Primary Wave Velocity Research Articles

Evaluation of the water weakening coefficient of sandstones by using non-destructive physical parameters

IntroductionThe presence of water significantly reduces the mechanical strength of rocks and induces various engineering geological hazards. The water weakening coefficient Kp is used to quantify this effect, defined as the ratio of wet uniaxial compressive strength to the dry value.MethodsA comprehensive physico-mechanical test was conducted on fifteen sandstones under dry and saturated conditions to predict the water weakening coefficient using easily obtainable physical parameters. Multiple linear regression was employed to establish the relationship between these parameters and the saturated water weakening coefficient.ResultsThe saturated water weakening coefficient decreases with increasing porosity and increases with higher Primary wave velocity (P-wave velocity). Rocks with higher porosity but lower P-wave velocity typically absorb more water. The P-wave velocity and clay mineral content were identified as the best predictors of the saturated water weakening coefficient (R2 = 0.82). Unsaturated water weakening coefficients at any water saturation level were well estimated using a previous exponential function.DiscussionThe roles of different clay minerals and P-wave velocity in the water weakening process of rocks are comprehensively discussed. This study enhances the understanding of the water weakening mechanism and provides an improved evaluation model for the water weakening coefficient of sandstones using physical parameters.

Shear-Wave Velocity Data Assists Modeling for Offshore Windfarm Development

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 35354, “Pseudo-3D Underwater Multichannel Analysis of Surface Waves for Offshore Windfarm Development,” by Stephan Unterseh and Luis McArthur, TotalEnergies, and Edouard Mouton, SismOcean. The paper has not been peer reviewed. Copyright 2024 Offshore Technology Conference. _ In the course of a research and development (R&D) project dedicated to quantitative ground modeling, underwater multichannel analysis surface-wave (UMASW) data were acquired within an offshore windfarm area currently in development in the North Sea. The goal of the project described in the complete paper was to test the added value of the shear wave velocity (Vs) interpreted from the UMASW, particularly as a propagation tool of geotechnical information. While UMASW, together with seismic refraction, is regularly used to characterize the ground for burial or trenching purposes, it appears also to bring valuable design parameters for offshore wind turbine foundations. Introduction To investigate the value of Vs in the performance of quantitative ground modeling studies, an internal R&D initiative was launched aimed at acquiring Vs data and the associated uncertainties of foundation depth of an offshore windfarm currently in development. These data will be tested at a later stage for the propagation of geotechnical parameters used in foundation design. The acquisition consisted of obtaining Vs data through UMASW methodologies around two distinct geotechnical boreholes and along a corridor tying the two areas. The UMASW commonly is used in combination with seismic refraction to perform burial assessment analysis of cable or pipeline or to characterize ground conditions before performance of horizontal deviated drilling. Thus, the data acquisition did not require extensive hardware development. A unique pseudo-3D processing technique nevertheless was implemented to allow for 3D data visualization and ground characterization. Site Conditions The selected site lies in the North Sea in water depths ranging from 20 to 30 m. The area was first investigated with standard geophysical techniques. Preliminary geotechnical investigation included 6-m-deep vibrocores and 60-m-deep drilled boreholes, with alternating cone penetration tests and push sampling and coring. P-S logging also was performed at key geotechnical locations to gather 1D primary wave velocities (Vp) and Vs. The seabed generally consists of a thin cover of Holocene dense sand, occasionally with boulders, overlying quaternary subglacial formation deposits, including moraine, gravelly sand, and clays of variable thicknesses. The bedrock is generally Jurassic and includes dense sand; hard clay; weak claystone; and, locally, strong limestone bands. The test locations were selected within the coverage of the geophysical data set in areas where variable lithologies occur and where the seabed was found free of boulders and outcrops because these are detrimental to UMASW acquisition. The lithology of the two boreholes performed within the test area is indicated in Table 1 of the complete paper.

Wave-based fault detection in concrete by the Full Waveform Inversion considering noise

In the field of non-destructive testing of concrete, the use of ultrasonic waves became state of the art, among other techniques. Nevertheless, there is still room for improvement, in particular concerning the resolution and robustness of the monitoring results.One approach is the application of the Full Waveform Inversion (FWI) originating from geotechnical engineering, known here as seismic tomography. The forward and backpropagation of waves within a numerical model are deployed to identify material parameters, like the primary and secondary wave velocity as well as density. This approach forms a non-linear, and ill-posed mathematical problem. Its solution is computationally demanding and time-consuming.Within the presented approach, the Full Waveform Inversion is used on a numerically simulated artificial concrete specimen of relatively large dimensions. Here, the synthetic ultrasound data is compromised by the consideration of different levels of Gaussian white noise. Additionally, several sizes and positions of faults are computed to simulate a variety of possible defects within the concrete material as in reality. Subsequently, the identifiability of the fault together with its recognition quality are investigated. Additionally, recommendations on sensor positioning and layout are given.

Assessing the effect of lime-zeolite on geotechnical properties and microstructure of reconstituted clay used as a subgrade soil

This study investigates the replacement of conventional stabilizers with eco-friendly alternatives, with a specific focus on enhancing pavement subgrade applications. This research aims to evaluate the impact of lime-zeolite treatment on the properties of clayey subgrades and its potential to outperform traditional stabilization methods. Various tests, such as Proctor compaction, Atterberg limits, swelling, and unconfined compressive strength (UCS), were performed considering the plasticity index variation. Optimal zeolite replacement led to significant improvements in the clayey soils' behavior. It reduced the plasticity index by up to 9.4% and almost eliminated swelling. Furthermore, unconfined compressive strength (UCS) values were enhanced by up to 7.56 times when compared to untreated soil. Ultrasonic pulse velocity (UPV) tests indicated substantial increases in primary wave velocity (Vp) and constrained modulus (Mv), reaching values of 2650 m/s and 9600 MPa, respectively, representing improvements of around 6.5 times and 50 times over untreated clay. The results highlight the remarkable efficacy of lime-zeolite substitution, particularly at a 25% replacement level. The improvements in plasticity, swelling, and strength characteristics signify the potential of this eco-friendly approach in pavement subgrade enhancement. The significant increases in UPV parameters provide insights into the improved structural integrity of the treated soils. This innovative approach offers valuable contributions to pavement subgrade design by addressing plasticity, swelling, and strength issues in clayey soils, ultimately leading to more sustainable and effective infrastructure projects.

Investigating strength development over time of industrial by-products using the resonance column free-free technique

Soil improvement using cementitious binders is used throughout the world to improve the strength and stiffness characteristics of soft soils. Strength verification is typically performed using unconfined compression tests; however, these are destructive and do not give detailed information on strength development over time. This note presents a laboratory investigation using the non-destructive resonant column free-free (RC-ff) technique to assess the primary wave velocity. This velocity is correlated to strength, and hence strength development over time can be investigated in detail using this simple and effective technique. Two soft clays, one inorganic and one organic, were improved with the industrial by-products cement kiln dust and ground-granulated blast-furnace slag in combination with cement. A semi-theoretical correlation between primary wave velocity and strength is proposed, and it is seen that this correlation is independent of these soil and binder types. This also applied to the seismic small-strain compressive modulus. The strength development up to 91 days of curing was investigated and it was seen that this highly depends on binder type, but to a lesser degree soil type. It is demonstrated that the RC-ff technique can be of great value both in engineering practice and research.

Uncertainties in Broadband Determination of the High-Frequency Spectral Decay, Kappa, in Eastern Canada

ABSTRACT Kappa (the high-frequency spectral decay slope at near-source distances; often referred to as κ0) is determined at 25 seismograph stations in Eastern Canada using broadband ground-motion modeling approaches. The database comprises Fourier spectra (effective amplitude spectrum for the horizontal component and the vertical component, 0.8–40 Hz) computed from 3318 earthquakes of moment magnitude M 1.5–5 recorded on stations within 150 km. Average kappa values for bedrock sites, having shear-wave velocities from 850 to 2400 m/s, are highly variable, ranging from −29 to +21 ms (horizontal) and −28 to +11 ms (vertical), but appear on average to be near-zero. The values obtained are sensitive to methodology, especially the necessary adjustments to the spectra to account for site amplification effects. Kappa values do not appear to correlate well with site parameters such as rock shear-wave velocity, average shear-wave velocity in the upper 30 m, primary wave velocity, site class, type and age of rock, or instrument housing. This lack of correlation may reflect the noted sensitivities to methodological factors. We conclude that kappa values in rock environments are not reliably estimated from such proxies and should be determined from recorded ground motions at a given location. On average, there is little evidence of significant high-frequency attenuation on rock sites beyond that already accounted for in ground-motion modeling by the empirical parameterization of regional Q-related path effects.

Characterization of sub-surface structure, using seismic refraction and multi-channel analysis of surface waves methods in Ajere Ekori Yakurr LGA of cross river state

The study was to characterize the sub surface at Agere in Ekori, using seismic refraction method, multichannel analysis of surface waves technique and borehole intrusive technique. Data were collected using a 12channel seismograph and other accessories required for seismic refraction data collection. Software called seismicimager was used to examine the data. The primary wave velocity in the first layer varied from 690 m/s at 4.2 m to 96 m/s at 7.3 m. A Vp range of 315 m/s to 484 m/s at a depth of 2 m is present inside the layer and represents the organic soil constituents. A Vp range of 669 m/s to 1756 m/s represents loose sand (dry), loose made ground (rubble), landfill rubbish, disturbed soil, and clay landfill, all within a depth of 2.3 m to 12.1 m. In addition to the borehole intrusive method, multichannel analysis of surface wave (MASW) techniques was used to calculate the soil profile based on velocity. The source was a 7 kg sledge hammer, the detectors (receivers) were 24 units of 4.5 Hz geophones, and the recorder was a Terraloc Mark 8 ABEM. Seismicimager software was used for analysis. At Ajere 1 through 6, the MASW test configuration employed 5 m geophone spacing and a source offset distance of 5 m, while at Ajere 7, it used 1 m geophone spacing and a source offset distance of 2 m. Near the boreholes, all of the MASW test arrays were run. The trustworthy seismic data from Ajere 1 to 6 at depths of 0.7 m to 13.1 m and 4.7 m to 17 m. Based on SPT N values, the results showed that the shear wave velocities had been classified into three layers of soil: very soft, soft, and firm. The velocities below 164 m/s, between 164 and 190, and 190 m/s to 320 m/s were classified as these soil types. In the meantime, a drilling invasive technique based on SPT N value determines changes in the soil layer. Hard material shear wave velocity data was not provided. In conclusion, because of its non-destructive, non-invasive nature and relative speed of evaluation, the MASW technique has the potential to be adapted in soil study to complement intrusive technique.

ARTERIAL STIFFNESS IN PREHYPERTENSIVE PATIENTS WITH PREDIABETES - A PILOT STUDY

Objective: Prediabetes is associated with higher cardiovascular risk and increased all-cause mortality in the general population. The aim of this study was to determine whether there are differences in primary laboratory findings and pulse wave velocity (PWV) between prehypertensive patients with and without prediabetes. Design and method: This study included 58 patients (39 women, 19 men) with prehypertension according to the JNC7 criteria from 2003 (systolic blood pressure [SBP] 120-139mmHg or diastolic blood pressure [DBP] 80-89mmHg based on 2 or more seated measurements on each of 2 or more office visits) from one family practice in Health center Zagreb-west. Patients were divided into two groups depending on having prediabetes (fasting plasma glucose [FPG] 5.6-6.9 mmol/L – according to American Diabetic Association (ADA) criteria from 2014). Basic laboratory tests (cholesterol, creatinine, fasting glucose, and potassium), anthropometric, 24h ambulatory blood pressure, and pulse wave velocity (PWV) measurements (with Agedio B900) were done in all patients. Renal function was calculated with the CKD-EPI formula (KDIGO 2020). Mann-Whitney U test, multiple linear regression model, and descriptive statistics were used in data processing in Statistica v.12.0. Results: Normal FPG was found in 41 patients (70.7%), while 17 patients had prediabetes (29.3%). Prehypertensive patients with prediabetes were older (median 58 vs. 54 years; p<0.01), had significantly higher uric acid concentration (median 324 vs 282 mmol/L; p<0.05), and higher PWV (median 8.20 vs. 7.45m/s; p<0.01). No differences were found in the concentration of potassium, LDL cholesterol, triglycerides, and body mass index (median 24kg/m2). FBG levels were independently and significantly associated with PWV (beta = 0.33; p<0.05). Conclusions: This pilot study indicates the possible existence of accelerated atherosclerosis in prehypertensive individuals with prediabetes compared to those with normal FPG. Research on a larger sample is needed to confirm these findings.

On the optimal localization of pendulum impacts using a non‐contact acoustic array

AbstractThe presented work aims to adapt a Geiger‐based method and localize pendulum impacts applied on a rigid steel plate using the data set of a 112 microphone array. The advantage compared to measurements with piezoelectric sensors, where normally a number of sensors are involved, is the superior number of microphones. To solve the Geiger algorithm on the three‐dimensional domain, at least data from three sensors and the primary wave velocity are required (four equations). Moreover, if the system of equations is overdetermined, an error minimization can be performed, for example, with the least‐squares method. Since in this work the distance between array and plate is constant, the algorithm can be even reduced to a two‐dimensional problem (only three equations required). Indeed, the superior overdetermination of 112 microphone data allows to index the optimal data set by combing microphone data and thus achieve the best localization results for the optimal microphone. This study is relevant to the scientific community because it will allow uncontrolled events cracks or other damage to be localized with a great accuracy and reliability.

Machine learning algorithm optimization for intelligent prediction of rock thermal conductivity: A case study from a whole-cored scientific drilling borehole

Rock thermal conductivity (TC) is a key parameter in geothermal, petroleum geology, and basin research. Although experimental analysis relying on core samples is currently an effective way to obtain the TC of rocks, it is not always feasible as most boreholes have no or limited cores, making it difficult to establish TC model of geological body efficiently and accurately. This study sheds light on how machine learning algorithms can be used to accurately predict rock TC with easily accessible and high-resolution logging data. Based on 295 measured TC data, logging data, and vertical seismic profile (VSP) data collected from the whole-cored CSDP-2 borehole, the models including random forest (RF), convolutional neural network (CNN), support vector regression (SVR), and particle swarm optimization-SVR (PSO_SVR), were applied to predict the TC of the entire borehole section. Using a confusion matrix analysis, the primary-wave velocity (PWV) from the VSP survey, measured density, and logging data, including shallow lateral resistivity (LLS), compensated neutron log (CNL), density (DEN), gamma rays (GR), spontaneous potential (SP), and acoustic transit time (AC), were used as the input variables for training models and TC prediction. The results showed that the geophysical parameters reflecting those properties related to mineral composition, porosity and reservoir fluids of geological body can be well used to predict TC through machine learning algorithms. Regardless of unconsolidated sediments or rocks, the RF model showed stronger applicability and higher accuracy in TC prediction compared to the PSO_SVR and CNN models, while the SVR model showed poor applicability in this case study. The PWV data can effectively improve the accuracy of TC prediction of all models, and the RF model finally yielded the excellent performance with a correlation coefficient (> 0.86) and root mean squared error (8%) between the predicted and measured values. Future research should focus on studying the weighted analysis for the correlation between geophysical parameters and TC and developing more accurate predictive models for wider applications.

Seismic bearing capacity of shallow foundations subjected to inclined and eccentric loading using modified pseudo-dynamic method

In this paper, a comprehensive parametric study is conducted to evaluate the seismic bearing capacity of shallow strip foundations overlying dry and cohesionless granular soil under the actions of inclined and eccentric loadings. For this purpose, a systematic combination of the lower-bound theorems of the limit analysis, the finite element method, and the nonlinear programming is implemented. The seismic loading condition is simulated by the well-established modified pseudo-dynamic (MPD) approach by accounting for the significant influence of phase difference as well as the primary and shear waves propagation through applying non-uniform inertia forces along the vertical and horizontal directions, respectively. Unlike the pseudo-static approach, in the so-called modified pseudo-dynamic loading, a more realistic dynamic nature of the seismic excitation is taken into account using various soil dynamic properties and spectral parameters of the problem under study. In this way, a more viable response of the shallow foundation subjected to seismic loading could be captured by simulating a visco-elastic material through the well-defined Kelvin-Voigt model. The modified pseudo-dynamic (MPD) method considers the influences of shear and primary wave velocities, amplification of earthquake loading, and period of lateral shaking. The current MPD approach is capable of considering the local site effects and damping characteristics of the soil deposit underneath shallow footing by adopting a non-uniform and nonlinear acceleration field inside the soil medium. The results of the seismic bearing capacity are presented in the forms of spectral responses and failure envelopes for the eccentric and inclined loadings. The results show that the failure envelopes of the shallow foundation subjected to either inclined or eccentric loading significantly shrink with the increase in the earthquake accelerations and decrease in the material damping of the underlying soil mass. The amount of changes in the size of failure envelopes in the normalized V-H and V-M spaces due to the variation of seismic intensity and material damping depends directly on the non-dimensional frequency of the earthquake excitation.

Investigation of Road Pavement Failures Using Active and Passive Surface Wave Methods in Parts of Calabar Municipality, Cross River State, Nigeria

The active and the passive techniques of surface wave were employed to investigate some major road pavement failures within the Calabar metropolis, Cross River State. The dispersion curves from MASW (active) and ReMi (passive) were inverted to give a 1D shear wave velocity model. The aim of this study was to comparatively investigate the major causes of the incessant road pavement failures especially few months after its construction and repairs within the study area using the shear wave velocity and blow count (N values). These roads are all located within the same geologic setting of the Calabar Coastal Plan Sand and showed evidence of road failures ranging from pot holes, alligator cracking, rutting and shear failure cracking etc. For each site, two sets of data were collected; the Passive and the Active seismic surface wave data. The survey was able to gather the following data from each location; shear wave velocity, primary wave velocity, N-values for both the active and the passive data which were both derived by the Seisimager surface wave software. The software was used to delineate low velocity layers within the depth of 4m – 6m at the failed portions of the survey sites exception of location 1 (the control site) which showed an ideal situation of increasing velocity with depth. These low velocity layers were inferred to be the major cause of the incessant failure of the pavements in the survey areas. These velocities and the N- values (blow count) were used to classify each location into sites C, D and E, according to the 1997 National Earthquake Hazards Reduction Program (NEHRP).

The theory of compression–shear coupled composite wave propagation in rock

AbstractThe wave velocity analysis of rock medium is the main method used to explore the internal compositions in the crust and research seismic. In this paper, a compression–shear coupled nonlinear elastic constitutive relation is established, which is consistent with the mechanical properties of rock and mineral medium under high pressure. On this basis, numerical solutions of the wave equation and plane wave analytical solutions for the primary and secondary wave velocities are obtained. As is indicated by the comparison with the linear elastic constitutive theory, the results reflect the compression–shear coupling characteristics of the rock, including the stress path effect and the compression–shear coupling wave effect. With different parameter values, the velocity of the secondary wave changes from lower than that of the elastic shear wave, to higher than that of the elastic shear wave. The research results are expected to provide meaningful explanations for the physical mechanisms of the supershear wave and sub‐Rayleigh wave, and guidance for the detection of rock and soil composition and the observation of seismic waves.

Subsurface Weathering Zone Determination Using Down-Hole Seismic Surveys, Majnoon Oil Field, Southern Iraq

Detecting the weathering zone is one of the required data correction steps to process reflection seismic data collected at the Majnoon oil field, south of Iraq. Two subsurface layers represent the weathering zone in this field. Those two layers were inferred by primary seismic waves utilizing the down-hole seismic method. Five wells in the studied area were drilled and named DH-1, DH-2, DH-3, DH-4 and DH-5. The collected seismic data was analyzed to determine the depths, thicknesses and lithology of the subsurface layers. The primary seismic wave velocities were calculated and applied to eliminate two sub-surface layers. The average primary wave velocities and thicknesses of the first layer were 374, 240, 211, 277, 370 m/s, and 2.8, 2, 2, 2, 4.9 m, respectively. In the second layer, the primary waves velocities were 1125, 1284, 1201, 1395 and 1008 m/s, and the thicknesses were 13.2, 11, 13, 11.5, 21.4 m. The first weathered layer represented on the five wells is clay. The second layer has different geometry on different wells, which is represented by a sandy clay layer on DH-1, and muddy clay on DH-2. Then, it is changed to be a silt layer in DH-3, sandy clay in DH-4 and DH-5.

Subgrade soil evaluation using integrated seismic refraction tomography and geotechnical studies: A case of Ajaokuta-Anyigba Federal highway, North-Central Nigeria

ABSTRACT Integrated seismic refraction tomography (SRT) and geotechnical tests were conducted on failed and stable sections of the Ajaokuta – Anyigba Highway, North-central Nigeria. This study was aimed at characterising the soil profile, determining the competence of the subgrade soils, and establishing relationships between geophysical and geotechnical parameters. Primary wave velocities (Vp) were calculated by using SeisImager/2D (V.2.9.1). The subgrade soils of the unstable segment were characterised by low Vp (358–607 m/s) while higher Vp (762–1417 m/s) characterised the stable segment. The geotechnical results confirmed the seismic refraction results. Geotechnical results revealed that the subgrades of the unstable section are generally classified as A-6 and A-7-6 clayey soils, with low to high plasticity, and a fair to poor subgrade rating. While the subgrades of the stable section are grouped as A-2-4 silty sands with low compressibility and good to excellent subgrade ratings. Simple linear regression analysis showed fairly strong positive correlations between Vp and sand with CBR (r = 0.81 and 0.78, respectively). On the other hand, fairly strong negative correlations were obtained between Vp and the plasticity index with fines (r = −0.63 and −0.82 respectively).

Hypocenter Determination and Estimation 1-D Velocity Models Using Coupled Velocity-Hypocenter Method

Hypocenter relocation is performed to obtain a high-precision hypocenter location (accurate earthquake location). An accurate earthquake location is the key problem in seismology. Further information from an accurate hypocenter location can be used for seismicity analysis, velocity structure study, and earthquake prone mapping as one of the earthquake mitigation efforts. In this research, the method used to relocate the earthquake hypocenter was the Coupled Velocity-Hypocenter. Relocations were conducted in the Central Sulawesi region; we located 40 local earthquake events with a magnitude of ≥ 3.8 ML and a depth of ≤ 25 km. The selected P-wave traveltimes were inverted from 5 seismic stations. The variance of initial velocity models used the 1-D Primary wave velocity model of North Sulawesi, Jeffrey-Bullen and Central Sulawesi. The relocation results show that most of the hypocenters are concentrated precisely in minor faults present in the research area, and the hypocenter distribution of the events indicated as destructive shallow earthquakes occurs at depths of about 5-15 km. The residual distributions resulting from the relocation using the initial velocity model of the Central Sulawesi region indicates an improved quality if compared to Jeffrey-Bullen velocity model and the North Sulawesi velocity model, with RMS error value of 0.08 seconds. This research concluded that the 1-D velocity model in the regional (Central Sulawesi Region) reference was suitable for determining the high-precision hypocenter location.

Petrophysics applied in mineralizations, hydrothermal alterations and lithology mapping: A case study from the Zn–Pb (Cu–Ag) epithermal deposit of Santa Maria, Brazil

ABSTRACTThe epithermal Zn–Pb (Cu–Ag) deposit of Santa Maria represents a distal magmatic‐hydrothermal system, whose mineralizations are controlled by fault systems located in the sedimentary units of the upper Camaquã Basin, above the tectonic units of the Sul‐Riograndense Shield. The hydrothermal alteration zones contain illite, chlorite and pyrite, besides galena, sphalerite, chalcopyrite and bornite. To improve the knowledge of this mineral system, this work investigated the petrophysical footprints of samples representing the predominant lithology, altered rocks and hydrothermal mineralization. The core samples of the predominant lithology, altered rocks and hydrothermal deposit mineralizations were used to determine the following petrophysical properties, density, magnetic susceptibility, primary wave velocity, resistivity, conductivity and chargeability. Moreover, the quantitative evaluation of minerals by scanning electron microscopy coupled with an automated image analysis system allowed us to map lithological and alteration processes. The results indicate density as the most effective physical property to map lithology, hydrothermal alteration and the Zn–Pb (Cu–Au) mineralization. Furthermore, all studied physical properties have moderate effectiveness in the alteration zones of known geological and geophysical anomalies in the Santa Maria deposit. Chargeability could be used, especially when sulphides are disseminated, but additional geological factors complicate its interpretation. The mineralogical and petrophysical diversity of the Santa Maria deposit provided vital data for geological–geophysical interpretations while allowing the creation of a key exploration plan to investigate the Zn–Pb (Cu–Au) mineralization. Finally, petrophysics should be used in prospection to help understand complex geological processes, their overlapping subpopulations and to accelerate mineral research while reducing the use of technical and financial resources and expenditure on ineffective geophysical methodologies.

Assessment of the relationship between clay soils consistency and kinematic parameters of elastic waves

Assessment of the water-physical characteristics of soils by indirect geophysical indicators is simpler. Indirect indicators provide an opportunity to characterize various volumes of the researched environment. The article presents the results of determining the kinematic parameters of elastic waves of clay soils at different values of the liquidity index. In the transition from soils of very stiff consistency to soils with stiff and firm-stiff consistency, a correlation is observed between the ratio of the secondary, primary wave velocities, and the values of the liquidity index of clay soils.

Joint inversion of Rayleigh wave fundamental and higher order mode phase velocity dispersion curves using multi‐objective grey wolf optimization

AbstractRayleigh wave dispersion curves can be inverted to retrieve subsurface seismic velocity profiles. The inverse problem is ill‐posed, nonlinear and poorly conditioned, necessitating the application of global optimization methods. We present the application of the multi‐objective grey wolf optimization algorithm to perform joint inversion of the phase velocity dispersion curves corresponding to the fundamental and higher order modes of Rayleigh waves to obtain shear (S‐) and primary (P‐) wave velocity profiles. Multi‐objective grey wolf optimization is an extension of the grey wolf optimization algorithm for application to multi‐objective optimization and can be adapted to solve joint inversion problems. We compare the joint inversion results obtained from the multi‐objective grey wolf optimizer with those obtained from Markov chain Monte Carlo and fundamental mode inversion using the grey wolf optimizer on synthetic examples. The errors associated with phase velocity measurements are simulated by adding frequency‐dependent noise, with a higher level of noise added to the phase velocities corresponding to lower frequencies as compared to the higher frequencies. In the multimode joint inversion problem, the multi‐objective grey wolf optimizer gives a suite of solutions corresponding to each model parameter. The suite of S‐wave and P‐wave velocity profiles estimated from the multi‐objective grey wolf optimizer matches closely with the true model for the synthetic case studies even in the presence of noise. However, the suite of solutions has a greater spread for the last few layers, qualitatively indicating a higher degree of uncertainty in the predicted model parameter. The uncertainty in the solution for the deeper layers is a consequence of the uncertainty in the phase velocity at lower frequencies. We demonstrate the efficacy of the algorithm on recorded data from a shallow seismic survey conducted at the Indian Institute of Technology Bombay. The results from the multi‐objective grey wolf optimizer are in close agreement with those from Markov chain Monte Carlo, and the depth of investigation is found to be greater in comparison to results from refraction traveltime inversion.

A multifrequency ultrasonic approach to extracting static modulus and damage characteristics of rock

Understanding the mechanical behavior of rock is a fundamental requirement for many geological explorations . Based on the frequency dependence of primary and shear wave velocities (P- and S-wave velocities), this work proposed a new approach to obtaining the static modulus of rocks without using empirical correlations. Six group granite specimens are treated by different temperatures, then the P- and S-wave velocities of these specimens at various frequencies were tested. The static moduli of all the specimens were calculated by deriving the newly proposed critical P- and S-wave velocities with a classical formula. The results showed that the static moduli of all the specimens obtained from the ultrasonic approach complied with the initial modulus obtained from uniaxial compression tests , demonstrating the reasonability of the proposed ultrasonic approach. The reasonability of the proposed approach was further proven by using a distinct lattice spring model. Numerical results showed that the calculated modulus is consistent with the true value. In addition, the standard deviation of wave velocities at different frequencies was adopted to describe the damage characteristics in rock, which well explained the change in damage variable during the thermal process. The proposed approach provides a potential method to fast obtain the static modulus and damage characteristics of rock.