Numerical simulation of seismic cone signals

2005 ◽  
Vol 42 (2) ◽  
pp. 574-586 ◽  
Author(s):  
John A Howie ◽  
Ali Amini
Keyword(s):  
Numerical Simulation ◽  
Wave Propagation ◽  
Finite Difference ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Field Effect ◽  
Near Field ◽  
Ground Conditions ◽  
Near Field Effect

Numerical analysis can provide insight into the effect of ground conditions on seismic signals recorded in downhole seismic testing. As part of a study of the interpretation of seismic cone data in complex ground conditions, this paper deals with the cases of wave propagation in (i) homogeneous soil and (ii) soil of increasing stiffness with depth. The main purpose of this study was to assess the validity of the use of the finite difference program FLAC for the simulation of the downhole seismic test. For realistic assumptions of material stiffness and damping, the main characteristics of field seismic cone penetration test (SCPT) seismic data were reproduced in the simulated data. Both displayed the same general shape of signal, number of oscillations, signal attenuation, frequency content, compression wave component (near-field effect), signal widening, and shift of the peak of the frequency spectrum with depth. Damping was shown to cause signal widening and dispersion, and the shear wave velocity, Vs, interpreted from the simulated wave traces varied with the interval method used to determine it. For a case history of field data, it was found that Vs varied by about 3%, depending on the analysis method used. The results show that finite difference modeling of wave propagation can provide useful insights into the factors affecting the interpretation of downhole seismic tests.Key words: seismic cone testing, shear wave velocity, signal widening, near-field effect, numerical simulation, finite difference.

Dyadic wavelet analysis of bender element signals in determining shear wave velocity

2020 ◽  
Vol 57 (12) ◽  
pp. 2027-2030
Author(s):  
Guan Chen ◽  
Fang-Tong Wang ◽  
Dian-Qing Li ◽  
Yong Liu
Keyword(s):  
Wavelet Transform ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Near Field ◽  
Bender Element ◽  
Dyadic Wavelet ◽  
Wavelet Transform Modulus Maxima ◽  
Dyadic Wavelet Transform ◽  
Modulus Maxima

Determining shear wave velocity is a critical technique in bender element tests, as it can be readily affected by near-field effects, wave reflection, and other factors. This study proposes a new method based on the dyadic wavelet transform modulus maxima. Combining the local modulus maxima of dyadic wavelet transform approximate coefficients at fine decomposition levels and an appropriate threshold value, the proposed method can automatically detect the target point. For validation, a comparative study among the dyadic wavelet transform modulus maxima, peak-to-peak, first arrival, and cross-correlation methods was carried out using 140 sets of bender element signals. The comparison results show that the proposed method not only mitigates the adverse effects of near-field, later major peaks, and noise contamination, but is also more robust in estimating shear wave velocity.

Simulation of downhole and crosshole seismic tests on sand using the hydraulic gradient similitude method

1990 ◽  
Vol 27 (4) ◽  
pp. 441-460 ◽  
Author(s):  
Li Yan ◽  
Peter M. Byrne
Keyword(s):  
Wave Propagation ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Stress Ratio ◽  
Velocity Ratio ◽  
Hydraulic Gradient ◽  
Empirical Equations ◽  
Wave Measurement

A method of simulating downhole and crosshole seismic shear-wave tests in a model under controlled stress conditionsis described. The downhole and shear wave in horizontal plane (SH) crosshole shear waves are generated and received along the principal stress axes using piezoceramic bender elements. The K0in situ stress conditions, including loading and unloading stress paths, are simulated by the hydraulic gradient similitude method, which allows high stresses simulating field conditions to be obtained. The horizontal stress during the tests is directly measured by a lateral total-stress transducer. The test data are used to evaluate various published empirical equations that relate shear-wave velocity and soil stress state. It is found that although the various empirical equations can predict the in situ shear-wave velocity profile reasonably well, only the equation that relates the shear-wave velocity to the individual principal stresses in the directions of wave propagation and particle motion can predict the variation of the velocity ratio between the downhole and SH crosshole tests. It was also found that the stress ratio has some effects on the downhole (or shear wave in vertical plane (SV) crosshole) shear-wave velocity, but not on the SH crosshole shear-wave velocity. This indicates that it is only the stress ratio in the plane of wave propagation that is important to the shear-wave velocity. Comparison between the downhole and SH crosshole shows that structure anisotropy is in the order of 10%. In addjtion, K0 values are predicted from shear-wave measurement and compared with measured ones. The difficulties in obtaining K0 values from shear-wave measurement are also discussed. Key words: hydraulic gradient, model tests, downhole and crosshole shear-wave tests, sand.

scholarly journals Evaluation of the shear wave velocity (VS) of an artificial carbonate sand obtained with the use of bender elements test

DYNA ◽  
2021 ◽  
Vol 88 (217) ◽  
pp. 211-219
Author(s):  
Samuel Felipe Mollepaza Tarazona ◽  
Bárbara Luiza Riz de Moura ◽  
Matias Faria Rodrigues ◽  
Maria Cascão Ferreira de Almeida ◽  
Marcio De Souza Soares de Almeida
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Mechanical Response ◽  
Near Field ◽  
Triaxial Tests ◽  
Dynamic Parameters ◽  
Bender Elements ◽  
Carbonate Sand ◽  
Confining Stress

Carbonate sand is characterized by the presence of fragile grains, which may influence their mechanical response due to the imposed loading; especially cyclic loading. The shear wave velocity (VS) provides relevant information for the design of foundation inserted in this type of soil, which can be obtained from laboratory tests with the use of bender elements (BE). This paper aims to evaluate the VS value of a carbonate sand from triaxial tests with BE using three methods in the time domain. The influence of loading, unloading and cycling on VS is also evaluated. The results confirmed that the confining stress affects the dynamic parameters. At higher stress levels, the signals aremore susceptible to the near field effects and the dynamic parameters are less influenced by cycling.

scholarly journals Bender elements in stiff cemented clay: shear wave velocity (Vs) correction by applying wavelength considerations

2019 ◽  
Vol 56 (7) ◽  
pp. 1034-1041 ◽  
Author(s):  
Qasim Khan ◽  
Sathya Subramanian ◽  
Dawn Y.C. Wong ◽  
Taeseo Ku
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Near Field ◽  
Shear Stiffness ◽  
Propagation Distance ◽  
Small Strain ◽  
Bender Element ◽  
Bender Elements ◽  
Sine Signal

For the quality control of cement mixing in clays, small-strain shear stiffness Gmax is now increasingly being used due to enhanced repeatability in shear wave velocity (Vs) measurements. These stiff cemented clays have higher resonant frequencies that require the use of higher input frequencies in bender element testing for reliable Vs measurements. However, the practical requirements for suitable signals (with minimal near-field effects and wave reflections) can often be difficult to implement. To facilitate such Vs measurements, the current study proposes a methodology that can correct Vs values corresponding to lower wave propagation distance to wavelength ratios (Ltt/λ) to more reliable values of Vs at reference Ltt/λ criterion suggested in previous studies (e.g., 2, 3.33, and 4). Two clay types are mixed with ordinary Portland cement and various mix ratios are utilized to cover a wider range of soil stiffnesses. Based on the collected database, it is found that the resulting fitting functions enable the reasonable estimation of the stabilized Vs values corresponding to the suggested Ltt/λ criterion regardless of the nature of the input sine signal.

Ground Vibration Characteristics for High-Speed Trains on Embankments

2013 ◽  
Vol 479-480 ◽  
pp. 239-243
Author(s):  
Yit Jin Chen ◽  
Song Wei Lin ◽  
Yi Jiun Shen
Keyword(s):  
Frequency Dependence ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
High Speed ◽  
Near Field ◽  
Ground Vibration ◽  
Frequency Range ◽  
High Speed Trains ◽  
Train Speed

This study explores the characteristics of ground vibration induced by Taiwan high-speed trains on embankments. A series of field measurement data is used for evaluating near-field vibration, far-field vibration, and vibration influence distance. Various influence factors, including train speed, ground shear wave velocity, frequency dependence, and volume of the structure, are applied for evaluation. Based on the analyses, the near-field ground vibration mainly depends on the train speed, ground shear wave velocity, and frequency dependence. The far-field vibration propagation is affected by ground shear wave velocity and frequency dependence. In general, the high frequency range has the highest attenuation coefficient and the low frequency range has the lowest. The influence distance in hard ground is the farthest, whereas the soft ground is the shortest. Finally, a specific ground vibration assessment is established using these characteristics.

Measuring shear wave velocity of granular material using the piezoelectric ring-actuator technique (P-RAT)

2015 ◽  
Vol 52 (9) ◽  
pp. 1302-1317 ◽  
Author(s):  
Mourad Karray ◽  
Mohamed Ben Romdhan ◽  
Mahmoud N. Hussien ◽  
Yannic Éthier
Keyword(s):  
Granular Material ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Near Field ◽  
Soil Improvement ◽  
Bender Element ◽  
Factors Affecting ◽  
A New Technique ◽  
P Rat

A precise evaluation of shear wave velocity, Vs, is a crucial issue in the design of foundations subjected to dynamic loading, liquefaction evaluation, and soil improvement control. Laboratory techniques such as resonant column (RC) and bender element (BE) have been developed over the years to measure Vs. At low strain (γ < 10−3), techniques based on piezoelectric elements (e.g., BE) can be considered superior to RC, as they can be used in conventional geotechnical devices (e.g., triaxial, oedometer, direct simple shear, etc.). However, it is a difficult task to verify that the obtained Vs values are correct and accurate, as there are several difficulties associated with these methods, including the mixed radiation of both primary and shear waves, near-field effects, boundary effects, and uncertain detection of first arrivals. This paper presents the use of a new technique to measure Vs in granular material, called the piezoelectric ring-actuator technique (P-RAT), developed at the Université de Sherbrooke. The paper also provides a detailed description of a unique interpretation method of the signals produced from this technique to minimize the difficulties associated with other techniques. The P-RAT has been incorporated into the well-known oedometer cell to measure the Vs of Péribonka sand through a series of oedometric tests, and the obtained results have been detailed, analyzed, and discussed in light of the basic state of knowledge of Vs and factors affecting it. Particular emphasis is also placed on the validation of the accuracy of the P-RAT by means of reliable experimental measurements available in literature.

scholarly journals Studies on a Piezoelectric Cylindrical Transducer for Borehole Dipole Acoustic Measurements

2021 ◽  
Vol 11 (3) ◽  
pp. 1036
Author(s):  
Yinqiu Zhou ◽  
Xiuming Wang ◽  
Yuyu Dai
Keyword(s):  
Numerical Simulation ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Low Frequency ◽  
Compressional Wave ◽  
Wave Measurements ◽  
New Development ◽  
Cylindrical Transducer ◽  
Simulation Results

In this article, a novel design of a piezoelectric dipole transducer is proposed for formation acoustic velocity measurement in the vicinity of a borehole with a frequency range of 0.4–6 kHz. The transducer which actuates a cylindrical shell to generate a pure dipole mode wave by using multiple piezoelectric bender bars is analyzed theoretically and simulated numerically by using the finite element method (FEM). Moreover, the transducer is fabricated and tested to compare with the numerical simulation results, which shows that the test and simulation results are in good agreement. Finally, compared with numerical simulation results of the traditional dipole transducer, it is shown that the proposed dipole transducer has higher transmitting sensitivities than commonly used ones, especially in low frequency responses. This work lays a foundation for the new development of the transducer in borehole dipole acoustic shear wave measurements. Especially, in a slow formation where the shear wave velocity is lower than that of compressional wave in the borehole fluid, the transducer could be used for highly efficient shear wave velocity measurements.

scholarly journals Studies of the shear wave velocity in soil cement under the anisotropic stress state

Vestnik MGSU ◽  
2020 ◽  
pp. 1372-1389
Author(s):  
Armen Z. Ter-Martirosyan ◽  
Evgeniy S. Sobolev
Keyword(s):  
Wave Propagation ◽  
Stress State ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Laboratory Tests ◽  
Triaxial Compression ◽  
Anisotropic Stress ◽  
Shear Wave Velocities ◽  
Soil Cement

Introduction. Deep soil mixing, that alters construction properties of foundations, allows to construct buildings and structures on the sites that have loose soils. As a rule, adverse geotechnical conditions are accompanied by dynamic forces that affect designed buildings and structures. The objective of these studies is to predict changes in mechanical properties of soils that follow the alteration of structural properties of a foundation. Soil cement is the focus of this study. Materials and methods. The findings of special laboratory tests of soil cement samples using the method of low amplitude torsional vibrations inside a resonant column in the anisotropic triaxial compression mode allowed to assess the effect of the supplementary vertical load on the velocity of shear elastic wave propagation. The co-authors present a description of the research method and provide an overview of the equipment used to conduct special laboratory tests. Tests were performed on undisturbed soil cement samples that had a natural water content. The anisotropic stress state of soil cement samples exposed to triaxial tests in the resonant column was caused by special behaviour features of the foundation. Results. In this study, laboratory tests had two stages. At the first stage, the effect of the vertical stress on the velocity of shear wave propagation was assessed. Correlation dependences between the shear wave velocity and the ratio of vertical and lateral stresses were obtained. At the second stage, shear wave propagation velocity values were identified at various combinations of lateral σ3 and vertical σ1 stresses. The results of the second stage are designated for the assessment of the effect of the anisotropic stress state and the projection of shear wave velocities at the stress levels anticipated on the site that will accommodate designed heavy structures. Conclusions. The findings allow to assess the effect of lateral and vertical stresses on changes of shear wave velocities in the triaxial compression mode. It was identified that at equal values of lateral stresses σ3, a 7-fold vertical stress σ1 increase leads to a 15 % increase in the shear wave velocity in soil cement Vs. At the same time, an increase in the ratio of vertical to lateral stresses σ1/σ3 by a factor of 15 causes an 11 % increase in the shear wave velocity. It is noted that the smaller the initial value of lateral stress σ3, the higher the rise in the shear wave velocity Vs in the course of testing. Correlation dependencies, presented in this study, can be used to assess the effect of the anisotropic state as the first approximation (for preliminary calculations) in the design of heavy structures on soil cement foundations.

Sign in / Sign up

Export Citation Format

Share Document