Spectral Analysis Of Surface Waves Research Articles

Shear wave velocity in surface sediments

Surface sediments of different nature are common in Iceland. Natural soil sites and man-made fillings commonly serve as foundations for different types of structures. In Civil engineering work it is fundamental to know the geotechnical properties of these materials in the upper 20–30 m. A seismic method called Spectral Analysis of Surface Waves (SASW) has been used in recent decades in Iceland to measure and evaluate shear wave velocity at different natural sites as well as in man-made fillings. The method is fast and involves low cost equipment. It gives reliable results down to 20 m depth by using sledge as a seismic source and copes with both soft and stiff soil sites. Furthermore, the technique can be applied at coarse grained gravelly sites where it can be difficult to use borehole and penetration methods. We describe the methodology used in these projects and review all SASW measurements carried out in Iceland. The soil strata at all test sites are classified based on sieve analysis when possible. Natural sites and man-made fillings are kept separated. A database and an open web site are introduced where all the SASW results can be viewed and shear wave profiles for different soil types and unlike sites can be compared. The main aim with the database and the webpage is to give scientists and engineers access to this data and enable them to compare stiffness at different sites.

Metamorphosing the SASW Method by 2D Wavefield Transformation

AbstractDispersion analysis in surface wave testing is conventionally associated with a certain method of data acquisition, such as phase angle analysis in the two-station spectral analysis of surface wave (SASW) method and two-dimensional (2D) multistation wavefield transformation in the multistation analysis of surface wave (MASW) method. A new procedure has been developed to reconstruct the SASW data as MASW-imitating data, taking advantage of the 2D multistation wavefield transformation to better analyze the SASW data. Numerical simulations and a real-world example demonstrate the feasibility of this procedure, but also reveal an unwanted side effect associated with aliasing. A common-receiver survey is proposed for future experiments to eliminate this unwanted side effect and at the same time increase the lateral resolution.

Prediction of long-term settlement on soft clay using shear wave velocity and damping characteristics

This paper presents a method of calculating long-term settlement of a loaded pad on soft clay at Klang, Selangor, Malaysia where the soil model is treated as an anelastic material of viscoelastic property. Initially, an elastic shear modulus ( G) value from shear wave velocity profiles of the seismic tests from spectral analysis of surface wave (SASW) and continuous surface wave (CSW) tests was obtained. A value of damping ( D) at an equivalent elastic strain is then calculated from the hysteresis of the plate load tests corrected to equivalent strain using the Damping–Strain formula. The calculated elastic settlement and its equivalent damping are then used to calculate the long-term settlement by applying the generalised viscoelastic formula. Comparisons to traditional methods of settlement predictions were made and the viscoelastic formula has shown better agreement to the observed settlement. Further modification of the settlement formula is introduced to improve the settlement accuracy to 10%.

The seismic signatures of the 2009 Shiaolin landslide in Taiwan

Abstract. The Shiaolin landslide occurred on 9 August 2009 after Typhoon Morakot struck Taiwan, claiming over 400 lives. The seismic signals produced by the landslide were recorded by broadband seismic stations in Taiwan. The time-frequency spectra for these signals were obtained by the Hilbert-Huang transform (HHT) and were analyzed to obtain the seismic characteristics of the landslide. Empirical mode decomposition (EMD) was applied to differentiate weak surface-wave signals from noise and to estimate the surface-wave velocities in the region. The surface-wave velocities were estimated using the fifth intrinsic mode function (IMF 5) obtained from the EMD. The spectra of the earthquake data were compared. The main frequency content of the seismic waves caused by the Shiaolin landslide were in the range of 0.5 to 1.5 Hz. This frequency range is smaller than the frequency ranges of other earthquakes. The spectral analysis of surface waves (SASW) method is suggested for characterizing the shear-wave velocities of the strata in the region.

Shallow-structure characterization by 2D elastic full-waveform inversion

Assessing the effectiveness of elastic full-waveform-inversion (FWI) algorithms when applied to shallow 2D structures in the presence of a complex topography is critically important. By using FWI, we overcome inherent limitations of conventional seismic methods used for near-surface prospecting (acoustic tomography and multichannel spectral analysis of surface waves). The elastic forward problem, formulated in the frequency domain, is based on a mixed finite-element P0-P1 discontinuous Galerkin method to ensure accurate modeling of complex topography effects at a reasonable computing cost. The inversion problem uses an FWI algorithm to minimize the misfit between observed and calculated data. Based on results from a numerical experiment performed on a realistic landslide model inspired from the morphostructure of the Super-Sauze earthflow, we analyzed the effect of using a hierarchical preconditioning strategy, based on a simultaneous multifrequency inversion of damped data, to mitigate the strong nonlinearities coming from the surface waves. This strategy is a key point in alleviating the strong near-surface effects and avoiding convergence toward a local minimum. Using a limited-memory quasi-Newton method improved the convergence level. These findings are analogous to recent applications on large-scale domains, although limited source-receiver offset ranges, low-frequency content of the source, and domination of surface waves on the signal led to some difficulties. Regarding the impact of data decimation on the inversion results, we have learned that an inversion restricted to the vertical data component can be successful without significant loss in terms of parameter imagery resolution. In our investigations of the effect of increased source spacing, we found that a sampling of 4 m (less than three times the theoretical maximum of one half-wavelength) led to severe aliasing.

Geospatial contour mapping of shear wave velocity for Mumbai city

Shear wave velocity is one of the most important input parameter in the analysis of geotechnical earthquake engineering problems, particularly to estimate site-specific amplification factor and ground response study. Dynamic in situ tests such as spectral analysis of surface waves (SASW) or multichannel analysis of surface waves (MASW) are very expensive. Also due to lack of specialized personnel, these tests are generally avoided in many soil investigation programs. Worldwide, several researchers have developed correlations between the SPT ‘N’ value and shear wave velocity ‘Vs’, which are useful for determining the dynamic soil properties. In the present study, more than 400 numbers of soil borehole data were collected from various geotechnical investigation agencies, government engineering institutes and geotechnical laboratories from different parts of Mumbai city, which is financial capital of India with highest population density. In this paper, an attempt has been made to develop the correlation between the SPT ‘N’ value and shear wave velocity ‘Vs’ for various soil profile of Mumbai city and compared with other existing correlations for different cities in India. Using Geographical Information System (GIS), a geospatial contour map of shear wave velocity profile for Mumbai city is prepared with contour intervals of 25 and 50 m/s. The scarcity of database or maps of shear wave velocity profile for Mumbai city will make the present geospatial contour maps extremely useful and beneficial to the designer, practitioners for seismic hazard study involved in geotechnical earthquake engineering.

Application of Spectral Analysis of Surface Wave Method for Rock Mass Characterization

The spectral analysis of surface wave (SASW) was introduced in the 1980s and it has since attracted the attention of researchers because it is a fast, inexpensive, non-destructive, and easy-to-use method for rock mass characterization. The SASW method was applied in excavation classification by Suharsono (2006) as well as in rock quality designation (RQD) determination (Suharsono et al., 2004); determination of flexible pavement and rigid pavement profiles (Ismail et al., 2001); and non-destructive evaluation and characterization of pavement systems (Nazarian and Stokoe, 1984). The aims of this article were to determine the RQD value and to conduct an excavation classification analysis using the SASW method. In the SASW method, Rayleigh waves are generated by impacting the ground with a hammer, which are then detected using two receivers placed on the ground surface and recorded by a spectrum analyzer. Forward and reverse configuration, which generates forward and reverse SASW profiles, is normally obtained by striking the hammer at the two opposite sides of the receivers, as shown in Figure 1. For sampling shallow material, small receiver spacing with high-frequency receivers and high-frequency sources are utilized. For sampling deeper material, low-frequency receivers are used with longer receiver spacing and low-frequency sources. The common receiver midpoint geometry (CRMG) introduced by Cho and Lin (2001), Joh (1996), and Suharsono and Samsudin (2003) was used for the receiver spacing configuration, as shown in Figure 2. Figure 1. Field configuration of SASW method. Figure 2. Common receivers midpoint geometry (CRMG) (after Cho and Lin [2001]; Joh [1996]; and Suharsono and Abdul Rahim Samsudin [2003]). The Rayleigh wave data were collected and transformed to the frequency domain by a dynamic signal analyzer. WinSASW 3.1.3 (Joh, 1996) geophysical software was used for the inversion process to produce profiles of shear wave …

Prediction of Shear Wave Velocity in Underground Layers Using SASW and Artificial Neural Networks

This research aims at improving the methods of prediction of shear wave velocity in underground layers. We propose and showcase our methodology using a case study on the Mashhad plain in north eastern part of Iran. Geotechnical investigations had previously reported nine measurements of the SASW (Spectral Analysis of Surface Waves) method over this field and above wells which have DHT (Down Hole Test) result. Since SASW utilizes an analytical formula (which suffers from some simplicities and noise) for evaluating shear wave velocity, we use the results of SASW in a trained artificial neural network (ANN) to estimate the un- known nonlinear relationships between SASW results and those obtained by the method of DHT (treated here as real values). Our results show that an appropriately trained neural network can reliably predict the shear wave velocity between wells accurately.

Spectral-analysis-surface-waves-method in ground characterization

The prediction of train induced vibration levels in structures close to railway tracks before track construction starts is important in order to avoid having to implement costly mitigation measures afterwards. The used models require an accurate characterization of the propagation medium i.e. the soil layers. To this end the spectral analysis of surface waves (SASW) method has been chosen among the active surface waves techniques available. As dynamic source a modal sledge hammer has been used. The generated vibrations have been measured at known offsets by means of several accelerometers. There are many parameters involved in estimating the experimental dispersion curve and, later on, thickness and propagation velocities of the different layers. Tests have been carried out at the Segovia railway station. Its main building covers some of the railway tracks and vibration problems in the building should be avoided. In the paper these tests as well as the influence of several parameters on the estimated soil profile will be detailed.

Geotechnical reconnaissance of the 2010 Darfield (Canterbury) earthquake

On 4 September 2010, a magnitude Mw 7.1 earthquake struck the Canterbury region on the South Island of New Zealand. The epicentre of the earthquake was located in the Darfield area about 40 km west of the city of Christchurch. Extensive damage was inflicted to lifelines and residential houses due to widespread liquefaction and lateral spreading in areas close to major streams, rivers and wetlands throughout Christchurch and Kaiapoi. Unreinforced masonry buildings also suffered extensive damage throughout the region. Despite the severe damage to infrastructure and residential houses, fortunately, no deaths occurred and only two injuries were reported in this earthquake. From an engineering viewpoint, one may argue that the most significant aspects of the 2010 Darfield Earthquake were geotechnical in nature, with liquefaction and lateral spreading being the principal culprits for the inflicted damage.
 Following the earthquake, an intensive geotechnical reconnaissance was conducted to capture evidence and perishable data from this event. The surveys were performed on foot, by car and from a helicopter over a period of six days. A broad-brush field reconnaissance was conducted in the first two days, followed by pin-point investigations at specific locations including detailed site inspections and field testing using: Dynamic Cone Penetration Test (DCPT), Swedish Weight Sounding (SWS), and Spectral Analysis of Surface Waves (SASW).
 This paper summarizes the observations and preliminary findings from this early reconnaissance work.

Field Evaluation of Dynamic Compaction on Granular Deposits

The dynamic compaction (DC) method is a versatile ground treatment technique with growing popularity. It is applicable to a wide variety of soil types and conditions, particularly sandy materials and granular fills. This study presents a case history of the dynamic compaction with a high energy level of 6,000 kN·m on granular deposits at a site in China. The reclaimed site featured loose backfill with heterogeneity and saturated silt. In order to properly deal with such soil conditions and to optimize the DC design, field tests were conducted to determine the influencing factors in DC. Deformation tests were performed to ascertain the rational spacing of impacts and the optimal number of drops and to provide proofs to the adjustment of the original DC procedure. Monitoring of the pore water pressure helped obtain the time delay between passes. The approach to assess the depth of improvement was discussed based on interpretations of the spectral analysis of surface waves (SASW) test. Analysis of the SASW and plate-load tests demonstrated significant improvement in the soils at the site, with no obvious weak layers. Following dynamic compaction, the allowable ground-bearing capacity and the depth of improvement at the site were no less than 270 kPa and 7.4 m, respectively.

Determination of the material damping ratio in the soil from SASW tests using the half-power bandwidth method

SUMMARY This paper presents a novel technique for the determination of the material damping ratio in shallow soil layers. It is based on the spectral analysis of surface waves (SASW) test. The technique is an alternative to existing methods, where the damping ratio is determined from the spatial decay of the Rayleigh wave. These methods rely on the knowledge of the geometric damping, and may lead to incorrect results if the geometric damping is calculated based on an inaccurate shear wave velocity profile. The existing methods may also lead to incorrect results when higher modes contribute to the wavefield in the soil. In the proposed technique, the wavefield is transformed to the frequency–wavenumber domain. The resulting frequency–wavenumber spectrum exhibits a peak that corresponds to the fundamental Rayleigh wave. The dispersion curve is derived from the peak’s position, whereas the attenuation curve is derived from its width, using the half-power bandwidth method. Due to the use of the appropriate wavenumber transformation, this method does not require the calculation of the geometric damping. In addition, the occurrence of higher Rayleigh modes does not affect the attenuation curve associated with the fundamental Rayleigh wave, as higher modes appear as separate peaks in the frequency–wavenumber spectrum that do not interfere with the peak corresponding to the fundamental Rayleigh wave (except at the osculation points). Three benchmark problems are considered to validate the outlined technique; the results are compared with those obtained using existing methods. All methods perform well when applied to a regular soil profile, where the stiffness of the soil increases with depth. For soil profiles with a soft layer trapped between two stiffer layers, or where the soil properties vary smoothly with depth, the proposed technique yields more accurate results than the existing methods. The practical applicability of the new method is finally illustrated using experimental data collected from a test site in Belgium.

Active and Passive Seismic as an Indicator of Large Equipment Interactions with the Oil Sand

The strain softening of oil sand in the underfoot of ultra class mobile mining equipment, due to the loading action of large mobile mining equipment such as trucks and shovels, yields a highly unstable condition for the operation of this ultra-class equipment. Soft ground conditions in oil sand, due to the low stiffness of the material a condition especially present in the summer, can cause high rack, pitch, and roll in trucks, leading to fatigue failure in structural compo- nents. For shovels, poor ground stability can cause twists in car bodies and undercarriages, resulting in major damages. Track and shovel frame failures due to this instability result in high maintenance costs. The authors carried out a geophysical study of the oil sand in order to evaluate the ground conditions under large mobile mining equipment. A geophysical investigation per- formed in summer 2001 encountered 6-8 m of thick soft material, commensurate with very low velocities, caused by the loosening of the surface material by heavy mining machinery and excavation; and a transi- tion zone of up to 25-26 m depth approaching the in situ oil sand below. The depth of the oil sand zones can be calculated by using the refraction analysis technique. Spectral Analysis of Surface Waves was used to estimate the ground stiffness. A new technique is proposed to evaluate the changing ground stiffness during the use of ultra-class mobile mining equipment.

Application of High Energy Dynamic Compaction in Coastal Reclamation Areas

High energy dynamic compaction (HEDC) is adopted in a coastal reclamation area because the grain size of backfilled soil mostly ranges between 20 cm and 100 cm. The in situ tests for evaluating the effectiveness of HEDC were performed on the backfilled soil ground. The crater depth per drop and the whole test zone elevations before and after HEDC were measured and analyzed. Dynamic penetration tests and spectral analysis of surface wave (SASW) tests were used for investigating the improvement depth. Furthermore, the allowable bearing capacity of HEDC treated ground was determined based on the results of plate-load tests. It was found that HEDC did not cause the ground surface heave during construction, and was more effective than low energy dynamic compaction (LEDC) in terms of applied energy utilization. Based on the test results, the improvement depth of HEDC at this site was not less than 14 m, and there was no obvious weak layer within the range of improvement depth. The allowable bearing capacities were larger than 160 kPa. The investigation results indicate that the HEDC technique is an effective way for improving backfilled coarse-grained soil in coastal reclamation areas. This technique helps to achieve both greater improvement depths and higher ground bearing capacities as compared with LEDC.

Nondestructive Identification of Freezing-Induced Cracks in Concrete Sleepers of High-Speed Railways in South Korea

The construction of a high-speed railway in South Korea was recently impeded by the unexpected problem of cracks in sleepers. These were presumably induced by the volume expansion of freezing water entrapped in the fastening assemblies during the winter. A total of 306,000 sleepers had to be investigated on an urgent basis for hairline cracks and possible latent cracks. These findings suggested that an appropriate nondestructive testing (NDT) technique for the inspection of concrete sleepers should be designed to meet two requirements: speed and reliability in testing. Research was performed to identify an optimal NDT technique by using sleepers with three different crack conditions: without any cracks, with a surface-opening crack, and with a hairline crack and possible latent cracks. Flexural rigidity rather than material stiffness or depth to multiple reflections was chosen as a key parameter for assessment of the structural integrity of a sleeper. The results allowed the design of a two-stage testing procedure: the flexural rigidity assessment of concrete tracks by antisymmetric Lamb (FRACTAL) waves technique for preliminary scanning and spectral analysis of surface waves (SASW) tests for in-depth investigation. A total of 18,177 sleepers that required testing were examined using FRACTAL tests, and 387 of these sleepers were double-checked using SASW tests. Before the overall examination of sleepers, a series of statistical analyses were performed to establish the criteria for defining the quality of a sleeper. The results of the FRACTAL test agreed with those of the SASW test in identifying sleepers with hairline cracks or possible latent cracks.

Kinerja dan Verifikasi Teknik Seismik Gelombang Permukaan Terintegrasi untuk Pengukuran Modulus Elastisitas Tanah Dasar

An integrated-spectral analysis of surface waves (ISASW) test has been recently proposed as an alternative technique in pavement evaluation and monitoring. ISASW technique is developed from the spectral analysis of surface wave (SASW) method which has been a well known nondestructive testing (NDT) for geotechnical and pavement structures. Surface wave propagation between a set of receivers were transformed to frequency domain using fast Fourier transform (FFT). Therefore, a phase spectrum was produced for measuring the time lag between receivers. A wavelet filtering on impulse response was used for constructing an enhanced phase spectrum. Using phase different method, an experimental dispersion curve was generated. Inversion analysis based on the 3-D stiffness matrix method was then performed in order to produce the shear wave velocity profile. The elastic modulus of pavement layer was calculated based on the linear elastic theory. In this paper, the performance of ISA SW measurement for determining the elastic modulus of pavement subgrade is presented in this paper. Verification on its elastic modulus obtained from ISASW technique was also conducted by using falling weight deflectometer (FWD) test. The result shows that the dispersion curves obtained in the ISASW test are sensitive to indicate the stiffness change in each layer of a pavement structure. Stiffer layer, i.e., pavement surface layer, can be indetified by the parameter of high frequency and phase velocity range; and vice versa. ISASW technique is also able to comprehensively investigate the elastic modulus of subgrade layer in exisiting pavement without any destruction. A good agreement of elastic modulus of subgrade layer from ISASW and FWD test was also pres ented.

A review of shallow seismic methods

Shallow seismic methods have historical roots dating to the 1930s, when limited shallow refraction work was performed using the Intercept-Time (IT) method. Because of high costs and the general lack of appropriate equipment - particularly data-processing equipment and software - the shallow-reflection and surface-wave techniques did not catch on as quickly as the refraction techniques. However, since 1980 substantial progress has been made in the development of all of the shallow seismic approaches. The seismic-reflection method has been used increasingly in applications at depths of less than 30 m, incorporating both the standard Common-Midpoint (CMP) method of the petroleum industry and the Common-Offset (CO) method, which was developed specifically as a low-cost technique for use in shallow surveying. In refraction studies, the Generalized Reciprocal Method (GRM) largely has replaced the classical intercept-time method, and tomographic approaches are rapidly gaining popularity. The Spectral Analysis of Surface Waves (SASW) has been developed by civil engineers, and surface-wave analysis involving many seismograph channels (MASW) recently has shown promise. With any of the shallow seismic methods, however, selecting the appropriate seismic recording equipment, energy sources, and data-acquisition parameters, along with processing and interpretation strategies, often is critical to the success of a project.

Penetration Type Field Velocity Probe for Soft Soils

The assessment of the shear stiffness of dredged soft ground and soft clay is extremely difficult due to soil disturbances caused during sampling and field access. Several in situ methods such as spectral analysis of surface waves, multichannel analysis of surface wave, cross hole, and downhole methods have been developed to measure the shear-wave velocity, but a few disadvantages hinder the adoption of existing methods to soft ground. This study presents a new apparatus, the penetration type field velocity probe (FVP), which overcomes several of the limitations of commonly used shear-wave measurement methods in the field. Design concerns of the FVP include the tip shape, soil disturbance, transducers, self acoustic insulation, protectors, and the electromagnetic coupling from transducer-to-transducer and cable-to-cable. The crosstalk between cables is eliminated by grouping and extra grounding of the cables. The shear-wave velocity of the FVP is directly calculated, without any inversion process, by using the travel distance and the travel time. After calibration tests are carried out in the laboratory, application tests in the field are conducted up to 29 m in depth. Calibration results show the velocity profiles obtained by the FVP and by the rods fitted with transducers are similar to each other. The experimental results obtained in the field show that the FVP can produce reasonable and detailed shear-wave velocity profiles in soft clay. This study suggests that the FVP may be an effective technique for measuring the shear-wave velocity in soft ground.

Developing Artificial Neural Network Models to Automate Spectral Analysis of Surface Wave Method in Pavements

The spectral analysis of surface waves (SASW) method is a nondestructive testing method of pavements based on the dispersive characteristic of seismic surface waves. The method can provide the thickness and stiffness of pavement layers. One of the more complex aspects of the SASW method is an iterative process to estimate the pavement parameters, called the inversion procedure. In this paper, the feasibility of completely automating the inversion process and substituting it with artificial neural network (ANN) models was explored. A number of different ANN models were developed using various ANN training strategies. To improve the performance of some ANN models, a sequential modeling technique was implemented. In the sequential modeling, some pavement parameters are estimated first from an initial set of ANN models, which is then the input to subsequent ANN models to estimate other parameters of interest. Furthermore, the performance of the ANN models was evaluated using a number of well-characterized pavement sections. The results illustrated that ANN models could estimate the upper layers’ parameters so well that they could replace the inversion process. The ANN models for other layers were capable of generating robust initial estimates for a well-constrained formal inversion that can be readily automated.

Evaluation of SASW Test Configurations and Associated Data Uncertainties in Generating Site Specific Dispersion Curves

Spectral analysis of surface waves (SASW) technique is an in-situ nondestructive method used for near surface soil site profiling. In the present study experimental uncertainties related to this method are assessed in connection with test configuration specification and data quality. Field experimentations have been conducted for this purpose with various spatial configurations of source to near receiver distance and inter-receiver distance under various impact source magnitudes and heights of fall. Based on the experimental findings, a method has been proposed to identify the frequency range of interest based on a threshold minimum cross power spectrum value. Further, it is proposed to consider subset stacking combination with good data quality which can be estimated based on weighted evaluation of the coherence of each frequency and importance of different frequency ranges. A procedure of obtaining the site specific dispersion curve is illustrated with due consideration to the issues associated with data quality and power spectra.