Surface Wave Testing Research Articles

Measurements of the elastic modulus of pavement subgrade layers using the SASW and FWD test methods

In pavement management systems, deflection basin tests, such as the Falling Weight Deflectometer test, are common techniques that are widely used, while the surface wave test, i.e. the Spectral Analysis of Surface Wave test, is recently employed as an alternative technique in pavement evaluation and monitoring. In this paper, the performance of both dynamic non-destructive tests on pavement subgrade investigation is presented. Surface wave propagation between a set of receivers was transformed into the frequency domain using the Fast Fourier Transform technique and subsequently a phase spectrum was produced to measure the time lag between receivers. Using the phase difference method, an experimental dispersion curve was generated. Inversion analysis based on the 3-D stiffness matrix method was then performed to produce a shear wave velocity profile. The elastic modulus of pavement layers was calculated based on linear elastic theory. In the Falling Weight Deflectometer test, seven geophones were used to collect in situ deflection data. Based on a back-calculation procedure with the ELMOD software, the elastic modulus of each flexible pavement layer can be obtained. Both techniques are able to comprehensively investigate the elastic modulus of the subgrade layer in existing pavement non-destructively. The elastic modulus between the Spectral Analysis of Surface Wave method and the Falling Weight Deflectometer test on the subgrade layer is observed to be in a good agreement. A correlation of the elastic modulus of thesubgrade layer from both techniques is also presented.

Effects of site stiffness and source to receiver distance on surface wave tests׳ results

By using six 4.5Hz geophones, surface wave tests were performed on four different sites by dropping freely a 65kg mass from a height of 5m. The receivers were kept far away from the source to eliminate the arrival of body waves. Three different sources to nearest receiver distances (S), namely, 46m, 56m and 66m, were chosen. Dispersion curves were drawn for all the sites. The maximum wavelength (λmax), the maximum depth (dmax) up to which exploration can be made and the frequency content of the signals depends on the site stiffness and the value of S. A stiffer site yields greater values of λmax and dmax. For stiffer sites, an increase in S leads to an increase in λmax. The predominant time durations of the signals increase from stiffer to softer sites. An inverse analysis was also performed based on the stiffness matrix approach in conjunction with the maximum vertical flexibility coefficient of ground surface to establish the governing mode of excitation. For the Site 2, the results from the surface wave tests were found to compare reasonably well with that determined on the basis of cross boreholes seismic tests.

Cyclic and dynamic behaviour of a soft pyroclastic rock

The mechanical behaviour under cyclic and dynamic conditions of a weakly cemented pozzolana, taken from the subsoil of a historical town in a seismically active area, was investigated through laboratory tests and in situ measurements. The geotechnical characterisation at laboratory scale is of particular importance as the small- and large-scale behaviour of these deposits is comparable, owing to the large discontinuity spacing. These soft pyroclastic rocks, which are found in many volcanic regions worldwide, are particularly interesting as they are often alternated with stronger volcanic rocks in thick sequences, constituting a significant impedance contrast that could increase the ground-shaking hazard. A cross-hole test and a spectral analysis of surface waves test, carried out on the ground surface and at the floor of an underground cavity, respectively, provided in situ vertical profiles of the shear wave velocity. Cyclic and dynamic properties were investigated in the laboratory through velocity measurements of ultrasonic pulses, cyclic simple shear, torsional shear and resonant column tests. Most testing procedures and devices, which were originally conceived for soils, posed some challenges. The collected data were used to analyse the influence of mean confining stress, strain amplitude and number of cycles on both shear stiffness and material damping.

Data analysis and visualization for the bridge deck inspection and evaluation robotic system

Abstract Background Bridge deck inspection is essential task to monitor the health of the bridges. Condition monitoring and timely implementation of maintenance and rehabilitation procedures are needed to reduce future costs associated with bridge management. A number of Nondestructive Evaluation (NDE) technologies are currently used in bridge deck inspection and evaluation, including impact-echo (IE), ground penetrating radar (GPR), electrical resistivity (ER), ultrasonic surface waves (USW) testing, and visual inspection. However, current NDE data collection is manually conducted and thus faces with several problems such as prone to human errors, safety risks due to open traffic, and high cost process. Methods This paper reports the automated data collection and analysis for bridge decks based on our novel robotic system which can autonomously and accurately navigate on the bridge. The developed robotic system can lessen the cost and time of the bridge deck data collection and risks of human inspections. The advanced software is developed to allow the robot to collect visual images and conduct NDE measurements. The image stitching algorithm to build a whole bridge deck image from individual images is presented in detail. The ER, IE and USW data collected by the robot are analyzed to generate the corrosion, delamination and concrete elastic modulus maps of the deck, respectively. These condition maps provide detail information of the bridge deck quality. Conclusions The automated bridge deck data collection and analysis is developed. The image stitching algorithm allowed to generate a very high resolution image of the whole bridge deck, and the bridge viewer software allows to calibrate the stitched image to the bridge coordinate. The corrosion, delamination and elastic modulus maps were built based on ER, IE and USW data collected by the robot to provide easy evaluation and condition monitoring of bridge decks.

Some Limits in the Use of the MASW Technique in Soils with Inclined Layers

The surface wave method is a characterization technique that allows obtaining the shear wave velocity profiles trough the measurement of the dispersion of surface waves coupled with an inversion procedure. Spectral and multichannel analysis of surface wave techniques are becoming, recently, a common investigation tool for site characterization. For the inversion of the surface wave dispersion curve, homogeneous or horizontally layered soil models are assumed and this hypothesis could represent a limitation on the practical use of the technique. In this paper, the numerical dispersion curves of a subsoil, constituted by two layers of elastic material separated by a horizontal or an inclined interface, are simulated by a finite element commercial code. This allows detecting some limits in the conventional interpretation of the surface wave tests. MASW experiments executed in two different sites in Molise Region (Italy), characterized by simple or complex stratigraphic conditions, are shown as examples to validate the assumption and the analyses made in the paper.

Dynamic Compaction of Ultra-High Energy in Combination with Ground Replacement in Coastal Reclamation Areas

This paper presents a case study of dynamic compaction (DC) on backfill ground for planned oil tanks located at Nanjing Bay. The ultra-high energy DC level of 18,000 kN · m was applied in the area tamping phase of the dynamic compaction. In combination with ground replacement technique by forcing crushed stones into the underlain cohesive layer, the high-compressibility of this layer was properly tackled. The construction techniques and ground improvement mechanisms are introduced and discussed. Field evaluations before and after the dynamic compaction, including surface wave test, plate load test, and soil sampling, showed that the ultra-high energy dynamic compaction in combination with ground replacement achieved much greater improvement depth and ground bearing capacity than conventional DC. Results show that dynamic compaction of 18,000 kN · m combined with ground replacement is of great merit in dealing with backfill ground with weak cohesive content in harbor development.

An explicit relation for the apparent phase velocity of Rayleigh waves in a vertically heterogeneous elastic half-space

S U M M A R Y This paper presents the mathematical derivation of an explicit relation for the apparent (or effective) phase velocity of Rayleigh waves in a vertically heterogeneous, isotropic elastic half-space for harmonic excitation. As a kinematical feature, the apparent phase velocity captures the superposition, in a spatial Fourier series, of the individual modes of propagation of Rayleigh waves and describes the speed of propagation of a composite waveform generated by a vertically oscillating point load. The relation, which is a function of the distance from the source, frequency and depth, depends explicitly on the modal phase and group velocities of Rayleigh waves, and their corresponding wavenumbers and eigenfunctions, which can be computed directly from the solution of the Rayleigh-wave eigenproblem. A practical scenario for the application of the notion of apparent Rayleigh-wave phase velocity is the modelling of the dispersion curve in the well-known surface wave measurement methods ‘spectral analysis of surface waves’ (SASW) and ‘multichannel analysis of surface waves’ (MASW). Apart from a theoretical motivation, the availability in surface wave testing of an explicit formula for the calculation of the apparent Rayleigh-wave phase velocity may lead to the development of a new class of inversion algorithms capable of taking into account the influence of all the modes of surface wave propagation. To demonstrate the exactness of the explicit relation, the predicted values of apparent phase velocity are compared to those computed synthetically from a numerical simulation of SASW and MASW testing for three case studies, which show both single as well as multiple mode dominance effects.

Transferring technology for surface-wave testing and seismic site-response analysis in Haiti

Haiti is one of the most impoverished nations in the world and is highly susceptible to earthquakes. An important part of seismic design is the measurement of the dynamic properties of soil and calculation of site-specific seismic site response. However, there is a capability gap in that geoscientists in Haiti might not be trained to carry out a proper analysis. A humanitarian project sponsored by the Society of Exploration Geophysicists Foundation program Geoscientists Without Borders was conducted to address that deficiency. The scope of the project included field geophysical seismic surface-wave testing at selected sites in Haiti, calculation of shear-wave velocity profiles, and calculation of seismic site response. A user's manual was written and given to a humanitarian engineering group active in Haiti along with the equipment used to perform field testing at the conclusion of the project. Efforts such as this enhance the self-sufficiency of Haiti with respect to seismic design, which ultimately will result in reduced loss of life during future earthquakes.

Densification of loosely deposited soft soils using the combined consolidation method

Dynamic consolidation (DC) has been widely used for a variety of soil types and conditions, particularly for soft soils, due to its superior results and low cost. However, soft soils become ‘rubbery soils’ when the groundwater table is high and the single DC method is used. In this paper, the combined consolidation (CC) method was applied to a site with loosely deposited soft soils in the Yangtze River Delta of China. This method integrates two technical construction characteristics, low-energy DC and vacuum dewatering. To properly manage these soil conditions and optimize the CC design, field tests were conducted to determine the factors that influence CC. Deformation tests that consider ground settlement, pore water pressure, and the groundwater table were performed to obtain rational construction parameters and to provide proof regarding the adjustment of the original CC procedure. Drilling sampling and cone penetration, surface wave, and plate loading tests were conducted to evaluate the overall effects of CC. The allowable bearing capacity and the depth of improvement at the site were estimated to exceed 120kPa and 6m, respectively. Both of these values meet the design requirements.

국내 콘크리트 표면차수벽형 석괴댐(CFRD) 사력존의 전단파 속도 분포 결정(II): 물성치의 공간 변동성에 의한 불확실성이 고려된 CFRD 사력존의 1차원 전단파 속도 주상도의 결정

This paper determines 1D shear wave velocity (Vs) distribution of rockfill zone of CFRD using Vs profile determined by the surface wave test. There exists uncertainty in the field test result because of a spatial variation of material property. The harmonic wavelet transform is used to evaluate the uncertainty of test result and generate random 1D Vs distributions which may exist in the rock fill zone. Through the statistical analysis of generated random Vs distributions, the representative 1D Vs distribution considering the uncertainty of test results is proposed for the rockfill zone of CFRD in Korea.

Seismic microzonation for Penang using geospatial contour mapping

Shear wave velocity (V s) and the fundamental site period of the subsurface condition are the primary parameters that affect seismic soil amplification in particular sites. Within the topmost layer of the soil, which measures 30 m, the average shear wave velocity V s30 is commonly used to build codes for site classification for the design of earthquake-resistant structures and to conduct microzonation studies. In this study, the development of a microzonation map for V s30 distribution, National Earthquake Hazard Reduction Program V s30 site classification, and a fundamental site period for Penang are presented. The multichannel analysis of surface wave (MASW) test was conducted for more than 50 sites with available borehole data to develop the microzonation maps. The ten selected V s profiles measured by MASW show a good correlation with the data obtained using empirical correlations in a previous study. The highest V s values were identified at the northeastern and southeastern parts of Penang Island, corresponding to the shallow bedrock and the outcrop zone. Conversely, the lowest V s values were found in the northwestern and southwestern parts of the Penang mainland owing to the thick layer of soft clay and silt deposits. The site period map shows the variation in site periods, with the highest value of 1.03 s at the western part of the Penang mainland and the lowest value of 0.02 s at the eastern part of the Penang Island. The microzonation maps developed in this study are vital to studies on seismic hazard and earthquake mitigation programs in Malaysia.

SASW testing of asphaltic pavement by dropping steel balls

A number of spectral analysis of surface waves tests were performed on asphaltic concrete pavement. These tests were performed by dropping steel balls on the pavement surface for different combinations of source to first receiver distance and receiver spacing. Four different values of ball's diameter, namely, 25·4 mm, 38·1 mm, 50·8 mm, and 76·2 mm, were used. The height of fall of the balls was varied from 0·25 m to 0·75 m. With an increase in diameter and height of fall of the ball, the maximum wavelength, up to which the shear wave velocity profile can be predicted, increases continuously. The increase in the values of diameter and height of fall of the ball also leads to a nominal increase in the minimum value of wavelength. The results presented in this paper would be useful for providing guidelines for deciding the height of fall of the balls based on the required exploration zone of the pavement.

Non-contact surface wave testing of pavements: comparing a rolling microphone array with accelerometer measurements

Rayleigh wave velocity along a straight survey line on a concrete plate is measured in order to compare different non-destructive data acquisition techniques. Results from a rolling non-contact dat ...

Comparison of SASW and MASW methods using MSOR approach – a case study

Non-destructive testing (NDT) is widely used in assessing the integrity and strength of concrete pavement system. In recent years, many surface-wave testing techniques have been introduced to evaluate pavements in terms of shear-wave velocity profiles. Spectral-Analysis-of-Surface-Wave (SASW) and Multichannel-Analysis-of-Surface-Wave (MASW) are the two most commonly used NDT methods among them. The paper presents a comparative study on the performance of two methods to examine the shear-wave velocity profile of a pavement system. Dispersion curves from both methods are compared and discussed. It is found that for the pavement system with a good lateral uniformity, both techniques can produce reasonable results.

Seismic microzonation of a nuclear power plant site with detailed geotechnical, geophysical and site effect studies

This paper highlights the seismic microzonation carried out for a nuclear power plant site. Nuclear power plants are considered to be one of the most important and critical structures designed to withstand all natural disasters. Seismic microzonation is a process of demarcating a region into individual areas having different levels of various seismic hazards. This will help in identifying regions having high seismic hazard which is vital for engineering design and land-use planning. The main objective of this paper is to carry out the seismic microzonation of a nuclear power plant site situated in the east coast of South India, based on the spatial distribution of the hazard index value. The hazard index represents the consolidated effect of all major earthquake hazards and hazard influencing parameters. The present work will provide new directions for assessing the seismic hazards of new power plant sites in the country. Major seismic hazards considered for the evaluation of the hazard index are (1) intensity of ground shaking at bedrock, (2) site amplification, (3) liquefaction potential and (4) the predominant frequency of the earthquake motion at the surface. The intensity of ground shaking in terms of peak horizontal acceleration (PHA) was estimated for the study area using both deterministic and probabilistic approaches with logic tree methodology. The site characterization of the study area has been carried out using the multichannel analysis of surface waves test and available borehole data. One-dimensional ground response analysis was carried out at major locations within the study area for evaluating PHA and spectral accelerations at the ground surface. Based on the standard penetration test data, deterministic as well as probabilistic liquefaction hazard analysis has been carried out for the entire study area. Finally, all the major earthquake hazards estimated above, and other significant parameters representing local geology were integrated using the analytic hierarchy process and hazard index map for the study area was prepared. Maps showing the spatial variation of seismic hazards (intensity of ground shaking, liquefaction potential and predominant frequency) and hazard index are presented in this work.

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.

탄성파시험의 이동성 확보를 위한 마이크로폰 센서의 활용

Social demand for the stability of structures lead to the development of the technology to accomplish it. The non-destructive seismic technique, which is able to assess structural integrity of infrastructures, belongs to this category. Seismic technique is focused on the measurement of seismic velocity propagating through the material, and has to utilize sensors coupled to material surface, which does not allow the testing to be performed on the fly. In this paper, a general vocal microphone, which works as a non-contact sensor, was adopted to facilitate seismic testing with mobility and efficiency improved. The target of using microphones was oriented toward quality assessment of compacted subgrade, stiffness evaluation and health monitoring of concrete structures. Experimental parametric study and field applications were performed to investigate reliability and efficiency of microphones. Finally, the optimal test configuration of microphones was suggested for resonance tests and surface-wave tests.

Two-dimensional imaging of soil–bedrock interface by short-array beamforming technique

The depth to soil–bedrock interface, which is one of the major parameters in the site response analysis, has been often investigated by surface-wave tests. The round-robin tests for a surface-wave method in Korea revealed that a long measurement array in surface-wave tests is not appropriate in locating soil–bedrock interface. In this paper, for the improved profiling of depth to soil–bedrock interface in 2-D image, short measurement array was introduced for the beamforming technique, which is a robust array processing technique adopted in a long-array format for stiffness profiling. Numerical simulation and field applications of the short-array beamforming technique indicate that the method is valid even for surface wave propagation with mode-related complexity. Depth to soil–bedrock interface and shear-wave velocity profiles determined by the short-array beamforming technique were in good agreement with layer stratifications of boring logs, resistivity map, shear-wave velocity profiles of downhole tests and CAP-SASW tests.

Dynamic characterization of soils and soft rocks of the Central Archeological Area of Rome

The paper presents the results of in-situ and laboratory tests aimed at defining the cyclic properties of soils and soft rocks of the Central Archeological Area of Rome in the framework of the seismic microzonation study of the area. The small-strain shear modulus \(\text{ G }_{0}\) (or analogously shear wave velocity \(\text{ V }_\mathrm{S}\)) and the curves expressing shear modulus G and damping ratio D variation with shear strain amplitude were investigated. A large amount of in-hole tests integrated with active surface wave tests were utilized to characterize the small-strain stiffness of the lithotypes identified in the area. Small-strain stiffness values determined by geophysical tests were further compared with those measured in the laboratory showing different behaviors of soils and soft rocks. The effects of sample disturbance and degree of jointing, for soils and soft rocks, respectively, was invoked to explain the observed differences. The shear modulus and damping ratio versus shear strain amplitude curves were determined by means of resonant column and cyclic shear tests, both simple and torsional. The experimental results were compared with literature data on similar soils highlighting some peculiar behaviors. In particular the role of fine matrix in sandy soils and organic matter content of clays on the cyclic properties was stressed. The results showed that an increase in fine matrix and organic content results in a stronger linearity and lower damping ratio.

Effect of Input Source Energy on SASW Evaluation of Cement Concrete Pavement

A series of spectral analyses of surface waves (SASW) tests were conducted on a cement concrete pavement by dropping steel balls of four different values of diameter (D) varying between 25.4 and 76.2 mm. These tests were performed (1) by using different combinations of source to nearest receiver distance (S) and receiver spacing (X), and (2) for two different heights (H) of fall, namely, 0.25 and 0.50 m. The values of the maximum wavelength (λmax) and minimum wavelength (λmin) associated with the combined dispersion curve, corresponding to a particular combination of D and H, were noted to increase almost linearly with an increase in the magnitude of the input source energy (E). A continuous increase in strength and duration of the signals was noted to occur with an increase in the magnitude of D. Based on statistical analysis, two regression equations have been proposed to determine λmax and λmin for different values of source energy. It is concluded that the SASW technique is capable of producing nearly a unique dispersion curve irrespective of (1) diameters and heights of fall of the dropping masses used for producing the vibration, and (2) the spacing between different receivers. The results presented in this paper can be used to provide guidelines for deciding about the input source energy based on the required exploration zone of the pavement.