scholarly journals The role of geophysics in the construction and stability assessment of tunnels

Warta Geologi ◽  
2021 ◽  
Vol 47 (3) ◽  
pp. 199-203
Author(s):  
Nik Adib Yaaziz ◽  
◽  
Mohd Hariri Arifin ◽  
Keyword(s):  
Geophysical Methods ◽  
Shear Zones ◽  
Vital Role ◽  
Tunnel Construction ◽  
Stability Assessment ◽  
Tectonic Structures ◽  
Satellite Imaging ◽  
Groundwater Condition ◽  
Geoelectrical Resistivity ◽  
Ground Condition

Geophysics play a vital role in the constructions of any major manmade structures in the world. One of those being the tunnels. In depth understanding of geophysical methods and a lot of information are needed in order to design a tunnel construction project. Comprehensive investigation on the ground condition has to be done before the field preparation study that will determine the stand-up time and the groundwater condition that may disrupt the tunnel construction. For tunnel stability assessment, an integration of geophysical methods is a must in order to obtain the most accurate results. Satellite imaging interpretation emphasizes on the structural tracing of negative lineament while field mapping emphasizes on location of underground seepage and major tectonic structures such as faults, joints and shear zones. Geoelectrical resistivity tomography survey is able to identify the differences in resistivity of Earth’s materials based on the water content inside of them. The best course of remediation could only be chosen once the output from all these studies are made available.

Imaging the Geology Ahead of a Tunnel Using Seismics and Adaptive Polarization Analysis

2020 ◽  
Vol 25 (2) ◽  
pp. 189-198
Author(s):  
Lei Chen ◽  
Chao Fu ◽  
Xinji Xu ◽  
Lichao Nie
Keyword(s):  
Time Window ◽  
Geophysical Methods ◽  
Weighting Coefficient ◽  
Tunnel Construction ◽  
Polarization Analysis ◽  
Polarization Direction ◽  
Tunnel Face ◽  
Seismic Method ◽  
Imaging Results ◽  
Geological Conditions

The seismic method is one of the main geophysical methods that are widely used to image the geology ahead of tunnels during tunnel construction. However, owing to the complex environment and limited observation aperture in a tunnel, symmetric false results (that appear in imaging results but not in the actual environment) frequently occur in imaging results. In a symmetric false reflection, false and true reflection points are axisymmetric around the tunnel axis. Such false results frequently cause errors in the interpretation of the geological conditions ahead of a tunnel face. To overcome this problem, a seismic method that uses adaptive polarization analysis was adopted to better image geological conditions. Based on an adaptive time window, the polarization characteristics of seismic signals were analyzed to calculate the main polarization direction. The symmetric false results in imaging results were suppressed by adopting a weighting coefficient based on the angle between the main polarization direction and ray direction. Numerical simulations revealed the superiority of the method when applied to synthetic data processing. Moreover, the method was applied to a diversion tunnel. The method successfully identified the fracture zones ahead of the tunnel face, thus significantly enhancing the safety of tunnel construction.

scholarly journals The northern Thessaly strong earthquakes of March 3 and 4, 2021, and their neotectonic setting

2021 ◽  
Vol 58 ◽  
pp. 222
Author(s):  
Alexandros Chatzipetros ◽  
Spyros Pavlides ◽  
Michael Foumelis ◽  
Sotiris Sboras ◽  
Dimitris Galanakis ◽  
...  
Keyword(s):  
Ground Deformation ◽  
Seismic Hazard Assessment ◽  
Shear Zones ◽  
Normal Faults ◽  
Seismogenic Fault ◽  
Rock Falls ◽  
Tectonic Structures ◽  
Northern Greece ◽  
Stress Changes ◽  
Active Tectonic

A sequence of earthquakes occurred on March 3rd and 4th in Northern Thessaly, northern Greece, associated with previously unknown, blind normal faults within the crystalline Palaeozoic basement of the Pelagonian geotectonic zone. Surficial ground deformation, such as liquefaction phenomena in fluvial plains, as well as soil fissures and rock falls, have been mapped. Geological indications of the unmapped seismic fault, i.e., reactivated shear zones, open cracks, etc., have been identified within the bedrock. Based on geological indications, the main fault projection to the surface could be considered a 15 km NW-SE trending structure and average dip of 45o to the NE. The seismic source of the main shock was modelled, and the Coulomb static stress changes calculated for receiver faults similar to the source. The determination of the active tectonic regime of the region by geodetic data and the well-known faults of NE Thessaly plain are also presented, as well as the revised historical and instrumental seismicity. This earthquake raises new concerns and challenges, revising some established views, such as the status of main stress orientations, the orientation of active tectonic structures, the occurrence of a seismogenic fault in a mountainous massif of crystalline rocks without typical geomorphological expression and the role of blind faults in Seismic Hazard Assessment.

scholarly journals An investigation of groundwater condition by geoelectrical resistivity method: A case study in Bengalon, East Kutai, East Kalimantan Province Indonesia

PROMINE ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 45-54
Author(s):  
Shalaho Dina Devy ◽  
Ibnu Hasyim
Keyword(s):  
Sea Water ◽  
Shallow Groundwater ◽  
Groundwater Potential ◽  
Residential Areas ◽  
Alluvial Deposits ◽  
Resistivity Method ◽  
East Kalimantan ◽  
Groundwater Condition ◽  
Geoelectrical Resistivity

Bengalon is located in East Kutai Regency, East Kalimantan Province. Bengalon is included in the Samarinda-Bontang groundwater basin. The development of agricultural and industrial areas, followed by an increase in residential areas, will cause an increase in the water demand. This study aims to determine the groundwater potential of alluvial areas using the resistivity geoelectric method. The resistivity survey resulted in subsurface lithology, shallow groundwater conditions in the form of depth, thickness, and location of the aquifer as well as the type of groundwater quality. There are 10 locations for geoelectric data collection using the 2D geoelectric method. The results showed that the majority of the aquifers were alluvial deposits consisting of sand and sandy clay. The resistance indicating groundwater is 1 - 4 Ω m, at a depth of 10 – 50 m with a thickness varying from 10 – 20 m which has been dominated by sand. The presence of sea water intrusion in aquifers causes the quality of groundwater to tend to be brackish because the research location is in a swamp area bordering the coast.

Enhancing base-metal exploration with seismic imagingThis article is one of a series of papers published in this Special Issue on the theme Lithoprobe — parameters, processes, and the evolution of a continent.

2010 ◽  
Vol 47 (5) ◽  
pp. 741-760 ◽  
Author(s):  
David W. Eaton ◽  
Erick Adam ◽  
Bernd Milkereit ◽  
Matthew Salisbury ◽  
Brian Roberts ◽  
...  
Keyword(s):  
Base Metal ◽  
Direct Detection ◽  
Mineral Exploration ◽  
Geophysical Methods ◽  
Shear Zones ◽  
Ore Deposits ◽  
Mining District ◽  
Borehole Data ◽  
Minimum Thickness ◽  
Metal Mining

Commencing in 1988 and continuing for 5 years, Lithoprobe acquired a series of high-resolution seismic experiments within and near base-metal mining camps in Canada, including the Abitibi subprovince of Quebec and Ontario, the world-class Sudbury Ni–Cu mining district, the Buchans mine in Newfoundland, and the Thompson Ni belt in Manitoba. This work, undertaken in close cooperation with the Geological Survey of Canada and major Canadian mining companies, stimulated an intensive and broadened series of followup studies with the common objective of assessing potential applications of multichannel seismic (MCS) imaging for deep mineral exploration and mine development. This research was motivated by a widely recognized disparity between the depths from which ores can be profitably mined (up to 2 km or more) and the resolving depths (typically <500 m) of commonly used geophysical methods for mineral exploration. Initial rock-property studies established that the expected contrast in acoustic impedance between ores and host rocks should be sufficient to generate observable reflections and (or) scattered waves. For an ore deposit to be directly detectable with MCS, however, it is also necessary for it to meet geometrical criteria including a minimum thickness of 1/8 wavelenth (typically ∼5 m) and a lateral extent similar to the Fresnel radius (typically ∼100 m). Both Lithoprobe and followup seismic studies, calibrated with borehole data, reveal that lithologic contacts that are characterized by large impedance contrast and significant lateral continuity, such as igneous intrusive contacts between mafic and felsic rocks, are the most likely features to be imaged with the MCS techniques. In some camps such as Buchans, however, faults and shear zones are better imaged than lithologic contacts. In either case, these studies show that well-designed and carefully processed seismic profiles can provide a valuable geophysical tool for interpreting the stratigraphic and structural framework of mineral systems and, more rarely, direct-detection capabilities for deep ore deposits.

scholarly journals Late to post-Variscan basement segmentation and differential exhumation along the SW Bohemian Massif, central Europe

Solid Earth ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 2277-2301
Author(s):  
Andreas Eberts ◽  
Hamed Fazlikhani ◽  
Wolfgang Bauer ◽  
Harald Stollhofen ◽  
Helga de Wall ◽  
...  
Keyword(s):  
Central Europe ◽  
Bohemian Massif ◽  
Gravity Data ◽  
Shear Zones ◽  
Magma Ascent ◽  
Tectonic Structures ◽  
Massif Central ◽  
Granite Emplacement ◽  
Variscan Basement ◽  
Block Segmentation

Abstract. The exposed Variscan basement in central Europe is well-known for its complex structural and lithological architecture resulting from multiple deformation phases. We studied the southwestern margin of the Bohemian Massif, which is characterized by major and long-lived shear zones, such as the Pfahl and Danube shear zones, extending over > 100 km and initiated during Variscan tectonics. We integrated Bouguer gravity anomaly and lidar topographic data analyses and combined our results with available data and observations from low-temperature thermochronology, metamorphic grades, and the exposed granite inventory to detect patterns of basement block segmentation and differential exhumation. Three NW–SE-striking basement blocks are bordered by the Runding, Pfahl, and Danube shear zones from the northeast to the southwest. Basement block boundaries are indicated by abrupt changes in measured gravity patterns and metamorphic grades. By applying high-pass filters to gravity data in combination with lineament analysis, we identified a new NNW–SSE-striking tectonic structure (Cham Fault), which further segments known basement blocks. Basement blocks that are segmented by the Cham Fault differ in the abundance and spatial distribution of exposed late Variscan granites and are further characterized by variations in apparent thermochronological age data. Based on our observations and analyses, a differential exhumation and tectonic tilt model is proposed to explain the juxtaposition of different crustal levels. Block segmentation along the NW–SE-striking Pfahl and Runding shear zones most likely occurred prior, during, and after late orogenic granite emplacement at ca. 320 ± 10 Ma, as some of the granites are cross-cut by the shear zones, while others utilized these structures during magma ascent and emplacement. In contrast, activity and block segmentation along the Cham Fault occurred after granite emplacement as the fault sharply truncates the granite inventory. Our study provides evidence of intense and continuous fault activities during late and post-orogenic times and highlights the importance of tectonic structures in the exhumation and juxtaposition of different crustal levels and the creation of complex lithological patterns in orogenic terrains.

scholarly journals Geological-structural mapping and geocronology of shear zones: A methodological proposal

2021 ◽  
Vol 48 (1) ◽  
pp. 81-122
Author(s):  
Anny Julieth Forero Ortega ◽  
Julián Andrés Lopéz Isaza ◽  
Nelson Ricardo López Herrera ◽  
Mario Andrés Cuéllar Cárdenas ◽  
Lina Maria Cetina Tarazona ◽  
...  
Keyword(s):  
Phase Equilibria ◽  
Finite Strain ◽  
Shear Zones ◽  
Petrographic Analysis ◽  
Tectonic Structures ◽  
Structural Mapping ◽  
Oriented Samples ◽  
Geological Evolution ◽  
Deformation Event ◽  
Definition Of

The deformation registered in rocks in the field can be characterized based on the structures preserved in outcrops, which can related be to wide discontinuity zones named faults and shear zones. The geological-structural mapping and the geochronology of these tectonic structures are a topic of great interest not only for tectonic modeling but also for reconstruction of the geological evolution of the national territory. The methodology suggest for the analysis of faults and shear zones is based on eight steps, including: 1) definition of the geological context in which the structure was developed; 2) photointerpretation, image geoprocessing, and geological-structural mapping of the structural and lithological characteristics of the faults and shear zones; 3) petrographic analysis of field-oriented samples; 4) quantification of strain orientation and geometry through 3D finite strain analyses and quantification of non-coaxiliaty of deformation through vorticity analyses; 5) SEM-TEM-EBSD microanalysis; 6) quantification of the P-T conditions of deformation through phase-equilibria modeling or conventional geothermobarometry; 7) dating of syn-kinematic minerals phases and mylonitic rocks through Ar-Ar analyses, in order to determine the reactivation and deformation ages of the structure, respectively, as well as the implementation of the U-Pb technique in syn-kinematic calcite crystals developed in the fault planes; and 8) dating of geological elements adjacent to the structure, such as syn-kinematic intrusive bodies associated with the deformation event using zircon U-Pb dating, rocks hydrothermally altered through Ar-Ar method, and zircon and apatite fission-tracks dating of the blocks adjacent to the faults for determining exhumation ages.

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