocity measurements in aggressive soil environments. The fabrication steps presented improve on previous recommendations. Bender element operation (including signal form, frequency, and amplitude) also affects signal quality and the accuracy of the measured travel time. Finally, recommendations for monitoring the health of the bender elements throughout the transducer life are outlined.
Book Synopsis Application of Bender Elements in Measuring Gmax of Sand Under K0 Condition by : X. Zeng
Download or read book Application of Bender Elements in Measuring Gmax of Sand Under K0 Condition written by X. Zeng and published by . This book was released on 1998 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: A new application of bender elements to measure the small strain shear modulus of sand in multiple shear planes under anisotropic loading is developed. The tests were conducted in a specially designed oedometer with the side of the ring smoothed by a Teflon sheet. The soil used in the tests is clean angular pool filter sand. The effects of size of bender elements on the results of shear wave velocity measurement are discussed. Shear modulus in four different shear planes during a loading-unloading cycle is presented. The results of experiments are compared with the Hardin-Blanford equation on Gmax, which shows good agreement. The influence of side friction of the oedometer is investigated.
Book Synopsis Study of Laboratory and Field Techniques to Measure Shear Wave Parameters - Frequency Effects by : Hassan Ali
Download or read book Study of Laboratory and Field Techniques to Measure Shear Wave Parameters - Frequency Effects written by Hassan Ali and published by . This book was released on 2015 with total page 157 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Advances in Geotechnical and Transportation Engineering by : Sireesh Saride
Download or read book Advances in Geotechnical and Transportation Engineering written by Sireesh Saride and published by Springer Nature. This book was released on 2020-04-09 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the selected peer-reviewed papers from the national conference Futuristic Approaches in Civil Engineering (FACE) 2019. This volume focuses on latest research and challenges in the field of geotechnical, transportation, environmental and water resources engineering. The first part focuses on alternative and sustainable pavement materials, maintenance and rehabilitation of roads, transportation planning, traffic engineering, hybrid vehicles, safety management, and intelligent transport systems. In the second part of the book, basic and advanced research in geotechnical engineering which can provide sustainable solutions to practical problems in foundations, retaining structures, soil dynamics, site characterization, slope stability, dams, rock engineering, environmental geotechnics, and geosynthetics are covered. The third part of the book includes current research in environment, and water resources engineering. The contents of this book will be useful for students, researchers as well as industry professionals.
Book Synopsis A Shear Wave Velocity Tomography System for Geotechnical Centrifuge Testing by : Nam-Ryong Kim
Download or read book A Shear Wave Velocity Tomography System for Geotechnical Centrifuge Testing written by Nam-Ryong Kim and published by . This book was released on 2010 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: In physical model tests using geotechnical centrifuge, it is important to evaluate soil properties during centrifugal acceleration due to the effect of stress conditions. A crosshole type shear wave velocity tomography testing system has been developed, and the distribution of maximum shear modulus in sand layers could be evaluated in the centrifuge. Piezoelectric bender elements are installed in the system as shear wave transmitters and receivers for travel time measurement. A driving and measurement system for bender element tests is prepared to be used under centrifuge operating environment. A series of tests using this system has been conducted with uniform sand samples, and the testing procedure and typical signals from bender elements are presented. Tomography inversion considering curved raypaths has been conducted using a total of 256 travel time data determined by measured signals because the first arrivals follow curved raypaths under a stress related linear variation in stiffness with depth. The maximum shear modulus variation with depth, or vertical effective stress, has been verified through comparison with resonant column test results, and the applicability of this system in general centrifuge testing has been confirmed.
