International Science Index

International Journal of Geological and Environmental Engineering

465
58002
Geochemistry and Tectonic Framework of Malani Igneous Suite and Their Effect on Groundwater Quality of Tosham, India
Abstract:
The objective of the study was to assess the role of mineralogy and subsurface structure on water quality of Tosham, Malani Igneous Suite (MIS), Western Rajasthan, India. MIS is the largest (55,000 km2) A-type, anorogenic and high heat producing acid magmatism in the peninsular India and owes its origin to hot spot tectonics. Apart from agricultural and industrial wastes, geogenic activities cause fluctuations in quality parameters of water resources. Twenty water samples (20) selected from Tosham and surrounding areas were analyzed for As, Pb, B, Al, Zn, Fe, Ni using Inductive coupled plasma emission and F by Ion Chromatography. The concentration of As, Pb, B, Ni and F was above the stipulated level specified by BIS (Bureau of Indian Standards IS-10500, 2012). The concentration of As and Pb in surrounding areas of Tosham ranged from 1.2 to 4.1 mg/l and from 0.59 to 0.9 mg/l respectively which is higher than limits of 0.05mg/l (As) and 0.01 mg/l (Pb). Excess trace metal accumulation in water is toxic to humans and adversely affects the central nervous system, kidneys, gastrointestinal tract, skin and cause mental confusion. Groundwater quality is defined by nature of rock formation, mineral water reaction, physiography, soils, environment, recharge and discharge conditions of the area. Fluoride content in groundwater is due to the solubility of fluoride-bearing minerals like fluorite, cryolite, topaz, and mica, etc. Tosham is comprised of quartz mica schist, quartzite, schorl, tuff, quartz porphyry and associated granites, thus, fluoride is leached out and dissolved in groundwater. In the study area, Ni concentration ranged from 0.07 to 0.5 mg/l (permissible limit 0.02 mg/l). The primary source of nickel in drinking water is leached out nickel from ore-bearing rocks. Higher concentration of As is found in some igneous rocks specifically containing minerals as arsenopyrite (AsFeS), realgar (AsS) and orpiment (As2S3). MIS consists of granite (hypersolvus and subsolvus), rhyolite, dacite, trachyte, andesite, pyroclasts, basalt, gabbro and dolerite which increased the trace elements concentration in groundwater. Nakora, a part of MIS rocks has high concentration of trace and rare earth elements (Ni, Rb, Pb, Sr, Y, Zr, Th, U, La, Ce, Nd, Eu and Yb) which percolates the Ni and Pb to groundwater by weathering, contacts and joints/fractures in rocks. Additionally, geological setting of MIS also causes dissolution of trace elements in water resources beneath the surface. NE–SW tectonic lineament, radial pattern of dykes and volcanic vent at Nakora created a way for leaching of these elements to groundwater. Rain water quality might be altered by major minerals constituents of host Tosham rocks during its percolation through the rock fracture, joints before becoming the integral part of groundwater aquifer. The weathering process like hydration, hydrolysis and solution might be the cause of change in water chemistry of particular area. These studies suggest that geological relation of soil-water horizon with MIS rocks via mineralogical variations, structures and tectonic setting affects the water quality of the studied area.
464
58166
Grain Size Characteristics and Sediments Distribution in Some Parts of Lekki Lagoon
Abstract:
A total of twenty bottom sediment samples were collected from the Lekki lagoon during the wet and dry season. The study was carried out to determine the textural characteristics, sediment distribution pattern and energy of transportation within the lagoon system. The sediment grain sizes and depth profiling was analysed using dry sieving method and Matlab algorithm for processing. The granulometric reveals fine grained sand both for the wet and dry season with an average mean value of 2.03 ϕ -2.88 ϕ respectively. Sediments were moderately sorted with an average Inclusive standard deviation of 0.77 ϕ -0.82 ϕ. Skewness varied from strongly coarse and near symmetrical 0.34- ϕ and 0.09 ϕ.The kurtosis average value was 0.87 ϕ and -1.4 ϕ (playkurtic and leptokurtic). Entirely, the bathymetry shows an average depth of 4.0m. The deepest and shallowest area has a depth of 11.2m and 0.5 m respectively. High concentration of fine sand was observed at deep areas compared to the shallow areas during wet and dry season. Statistical parameter results show that the overall sediments are sorted, and deposited under low energy condition over a long distance. However, sediment distribution and sediment transport pattern of Lekki lagoon is controlled by low energy current and the down slope configuration of the bathymetry enhances the sorting and the deposition rate in the Lekki lagoon.
463
58811
Assessment of the Energy Balance Method in the Case of Masonry Domes
Abstract:
Masonry dome structures had been widely used for covering large spans in the past. The seismic assessment of these historical structures is very complicated due to the nonlinear behavior of the material, their rigidness and special stability configuration. The assessment method based on energy balance concept, as well as, the standard pushover analysis are used to evaluate the effectiveness of these methods in the case of masonry dome structures. The Soltanieh dome building is used as an example that two methods are applied to it. The performance points are given from superimposing the capacity and demand curves in Acceleration Displacement Response Spectra (ADRS) and energy coordination are compared with the nonlinear time history analysis as the exact result. The results show a good agreement between the dynamic analysis and the energy balance method, but standard pushover method does not provide an acceptable estimation.
462
58357
Seismic Hazard Assessment Using Complex Network of Earthquakes
Abstract:
Earthquakes are complex phenomena, exhibiting complex correlations in space, time, and magnitude. Although the reductionist point of view offers incredible insight into the mechanics of individual earthquakes, a clearer definition of seismicity is still lacking. Recently, the concept of complex networks has been used to shed light on the statistical and dynamical characteristics of regional seismicity. This work proposes a seismic hazard assessment method using weighted and directed complex networks. The geographical map of the Philippine archipelago was divided into cells, which served as a node whenever an earthquake whose magnitude is above a certain threshold occurred therein. The edges are links representing the correlation between any two earthquakes as measured by a metric which incorporates the fundamental space, time and magnitude statistics of seismicity including the Gutenberg-Richter power law. A new earthquake can have connections to all events prior to it but will only create links to the events which have correlation weights above a certain value, making these earthquakes its most likely predecessors. The node strength is calculated as the summation of all the weights of the incoming links. The node strength represents the ability of a region to generate highly correlated events and can, therefore, be taken as an estimator of seismic activity and the potential of a region to earthquake risk. The results show that points in the hazard map which are found to have high node strengths correspond to regions with known faults and trenches and the highest strength values correspond to the areas where major earthquakes have occurred. As an extension, a forecast model was generated, from the same network algorithm that would show which areas are more likely to become the locations of the next earthquake.
461
54153
Petrography and Mineral Chemical Study of Younger Quartzofeldspathic Bodies in Chakdara Granite Gneiss, Northwest Pakistan
Abstract:
The Chakdara granite gneiss is an extension of Swat granite gneisses. It is characterized by biotite bands and the occurrence of fluorite and blue beryl. Younger phases (quartzofeldspathic veins) occur within gneisses are characterized by various mineral phases that include beryl, biotite, phlogopite, annite, muscovite, ilmenite-pyrophanite, monazite, zircon, apatite, magnetite and minor amounts of sphene, rutile, and ulvöspinel. The present paper is an attempt to address the detailed mineral chemistry and genesis of minerals occurring in these younger phases. These quartzofeldspathic veins are assumed to be of hydrothermal origin on the basis of Th2O content in monazite, Zr/Hf ratio in zircon, REE enrichment, and Ce/Y ratio of allanite. Biotite in the present study is characterized by high F content. Muscovite is phengitic and contains very high amounts of Fe as compared to the normal muscovites. The Th2O content for monazite is low (0.81-1.56 wt. %) like those of hydrothermal origin. The Zr/Hf ratio in zircon is variable for different analyses but mostly falls in the range of ~ 41 and above. Allanite is generally unaltered and characterized by LREE enrichment. The properties of beryl and columbite in the present study show pegmatitic features.
460
57917
Characterization of Organic Matter in Spodosol Amazonian by Fluorescence Spectroscopy
Abstract:
Soil organic matter (SOM) plays an important role in maintaining soil productivity, accounting for promoting biological diversity. The main components of the SOM are the humic substances, which it can be fractionated according to its solubility in humic acid (HA), fulvic acids (FA) and humin (HU). The determination of the chemical properties of organic matter, as well as its interaction with metallic species, is an important tool for understanding the structure of the humic fractions. Fluorescence Spectroscopy has been studied as a source of information about what is happening at the molecular level these compounds. Specially, soils of Amazons region that are an important ecosystem of the planet. Front context, the aimed of this study is to understand the molecular and structural composition of humic acid samples of Spodosol Amazonian using the fluorescence emission-excitation matrix (EEM) and Time resolved Fluorescence Spectroscopy (TRFS). The results showed that the samples of HA showed two fluorescent components, being a more complex structure and the other with simpler structure, which was also seen in TRFS, through evaluation of each sample lifetime. Thus, studies of this nature becomes important because it aims to evaluate the molecular and structural characteristics of the humic fractions in the region that is considered one of the most important in the world, the Amazon.
459
56526
Growth Patterns of Pyrite Crystals Studied by Electron Back Scatter Diffraction (EBSD)
Abstract:
Natural formed pyrites (FeS2) are frequent sulfides in sedimentary and metamorphic rocks. Growth textures of idiomorphic pyrite assemblages reflect the conditions during their formation in the geologic sequence, furtheron the local texture analyses of the growth patterns of pyrite assemblages by EBSD reveal the possibility to resolve the growth conditions during the formation of pyrite at the micron scale. The spatial resolution of local texture measurements in the Scanning Electron Microscope used can be in the nanomete scale. Orientation contrasts resulting from domains of smaller misorientations within larger pyrite crystals can be resolved as well. The electron optical studies have been carried out in a Field-Emission Scanning Electron Microscope (FEI Quanta 200) equipped with a CCD camera to study the orientation contrasts along the surfaces of pyrite. Idiomorphic cubic single crystals of pyrite, polycrystalline assemblages of pyrite, spherically grown spheres of pyrite as well as pyrite-bearing ammonites have been studied by EBSD in the Scanning Electron Microscope. Samples were chosen to show no or minor secondary deformation and an idiomorphic 3D crystal habit, so the local textures of pyrite result mainly from growth and minor from deformation. The samples studied derived from Navajun (Spain), Chalchidiki (Greece), Thüringen (Germany) and Unterkliem (Austria). Chemical analyses by EDAX show pyrite with minor inhomogeneities e.g., single crystals of galena and chalcopyrite along the grain boundaries of larger pyrite crystals. Intergrowth between marcasite and pyrite can be detected in one sample. Pyrite may form intense growth twinning lamellae on {011}. Twinning, e.g., contact twinning is abundant within the crystals studied and the individual twinning lamellaes can be resolved by EBSD. The ammonites studied show a replacement of the shale by newly formed pyrite resulting in an intense intergrowth of calcite and pyrite. EBSD measurements indicate a polycrystalline microfabric of both minerals, still reflecting primary surface structures of the ammonites e.g, the Septen. Discs of pyrite (“pyrite dollar”) as well as pyrite framboids show growth patterns comprising a typical microfabric. EBSD studies reveal an equigranular matrix in the inner part of the discs of pyrite and a fiber growth with larger misorientations in the outer regions between the individual segments. This typical microfabric derived from a formation of pyrite crystals starting at a higher nucleation rate and followed by directional crystal growth. EBSD studies show, that the growth texture of pyrite in the samples studied reveals a correlation between nucleation rate and following growth rate of the pyrites, thus leading to the characteristic crystal habits. Preferential directional growth at lower nucleation rates may lead to the formation of 3D framboids of pyrite. Crystallographic misorientations between the individual fibers are similar. In ammonites studied, primary anisotropies of the substrates like e.g., ammonitic sutures, influence the nucleation, crystal growth and habit of the newly formed pyrites along the surfaces.
458
58077
Ichnofacies and Microfacies Analysis of Late Eocene Rocks in Fayum Area, Egypt and Their Paleoenvironmental Implications
Abstract:
Abstract- The Late Eocene rocks (Qasr El-Sagha ) Formation, north east of Birket Qarun in Fayum area of Egypt reveals 6 Ichnogenera Thalassinoides Ehrenberg, 1944, Ophiomorpha Lundgren (1891), Skolithos Haldemann (1840), Diplocraterion Torell, 1870, Arenicolites Salter, 1857 and Planolites Nicholson, 1873. These Ichnogenera are related to Skolithos ichnofacies of typical sandy shoreline environment, only the ichnogenus Planolites is related to Cruziana ichnofacies, which occurs in somewhat deeper water than the Skolithos ichnofacies. Four microfacies types have been distinguished from the study sections, Mudstone, Sandy micrite (wackstone), Sandy dolomitic ferruginous biomicrite (Packstone), Sandy glauconitic biomicrite (packstone). The ichnofacies and the microfacies study indicates that the study area was deposited in shelf lagoon with open circulation environment
457
60108
Numerical Modelling of Shear Zone and Its Implications on Slope Instability at Letseng Diamond Open Pit Mine, Lesotho
Abstract:
Rock mass damage due to shear tectonic activity has been investigated largely in geoscience where fluid transport is major interest. However, little has been studied on the effect of shear zones on rock mass behavior and its impact on stability of rock slopes. At Letšeng Diamond open pit mine in Lesotho, the shear zone composed of sheared kimberlite material, calcite and altered basalt is forming part of the haul ramp into the main pit cut 3. The alarming rate at which the shear zone is deteriorating has triggered concerns about both local and global stability of pit wall. This case study presents numerical modelling of open pit slope affected by shear zone at Letšeng Diamond Mine (LDM). Analysis of the slope involved development of the slope model by using two-dimensional finite element code Phase2. Interfaces between shear zone and host rock were represented by special joint elements incorporated in finite element model. The analysis of structural geological mapping data provided a good platform to understand the joint network, major joints including shear zones were incorporated into the model for simulation. This approach proved successful by demonstrating that continuum modelling can be used to evaluate evolution of stresses, strain, plastic yielding and failure mechanisms that are consistent with field observations. Structural control due to geological shear zone structure proved to be important in its location, size and orientation. Furthermore, the model analyzed slope deformation and sliding along non daylighting shear zone. This type of approach can be dedicated to best selection of risk mitigation strategies with respect to human lives and property within mine pits by deformation predictions and location of failure surfaces for slope support systems.
456
59463
Optimizing Solids Control and Cuttings Dewatering for Water-Powered Percussive Drilling in Mineral Exploration
Abstract:
The Deep Exploration Technologies Cooperative Research Centre (DET CRC) is researching and developing a new coiled tubing based greenfields mineral exploration drilling system utilising down-hole water-powered percussive drill tooling. This new drilling system is aimed at significantly reducing the costs associated with identifying mineral resource deposits beneath deep, barren cover. This system has shown superior rates of penetration in water-rich, hard rock formations at depths exceeding 500 metres. With fluid flow rates of up to 120 litres per minute at 200 bar operating pressure to energise the bottom hole tooling, excessive quantities of high quality drilling fluid (water) would be required for a prolonged drilling campaign. As a result, drilling fluid recovery and recycling has been identified as a necessary option to minimise costs and logistical effort. While the majority of the cuttings report as coarse particles, a significant fines fraction will typically also be present. To maximise tool life longevity, the percussive bottom hole assembly requires high quality fluid with minimal solids loading and any recycled fluid needs to have a solids cut point below 40 microns and a concentration less than 400 ppm before it can be used to reenergise the system. This paper presents experimental results obtained from the research program during laboratory and field testing of the prototype drilling system. A study of the morphological aspects of the cuttings generated during the percussive drilling process shows a strong power law relationship for particle size distributions. This data is critical in optimising solids control strategies and cuttings dewatering techniques. Optimisation of deployable solids control equipment is discussed and how the required centrate clarity was achieved in the presence of pyrite-rich metasediment cuttings. Key results were the successful pre-aggregation of fines through the selection and use of high molecular weight anionic polyacrylamide flocculants and the techniques developed for optimal dosing prior to scroll decanter centrifugation, thus keeping sub 40 micron solids loading within prescribed limits. Experiments on maximising fines capture in the presence of thixotropic drilling fluid additives (e.g. Xanthan gum and other biopolymers) are also discussed. As no core is produced during the drilling process, it is intended that the particle laden returned drilling fluid is used for top-of-hole geochemical and mineralogical assessment. A discussion is therefore presented on the biasing and latency of cuttings representivity by dewatering techniques, as well as the resulting detrimental effects on depth fidelity and accuracy. Data pertaining to the sample biasing with respect to geochemical signatures due to particle size distributions is presented and shows that, depending on the solids control and dewatering techniques used, it can have unwanted influence on top-of-hole analysis. Strategies are proposed to overcome these effects, improving sample quality. Successful solids control and cuttings dewatering for water-powered percussive drilling is presented, contributing towards the successful advancement of coiled tubing based greenfields mineral exploration.
455
59480
Parameter Selection and Monitoring for Water-Powered Percussive Drilling in Green-Fields Mineral Exploration
Abstract:
The Deep Exploration Technologies Cooperative Research Centre (DET CRC) is researching and developing a new coiled tubing based greenfields mineral exploration drilling system utilising downhole water powered percussive drill tooling. This new drilling system is aimed at significantly reducing the costs associated with identifying mineral resource deposits beneath deep, barron cover. This system has shown superior rates of penetration in water-rich hard rock formations at depths exceeding 500 meters. Several key challenges exist regarding the deployment and use of these bottom hole assemblies for mineral exploration, and this paper discusses some of the key technical challenges. This paper presents experimental results obtained from the research program during laboratory and field testing of the prototype drilling system. A study of the morphological aspects of the cuttings generated during the percussive drilling process is presented and shows a strong power law relationship for particle size distributions. Several percussive drilling parameters such as RPM, applied fluid pressure and weight on bit have been shown to influence the particle size distributions of the cuttings generated. This has direct influence on other drilling parameters such as flow loop performance, cuttings dewatering, and solids control. Real-time, accurate knowledge of percussive system operating parameters will assist the driller in maximising the efficiency of the drilling process. The applied fluid flow, fluid pressure, and rock properties are known to influence the natural oscillating frequency of the percussive hammer, but this paper also shows that drill bit design, drill bit wear and the applied weight on bit can also influence the oscillation frequency. Due to the changing drilling conditions and therefore changing operating parameters, real-time understanding of the natural operating frequency is paramount to achieving system optimisation. Several techniques to understand the oscillating frequency have been investigated and presented. With a conventional top drive drilling rig, spectral analysis of applied fluid pressure, hydraulic feed force pressure, hold back pressure and drill string vibrations have shown the presence of the operating frequency of the bottom hole tooling. Unfortunately, however, with the implementation of a coiled tubing drilling rig, implementing a positive displacement downhole motor to provide drill bit rotation, these signals are not available for interrogation at the surface and therefore another method must be considered. The investigation and analysis of ground vibrations using geophone sensors, similar to seismic-while-drilling techniques have indicated the presence of the natural oscillating frequency of the percussive hammer. This method is shown to provide a robust technique for the determination of the downhole percussive oscillation frequency when used with a coiled tubing drill rig.
454
59893
Diagenesis of the Permian Ecca Sandstones and Mudstones, in the Eastern Cape Province, South Africa: Implications for the Shale Gas Potential of the Karoo Basin
Abstract:
Diagenesis is the most important factor that affects or impact the reservoir property. Despite the fact that published data gives a vast amount of information on the geology, sedimentology and lithostratigraphy of the Ecca Group in the Karoo Basin of South Africa, little is known of the diagenesis of the potentially feasible shales and sandstones of the Ecca Group. The study aims to provide a general account of the diagenesis of sandstones and mudstone of the Ecca Group. Twenty-five diagenetic textures and structures are identified and grouped into three regimes or stages that include eogenesis, mesogenesis and telogenesis. Clay minerals are the most common cementing materials in the Ecca sandstones and mudstones. Smectite, kaolinite and illite are the major clay minerals that act as pore lining rims and pore-filling cement. Most of the clay minerals and detrital grains were seriously attacked and replaced by calcite. Calcite precipitates locally in pore spaces and partly or completely replaced feldspar and quartz grains, mostly at their margins. Precipitation of cements and formation of pyrite and authigenic minerals as well as little lithification occurred during the eogenesis. This regime was followed by mesogenesis which brought about an increase in tightness of grain packing, loss of pore spaces and thinning of beds due to weight of overlying sediments and selective dissolution of framework grains. Compaction, mineral overgrowths, mineral replacement, clay-mineral authigenesis, deformation and pressure solution structures occurred during mesogenesis. During rocks were uplifted, weathered and unroofed by erosion, this resulted in additional grain fracturing, decementation and oxidation of iron-rich volcanic fragments and ferromagnesian minerals. The rocks of Ecca Group were subjected to moderate-intense mechanical and chemical compaction during its progressive burial. Intergranular pores, matrix micro pores, secondary intragranular, dissolution and fractured pores are the observed pores. The presence of fractured and dissolution pores tend to enhance reservoir quality. However, the isolated nature of the pores makes them unfavourable producers of hydrocarbons, which at best would require stimulation. The understanding of the space and time distribution of diagenetic processes in these rocks will allow the development of predictive models of their quality, which may contribute to the reduction of risks involved in their exploration.
453
55083
Seizure Effects of FP Bearings on the Seismic Reliability of Base-Isolated Systems
Abstract:
This study deals with the seizure effects of friction pendulum (FP) bearings on the seismic reliability of a 3D base-isolated nonlinear structural system, designed according to Italian seismic code (NTC08). The isolated system consists in a 3D reinforced concrete superstructure, a r.c. substructure and the FP devices, described by employing a velocity dependent model. The seismic input uncertainty is considered as a random variable relevant to the problem, by employing a set of natural seismic records selected in compliance with L’Aquila (Italy) seismic hazard as provided from NTC08. Several non-linear dynamic analyses considering the three components of each ground motion have been performed with the aim to evaluate the seismic reliability of the superstructure, substructure, and isolation level, also taking into account the seizure event of the isolation devices. Finally, a design solution aimed at increasing the seismic robustness of the base-isolated systems with FPS is analyzed.
452
59055
A Nonlinear Exponential Model for Seismic Isolators Having Hardening or Softening Behavior at Large Displacements
Abstract:
Base isolation is a widely accepted technique for seismic protection of structures adopting special devices called seismic isolators. There are two common types of seismic isolation bearings, namely, elastomeric and sliding bearings. The former take advantage of the flexible properties of rubber to achieve low horizontal stiffness whereas the latter rely on the action of sliding to provide horizontal flexibility and on the friction damping occurring at the sliding interface to dissipate energy. Metal devices, such as wire rope isolators, can be used as recentering devices in combination with flat or curved surface sliders. Seismic devices generally exhibit symmetric softening force-displacement hysteresis loops within a relatively large displacements range, that is, under the design earthquake loading. At large displacements, several isolators, such as high damping rubber bearings and wire rope isolators, exhibit a hardening stiffness whereas others, such as unbounded elastomeric bearings, display a softening behavior with a negative tangent stiffness. The differential equation Wen model, widely used for modeling the uniaxial behavior of elastomeric bearings, sliding bearings and wire rope isolators within the relatively large displacements range, is unable to efficiently capture their behavior at large displacements. Thus, in this work, a one dimensional (1D) phenomenological model accommodating the hysteretic behavior at both relatively large and large displacements ranges is proposed. The basic idea is to consider a nonlinear hysteretic exponential element and a nonlinear elastic exponential element connected in parallel. The former stems from the hypothesis that the tangent horizontal stiffness exponentially decreases with increasing displacements within the relatively large displacements range and requires the evaluation of only three parameters, namely, the initial tangent stiffness, the asymptotic tangent stiffness of the relatively large displacements range, and a parameter defining the transition from the initial to the asymptotic tangent stiffness. The latter requires only two parameters and allows to modify the hysteresis loop shape obtained with the hysteretic element so to simulate the increase or decrease of the tangent stiffness at large displacements. The proposed Nonlinear Exponential Model (NEM) has been validated by comparing the experimental hysteresis loops obtained from horizontal dynamic tests, performed on a Wire Rope Isolator (WRI) and a Recycled Rubber-Fiber Reinforced Bearing (RR-FRB) at the Department of Industrial Engineering of the University of Naples Federico II, with those predicted analytically. Good agreement between the analytical and experimental results shows that the proposed NEM is able to predict with good accuracy the response of the tested WRI and RR-FRB, having a hardening and softening behavior at large displacements, respectively. Compared to the Wen model, the proposed NEM allows to simulate the dynamic behavior of seismic isolators within the relatively large displacements range avoiding the numerical solution of the first order nonlinear differential equation for each time step of a nonlinear dynamic analysis and reducing the number of model parameters to be identified. Furthermore, the proposed model is able to capture the smooth transition of the hysteresis loops from the relatively large to the large displacements range using only the five parameters evaluated from the experimental hysteresis loops with the largest amplitude.
451
59056
Nonlinear Dynamic Analysis of Base-Isolated Structures Using a Mixed Integration Method: Stability Aspects and Computational Efficiency
Abstract:
In most practical civil engineering problems, the increasing complexity of structural models requires the use of a partitioned solution approach in which a discrete structural model is decomposed into interacting substructures. The above-mentioned partitioned solution approach can be easily applied to seismically base-isolated structures being the decomposition of the discrete structural model of such structures driven by physical considerations: the base isolation system is much more flexible than the superstructure to decouple the latter from the earthquake ground motion. In this work, a Mixed Explicit-Implicit time integration Method (MEIM) is proposed for the nonlinear dynamic analysis of base-isolated structures under earthquake excitation: in each time step of the analysis, the nonlinear response of the base isolation system is computed first using the explicit conditionally stable central difference method, then the implicit unconditionally stable Newmark’s constant average acceleration method is employed to evaluate the superstructure linear response. The presented MEIM is conditionally stable due to the use of the central difference method. Thus, a procedure to evaluate the critical time step is first developed for two-dimensional (2D) base-isolated structures and then extended to the three-dimensional (3D) case. The proposed partitioned solution approach is employed to analyze a 3D base-isolated structure with a friction pendulum bearing system subjected to bidirectional ground motion. The main aim of the numerical application is to investigate the stability and the computational efficiency of the MEIM when adopted for the nonlinear dynamic analysis of base-isolated structures having seismic isolators with very high initial stiffness values, such as friction pendulum bearings, for which the critical time step could become smaller than the one used to define accurately the earthquake excitation. The numerical results are compared to those obtained using a conventional monolithic solution approach, that is, the implicit unconditionally stable Newmark’s constant acceleration method used in conjunction with the iterative pseudo-force procedure. As far as the stability is concerned, in the numerical application presented in this paper, the critical time step continues to be larger than the ground acceleration time step in spite of the very high initial stiffness of the seismic isolators. As regards the computational efficiency, it is shown that the MEIM, performed with a time step equal to 0.001 s, continues to require less computational effort than the conventional solution method performed using a time step of 0.005 s. It transpires that the proposed partitioned solution approach preserves its computational efficiency even if a smaller time step size has to be selected due to stability requirements.
450
59057
Speeding up Computations in Nonlinear Time History Analysis of Base-Isolated Structures Using a Nonlinear Exponential Model
Abstract:
Seismic isolation bearings are special devices able to provide flexibility and energy dissipation capacity in horizontal directions, sufficient vertical stiffness to resist service loading, rigidity under low levels of later loads due to wind or minor earthquakes, and recentering capability. A mathematical model is required to predict the dynamic behavior of seismic isolators. Within a relatively large displacements range, generally reached under the design dynamic loading, models with bilinear characteristics can represent the dynamic behavior of elastomeric bearings, such as High Damping Rubber Bearings (HDRBs), Lead Rubber Bearing (LRBs), whereas models with rigid-plastic characteristics can be adopted to simulate the dynamic response of sliding bearings, such as Spherical Sliding Bearings (SSBs), Friction Pendulum Bearings (FPBs), and Flat Sliding Bearings (FSBs). The widely used differential equation model developed by Wen has been adapted for modeling the uniaxial behavior of both elastomeric and sliding bearings and has been implemented in many computer programs such as 3D-BASIS, SAP2000 and ETABS. As the Wen model requires the numerical solution of a first order nonlinear Ordinary Differential Equation (ODE) for each time step of a nonlinear time history analysis, the use of such conventional model can increase the computational effort very significantly. The main aim of this work is to speed up numerical computations in the nonlinear dynamic analysis of seismically base-isolated structures by using a Nonlinear Exponential Model (NEM) able to reproduce the dynamic behavior of seismic isolators within the relatively large displacements range and to simulate the increase of the tangent stiffness displayed by several types of seismic isolators, such as HDRBs, at large displacements, without requiring the solution of a nonlinear ODE for each time step of the analysis. In order to show the decrease in the required computational effort when the proposed mathematical model is adopted, a three dimensional (3D) base-isolated structure with a lead rubber bearing system subjected to earthquake excitation is analyzed. The nonlinear dynamic equilibrium equations are solved using the implicit unconditionally stable Newmark’s constant average acceleration method used in conjunction with the pseudo-force iterative procedure. The comparison of the numerical results obtained modeling the seismic isolators using the proposed NEM with those obtained adopting the conventional Wen model shows a significant reduction of the total computational time due to the use of the proposed analytical model.
449
59153
Effect of Horizontal Joint Reinforcement on Shear Behaviour of RC Knee Connections
Abstract:
To investigate seismic performance of beam-column knee joints, four full-scale reinforced concrete beam-column knee joints, which were fabricated to simulate those in as-built RC frame buildings designed to ACI 318-14 and ACI-ASCE 352R-02, were tested under reversed cyclic loading. In the experimental programme, particular emphasis was given to the effect of horizontal reinforcement (in format of inverted U-shape bars) on the shear strength and ductility capacity of knee joints. Test results are compared with those predicted by four seismic design codes, including ACI 318-14, EC8, NZS3101, and GB50010. It is seen that the current design codes of practice cannot accurately predict the shear strength of seismically designed knee joints.
448
59158
Seismic Response Evaluation of Shear Wall Structures Using the Design Spectrum (DSE) Procedure
Abstract:
In this paper, the application of the design spectrum (DSE) method for the seismic evaluation of the reinforced concrete (RC) shear wall structures is presented. The DSE method includes a nonlinear pushover analysis procedure, using consecutive pushover technique and a linear elastic modal response analysis procedure. By considering the combination of modes in both elastic and inelastic cases, it is found from the case study that the proposed DSE method is capable of predicting the seismic performance of RC shear wall structures, including internal forces and deformations very well. Owing to the high efficiency, good accuracy as well as spectrum-based calculation procedure, the DSE is considered as one of the best methods of procedure for the quick evaluation of seismic performance of RC shear wall structures.
447
60408
Parametric Non-Linear Analysis of R.C. Frames with Supplemental Damping Systems
Abstract:
This paper focuses on parametric analysis of reinforced concrete structures equipped with supplemental damping braces. Practitioners still lack sufficient data for current design of damper added structures and often reduce the real model to a pure damper braced structure even if this assumption is neither realistic nor conservative. In the present study, the damping brace is modeled as made by a linear supporting brace connected in series with the viscous/hysteretic damper. Deformation capacity of existing structures is usually not adequate to undergo the design earthquake. In spite to this, additional dampers could be introduced strongly limiting structural damage to acceptable values or, in some cases, reducing frame response to elastic behavior. This work is aimed at providing useful considerations for retrofit of existing buildings by means of supplemental damping braces. The study explicitly takes into consideration variability of (a) relative frame to supporting brace stiffness, (b) dampers’ coefficient (viscous coefficient or yielding force), (c) non-linear frame behavior. Non-linear time history analysis have been run to account for both dampers’ behavior and non-linear plastic hinges modeled by Takeda hysteretic type. Parametric analysis based on previous studies on linear frames provide reference values for damping system design. With respect to bare frame configuration, the seismic response of the damper-added frame is strongly improved, limiting deformations to acceptable values far below ultimate capacity. Results of the analysis also demonstrated the beneficial effect of stiffer supporting braces, thus highlighting inadequacy of simplified pure damper models. At the same time, the effect of variable damping coefficient or yielding force has to be treated as an optimization problem.
446
60685
Estimation of Source Parameters and Moment Tensor Solution through Waveform Modeling of 2013 Kishtwar Earthquake
Abstract:
Abstract---The Jammu and Kashmir (J&K) region of the Northwest Himalaya had witnessed many devastating earthquakes in the recent past and has remained unexplored for any kind of seismic investigations except scanty records of the earthquakes that occurred in this region in the past. In 2013, two moderate earthquakes of Mw 5.7 of 1st May and Mw 5.1 of 2nd August occurred in the Kishtwar region of Jammu & Kashmir. These earthquakes occurred between the Northwest of 1905 Kangra earthquake (Mw 7.8) and Southeast of 2005 Kashmir earthquake (Mw 7.6). In this study we have used local seismic data of year 2013 that was recorded by the network of Broadband Seismographs in J&K. During this period, our seismic stations recorded about 207 earthquakes including two moderate events of Mw 5.7 on 1st May, 2013 and Mw 5.1 of 2nd August, 2013. We analyzed the events of Mw 3-4.6 and the main events only (for minimizing the error) for source parameters, b value and sense of movement through waveform modeling for understanding seismotectonics and seismic hazard of the region. It has been observed that most of the events are bounded between 32.9o N – 33.3o N latitude and 75.4o E – 76.1o E longitudes, Moment Magnitude (Mw) ranges from Mw 3 to 5.7, Source radius (r) 0.21 to 3.5 km, stress drop ranges from 1.90 bars to 71.1 bars and Corner frequency ranges from 0.39 – 6.06 Hz. The b-value for this region was found to be 0.83± 0 from these events which is lower than the normal value (b=1), indicating the area is under high stress. The travel time inversion and wave form inversion method suggest focal depth up to 10 km probably above the detachment depth of the Himalayan region. Moment tensor solution of the (Mw 5.1, 02:32:47 UTC) main event of 2nd August suggested that the source fault is striking at 295o with dip of 33o and rake value of 85o. It was found that these events form intense clustering of small to moderate events within a narrow zone between Panjal Thrust and Kishtwar Window. Moment tensor solution of the main events and their aftershocks indicating thrust type of movement is occurring in this region.
445
60687
Determination of Crustal Structure and Moho Depth within the Jammu and Kashmir Region, Northwest Himalaya through Receiver Function
Abstract:
Abstract-The Jammu and Kashmir (J&K) region of Northwest Himalaya has a long history of earthquake activity which falls within Seismic Zones IV and V. To know the crustal structure beneath this region we utilized teleseismic receiver fuction method. This paper presents the results of the analyses of the teleseismic earthquake waves recorded by 10 seismic observatories installed in the vicinity of major thrusts and faults. The teleseismic waves at epicentral distance between 30o and 90o with moment magnitudes greater than or equal to 5.5 that contains large amount of information about the crust and upper mantle structure directly beneath a receiver has been used. The receiver function (RF) technique has been widely applied to investigate crustal structures using P-to-S converted (Ps) phases from velocity discontinuities. The arrival time of the Ps, PpPs and PpSs+ PsPs converted and reverberated phases from the Moho can be combined to constrain the mean crustal thickness and Vp/Vs ratio. Over 500 receiver functions from 10 broadband stations located in the Jammu & Kashmir region of Northwest Himalaya were analyzed. With the help of H-K stacking method, we determined the crustal thickness (H) and average crustal Vp/Vs ratio (K) in this region. We also used Neighbourhood algorithm technique to verify our results. The receiver function results for these stations show that the crustal thickness under Jammu & Kashmir ranges from 45.0 to 53.6 km with an average value of 50.01 km. The Vp/Vs ratio varies from 1.63 to 1.99 with an average value of 1.784 which corresponds to an average Poisson’s ratio of 0.266 with a range from 0.198 to 0.331. High Poisson’s ratios under some stations may be related to partial melting in the crust near the uppermost mantle. The crustal structure model developed from this study can be used to refine the velocity model used in the precise epicenter location in the region, thereby increasing the knowledge to understand current seismicity in the region.
444
57083
A Comparison of Tsunami Impact to Sydney Harbour, Australia at Different Tidal Stages
Abstract:
Sydney Harbour is an iconic location with a dense population and low-lying development. On the east coast of Australia, facing the Pacific Ocean it is exposed to several tsunamigenic trenches. This paper is part of the most detailed assessment of the potential for earthquake-generated tsunami impact on Sydney Harbour to date. Although it is common for tsunami modelling to use a static tide, it is known that tsunami wave trains and tide interact in a non-linear manner in estuaries. Tide-tsunami interactions can both intensify or dampen the effects of tsunami, depending on mean basin depth. It has also been shown that tidal range is a factor in the influence of non-linear tide-tsunami interactions and that the non-linear contribution decreases upstream. Sydney Harbour’s tidal range is 1.5m, and the spring tides from January 2015 that are used in the modelling for this study are close to the full tidal range. The tsunami wave trains modelled include tsunami generated from earthquakes of magnitude 7.5, 8.0, 8.5 and 9.0 MW from the Puysegur and New Hebrides trenches as well as the historical 1960 Chilean tsunami and 2011 Tohoku event. The same wave trains are modelled at different tidal stages. The tsunami wave train is positioned so that the largest wave coincides with high tide, low tide, falling tide and rising tide. Using the hydrodynamic model ANUGA, results are compared by the impact parameters of inundation area, maximum current speeds, wave heights and depth variation. Preliminary results are available for comparison between the high tide and low tide models. These results show that maximum inundation area for the high tide models is approximately double the maximum inundation area for the low tide models. Maximum current speeds do not show significant or consistent difference across the locations and wave trains modelled. Wave heights are similar for the wave trains from earthquakes of less than 8.5MW, but for wave trains from earthquakes of 8.5MW and 9.0MW, wave heights are significantly larger for the low tide models. Minimum depths, which are a consideration for under keel clearance, are much lower for the low tide models and maximum depths, which are important for bridge clearance, are higher for the high tide models. Both high tide and low tide models show depth ranges greater than that of a tide only model. Results show that no one tidal stage is consistently more impactful across all parameters and so tide must be a consideration for both tsunami modelling and emergency management planning.
443
56529
Remote Sensing and Gis Use in Trends of Urbanization and Regional Planning
Abstract:
The paper attempts to study various facets of urbanization and regional planning in the framework of the present conditions and future needs. Urbanization is a dynamic system in which development and changes are prominent features; which implies population growth and changes in the primary, secondary and tertiary sector in the economy. Urban population is increasing day by day due to a natural increase in population and migration from rural areas, and the impact is bound to have in urban areas in terms of infrastructure, environment, water supply and other vital resources. For the organized way of planning and monitoring the implementation of Physical urban and regional plans high-resolution satellite imagery is the potential solution. Now the Remote Sensing data is widely used in urban as well as regional planning, infrastructure planning mainly telecommunication and transport network planning, highway development, accessibility to market area development in terms of catchment and population built-up area density. With Remote Sensing it is possible to identify urban growth, which falls outside the formal planning control. Remote Sensing and GIS technique combined together facilitate the planners, in making a decision, for general public and investors to have relevant data for their use in minimum time. This paper sketches out the Urbanization modal for the future development of Urban and Regional Planning. The paper suggests, a dynamic approach towards regional development strategy.
442
60585
Tectono-Thermal Evolution of Ningwu-Jingle Basin in North China Craton: Constraints from Apatite (U–Th-Sm)/He and Fission Track Thermochronology
Abstract:
Ningwu-Jingle basin is a structural syncline which has undergone a complex tectono-thermal history since Cretaceous. It stretches along the strike of the northern Lvliang Mountains which are the most important mountains in the middle and west of North China Craton. The Mesozoic units make up of the core of Ningwu-Jingle Basin, with pre-Mesozoic units making up of its flanks. The available low-temperature thermochronology implies that Ningwu-Jingle Basin has experienced two stages of uplifting: 94±7Ma to 111±8Ma (Albian to Cenomanian) and 62±4 to 75±5Ma (Danian to Maastrichtian). In order to constrain its tectono-thermal history in the Cenozoic, both apatite (U-Th-Sm)/He and fission track dating analysis are applied on 3 Middle Jurassic and 3 Upper Triassic sandstone samples. The central fission track ages range from 74.4±8.8Ma to 66.0±8.0Ma (Campanian to Maastrichtian) which matches well with previous data. The central He ages range from 20.1±1.2Ma to 49.1±3.0Ma (Ypresian to Burdigalian). Inverse thermal modeling is established based on both apatite fission track data and (U-Th-Sm)/He data. The thermal history obtained reveals that all 6 sandstone samples cross the high-temperature limit of fission track partial annealing zone by the uppermost Cretaceous and that of He partial annealing zone by the uppermost Eocene to the early Oligocene. The result indicates that the middle and west of North China Craton is not stable in the Cenozoic.
441
57566
Hydrofracturing for Low Temperature Waxy Reservoirs: Problems and Solutions
Abstract:
Hydrofracturing is the most prominent but at the same time expensive, highly skilled and time consuming well stimulation technique. Due to high cost and skilled labor involved, it is generally carried out as the consummate solution among other well stimulation techniques. Considering today’s global petroleum market, no gaffe or complications could be entertained during fracturing, as it would further hamper the current dwindling economy. The literature would be dealing with the challenges encountered during fracturing low temperature waxy reservoirs and the prominent solutions to overcome such teething troubles. During fracturing treatment for, shallow and high freezing point waxy oil reservoirs, the first line problems are to overcome uncompleted breakdown, uncompleted cleanup of fracturing fluids and cold damages to the formations by injecting cold fluid (fluid at ambient conditions). Injecting fracturing fluids at ambient conditions have the tendency to decrease the near wellbore reservoir temperature below the freezing point of oil reservoir and hence leading to wax deposition around the wellbore thereby hampering the fluid production as well as fracture propagation. To overcome such problems, solutions such as hot fracturing fluid injection, encapsulated heat generating hydraulic fracturing fluid system, and injection of wax inhibitor techniques would be discussed. The paper would also be throwing light on changes in rheological properties occurred during heating fracturing fluids and solutions to deal with it taking economic considerations into account.
440
57948
Borate Crosslinked Fracturing Fluids: Laboratory Determination of Rheology
Abstract:
Hydraulic fracturing has become an essential procedure to break apart the rock and release the oil or gas which are trapped tightly in the rock by pumping fracturing fluids at high pressure down into the well. To open the fracture and to transport propping agent along the fracture, proper selection of fracturing fluids is the most crucial components in fracturing operations. Rheology properties of the fluids are usually considered the most important. Among various fracturing fluids, Borate crosslinked fluids have proved to be highly effective. Borate in the form of Boric Acid, borate ion is the most commonly use to crosslink the hydrated polymers and to produce very viscous gels that can stable at high temperature. Guar and HPG (Hydroxypropyl Guar) polymers are the most often used in these fluids. Borate gel rheology is known to be a function of polymer concentration, borate ion concentration, pH, and temperature. The crosslinking using Borate is a function of pH which means it can be formed or reversed simply by altering the pH of the fluid system. The fluid system was prepared by mixing base polymer with water at pH ranging between 8 to 11 and the optimum borate crosslinker efficiency was found to be pH of about 10. The rheology of laboratory prepared Borate crosslinked fracturing fluid was determined using Anton Paar Rheometer and Fann Viscometer. The viscosity was measured at high temperature ranging from 200ᵒF to 250ᵒF and pressures in order to partially stimulate the downhole condition. Rheological measurements reported that the crosslinking increases the viscosity, elasticity and thus fluid capability to transport propping agent.
439
59714
Seismic Frequency Approach to Pore Pressure Prediction
Abstract:
Pore fluid pressure in excess of the hydrostatic pressure pose significant threats to the safety and economic drilling operations, especially deepwater and near salt field drilling being the challenge. High percentage of the Non-productive Time is due to issues regarding unexpected pore pressure encountered during drilling. Prior to drilling, proper planning is a key to lowering costs and increasing safety hence the need a better practice approach to pore pressure prediction by seismic surveys. The seismic frequency based method has been suggested as a tool for pore pressure prediction. This method is influenced by formation grain-to-grain contacts that is controlled by effective stress. The frequency response of seismic signals in normal pressured formation and overpressured formation are discussed in this paper. The dependency on the grain-to-grain contact allows the application of seismic frequency based to be a promising approach compared to the formation properties dependent seismic interval velocities approach for pore pressure prediction.
438
60692
The Contribution of Geophysical in the Prevention of Urban Risk. Cheria Plateau Case.
Abstract:
The locality of Cheria is characterized by a predominance of carbonate formations. In urban development and expansion of built-up areas, is a constraint because of the vulnerability of these geological formations. Indeed, because of the dissolution phenomenon has led to the emergence and collapse of cavities. To prevent this situation, the contribution of the geophysical investigation is very important. In, the locality of Cheria, Two phenomena have emerged to explain the collapses, the first is assigned a filling process in the cavities, and the second is due to a weakening of the resistance that collapses limestone slab shear phenomenon. These structures called dolines (sinkholes), of sub circular shape and with diameters up to over 20 meters and a depth of more than four meters. The contribution of geophysics and particularly tomography technique allows better visualization of the structure; this Technique can also locate the area at risk. By the electric method, it is possible to locate deep location of these cavities and develop a mapping of risk.
437
58499
Erosion Susceptibility Zoning and Prioritization of Micro-Watersheds: A Remote Sensing-Gis Based Study of Asan River Basin, Western Doon Valley, India
Abstract:
The present study highlights the estimation of soil loss and identification of critical area for implementation of best management practice is central to the success of soil conservation programme. The quantification of morphometric and Universal Soil Loss Equation (USLE) factors using remote sensing and GIS for prioritization of micro-watersheds in Asan River catchment, western Doon valley at foothills of Siwalik ranges in the Dehradun districts of Uttarakhand, India. The watershed has classified as a dendritic pattern with sixth order stream. The area is classified into very high, high, moderately high, medium and low susceptibility zones. High to very high erosion zone exists in the urban area and agricultural land. Average annual soil loss of 64 tons/ha/year has been estimated for the watershed. The optimum management practices proposed for micro-watersheds of Asan River basin are; afforestation, contour bunding suitable sites for water harvesting structure as check dam and soil conservation, agronomical measure and bench terrace.
436
60635
Mapping of Alteration Zones in Mineral Rich Belt of South East Rajasthan Using Remote Sensing Techniques
Abstract:
Remote sensing techniques have emerged as an asset for various geological studies. Satellite images obtained by different sensors contain plenty of information related to the terrain. Digital image processing further helps in customized ways for the prospecting of minerals. In this study an attempt has been made to map the hydrothermally altered zones using multispectral and hyperspectral datasets of South East Rajasthan. Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) and Hyperion (Level1R) dataset have been processed to generate different Band Ratio Composites (BRCs). For this study ASTER derived BRCs were generated to delineate the alteration zones, gossans, abundant clays and host rocks. ASTER and Hyperion images were further processed to extract mineral end members and classified mineral maps have been produced using Spectral angle mapper (SAM) method. Results were validated with the geological map of the area which shows positive agreement with the image processing outputs. Thus, this study concludes that the band ratios and image processing in combination play significant role in demarcation of alteration zones which may provide pathfinders for mineral prospecting studies.