查看更多>>摘要：In this paper, uniaxial compression tests were carried out on granite specimens with different rift plane orientations to investigate the effect of the rift plane on the fracture mechanisms. The spatial distribution of acoustic emission and the corresponding fractal dimension are calculated and analyzed to describe the evolution of the microcracks. The results show the compression strength is much higher when the loading direction is perpendicular to the rift plane. Stress thresholds for crack initiation and crack damage are identified using the volumetric strain. The stress threshold for crack initiation is found to be 53% of the failure stress, independent of the rift plane orientation. The spatial distribution of acoustic emission events reveals that when the rift plane is parallel to the loading direction the microcracks spreading is more scattered than that when the rift plane is perpendicular to the loading direction. The larger fractal dimension in the former case during the whole compression process also validates this conclusion. Due to the anisotropy of the specimen, the fractal dimension shows a trend of overall increase during the compression and reaches a stable value before the specimen fails. The fractal dimension of acoustic emission events can be a quantitative characteristic serving as an early warning for the coming failures.
查看更多>>摘要：The rapid detection of urban road disasters has become an urgent problem. The continuous towed geophysical method is an important method for rapid general detection. Ground-penetrating radar and transient electromagnetic have realized continuous towed detection, but the seismic method cannot do it. The reflection seismic method has the advantages of deep detection depth and high resolution. To adapt to the rapid deployment of geophones on urban hardened pavement, a gravity geophone was designed to realize towed acquisition. However, the data acquisition is far from meeting the needs of large area rapid detection on urban roads. In this paper, a continuous towed seismic data collection method is proposed for the first time, that is, the vibration generated by the friction between the geophone base and the ground is used as the seismic source to realize the rapid data acquisition on the urban roads. When the vehicle-mounted seismic equipment is used and the required lateral resolution is 0.5 m, the continuous towed seismic data acquisition efficiency is about 5 km/h. Continuous towed seismic data has a low-resolution and low signal-to-noise ratio, and the real weak reflected signal is drowned by strong energy noise. To solve these problems, this paper proposes a correlation stack method to extract the stack section. When seismic data is collected with the continuous towed seismic equipment, the seismic source signal is not the approximate sharp plus signal, so the resolution of the extracted stack section is still low. Single detection results are difficult to distinguish near-surface structures. The continuous towed seismic acquisition method has a low cost and can realize the rapid repeated detection of the same survey line. The model data and measured data prove that the proposed data acquisition scheme and data processing method have the following advantages: 1) The continuous towed seismic acquisition method can improve the data acquisition efficiency, reduce the cost of data acquisition, and is suitable for large area rapid detection. 2) The correlation stack method can extract reflected signals with real weak energy. 3) Stack processing for multiple detection data can improve the resolution and enhance the energy of real weak signals. The continuous towed seismic data acquisition and the data processing method can realize the rapid inspection and detection of urban roads and has practical engineering application value.
查看更多>>摘要：Design solutions used in the construction of roadbeds require homogeneity of the properties of the structure over long sections. At the same time, the verification of quality of the construction of railways and highways roadbeds is based on local determination of density and other mechanical characteristics of structural layers. In this work, to overcome this drawback, a method is proposed for continuous determination of the properties of structural layers under construction. It is based on the GPR method calibrated by direct measurements of the construction material density. The algorithms of the developed method are implemented in the form of a computer code adapted for use in the construction of roadbeds of railways. The effectiveness of the developed method and computer code were tested on the section of a roadbed under construction. Field measurements were carried out using the series "OKO" GPR and the antenna unit operating at a frequency of 1700 MHz to estimate the density of the subgrade soil in various depth sections. A good agreement is shown between the GPR data and the direct measurements. The obtained radargrams were used to estimate the density of the subgrade soil at depths up to 0.6 m. A good matching between the results obtained by processing the GPR data with the developed computer code and the ones obtained by direct measurements is demonstrated.
Khosravi, MarziehTabasi, SomayehEldien, Hany HossamMotahari, Mohammad Reza...
18页
查看更多>>摘要：Determination of rock properties as materials, foundations and sites of civil projects, is one of the priorities. This study aimed to assess the relationship between static elastic modulus (Es) and dynamic elastic modulus (Ed) and to estimate static properties and shear wave velocity (Vs) using simple regression (SR), support vector regression (SVR), multivariate linear regression (MVLR) and artificial neural network (ANN) methods based on compressional wave velocity and physical properties. For this purpose, first geomechanical characteristics of 80 specimens of the limestone rocks from the Asmari and Ilam formations in Karun 4 (K4) and Karun 2 (K2) dam sites, in southwestern Iran were measured. Then, data related to the various studies from different parts of the world were collected and a global relationship was presented. The average Ed obtained from the various relationships of different researchers was equal to 19.90 GPa, which is less than the average Ed of the present study (31.20 GPa). According to the most accurate fit, the presented relationship between Es and Ed was power. The analysis of all model hypotheses by MVLR showed that it is possible to estimate the static and dynamic properties. Predicting dynamic and static parameters of the limestone rocks using Sigmoid transfer functions and Hyperbolic tangents and various training rules showed that the Sigmoid transfer function and Levenberg-Marquardt training law have the best performance in predictions. Comparison of the methods performance in estimating Vs and static properties showed that the SVR has higher accuracy than other methods.
查看更多>>摘要：The attenuation and dispersion of seismic waves change with frequency. So, it is unreasonable to compensate absorption and attenuation using the full-frequency band seismic data directly. In this study, we propose a seismic high-resolution processing workflow based on the enhanced multi-channel variational mode decomposition (EMVMD). Frist, we aim to adopt the multi-channel variational mode decomposition (MVMD) to decompose seismic data into several band-limited intrinsic mode functions (IMFs). Then, we explain the relationship between the IMFs and the different scale structures, and propose a strategy to determine the number of IMFs by introducing the contraction operator mapping (COM) and the scale-space representation (SSR). Note that we name the MVMD with a number selection strategy as the enhanced MVMD (EMVMD). Next, we adopt the adaptive spectrum-broadening method (ASBM) to separately improve the resolution of each decomposed IMF. Afterward, we can easily obtain the enhanced seismic data with a high resolution by summing the processed IMFs. Finally, we apply the proposed workflow (EMVMD-ASBM) to synthetic and field data to testify its validity and effectiveness for enhancing the resolution of the post-stack seismic data.
查看更多>>摘要：This paper proposes a Probabilistic Neural Network (PNN) based framework for classification of lithology from a number of seismic attributes. The PNN has been the natural choice for classification in several research areas due to its insensitivities towards outliers and higher computational speed compared to multilayer perceptron (MLP) networks. Initially, the lithology is labelled into four classes such as sand, shaly sand, sandy shale, and shale through thorough analysis of multiple well logs by a proficient geologist. The seismic attributes and well logs pertaining to twelve closely spaced boreholes from a western onshore hydrocarbon field in India are used in this study. The performance of the designed framework consisting of preprocessing, classification, and lithological maps generation stages is compared with existing supervised classifiers in terms of classification accuracy, sensitivity, and specificity and the results are reported. The selection of appropriate parameters associated with individual classifier and importance of individual seismic predictors are also investigated. Finally, lithology maps indicating the different classes are produced using the tuned parameters of PNN over the study area. This framework would be of immense help to geologists along with other geological measures to estimate the probability of the presence of hydrocarbon in a large study area.
查看更多>>摘要：Lacustrine sediments in areas of arid Central Asia are sensitive records for paleoenvironmental variations largely associated with the westerlies, targeting the possible transitional linkage between the North Atlantic climate zone and monsoonal eastern Asia. An extensive cognition of paleoenvironmental proxies is a precondition for better deciphering and refining the paleoenvironmental setting. In this study, a combined analysis of magnetic, granulometric and geochemical properties was carried out on lacustrine sediment from the northeastern part of the Yili Basin in northwest China. Results show that magnetic properties within different sedimentary layers may largely respond to the mineral preservation in relation to hydrodynamic inputs and post-depositional alteration. Magnetic concentration was potentially dominated by the input flux of detrital materials, but the depletion of magnetic concentration in the middle part of the section probably arises from post-depositional alteration of the ferrimagnetic phases in sediment with high organic content. This depletion also leads to an enhancement of the fine-grained magnetic phases. Based on the analysis of magnetic and other non-magnetic proxies, three phases of paleoenvironmental variation were identified with regard to the changes in hydrodynamic conditions. Strong hydrodynamic conditions dominated in the lower part of the sections, while there were weaker conditions operated in the middle part of the section, which also underwent post-depositional processes. The upper part of the section experienced undulating hydrodynamic conditions. In addition, this study proposed that the chi ARM/ SIRM ratio possibly has the potential to indicate paleoenvironmental changes and emphasized that the sole usage of magnetic data alone would not deliver comprehensive information of paleoenvironmental evolution. Furthermore, this study also suggests that interdisciplinary study of magnetic transformation in lacustrine sediments is still essential in the future.
da Silva, Ana CamilaResende, Isabelada Costa, Rodrigo CintraUagoda, Rogerio Elias Soares...
13页
查看更多>>摘要：The groundwater flow in fractured rock is an important process that allows to understand the hydrological dynamics at hillslope scales as well the increase of pore pressure at specific points in the soil-rock contact. Exfiltration from bedrock fractures on the failure surfaces and stability problems related to structural charac-teristics of rocks are common in the highland region of Rio de Janeiro, which were identified in a landslide scar resulting from a translational shallow landslide at the soil-bedrock interface triggered by the extreme rainfall events in January 2011. Considering the temporary springs from bedrock fractures in fresh landslide scars this research aims to analyze, through Ground Penetration Radar (GPR), the structure of the rock and the pattern of fractures in subsurface to understandand the hole the existence of a network of fractures in the slope hydro-geological dynamics and possible consequences for its stability. GPR results proved the existence of fissural suspended aquifers near the surface and sub-vertical tectonic fractures acting as geological barriers that create saturation zones inducing the formation of suspended discontinuous aquifers. It is possible that the fracture systems are determinant for the deflagration of mass movement in the region, mainly of translational shallow types, on slopes covered by saprolites overlying fractured rocks.
查看更多>>摘要：Multiple attenuation is an important issue in seismic exploration. The high-resolution parabolic Radon transform (RT) is a widely used multiple attenuation method for the advantages of simple principle and low computational cost. In the Radon domain, however, the curvatures of primaries and multiples are difficult to focus on, sometimes even close to or overlap with each other, which makes their separation faces great difficulties, and ultimately leads to multiple leakages existing in the attenuation results. To eliminate the multiple leakages caused by the high-resolution parabolic RT, we propose a new multiple-attenuation method that combines the highresolution parabolic RT with the connected-component analysis. The high-resolution parabolic RT is used to obtain the estimated multiples in the input data. Based on the estimated multiples, the connected-component analysis can fully use the continuity of multiples in the input data to eliminate the multiple leakages. The industrial model data are validated by both the proposed and the high-resolution parabolic RT methods. Comparing their attenuation results, we conclude that not only does the proposed method achieve better performance even under complex geological structures, it is also suitable for common-midpoint gathers before normal moveout.
NSTL
Elsevier