| 1. |
- Adamopoulos, Stergios, et al.
(författare)
-
Adhesive bonding of beech wood modified with a phenol formaldehyde compound
- 2012
-
Ingår i: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 70:6, s. 897-901
-
Tidskriftsartikel (refereegranskat)abstract
- Untreated (controls) and phenol–formaldehyde (PF)-modified beech wood (10 and 25 % solid content) were glued with phenol resorcinol formaldehyde (PRF) and polyvinyl acetate (PVAc). Shear strength of PRF-bonded specimens was higher than that of PVAc-bonded ones under dry and wet conditions irrespective of the pre-treatment. Under dry conditions, only PVAc-bonded specimens exhibited reduction in shear strength due to PF-modification with 25 % PF concentration as compared to the controls. PF treated wood provided inferior bonding under wet conditions with the exception of 25 % PF concentration specimens glued with PRF adhesive. Modification with PF resulted in a decrease of adhesive penetration into the porous network of interconnected cells, especially at 25 % PF concentration.
|
|
| 2. |
- Bastani, Alireza, et al.
(författare)
-
Development of bonding strength of modified birch veneers during adhesive curing
- 2016
-
Ingår i: Wood research. - 1336-4561. ; 61:2, s. 205-214
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigated the bonding strength development of furfurylated, N-methylolmelamine (NMM) modified and thermally treated birch veneers glued with hot curing phenolformaldehyde (PF) adhesive in different pressing (20, 160 s) and open assembly times (20 s, 10min). For testing, the automated bonding evaluation system ABES was used with 2 N.mm-2applied pressure at 130°C. The bonding strength of both modified and unmodified samplesincreased significantly by prolongation of the pressing time from 20 to 160 s in all cases andfor both open assembly times. A deviation was observed for the samples treated at 220°C andat 20 s open assembly time. With the exception of NMM modified veneers, bonding strengthdid not change significantly by increasing the assembly time in the case of 20 s pressing forboth modified and unmodified samples. At 160 s pressing time, extension of the assembly timedeveloped a better bonding for controls, NMM modified and thermally treated veneers at 180°C.The combination of 10 min assembly time and 160 s pressing time proved as the optimal bondingcondition for controls, NMM modified and thermally treated veneers at 180°C while the highestbonding strength was noted in 20 assembly time and 160 s pressing time for furfurylated veneers.In most of the cases modification affected negatively the bonding performance of the veneers, inparticular for furfurylated and NMM modified samples.
|
|
| 3. |
- Bastani, Alireza, et al.
(författare)
-
Effect of open assembly time and equilibrium moisture content on the penetration of polyurethane adhesive into thermally modified wood
- 2017
-
Ingår i: The journal of adhesion. - : Taylor & Francis. - 0021-8464 .- 1563-518X .- 1545-5823. ; 93:7, s. 575-583
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of wood moisture content and open assembly time on penetration of polyurethane (PU) adhesive into thermally treated Scots pine (195 and 210°C) was investigated according to effective (EP) and maximum penetration (MP) measurements using fluorescence microscopy. For samples treated at 195°C, a higher EP was noted at 8.6% equilibrium moisture content (EMC) after both assembly times (15 and 30 min) while for samples treated at 210°C, increasing wood moisture content resulted in a significant decrease in EP at 12.5% EMC after 15 min assembly time. Extending open assembly time was found to increase the EP of PU adhesive only in the case of samples treated at 195°C and with 8.6% EMC. For samples treated at both treatment temperatures and after shorter open assembly time, the highest MP observed at moderate EMC levels of 8.6 and 8.2% and the lowest at the higher EMC levels of 13.2 and 12.5%.
|
|
| 4. |
- Bastani, Alireza, et al.
(författare)
-
Gross adhesive penetration in furfurylated, N-methylol melamine-modified and heat-treated wood examined by fluorescence microscopy
- 2015
-
Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 73:5, s. 635-642
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigated the radial penetration of three conventional cold-set wood adhesives [emulsion polymer isocyanate (EPI), poly (vinyl acetate) (PVAc), one-component polyurethane (PU)] into various degrees of furfurylated and N-methylol melamine-modified (NMM) Scots pine, and heat-treated Scots pine and beech based on measurements of effective (EP) and maximum penetration (MP) from microscopic observations. EP of EPI adhesive decreased after modification with higher concentration of furfuryl alcohol while an improved penetration was recorded for PVAc into furfurylated wood. A deeper penetration was observed for all adhesives into wood treated with lower concentration of furfuryl alcohol. The EP of EPI and PU adhesives reduced after NMM treatment but it increased in the case of PVAc. In spite of reduction of EP of PU after NMM treatment, it represented a deeper penetration among all adhesives possibly due to its lower molecular weight. For Scots pine, increasing the treatment temperature improved EP of all adhesives while for beech, the EP of PU and PVAc increased largely in the case of samples treated at 195 °C. Visual analysis of fluorescence microscopy pictures provided more detailed information on modality of penetration. The results are useful for understanding the interaction among common adhesives and modified materials, and can be used in future research to explain the bonding behavior of modified wood.
|
|
| 5. |
- Bastani, Alireza, et al.
(författare)
-
Shear strength of furfurylated, N-methylol melamine and thermally modified wood bonded with three conventional adhesives
- 2017
-
Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; 12:4, s. 236-241
-
Tidskriftsartikel (refereegranskat)abstract
- The shear strength of furfurylated, N-methylol melamine (NMM) and thermally modified wood bonded with emulsion polymer isocyanate, polyvinyl acetate (PVAc), and polyurethane (PU) adhesives was examined. Furfurylation and NMM modification of Scots pine had a significant negative effect on the bonding strength with all adhesives irrespective of the treatment intensity. The obtained low-shear strength values were related to the brittle nature of the wood after modifications rather to the failure of the bondline. PVAc showed a better bonding performance with both furfurylated and NMM modified wood while the combination of furfurylated wood and PU gave the highest reduction in bonding strength (47–51%). Shear strength also decreased significantly after thermal modification in both Scots pine (36–56%) and beech (34–48%) with all adhesives. With the exception of thermally modified beech samples bonded with PU, bondline was found to be the weakest link in thermally modified wood as it was revealed by the wood failure surfaces. Bondline thickness and effective penetration of adhesives did not relate to the shear strength of all modified wood materials. The lower shear strength of modified wood could be attributed to other factors, such as the reduced chemical bonding or mechanical interlocking of adhesives, and the reduced strength of brittle modified wood substrate.
|
|
| 6. |
- Bastani, Alireza, et al.
(författare)
-
Study of adhesive bondlines in modified wood with fluorescence microscopy and X-ray micro-computed tomography
- 2016
-
Ingår i: International Journal of Adhesion and Adhesives. - : Elsevier BV. - 0143-7496 .- 1879-0127. ; 68, s. 351-358
-
Tidskriftsartikel (refereegranskat)abstract
- The quantitative penetration of three coldset wood adhesives [one-component polyurethane (PU), emulsion polymer isocyanate (EPI), poly (vinyl acetate) (PVAc)] under hydraulic pressure into different types of modified wood was studied using fluorescence microscopy and the results were compared to these of a previous study without pressure on adjacent wood samples. The effective penetration (EP) of PU was negatively affected by furfurlylation and NMM modification when pressure was applied. For PVAc, 30% NMM treatment and heat treatment of Scots pine and beech at 210 °C had a negative effect on its EP, but against this the EP of this adhesive increased after heat treatment of beech at 195 °C. In the case of furfurylation, the depth of penetration of all adhesives was less into wood treated with higher concentration of furfuryl alcohol. PU showed a much deeper penetration into NMM-modified and heat-treated wood than the other adhesives with the exception of heat-treated beech at 195 °C. Application of pressure led to rather different results as compared to the EP data when no pressure was applied. The three-dimensional (3D) visualisation of the penetration of PU adhesive into heat-treated Scots pine was also examined by X-ray micro-computed tomography (XµCT). The 3D flow pattern of PU adhesive into heat-treated Scots pine was clearly depicted by XµCT.
|
|
| 7. |
- Bastani, Alireza, et al.
(författare)
-
Water uptake and wetting behaviour of furfurylated, N-methylol melamine modified and heat-treated wood
- 2015
-
Ingår i: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 73:5, s. 627-634
-
Tidskriftsartikel (refereegranskat)abstract
- This study reports on the water uptake (WU) and wetting properties of different modified wood materials; furfurylated and N-methylol melamine (NMM) modified Scots pine, and heat-treated (Vacu3 method) Scots pine and beech. All modifications caused a substantial reduction in WU in the longitudinal, tangential and radial directions both after short (24 h) and long contact times (168, 336 h) with a saturated sponge. The water uptake coefficient (w t ) was reduced by approximately 71–89 % in furfurylated wood, with the higher weight percent gain (WPG) providing a slightly greater reduction. The reduction in WU was not found to depend on the NMM solid content. The NMM treatment had the maximum effect on the reduction of tangential w t by 80–84 % and was much smaller in the longitudinal direction (31–68 %). The treatment temperature of 195 °C gave lower WU values than treatment at 210 °C, and the only exception was the radial direction of Scots pine. The longitudinal w t of heat-treated beech represented the highest reduction by 81–89 %, while radial w t was less affected in both species. Sessile drop apparent contact angles for water and diidomethane and corresponding surface energies on planed tangential and radial wood surfaces revealed an increased hydrophobicity and reduced polarity of modified wood. Furfurylated and NMM modified tangential surfaces had a higher increase of apparent contact angles than the radial surfaces but this was not observed in the case of heat treatment. Heat-treated wood showed reduced wetting of surfaces only with water. Apparent contact angles did neither differ with treatment temperature nor with the NMM resin load. The disperse component of surface energy was slightly increased by 20 % maximum in modified wood, while the polar components showed a dramatic decrease by −30 to −90 % with no major differences among treatments and intensities, and between surfaces. The results provide a better understanding of the hygroscopic behaviour of modified wood, which might be useful to predict its adhesion with various polymers such as glues, coatings and paints.
|
|
| 8. |
- Bastani, Mehrdad, 1960-, et al.
(författare)
-
3D magnetic susceptibility model of a deep iron-oxide apatite-bearing orebody incorporating borehole data in Blötberget, Sweden
- 2019
-
Konferensbidrag (refereegranskat)abstract
- We have processed and modelled in 3D available airborne magnetic data flown over the Blötberget iron-oxide deposit in central Sweden. 3D magnetic susceptibility models were then compared to the existing borehole information, downhole logging data and ground geological observations. Use of such information in the 3D inversion of the magnetic field data in the form of a reference model has considerably improved the 3D model in resolving the deeper parts of the iron-oxide orebody as well as the geometry of nearby geological structures. Unconstrained inversion results, however, do not resolve the true dip and depth extension of the iron-oxide orebody.
|
|
| 9. |
- Bastani, Mehrdad, et al.
(författare)
-
Boat-towed radio-magnetotellurics : A new technique and case study from the city of Stockholm
- 2015
-
Ingår i: Geophysics. - 0016-8033 .- 1942-2156. ; 80:6, s. B193-B202
-
Tidskriftsartikel (refereegranskat)abstract
- We have developed a new data acquisition system and technique to measure the radio magnetotelluric (RMT) signals from distant radio transmitters with the objective of mapping and modeling electric resistivity structures below a river or lake. The acquisition system is towed by a boat; therefore, we call the technique boat-towed RMT. The data acquisition is fast with a production rate of approximately 1 km/hr using a nominal sampling spacing of 10–15 m. Given the ample number of radio transmitters available in most parts of the world, the method can be used for near-surface studies of various targets. We have developed boat-towed RMT measurements on Lake Mälaren near the city of Stockholm in Sweden to determine the feasibility of the method. Approximately 15 km of RMT data were collected during three days above a planned 60-m-deep bypass tunnel with the goal of providing information on the bedrock depth and possible weak zones within the bedrock. The measured resistivity and phase data were of high quality with errors on the order of a few percent. The resistivity models from 2D inversion of the data showed a good correlation with available geologic data in resolving bedrock depth and also resistivity layering within the lake. Resistivity maps derived from the dense 2D models suggested a northeast–southwest-striking low-resistivity zone at less than a 30-m depth. The zone likely represents fractured crystalline bedrock. The boat-towed RMT technique is well suited for water bodies with moderate electric resistivity such as in brackish and freshwater environments.
|
|
| 10. |
|
|
| 11. |
- Bastani, Mehrdad, et al.
(författare)
-
Boat-towed RMT Measurements on the Water Surface over the Äspö Hard Rock Tunnel in Sweden
- 2016
-
Konferensbidrag (refereegranskat)abstract
- We carried out 3 km of radio magnetotelluric measurements in three hours on the water surface using a new boat-towed platform at the Borholm Fjord over the Äspö Tunnel in Sweden. The new platform was stable and use of DGPS receiver at the location of electromagnetic sensors facilitated faster data acquisition. The data were inverted in 2D and the resulting resistivity models revealed detailed information about the geological structures below the water. The estimated water depths were compared to the on-site echo sounder data that were collected simultaneously. We observed very close match between the two. The very low resistivity overburden (< 1 Ohmm) thickens towards the south-eastern part of the area with thicknesses > 10 m. After incorporating the RMT data that were acquired on the land at the northern part of the area a low resistivity zone that dips towards the northwest was resolved in the resistivity model. We interpret this zone as a major weak/fracture zone that is observed at depth inside the Äspö Tunnel. The low resistivity of water and overburden has strongly limited the depth penetration of the method and we suggest use of methods with deeper penetration such as controlled source magnetotelluric.
|
|
| 12. |
- Bastani, Mehrdad, et al.
(författare)
-
Combined use of controlled-source and radio-magnetotelluric methods for near surface studies
- 2015
-
Konferensbidrag (refereegranskat)abstract
- Combination of the controlled source and radio magnetotelluric, the so-called CSRMT, method has been used in modelling near surface electrical resistivity structures with the main aim of studying mineralization and engineering issues. In the controlled source mode, we used a remotely controlled double horizontal magnetic dipole that transmits signal in the frequency range 1-12.5 kHz. The signal sources for the RMT method are the distant radio transmitters in the frequency range 14-250 kHz. Three near surface case studies are presented in this work. In the first case, conductive hydrothermal stockwork copper deposits in an area in Iran were modelled in 2D and the results were compared to the existing borehole information. In the second case located in Greece using the CSRMT method we could model the location and geometry of a subvertical fault that was covered by conductive quaternary sediments. In the third case from Sweden, 3D resistivity models from the inversion of CSRMT data were used to determine presence and boundaries of quick-clay formation and a coarse-grained layer that is in turn responsible for a peculiar retrogressive landslide type in the study area. The three case studies have proven that a combination of controlled source and radio magnetotelluric methods has a considerable potential in addressing near surface problems. Comparison between the existing borehole data and the resistivity models from the inversion of the CSRMT data in each study area revealed reasonable correlation in delineating target structures especially depth to the good conductors. However, special attention needs to be given when using the CSMT data, especially at lower frequencies where they may be affected by the near-field phenomenon.
|
|
| 13. |
- Bastani, Mehrdad, et al.
(författare)
-
Delineating hydrothermal stockwork copper deposits using controlled-source and radio-magnetotelluric methods : A case study from northeast Iran
- 2009
-
Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 74:5, s. B167--B181
-
Tidskriftsartikel (refereegranskat)abstract
- Radio- and controlled-source-tensor magnetotelluric (RMT and CSTMT) methods are used to target hydrothermal veins of copper mineralization. The data were acquired along six eastwest- and three north-south-trending profiles, covering an area of about 500 x 400 m(2). The tensor RMT data were collected in the 10-250-kHz frequency band. A double horizontal magnetic dipole transmitter in the 4-12.5-kHz frequency range allowed us to constrain the deeper parts of the resistivity models better. To obtain optimum field parameters, ground magnetic profiling was conducted prior to the RMT and CSTMT surveys. Although the study area (in Iran) is remote, a number of radio transmitters with acceptable signal-to-noise ratio were utilized. The 2D inversion of RMT data led to unstable resistivity models with large data misfits. Thus, the RMT data were used to complement and analyze the near-surface resistivity anomalies observed in the 2D CSTMT models. Analyses of strike and dimensionality from the CSTMT data suggests that the low-resistivity structures are mainly three dimensional; therefore, 2D inversion of determinant data is chosen. Independent 2D inversion models of the determinant CSTMT data along crossing profiles are in good agreement. Known copper mineralization is imaged well in the CSTMT models. The thinning of the conductive overburden correlates very well with magnetic highs, indicating the bedrock is resistive and magnetic. In this sense, the magnetic and electromagnetic fields complement each other. Analysis of the 2D resistivity models indicates the volcanic rock deepens at the center of the study area. This zone is associated with a magnetic low and therefore is recommended for detailed exploration work.
|
|
| 14. |
- Bastani, Mehrdad, et al.
(författare)
-
Radio-magnetotelluric and controlled-source magnetotelluric surveys on a frozen lake : Opportunities for urban applications in Nordic countries
- 2022
-
Ingår i: Near Surface Geophysics. - : John Wiley & Sons. - 1569-4445 .- 1873-0604. ; 20:1, s. 30-45
-
Tidskriftsartikel (refereegranskat)abstract
- In a novel approach, we have carried out controlled-source and radio-magnetotelluric measurements in the frequency range of 2-250 kHz on a frozen lake located over a planned major multi-lane underground road tunnel near the city of Stockholm. The aim was to gain a better understanding of the resistivity variations above and, potentially, within the crystalline bedrock. Previous studies on the lake water using the boat-towed radio-magnetotelluric technique at the higher end of the frequency band lacked resolution at depth and could not provide conclusive information about bedrock level and potential fracture systems within the bedrock. Taking advantage of Nordic winters, we measured four profiles on the frozen lake complementing the previously acquired boat-towed radio-magnetotelluric data utilizing a double horizontal magnetic dipole transmitter that generated signals down to 1 kHz. The new resistivity models, incorporating the lower frequency data, show improvements and deeper penetrations based on a combined analysis of penetration depth, data misfits and sensitivity studies. The resistivity models also show better correlation with the available high-resolution shallow water seismic reflection data and the geological observations. A potential fracture system within the bedrock can also be inferred better in the new models. The idea of running similar surveys on frozen lakes can be further exploited in similar conditions in countries such as Sweden, where approximately 7% of the land is covered by freshwater bodies and poorly explored for infrastructure planning projects.
|
|
| 15. |
- Brodic, Bojan, et al.
(författare)
-
Multi-component digital-based seismic landstreamer and boat-towed radio-magnetotelluric acquisition systems for improved subsurface characterization in the urban environment
- 2017
-
Ingår i: First Break. - Amsterdam, Netherlands. - 0263-5046 .- 1365-2397. ; 35:8, s. 41-47
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- It is estimated that urban life will be the norm for around 60% of the world’s population by 2040, leading to a more centralized distribution of people and making the city as the main place of residence (Whiteley, 2009). This population centralization inherently implies rapidly expanding cities and imposes the need for more infrastructure within, around and between the present city boundaries. However, infrastructure projects nowadays have to follow strict civil engineering standards that require detailed knowledge of subsurface conditions during different stages of the construction processes. Since direct methods conventionally used for site characterization (e.g., drilling and/or core testing) are still relatively expensive the focus in the last two decades has been on non-invasive, geophysical methods. However, geophysical site characterization in urban areas is not an easy task owing to numerous challenges and various types of noise sources. Challenges such as electric/electromagnetic (EM) noise, pipelines and other subsurface objects (sometimes even unknown or undocumented), the inability to properly couple sensors because of pavement, traffic noises and limited space are common in urban environment. Since geophysical surveys need to be done with the least amount of disturbances to the environment, residents and traffic, new geophysical techniques for fast, non-invasive and high-resolution site characterization are needed. To overcome some of these challenges, a nationwide joint industry-academia project was launched in 2012 TUST GeoInfra, www.trust-geoinfra.se). As a component in the project, Uppsala University developed two new data acquisition systems. These are a fully digital MEMS-based (Micro-machined Electro-Mechanical Sensor) three component (3C) seismic landstreamer and a boat-towed radio-magnetotelluric (RMT) acquisition system. Both systems were specifically designed to address urban environments with the RMT system particularly aiming at efficient and cost-effective geophysical surveying on shallow-water bodies, which constitute 7% of Scandinavia. In this article, we will describe the two systems and present two case studies illustrating their potential. A number of published accounts are now available from the two systems showing what type of problems they can address (e.g., Bastani et al., 2015; Brodic et al., 2015; Malehmir et al., 2015a, 2015b, 2016a, 2016b, 2017; Dehghannejad et al., 2017; Maries et al., 2017; Mehta et al., 2017; Brodic et al., 2017).
|
|
| 16. |
- Brodic, Bojan, et al.
(författare)
-
Multicomponent broadband digital-based seismic landstreamer for near-surface applications
- 2015
-
Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 123, s. 227-241
-
Tidskriftsartikel (refereegranskat)abstract
- During the last few decades there has been an increased demand for infrastructure, along with a greater awareness of environmental issues in the construction industry. These factors have contributed to an increased interest in using seismic methods for near surface characterization, particularly in urban environments. Seismic sensors not affected by anthropogenic electromagnetic noise are therefore important, as well as an acquisition system that is easy to deploy, move and non-invasive. To address some of these challenges, a multicomponent broadband MEMS (micro-electro mechanical system) based landstreamer system was developed. The landstreamer system is fully digital, therefore it is less sensitive to electrical or electromagnetic noise. Crosstalk, leakage and tilting tests show that the system is superior to its predecessors. The broadband nature of the sensors (theoretically 0–800 Hz), 3C (three-component) recording and the close spacing of the sensors enable high-resolution imaging. The current streamer configuration consists of 20 sensors 4 m apart and 80 sensors 2 m apart. The streamer can easily be combined with wireless recorders for simultaneous data acquisition. In this study, we present results from testing of the streamer with various sources, such as a shear wave vibrator and different types of impact sources. MEMS-sensors and their high sensitivity allowed recording clear reflections that were not observed with coil-based sensors. A complementary test was also carried out at a planned access ramp for an urban tunnel where potential poor quality rocks had been identified by drilling. First-break traveltime tomography showed that these poor quality rocks correlate with low velocity zones. The presented landstreamer system has great potential for characterizing the subsurface in noisy environments.
|
|
| 17. |
- Cheraghi, Saeid, et al.
(författare)
-
Scaling behavior and the effects of heterogeneity on shallow seismic imaging of mineral deposits : a case study from Brunswick No. 6 mining area, Canada
- 2013
-
Ingår i: Journal of Applied Geophysics. - : Elsevier. - 0926-9851 .- 1879-1859. ; 90, s. 1-18
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied the scaling behavior of compressional-wave velocity and density logs from an exploration borehole that extends down to about 700 m depth in the Brunswick No. 6 mining area, Bathurst Mining Camp, Canada. Using statistical methods, vertical and horizontal scale lengths of heterogeneity were estimated. Vertical scale length estimates from the velocity, density and calculated acoustic impedance are 14 m, 33 m, and about 20 m, respectively. Although the estimated scale length for the acoustic impedance implies a weak scattering environment, elastic finite difference modeling of seismic wave propagation in 2D heterogeneous media demonstrates that even this weak scattering medium can mask seismic signals from small, but yet economically feasible, massive sulphide deposits. Further analysis of the synthetic seismic data suggests that in the presence of heterogeneity, lenticular-shaped targets may only exhibit incomplete diffraction signals whereby the down-dip tails of these diffractions are mainly visible on the stacked sections. Therefore, identification of orebody generated diffractions is much easier on the unmigrated stacked sections than on migrated stacked sections. The numerical seismic modeling in 2D heterogeneous media indicates that in the presence of large horizontal, but small vertical scale lengths (structural anisotropy), identification of massive sulphide deposits is possible, but their delineation at depth requires detailed velocity modeling and processing algorithms which can handle the anisotropy.
|
|
| 18. |
-
Dynamic Positioning based on Voronoi Cells (DPVC)
- 2006. - 1
-
Samlingsverk (redaktörskap) (refereegranskat)abstract
- In this paper we are proposing an approach for flexible positioning of players in Soccer Simulation in a Multi-Agent environment. We introduce Dynamic Positioning based on Voronoi Cells (DPVC) as a new method for players' positioning which uses Voronoi Diagram for distributing agents in the field. This method also uses Attraction Vectors that indicate agents' tendency to specific objects in the field with regard to the game situation and players' roles. Finally DPVC is compared with SBSP as the conventional method of positioning.
|
|
| 19. |
- Lundberg, Emil, et al.
(författare)
-
3D reflection seismic investigation over a quick-clay landslide scar in Lilla Edet, south-westernSweden
- 2012
-
Konferensbidrag (refereegranskat)abstract
- This project is part of a multidisciplinary research projectsponsored by the Society of Exploration Geophysiciststhrough the Geoscientists Without Borders (GWB)program. The 3D P-wave seismic data were acquired over alandslide scar close to Lilla Edet in south-west Sweden.The survey area is located on the shoreline of a major riverthat follows a 4 km wide fault zone. The area is known forhosting unstable quick-clays that could potentially causelandslides. The main objective of the 3D seismic was todefine the bedrock topography and layering within the clayformation. The 3D seismic data will form a base model thatwill assist the interpretations of the other geophysical data,which were collected at the same location. The quality ofthe data is good and the top of the crystalline bedrock and acoarse layer within the clay formation were detected. Thedepth to the coarse layer could be correlated using existinggeotechnical boreholes. A similar north-northeast extendingridge shaped structure was found in the coarser layer and inthe bedrock topography. The top of the bedrock is,however, dipping about 15° towards north while the coarselayer in the clay formation is fairly flat. The coarse layer islocated approximately 20 m below the surface and the topof the bedrock reaches a maximum depth of about 120 m.The geometry of the coarse layer may be important for thedirection of fresh water flow, which can leach salt from theclays, creating unstable quick-clays, at the location of thelandslide area.
|
|
| 20. |
- Lundberg, Emil, et al.
(författare)
-
High-resolution 3D reflection seismic investigation over a quick-clay landslide scar in southwest Sweden
- 2014
-
Ingår i: Geophysics. - 0016-8033 .- 1942-2156. ; 79:2, s. B97-B107
-
Tidskriftsartikel (refereegranskat)abstract
- Quick-clay landslides often occur in the northern hemisphere in areas that were covered by Pleistocene glaciation. They are particularly common along the shorelines of the Göta River in southwestern Sweden. Characterization of potential landslide areas and identification of features that indicate high risk are necessary to better understand the triggering mechanisms of these events. Therefore, an intensive characterization project has been initiated at the location of the Fråstad landslide in Sweden. Part of the characterization program included the acquisition of 3D reflection seismic data to image structures in the normally consolidated sediments, as well as the bedrock topography below the landslide scar. Two seismic horizons within the glacial and post-glacial sediments were observed. The shallowest seismic horizon (here referred to as S1) corresponds to a coarse-grained layer that was previously detected by eight geotechnical boreholes located within the 3D survey area. Discontinuities in S1, mapped by the 3D reflection seismic data, occur across a zone that correlates with the landslide scar boundary, suggesting that this zone may have played a role in triggering and/or in limiting the extension of the landslide. If S1 is truncated by or mixed with clays in this zone, then the outflow of water from the permeable S1 into the clays above may have increased the amount of quick-clays above this zone. The increased outflow of water may also have caused a higher pore-water pressure south of the zone, which in turn could have acted as a trigger for the landslide. This study shows the potential of using the 3D reflection seismic method as a complement to drilling and other geophysical methods when performing landslide site investigations. It also demonstrates the importance of further investigating the relationship between 3D subsurface geometries and landslide development.
|
|
| 21. |
- Malehmir, Alireza, et al.
(författare)
-
A multidisciplinary geophysical and geotechnical investigation of quick clay landslides in Sweden
- 2013
-
Konferensbidrag (refereegranskat)abstract
- Landslides are one of the most commonly occurring naturaldisasters. They claim hundreds of human lives and costbillions of dollars every year. In order to providegeophysical tools and techniques to better characterize sitesprone to slide, we have been carrying out and evaluatingpotential utility of several geophysical surveys over a quickclay landslide site in southwest Sweden since 2011. Themeasurements include 2D and 3D P- and S-wave highresolution surface seismics, radio- and controlled-sourceelectromagnetics, geoelectrics, ground gravity andmagnetic surveys. A particular focus here is given to theseismic studies in the site. Combined with downholegeophysical and geotechnical measurements, we show thatmajority of reflections correlate well with sandy-siltyformations in the site. Quick clays often occur above theseformations, which may be an indication of the role ofcoarse-grained formations to not only partly form quickclays but also triggering them when pore-water pressure issignificantly increased.
|
|
| 22. |
- Malehmir, Alireza, et al.
(författare)
-
Delineating structures controlling sandstone-hosted base-metal deposits using high-resolution multicomponent seismic and radio-magnetotelluric methods : a case study from Northern Sweden
- 2015
-
Ingår i: Geophysical Prospecting. - : Wiley. - 0016-8025 .- 1365-2478. ; 63:4, s. 774-797
-
Tidskriftsartikel (refereegranskat)abstract
- Over the past few decades seismic methods have increasingly been used for the exploration of mineral, geothermal, and groundwater resources. Nevertheless, there have only been a few cases demonstrating the advantages of multicomponent seismic data for these purposes. To illustrate some of the benefits of three-component data, a test seismic survey, using 60 digital three-component sensors spaced between 2 m and 4 m and assembled in a 160 m-long prototype landstreamer, was carried out over shallow basement structures underlying mineralized horizons and over a magnetic lineament of unknown origin. Two different types of seismic sources, i.e., explosives and a sledgehammer, were used to survey an approximately 4 km-long seismic profile. Radio-magnetotelluric measurements were also carried out to provide constraints on the interpretation of the seismic data over a portion of the profile where explosive sources were used. Good quality seismic data were recorded on all three components, particularly when explosives were used as the seismic source. The vertical component data from the explosive sources image the top of the crystalline basement and its undulated/faulted surface at a depth of about 50 m-60 m. Supported by the radio-magnetotelluric results, however, shallower reflections are observed in the horizontal component data, one of them steeply dipping and associated with the magnetic lineament. The vertical component sledgehammer data also clearly image the crystalline basement and its undulations, but significant shear-wave signals are not present on the horizontal components. This study demonstrates that multicomponent seismic data can particularly be useful for providing information on shallow structures and in aiding mineral exploration where structural control on the mineralization is expected.
|
|
| 23. |
- Malehmir, Alireza, et al.
(författare)
-
Geophysical assessment and geotechnical investigation of quick-clay landslides - a Swedish case study
- 2013
-
Ingår i: Near Surface Geophysics. - : Wiley. - 1569-4445 .- 1873-0604. ; 11:3, s. 341-350
-
Tidskriftsartikel (refereegranskat)abstract
- We present a preliminary assessment of the potential utility of various geophysical measurements carried out over a quick-clay landslide site in south-west Sweden. The multidisciplinary approach includes active P- and S-wave seismic investigations, including 2D and 3D reflection and refraction surveys, passive single and 3C seismic surveys, electrical resistivity tomography and electromagnetic surveys including controlled-source and radio-magnetotellurics, ground-penetrating radar and potential field studies. The P-wave and particularly S-wave reflection seismic data show a high-resolution image of bedrock topography and the stratigraphy of a 100 m thick sequence of sediments that lies on top, which include lightly consolidated quick-clays. Of particular interest is the identification of a layer of relatively coarse-grained material between 10-20 m below the ground surface. Geotechnical investigations indicate that most but not all quick-clays at the site are located above this layer. Further studies are required to determine the importance of their relationship and whether the coarse-grained layer may have had a role in triggering quick-clay landslides in the region. Geoelectrical and electromagnetic methods provide high-resolution images of the unconsolidated subsurface and particularly the normal and leached clays. Radio-magnetotelluric methods proved valuable near the river where traditional geoelectrical methods failed to provide sufficient depth coverage. The study shows that geophysical data are able to image major subsurface structures associated with quick-clay landslides.
|
|
| 24. |
- Malehmir, Alireza, et al.
(författare)
-
High-resolution Multicomponent Hardrock Seismic Imaging of Mineral Deposits and their Host Rock Structures
- 2014
-
Konferensbidrag (refereegranskat)abstract
- Although applied in the past, there are only a few cases demonstrating the advantages of multicomponentseismic data for mineral exploration. To illustrate this, a test survey using sixty 3C-digital sensors, spacedbetween 2 to 4 m and assembled in a 160 m long landstreamer, was carried out to provide information onshallow structures hosting mineralization and also a magnetic lineament with an unknown origin. Thesurvey, totally about 1.3 km long, was complemented by Radio MagnetoTelluric (RMT) measurements.Although an explosive source was used to generate the seismic signal, the seismic data show good qualityfor all the three components. Supported by the RMT results, clear reflections are observed in thehorizontal component data at about 25 m depth, one of them steeply dipping, likely associated with themagnetic lineament. Field static corrections were well estimated thanks to the close shot and receiverspacing and the broadband frequency content of the data. This study demonstrates that multicomponentseismic data can be useful for providing information on shallow structures and linking them to the surfacegeology. The vertical component data, however, show deeper penetration and better image the crystallinebasement and its undulated/faulted surface at about 50 m depth.
|
|
| 25. |
- Malehmir, Alireza, et al.
(författare)
-
High-resolution reflection seismic investigations of quick-clay and associated formations at a landslide scar in southwest Sweden
- 2013
-
Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 92, s. 84-102
-
Tidskriftsartikel (refereegranskat)abstract
- We present high-resolution reflection seismic data from four lines (total 1.9 km) that cross a quick-clay landslide scar located close to the shore of the Gota River in southwest Sweden, and compare the results with geotechnical data from boreholes. The seismic data allow the imaging of bedrock topography and normally to weakly consolidated sediments to a subsurface depth of about 100 m. Different types of seismic sources, including sledgehammer, accelerated weight-drop and dynamite were utilized and compared with each other. Analysis of their power spectra suggests that weight-drop and dynamite have higher frequency content and energy than the sledgehammer, which makes these two sources suitable also for waveform tomography and surface-wave data analysis. The shallowest non-bedrock reflector is observed at about 10-20 m below the surface, it overlays the bedrock, and is interpreted to originate from the contact between clay formations above and a coarse-grained layer below. The coarse-grained layer appears to be spatially linked to the presence of quick-clays. It is a regional scale formation, laterally heterogeneous, which deepens to the west of the study area and correlates well with the available geotechnical data. Continuity of the coarse-grained layer becomes obscured by the landslide scar. There may be a link between the coarse-grained layer and landslides in the study area, although this possibility requires further hydrogeological and geotechnical investigations. Reflectors from the top of the bedrock suggest a depression zone with its deepest point below the landslide scar and a bowl-shaped structure in the northern portion of one of the seismic lines.
|
|
| 26. |
- Malehmir, Alireza, et al.
(författare)
-
Near-Surface Geophysical Characterization of Areas Prone to Natural Hazards : A Review of the Current and Perspective on the Future
- 2016
-
Ingår i: Advances in Geophysics. - : Elsevier. - 0065-2687 .- 2162-7622. ; 57, s. 51-146
-
Tidskriftsartikel (refereegranskat)abstract
- Natural hazards such as landslides, floods, rockfalls, earthquakes, volcanic eruptions, sinkholes, and snow avalanches represent potential risks to our infrastructures, properties, and lives. That potential will continue to escalate with current and continued human encroachment into risk areas. With the help of geophysical techniques many of those risks can be better understood and quantified, thereby minimized and at least partly mitigated through accurate, site-specific, and proper planning and engineering. On occasions these hazards simply cannot be avoided, but better characterization and therefore understanding of the subsurface geology and natural processes responsible for the threats is possible through integration of various cost-effective geophysical methods with relevant geotechnical, geomechanical, and hydrogeological methods. With the enhanced characterization possible when geophysics is incorporated into natural hazard analysis, potential risks can be better quantified and remediation plans tuned to minimize the threat most natural hazards present to civilizations. In this article we will first review common geophysical methods that can be and have been utilized in studying natural hazard prone areas, then we provide selected case studies and approaches using predominantly our own examples, and finally a look into the future detailing how these methods and technologies can be better implemented and thereby more time- and cost-effective and provide improved results.
|
|
| 27. |
- Malehmir, Alireza, et al.
(författare)
-
Post-glacial reactivation of the Bollnas fault, central Sweden : a multidisciplinary geophysical investigation
- 2016
-
Ingår i: Solid Earth. - : Copernicus GmbH. - 1869-9510 .- 1869-9529. ; 7:2, s. 509-527
-
Tidskriftsartikel (refereegranskat)abstract
- Glacially induced intraplate faults are conspicuous in Fennoscandia where they reach trace lengths of up to 155 km with estimated magnitudes up to 8 for the associated earthquakes. While they are typically found in northern parts of Fennoscandia, there are a number of published accounts claiming their existence further south and even in northern central Europe. This study focuses on a prominent scarp discovered recently in lidar (light detection and ranging) imagery hypothesized to be from a post-glacial fault and located about 250 km north of Stockholm near the town of Bollnas. The Bollnas scarp strikes approximately north-south for about 12 km. The maximum vertical offset in the sediments across the scarp is 4-5m with the western block being elevated relative to the eastern block. To investigate potential displacement in the bedrock and identify structures in it that are related to the scarp, we conducted a multidisciplinary geophysical investigation that included gravity and magnetic measurements, high-resolution seismics, radio-magnetotellurics (RMT), electrical resistivity tomography (ERT) and ground-penetrating radar (GPR). Results of the investigations suggest a zone of low-velocity and high-conductivity in the bedrock associated with a magnetic lineament that is offset horizontally about 50m to the west of the scarp. The top of the bedrock is found similar to 10m below the surface on the eastern side of the scarp and about similar to 20m below on its western side. This difference is due to the different thicknesses of the overlying sediments accounting for the surface topography, while the bedrock surface is likely to be more or less at the same topographic level on both sides of the scarp; else the difference is not resolvable by the methods used. To explain the difference in the sediment covers, we suggest that the Bollnas scarp is associated with an earlier deformation zone, within a wide (> 150 m), highly fractured, water-bearing zone that became active as a reverse fault after the latest Weichselian deglaciation.
|
|
| 28. |
- Mehta, Suman, 1988-, et al.
(författare)
-
Analysis of resolution and sensitivity of boat-towed RMT dataover Lake Mälaren, Stockholm
-
Ingår i: Interpretation. - 0020-9635 .- 2169-4494.
-
Tidskriftsartikel (refereegranskat)abstract
- We examine the resolution and sensitivity of water-borne boat-towed multi-frequencyradio magnetotelluric (RMT) data for delineating weak zones in crystalline environmentunder a lake or a river. 2D modeling of RMT data in joint transverse electric (TE) andtransverse magnetic (TM) and determinant mode of 40 profiles over two water passages fromLake Mälaren near the city of Stockholm was used for this purpose. The 2D modeling revealsthat the estimated models have responses that fit the observed data reasonably well. Themodels show an overall agreement when compared with existing marine seismic results,bathymetry data and other available geological knowledge from the site. A low-resistivityzone observed in the middle of all profiles is suggested to be from a fracture/fault zonestriking in the direction of the water passages. Because RMT is an inductive-based method,the presence of conductive lake sediments shields scanning the underlying fractured bedrock.To reliably interpret the RMT data, synthetic modeling using a three-layered generic modelwith a conductive layer of varying thickness sandwiched between resistive water andfractured crystalline bedrock was performed. The modeling results suggest that lowerfrequency signal is required to have greater depth of penetration that would better resolve thebedrock and fracture zone although some evidence of fractured bedrock can still be inferredfrom the data. The study also shows the advantage of having a water layer that acts as a nearhomogeneous medium that eliminates near surface static shift effects. We propose that theboat-towed RMT acquisition system should be upgraded to enable controlled-source acquisition to improve the depth penetration and to overcome the shortcomings of usingradio-frequencies as signal.
|
|
| 29. |
|
|
| 30. |
- Mehta, Suman, 1988-, et al.
(författare)
-
CSRMT Survey on Frozen Lake - A New Technique with an Example from the Stockholm Bypass Tunnel
- 2017
-
Konferensbidrag (refereegranskat)abstract
- More than 7% of the Scandinavian landmass is covered with fresh-water bodies in the form of lakes and rivers. This poses a unique challenge to carry out electromagnetic survey on shallow-water bodies for various purposes for example geotechnical investigations. Recently boat-towed RMT (radio-magnetotelluric) technique was introduced and used for measurements over the Lake Mälaren in Stockholm, Sweden. The RMT covers a wide range of frequencies (10-250 kHz) and provides good resolution for shallow subsurface studies although it lacks resolution at greater depths. Using controlled-source frequencies in the range of 1-10 kHz sufficient penetration depths can be achieved for most of the near surface targets. In this study, we present the results from the combined use of controlled-source and RMT (CSRMT) data that were obtained over frozen Lake Mälaren. The objective of this study was to map bedrock surface and fractures in the middle of the profile where using only RMT data these were not adequate. We demonstrate a new technique where CSRMT surveys were carried out over frozen-shallow-water bodies and we expect the idea to be used in the near future for other applications where moderately-resistive water bodies are present.
|
|
| 31. |
- Mehta, Suman, 1988-
(författare)
-
Development of RMT techniques for urban infrastructure planning : Stockholm Bypass (Förbifart) case study
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The tensor radio-magnetotelluric (RMT) method has extensively been used in near-surface investigations to obtain resistivity models of the subsurface. The main objective of this thesis is to further develop the RMT survey technique for a less paid attention and challenging environment namely on shallow water bodies and in the urban environment. The other objective is to develop a new processing technique to enhance the resolution and sensitivity of the tensor RMT method. For the first time a data acquisition system called ‘boat-towed RMT’ is introduced that has the capability to measure tensor RMT data on water bodies like lakes and rivers. A RMT survey carried out on Lake Mälaren near the city of Stockholm shows the capability and efficiency of the boat-towed RMT system. The resistivity models obtained from the RMT data are consistent from one line to another and show good correlation with the existing geological and drill core data. In general, a three-layer resistivity model was obtained that has a conductive layer interpreted as lake sediments, which is sandwiched between high resistive bedrock and resistive water column. A coherent discontinuity of low resistivity zone was observed in bedrock across all the lines. It was interpreted to originate from a major fracture zone striking in the direction of water bodies. However, due to the lack of penetration, RMT method alone was insufficient to provide a conclusive interpretation of this. Synthetic analysis was performed and showed that lower frequencies using controlled-sources are required to obtain the desired penetration depth. We took the advantage of the Swedish winters and carried out controlled-source RMT measurements on frozen lake at the same location. The new controlled-source models have enough depth penetration to delineate fractured bedrock. Furthermore, in order to improve the resolution and sensitivity of tensor RMT data, a new processing technique was developed that preserves the identity of each transmitter and allows improved resistivity model of the subsurface. These new acquisition and processing techniques should be useful in many different applications for urban infrastructure planning projects especially in Scandinavia where 7% of the land is covered by fresh water bodies and is poorly explored for these purposes.
|
|
| 32. |
|
|
| 33. |
- Mehta, Suman, 1988-, et al.
(författare)
-
Resolution and sensitivity of boat-towed RMT data to delineate fracture zones - Example of the Stockholm bypass multi-lane tunnel
- 2017
-
Ingår i: Journal of Applied Geophysics. - : ELSEVIER SCIENCE BV. - 0926-9851 .- 1879-1859. ; 139, s. 131-143
-
Tidskriftsartikel (refereegranskat)abstract
- The resolution and sensitivity of water-borne boat-towed multi-frequency radio-magnetotelluric (RMT) data for delineating zones of weaknesses in bedrock are examined in this study. 2D modeling of RMT data along 40 profiles in joint transverse electric (TE) and transverse magnetic (TM) as well as determinant mode was used for this purpose. The RMT data were acquired over two water passages from the Lake Malaren near the city of Stockholm where one of the largest underground infrastructure projects, a multi-lane tunnel, in Europe is currently being developed. Comparison with available borehole coring, refraction seismic and bathymetric data was used to scrutinize the RMT resistivity models. A low-resistivity zone observed in the middle of all the profiles is suggested to be from fracture/fault zones striking in the same direction as the water passages. Drilling observations confirm the presence of brittle structures in the bedrock, which manifest themselves as zones of low-resistivity and low-velocity in the RMT and refraction seismic data, respectively. Nevertheless, RMT is an inductive electromagnetic method hence the presence of conductive lake sediments may shield detecting the underlying fractured bedrock. The loss of resolution at depth implies that the structures within the bedrock under the lake sediments cannot reliably be delineated. To support this, a synthetic data analysis was carried out providing useful information on how to improve and plan the lake measurements for future studies. Synthetic modeling results for example suggested that frequencies as low as 3 kHz would be required to reliably resolve the bedrock and fracture zone within it in the study area. The modeling further illustrated the advantage of a fresh water layer that acts as a near-surface homogeneous medium eliminating the static shift effects. While boat-towed RMT data provided substantial information about the subsurface geology, the acquisition system should be upgraded to enable controlled-source data acquisition to increase the penetration depth and to overcome the shortcomings of using only radio-frequencies.
|
|
| 34. |
- Sadeghi, Martiya, et al.
(författare)
-
GIS-based mineral system approach for prospectivity mapping of iron-oxide apatite-bearing mineralisation in Bergslagen, Sweden
- 2019
-
Ingår i: LIFE WITH ORE DEPOSITS ON EARTH, PROCEEDINGS OF THE 15TH SGA BIENNIAL MEETING, 2019, VOLS 1-4. - : SOC GEOLOGY APPLIED MINERAL DEPOSITS-SGA. - 9780852619643 ; , s. 1216-1219
-
Konferensbidrag (refereegranskat)abstract
- Bergslagen is one of the richest mineral districts in Sweden for base and precious/critical minerals and metals. In this work a mineral system approach for targeting of iron-oxide apatite-bearing mineralisation has been developed. GIS-based mapping of prospectivity for this type of mineralisation has been carried out with a focus on Ludvika mining area from Blotberget to Haksberg with known and high-quality iron-oxide deposits. According to spatial analysis on mappable criteria's, strong positive airborne magnetic anomalies, density of structures and the contact between felsic volcanic rocks and granites are crucial for this type of mineralisation in the study area This GIS-based model will also be used in targeting of iron-oxide deposits at depth in the Blotberget area. However, the mineral systems approach considers the origin of deposits in the framework of lithospheric-scale processes from the time-honored aspects of the source, fluids, transport and physical and/or thermo-dynamical traps. Applied to exploration strategy, this approach allows for more predictive models. Rather than matching patterns, knowledge of the underlying geological processes and tectonic-structural setting can be used for identifying areas with higher probability of finding deposits of interest. Furthermore, this method can broaden the scope of prospectivity indicators and allows for earlier and more efficient fertility assessments.
|
|
| 35. |
- Shan, Chunling, et al.
(författare)
-
3D resistivity models from inversion of controlled source and radio-magnetotelluric (CSRMT) data at a quick-clay site in southwestern Sweden
- 2013
-
Konferensbidrag (refereegranskat)abstract
- We have collected 3D tensor Controlled Source- and RadioMagnetotelluric data at a quick-clay site in southwesternSweden with the aim to image the geological structures thathave given rise to retrogressive landslides in the area. The3D resistivity models show layering within the glacial andpost-glacial sediments including marine clay, quick-clayand coarser grain sands. Because of the smoothingregularization used in the inversion, the lateral and depthextents of the quick-clays cannot be determined just byusing the resistivity model. The depth to the top of theresistive crystalline bedrock is to some extent uncertain.However, the geometry of the sediments and bedrock seenin the 3D resistivity model correlates reasonably well withthe results from the high resolution reflection seismic datacollected along the same lines in the site. The results showthat the bedrock deepens towards the river in the northernpart of the site.
|
|
| 36. |
- Shan, Chunling, 1986-, et al.
(författare)
-
Integrated 2D modeling and interpretation of geophysical and geotechnical data to delineate quick clays at a landslide site in southwest Sweden
- 2014
-
Ingår i: Geophysics. - 0016-8033 .- 1942-2156. ; 79:4, s. 61-75
-
Tidskriftsartikel (refereegranskat)abstract
- Radio Magnetotellurics (RMT), Electrical Resistivity Tomography (ERT) and high-resolution reflection seismic data were collected along four lines to image the geometry and physical properties of geological structures at a quick-clay landslide site in southwest Sweden. The site is situated in the Göta River valley where the normally consolidated materials mainly consist of glacial and post-glacial sediments. Geotechnical data suggest presence of quick clays above coarse-grained layers. These layers play a key role in the formation of quick clays and landslide triggering. The RMT and ERT data were individually and jointly inverted in 2D to study the resolution of resulting models for each data set. The resistivity models from the joint inversions demonstrate superior resolution and accuracy than individual ones. The geometry and location of shallower structures resolved in the 2D resistivity models from joint RMT+ERT inversions correlate well with those imaged in the reflection seismic data and observed in the existing geotechnical boreholes. The models are poor in resolving deeper resistive bedrock at locations where the thickness of the conductive overburden exceeds a certain limit. However, information from the reflection seismic data could be used to estimate the depth to the top of the bedrock along all the four lines. Comparison between the geotechnical data and the resistivity models suggests that quick clays overlying the coarse-grained layer have higher electrical resistivity than the marine clays. The obtained results were further validated and refined by performing synthetic tests. This study shows that integration of ERT and RMT data with reflection seismic data is ideal for quick-clay landslide studies especially when the clay materials are thick.
|
|
| 37. |
- Shan, Chunling, 1986-, et al.
(författare)
-
Integration of controlled-source and radio-magnetotellurics, electrical resistivity tomography and reflection seismics to delineate 3D structures of a quick-clay landslide site in southwest Sweden
- 2016
-
Ingår i: Geophysics. - 0016-8033 .- 1942-2156. ; 81:1, s. B13-B29
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Three-dimensional radio magnetotelluric (RMT), controlled-source radio magnetotelluric (CSRMT), electrical resistivity tomography (ERT), and high-resolution reflection seismic data were acquired at a quick-clay landslide site close to the Göta River in southwest Sweden. These data were collected with the main objectives of evaluating the performance of each method and delineating different subsurface materials down to the bedrock, which in turn control a peculiar and hazardous retrogressive-type landslide. These materials consist of mainly marine clays, quick clays, sand to gravel and the crystalline bedrock. The RMT, CSRMT and ERT data were inverted separately using 3D inversion schemes and the independent results from 3D processing of reflection seismic data together with the existing geotechnical data were used for their interpretations. The 3D CSRMT resistivity model shows the highest depth penetration and well resolves the geometry of the bedrock. The RMT and ERT models, however, show better resolution closer to the surface because of their denser data coverage compared with the CSRMT data. Considerable correlations in resolving a coarse-grained layer and the bedrock were observed between the CSRMT model and the 3D reflection seismic data. Because an Occam-type regularization was used in the inversion, the lateral and depth extent of the quick clays cannot accurately be determined just by using the resistivity models. The depth to the top of the resistive crystalline bedrock is to some extent uncertain. Comparisons with the borehole data suggest that the resistivity models are poor in resolving the sharp boundary between the quick clays and their underlying more resistive coarse-grained materials. The upper boundary of the more conductive marine clays underlain by the coarse-grain materials was well modeled by the CSRMT data. This study illustrates the potentials of 3D geophysical data especially when different types are collected and particularly for better site characterizations.
|
|
| 38. |
|
|
| 39. |
- Wang, Shunguo, et al.
(författare)
-
Boat-towed radio-magnetotelluric and controlled source audio-magnetotelluric study to resolve fracture zones at Äspö Hard Rock Laboratory site, Sweden
- 2019
-
Ingår i: Geophysical Journal International. - : OXFORD UNIV PRESS. - 0956-540X .- 1365-246X. ; 218:2, s. 1008-1031
-
Tidskriftsartikel (refereegranskat)abstract
- Boat-towed radio-magnetotelluric (RMT) measurements using signals between 14 and 250 kHz have attracted increasing attention in the near-surface applications for shallow water and archipelago areas. A few large-scale underground infrastructure projects, such as the Stockholm bypass in Sweden, are planned to pass underneath such water zones. However, in cases with high water salinity, RMT signals have a penetration depth of a few metres and do not reach the geological structures of interest in the underlying sediments and bedrock. To overcome this problem, controlled source signals at lower frequencies of 1.25 to 12.5 kHz can be utilized to improve the penetration depth and to enhance the resolution for modelling deeper underwater structures. Joint utilization of boat-towed RMT and controlled source audio-magnetotellurics (CSAMT) was tested for the first time at the Aspo Hard Rock Laboratory (HRL) site in south-eastern Sweden to demonstrate acquisition efficiency and improved resolution to model fracture zones along a 600-m long profile. Pronounced galvanic distortion effects observed in 1-D inversion models of the CSAMT data as well as the predominantly 2-D geological structures at this site motivated usage of 2-D inversion. Two standard academic inversion codes, EMILIA and MARE2DEM, were used to invert the RMT and CSAMT data. EMILIA, an object-oriented Gauss-Newton inversion code with modules for 2-D finite difference and 1-D semi-analytical solutions, was used to invert the RMT and CSAMT data separately and jointly under the plane-wave approximation for 2-D models. MARE2DEM, a Gauss-Newton inversion code for controlled source electromagnetic 2.5-D finite element solution, was modified to allow for inversions of RMT and CSAMT data accounting for source effects. Results of EMILIA and MARE2DEM reveal the previously known fracture zones in the models. The 2-D joint inversions of RMT and CSAMT data carried out with EMILIA and MARE2DEM show clear improvement compared with 2-D single inversions, especially in imaging uncertain fracture zones analysed in a previous study. Our results show that boat-towed RMT and CSAMT data acquisition systems can be utilized for detailed 2-D or 3-D surveys to characterize near-surface structures underneath shallow water areas. Potential future applications may include geo-engineering, geohazard investigations and mineral exploration.
|
|
| 40. |
- Wang, Shunguo, et al.
(författare)
-
Controlled Source Boat-towed Radio-magnetotellurics for Site Investigation at Äspö Hard Rock Laboratory, Southeastern Sweden
- 2017
-
Konferensbidrag (refereegranskat)abstract
- The radio-magnetotelluric (RMT) method has traditionally been used for land investigations. However, with the development of the boat-towed RMT system, this method is used on shallow water. The lowest frequency of the RMT method is about 14 kHz and in addition water resistivity is quite low in some cases, therefore controlled source measurements is naturally considered for data acquisition. In order to resolve a fracture zone under a brackish water body, the controlled source boat-towed RMT (CSRMT) approach was tested. CSRMT and RMT one-dimensional inversions were carried out separately to analyze galvanic distortions and source effects in our dataset. Serious distortions observed in both inversions as well as the two-dimensional (2D) structure observed in our previous study made us consider 2D inversion for modeling the data. Due to the sufficiently large distance between transmitter and receivers, the CSRMT data were inverted using a 2D inversion code originally designed for plane-wave RMT data. Occam and damped Occam schemes were used in our 2D inversions for CSRMT and RMT data. The results show that CSRMT can better resolve the fracture zone than RMT. This study further illustrates the use of the boat-towed RMT system and particularly when combined with controlled source.
|
|
| 41. |
- Wang, Shunguo, et al.
(författare)
-
Geophysical characterization of areas prone to quick-clay landslides using radio-magnetotelluric and seismic methods
- 2016
-
Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 677, s. 248-260
-
Tidskriftsartikel (refereegranskat)abstract
- Landslides attributed to quick clays have not only considerable influences on surface geomorphology, they have caused delays in transportation systems, environmental problems and human fatalities, especially in Scandinavia and North America. If the subsurface distributions of quick clays are known, potential damages can be mitigated and the triggers of landslides can better be studied and understood. For this purpose, new radio-magnetotelluric (RMT) and seismic data were acquired in an area near the Gota River in southwest Sweden that contains quick clays and associated landslides. High-resolution data along 4 new lines, in total 3.8 km long, were acquired and merged with earlier acquired data from the site. Velocity and resistivity models derived from first breaks and RMT data were used to delineate subsurface geology, in particular the bedrock surface and coarse-grained materials that overlay the bedrock. The latter often are found underlying quick clays at the site. Comparably high resistivity and sometimes high-velocity regions within marine clays are attributed to a combination of leached salt from marine clays or potential quick clays and coarse-grained materials. The resistivity and tomographic velocity models suggest a much larger role of the coarse-grained materials at the site than previously thought, but they also suggest two different scenarios for triggering quick-clay landslides at the site. These scenarios are related to the erosion of the riverbank, increased pore-pressure and surface topography when close to the river and human activity when away from the river and where bowl-shaped bedrock surrounds the sediments.
|
|
| 42. |
- Wang, Shunguo
(författare)
-
Joint inversion and integration of multiple geophysical data for improved models of near-surface structures
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Geophysical methods are non-invasive and allow an effective way of understanding subsurface structures and their physical properties. One of the main challenges is the often non-uniqueness of the geophysical models and that several different models can explain a dataset to an agreeable fit. Moreover, noise and limitations in resolution, which are inherent to field data, are additional obstacles for obtaining a true physical property model of the subsurface. Facing all these challenges, geophysicists have dedicated their efforts for decades to recover models that represent, as close as possible, the true subsurface. Joint inversion and integration of multiple geophysical data are two main approaches that I studied to better resolve subsurface structures. I further used these approaches, together with new software and hardware implementations for data acquisition and inversion, for near-surface applications. In this thesis, radio-magnetotelluric (RMT), boat-towed RMT, boat-towed controlled source MT (CSMT), electrical resistivity tomography (ERT), and first-arrival traveltime tomography are jointly used for quick clay investigations and fracture zone delineation under shallow water-bodies. The joint approach, as compared with any individual method, shows a better ability to both resolve the geological targets and to assist in understanding the subsurface geology that hosts these targets. For examples: by performing the joint inversion of lake-floor ERT and boat-towed RMT data, a fracture zone is better delineated with greater details compared with single inversion; by employing boat-towed CSMT measurements and jointly inverting with boat-towed RMT data, the subsurface structures, especially at greater depth, are better resolved than by inverting each dataset alone.During my PhD studies, two types of new implementations were employed. (1) Boat-towed data acquisition system was implemented to expand the RMT and CSMT method from land to shallow-water applications. This is significant since many large-scale underground infrastructures are likely to cross these water zones (for example multi-lane train or bypass tunnels, such as the Stockholm bypass). (2) The modification of a well-structured code EMILIA allows joint inversion of boat-towed RMT and lake-floor ERT datasets, and the modification of another well-structured code MARE2DEM can accurately model high frequency CSMT data and handle joint inversion of boat-towed RMT and boat-towed CSMT datasets. Thus, the code modification as another type of new implementation guarantees the success of near-surface applications using the boat-towed RMT and CSMT data acquisition systems.Studies conducted during my PhD work, included under the SEG-GWB (the Society of Exploration Geophysicists - Geoscientists Without Borders) program and the TRUST (TRansparent Underground STructure) umbrella project, are useful for near-surface applications including, for examples, engineering purposes such as planning of underground infrastructures, site characterization in connection with energy or waste storage, and geohazard investigations.
|
|
| 43. |
- Wang, Shunguo, et al.
(författare)
-
Joint inversion of lake-floor electrical resistivity tomography and boat-towed radio-magnetotelluric data illustrated on synthetic data and an application from the Äspö Hard Rock Laboratory site, Sweden
- 2018
-
Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 213:1, s. 511-533
-
Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity tomography (ERT) method provides moderately good constraints for both conductive and resistive structures, while the radio-magnetotelluric (RMT) method is well suited to constrain conductive structures. Additionally, RMT and ERT data may have different target coverage and are differently affected by various types of noise. Hence, joint inversion of RMT and ERT data sets may provide a better constrained model as compared to individual inversions. In this study, joint inversion of boat-towed RMT and lake-floor ERT data has for the first time been formulated and implemented. The implementation was tested on both synthetic and field data sets incorporating RMT transverse electrical mode and ERT data. Results from synthetic data demonstrate that the joint inversion yields models with better resolution compared with individual inversions. A case study from an area adjacent to the Ä spö Hard Rock Laboratory (HRL) in southeastern Sweden was used to demonstrate the implementation of the method. A 790-m-long profile comprising lake-floor ERT and boattowed RMT data combined with partial land data was used for this purpose. Joint inversions with and without weighting (applied to different data sets, vertical and horizontal model smoothness) as well as constrained joint inversions incorporating bathymetry data and water resistivity measurementswere performed. The resultingmodels delineate subsurface structures such as a major northeasterly directed fracture system, which is observed in the HRL facility underground and confirmed by boreholes. A previously uncertain weakness zone, likely a fracture system in the northern part of the profile, is inferred in this study. The fractures are highly saturated with saline water, which make them good targets of resistivity-based geophysical methods. Nevertheless, conductive sediments overlain by the lake water add further difficulty to resolve these deep fracture zones. Therefore, the joint inversion of RMT and ERT data particularly helps to improve the resolution of the resistivity models in areas where the profile traverses shallow water and land sections. Our modification of the joint inversion of RMT and ERT data improves the study of geological units underneath shallow water bodies where underground infrastructures are planned. Thus, it allows better planning and mitigating the risks and costs associated with conductive weakness zones.
|
|
| 44. |
|
|
