V. Vishal

A comparative study of generalized regression neural network approach and adaptive neuro-fuzzy inference systems for prediction of unconfined compressive strength of rocks

The engineering properties of rocks play a significant role in planning and designing of mining and civil engineering projects. A laboratory database of mechanical and engineering properties of rocks is always required for site characterization and mineral exploitation. Due to discontinuous and variable nature of rock masses, it is difficult to obtain all physicomechanical properties of rocks precisely. Prediction of unconfined compressive strength from seismic wave velocities (Compressional wave, Shear wave) and density of rock using generalized regression neural network (GRNN) and adaptive neuro-fuzzy inference systems (ANFIS) can be appropriate and alternate methods to minimize the time and cost of tests. GRNN and ANFIS models were trained with 41 data sets using conjugate gradient descent algorithms and hybrid learning algorithm, respectively. Performance of both the models was examined with 15 testing data sets. In the present study, obtained network performance indices such as correlation coefficient, mean absolute percentage error, root mean square error and variance account for indicate high performance of predictive capability of GRNN system and closer to actual data over the ANFIS.

An Empirical Correlation of Index Geomechanical Parameters with the Compressional Wave Velocity

The geomechanical strength of rockmass plays a key role in planning and design of mining and civil construction projects. Determination of geomechanical properties in the field as well as laboratory is time consuming, tedious and a costly affair. In this study, density, slake durability index, uniaxial compressive strength (UCS) and P-wave velocity tests were conducted on four igneous, six sedimentary and three metamorphic rock varieties. These properties are crucial and used extensively in geotechnical engineering to understand the stability of the structures. The main aim of this study is to determine the various mechanical properties of 13 different rock types in the laboratory and establish a possible and acceptable correlation with P-wave velocity which can be determined in the field as well as laboratory with ease and accuracy. Empirical equations were developed to calculate the density, slake durability index and UCS from P-wave velocities. Strong correlations among P-wave velocity with the physical properties of different rock were established. The relations mainly follow a linear trend. Student’s ‘t’ test and ‘F’ test were performed to ensure proper analysis and validation of the proposed correlations. These correlations can save time and reduce cost during design and planning process as they represent a reliable engineering tool.

Methane and CO2 Adsorption Capacities of Kerogen in the Eagle Ford Shale from Molecular Simulation

Over the past decade, the United States has become a world leader in natural gas production, thanks in part to a large-fold increase in recovery from unconventional resources, i.e., shale rock and tight oil reservoirs. In an attempt to help mitigate climate change, these depleted formations are being considered for their long-term CO2 storage potential. Because of the variability in mineral and structural composition from one formation to the next (even within the same region), it is imperative to understand the adsorption behavior of CH4 and CO2 in the context of specific conditions and pore surface chemistry, i.e., relative total organic content (TOC), clay, and surface functionality. This study examines two Eagle Ford shale samples, both recovered from shale that was extracted at depths of approximately 3800 m and having low clay content (i.e., less than 5%) and similar mineral compositions but distinct TOCs (i.e., 2% and 5%, respectively). Experimentally validated models of kerogen were used to the estimate CH4 and CO2 adsorption capacities. The pore size distributions modeled were derived from low-pressure adsorption isotherm data using CO2 and N2 as probe gases for micropores and mesopores, respectively. Given the presence of water in these natural systems, the role of surface chemistry on modeled kerogen pore surfaces was investigated. Several functional groups associated with surface-dissociated water were considered. Pressure conditions from 10 to 50 bar were investigated using grand canonical Monte Carlo simulations along with typical outgassing temperatures used in many shale characterization and adsorption studies (i.e., 60 and 250 °C). Both CO2 and N2 were used as probe gases to determine the total pore volume available for gas adsorption spanning pore diameters ranging from 0.3 to 30 nm. The impacts of surface chemistry, outgassing temperature, and the inclusion of nanopores with diameters of less than 1.5 nm were determined for applications of CH4 and CO2 storage from samples of the gas-producing region of the Eagle Ford Shale. At 50 bar and temperatures of 60 and 250 °C, CH4 adsorption increased across all surface chemistries considered by 60% and 2-fold, respectively. In the case of CO2, the surface chemistry played a role at both 10 and 50 bar. For instance, at temperatures of 60 and 250 °C, CO2 adsorption increased across all surface chemistries by 6-fold and just over 2-fold, respectively. It was also found that at both 10 and 50 bar, if too low an outgassing temperature is used, this may lead to a 2-fold underestimation of gas in place. Finally, neglecting to include pores with diameters of less than 1.5 nm has the potential to underestimate pore volume by up to 28%. Taking into consideration these aspects of kerogen and shale characterization in general will lead to improvements in estimating the CH4 and CO2 storage potential of gas shales.

Investigating the frictional response of granitic rock surface: An experimental approach

Rock friction varies as a function of mainly four parameters that are waiting time and velocity of motion between two frictional surfaces, surface roughness and normal stress. In this paper, a study on former two aspects of rock frictional behaviour has been attempted for granitic rock surface. In one experiment, waiting time for which the two surfaces remain in contact is increased from 20 seconds to 18 hours. In the second experiment, waiting time is kept constant for a series of rock slip experiments where the velocity is increased from 10μm/sec to 350μm/sec. The value of critical velocity is obtained from transformation of the stick slip motion to steady motion occurs. The relation of coefficients of dynamic and static friction with increasing velocity of motion is studied and these are used to calculate the frictional constants, namely ‘a’ and ‘b’ specific to the chosen simulation type.

Numerical simulation of fault reactivation phenomenon

Two-dimensional finite element method was used for evaluating the effect of orthogonal compression on precursor faults. The tendency of reactivation of precursor faults as thrust or normal was analyzed involving the positions and angles of precursor faults with the stresses, strains and displacements. Twelve cases were taken up with different combinations of precursor fault angles (high, >45° and low, <45°) and fault positions for analysis. Different positions and angles of precursor faults are correlated with stresses, strains, and displacements and are discussed in detail. It is hoped that this would help in understanding the past and the present geodynamics of the earth’s crust.

Effect of carbon dioxide sequestration on the mechanical properties of Deccan basalt

Carbon dioxide sequestration is considered to be an efficient method of curbing the release of carbon dioxide emissions into the atmosphere and to mitigating corresponding effects on climate change. In this regard, basaltic rocks are among the potential repositories due to their ability to trap carbon dioxide in form of carbonate minerals. A series of laboratory-scale saturation experiments was conducted on three types of basalts that were collected from different horizons of the Deccan Volcanic Province (DVP), India. The basalt cores were treated in a saturation chamber for different exposure periods under low-pressure and room-temperature conditions. A set of key mechanical, physical, and chemical properties of the pre- and post-treated samples were analyzed to identify saturation-related changes. The results show that exposure of the basalts to carbon dioxide has a strong effect on their strength. However, the extent of the effect is different for different types of basalts and is strongly controlled by the exposure time, the mineralogical composition, and rock texture. X-ray diffraction and scanning electron microscopy (SEM) show that saturation leads to dissolution of the mafic minerals, and precipitation of new carbonate minerals in the cracks and vesicles of the host rock. These changes in the mineralogical content and the development of micro-cracks in the samples are interpreted as being the primary factors that affect the loss of integrity in the rock.

Study of Slopes Along River Teesta in Darjeeling Himalayan Region

Landslides of different magnitudes are frequent in different regions of the morpho-dynamically active Himalayan regions. Geologically, the presence of young active fold mountains, some rejuvenated faults along with the anthropogenic factors such as unplanned urbanization in risk areas, widening of roads along cut slopes, environmental degradation and population expansion play a significant role in the occurrence of such geohazards. The landslide zones have been identified for Indian scenario to demarcate the locales susceptible to landslides and various studies are being carried out in the high risk areas to mitigate the probability of occurrence of hazards. Assessment of stability of such areas by developing models can act as early warning systems and help to implement preventive and mitigative measures to minimize the damage level. The present work focuses a similar study in a landslide prone area with evidences of recent and paleo landslides in Darjeeling—Himalayan area of India. The Birrik fault cuts across the River Teesta in the foothills of the Darjeeling Himalayan fold and thrust belt and in the close vicinity lies the National Highway No. 31A. This area has a hilly topography and some high angle slopes are further aggravated by the presence of active thrust. Evidences of landslides were observed in the field and samples were collected from the adjoining areas of slide for determination of their geomechanical properties. There are many methods to analyze the slope conditions like Slope Mass Rating, limit equilibrium method, kinematic tools, numerical simulations etc. These approaches are good to see the disturbances within the rock mass due to change in its dynamics. In this study, slope mass rating was used to evaluate the health of slopes based on various rock parameters, as determined in the laboratory. This study will be helpful to monitor the slope conditions in this area and to design the preventive measures to minimize the chances of failure, which is required for smooth transportation through highway NH 31A. It can also be set an example for regions with similar geological and geotechnical conditions, especially in the Lower Himalayan regions.

Sensitivity analysis of coupled processes and parameters on the performance of enhanced geothermal systems

Abstract3-D modeling of coupled thermo-hydro-mechanical (THM) processes in enhanced geothermal systems using the control volume finite element code was done. In a first, a comparative analysis on the effects of coupled processes, operational parameters and reservoir parameters on heat extraction was conducted. We found that significant temperature drop and fluid overpressure occurred inside the reservoirs/fracture that affected the transport behavior of the fracture. The spatio-temporal variations of fracture aperture greatly impacted the thermal drawdown and consequently the net energy output. The results showed that maximum aperture evolution occurred near the injection zone instead of the production zone. Opening of the fracture reduced the injection pressure required to circulate a fixed mass of water. The thermal breakthrough and heat extraction strongly depend on the injection mass flow rate, well distances, reservoir permeability and geothermal gradients. High permeability caused higher water loss, leading to reduced heat extraction. From the results of TH vs THM process simulations, we conclude that appropriate coupling is vital and can impact the estimates of net heat extraction. This study can help in identifying the critical operational parameters, and process optimization for enhanced energy extraction from a geothermal system.

Stability assessment of Himalayan road cut slopes along National Highway 58, India

Himalaya is one of the most tectonically and seismically active mountain chains in the world having complex geological and geotechnical conditions. The Himalayan region experiences frequent slope failure posed due to various natural and anthropogenic causes. Slope instability issues have consequent effects on the socio-economic development of the people and the region in a large scale. In the present study, stability analysis of vulnerable road cut slopes along NH-58 from Rishikesh to Devprayag in the Lesser Himalayas has been conducted. Critical slopes were identified by considering the geological and the geotechnical complexities within the region. Rock mass characterisation techniques have been employed for slope stability assessment. Rock mass rating (RMR), slope mass rating (SMR) and continuous slope mass rating (CSMR) methods have been applied to evaluate different stability levels of rock mass along the highway. Spatial variation of stability classes using RMR, SMR and CSMR techniques has been analysed on geographic information system (GIS) tool. Kinematic analysis technique was also employed to identify the different modes of structurally controlled failures in jointed rock mass. Accordingly remedial measures have been suggested to improve slope stability.

Geologic carbon sequestration

Carbon capture and storage can simply be defined as capturing of waste CO2 from industrial sources at various stages (ex. pre-, postcombustion etc.), transporting it to a storage site (through pipelines etc.) and then depositing it underground so that the CO2 will not re-enter the atmosphere for a geologically significant long time. Because of the low prices of fossil fuels and lesser statutory restrictions in developing countries (which are primarily dependent on this form of energy), aided by slow development and high cost of alternative energy projects, the CO2 emission into the atmosphere has been ever increasing. The long lasting effects of such high levels of CO2 in atmosphere can portray an image of an impending catastrophe but a better approach would be to avoid those and look into the solutions to minimize the CO2 levels in atmosphere. This introductory chapter offers an insight into the technologies and the techniques that have been developed for carbon capture followed by transporting methods (and their problems) and ends with discussing the various storage technologies.