Localization of Deep Voids through Geophysical Signatures of Secondary Dewatering Features

Geophysics ◽  
2021 ◽  
pp. 1-81
Author(s):  
Dan R. Glaser ◽  
Katrina Burch ◽  
Dennis L. Brinkley ◽  
Philip Reppert
Keyword(s):  
Seismic Refraction ◽  
Geophysical Methods ◽  
Mixing Model ◽  
Time Domain Reflectometry ◽  
Groundwater Table ◽  
Void Space ◽  
Investigation Area ◽  
Measurement Geometry ◽  
Lateral Localization ◽  
Ground Penetrating

Discrete deep targets are a significant challenge for most surface-based geophysical techniques, even when considering high property contrasts. Generally, surface-based geophysical methods lose lateral and vertical resolution with depth as a result of poor measurement geometry and increased signal attenuation. The poor measurement geometry can be overcome through use of cross-borehole methods, but lateral localization is still needed for optimal borehole placement. As such, a relatively small, deep void located near the maximum depth of investigation is very unlikely to be detected. Yet, secondary features associated with these voids can be exploited for enhanced detection performance. When voids are located below the groundwater table a significant amount of dewatering and pumping is required to make them a functional passageway. This dewatering not only removes water from the void space but also the surrounding formation, resulting in a much larger, if more diffuse, secondary target: an induced groundwater table gradient. Many geophysical sensing methods are sensitive to subsurface moisture content. Here we implement a two-dimensional (2D) joint-petrophysical mixing-model, using inverted electrical resistivity tomography and inverted seismic refraction models to sense changes in the groundwater table gradient. Results are validated using depth to bedrock, groundwater-surface water information, ground-penetrating radar, and time-domain reflectometry methods. Our initial proof of concept is applied to a shallow area with a significant soil moisture gradient, through different surface soil types and bedrock. The 2D joint-petrophysical mixing-model results were used to generate an estimate of air, moisture, and matrix percent fractions in the investigation area, providing a clear delineation of the groundwater surface.

Effectiveness of Geophysical Methods in Calcareous Harbor Fills

2013 ◽  
Author(s):  
Horst G. Brandes
Keyword(s):  
Ground Penetrating Radar ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Fill Material ◽  
Object Locations ◽  
Ground Penetrating

The effectiveness of electromagnetic (EM), ground penetrating radar (GPR) and seismic refraction (SR) were evaluated by surveying a shallow trench in which a number of objects of varying composition and size were buried. The trench was excavated in granular calcareous fill material. An experienced geophysical contractor was asked to provide blind predictions of object locations using each of the techniques in turn. GPR with a 400 MHz antenna was the most successful, followed by SR and EM surveying. GPR and SR were also carried out at the port of Hilo to investigate complex subsurface conditions.

Geophysical characterization of inactive/active rock glaciers in the semi-arid Andes using seismic, geoelectrics and GPR

2020 ◽  
Author(s):  
remi valois ◽  
Nicole Schafer ◽  
Giulia De Pasquale ◽  
Gonzalo Navarro ◽  
Shelley MacDonell
Keyword(s):  
Electrical Resistivity ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Late Summer ◽  
Relevant Information ◽  
Refraction Tomography ◽  
Rock Glaciers ◽  
Ice Content ◽  
Ground Penetrating

<p>Rock glaciers play an important hydrological role in the semiarid Andes (SA; 27º-35ºS). They cover about three times the area of uncovered glaciers and they are an important contribution to streamflow when water is needed most, especially during dry years and in the late summer months. Their characteristics such as their extension in depth and their ice content is poorly known. Here, we present a case study of one active rock glacier and periglacial inactive geoform in Estero Derecho (~30˚S), in the upper Elqui River catchment, Chile. Three geophysical methods (ground-penetrating radar and electrical resistivity and seismic refraction tomography) were combined to detect the presence of ice and understand the internal structure of the landform. The results suggest that the combination of electrical resistivity and seismic velocity provide relevant information on ice presence and their geometry. Radargrams shows diffraction linked to boulders presence but some information regarding electromagnetic velocity could be extracted. These results strongly suggest that such landforms contain ice, are therefore important to include in future inventories and should be considered when evaluating the hydrological importance of a particular region.</p><p> </p>

scholarly journals Shallow Geophysical Techniques to Investigate the Groundwater Table at the Giza Pyramids Area, Giza, Egypt

2017 ◽  
Author(s):  
Sharafeldin M. Sharafeldin ◽  
Khalid S. Essa ◽  
Mohamed A. S. Youssef ◽  
Zein E. Diab
Keyword(s):  
Water Table ◽  
Ground Penetrating Radar ◽  
Seismic Refraction ◽  
Groundwater Table ◽  
High Resistivity ◽  
Electrical Resistivity Imaging ◽  
Shallow Seismic ◽  
Geophysical Techniques ◽  
Electrical Resistivities ◽  
Ground Penetrating

Abstract. Geophysical studies were performed along selected locations across the Pyramids Plateau to investigate the groundwater table and the near aquifer, which harmfully affected the existed monuments of the Giza Pyramids and Sphinx. Electrical Resistivity Imaging (ERI), Shallow Seismic Refraction (SSR) and Ground Penetrating Radar (GPR) techniques were carried out along selected profiles in the plateau. Ten ERI, twenty six SSR and nineteen GPR profiles were performed at the sites. The ERI survey shows that, the groundwater table is at elevations varying from 13 to 18 m above the sea level (asl) and low resistivity values near the surface at the Great Sphinx. ERI profiles, which were applied southeast of the Middle Pyramid (Khafre), show high resistivity values near the surface, and water table is located at elevations ranging from 22 to 40 m asl, while the ERI profiles conducted south of Menkaure, show almost high resistivity near the surface. The groundwater table is located at elevations ranging between 45 and 58 m asl. The aquifer layer shows electrical resistivities ranging between 10 and 50 Ohm.m. The considerable high change in the groundwater table is due to the rapid increases of topography from the Great Sphinx towards the Small Pyramids (Menkaure), where this part looks-like a scarp. The SSR Survey is transmitted to know the different velocities and types of the layers, which can help in knowing the saturated layers in the area. The GPR Survey is performed to delineate the water table, which gives good matching with the ERI results.

Case Study

2018 ◽  
pp. 213-229
Author(s):  
Kebabonye Laletsang ◽  
Baram Montshiwa
Keyword(s):  
Seismic Refraction ◽  
Ground Vibration ◽  
Groundwater Table ◽  
Geophysical Survey ◽  
Loose Sand ◽  
Low Frequencies ◽  
Subsurface Geology ◽  
Ground Penetrating ◽  
The Village

A geophysical survey was carried out in 2012 to map the subsurface geology at a quarry and the village to determine if an alleged damage to houses could have been caused by blasting activity in the quarry. The survey included seismic refraction and reflection recorded with the same spread at source and receiver spacing of 2 m, 3 m, and 5 m. The signal source was a 28-lb. sledge hammer stacked 10 times to increase the S/N. Ground penetrating radar (GPR) was also recorded at a trace spacing of 0.3 m to provide detailed images of the subsurface near the damaged buildings using a 50 MHz unshielded antenna. The seismic refraction and reflection profiles show that the village is underlain by 0-4 m of loose sand, 4-10 m of fractured calcrete, and up to 50 m of fractured silcrete, with the groundwater table at 10-15 m. The GPR images show that the damaged houses sit on thick sand, which cushions them against severe ground vibration. The houses were found to have suffered more damage on the superstructure and this is possibly due to ground vibration amplification at low frequencies of 30-40 Hz.

Detecting fold structures at the southern flank of the Neogene Vienna Basin in eastern Austria using near-subsurface geophysical methods

2015 ◽  
Vol 3 (3) ◽  
pp. SY13-SY26 ◽  
Author(s):  
Werner Chwatal ◽  
Hermann Häusler ◽  
Ingrid Kreutzer ◽  
Jürgen Scheibz ◽  
Friedrich Steirer
Keyword(s):  
Geophysical Methods ◽  
Vienna Basin ◽  
Resistivity Tomography ◽  
Investigation Area ◽  
Uppermost Layer ◽  
Geophysical Investigations ◽  
Eastern Austria ◽  
Almost All ◽  
Ground Penetrating ◽  
Southern Flank

At the southern flank of the Vienna Basin, spectacular fold structures were exposed in the former Steinbrunn sand pit. The succession of Upper Pannonian age consists of decimeter- to meter-thick sandy, silty, and clayey beds, which are overlain by sandstone beds. Previously, these fold structures have been interpreted differently as of tectonic but also gravitational origin. To gain a more detailed insight into the 3D distribution and orientation of the folds, high-resolution geophysics such as electrical resistivity tomography (ERT), ground-penetrating radar (GPR), and electromagnetics (EM) were applied for mapping the subsurface in the surroundings of the sand pit. The EM results found that the uppermost layer was more clayey northwest and sandier southeast of the sand pit. To directly compare ERT and GPR results with the lithology of the fold structures observed in the sand pit, reference profiles behind the wall of the sand pit were performed. Both methods clearly revealed fold structures parallel to the folded Pannonian strata of the outcrop. Although the GPR data displayed boundaries between sandy and clayey sediments, and thus clearly imaged the fold geometry of the succession, the resistivities in the ERT profiles portrayed a smoother image. Almost all GPR profiles revealed wavelike structures with axes in the southeastern direction and dome-shaped structures with axes in the southwestern direction, deepening toward the west. This pattern was comparable with the sections of rounded buckle folds, which underlie almost the entire investigation area of approximately [Formula: see text] in size. Compared with fold structures as documented from a neighboring abandoned coal mine, the geophysical investigations around the Steinbrunn sand pit supported the hypothesis of a tectonic origin, formed by simple buckling of a planar surface and its confining volume along the southeastern flank of the Vienna Basin in Plio/Pleistocene times.

Detection of the near surface structure through a multidisciplinary geophysical approach

2011 ◽  
Vol 3 (4) ◽  
Author(s):  
Eleni Kokinou ◽  
Apostolos Sarris
Keyword(s):  
Seismic Refraction ◽  
Geophysical Methods ◽  
Near Surface ◽  
The Road ◽  
Resistivity Method ◽  
Conductivity Anomalies ◽  
2D Resistivity Imaging ◽  
Limestone Rock ◽  
Ground Penetrating ◽  
2D Resistivity

AbstractThe present survey aimed to image the subsurface structure, including karstic voids, and to evaluate the extent of the heterogeneities that can result in potentially dangerous collapse of road segments overlying these features. A multidisciplinary geophysical approach (seismic refraction, frequency domain electromagnetic and ground penetrating radar) in combination with a detailed geological survey indicated the presence of tectonic faults as well as velocity and conductivity anomalies along an old road within the area of Akrotiri at Chania (Crete). Due to the presence of subsurface fuel pipes, perpendicular to the direction of the road, 2D resistivity imaging was excluded from the applied geophysical methods.Interpretation of the geophysical data revealed that the section of the road investigated overlies prominent voids attributed mostly to karst features. The conductivity and velocity anomalies are interpreted to indicate an area where the host limestone rock has been downthrown by faulting and associated karstification. The continuation of this fault zone was observed in the slope of the road during later excavations. Interpretation, using geographic information systems (GIS) to integrate data, allowed these controls and relationships to be understood and monitored. The above methodology was proved successful for areas where the application of resistivity method is not possible.

scholarly journals Shallow geophysical techniques to investigate the groundwater table at the Great Pyramids of Giza, Egypt

2019 ◽  
Vol 8 (1) ◽  
pp. 29-43 ◽  
Author(s):  
Sharafeldin M. Sharafeldin ◽  
Khalid S. Essa ◽  
Mohamed A. S. Youssef ◽  
Hakan Karsli ◽  
Zein E. Diab ◽  
...  
Keyword(s):  
Water Table ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Groundwater Table ◽  
Near Surface ◽  
Groundwater Aquifer ◽  
Geophysical Surveys ◽  
Subsurface Layers ◽  
Average Water ◽  
Ground Penetrating

Abstract. The near-surface groundwater aquifer that threatened the Great Pyramids of Giza, Egypt, was investigated using integrated geophysical surveys. A total of 10 electrical resistivity imaging, 26 shallow seismic refraction, and 19 ground-penetrating radar surveys were conducted in the Giza Plateau. Collected data for each method were evaluated by state-of-the art processing and modeling techniques. A three-layer model depicts the subsurface layers and better delineates the groundwater aquifer and water table elevation. The resistivity of the aquifer layer and seismic velocity vary between 40 and 80 Ωm and between 1500 and 2500 m s−1, respectively. The average water table elevation is about +15 m, which is safe for the Great Sphinx, but it is still subjected to potential hazards from the Nazlet El-Samman suburb where the water table elevation reaches 17 m. A shallower water table at the Valley Temple and the tomb of Queen Khentkawes, with a low topographic relief, represents severe hazards. It can be concluded that a perched groundwater table is detected in the elevated topography to the west and southwest that might be due to runoff and capillary seepage.

Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco

2020 ◽  
Vol 25 (3) ◽  
pp. 415-423
Author(s):  
Ahmed Lachhab ◽  
El Mehdi Benyassine ◽  
Mohamed Rouai ◽  
Abdelilah Dekayir ◽  
Jean C. Parisot ◽  
...  
Keyword(s):  
Heavy Metals ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Low Frequency ◽  
Electrical Current ◽  
P Wave ◽  
Low Resistivity ◽  
Refraction Tomography ◽  
Geophysical Surveys

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

Application of geophysical methods for the investigation of the large gravitational mass movement of Séchilienne, France

2005 ◽  
Vol 42 (4) ◽  
pp. 1105-1115 ◽  
Author(s):  
O Meric ◽  
S Garambois ◽  
D Jongmans ◽  
M Wathelet ◽  
J L Chatelain ◽  
...  
Keyword(s):  
Rock Mass ◽  
Mass Movement ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Time Lapse ◽  
Gravitational Mass ◽  
Electrical Tomography ◽  
Refraction Tomography ◽  
Geophysical Surveys ◽  
Geophysical Techniques

Several geophysical techniques (electromagnetic profiling, electrical tomography, seismic refraction tomography, and spontaneous potential and seismic noise measurement) were applied in the investigation of the large gravitational mass movement of Séchilienne. France. The aim of this study was to test the ability of these methods to characterize and delineate the rock mass affected by this complex movement in mica schists, whose lateral and vertical limits are still uncertain. A major observation of this study is that all the zones strongly deformed (previously and at present) by the movement are characterized by high electrical resistivity values (>3 kΩ·m), in contrast to the undisturbed mass, which exhibits resistivity values between a few hundred and 1 kΩ·m. As shown by the surface observations and the seismic results, this resistivity increase is due to a high degree of fracturing associated with the creation of air-filled voids inside the mass. Other geophysical techniques were tested along a horizontal transect through the movement, and an outstanding coherency appeared between the geophysical anomalies and the displacement rate curve. These preliminary results illustrate the benefits of combined geophysical techniques for characterizing the rock mass involved in the movement. Results also suggest that monitoring the evolution of the rock mass movement with time-lapse geophysical surveys could be beneficial.Key words: gravitational movement, geophysical methods, Séchilienne.

scholarly journals Geophysical identification of voids and loosened zones in the shallow subsurface of post-mining areas

2018 ◽  
Vol 66 ◽  
pp. 01001 ◽  
Author(s):  
Zenon Pilecki
Keyword(s):  
Rock Mass ◽  
Geophysical Methods ◽  
Ore Deposits ◽  
Hard Coal ◽  
Shallow Subsurface ◽  
Mining Areas ◽  
Upper Silesian Coal Basin ◽  
Discontinuous Deformation ◽  
Ground Penetrating ◽  
Terrain Surface

The shallow historic exploitation of Zn-Pb/Fe ore deposits as well as hard coal has generated many discontinuous deformations on the terrain surface in the Upper Silesian Coal Basin/Poland. Discontinuous deformations occur in different forms as sinkholes, synclines, cracks, faults or ditches. The basic cause of their occurrence is the presence of void and loosened zones in the shallow subsurface. If the appropriate conditions arise, the sinkhole process begins to move upwards and may cause a discontinuous deformation on the terrain surface. Typically, geophysical methods are used for void and loosened zone identification. The most effective methods are gravimetric, seismic, electric resistivity and ground penetrating radar (GPR). Geophysical testing, requires distinct changes in the physical properties in the rock mass. The identified geophysical anomalies should be verified by control borehole and borehole tests to confirm the presence of the void and loosened zones in the rock mass. The results of control drilling and borehole tests determine the need to apply treatment works. In order to assess the threat of the occurrence of discontinuous deformations in the areas of historical shallow mining in Upper Silesia, a classification system based on geophysical tests has also been developed.

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