Search results for: basement rock

Authors: Mohit Kumar

Abstract:

Natural fractures are classified in two broad categories of joints and faults on the basis of shear movement in the deposited strata. Natural fracture always has high structural relationship with extensional or non-extensional tectonics and sometimes the result is seen in the form of micro cracks. Geological evidences suggest that both large and small-scale fractures help in to analyze the seismic anisotropy which essentially contribute into characterization of petro physical properties behavior associated with directional migration of fluid. We generally question why basement study is much needed as historically it is being treated as non-productive and geoscientist had no interest in exploration of these basement rocks. Basement rock goes under high pressure and temperature, and seems to be highly fractured because of the tectonic stresses that are applied to the formation along with the other geological factors such as depositional trend, internal stress of the rock body, rock rheology, pore fluid and capillary pressure. Sometimes carbonate rocks also plays the role of basement and igneous body e.g basalt deposited over the carbonate rocks and fluid migrate from carbonate to igneous rock due to buoyancy force and adequate permeability generated by fracturing. So in order to analyze the complete petroleum system, FMC (Fluid Migration Characterization) is necessary through fractured media including fracture intensity, orientation and distribution both in basement rock and county rock. Thus good understanding of fractures can lead to project the correct wellbore trajectory or path which passes through potential permeable zone generated through intensified P-T and tectonic stress condition. This paper deals with the analysis of these fracture property such as intensity, orientation and distribution in basement rock as large scale fracture can be interpreted on seismic section, however, small scale fractures show ambiguity in interpretation because fracture in basement rock lies below the seismic wavelength and hence shows erroneous result in identification. Seismic attribute technique also helps us to delineate the seismic fracture and subtle changes in fracture zone and these can be inferred from azimuthal anisotropy in velocity and amplitude and spectral decomposition. Seismic azimuthal anisotropy derives fracture intensity and orientation from compressional wave and converted wave data and based on variation of amplitude or velocity with azimuth. Still detailed analysis of fractured basement required full isotropic and anisotropic analysis of fracture matrix and surrounding rock matrix in order to characterize the spatial variability of basement fracture which support the migration of fluid from basement to overlying rock.

Keywords: basement rock, natural fracture, reservoir characterization, seismic attribute

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Authors: N. Hadj Mohamed, A. Boutaleb

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The Beni Snouss area is characterized by horst and graben structures and it comprises deformed Palaeozoic sedimentary and magmatic rocks overlapping by Mesozoic sediments. Two structural units are distinguished: a Palaeozoic basement and a Mesozoic cover. The study area is densely faulted and major faults strike N110° to N140° and dip vertically The mineralized fault zones are readily distinguishable by their argillic wall rock alteration. The fault zones that are filled with mineralizations, aplites, microgranites and quartz run roughly parallel to each other and are apparently in the same fault system. The Palaeozoic basement rocks contain mineralization occurring as veins, veinlets and disseminations. The Liassic carbonate platform sequence contains Ba (Pb-Zn) sulphide deposits occurring mainly as strata bound, and open space filling.

Keywords: Algeria, basement, Beni Snouss, cover

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Authors: Collins C. Chiemeke, I. B. Osazuwa, S. O. Ibe, G. N. Egwuonwu, C. D. Ani, E. C. Chii

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The study area is Zaria, located in the basement complex of northern Nigeria. The rock type forming the major part of the Zaria batholith is granite. This research work was carried out to compare the responses of seismic refraction tomography and resistivity tomography in the same geologic environment and under the same conditions. Hence, the choice of the site that has a visible granitic outcrop that extends across a narrow stream channel and is flanked by unconsolidated overburden, a neutral profile that was covered by plain overburden and a site with thick lateritic cover became necessary. The results of the seismic and resistivity tomography models reveals that seismic velocity and resistivity does not always simultaneously increase with depth, but their responses in any geologic environment are determined by changes in the mechanical and chemical content of the rock types rather than depth.

Keywords: environment, resistivity, response, seismic, velocity

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Authors: A. Ikusika, O. I. Poppola

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This study was carried out to delineate possible structures that may favour the accumulation of tantalite, a magnetic mineral. A ground based technique was employed using proton precision magnetometer G-856 AX. A total of ten geophysical traverses were established in the study area. The acquired magnetic field data were corrected for drift. The trend analysis was adopted to remove the regional gradient from the observed data and the resulting results were presented as profiles. Quantitative interpretation only was adopted to obtain the depth to basement using Peter half slope method. From the geological setting of the area and the information obtained from the magnetic survey, a conclusion can be made that the study area is underlain by a rock unit of accumulated minerals. It is therefore suspected that the overburden is relatively thin within the study area and the metallic minerals are in disseminated quantity and at a shallow depth.

Keywords: basement, drift, magnetic field data, tantalite, traverses

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Authors: M. D. Dogara, G. C. Afuwai, O. O. Esther, A. M. Dawai

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The geology of Northern Nigeria is under intense investigation particularly that of the northwest believed to be of the basement complex. The variability of the lithology is consistently inconsistent. Hence, the need for a close range study, it is, in view of the above that, two geophysical techniques, the vertical electrical sounding employing the Schlumberger array and seismic refraction methods, were used to delineate the geoelectric and geovelocity parameters of the basement complex of northwestern Nigeria. A total area of 400,000 m² was covered with sixty geoelectric stations established and sixty sets of seismic refraction data collected using the forward and reverse method. From the interpretation of the resistivity data, it is suggestive that the area is underlain by not more than five geoelectric layers of varying thicknesses and resistivities when a maximum half electrode spread of 100m was used. The result of the interpreted seismic data revealed two geovelocity layers, with velocities ranging between 478m/s to 1666m/s for the first layer and 1166m/s to 7141m/s for the second layer. The results of the two techniques, suggests that the area of study has an undulating bedrock topography with geoeletric and geovelocity layers composed of weathered rock materials.

Keywords: basement complex, delineation, geoelectric, geovelocity, Nigeria

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Authors: Rahman Abdullayev

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Rituals took place during the rock art production or in the rock art sites can be found reflection in contemporary culture. But the form of rituals was conducted in association with rock art production still uncertain. The main purpose of this research is to define the form of ritual activities that took place in the rock art sites, by the example of Bronze Age rock art of Gobustan. For ritual activity location of the rocks which were selected for making petroglyphs has important significance. Thus, not all the rocks which were suitable for rock art were used for this purpose. If in Upper Paleolithic, Mesolithic, Neolithic periods Gobustan inhabitants executed petroglyphs on the wall of rock shelters, but in Bronze Age they made it on rocks which are in front of the large, open spaces. A recent study of the location of Bronze Age rock art of Gobustan and involving ethnographic information to the interpretation of drawings allows defining the form of rituals which took place in Gobustan at Bronze Age.

Keywords: Bronze Age, Gobustan, ritual, rock art

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Authors: Ahmed T. Farid, Muhammed Rizwan

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Geotechnical study for evaluating soil or rock permeability is a highly important parameter. Permeability values for rock formations are more difficult for determination than soil formation as it is an effect of the rock quality and its fracture values. In this research, the prediction of in situ permeability of limestone rock formations was predicted. The limestone rock permeability was evaluated using Lugeon tests (in-situ packer permeability). Different sites which spread all over the Riyadh region of Saudi Arabia were chosen to conduct our study of predicting the in-situ permeability of limestone rock. Correlations were deducted between the values of in-situ permeability of the limestone rock with the value of the rock quality designation (RQD) calculated during the execution of the boreholes of the study areas. The study was performed for different ranges of RQD values measured during drilling of the sites boreholes. The developed correlations are recommended for the onsite determination of the in-situ permeability of limestone rock only. For the other sedimentary formations of rock, more studies are needed for predicting the actual correlations related to each type.

Keywords: In situ, packer, permeability, rock, quality

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Authors: B. S. Jatau, Baba Adama, S. I. Fadele

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Electrical resistivity investigation was carried out around Bomo area, Zaria, Kaduna state in order to study the subsurface geologic layer with a view of determining the depth to the bedrock and thickness of the geologic layers. Vertical Electrical Sounding (VES) using Schlumberger array was carried out at fifteen (15) VES stations. ABEM terrameter (SAS 300) was used for the data acquisition. The field data obtained have been analyzed using computer software (IPI2win) which gives an automatic interpretation of the apparent resistivity. The VES results revealed heterogeneous nature of the subsurface geological sequence. The geologic sequence beneath the study area is composed of hard pan top soil (clayey and sandy-lateritic), weathered layer, partly weathered or fractured basement and fresh basement. The resistivity value for the topsoil layer varies from 40Ωm to 450Ωm with thickness ranging from 1.25 to 7.5 m. The weathered basement has resistivity values ranging from 50Ωm to 593Ωm and thickness between 1.37 and 20.1 m. The fractured basement has resistivity values ranging from 218Ωm to 520Ωm and thickness of between 12.9 and 26.3 m. The fresh basement (bedrock) has resistivity values ranging from 1215Ωm to 2150Ωm with infinite depth. However, the depth of the earth’s surface to the bedrock surface varies between 2.63 and 34.99 m. The study further stressed the importance of the findings in civil engineering structures and groundwater prospecting.

Keywords: electrical resistivity, CERT (CT), vertical electrical sounding (VES), top soil (TP), weathered basement (WB), partly weathered basement (PWB), fresh basement (FB)

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Authors: Mohammad Mohammadi, Mojtaba Askari, Mohammad Farouq Hossaini

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An intrinsic property of rock mass known as rock bolt supporting factor (RSF) or rock bolting capability of rock mass was developed and used for explanation of the mechanism of rock bolting practice. Based on the theory of RSF, numeral values can be assigned to each given rock mass to show the capability of that rock mass to be reinforced by rock bolting. For determination of shotcrete thickness, both safety and cost must be taken into account. The present paper introduces a scientific approach for determination of the necessary shotcrete thickness in underground structures for support purposes using the concept of rock bolt supporting factor (RSF). The proposed approach makes the outcome of shotcrete design one step more accurate than before. The actual dataset of 500 meters of Alborz Tunnel length is used as an example of the application of the approach.

Keywords: rock bolt supporting factor (RSF), shotcrete design, underground excavation, Alborz Tunnel

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Authors: Samia Ait Ali Yahia

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In Algeria, the most impressive and most known prehistoric art is the painted or engraved rock art which is present with abundance in several regions. The existence of rock art in Great Kabylia region has been known for over sixty years. The main purpose of this research is to show the dangers facing these rock paintings and engravings and what are the arrangements for their protection and recovery. As every vestige destroyed is a part of the world's memory which disappears, some steps have to be taken in order to protect these historical and archaeological heritages.

Keywords: rock paintings and engravings, preservation, valorization, Kabylia

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Authors: Soo-yeon Seo, Su-jin Jung

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In recent years, the need for remodeling of many apartments built 30 years ago is increasing. Therefore, researches on the structural reinforcement technology of existing apartments have been conducted. On the other hand, there is a growing need for research on the existing underground space expansion technology to expand the parking space required for remodeling. When expanding an existing underground space, for earthworks, an earth retaining wall must be installed between the existing apartment building and it. In order to maximize the possible underground space, it is necessary to minimize the thickness of the portion of earth retaining wall and underground basement wall. In this manner, the calculation procedure is studied for the evaluation of shear strength of the composite basement wall corresponding to shear span-to-depth ratio in this study. As a result, it was shown that the proposed calculation procedure can be used to evaluate the shear strength of the composite basement wall as safe. On the other hand, when shear span-to-depth ratio is small, shear strength is very underestimated.

Keywords: underground space expansion, combined structure, temporary retaining wall, basement wall, shear connectors

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Authors: Natália Botica, Luís Luís, Paulo Bernardes

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The Côa Valley, listed World Heritage since 1998, presents more than 1300 open-air engraved rock panels. The Archaeological Park of the Côa Valley recorded the rock art motifs, testing various techniques based on direct tracing processes on the rock, using natural and artificial lighting. In this work, integrated in the "Open Access Rock Art Repository" (RARAA) project, we present the methodology adopted for the vectorial drawing of the rock art motifs based on orthophotos taken from the photogrammetric survey and 3D models of the rocks. We also present the information system designed to integrate the vector drawing and the characterization data of the motifs, as well as the open access sharing, in order to promote their reuse in multiple areas. The 3D models themselves constitute a very detailed record, ensuring the digital preservation of the rock and iconography. Thus, even if a rock or motif disappears, it can continue to be studied and even recreated.

Keywords: rock art, archaeology, iron age, 3D models

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Authors: Sukran Acikel, Mehmet Ekmekci, Otgonbayar Namkhai

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Lignite coal fields in western Turkey generally occurs in tensional Neogene basins bordered by major faults. Karacahisar coal field in Mugla province of western Turkey is a large Neogene basin filled with alternation of silisic and calcerous layers. The basement of the basin is composed of mainly karstified carbonate rocks of Mesozoic and schists of Paleozoic age. The basement rocks are exposed at highlands surrounding the basin. The basin fill deposits forms shallow, low yield and local aquifers whereas karstic carbonate rock masses forms the major aquifer in the region. The karstic aquifer discharges through a spring zone issuing at intersection of two major faults. Municipal water demand in Bodrum city, a touristic attraction area is almost totally supplied by boreholes tapping the karstic aquifer. A well field has been constructed on the eastern edge of the coal basin, which forms a ridge separating two Neogene basins. A major concern was raised about the plausible impact of mining activities on groundwater system in general and on water supply well field in particular. The hydrogeological studies carried out in the area revealed that the coal seam is located below the groundwater level. Mining operations will be affected by groundwater inflow to the pits, which will require dewatering measures. Dewatering activities in mine sites have two-sided effects: a) lowers the groundwater level at and around the pit for a safe and effective mining operation, b) continuous dewatering causes expansion of cone of depression to reach a spring, stream and/or well being utilized by local people, capturing their water. Plausible effect of mining operations on the flow of the spring zone was another issue of concern. Therefore, a detailed representative hydrogeological conceptual model of the site was developed on the basis of available data and field work. According to the hydrogeological conceptual model, dewatering of Neogene layers will not hydraulically affect the water supply wells, however, the ultimate perimeter of the open pit will expand to intersect the well field. According to the conceptual model, the coal seam is separated from the bottom by a thick impervious clay layer sitting on the carbonate basement. Therefore, the hydrostratigraphy does not allow a hydraulic interaction between the mine pit and the karstic carbonate rock aquifer. However, the structural setting in the basin suggests that deep faults intersecting the basement and the Neogene sequence will most probably carry the deep groundwater up to a level above the bottom of the pit. This will require taking necessary measure to lower the piezometric level of the carbonate rock aquifer along the faults. Dewatering the carbonate rock aquifer will reduce the flow to the spring zone. All findings were put together to recommend a strategy for safe and effective mining operation.

Keywords: conceptual model, dewatering, groundwater, mining operation

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Authors: Collins C. Chiemeke, A. Onugba, P. Sule

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High resolution seismic reflection has recently been carried out on Zaria batholith, with the aim of characterizing the granitic Zaria batholiths in terms of its lithology. The geology of the area has revealed that the older granite outcrops in the vicinity of Zaria are exposures of a syntectonics to late-tectonic granite batholiths which intruded a crystalline gneissic basement during the Pan-African Orogeny. During the data acquisition the geophone were placed at interval of 1 m, variable offset of 1 and 10 m was used. The common midpoint (CMP) method with 12 fold coverage was employed for the survey. Analysis of the generated 3D surface of the p wave velocities from different profiles for densities and bulk modulus revealed that the rock material is more consolidated in South East part of the batholith and less consolidated in the North Western part. This was in conformity with earlier identified geology of the area, with the South Eastern part majorly of granitic outcrop, while the North Western part is characterized with the exposure of gneisses and thick overburden cover. The difference in lithology was also confirmed by the difference in seismic sections and Arial satellite photograph. Hence two major lithologies were identified, the granitic and gneisses complex which are characterized by gradational boundaries.

Keywords: basement complex, batholith, high resolution, lithologies, seismic reflection

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Authors: Mohamed Dhaoui, Hakim Gabtni

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The migration of hydrocarbons is a fairly complicated process that depends on several parameters, both structural and sedimentological. In this study, we will try to determine secondary migration paths which convey hydrocarbon from their main source rock to the largest reservoir of the Paleozoic petroleum system of the Tunisian part of Ghadames basin. In fact, The Silurian source rock is the main source rock of the Paleozoic petroleum system of the Ghadames basin. However, the most solicited reservoir in this area is the Triassic reservoir TAGI (Trias Argilo-Gréseux Inférieur). Several geochemical studies have confirmed that oil products TAGI come mainly from the Tannezuft Silurian source rock. That being said that secondary migration occurs through the fault system which affects the post-Silurian series. Our study is based on analysis and interpretation of gravity data. The gravity modeling was conducted in the northern part of Ghadames basin and the Telemzane uplift. We noted that there is a close relationship between the location of producing oil fields and gravity gradients which separate the positive and negative gravity anomalies. In fact, the analysis and transformation of the Bouguer anomaly map, and the residual gravity map allowed as understanding the architecture of the Precambrian in the study area, thereafter gravimetric models were established allowed to determine the probable migration path.

Keywords: basement, Ghadames, gravity, hydrocarbon, migration path

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Authors: Olumide J. Adedapo

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In this work, geothermal energy resource maps of the Niger Delta Basin were constructed using borehole thermal log data from over 300 deep wells. Three major geothermal anomalies were delineated and quantitatively interpreted in both onshore and offshore parts of the Niger Delta. The geothermal maps present the distribution of geothermal energy stored in the sedimentary rock mass in two ways: the accessible resources in depth interval 0-4000 m and static geothermal energy resources stored in the complete sedimentary infill of the basin (from the ground surface to the basement). The first map shows two major onshore anomalies, one in the north (with maximum energy values, 800 GJ/m2), another in the east to northeastern part (maximum energy values of 1250–1500 GJ/m2). Another two major anomalies occur offshore, one in the south with values of 750-1000 GJ/m2, occurring at about 100 km seawards and the other, in the southwest offshore with values 750-1250 GJ/m2, still at about 100 km from the shore. A second map of the Niger Delta shows a small anomaly in the northern part with the maximum value of 1500 GJ/m2 and a major anomaly occurring in the eastern part of the basin, onshore, with values of 2000-3500 GJ/m2. Offshore in the south and southwest anomalies in the total sedimentary rock mass occur with highest values up to 4000GJ/m2, with the southwestern anomaly extending west to the shore. It is much of interest to note the seaward–westward extension of these anomalies both in size, configuration, and magnitude for the geothermal energy in the total sedimentary thickness to the underlying basement. These anomalous fields show the most favourable locations and areas for further work on geothermal energy resources.

Keywords: geothermal energy, offshore, Niger delta, basin

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Authors: Li Hung-Hui, Chen Chi-Chieh, Yang Zon-Yee

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This study aims to explore the impact energy absorption in the fragmented processes of rock samples during the split-Hopkinson-pressure-bar tests. Three kinds of rock samples including granite, marble and sandstone were tested. The impact energy absorptions were calculated according to the incident, reflected and transmitted strain wave histories measured by a oscilloscope. The degree of fragment rocks after tests was quantified by the box dimension of the fractal theory. The box dimension of rock fragments was obtained from the particle size distribution curve by the sieve analysis. The results can be concluded that: (1) the degree of rock fragments after tests can be well described by the value of box dimension; (2) with the impact energy absorption increasing, the degrees of rock fragments are varied from the very large fragments to very small fragments, and the corresponding box dimension varies from 2.9 to 1.2.

Keywords: SHPB test, energy absorption, rock fragments, impact loading, box dimension

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Authors: Ibrahim Abdel Gadir Malik, Dafalla Siddig Dafalla, Osama Abdelgadir El-Bushra

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Geological and engineering characteristics of intact rock and the discontinuity surfaces was used to describe and classify rock mass into zones based on mechanical and physical properties. Many conditions terms that affect the rock mas; such as Rock strength, Rock Quality Designation (RQD) value, joint spacing, and condition of joint, water condition with block size, joint roughness, separation, joint hardness, friction angle and weathering were used to classify the rock mass into: Good quality (class II) (RMR values range between 75% and 56%), Good to fair quality (class II to III) (RMR values range between 70% and 55%), Fair quality (class III) (RMR values range between 60% and 50%) and Fair to poor quality (Class III to IV) (RMR values, range between (50% and 35%).

Keywords: rock strength, RQD, joints, weathering

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Authors: Claudia H. Swanson, Jens Günster

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This research addresses the densification via compaction and sintering of naturally occurring rock salt which was motivated by the fact that in a saline environment rock salt is thermodynamically stable and does show a mechanical behavior compatible to the surrounding host material. The sintering of rock salt powder compacts was systematically investigated using temperature and pressure as variables for the sinter process. The behavior of rock salt showed segregations of anhydrite, CaSO4 - the major impurity found in rock salt, to the grain boundaries between individual sodium chloride crystals. Powder compacts treated with lower pressures lost those anhydrite segregates over time while high pressure treated compacts remained with anhydrite segregates. The density reached in this study is 2.008 g cm-3 corresponding to a density of 92.5 % of the theoretical value. This high density is making the sintering a promising technique for rock salt as applications in underground appropriate environment.

Keywords: rock salt, sinter, anhydrite, nuclear safety

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Authors: Murtala Gada Abubakar, Aliyu T. Umar

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A substantial part of Nigeria is part of semi-arid areas of the world, underlain by basement complex (hard) rocks which are very poor in both transmission and storage of appreciable quantity of water. Recently, a growing attention is being paid on the need to develop water resources in these areas largely due to concerns about increasing droughts and the need to maintain water security challenges. While there is ample body of knowledge that captures the hydrological behaviours of the sedimentary part, reported research which unambiguously illustrates water distribution in the basement complex of the Sokoto basin remains sparse. Considering the growing need to meet the water requirements of those living in this region necessitated the call for accurate water balance estimations that can inform a sustainable planning and development to address water security challenges for the area. To meet this task, a one-dimensional soil water balance model was developed and utilised to assess the state of water distribution within the Sokoto basin basement complex using measured meteorological variables and information about different landscapes within the complex. The model simulated the soil water storage and rates of input and output of water in response to climate and irrigation where applicable using data from 2001 to 2010 inclusive. The results revealed areas within the Sokoto basin basement complex that are rich and deficient in groundwater resource. The high potential areas identified includes the fadama, the fractured rocks and the cultivated lands, while the low potential areas are the sealed surfaces and non-fractured rocks. This study concludes that the modelling approach is a useful tool for assessing the hydrological behaviour and for better understanding the water resource availability within a basement complex.

Keywords: basement complex, hydrological processes, Sokoto Basin, water security

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Authors: Jian-Xiu Wan, Yao Yin

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In complex terrain and poor geological conditions areas, Railway, highway and other transportation constructions are still strongly developing. However, various geological disasters happened such as landslide, rock heap and so on. According to the results of geological investigation, the form of skirt (trapezoidal), semicircle and triangle rock heaps are mainly due to complex internal force and external force, in a certain extent, which is related to the terrain, the nature of the rock mass, the supply area and the surface shape of rock heap. Combined with the above factors, discrete element numerical simulation of rock mass is established under different terrain conditions based on 3DEC, and accelerated formation process of rock heap under seismic action is simulated. The fragmentation structure supply area is calculated, in which the most dangerous area is located. At the same time, the formation mechanism and development process are studied in different terrain conditions, and the structure of rock heap is judged by section, which can provide a strong theoretical and technical support for the prevention and control of geological disasters.

Keywords: 3DEC, fragmentation structure, rock heap, slope, seismic action

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Authors: Md. Selim Reza, Mohammad Zohir Uddin

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Geophysical logging technique was conducted in a borehole in the north-western part of Bangladesh. The main objectives of this study were to identify the subsurface lithology and the presence of magnetic minerals within the basement complex. In this survey, full waveform sonic, magnetic susceptibility and natural gamma logs were conducted up to the depth of 660 m. From sonic log, three distinct velocity zones were observed at depths ranging from 20 m to 81 m, 81m to 360 m and 420 m to 660 m having the average velocity of 1600 m/s indicating unconsolidated sediment, 2500 m/s indicating hard, compact and matured sediments and 6300 m/s indicating basement complex respectively. Some low-velocity zones within the basement were identified as fractures/fissures. Natural gamma log was carried out only in the basement complex. According to magnetic susceptibility log, broadly three important zones were identified which had good agreement with the natural gamma, sonic as well as geological logs. The zone at the depth from 460 m to 470 m had the average susceptibility value of 3445 cgs unit. The average natural gamma value and sonic velocity in this zone are 150 cps and 3000 m/s respectively. The zone at the depth from 571 m to 598 m had the average susceptibility value of 5158 cgs unit with the average natural gamma value and sonic velocity are 160 cps and 6000 m/s respectively. On the other hand, the zone at the depth from 598 m to 620 m had the average susceptibility value of 1998 cgs unit with the average natural gamma value and sonic velocity show 200 cps and 3000 m/s respectively. From the interpretation of geophysical logs the 1st and 3rd zones within the basement complex are considered to be less significant whereas the 2nd zone is described as the most significant for magnetic minerals. Therefore, more drill holes are recommended on the anomalous body to delineate the extent, thickness and reserve of the magnetic body and further research are needed to determine the quality of mineral resources.

Keywords: basement complex, fractures/fissures, geophysical logging, lithology, magnetic susceptibility

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Authors: Samia Ait Ali Yahia

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The rock paintings of Grande Kabylia contain a good number of Libyan inscriptions. Of the 54 sites discovered, 23 have inscriptions painted in red ocher. We find them in rock shelters, on blocks of sandstone in the northern part of Kabylia. Our job is to collect as many cave paintings as possible with Libyan inscriptions. Then we will make an analysis on the epigraphic level, the different forms of the characters and their frequencies. The other purpose of this research is to bring out the different characters used in these paintings and compare them with those of the Libyan steles of Grande Kabylia.

Keywords: Grande Kabylia, Libyan inscriptions, Libyan stele, rock paintings

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Authors: N. Reppas, Y. L. Gui, B. Wetenhall, C. T. Davie, J. Ma

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A theoretical constitutive model describing the stress-strain behavior of rock subjected to different confining pressures is presented. A bounding surface plastic model with hardening effects is proposed which includes the effect of temperature drop. The bounding surface is based on a mapping rule and the temperature effect on rock is controlled by Poisson’s ratio. Validation of the results against available experimental data is also presented. The relation of deviatoric stress and axial strain is illustrated at different temperatures to analyze the effect of temperature decrease in terms of stiffness of the material.

Keywords: bounding surface, cooling of rock, plasticity model, rock deformation, elasto-plastic behavior

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Authors: Nikolaos Reppas, Yilin Gui, Ben Wetenhall, Colin Davie

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Injection of CO2 inside wellbore can induce different kind of loadings that can lead to thermal, hydraulic, and mechanical changes on the surrounding rock. A dual-porosity theoretical constitutive model will be presented for the stability analysis of the wellbore during CO2 injection. An elastoplastic damage response will be considered. A bounding yield surface will be presented considering damage effects on sandstone. The main target of the research paper is to present a theoretical constitutive model that can help industries to safely store CO2 in geological rock formations and forecast any changes on the surrounding rock of the wellbore. The fully coupled elasto-plastic damage Thermo-Hydraulic-Mechanical theoretical model will be validated from existing experimental data for sandstone after simulating some scenarios by using FEM on MATLAB software.

Keywords: carbon capture and storage, rock mechanics, THM effects on rock, constitutive model

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Authors: Vathna Suy, Ki-Il Song

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In order to store highly pressurized gas such as an isothermal compressed air energy storage, Lined Rock Caverns (LRC) are constructed underground and supported by layers of concrete, steel and rock masses. This study aims to numerically investigate the performance of rock masses which serve as a support of Lined Rock Cavern subjected to high cyclic pressure loadings. FLAC3D finite different software is used for the simulation since the software can effectively model the behavior of concrete lining and steel plate with its built-in structural elements. Cyclic pressure loadings are applied onto the inner surface of the cavern which then transmitted to concrete, steel and eventually to the surrounding rock masses. Changes of stress and strain are constantly monitored throughout all the process of loading operations. The results at various monitoring locations are then extracted and analyzed to assess the response of the rock masses, specifically on its ability to absorb energy during loadings induced by the changes of cyclic pressure loadings inside the cavern. By analyzing the obtained data of stress-strain relation and taking into account the behavior of materials under the effect of strain-dependency, conclusions on the performance of rock masses subjected to high cyclic loading conditions are drawn.

Keywords: cyclic loading, FLAC3D, lined rock cavern (LRC), strain-dependency

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Authors: Junlong Shang, Zhengxian Chua, Hoongping Peh, Zhiye Zhao

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Due to scarce land resources in Singapore, it is imperative to increase water storage capacities to meet the increasing demand of water to secure a sustainable development, which can be achieved in the underground by rock caverns. In this paper, a preliminary study on the effects of cavern span, height and radius on the cavern stability is presented to provide a guidance on the cavern construction in the context of Singapore. It is found that the radius of caverns should be around half of the span width (i.e., B/R=2) to reduce vertical displacement at the crown of cavern. The smaller the rock cover, the smaller displacement. The minimum rock thickness should be at least the same as the cavern span to eliminate excessive yielded element. Finally, rock support system is introduced to maintain the profile of caverns.

Keywords: cavern dimension, numerical modelling, sustainable development, underground rock cavern

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Authors: J. K. Adedeji, S. T. Ijatuyi

Abstract:

The application of neural network using pattern recognition to study the fluid dynamics and predict the groundwater reservoirs properties has been used in this research. The essential of geophysical survey using the manual methods has failed in basement environment, hence the need for an intelligent computing such as predicted from neural network is inevitable. A non-linear neural network with an XOR (exclusive OR) output of 8-bits configuration has been used in this research to predict the nature of groundwater reservoirs and fluid dynamics of a typical basement crystalline rock. The control variables are the apparent resistivity of weathered layer (p₁), fractured layer (p₂), and the depth (h), while the dependent variable is the flow parameter (F=λ). The algorithm that was used in training the neural network is the back-propagation coded in C++ language with 300 epoch runs. The neural network was very intelligent to map out the flow channels and detect how they behave to form viable storage within the strata. The neural network model showed that an important variable g_r (gravitational resistance) can be deduced from the elevation and apparent resistivity p_a. The model results from SPSS showed that the coefficients, a, b and c are statistically significant with reduced standard error at 5%.

Keywords: gravitational resistance, neural network, non-linear, pattern recognition

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Authors: Hamid Reza Nejati, Amin Nazerigivi, Ahmad Reza Sayadi

Abstract:

Failure mechanism of rocks is one of the fundamental aspects to study rock engineering stability. Rock is a material that contains flaws, initial damage, micro-cracks, etc. Failure of rock structure is largely due to tensile stress and was influenced by various parameters. In the present study, the effect of brittleness and loading rate on the physical and mechanical phenomena produced in rock during loading sequences is considered. For this purpose, Acoustic Emission (AE) technique is used to monitor fracturing process of three rock types (onyx marble, sandstone and soft limestone) with different brittleness and sandstone samples under different loading rate. The results of experimental tests revealed that brittleness and loading rate have a significant effect on the mode and number of induced fracture in rocks. An increase in rock brittleness increases the frequency of induced cracks, and the number of tensile fracture decreases when loading rate increases.

Keywords: brittleness, loading rate, acoustic emission, tensile fracture, shear fracture

Procedia PDF Downloads 474

Authors: Janusz Kwaśniewski, Ireneusz Dominik, Krzysztof Lalik

Abstract:

The knowledge about rock layers thickness, especially above drilled mining pavements are crucial for workers safety. The measuring systems used nowadays are generally imperfect and there is a strong demand for improvement. The application of a new type of a measurement system called Self-Excited Acoustical System is presented in the paper. The system was applied until now to monitor stress changes in metal and concrete constructions. The change in measurement methodology resulted in possibility of measuring the thickness of the rocks above the tunnels as well as thickness of a singular rock layer. The idea is to find two resonance frequencies of the self-exited system, which consists of a vibration exciter and vibration receiver placed at a distance, which are coupled with a proper power amplifier, and which operate in a closed loop with a positive feedback. The resonance with the higher amplitude determines thickness of the whole rock, whereas the lower amplitude resonance indicates thickness of a singular layer. The results of the laboratory tests conducted on a group of different rock materials are also presented.

Keywords: auto-oscillator, non-destructive testing, rock thickness measurement, geotechnic

Procedia PDF Downloads 373