查看更多>>摘要：The granite body, or referred to as boulder, that shows high resistivity in the near-surface is a common geohazard in pipeline construction by trenchless technology. The GEM-2 system using small coils as the transmitter and receiver (Tx-Rx) has been widely used to delineate the low resistivity target with 1D results in the near-surface due to its efficiency and non-invasive characteristics. However, the 3D inversion might be preferred since the boulder is highly resistive and has a three-dimensional (3D) structure. To study the effectiveness of boulder detection using GEM-2 system and 3D inversion, we use the footprint-guided compact finite element method (CFEM) for 3D numerical modeling, and Gauss-Newton optimization is applied to delineate the 3D structure of the boulder. Because of the recorded response is dominated by the induced current within a limited volume directly below the Tx, the modeling volume of each Tx-Rx pair is defined as subareas of the entire survey area, and the sensitivity is explicitly calculated along with the modeling process. We setup an experiment with granite boulder scenario and conduct a GEM-2 test survey to show the performance of our 3D inversion method in practice. The inversion results illustrate that our inversion algorithm has a higher horizontal resolution than the previous 1D inversion, and the three-dimensional contour of the boulder is indicated by relatively high resistivity.
Uyanik, N. AytenOncu, ZiyaBozcu, MustafaUyanik, Osman...
13页
查看更多>>摘要：This study aims to determine the radioactivity properties of the geological units outcropped in the area between Sandikli-S,uhut (Afyonkarahisar) and reveal the origin and boundary relations of geological units by taking advantage of these properties. The geologic units outcropping in the region consist of Paleozoic metamorphics, Mesozoic olistrostromal sediments and mega limestone blocks, Tertiary volcanic and volcaniclastics, and fluvial and lacustrine sediments. In the contacts of these geological units, alteration zones developed at the influence of thermal fluids due to volcanic activity. These zones exhibit different radiological characteristics depending on the lithological features of the geological units and their proximity to volcanic activity. The measured 238U, 232Th and, 40K activity concentrations, U/Th, Th/U, Th/K, and U/K values, Efimov parameter depending on these activity concentrations indicate characterizations that can estimate the boundaries of the alteration zones and geological units. The alteration zones and limits of geological units were determined using the maps generated from measured and calculated parameters. In addition, many trachyandesitic dykes and thin lava levels that could not be marked in the units signed as agglomerate, tuff, and lava in the geological map, were determined on the radioactive maps with high anomaly values.
查看更多>>摘要：The geophysical survey presented in this paper deals with the combined application of multiple geophysical methods in the area where the new University of Wester Macedonia is to be build. The aim of the survey was to investigate the optimal methodological approach regarding the detection of karst features on limestone rocks. Electric Resistivity Tomography (ERT), Seismic Refraction Tomography (SRT) and Multichannel Analysis of Surface Waves (MASW) were applied. All measurements took place at the area of building C, where a cavity was observed on the surface. ERT was initially applied in order to delineate known features and determine a 3D geoelectric model. Seismic exploration followed in order to evaluate the potential of seismic methods in karst environment and the overall combined interpretation. The results highlighted the main advantages and disad-vantages of each method, confirming the importance of joint interpretation. Seismic methods were crucial for the clarification of ambiguous ERT results caused by a resistive environment. Synthetic modeling and real data inversion proved that refraction tomography is a useful and reliable tool in cavity detection. MASW can be used as a complementary technique as it still faces challenges in the delimitation of karst features.
查看更多>>摘要：This article presents the successful application of several geophysical methods in archaeological prospection with integration of LiDAR data and examination of historical documents. The locality of interest is situated in an urban area of Bratislava city on the Danube River where no previous archaeological research has been undertaken. It comprises the oldest public park in Central Europe which is surrounded by a fortification system dating to the Napoleonic siege of Pressburg (Bratislava) in 1809. Urban areas are often challenging for conducting archaeo geophysical investigation due to limited access and existing obstacles of modern origin. For the purposes of this investigation shallow geophysical survey methods were applied including magnetometry, ground penetrating radar (GPR), 2D electrical resistivity tomography (ERT) and electrical resistance survey. Magnetometry was used to obtain a general view of the survey areas and to help to target the following surveys. ERT and GPR were used to explore detected features in more detail and obtain information about their shape and depth. The results of the survey show the importance of the combined approach using multiple geophysical methods while also highlighting their benefits and limitations. The survey was successful in investigating the basic elements of the fortification system which includes a rampart, a ditch and a bastion. The results have revealed information about the current state of the ramparts as well as their original construction. Also, the previously unrecorded remains of a bastion were identified along with previous phases of the fortification. The results obtained reveal the archaeological potential of this historical locality and help to better understand its extension, which is essential for its future protection and development.
查看更多>>摘要：Geoid determination for Egypt faces several challenges. There are large gravity data gaps, gravity data come from different sources, were measured during different decades, and some lack information about their precision. The aim of the paper is to find out a new geoid model for Egypt using the advantages of the shallow-layer method. The shallow-layer method is different from the traditional Stokes and Molodenesky geoid determination methods as it comes from the definition of the geoid itself. In our work, we apply the shallow-layer method to determine a 5 ' x 5 ' geoid model for Egypt which ranges from (21 circle < phi < 32 circle; 24 circle < lambda < 37 circle). The global digital topographic model DTM2006.0, the Danish National Space Center DNSC08 model, the EGM2008 gravity field model, and the CRUST2.0 crust model were used to distinguish boundaries for the shallow-layer and determine its interior structure. To validate and test the computed geoid, four gravimetric geoid models for Egypt were computed using different techniques, the Meissl-geoid using modified Stokes kernel after Meissel, the Wong-geoid using modified Stokes kernel after Wong and Gore, the Heck-geoid using modified Stokes kernel after Heck and Gruninger, and the window-geoid using window technique. All the computed geoid models were validated using the available GPS benchmark stations in Egypt. The difference between the computed geoid models and GPS benchmark station shows that the shallow-layer method gives the most precise geoid with the narrowest range and smallest standard deviation. The standard deviation of geoid differences for the geoid computed using the shallow-layer method (Shen-geoid) drops by about 0.37 m compared to the Stokes/Meissl geoid, which means that the calculated Shen-geoid fits GPS benchmarks better than the computed gravimetric geoid (using the available gravity data) for Egypt. The results demonstrate that the shallow-layer method can estimate the geoid at higher accuracy.
查看更多>>摘要：Tunnel boring machine (TBM) construction is a safe and efficient tunnel construction method at this stage, which contributes to the essential role of ahead prospecting methods, an essential prerequisite for ensuring the safety of TBM construction. Due to the high interference in the TBM tunnel environment, it is difficult to effectively apply multiple ahead prospecting methods. The existing geophysical methods are restricted because of the extremely small prospecting space in the TBM tunnel environment. Also, the TBM tunnel environment is required to introduce high-resolution detection methods. This paper proposes an ahead prospecting method suitable for TBM tunnel, using the simulation of three-dimensional vector finite element. Specifically, this prospecting method uses transient electromagnetic electrical radiation sources to emit and receives the Ex. Besides, the full field apparent resistivity imaging method is used to perform imaging interpretation of the adverse geological structures in front of the tunnel face in a semi-quantitative manner, to obtain the prospecting results required for the ahead prospecting in TBM tunnel.
查看更多>>摘要：Frequency-domain electromagnetic (FDEM) data are commonly inverted to characterize subsurface geoelectrical properties using smoothness constraints in 1D inversion schemes assuming a layered medium. Smoothness constraints are suitable for imaging gradual transitions of subsurface geoelectrical properties caused, for example, by varying sand, clay, or fluid content. However, such inversion approaches are limited in characterizing sharp interfaces. Alternative regularizations based on the minimum gradient support (MGS) stabilizers can, instead, be used to promote results with different levels of smoothness/sharpness selected by simply acting on the so-called focusing parameter. The MGS regularization has been implemented for different kinds of geophysical data inversion strategies. However, concerning FDEM data, the MGS regularization has only been implemented for vertically constrained inversion (VCI) approaches but not for laterally constrained inversion (LCI) approaches. We present a novel LCI approach for FDEM data using the MGS regularization for the vertical and lateral direction. Using synthetic and field data examples, we demonstrate that our approach can efficiently and automatically provide a set of model solutions characterized by different levels of sharpness and variable lateral consistencies. In terms of data misfit, the obtained set of solutions contains equivalent models allowing us also to investigate the non-uniqueness of FDEM data inversion.
查看更多>>摘要：Ground Penetrating Radar (GPR) is a non-destructive and efficient underground survey equipment, which has been widely used in the field of highway safety.Nowadays, it is common to manually interpret the GPR data detected on the highway to find the layer-interface. But, its efficiency and accuracy can no longer meet the needs of various engineering projects. In this manuscript, we propose a geological layer-interface detection framework based on Faster R-CNN, which is used to ensure the safety of highway traffic. The framework can realize the needs of end-to-end and real-time detection. We conduct a lot of experiments on the dataset of highway GPR profile, and the results show that the framework based on Faster R-CNN can be highly effectively used for highway underground layer-interface detection, and the precision of the model can reach 98.30%.
查看更多>>摘要：In this paper, the effectiveness of optimized and conventional resistivity arrays for resolving shallow geological features was investigated at Penang Island, Malaysia. The assessment was between the inversion results from Noise-Weighted Compare R (NWCR) optimized arrays, and commonly used conventional arrays (Dipole-Dipole (DD) and Wenner-Schlumberger (WS)). This is demonstrated using two field cases studies. The first case was conducted at an area characterized by fractures /cracks in the walls and ceiling of a heritage building in Georgetown city. The aim was to identify the weakness zone responsible for the observed fractures. The second case study was conducted in the main campus of Universiti Sains Malaysia (USM), to delineate the interface between the granitic bedrock and the unconsolidated sediments. In the first case, the results show a layer with a resistivity value of less than 2 Ohm-m between 2 m to 6 m depth. This layer could be the weak zone in the investigated area. The NWCR optimized arrays detected this zone better than the DD and WS. This finding correlates quite well with the shear wave velocity (Vs) model, with Vs less than 115 m/s in the same line and depth. For the second case study, the results were compared with the borehole log in the middle of the resistivity line. The ERT model obtained from the NWCR defines the granitic surface at around 32 m depth, which correlates well with the borehole log, while the model from the DD arrays underestimated depth. In summary, the NWCR optimized arrays give a more accurate image of the subsurface resistivity distribution, followed by the DD array. The WS array performed the least.
查看更多>>摘要：The computationally expensive cost and complexity are practical challenges in solving the three-dimensional (3D) inverse problem in the time domain, and many real-world surveys are still inverted in one dimension (1-D). We present a new way to invert transient electromagnetic (TEM) data from a rectangular fixed loop to image subsurface electrical conductivity, which overcomes this limitation and permits efficient implementation of the inversion process on a personal computer. A TEM signal was transformed to the real and imaginary components of a frequency-domain (FD) electromagnetic (EM) response. The transformation was performed by a regularization inversion method. The recovered FD EM response was used as the data for the 3-D inversion. The forward problem and sensitivity were solved by using a staggered-grid finite-difference technique in the FD, and the background Green's function was carried out using the virtual interface method. The non-linear conjugate gradient method (NLCG) was employed to solve the 3-D inverse problem. A synthetic example revealed the basic functionality of the approach, and the FD inversion of a TEM field dataset acquired in the northeastern Qinshui Basin, Shanxi Province, China demonstrated a real-world application. Our inversion approach is general and suitable for different-type sources, such as a vertical magnetic dipole or horizontal electric dipole.
NSTL
Elsevier