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27th Annual Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP)
- Conference date: 16 Mar 2014 - 20 Mar 2014
- Location: Boston, USA
- Published: 16 March 2014
1 - 20 of 53 results
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A Description Of An Effective Sinkhole Investigation Approach: A Case Study Of A Site In Greene County, Missouri
Authors S.C. Nwokebuihe, E.V. Torgashov and N.L. AndersonA sinkhole had developed and led to the subsidence of a portion of the parking lot of a residential building in Nixa, Missouri. The sinkhole was characterized using a combination of the geophysical data (multichannel analysis of surface waves and the electrical resistivity tomography) and supplemental data (aerial photographs, topographic and geological maps and borings). The interpretation of the data indicated that a fault trending northwest – southeast runs across the site and is underlain by shallow, fractured limestone bedrock of the Burlington Keokuk formation. The sinkhole is understood to have been triggered by the excavation of a surface drainage channel and pit adjacent to the building in order to check flooding. However, the action led to the increased concentration of flow of surface water into the fault zone, hence causing an increased dissolution of bedrock and raveling of sediments into the formed cavities and subsequently sinkhole development.
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Reflection Of Winter Road Salinity In P-THEM Data
By A. VetrovDuring the development of the P-THEM system, the author and his colleagues have made numerous test surveys on different sites in Quebec and Ontario. One of the test sites, the Alliston area, has been selected for the P-THEM system tests in June 2010. The area is a developed urban zone in the Greater Toronto Area, Ontario, Canada. Geologically, the area is represented with Quaternary sediments with underlying bedrocks of the Ordovician formation. The close distance of the area to Holland Landings airport made it preferable for testing system functionality. After processing observation data, the salty soil along roads where the salt is spread during winter time has been detected on the Tau-map. Another test flight in January 2013 showed an identical image. The achieved results of the surveys show the possibility of the time-domain electromagnetic (TDEM) airborne system for applications in the characterization of environmental properties, such as the detection of surface and near surface pollution.
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Optimization Of A Mobile Capacitatively-Coupled Geophysical Survey Used For Electrical Resistivity Tomography
Authors T.C. Goode, T.P.A. Ferré and A.C. HinnellImproving the efficiency of geophysical surveys is becoming more important with the increased application of geophysical methods in subsurface investigations. With this in mind, we propose a relatively simple optimization approach for mobile geophysical surveys. Our approach specifically evaluates the use of a capacitatively-coupled resistivity (CCR) array for electrical resistivity tomography (ERT). We demonstrate our approach through simulating a small number of CCR surveys used to identify and discriminate a target tunnel of interest from other similar tunnels in the subsurface. These examples provide insights into the practical application of the optimization process developed through this study. The mobile electrode arrays that were evaluated used a dipole-dipole configuration with a maximum survey length of 50 m. By evaluating different CCR survey designs and their respective measurement responses to buried tunnels of different size and depth, we show a means to identify and discriminate among tunnels using only voltage measurements. The differences in voltage between surveys were used to create an error response surface for a range of tunnel sizes and depths. These error response surfaces can be converted into target discrimination maps which identify tunnels that can and cannot be discriminated from a selected target tunnel. The fractional discrimination for each tunnel obtained from the target discrimination maps is used to create target identifiability maps which indicate the ability for each survey to discriminate among a range of target tunnels. Considering all possible target tunnels, the average target discrimination for a survey was selected as a measure of survey efficiency. Using this measure of survey efficiency, we provide examples of the potential impact of survey design and speed on the discrimination of target tunnels. In turn, we identify the survey with the highest efficiency and the least number of survey measurements as our optimal survey design.
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Classification Of Cued Metalmapper Data Using Data Mining Techniques
By D. HallA total of 1444 MetalMapper cued soundings were inverted for polarizability transients and then analyzed using data mining techniques to classify anomalous responses as either likely targets of interest or unlikely to be targets of interest. Polarizability transients were parameterized using six scalar moments covering size, shape, and persistence. Additional parameters were generated using a curve fitting algorithm to calculate the best fit coefficients of a polynomial function matching the polarizability transients in log/log space. Parameters were then evaluated using principal component analysis and visual observation to reduce the parameter set to the most definitive elements. Data mining algorithms including the clustering approach K means, and the classifier multi-layer perceptron were used to evaluate training data with known anomaly sources. Approaches developed and refined using training data were then applied to responses with unknown anomaly sources to determine if they represented targets of interest or were unlikely to be targets of interest. Anomalies were ranked according to the likelihood that they represented a target of interest. All of the targets of interest were recovered within the first 13 percent of the ranked list.
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Critical Depths For Higher Modes By Minimally-Invasive Seismic Profiling: Simulations And Field Test
Authors J.C. Ashlock and S. LinTo measure more complete multi-mode dispersion data and thus improve the accuracy of inversion profiles, the authors recently developed a minimally-invasive hybrid surface-and-borehole method. The new method employs a borehole geophone at selected depths to record seismic waves from a moving source on the soil surface. The goal of this paper is to develop a procedure for estimating the ranges of optimum geophone depths for capturing the higher modes. Stiffness matrix and finite element-based numerical simulations of the hybrid testing method are performed to identify the relationships between critical geophone depths and cut-off frequencies. A preliminary field test is conducted using a vertical geophone placed at five depths while impacts are applied to the soil surface over a range of offsets. Dispersion images from the five geophone depths were superimposed to produce a dispersion image having three modes with improved clarity relative to the surface-only MASW method. A comparison of the experimental and theoretical cut-off frequencies of higher modes is used to validate the prediction of critical depths by the stiffness matrix method. Matching of such experimental and theoretical cut-off frequencies is proposed as additional optimization constraints to reduce the uncertainty of final inversion profiles.
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Comparison Of MASW And MSOR For Surface Wave Testing Of Pavements
Authors S. Lin and J.C. AshlockThis paper presents a computational and experimental study on seismic stiffness profiling of pavements 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. Effects of different receiver coupling methods on the test results are examined. 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 site with the same testing system are compared, and MASW is found to enable measurement of dispersion data to much higher frequencies than MSOR. Inversion results from MASW and MSOR data at the same site are compared, and it is found that MASW is able to provide measurements of the stiffness of the surface layer with reduced variability.
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Method For Isolation Of Gravity Signatures Due To Major Earthquakes From Satellite Gravity Data
Authors A. Pant and R.G. SastryOften, satellite gravity (GRACE Satellite) is employed to infer near surface fluid exchanges and budgets on a global scale. However, devastating major earthquakes in offshore regions involving mass-wastage must also have a significant gravity signals in satellite gravity campaigns. But their isolation is masked by other time-varying fluid exchange signals near earth’s surface. Here, our differential data analysis (Spherical harmonics) attended by spectral filtering has successfully isolated weak gravity signals in micro-Gal range for three major earthquakes. For illustration purpose we include Sumatra earthquake (2004). Our method could infer the rupture zone in the source region. Presently, a combined seismological and gravity modeling of satellite gravity derived gravity signals are underway. These efforts if successful could be a huge step in predicting earthquakes.
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Web-Based Database Of Integrated Geophysical Method For Levee Safety Assessment
Authors K. Hayashi, T. Takahashi, T. Inazaki, K. Kitao and T. KitaIn order to evaluate the safety of levees based on an integrated geophysical method, a web-based database containing results of the integrated geophysical method, boring logs and levee safety assessment records was constructed. We collected the results of surface wave methods and resistivity methods performed at 37 Japanese rivers as well as the results of borings conducted on survey lines of geophysical methods. A land streamer and a capacitively-coupled resistivity method were generally used in the data acquisition of the surface wave methods and the resistivity methods, respectively. Analyzed results were saved as a standard XML format defined by The Society of Exploration Geophysicists of Japan. The web-based database consists of four parts: A) a database of the geophysical investigation results, B) a database of levee safety assessment and maintenance records, C) a database of blow counts (N-value), soil type, S-wave velocity (Vs) and resistivity, and D) a database of Vs, resistivity and laboratory tests. Data registered for the database is as follows: length of about 650 km of geophysical investigation results, about 400 boring logs, about 4,000 relationships of Vs, resistivity, N-value and soil type, about 1,000 relationships of Vs, resistivity and laboratory tests, 340 km of levee safety assessment and maintenance records. The database was constructed on a web server using MySQL and PHP so that users access to the database through the internet. This paper presents an outline of the database, an example of data, and an application example of the database and proposes a management framework of the database in the future.
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Monitoring Of Joint Systems Time-Lapse Behaviour Via Ert
Authors J. Jirku, J. Barta, J. Knez and J. VilhelmElectrical resistivity tomography (ERT) as a tool for monitoring the processes and time-related changes in geological environments has made great progress in recent years and has become standard for observing natural phenomena. This method is simple to use and it often provides high-quality results that are well interpreted. Our research is based on observing time-lapse changes of the physical parameters (conductivity, for instance) of joints systems (mostly in crystalline massifs). The primary aim is to develop a monitoring system mostly for the needs of deep repositories of nuclear waste. Geophysical research of such repositories has so far dealt only with one-off research (no time-monitoring) of potential host rock´s properties. Contrary to this, our developed system and methodology is unique in continuously measuring the physical properties (in this case, electrical resistivity) of the rock massif. This system will be permanently fixed in the field and by observing changes in measured data reports if any remarkable occurrence in the EDZ zone is or was happening (for example, opening or closing of the joints or micro-fractures). Today, our monitoring system is being developed and tested at the field base in Bedrichov (northern Bohemia). The Bedrichov gallery is approximately 2.5 km long and continuously leads through one type of granite massif. Point 792, where a significant geological fracture zone goes through, was chosen as an ideal place for taking repeated measurements via our ERT system. Currently, we test the measurement quality, such as whether our system provides real data and is able to reliably observe resistivity changes measured at ERT profiles.
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Optimized Interpretation Of Sageep 2011 Blind Refraction Data With Fresnel Volume Tomography And Plus-Minus Refraction
More LessWe improve the resolution of subsurface P-wave velocity tomograms with Fresnel Volume Tomography and Wavepath Eikonal Traveltime inversion, by iteratively decreasing the wavepath width. We use the SAGEEP 2011 blind refraction synthetic traveltime data to compare our tomograms with the known true model. We compare weighting of the wavepath velocity update with a Ricker wavelet vs. weighting with a Gaussian bell function. Plotting Plus-Minus refractors obtained with layer-based interpretation on the 2D velocity tomogram better visualizes both methods. Tomograms from an iterative approach of wavepath adjustment show improvement over the standard ray-based method.
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Use Of An MASW Survey To Assess Flood Damaged Road – A Case History
Authors K. Suto and R. KristinofAn MASW survey was carried out over and around a road severely damaged by flood waters, and in the creek-bed below. The MASW technique was adopted because a significant amount of the site was accessible only by foot. The survey comprised 936 metres in six lines, on which 85 points were analysed for S-wave velocity profile. From the S-wave velocity, Young’s modulus and pseudo-N values were estimated, assuming density and Vp/Vs ratio and an empirical equation. While the data quality was reasonable and free of background noise, the analysis was challenging due to quick lateral variation of the S-wave velocity. The use of relatively fewer traces for lateral resolution results in a low signal-to-noise ratio, and identifying the fundamental mode Rayleigh wave in the frequency-phase velocity domain becomes difficult. To combat this, a number of mute parameters were tried to improve the dispersion images. The results show S-wave velocity sections with rapid variation and reasonably consistent confidence levels. The S-wave velocity sections were used to infer the depth to bedrock beneath the road, providing information on foundation depths on which gabion slope retention structures could be founded. Information on depth to bedrock was also used to inform how much a particular section of the road could be lowered, thereby reducing the height of planned slope retaining structures, and thus the overall capital construction cost of the project. The line along the creek bed was difficult to analyse due to the weak signal to the distant geophones, however the results provided a reasonably accurate interpretation of the thickness of fluvial sediments, which was proven during construction. Overall the results of the survey correlated well with boreholes drilled in areas where vehicular access was possible; following close correlation in those areas, the survey data was successfully extrapolated to other areas where access was only possible by foot.
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Sub-Slab Characterization Of Gavins Point Spillway With Ground Penetrating Radar Mapping
Authors G. Byer and R. GrabowskiHistoric Missouri River flooding in June 2011, prompted the USACE1 to conduct physical inspection of exposed spillway slabs, supplemented with concrete coring and Ground Penetrating Radar (GPR) testing, as part of an overall risk evaluation of the six Missouri River Main Stem Dams in Montana, North Dakota, South Dakota, and Nebraska (USACE, 1998). In addition, the USACE mimicked operational conditions during the flood event to evaluate effects on the vertical/lateral subdrain systems beneath the spillway slab at Gavins Point Dam, near Yankton, South Dakota. The spillway gates were operated at 12,000 cfs flow with various configurations of gates discharging. Anomalous conditions observed during the half-day test suggested pressurization beneath the spillway slab. Further evaluation was performed with GPR on normally inundated portions of the spillway slab to evaluate the effects of this condition. During an 8-hour period, the Missouri River was lowered, exposing the upper spillway slab. Three teams simultaneously operated three 250-MHz GPR systems to gather bidirectional data on 2-foot centers in an area of approximately 54,590 square feet. Concurrently, concrete coring was performed near damaged vertical drains found during the half-day test. The GPR data were subjected to thorough data processing including: 1) amplitude mapping; 2) digitization and mapping of the top of bedrock; and 3) line-by-line inspection for trains of multiple reflections, shadows, and pull-up/push-down in travel time to bedrock. Based on knowledge regarding construction details, a conceptual model was developed from which prediction of the behavior of the GPR wavelet was made under various scenarios where void thickness and fill (water or air) were considered. Based on this conceptual model, the aerial extents and thicknesses of voids beneath the spillway slab were interpreted. Post-interpretation sonic drilling and borehole geophysical logging were performed to help constrain the conceptual site model and GPR anomalies. Interpretation of the void extents and a hydraulic explanation of void formation by considering multiple lines of geophysical, hydraulic, and other observational evidence provided an enhanced understanding of subslab conditions. This improved understanding was used to inform decisions on post-flood repair strategies as well as the implementation of risk reduction measures to improve the function and reliability of the slab subgrade.
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Interpretation Of Seismic Tomography Results Using Data Quality And Residual Error Maps
Authors . Fechner, L. Karl, S. Mackens, W. Albers and D. TweetonIn seismic borehole tomography, the interpretation of the results is commonly limited to the comparison of the velocity map, the ray coverage, and the global root mean square RMS residual. However, the quality of the seismic data has a significant influence on the accuracy of the arrival time picking but is generally not considered in the inversion. This paper presents an enhancement of the inversion taking into account the data quality, based on the signal-to-noise ratio, by using it to weight the travel time residuals in each iteration step. This implementation also calculates the spatial distribution of the data quality and the distribution of the residual remaining at the end of the inversion, which are used to support the evaluation of a velocity map. The effect of the data weighting is studied on a field data set. Quality and residual maps are given and their relevance for the interpretation is discussed. The results indicate that areas of exceptionally high signal attenuation can be identified by means of the quality information.
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Intelligent Meshing For Geophysical Inverse Problems Using Unstructured Meshes
Authors T.-K. Chou, M. Chouteau and J.-S. DubéMesh generation to solve geophysical forward problems is a thoroughly studied area that has seen the development of many methods and techniques. In geophysical inverse problems, a priori structured mesh is often used for inversion because the geometry of the underlying subsurface structures is unknown and mesh refinement is applied if needed by the user only after observing the inversion results. We present an intelligent meshing approach for an electrical resistivity tomography inverse problem. This new approach uses the Harris corner and edge detectors that are based on the local autocorrelation function of a signal (Harris and Stephens, 1988). The process optimizes the size of the inverse problem by refining areas where the boundaries of physical structure seems to be important and generates a more appropriate and optimum mesh for the inverse problem. The performance and robustness of the proposed algorithm are determined through a series of tests using 2D ERT modelled data and survey data. Tests on modelled data have demonstrated that the proposed meshing technique can reduce data misfit, produce a better model reconstruction, minimize the size of the inverse problem and reduce computational resource requirement. Tests on survey data from application such as ground water mapping have demonstrated that this new meshing approach produced data fit and inverse solutions that are comparable to conventional meshing and fine meshing techniques while minimizing the size of the inverse problem.
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3D Stochastic Gravity Inversion On Unstructured Meshes
Authors P. Shamsipour, M. Chouteau, D. Marcotte and E. SchetselaarThe stochastic gravity inversion on unstructured meshes is presented. The unstructured meshes are used because they provide the flexibility required to closely approximate complicated geological structures. Sharp topographic relief and geological bodies of complex shapes are usually more accurately described by unstructured meshes rather than with regular grids. The forward method has a closed form solution and gives accurate results. A geostatistical method is applied to invert the gravity data.
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Potential Field Inversion On Nodes For Stochastic Inversion Models
Authors D. Marcotte, P. Shamsipour and M. ChouteauInstead of applying gravity inversion on a large number of small prisms which is computationally very expensive, it is proposed to perform inversion on a limited number of nodes which include all the available point density data (if any) plus points sampling the inversion space fairly. It is also possible to include sets of linear constraints in the inversion. If no noise is present, the inverted field reproduces exactly the added constraints and the gravity field. These methods can be applied to the magnetic potential as well as the joint inversion of gravity-magnetic field data.
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The Application Of Monte Carlo Simulation To Borehole Gamma-Gamma Density And Spectral Gamma Calibrations
Authors J.R. Stowell and L.M. MartinezThe application of the Monte Carlo statistical processing method, originally developed during the Manhattan project in the 1940s, was originally restricted to government lab work with applications focusing on nuclear weapon design, nuclear reactor design and other radiometric processes. With the development of ever more powerful computers, numerical processing that required a room-full of main frames 25 years ago can now be accomplished on a high end lap-top. While the learning curve on the use of MCNP modeling can be steep, the availability of modern PCs and access to the code now allows others to make use of this powerful tool to assist in the development of better borehole nuclear measurements. It is now possible to find commercial providers who will model downhole tools and predict their response to natural gamma radiation in earth formations, and provide real time spectral concentrations based on MCNP and correlation with known physical models. Stability and repeatability of downhole spectral measurements has been difficult to accomplish and these methods promise much better results. In addition, the application of MCNP to other borehole radiometric measurements, such as gamma-gamma density and litho-density may provide users with much needed confirmation of field calibrations results and the normal drift associated with source half-life, borehole corrections, and overall tool performance. MCNP modeling may also be used to design better source shields and calibration fixtures to allow more accurate and safer field operations. This paper will review some of the current MCNP borehole spectral applications, as well as present examples of MCNP applied to slim-hole gamma-gamma density tools, source shields and calibration fixtures.
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Electrical-Leak Testing Of Geomembrane-Lined Basins
Authors P.J. Hutchinson, B.J. Teschke and M.H. BeirdImpermeable geomembrane-lined basins are used to contain waste water and solid waste. Postinstallation penetrations, seam failures and imperfections in the geomembrane sheet are not uncommon and provide an avenue for waste water and leachate to escape into the environment. Electrical leak testing of geomembrane integrity is based upon the mise-á-la-masse or ‘chargedbody potential’ electrical resistivity test. The leak test of a geomembrane liner consists of placing a current electrode within the basin and another current electrode in a semi-infinite distance away from the basin. Penetrations of the geomembrane liner provide a current pathway that can be located and mapped.
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High-Frequency Surface Wave Measurement For The Pavement Structural Analysis
Authors T. Inazaki, K. Aoike, T. Kita and K. HayashiDevelopment of non-destructive and high performance testing methods has been requested for the pavement assessment. While FWD (Falling Weight Deflectometer) has been widely utilized as such NDT equipment in Japan, the inversion process of FWD is still ambiguous. Dynamic response of the surface pavement is simplified to static torsional deformation. In contrast, high-frequency surface wave measurements are capable to provide detailed information on the pavement. The authors have started a research project on non-contact, continuous surface wave measurement using arrayed microphone. At the initial phase, we conducted fundamental measurements using piezoelectric accelerometer array. A total of 48 accelerometers were pasted on the pavement surface with clay pad at 10 cm intervals. Observed data showed clear dispersion in the frequency range from 40 to 5000 Hz, and analyzed as A0 mode Lamb waves or normal mode surface waves using a generic algorithm (GA) technique. Parameter study was conducted on the surface pavement structure to the responses of dispersion curves of surface waves. Combined with parameter sturdy, GA inversion successfully reconstructed surface pavement Swave velocity structure. The estimated structure was verified by comparative measurement using double frequency (300 and 800 MHz) antenna system GPR as well as check drilling.
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Cross-Plot Analysis By Using Rock Physics-Based Thresholds For An Evaluation Of Unsaturated Soil
Cross-plot of resistivity and S-wave velocity (Vs) is one of the effective methods to evaluate earth structure, e.g. river levee, because both properties are relatively easy to be obtained by geophysical methods such as capacitive resistivity survey and surface wave method. From the cross-plot of the two geophysical properties, we can interpret the soil types and looseness based on the observations that resistivity and Vs are sensitive to the grain size and looseness of the soils, respectively. For example, dividing the cross-plot by two individual thresholds for resistivity and Vs is the easiest way to interpret the data; however, setting appropriate thresholds is the most challenging issue in this methodology. In order to overcome this problem, in this study, I propose the way to determine the objective thresholds by using rock physics models. Particularly, the effect of water saturation is significant to interpret shallow subsurface; thus I modify the parallel circuit model for the resistivity prediction to account for the saturation effect. For the Vs prediction, I apply the soft sand model with considering clay content. These rock physics models enable us to connect the two properties by two common parameters: porosity and clay content. Both parameters are included in the models. Therefore, if we assume that porosity and clay content are proxies for looseness and grain size respectively, we are able to select certain values of porosity and clay content as the thresholds to discriminate the data indicating vulnerable area in the cross-plot. Preliminary analysis shows that the segmentation done by the rock physics-based thresholds gives a reasonable result that agrees with a previous study and the geophysical dataset obtained at various river levees.
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