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(a) Illustration of the Äspö Hard Rock Laboratory in the Simpevarp peninsula, Sweden. The study tunnel (TAS04) is situated at a depth of 410 m. Figure modified from SKB (2016), courtesy of SKB, Illustrator: Jan Rojmar. (b) Orthophotography of the tunnel floor showing the geological limit between fine -grained granite (to the left), Äspö diorite and Ävrö granodiorite (to the right) indicated by yellow and blue dashed lines, shallow pre -existing boreholes represented by black dots with oxidation (orange traces) and concrete plates delimited by red dashed lines. The three new boreholes (BH1, BH2 and BH3 indicated by red circles with crosses) were drilled in the granitic formation with locations chosen based on the GPR results. (Figure size: 2 column fitting; Colors: yes)
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Identifying fractures in the subsurface is crucial for many geomechanical and hydrogeological applications. Here, we assess the ability of the Ground Penetrating Radar (GPR) method to image open fractures with sub-mm apertures in the context of future deep disposal of radioactive waste. GPR experiments were conducted in a tunnel located 410 m below...
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... (EM) waves with wavelengths on the m-scale respond to fractures with sub-millimetric aperture because of the strong contrast in electrical properties between the fracture filling and the surrounding rock matrix and because of multiple internal reflections between the fracture walls generating wavelet interferences (the thin-bed response) (Bradford & Deeds, 2006;Deparis & Garambois, 2008;Grégoire & Hollender, 2004;Sassen & Everett, 2009;Shakas & Linde, 2015). At repository depth (~400-600 m below sea level), the fracture aperture can be very small and it is not yet clear whether observed GPR reflections in such an environment are primarily related to water-filled fractures and not to other geological interfaces (e.g., dike intrusion, In this contribution, we present a 3-D GPR imaging experiment performed at 410 m depth in the Äspö Hard Rock Laboratory, Sweden (Figure 1a). The GPR data h been migrated to form a 3-D ave network of reflectors, hereafter, named GPR fractures. ...
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... GPR data h been migrated to form a 3-D ave network of reflectors, hereafter, named GPR fractures. After the GPR experiment, three 9-m deep boreholes were drilled in the zone (Figure 1b), mapped with televiewer logging, and hydraulically tested to ground-truth the GPR results. J o u r n a l P r e -p r o o f 5 Our main aims are to address the following questions: ...
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... Äspö Hard Rock Laboratory (HRL) is an underground research facility below the island of Äspö located approximately 300 km south of Stockholm on the peninsula of Simpevarp surrounded by the Baltic Sea (Figure 1a). It was constructed in 1986(Cosma et al., 2001) by the Swedish Nuclear Fuel and Waste Management Company (SKB) as a R&D site to develop new methodologies and technologies to build the know-how needed to construct a hard rock repository for nuclear waste. ...
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... was constructed in 1986(Cosma et al., 2001) by the Swedish Nuclear Fuel and Waste Management Company (SKB) as a R&D site to develop new methodologies and technologies to build the know-how needed to construct a hard rock repository for nuclear waste. It contains a main tunnel of 3.6 km length and several side-tunnels extending from the surface down to 450 m depth (Figure 1a) (SKB, 2016). The geology is mainly composed of fractured granitic rocks that are more than 1.7 billion years old ( Cosma et al., 2001). ...
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... tunnel is 36 m long, 4.2 m wide and 5.3 m high. Its geology is composed by three main rock types: fine-grained granite, Äspö diorite and Ävrö granodiorite, with some pegmatite veins (Figure 1b) (Ericsson et al., 2015;Ericsson et al., 2018). Geotechnical (check of drilling and charging), geological (fracture J o u r n a l P r e -p r o o f 6 mapping), geophysical (surface GPR) and hydrogeological (42 borehole drillings of 2 m depth and hydraulic tests) investigations were used to characterize superficial fractures induced by the blasting. ...
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... was found that the excavation-damage zone (EDZ) was 0.5 m thick ( Ericsson et al., 2015;Ericsson et al., 2018). The EDZ was removed by cutting and sawing the tunnel floor with a diamond wire along 20 m of the tunnel length; it is in the resulting very flat area that our GPR measurements were performed ( Figure 1b). ...
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... of technical constraints, the boreholes had to be separated by at least 3 m and located at a certain distance away from the 42 shallow pre-existing boreholes and concrete plates. The final locations of the boreholes are seen in Figure 1b. ...
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... boreholes with the transmissive zones highlighted are plotted together with crossing migrated 450 MHz GPR slices in Figure 10. Strong and large sub-horizontal reflections traversing the boreholes are highlighted. ...
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... the position and orientation information, we could implement the fractures into our database, describing the fractures as disks centered on the boreholes. This enables a detailed assessment of the agreement between the GPR reflections and the fractures seen in the core logging (Figure 11, Figure 12, Figure 13). ...
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... the position and orientation information, we could implement the fractures into our database, describing the fractures as disks centered on the boreholes. This enables a detailed assessment of the agreement between the GPR reflections and the fractures seen in the core logging (Figure 11, Figure 12, Figure 13). ...
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... the position and orientation information, we could implement the fractures into our database, describing the fractures as disks centered on the boreholes. This enables a detailed assessment of the agreement between the GPR reflections and the fractures seen in the core logging (Figure 11, Figure 12, Figure 13). ...
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... present the fracture positions in terms of depth, orientation (strike and dip) and opening (sealed or open) using tadpole plots (Figure 11a, Figure 12a and Figure 13a). This interpretation is based on televiewer and core inspection in the laboratory. ...
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... present the fracture positions in terms of depth, orientation (strike and dip) and opening (sealed or open) using tadpole plots (Figure 11a, Figure 12a and Figure 13a). This interpretation is based on televiewer and core inspection in the laboratory. ...
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... present the fracture positions in terms of depth, orientation (strike and dip) and opening (sealed or open) using tadpole plots (Figure 11a, Figure 12a and Figure 13a). This interpretation is based on televiewer and core inspection in the laboratory. ...
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... interpretation is based on televiewer and core inspection in the laboratory. Each borehole is represented by a cylinder divided into 1-m sections used for hydraulic measurements with indication of GPR reflections crossing the borehole and the sections with recorded outflows above the measurements limit (Figure 11b, Figure 12b and Figure 13b). Fence diagrams are used to highlight strong GPR reflections along the boreholes and to compare them with fractures seen on cores (Figure 11c,d, Figure 12c,d and Figure 13c). ...
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... interpretation is based on televiewer and core inspection in the laboratory. Each borehole is represented by a cylinder divided into 1-m sections used for hydraulic measurements with indication of GPR reflections crossing the borehole and the sections with recorded outflows above the measurements limit (Figure 11b, Figure 12b and Figure 13b). Fence diagrams are used to highlight strong GPR reflections along the boreholes and to compare them with fractures seen on cores (Figure 11c,d, Figure 12c,d and Figure 13c). ...
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... interpretation is based on televiewer and core inspection in the laboratory. Each borehole is represented by a cylinder divided into 1-m sections used for hydraulic measurements with indication of GPR reflections crossing the borehole and the sections with recorded outflows above the measurements limit (Figure 11b, Figure 12b and Figure 13b). Fence diagrams are used to highlight strong GPR reflections along the boreholes and to compare them with fractures seen on cores (Figure 11c,d, Figure 12c,d and Figure 13c). ...
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... borehole is represented by a cylinder divided into 1-m sections used for hydraulic measurements with indication of GPR reflections crossing the borehole and the sections with recorded outflows above the measurements limit (Figure 11b, Figure 12b and Figure 13b). Fence diagrams are used to highlight strong GPR reflections along the boreholes and to compare them with fractures seen on cores (Figure 11c,d, Figure 12c,d and Figure 13c). To do so, we superimposed fractures from core log data on the GPR sections crossing the borehole, and observed the match based on fracture depth, strike and dip. ...
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... borehole is represented by a cylinder divided into 1-m sections used for hydraulic measurements with indication of GPR reflections crossing the borehole and the sections with recorded outflows above the measurements limit (Figure 11b, Figure 12b and Figure 13b). Fence diagrams are used to highlight strong GPR reflections along the boreholes and to compare them with fractures seen on cores (Figure 11c,d, Figure 12c,d and Figure 13c). To do so, we superimposed fractures from core log data on the GPR sections crossing the borehole, and observed the match based on fracture depth, strike and dip. ...
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... the transmissive region, all open fractures have dips exceeding 60°. Consequently, no GPR fracture was identified (Figure 10, 13). ...
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... total of 3513 fracture traces have been observed on tunnel walls and stored in the SKB database together with their fracture characteristics: trace length, orientation (dip and strike), aperture, mineral filling and fracture shape. The trace length density distribution per unit surface is shown in Figure 14. It exhibits two different scaling behaviors above and below 3.6 m even after removing censoring and edge biases (Laslett, 1982), that is, fracture traces smaller than 1 m and larger than 8.6 m. ...
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... stereonet of fracture trace orientation poles (i.e., one pole per fracture) is given in Figure 15a. It shows three main orientation poles: two vertical ones trending NW and NE, and one horizontal. ...
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... the density and orientation characteristics, the 3-D distribution of fracture sizes is then calculated (Figure 14), which gives the number of fractures per unit area, per unit pole angle and per unit volume. ...
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... comparison with the orientation distribution deduced from fracture traces shows that the GPR fracture orientation (picked from all frequencies) corresponds to the sub-horizontal poles (dip <35°) of the fracture traces (Figure 15b). Since the GPR has imaged the fractures with area from 1 to 10m 2 and dip less than 35°, we compared the same fracture population in the 3-D statistical model. ...
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... the GPR has imaged the fractures with area from 1 to 10m 2 and dip less than 35°, we compared the same fracture population in the 3-D statistical model. We first estimated the detection capacity of GPR by dividing the observed density ( total surface by unit of volume per dip range) with the 3-D modeled density calculated in the section 6.2 ( Figure 16a). The observed fluctuations between 0 and 20-25° may be due to the limited number GPR fractures, but there is a clear cut-off of detection above 25° even if some GPR fractures are detected between 25-35°. ...
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... to the GPR fracture dip cut-off, the area distribution of GPR fractures have been calculated (e.g., number of fractures per unit area and unit volume) for all fractures dipping less than 25° ( Figure 16b). In a log-log plot, it appears to follow the same power-law trend as the 3-D modeled area distribution. ...
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... dashed line represents the plot of the modeled distribution area for fractures in the same dip range considering that 80% of the actual fractures are detected. A remarkable result is that it fits well the GPR data within the data uncertainties (Figure 16b). The fact that the fracture area distribution in the range 1-10 m 2 is similar to the 3-D area distribution modeled by extrapolating the tunnel fracture traces means that the GPR is able to image the fractures in proportion to the length distribution trend (no size selection). ...
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... this, we run 3-D simulations where fracture networks are generated with a power-law size distribution and nonuniform orientations, and fracture traces are identified on the wall of a cylindric tunnel. We then calculate the trace size distributions, fit them with a power law, and compare the fit with Piggott's formulae ( Figure A 1). The ratio between the power-law fits and Piggott's formulae reaches 1.5, 1.2, ...
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... Ground Penetrating Radar (GPR) from geophysical methods provides precise information about the location of near-surface structures underground. Thus, it is widely used in geotechnical and mining applications such as determination of fracture orientation in marble quarries (Grandjean and Gourry 1996;Kadioglu 2008;Sambuelli and Calzoni 2010;Benedetto et al. 2012;Seren et al. 2012;Ogretmen and Seren 2014;Rizzo et al. 2019;Tandon et al. 2021;Wu et al. 2021;Molron et al. 2020Molron et al. , 2021Zhang et al. 2022;Liu et al. 2023). 2D mapping of faults or fractures and rockfall protection projects are also used (Benson 1995;Toshioka et al. 1995;Stevens et al. 1995;Grasmueck 1996;Demanet et al. 2001;Rashed et al. 2003;Pipan et al. 2003;Grasmueck et al. 2005;Jeannin et al. 2006;Roch et al. 2006;Walton et al. 2015;Arosio 2016;Seung-Ho Baek et al. 2017;Sibul et al. 2017). ...
The aim of this study is to investigate the rockfall potential of the steep rock slope above the Sumela Monastery (Trabzon, Türkiye) by using Ground Penetrating Radar (GPR) and surface fracture analysis on discontinuity. In this context, studies were carried out on 10 risky blocks determined after the investigations made by a team of industrial mountaineering and observations on the orthophotos. The discontinuity analysis data on the rock masses containing of mainly andesites and basalts were combined with discontinuities observed in the ground penetrating radar sections (radargrams) and the risk status of the blocks was revealed by using the location and characteristics of the dominant discontinuities. By using GPR data, discontinuities with 4 main sets were detected in 3 blocks at a depth of 2.0–2.5 m from the surface and the loose rocks were removed from the slopes using a combination of manual and mechanical techniques, including the use of lifting jacks and jackhammers, as well as explosives. In another block where GPR measurements were taken, a main fracture was detected from the surface to a depth of 2 m, but the continuity of the fracture to a deeper depth was not observed. Thus, this block was reinforced together by wrapping them with steel nets. Ground penetrating radar measurements could not be taken from the other six blocks because they did not have smooth surfaces. The stability of these blocks, which are smaller than the others, was assessed using observational data collected in situ by industrial climbers. In addition, the monastery was opened to visitors after the other small blocks on the slope that were at risk of falling were dropped. It has been demonstrated that fracture-crack systems of rocks on steep and weathered rock slopes, which are difficult to apply in rock engineering studies, can be successfully visualized using GPR measurement.
... These acquisitions typically involve surveying along closely spaced parallel survey lines to gain a more comprehensive understanding of near-surface structures [3]. The utilization of 3D GPR data has become increasingly common for various applications, including archaeological site investigation (e.g., [4,5]), bedrock fracture mapping (e.g., [3,6]), glacier drainage network imaging (e.g., [7,8]), transportation infrastructure characterization (e.g., [9,10]), and animal burrow mapping (e.g., [11,12]). ...
... This ensures that the moveout of diffraction events is properly sampled in the time-space domain. While such data are of extremely high quality and permit high-resolution detailed images of subsurface structure in 3D (e.g., [6,13]), the required close line spacing makes it impractical in many cases to acquire them [14]. For 100 MHz center-frequency data in a soil having a radar velocity of 0.1 m/ns, for example, a sample spacing of 0.25 m is required for the full-resolution conditions to be satisfied. ...
Ground-penetrating radar (GPR) is a popular geophysical tool for mapping the underground. High-resolution 3D GPR data carry a large amount of information and can greatly help to interpret complex subsurface geometries. However, such data require a dense collection along closely spaced parallel survey lines, which is time consuming and costly. In many cases, for the sake of efficiency, a choice is made during 3D acquisitions to use a larger spacing between the profile lines, resulting in a dense measurement spacing along the lines but a much coarser one in the across-line direction. Simple interpolation methods are then commonly used to increase the sampling before interpretation, which can work well when the subsurface structures are already well sampled in the across-line direction but can distort such structures when this is not the case. In this work, we address the latter problem using a novel multiple-point geostatistical (MPS) simulation methodology. For a considered 3D GPR dataset with reduced sampling in the across-line direction, we attempt to reconstruct a more densely spaced, high-resolution dataset using a series of 2D conditional stochastic simulations in both the along-line and across-line directions. For these simulations, the existing profile data serve as training images from which complex spatial patterns are quantified and reproduced. To reduce discontinuities in the generated 3D spatial structures caused by independent 2D simulations, the target profile being simulated is chosen randomly, and simulations in the along-line and across-line directions are performed alternately. We show the successful application of our approach to 100 MHz synthetic and 200 MHz field GPR data under multiple decimation scenarios where survey lines are regularly deleted from a dense 3D reference dataset, and the corresponding reconstructions are compared with the original data.
... Their findings indicated that ground-penetrating radar is an effective tool for solving the problem of deep gold mining. In 2020, Molron et al. [17] evaluated the detection capability of GPR for cracks. Their results indicated that GPR imaging can effectively detect open sub-horizontal fractures with submillimeter apertures. ...
Fracture zones in front of tunnel faces can easily cause falling blocks and landslides during the construction process. Using seismic waves and ground-penetrating radar (GPR) data, we extracted the features of fracture zones and achieved the advanced prediction of tunnel fracture zones. The energy variation in the reflected waves propagated by seismic waves at interfaces with different impedances of contact waves was found to manifest as positive and negative reflections, and the amplitude of reflected signals within the fracture zone areas thus increased. We designed a superimposed velocity spectrum, divided the areas of variation in wave velocity, and constructed the three-dimensional spatial distribution of the tunnel fracture zones. Based on the phase change, increase in amplitude, and increase in the center-frequency characteristics of the one-dimensional time waveform of the electromagnetic waves in the fault zone area (A-scan), we located the characteristic points of the fracture zones and observed the occurrence of in-phase axis misalignment in two-dimensional scanning (B-scan). We then implemented the identification of fracture zones. This method predicted the fractured area in the rock surrounding the Liangwangshan Tunnel, and during the tunnel excavation, the fracture zones appeared in the recognition area.
... In recent decades, seismic data combined with core and optical televiewer images have been used to analyze the structure and degree of development of fractures in sedimentary basins [17,20]. When studying the effect of fractures in lower Tertiary sandstone on the leakage of fluid in the North Sea Basin, Løseth et al. [21][22][23] identified the vertical discontinuity zone in seismic sections and discussed its relationship with seismic anomalies. ...
... This constant movement led to multiple stages of landslides in the Miocene [39]. Furthermore, the basin experienced a period of post-rift rapid thermal subsidence during the Miocene, generating overpressurization phenomena [20], diapirs, gas chimneys, and hydraulic fractures. These basin conditions were favorable for the migration and accumulation of complex oil and gas. ...
The Qiongdongnan Basin (QDNB), located in the north of the South China Sea, is a Cenozoic rift basin with abundant oil and gas resources. Large flake hydrates have been found in the core fractures of Quaternary formations in the deep-water depression of the QDNB. In order to understand the spatial distribution patterns of these fractures, their geneses in sedimentary basins, and their influences on gas migration and accumulation, such fractures have been observed using high-resolution 3D seismic images and visualization techniques. Four types of fractures and their combinations have been identified, namely bed-bounded fractures/microfaults, unbounded fractures, fracture bunches, and fracture clusters. Bed-bounded fractures/microfaults are mainly short and possess high density; they have developed in mass transport depositions (MTDs) or Meishan and Sanya Formations. The unbounded fractures/microfaults that occur in Miocene–Pliocene formations are mainly long and discrete, and are dominantly caused by strong tectonic movements, the concentration of stress, and sustained intense overpressure. The fracture bunches and fracture clusters that occur in Oligocene–Early Miocene formations have commonly developed with the accumulation of large numbers of fractures and may be related to the release of pressure, diapirs, and basement fault blocks (228.9 ± 1 Ma). In this study, six fluid charging or leakage models are proposed based on distinct fracture types, assuming the uniform conductivity of each fracture. In a 3D space view, a vertical decrease in the fracture scale (number or density) will more likely result in gas supply than dispersion, thus promoting the accumulation of gas in the reservoirs. Nevertheless, the fractures above the Bottom Simulating Reflect (BSR)/seismic anomaly are excessively developed, and bed-bounded fractures within a particular layer, such as MTDs, can easily cause seabed leakage. These results are useful for explaining the vertical migration of gas/fluids in areas and formations with less developed gas chimneys, faults, diapirs, and other structures, particularly in post-rifting basins.
... 현재 원자력 발전을 하는 많은 국가에서 URL을 건설하 여 다양한 연구를 수행하고 있다. 대표적으로는, 핀란드의 Onkalo (Heikkinen et al., 2021;Follin et al., 2021), 스웨덴 의 Äspö Hard Rock Laboratory(HRL) (Molron et al., 2020;Walton et al., 2015), 스위스의 Mont Terri URL (Cosma and Enescu, 2001;Manukyan et al., 2012)과 Grimsel Test Site(GTS) (Giertzuch et al., 2020), 미국의 Yucca 산 URL (Ramirez et al., 1997), 프랑스의 Tournemire URL (Lopes et al., 2019a;Cosenza et al., 2007), 일본의 Mizunami (Wu et al., 2021;Suzuki et al., 2004) (Kwon and Kim, 2017). ...
... 천연 방벽은 처분 시 설을 둘러싼 자연 암반과 토양의 전반적인 천연 지하구조 를 말한다. 이와 달리 공학적 방벽은 폐기물을 밀봉하기 위한 인공물로서 일반적으로 폐기물을 담은 처분용기(Canister), 완충재(Buffer), 뒷채움재(Backfill)가 주로 검토되고 있다 (Martin et al., 2007) Lesparre et al., 2013;Walton et al., 2015), 암반 균 열 분포 및 투수성 평가(e.g., Cosma and Enescu, 2001;Molron et al., 2020;Wu et al., 2021), 지하수 변화 모니터 링(e.g., Giertzuch et al., 2020;Manukyan et al., 2012;Baek et al., 2017;Maineult et al., 2013), 열응력 작용 평가 (e.g., Ramirez et al., 1997;Siren et al., 2015;Cosenza et al., 2007) (Ramirez et al., 1997;Wu et al., 2021). (Gibert et al., 2006), 다른 물리탐사법과 함께 사용하여 복합 탐사를 수행하기도 한다 (Suzuki et al., 2004;Walton et al., 2015). ...
... The GPR method has proved its ability as a valuable geophysical technique to enter the quarrying and construction industries to map the fractures at different stages: during exploration and extraction in quarries to reduce the production costs and wastes [6,7,[10][11][12][18][19][20], and for post-production demands to repair and restore the stones [21]. From various research studies that use the GPR method to study rock fractures, we can mention the theoretical models and laboratory experiments used to characterize rock discontinuities [18][19][20][21][22][23][24][25][26], in situ GPR surveys to detect fractures at different zones of quarries or in historical buildings [7,10,12,15,22,[27][28][29][30], and 3D GPR acquisitions for 3D reconstruction of the fractures and other features [11,12,[31][32][33][34]. Most of these studies are focused on the application of the GPR method to detect rock/stone fractures to optimize the quarrying activities and to preserve the constructions. ...
The objective of this study is to test the feasibility of time-lapse GPR measurements for the quality control of repairing operations (i.e., injections) on marble blocks. For the experimental activities, we used one of the preferred repairing fillers (epoxy resin) and some blocks from one of the world’s most famous marble production area (Carrara quarries in Italy). The selected blocks were paired in a laboratory by overlapping one over the other after inserting very thin spacers in order to simulate air-filled fractures. Fractures were investigated with a 3 GHz ground-penetrating radar (GPR) before and after the resin injections to measure the amplitude reduction expected when the resin substitutes the air. The results were compared with theoretical predictions based on the reflection coefficient predicted according to the thin bed theory. A field test was also performed on a naturally fractured marble block selected along the Carrara shore. Both laboratory and field tests validate the GPR as an effective tool for the quality control of resin injections, provided that measurements include proper calibration tests to control the amplitude instabilities and drift effects of the GPR equipment. The method is accurate enough to distinguish the unfilled fractures from the partially filled fractures and from the totally filled fractures. An automatic algorithm was developed and successfully tested for the rapid quantitative analysis of the time-lapse GPR profiles collected before and after the injections. The whole procedure is mature enough to be proposed to the marble industry to improve the effectiveness of repair interventions and to reduce the waste of natural stone reserves.
... Nevertheless, recent advances shed light on some innovative solutions to tackle those problems. For fractured aquifers, recent studies in fracture modeling such as realistic flow characterization and mechanical coupling using discrete fracture networks Maillot et al., 2016;Lei et al., 2017), innovative inverse methodologies (Pieraccini, 2020), and characterization techniques (Dorn et al., 2011(Dorn et al., , 2012a(Dorn et al., , 2013Molron et al., 2020Molron et al., , 2021 Table 2B2) pushed forward our ability to account for the complexity of fractured media. More generally, cloud computing combined with increasing computational power is one avenue to allow modeling the subsurface at a higher 4D resolution for an increasing number of applications in the future (Hayley, 2017;Kurtz et al., 2017). ...
Essentially all hydrogeological processes are strongly influenced by the subsurface spatial heterogeneity and the temporal variation of environmental conditions, hydraulic properties, and solute concentrations. This spatial and temporal variability generally leads to effective behaviors and emerging phenomena that cannot be predicted from conventional approaches based on homogeneous assumptions and models. However, it is not always clear when, why, how, and at what scale the 4D (3D + time) nature of the subsur-face needs to be considered in hydrogeological monitoring, modeling, and applications. In this paper, we discuss the interest and potential for the monitoring and characterization of spatial and temporal variability, including 4D imaging, in a series of hydrogeological processes: (1) groundwater fluxes, Published by Copernicus Publications on behalf of the European Geosciences Union. 256 T. Hermans et al.: Advancing measurements of heterogeneity and dynamic processes (2) solute transport and reaction, (3) vadose zone dynamics, and (4) surface-subsurface water interactions. We first identify the main challenges related to the coupling of spatial and temporal fluctuations for these processes. We then highlight recent innovations that have led to significant breakthroughs in high-resolution space-time imaging and model-ing the characterization, monitoring, and modeling of these spatial and temporal fluctuations. We finally propose a classification of processes and applications at different scales according to their need and potential for high-resolution space-time imaging. We thus advocate a more systematic characterization of the dynamic and 3D nature of the subsurface for a series of critical processes and emerging applications. This calls for the validation of 4D imaging techniques at highly instrumented observatories and the harmonization of open databases to share hydrogeological data sets in their 4D components .
... The detection of fractures of various scale, from millimetric up to a decametric scale, represents another topic widely researched with GPR, where its geometrical reconstruction capability has made it a valuable tool for characterizing mining sites and rock masses, improving quarries and extraction processes, and determining unstable rock slopes [241][242][243][244]. Another successful application of GPR within this domain is the determination of fracture openings and fillings [245][246][247], crucial for several environmental and engineering applications, including the accessibility of geothermal energy. Fractures and faults represent the primary conduits for the transport of heated fluids needed for geothermal energy, and therefore a detailed knowledge on the fracture network is essential to increase the efficiency of the energy-transition process [248][249][250][251][252]. ...
... Table 5 provides a list of published reviews on the mentioned GPR geological applications. [245,253,286,299]. Copyright 2020/2021, Elsevier. ...
... Considering that the geophysical response of complex geological bodies exhibits different physical properties due to the fact that such horizons are composed of a combination of layers with contrasting properties and are caused by a host of geological, geotechnical, and climatic factors, a multidisciplinary approach is often recommended to gather an in-depth understanding of the features. Typically, this involves the GPR technique as [245,253,286,299]. Copyright 2020/2021, Elsevier. ...
Thanks to its non-destructive, high-resolution imaging possibilities and its sensitivity to both conductive and dielectric subsurface structures, Ground-Penetrating Radar (GPR) has become a widely recognized near-surface geophysical tool, routinely adopted in a wide variety of disciplines. Since its first development almost 100 years ago, the domain in which the methodology has been successfully deployed has significantly expanded from ice sounding and environmental studies to precision agriculture and infrastructure monitoring. While such expansion has been clearly supported by the evolution of technology and electronics, the operating principles have always secured GPR a predominant position among alternative inspection approaches. The aim of this contribution is to provide a large-scale survey of the current areas where GPR has emerged as a valuable prospection methodology, highlighting the reasons for such prominence and, at the same time, to suggest where and how it could be enhanced even more.
... Past researchers conducted concrete investigation or assessment based on reinforced concrete slab sample prepared in laboratory environment using GPR frequency between 1.6 GHz to 2.6 GHz (Lakshmi et al., 2016;Molron et al., 2020;Rathod et al., 2019;Razak et al., 2015;Sangoju, 2017;Zaki et al., 2018) . In Malaysia, there is less published research on SFRC examination utilising GPR. ...
Ground Penetrating Radar (GPR) is a real-time instrument designed as an NDT technique that is currently widely used for assessment of concrete structure in the construction field and civil engineering application. The growing demand for concrete with better performance characteristics in compressive and flexural strength has introduced to application steel fibre in concrete. This study is to assess the location steel fibre in Steel Fibre Reinforced Concrete (SFRC) by using GPR, determine compressive and flexural strength of SFRC and correlation between compressive and flexural strength conducted by using 3D analysis Response Surface Methodology (RSM) using software Design Expert Version 11. A proposed sample model prepared in laboratory condition in order to assess the steel fibre location, compressive and flexural strength of SFRC. The sample consists of beam size 100mm x 100mm x 500mm length, using different steel fibre fraction volume of 0.5%, 1.0% and 1.5% mixed with High Performance Concrete (HPC) grade C60 mix. The sample shall be scanned and tested using GPR equipment, Rebound Hammer Test and 3000kN compression test machine for compressive strength and UTM-1000 machine for flexural strength. The GPR reading, Rebound Hammer Test, Compressive and Flexural Strength Test shall be taken at 7 days, 21 days, and 28 days. The result for the SFRC sample beam shows a hazy image like a radio static wave and multiple hyperbola overlapping each other and the hazy image is more for 1.5% steel fibre fraction volume. The optimum value of 0.5% steel fibre fraction volume in terms of compressive strength, optimum value of 1.5% steel fibre volume fraction in terms of flexural strength. Analysis of variance (ANOVA) response steel fibre for sum of square value is 9.78 and F-value is 9.98. The correlation for compressive and flexural strength shows R2 value of 0.8694 and the model is fit. The 3D analysis RSM model suggests 1.5% steel fibre fraction volume is the optimum value and more likely to improve the compressive and flexural strength of SRFC with HPC grade C60 mix.
... The characterization of fractured aquifers remains particularly complicated. In recent years, many efforts have been made to characterize fractures (e.g., Guevara-Mansilla et al., 2020;Molron et al., 2020;Mézquita González et al., 2021), to model them using discrete fracture network (Maillot et al., 2016;Medici et al., 2021) or to include those characteristics in calibration processes (Ringel et al., 2019;Medici et al., 2021). However, the identification of individual fractures can only be made locally using borehole data or high-resolution geophysical methods such as ground penetrating radar (Molron et al., 2020). ...
... In recent years, many efforts have been made to characterize fractures (e.g., Guevara-Mansilla et al., 2020;Molron et al., 2020;Mézquita González et al., 2021), to model them using discrete fracture network (Maillot et al., 2016;Medici et al., 2021) or to include those characteristics in calibration processes (Ringel et al., 2019;Medici et al., 2021). However, the identification of individual fractures can only be made locally using borehole data or high-resolution geophysical methods such as ground penetrating radar (Molron et al., 2020). For water management purposes, it is generally illusory to include every single fractures in a conceptual or numerical model of the aquifer. ...
Fractured and karst aquifers are important groundwater reservoirs and are widely used to provide drinking water to the population. Because of the presence of the fractures with varying geometry and properties providing preferential flow paths, fractured aquifers are highly heterogeneous and difficult to characterize and model. In this context, geophysical methods can provide relevant spatially distributed data about the presence of fractures, that can be further integrated in hydrological and groundwater models. In this contribution, we present a case study of a groundwater extraction site in a fractured chalk aquifer in Voort (Belgium), used for the production of drinking water. First, the presence of fractures in the vicinity of the extraction site and their orientation is imaged using electrical resistivity tomography. Based on the available data and the objectives of the study, it is chosen to model only the groundwater component and to simplify the unsaturated zone processes through an average recharge rate. Then, the detected fractures are included in the groundwater model to improve the calibration and the predictive capacity of the model. The results show that a set of parallel fractures crosses the modeled area, whose orientation is in accordance with the tectonic setting. Including these fractures in the model, a more satisfactory calibration was achieved, helping to better understand the hydrogeological behavior of the aquifer. Finally, the acquired knowledge is used to propose new management scenarios for the extraction site minimizing its impact.
