Multichannel Analysis Of Surface Waves Testing Research Articles

Variability in receivers responses of MASW test on undulated grounds: A numerical perspective

This article presents methodological and signal processing cautions associated with utilizing the multichannel analysis of surface waves (MASW) test for determining shear wave velocity (Vs) profiles on undulated ground surfaces. The past studies highlight that the conventional MASW test, which is suitable for flat ground surfaces, may not directly apply to undulated grounds with features like heave, crest, etc. Previous studies on MASW test lack an understanding of the influence of source and receiver positioning on various undulations. Three scenarios of ground undulations were created in GiD software and analyzed in the OpenSEES software framework. There were 12 receivers used for these ground undulations based on the Fourier amplitude spectrum attenuation. The receivers' responses (horizontal and vertical components of wavefields) from these ground undulations were analyzed through signal processing using cross-correlation, time-lag, and wavelet coherence. Notably, the undulated topography significantly impacted the vertical components of the wavefield. The phase angle variations from wavelet coherence could be used to determine the minimum frequency of the dispersion curve for these ground undulations. Significant variations in the phase velocity were observed at lower frequencies in the presence of ground undulations, while on a flat surface, they remained unaffected. The effect of under−/over-estimation of Vs (in the range of 50–100 m/s) was successfully demonstrated in each respective undulation with the methodological and processing cautions needed in the MASW analysis.

Critical speed of ballasted railway tracks: Influence of ballast and subgrade degradation

Track substructure layers such as ballast and subgrade involve progressive degradation with time in relation to the loading history. Degradation of track components directly influences the dynamic track response including the displacements and stresses. Determining the influence of real-world substructure degradation problems such as particle breakage, ballast fouling and mud pumping on the critical speed of a given track is essential to design ballasted tracks for high-speed passenger and freight trains. In this paper, a coupled rheological-continuum model is developed to predict the track dynamic response for different train speeds and axle loads. In this novel approach, field dispersion curves obtained from MASW (Multichannel Analysis of Surface Waves) testing can be adopted along with the proposed analytical model to predict the critical speed of track as well as the corresponding dynamic stress state in the substructure layers. Analytical modelling shows that problems such as ballast fouling and mud pumping lead to reduction in the computed critical speed, while also amplifying the dynamic stress response at lower train speeds. The influence of substructure degradation is found to be more prominent for heavy-haul (freight) trains imparting higher axle loads, when compared to passenger trains. Practical insights highlighting the influence of track improvements such as placing a thicker ballast layer and the addition of a capping layer on the critical speed are presented in this study with the objective of rejuvenating future track design.

Novel techniques for in situ estimation of shear-wave velocity and damping ratio through MASW testing – I: a beamforming procedure for extracting Rayleigh-wave phase velocity and phase attenuation

SUMMARY A robust, in situ estimate of shear-wave velocity VS and the small-strain damping ratio DS (or equivalently, the quality factor QS) is crucial for the design of buildings and geotechnical systems subjected to vibrations or earthquake ground shaking. A promising technique for simultaneously obtaining both VS and DS relies on the Multichannel Analysis of Surface Waves (MASW) method. MASW can be used to extract the Rayleigh wave phase velocity and phase attenuation data from active-source seismic traces recorded along linear arrays. Then, these data can be inverted to obtain VS and DS profiles. This paper introduces two novel methodologies for extracting the phase velocity and attenuation data. These new approaches are based on an extension of the beamforming technique which can be combined with a modal filter to isolate different Rayleigh propagation modes. Thus, the techniques return reliable phase velocity and attenuation estimates even in the presence of a multimode wavefield, which is typical of complex stratigraphic conditions. The reliability and effectiveness of the proposed approaches are assessed on a suite of synthetic wavefields and on experimental data collected at the Garner Valley Downhole Array and Mirandola sites. The results reveal that, under proper modelling of wavefield conditions, accurate estimates of Rayleigh wave phase velocity and attenuation can be extracted from active-source MASW wavefields over a broad frequency range. Eventually, the estimation of soil mechanical parameters also requires a robust inversion procedure to map the experimental Rayleigh wave parameters into soil models describing VS and DS with depth. The simultaneous inversion of phase velocity and attenuation data is discussed in detail in the companion paper.

Novel techniques for in situ estimation of shear-wave velocity and damping ratio through MASW testing part II: a Monte Carlo algorithm for the joint inversion of phase velocity and phase attenuation

SUMMARY This paper deals with in situ characterization of the small-strain shear-wave velocity VS and damping ratio DS from an advanced interpretation of Multi-channel Analysis of Surface Waves (MASW) surveys. A new approach based on extracting Rayleigh wave data using the CFDBFa method has been discussed in the companion paper. This paper focuses on mapping the experimental Rayleigh wave phase velocity and attenuation into profiles of VS and DS versus depth, which is achieved through a joint inversion procedure. The joint inversion of phase velocity and attenuation data utilizes a newly developed Monte Carlo global search algorithm, which implements a smart sampling procedure. This scheme exploits the scaling properties of the solution of the Rayleigh eigenvalue problem to modify the trial earth models and improve the matching with the experimental data. Thus, a reliable result can be achieved with a limited number of trial ground models. The proposed algorithm is applied to the inversion of synthetic data and of experimental data collected at the Garner Valley Downhole Array site, as described in the companion paper. In general, inverted soil models exhibit well-defined VS profiles, whereas DS profiles are affected by larger uncertainties. Greater uncertainty in the inverted DS profiles is a direct result of higher variability in the experimental attenuation data, the limited wavelength range at which reliable values of attenuation parameters can be retrieved, and the sensitivity of attenuation data to both DS and VS. Nonetheless, the resulting inverted earth models agree well with alternative in situ estimates and geological data. The results stress the feasibility of retrieving both stiffness and attenuation parameters from active-source MASW testing and the effectiveness of extracting in situ damping ratio estimates from surface wave data.

Pemodelan Estimasi Kecepatan Rambat Gelombang Geser Tanah (VS30) Berbasis Topografi, Geomorfologi dan Geologi

The 30 m top layer of soil as the medium of propagation of the earthquake wave is the closest to the structure of the building, and could have different effects depending on the type of soil and topography. The Indonesian earthquake code for building and non building structures known as SNI 1726-2012 using the directly measured VS30 as the primary parameter to identify the stiffness effect of sediment. The VS30 can be measured using non invasive methods, such as multi-channel analysis of surface waves (MASW). Direct, invasive measurements of VS30 around Indonesia would be difficult to implement due to the vastness of the country and the high cost nature of the testing. To provide an alternative to the direct measurement, VS30 estimation models have been developed. VS30 estimates using topography in the form of slopes are commonly used in North America, while geomorphological units are used in Japan. This research was carried out by correlating VS30 direct measurements with topographical, geomorphological and geological attributes. The VS30 obtained from series of MASW tests, the topographic slope and elevation from the Shuttle Radar Topography Mission (SRTM) 30 arcsec data, the geomorphology units data which are Structural, Karst, Vulkanik, Fluvial and Marine from landsystem map and the geologic age data from Geological Survey Centre (PSG). Data were analyzed by linear regression and spatial analysis. VS30 estimation modeling produces models with four variables, namely elevation, slope, geomorphological unit and geological age in the regions of Palu. Four proxy based estimates provide values that are slightly higher or lower but in a range not so far from direct measurements. The results of data processing analysis shows that local conditions greatly affect VS30 estimates in Palu. The VS30 estimation model in the form of a logarithmic equation is as follows, Log VS30 = -3.925 + 0.062 log(s) + 0.069 log(Ev) + 0.665 log(G) + 1.824 log(A) gives a slightly higher or lower value but in a range not far from direct measurement. This VS30 estimation model is suitable for soil classification on a regional scale and can be adopted for microzonation maps or real-time shake map.

Multivariate geophysical index-based prediction of the compression index of fine-grained soil through nonlinear regression

The determination of consolidation settlement is highly significant in fine-grained soil. However, evaluating compression index (Cc) is time-consuming and cumbersome. For the approximate estimation of Cc, several correlations based on various geotechnical properties have been established, involving boreholes and sample extraction. In such circumstances, non-invasive geophysical techniques can provide a quick and cost-effective alternative in predicting the compression index. In this study, two geophysical techniques, namely electrical resistivity tomography (ERT) and multichannel analysis of surface waves (MASW), were coupled together to predict the compression index of fine-grained soil at Silchar, Assam, India. Electrical resistivity (R) and shear wave velocity (Vs) were determined from the ERT and MASW test respectively, and a nonlinear regression technique was employed to estimate the Cc. The R2 and RMSE values observed from the regression analysis are 0.874 and 0.036, respectively with R and Vs as independent variables. The multiple-geophysical index-based technique resulted in a 20% improvement in the R2 value of the nonlinear fit compared to that obtained using individual geophysical index-based predictions. The computation of statistical indices validates the regression results. Further, the geophysical index-based predictions of Cc were compared with the conventional method of determining Cc using the geotechnical parameters including liquid limit, water content, and void ratio. The concept and the proposed empirical equation can be implemented for different locations, thereby benefiting the researchers and the construction engineers.

Detection of subterranean cavities and anomalies using multichannel analysis of surface wave

ABSTRACT Both underground cavities and anomalies are important issues which may cause damage to ground strata and subsequently to their overlaying structures due to subsidence and excessive settlement. Thus, the first step of stabilising the ground and preventing undesired damages is detecting these cavities. In this paper, multichannel analysis of surface waves (MASW) test as a general surface wave method is utilised for obtaining the properties of the ground and the coherence function of two adjacent signals to establish an approach for detecting multiple underground anomalies. In this regard, MASW tests were performed in five numerical models of homogeneous half-space with multiple cavities. The extent of the signals’ coherence of acquired seismic data of each couple of adjacent signals was plotted to delineate the cavity and anomaly location. The results of coherence values showed a distinguishable-coherence zone in the spectrum. Two main categories of cavities and buried concrete masses were investigated via the coherence function, indicating a decline in the cavity position and a rise in the concrete mass position. Eventually, to test the validity of the method, two sets of real data were employed. The results of both numerical and experimental data showed the accuracy of the method.

Modal analysis of Rayleigh waves using classical MASW-MAM approach: Site investigation in a reclaimed land

Surface wave tests such as the multi-channel analysis of surface waves (MASW) and microtremor array measurements (MAM) offer a fast and convenient way of measuring the shear wave velocity (Vs) of the ground for geotechnical site investigation due to their non-intrusive nature. However, it has been widely reported that the accuracy and resolution of the Vs profile depend on the construction of the dispersion image and its interpretation. While many advanced computational techniques have been proposed to process surface waves into a final Vs profile, we opted for the classical ‘picking and inverting’ approach in the current study. This is in view of the lower required computation power as well as the relatively uniform geology of the site. Surface wave tests (MASW, MAM and horizontal-to-vertical spectral ratio) were carried out at a remote reclaimed land in Singapore. A systematic methodology for the modal analysis of Rayleigh waves based on combined MASW and MAM tests is presented. The MAM dispersion image was constructed using the phase shift method, the extended spatial autocorrelation (ESAC), and the refraction microtremor (ReMi) method but a meaningful dispersion curve could only be obtained using the phase shift. Due to the modes of energy in the low frequency regime being unclear in the dispersion image, an idealized synthetic model of the site was set up to guide the mode identification process. The combined dispersion curve and HVSR profile were jointly inverted to construct the final Vs profile, which agreed quite well with the seismic cross-hole tomography experiments and bore-log information. It is also demonstrated that the inversion of the fundamental mode alone led to slight errors and low resolution in the final velocity profile, even for such a simple soil stratigraphy.

The combined use of MASW and resistivity surveys for levee assessment: A case study of the Melvin Price Reach of the Wood River Levee

Capacitively-Coupled Resistivity (CCR) and Multichannel Analysis of Surface Waves (MASW) were performed on the Melvin Price reach of the Wood River Levee that has experienced considerable piping through the foundation soil causing numerous sand boils along the landside toe of the levee. Tests were performed along the centerline crest, the landside toe, and the riverside berm of the levee. This study combined the strengths of MASW and CCR testing to resolve the distribution and stiffness of cohesive and non-cohesive materials in the body and foundation of the levee, where invasive testing was not ideal. MASW and CCR were shown to complement each other in the evaluation. CCR successfully classified the near surface clay and sand deposits along the levee and was particularly effective for soil deposits with a high degree of saturation. MASW revealed that a deeper clay layer, appears to be discontinuous at locations where old river bars cross under the levee. These bars may have eroded portions of the deeper clay layer, locally enhancing seepage rates through the foundation materials and influencing the formation of sand boils during large flood events. The use of MASW and CCR also successfully detected the locations of the major utilities crossing the levee. While CCR was the most effective method for detecting conductive utilities, MASW was more effective at detecting utilities which increased the overall stiffness of the subsurface either due to the utility itself or the backfill material around the utility. A site-specific SPT-Vs correlation was developed from the co-located boreholes and shear wave velocity profiles. Comparison of the correlation with previous studies indicates that soil stiffness and geologic age are important factors affecting SPT-Vs correlations. For levee soil deposits, which are typically young, a lower bound SPT-Vs correlation developed using similar soil deposits to the study area should be considered.

Evaluation of shear geophones in MASW testing

Dynamic properties such as wave velocities and damping ratios are required for dynamic analyses of sites. Wave velocities in field are typically evaluated by MASW (Multichannel Analysis of Surface Waves). MASW is favoured due to its ability to resolve hidden layers and better characterisation of shallow depths. Vertical geophones that measure vertical component of motion are typically used in MASW. Shear geophones that measure the horizontal component of motion are increasingly being used in seismic surveys; however, their ability to measure Raleigh velocities in MASW testing has not been evaluated. This study presents the results of numerical simulations and experimental program that evaluates the suitability of shear geophones in MASW. The shear wave velocity profiles from vertical and horizontal components of particle motion due to Raleigh wave propagation are computed and compared. The results of this study suggest that shear geophones can be used in lieu of vertical geophones in MASW testing. Simultaneous measurements of horizontal and vertical components of particle motion can become a promising technique in future to isolate surface waves and enhance Raleigh modes using correlation techniques.

The Simple Lamb Wave Analysis to Characterize Concrete Wide Beams by the Practical MASW Test.

In recent years, the Lamb wave analysis by the multi-channel analysis of surface waves (MASW) for concrete structures has been an effective nondestructive evaluation, such as the condition assessment and dimension identification by the elastic wave velocities and their reflections from boundaries. This study proposes an effective Lamb wave analysis by the practical application of MASW to concrete wide beams in an easy and simple manner in order to identify the dimension and elastic wave velocity (R-wave) for the condition assessment (e.g., the estimation of elastic properties). This is done by identifying the zero-order antisymmetric (A0) and first-order symmetric (S1) modes among multimodal Lamb waves. The MASW data were collected on eight concrete wide beams and compared to the actual depth and to the pressure (P-) wave velocities collected for the same specimen. Information is extracted from multimodal Lamb wave dispersion curves to obtain the elastic stiffness parameters and the thickness of the concrete structures. Due to the simple and cost-effective procedure associated with the MASW processing technique, the characteristics of several fundamental modes in the experimental Lamb wave dispersion curves could be measured. Available reference data are in good agreement with the parameters that were determined by our analysis scheme.

Surface-wave testing of soil sites using multichannel simulation with one-receiver

This paper presents a study on the application of the multichannel simulation with one-receiver (MSOR) surface-wave testing method for geophysical profiling of soil sites. The MSOR method reverses the roles of source and receiver in the widely-used multi-channel analysis of surface waves (MASW) method. To examine the feasibility and accuracy of utilizing MSOR for soil sites, finite element simulations of MSOR testing are performed for three types of soil profiles containing horizontal interfaces, a vertical fault, and a dipping interface, respectively. The effects of variations in the moving impact locations on the uncertainty and repeatability of the dispersion trends are analyzed for the different soil profiles. Real-world case studies are carried out to examine the equivalency of the MSOR and MASW methods for quantifying surface-wave dispersion trends of soil profiles, as well as the advantages of MSOR testing with embedded geophones to obtain more extensive multimodal dispersion data. From the computational simulations and field case studies, MSOR is demonstrated to be equivalent to MASW testing for practical purposes. In addition, MSOR has the advantages of reduced instrumentation cost, improved portability, enhanced ability to measure multi-mode dispersion curves by utilizing borehole geophones, and the potential for improving efficiency of 3-D stiffness profiling.

Multichannel Analysis of Surface Waves and Down-Hole Tests in the Archeological “Palatine Hill” Area (Rome, Italy): Evaluation and Influence of 2D Effects on the Shear Wave Velocity

A joint analysis of down-hole (DH) and multichannel analysis of surface waves (MASW) measurements offers a complete evaluation of shear wave velocity profiles, especially for sites where a strong lateral variability is expected, such as archeological sites. In this complex stratigraphic setting, the high “subsoil anisotropy” (i.e., sharp lithological changes due to the presence of anthropogenic backfill deposits and/or buried man-made structures) implies a different role for DH and MASW tests. This paper discusses some results of a broad experimental program conducted on the Palatine Hill, one of the most ancient areas of the city of Rome (Italy). The experiments were part of a project on seismic microzoning and consisted of 20 MASW and 11 DH tests. The main objective of this study was to examine the difficulties related to the interpretation of the DH and MASW tests and the reliability limits inherent in the application of the noninvasive method in complex stratigraphic settings. As is well known, DH tests provide good determinations of shear wave velocities (Vs) for different lithologies and man-made materials, whereas MASW tests provide average values for the subsoil volume investigated. The data obtained from each method with blind tests were compared and were correlated to site-specific subsurface conditions, including lateral variability. Differences between punctual (DH) and global (MASW) Vs measurements are discussed, quantifying the errors by synthetic comparison and by site response analyses. This study demonstrates that, for archeological sites, VS profiles obtained from the DH and MASW methods differ by more than 15 %. However, the local site effect showed comparable results in terms of natural frequencies, whereas the resolution of the inverted shear wave velocity was influenced by the fundamental mode of propagation.

Comparison of MASW and MSOR for Surface Wave Testing of Pavements

This paper presents a computational and experimental study on seismic stiffness profiling of layered pavement systems using the multi-channel analysis of surface waves (MASW) and multi-channel simulation with one receiver (MSOR) testing procedures. Development of a new custom-programmed data acquisition system for MASW and MSOR testing using MATLAB software and National Instruments hardware are detailed. A receiver coupling method is presented, which was found to perform the best among several methods examined by the authors. The cross-correlation function is employed to statistically quantify the repeatability of impacts, which is critical for MSOR tests in which multi-channel records are simulated by performing multiple impacts over a range of incremental offsets from a single fixed receiver. Experimental dispersion data from MASW and MSOR tests performed at the same asphalt pavement site with the same testing system are compared, and MASW is found to enable measurement of dispersion data to much higher frequencies using the authors’ methods than MSOR. Inversion results from the MASW and MSOR data at the same asphalt pavement site also are compared, and it is found that MASW is able to provide measurements of the stiffness of the pavement surface layer with reduced variability.

Condition Assessment of Cementitious Materials Using Surface Waves in Ultrasonic Frequency Range

Surface waves propagating in a medium provide information about the mechanical properties and condition of the material. Variations in the material condition can be inferred from changes in the surface wave characteristics. Multichannel analysis of surface waves (MASW) is a well-established surface wave method used for determination of the shear-wave profile of the soil layers near the surface. The MASW test configuration is also applicable to assess the condition of construction materials using appropriate frequency range. Previous studies on the detection of surface-breaking cracks in concrete elements, using the dispersion and attenuation of ultrasonic waves, were successful; however, a complete damage assessment of the whole element was not in the scope of these studies. In this study, different wave characteristics, such as Rayleigh wave velocity, wave attenuation, and phase velocity dispersion, are investigated to evaluate their sensitivity to the damage in a medium. The condition of a test specimen, which is a half-space medium made of cement and sand, is evaluated using ultrasonic transducers for different damage cases. The recorded signals are processed using the Fourier and wavelet transforms to determine the surface wave characteristics. A new dispersion index (DI) is introduced, which represents the global correlation between the dispersion of phase velocity and damage level. All features are found to be capable of reflecting the damage in the test medium with different levels of sensitivity. Among the investigated parameters, the proposed dispersion index shows high sensitivity and linear correlation with the damage.

Dynamic Site Characterization and Correlation of Shear Wave Velocity with Standard Penetration Test ‘N’ Values for the City of Agartala, Tripura State, India

Seismic site characterization is the basic requirement for seismic microzonation and site response studies of an area. Site characterization helps to gauge the average dynamic properties of soil deposits and thus helps to evaluate the surface level response. This paper presents a seismic site characterization of Agartala city, the capital of Tripura state, in the northeast of India. Seismically, Agartala city is situated in the Bengal Basin zone which is classified as a highly active seismic zone, assigned by Indian seismic code BIS-1893, Indian Standard Criteria for Earthquake Resistant Design of Structures, Part-1 General Provisions and Buildings. According to the Bureau of Indian Standards, New Delhi (2002), it is the highest seismic level (zone-V) in the country. The city is very close to the Sylhet fault (Bangladesh) where two major earthquakes (M w > 7) have occurred in the past and affected severely this city and the whole of northeast India. In order to perform site response evaluation, a series of geophysical tests at 27 locations were conducted using the multichannel analysis of surface waves (MASW) technique, which is an advanced method for obtaining shear wave velocity (V s) profiles from in situ measurements. Similarly, standard penetration test (SPT-N) bore log data sets have been obtained from the Urban Development Department, Govt. of Tripura. In the collected data sets, out of 50 bore logs, 27 were selected which are close to the MASW test locations and used for further study. Both the data sets (V s profiles with depth and SPT-N bore log profiles) have been used to calculate the average shear wave velocity (V s30) and average SPT-N values for the upper 30 m depth of the subsurface soil profiles. These were used for site classification of the study area recommended by the National Earthquake Hazard Reduction Program (NEHRP) manual. The average V s30 and SPT-N classified the study area as seismic site class D and E categories, indicating that the city is susceptible to site effects and liquefaction. Further, the different data set combinations between V s and SPT-N (corrected and uncorrected) values have been used to develop site-specific correlation equations by statistical regression, as ‘V s’ is a function of SPT-N value (corrected and uncorrected), considered with or without depth. However, after considering the data set pairs, a probabilistic approach has also been presented to develop a correlation using a quantile–quantile (Q–Q) plot. A comparison has also been made with the well known published correlations (for all soils) available in the literature. The present correlations closely agree with the other equations, but, comparatively, the correlation of shear wave velocity with the variation of depth and uncorrected SPT-N values provides a more suitable predicting model. Also the Q–Q plot agrees with all the other equations. In the absence of in situ measurements, the present correlations could be used to measure V s profiles of the study area for site response studies.

Evaluating the effectiveness of rolling impact compaction at a brownfield site with high and low frequency seismic surface waves and geotechnical testing

ABSTRACTUsing a case study from a brownfield site in Australia that contained substantial uncontrolled crushed rock fill, we demonstrate that innovative geophysics and ground improvement using rolling dynamic compaction can provide alternatives to costly excavation, removal and re‐engineering of soils. This approach can also overcome some of the limitations of conventional geotechnical testing in such conditions. The process we have developed involves selection and levelling of trial areas within larger brownfield sites. These are initially screened with electromagnetic geophysics to target environmental sampling sites, buried objects and local areas of potentially unsuitable or contaminated soils for removal and replacement. High and low frequency surface wave testing is then completed along closely spaced lines within the trial areas using specially adapted Multi‐channel Analysis of Surface Waves (MASW) methods and a modified land streamer. This provides S‐wave velocity distributions within fill and deeper materials over two depth ranges, at high vertical resolution from approximately 0 to 2 m and at lower resolution from 2 to ~10 m. These results are compared with geotechnical engineering test information. Ground improvement works are then undertaken using rolling dynamic compaction with a ‘square’ impact roller.Within this brownfield trial area, geotechnical testing showed that post‐compaction in‐situ densities increased by about 6 to 10%, while S‐wave velocities increased by up to 40%. This clearly demonstrates the sensitivity of S‐wave velocities to soil and fill modulus. The S‐wave velocity sections also showed the consistency of the landform created by impact rolling and that both high and low frequency MASW testing is needed for more accurate assessment of the densification of both shallow and deeper fill. Normalized S‐wave velocity difference sections and Cone Penetrometer Testing (CPT) provided a clear indication of the depth of influence of the impact rolling.A relationship was developed between post‐compaction S‐wave velocity and Dry Density Ratio (DDR) that formed the basis of a viable geotechnical verification strategy for the ground improvement works on the larger brownfield site. Electromagnetic and advanced surface wave geophysics, combined with innovative ground improvement methods by rolling dynamic compaction, represent an advance over current practice for brownfield site development.

Assessment of ground compaction using multi‐channel analysis of surface wave data and cone penetration tests

ABSTRACTThe construction of a new industrial and commercial area in 2009 at the Givors’ former glass factory area in France involved heavy dynamic compaction work. For the purpose of founding the new buildings, it was necessary to improve the ground mechanical properties of 7–15 m of well‐graded gravel backfill lying on geotechnical bedrock. In order to assess the quality and depth of ground compaction, cone penetration tests are often performed before and after compaction. The method is intrusive and a one‐location test. It requires a substantial amount of time to evaluate a large area and evaluation quality is quite dependent on the operation technique and soil type. In this paper, the quality and extent of ground compaction were evaluated using results from the in situ Multi‐Channel Analysis of Surface Waves (MASW) seismic method and cone penetration tests (CPT). MASW tests were used to determine shear‐wave velocity () profiles before and after compaction and CPT tests were adopted to determine the correlation between and the measured penetration resistance () improvement along profiles. The results of this study show the effectiveness of surface waves for the evaluation of compaction performance and demonstrate the potential of this technique to engineering and environmental problems.

Seismic Site Classification and Correlation between Standard Penetration Test N Value and Shear Wave Velocity for Lucknow City in Indo-Gangetic Basin

Subsurface lithology and seismic site classification of Lucknow urban center located in the central part of the Indo-Gangetic Basin (IGB) are presented based on detailed shallow subsurface investigations and borehole analysis. These are done by carrying out 47 seismic surface wave tests using multichannel analysis of surface waves (MASW) and 23 boreholes drilled up to 30 m with standard penetration test (SPT) N values. Subsurface lithology profiles drawn from the drilled boreholes show low- to medium-compressibility clay and silty to poorly graded sand available till depth of 30 m. In addition, deeper boreholes (depth >150 m) were collected from the Lucknow Jal Nigam (Water Corporation), Government of Uttar Pradesh to understand deeper subsoil stratification. Deeper boreholes in this paper refer to those with depth over 150 m. These reports show the presence of clay mix with sand and Kankar at some locations till a depth of 150 m, followed by layers of sand, clay, and Kankar up to 400 m. Based on the available details, shallow and deeper cross-sections through Lucknow are presented. Shear wave velocity (SWV) and N-SPT values were measured for the study area using MASW and SPT testing. Measured SWV and N-SPT values for the same locations were found to be comparable. These values were used to estimate 30 m average values of N-SPT (N30) and SWV (Vs30) for seismic site classification of the study area as per the National Earthquake Hazards Reduction Program (NEHRP) soil classification system. Based on the NEHRP classification, the entire study area is classified into site class C and D based on Vs30 and site class D and E based on N30. The issue of larger amplification during future seismic events is highlighted for a major part of the study area which comes under site class D and E. Also, the mismatch of site classes based on N30 and Vs30 raises the question of the suitability of the NEHRP classification system for the study region. Further, 17 sets of SPT and SWV data are used to develop a correlation between N-SPT and SWV. This represents a first attempt of seismic site classification and correlation between N-SPT and SWV in the Indo-Gangetic Basin.

Use of Surface Waves in Statistical Correlations of Shear Wave Velocity and Penetration Resistance of Chennai Soils

Shear wave velocity (Vs) is one of the most important input parameter to represent the stiffness of the soil layers. It is preferable to measure Vs by in situ wave propagation tests, however it is often not economically feasible to perform the tests at all locations. Hence, a reliable correlation between Vs and standard penetration test blow counts (SPT-N) would be a considerable advantage. This paper presents the development of empirical correlations between Vs and SPT-N value for different categories of soil in Chennai city characterized by complex variation of soil conditions. The extensive shear wave velocity measurement was carried out using Multichannel Analysis of Surface Waves (MASW) technique at the sites where the SPT-N values are available. The bender element test is performed to compare the field MASW test results for clayey soils. The correlations between shear wave velocity and SPT-N with and without energy corrections were developed for three categories of soil: all soils, sand and clay. The proposed correlations between uncorrected and energy corrected SPT-N were compared with regression equations proposed by various other investigators and found that the developed correlations exhibit good prediction performance. The proposed uncorrected and energy corrected SPT-N relationships show a slight variation in the statistical analysis indicating that both the uncorrected and energy corrected correlations can predict shear wave velocity with equal accuracy. It is also found that the soil type has a little effect on these correlations below SPT-N value of about 10.