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25th Symposium on the Application of Geophpysics to Engineering & Environmental Problems
- Conference date: 25 Mar 2012 - 29 Mar 2012
- Location: Tucson, USA
- Published: 25 March 2012
21 - 40 of 195 results
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INTERPRETING NUCLEAR MAGNETIC RESONANCE RELAXATION MEASUREMENTS IN UNSATURATED POROUS MEDIA
Authors Sam Falzone and Kristina KeatingNear-surface geophysical applications of nuclear magnetic resonance (NMR) have primarily focused on interpreting NMR measurements under the assumption that the measured volume is fully saturated; however, as NMR is used for a wider set of near surface applications, an improved understanding of NMR measurements of unsaturated porous media will be needed. Our research focuses on using laboratory measurements to understand the relationship between the NMR relaxation time (T- 2) and the water content of unsaturated porous geologic material. A limited number of recent studies have determined how the shape and magnitude of the T2-water content relationship varies with the surface-area-to-volume ratio (S/V) of a porous media. Although it is well known that in fully-saturated porous material T2 is affected by the surface relaxivity (a parameter that quantifies the ability of a pore surface to enhance relaxation) as well as S/V, there have been no studies that explore the effect of surface relaxivity on the T2-water content relationship. We will present results from a laboratory study designed to understand the effect of both surface relaxivity and S/V on the T2-water content relationship.
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UNDERSTANDING THE SPATIOTEMPORAL DISTRIBUTION OF SOIL MOISTURE AT INTERMEDIATE SPATIAL SCALES USING GEOPHYSICAL METHODS
Authors Trenton Franz, Ty Ferre and Marek ZredaThe spatiotemporal distribution of soil moisture is critical for partitioning the water, energy, and carbon cycles at a variety of scales. In drylands, soil moisture is intimately linked to rainfall recycling shown through autocorrelation with future events. In this research, we investigate different soil moisture datasets collected at various scales from the Santa Rita Experimental Range in southern Arizona and Tonzi Ranch in northern California. We will present a series of electromagnetic induction surveys (EMI) that were collected within the footprint of a continuously recording cosmic ray probe (COSMOS). By performing the surveys within a COSMOS footprint we are able to better understand and interpret the information from the less rigorous but data rich EMI surveys. With this spatial information we are able to better understand the controls of topography, texture, and soil depth on the organization of vegetation at the landscape scale. Finally, we are able to quantify the uncertainty and support volume of each instrument through modeling experiments with the goal of obtaining more accurate information about the inferred fluxes.
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Use of Electrical Resistivity Surveying to Evaluate Collapse Potential Related to Road Construction over a Cave
Authors D.W. Lambert, G.L. Adams and B. FodorGeophysical surveying using the electrical resistivity method was used to help determine the potential for collapse that could occur resulting from the construction of a road over a known cave in the City of Kirkwood (City), Missouri. The City is installing a new water main which will require construction of an access road through Koestering Park. Underlying the park is historic Watson Cave, which was mapped in 1961. The width and height of the cave varies and appears to be influenced by the presence of vertical fractures that have been widened by solutioning. The depth to the top of the cave is unknown. Exploration by non-intrusive electrical resistivity surveying was performed rather than drilling or test pit exploration because the City desired to limit damage to the cave and densely wooded areas within the park. Electrical resistivity data were collected using a dipole-dipole array along the proposed road alignment. The data exhibited a valuable signature of a high-resistivity anomaly due to the presence of this cave of known dimensions. Based on the survey results, the depth to the top of the cave was estimated to be approximately 30 feet. Also identified, however, were nine other high-resistivity anomalies (possible voids) along the proposed road alignment. The interpretation of these anomalies, in some cases, suggested possible depths to voids of less than seven feet. It was concluded that the limited traffic loads caused by low speed construction-type vehicles would not significantly increase the potential for cave collapse at Watson Cave due to the approximately 30-foot depth of the feature. However, the interpreted shallower features have a comparatively higher potential for collapse. Recommendations included using a Bailey bridge to span large features and using a geogrid-reinforced crushed rock mat to distribute/dissipate heavy wheel loads over narrower features.
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A COMPARISON OF AEM INVERSION METHODS FOR DISCONTINUOUS PERMAFROST NEAR FORT YUKON, ALASKA
Authors Burke Minsley, Leif Cox, Ross Brodie, Glenn Wilson, Jared Abraham and Micheal ZhdanovPermafrost is a predominant physical feature of Arctic and sub-Arctic regions, and is sensitive to climate change. How warming of the permafrost affects near-surface hydrologic processes, ecosystems, and infrastructure is not clearly understood. A better understanding of the dynamic distribution and physical properties of permafrost, from continuous to discontinuous, provides knowledge of how the permafrost may change in the future and help inform engineering and sustainable management strategies. In June 2010, the US Geological Survey acquired 875 line km of RESOLVE frequency-domain airborne electromagnetic (AEM) data over a ~300 sq. km block near Fort Yukon in Alaska for imaging permafrost characteristics at various scales.
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OPTIMIZING ERT SURVEYS FOR TUNNEL DETECTION
Authors Tomas Goode and Ty FerreWe consider the problem of designing an electrical resistivity tomography (ERT) survey that is best able to discriminate a subsurface target among a population of similar targets. The targets being considered are horizontal buried tunnels with circular cross sections. Potential target tunnels vary in their radius and depth but, they have a constant electrical conductivity. They are evaluated singly, embedded in a homogeneous background with a differing electrical conductivity.
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MONITORING A NOVEL APPROACH TO MONITOR ENHANCED RECHARGE WITH TIME LAPSE GRAVITY
Authors Ty Ferre, Deborah Tosline and Damian GoschWe present work conducted in cooperation with the Bureau of Reclamation as part of their Enhanced Recharge Demonstration Project. The purpose of this project was to monitor the performance of a novel recharge enhancement approach based on diverting water from a main channel through a secondary channel within the floodplain. We located gravity stations along a 75 m transect that was perpendicular to the channels and extended from the midpoint between the main and excavated channels. We monitored over a period of 75 days. During this period, seepage loss measurements and streambed hydraulic conductivity measurements showed decreasing infiltration capacity with time. This response may be due to deposition of fine sediments and/or biological activity. Gravity responses mirrored these changes, showing rapid increases in water mass at early time, followed by a slow, steady decrease in stored mass. In addition, the gravity measurements gave a unique perspective on the extent of lateral movement of infiltrated water. Based on these results, we suggest that gravity monitoring could be a key component of monitoring of water movement adjacent to natural and engineered channels.
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GRAVITY-MEASURED WATER STORAGE CHANGE AND SUBSURFACE HYDRAULIC PROPERTIES AT A MANAGED RECHARGE FACILITY IN TUCSON, USA.
Authors Jeffrey Kennedy, Ty Ferre, Benjamin Creutzfeldt and Andreas GüntnerThe storage of subsurface water is central to Arizona’s future sustainable water supplies. Presently large amounts of water delivered from the Colorado River by Central Arizona Project canals (over 400,000 acre-feet/year permitted capacity) are stored underground at artificial recharge facilities to augment future water supplies. As the demand for Colorado River water increases and the energy required to transport, store, and recover this water becomes more costly, the importance of proper management and siting of recharge facilities increases. In this study, we combine different gravimeters (superconducting, absolute, and spring gravimeters) and advanced analysis methods to improve monitoring of subsurface storage and the characterization of subsurface hydraulic properties at Tucson Water’s Southern Avra Valley Storage and Recovery Project (SAVSARP) infiltration basins.
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SIMULTANEOUS PROXIMAL SENSING OF SOIL PHYSICAL, CHEMICAL, AND BIOLOGICAL PROPERTIES
Authors Erik Lund and Chase MaxtonSoil electrical conductivity (EC) sensing can rapidly delineate areas of contrasting soil properties within agricultural fields. Unless the signal is responding to a dominant soil property such as salinity or claypan, calibrating the signal in farm fields to specific properties has proven difficult. As a result, while the practice of soil EC mapping is receiving widespread acceptance in commercial agriculture, it is being adopted primarily as a soil pattern delineator. Recent advancements in proximal soil sensing allow for the mapping of soil properties such as organic matter using an optical sensor, and pH using an electrochemical sensor, along with soil EC. Also, elevation data from GPS receivers can provide co-located information about the topography of the field. When fields are mapped with all these sensors mounted on one platform, and calibration soil sample data are available, multivariate analysis techniques can be applied to calibrate the sensor readings to specific soil properties. Results from a multi-field, multi-state study show effective calibrations can be accomplished to a variety of soil properties using this sensorfusion approach.
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A SIMPLE AND EFFECTIVE DATA ACQUISITION PLANNING, PROCESSING AND GUIDANCE SYSTEM FOR CONDUCTING PARALLEL SWATH ELECTROMAGNETIC SURVEYS USING GEM 2 IN SUBSURFACE DRIP IRRIGATION MONITORING, POWDER RIVER BASIN, WYOMING
More LessThe National Energy Technology Laboratory and the U.S. Geological Survey are collaborating with BeneTerra LLC to comprehensively monitor a sub-surface drip irrigation (SDI) system at a site in the Powder River Basin (PRB) of Wyoming. Irrigation water for the SDI system is coalbed natural gas (CBNG) co-produced water. The study is being conducted at the Headgate Draw area, located approximately 17 km south of Arvada, Wyoming at the confluence of Crazy Woman Creek and the Powder River. The study site encompasses six alfalfa fields and covers an approximate area of 1.2 km2 (Figure 1).
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FIFTH YEAR OF SUBSURFACE DRIP IRRIGATION MONITORING USING GEM2 ELECTROMAGNETIC SURVEYS, POWDER RIVER BASIN, WYOMING
By James SamsThe National Energy Technology Laboratory and the U.S. Geological Survey are collaborating with BeneTerra LLC to comprehensively monitor a sub-surface drip irrigation (SDI) system at a site in the Powder River Basin (PRB) of Wyoming. Irrigation water for the SDI system is coalbed natural gas (CBNG) co-produced water. The study is being conducted at the Headgate Draw area, located approximately 17 km south of Arvada, Wyoming at the confluence of Crazy Woman Creek and the Powder River. The study site encompasses six alfalfa fields and covers an approximate area of 1.2 km2.
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UNKNOWN BRIDGE CHARACTERISTICS PROGRAM
More LessThe unknown bridge foundations issue remains one of the most persistent problems facing the bridge engineering community. Bridges are classified as having unknown foundations when the type (spread footing, piles, columns), material (steel, concrete, or timber), dimensions (length, width, or thickness), reinforcing, and/or elevation are unknown (HEC 18). The national cooperative highway research program (NCHRP) Project 21-5 devoted considerable effort in developing new test methods to address this issue and some good progress was reported. However, there are still concerns on the reliability of the available technologies and associated costs.
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A HYBRID METHOD FOR FIRST BREAK AUTO PICKING
By Don ZhaoFirst break picking is a basic procedure in first arrival tomography. There are a few of first break auto picking approaches available, such as energy ratio, AIC, and tracking. These methods work well with noise free data, but applied to field data, none of them are robust and large bias from the desired picks may present. A hybrid auto picking method is proposed. It first uses the energy ratio to generate a sketch of T-X curve, from which a velocity versus offset function is built, then employs AIC approach with the search range limited by the velocity versus offset function, finally adjusts the picks by correlation of the wavelet of adjacent traces. This method is proven by lots of experiments with a variety of data in refraction and cross-well tomography.
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3D GPR Real-Time Automated Detection of Buried Utilities
Authors P. Mazzucchelli, D. Molteni, N. di Buono and E. Cottinomini-trench" technique (addressed in ITU L.83 recommendation) requires that non-destructive mapping of buried services enhances its productivity to match the improvements of new digging equipment. Therefore, the development of a fully automated and real-time 3D GPR processing system plays a key-role in overall optical network deployment profitability. We propose a novel processing scheme whose goal is the automated processing and detection of buried targets, that can be applied in real-time to 3D GPR array system (16 antennas, 900 MHz central frequency). After the standard pre-processing steps, the antenna records are continuously focused during acquisition, by the mean of Kirchhoff depth-migration algorithm, to build pre-stack reflection angle gathers G(x, θ; v) at nv different velocities. The analysis of pre-stack reflection angle gathers plays a key-role in automated detection: by the mean of correlation estimate computed for all the nv reflection angle gathers, targets are identified and the best local propagation velocities are recovered. The data redundancy of 3D GPR acquisitions highly improves the proposed automatic detection reliability. The proposed approach allows to process 3D GPR data and automatically detect buried utilities in real-time on a laptop computer, without the need of skilled interpreters and without specific high performance hardware. More than 100 Km of acquired data prove the feasibility of the proposed approach.
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NEURAL NETWORK AND SUPPORT VECTOR MACHINE CLASSIFICATION OF UXO USING MAGNETICS FINITE ELEMENT MODELING DATA
Authors Matthew Bray, Curtis Link and Clifton YoumansA recently completed Montana Tech study used finite element modeling to calculate magnetic dipole moments for realistic unexploded ordnance (UXO) shapes found at Montana Army National Guard training sites. The modeling approach compared predictions from a simple prolate spheroid model, typical for conventional modeling, with a complex shape constructed using computer aided design (CAD). The complex shapes embody all of the features of the actual UXO bodies. Results showed that the larger, more accurate dipole moments calculated from the complex shape can be used to adjust the dipole moment discrimination level, ultimately reducing the number of targets to be dug.
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CALIBRATING SEISMIC REFRACTION MEASUREMENTS FOR ACCURATE AQUIFER VOLUME ESTIMATION IN A TROPICAL AREA: CAIRNS, AUSTRALIA
Authors Douglas Desper, Curtis Link and Paul NelsonThe Cairns (Australia) Regional Council on Water and Waste is committed to maintaining long term viability of the water supply to the rapidly increasing population of the Cairns region while ensuring a sufficient and safe water supply to maintain the natural environmental values of the rainforests, rivers, and reefs. Currently, the Copperlode Falls Dam supplies the majority of the water to the Cairns region, but this water source will not be sufficient to sustain the projected future growth of the area. The Council is investigating the feasibility of the nearby Mulgrave River Aquifer to supply the future water needs for the Cairns region while at the same time maintaining an equitable distribution of water among domestic, industrial, commercial, and agricultural users.
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MULTIPLE SEISMIC METHODS AND GRAVITY FOR DEFINING THE ANCESTRAL MISSOURI RIVER CHANNEL NEAR GREAT FALLS, MT, USA
Authors Curtis Link and Larry SmithStarting fall 2011 and continuing into spring 2012, the seismic prospecting class at Montana Tech designed and carried out a project focused on defining the preglacial paleochannel of the Missouri river near Great Falls, MT, USA. Although local water well driller’s logs can be interpreted unambiguously to determine presence of the channel, the well control, although dense in developed areas, is sparse throughout the area of interest. Approximate depth to the paleochannel is estimated at approximately 30-100m. As the paleochannel represents a prolific aquifer, there is significant interest in accurately locating it for future development and irrigation use.
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DETECTING BLIND FAULTS USING RAYLEIGH WAVE REFLECTIVITY
Authors Craig Hyslop and Robert StewartFinding faults near the surface is important for construction and engineering applications. It is difficult to locate them because there is often no surface expression, i.e. they are blind faults. We have developed a novel method for extracting Rayleigh wave reflectivity from sharp boundaries and tested it on modeled and field data. Rayleigh waves are particularly suited to detecting blind faults because of their presence extending into the shallow subsurface. Others have studied the complex wavefield due to heterogeneous impedance contrasts in the near surface scattering Rayleigh waves into P, S, and other Rayleigh waves. However, if contrasts are conformed to a boundary, such as a fault, scattered waves give way to reflected waves and a less complex wavefield. To find reflectivity, we determine phase velocity and amplitude for the outgoing Rayleigh wave and deconvolve the reflected wave with the outgoing wave while in a phase matched domain.
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VARIABILITY OF GRM AND REFRACTION TOMOGRAPHY RESULTS EXAMPLE: WATER RESOURCE INVESTIGATIONS IN WESTERN MASSACHUSETTS
More LessFive linear seismic surveys were conducted at the Clark Art Institute in Williamstown, MA to locate water-bearing bedrock fractures. Supply wells and return wells are needed to support an open-loop geothermal system requiring 550 gpm, with future expansion of the system planned.
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UNDERSTANDING GEOLOGIC CONTROLS ON GROUNDWATER USING BOREHOLE GEOPHYSICS EXAMPLE: LANDFILL IN EAST-CENTRAL NEW YORK
More LessBorehole geophysical logging of five bedrock wells was performed as part of a bedrock characterization study in support of groundwater investigations near a landfill in east-central New York. The investigation area is situated within an upland valley. Although the regional hydraulic gradient was generally understood, factors controlling variations in the groundwater flow patterns and potential vertical and horizontal pathways for landfill leachate around the vicinity were not. Contaminants of primary concern within the areas of investigation include VOCs in groundwater at concentrations above drinking water standards.
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ANALYSIS OF THE IVI MINIVIBI PERFORMANCE FOR HIGH FREQUENCY REFLECTION DATA
Authors Craig Hendrix and Richard D. MillerUnderstanding the vibrator-earth response is a pivotal part in addressing problems that decrease the fidelity of vibroseis data. If the vibrator output (ground force) is known, raw vibroseis data can be optimized for resolution and signal-to-noise ratio of the seismic waveform. The source signature, however, is non-unique and varies from shotpoint to shotpoint and from sweep to sweep. Nonlinear complexities within the vibrator’s hydraulic system, tower structure, baseplate flexure, and the ground response to force exerted by the vibrator baseplate increase irregularities in the vibroseis signal. Measuring and analyzing the response of the vibrator baseplate to a specific drive signal can help determine optimal recording positions on the baseplate to recover the ground force signal. When used to correlate or deconvolve raw data, an accurate approximation of the vibrator output will increase data resolution.
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