Assessing impacts of sea level rise on seawater intrusion in a coastal aquifer with sloped shoreline boundary

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.International Association for Hydro-environment Engineering and Research, Asia Pacific Division.This paper investigates the effect of gradual and instantaneous sea level rise (SLR) on the seawater intrusion (SWI) process in coastal aquifer systems with different levels of land-surface inundation. A set of hypothetical case studies with different shoreline slopes is used to conduct this numerical experiment. For the purpose of numerical modelling, a future rate of SLR from 2015 to 2100 is considered based on the moderate expectation of the Intergovernmental Panel on Climate Change (IPCC, 2001). The gradual SLR is implemented in two different stages. First, continuous and nonlinear rising of sea level is imposed starting from year 2015 up to the end of the century. After that the final value of sea level is maintained as constant in order to assess the response time spanning to a new steady state condition. The effects of pumping resulting in lowering of groundwater level are also considered together with the dynamic variation of sea level. The results show that the rate and the amount of SWI are considerably greater in aquifers with flat shoreline slopes compared with those with steep slopes. Moreover, a shorter period of time is required to reach a new steady state condition in systems with flatter slopes. The SWI process is followed by a significant depletion in quantity of freshwater resources at the end of the century. The situation is exacerbated with combined action of SLR and over-abstraction. Finally, by considering the effect of inundation of the shoreline due to gradual SLR, the sensitivity of the system to the main aquifer parameters including molecular diffusion of solute, dispersion, hydraulic conductivity and porosity is investigated

Study of hydraulic fracturing for gas drainage in a coalmine in Iran

This is the author accepted manuscript. The final version is available from Thomas Telford (ICE Publishing) via the DOI in this record.Hydraulic fracturing (HF) is one of the methods to make coalmining operation safer and more economic. One of the hazards in underground coal mining operation is the sudden coal gas emission leading to coal explosion. To reduce the risk of gas emissions to ensure safer mining, it is necessary to pre-drain coal seams and surrounding layers. The most important parameters affecting the HF process of a coal seam are: dip, thickness, seam uniformity, roof and floor conditions, reserve of coal seam and coal strength. This paper presents the development and application of a fuzzy model to predict the efficiency of hydraulic fracturing, considering the above factors. In the developed model, the efficiency of hydraulic fracturing of coal seams is calculated as a dimensionless numerical index within the range 0-100. The suggested numerical scale categorizes the efficiency of HF of seams to very low, low, medium, high and very high, each one being specified by a numerical range as a subset of the above range (0-100). The model is used to study the potential of hydraulic fracturing in a coal bed in PARVADEH 4 coalmine in Iran, which will be undergoing stress variation due to future mining activities. The mine consists of 5 seams C1, C2, B1, B2 and D with different characteristics. The results show that the seams C1 and B2 with predicted 94.6% and 81.2% efficiency, have high potential for gas drainage, and considering dip, uniformity and thickness it is suitable to use HF technique. The B1 seam with 31.8 percent efficiency has low potential for gas drainage by HF. HF would not be appropriate for both of C2 and D seams with 7.5 percent efficiency

Numerical analysis of fluid-rock interactions in hydraulic fracturing

This is the author accepted manuscript. The final version is available from Thomas Telford via the DOI in this recordHydraulic fracturing is a process of fluid injection into the well. This process creates tensile stresses in the rock in order to overcome the tensile strength of the formation. In this study, a three-phase hydro-mechanical model is developed for simulating hydraulic fracturing. The three phases include: porous solid, fracturing fluid and reservoir fluid. Two numerical simulators (ANSYS Fluent for fluid flow and ANSYS Mechanical for geomechanical analysis) are coupled together to model multiphase fluid flow in hydraulically fractured rock undergoing deformations, ranging from linear elastic to large, nonlinear inelastic deformations. The two solvers are coupled, using system coupling in ANSYS Workbench. The coupled problem of fluid flow and fracture propagation is solved numerically. The fluid flow model involves solving the Navier-Stokes equations using the finite volume method. The flow model is coupled with the geomechanics model to simulate the interaction between fluid flow inside the fracture with rock deformations. For any time step, the pore pressures from the flow model are used as input for the geomechanics model for the determination of stresses, strains, and displacements. The strains derived from the gomechanics model are in turn used to calculate changes to the reservoir parameters that are fed as input to the flow model. This iterative process continues until both (fluid and solid) models are converged. A parametric study is conducted by changing various model parameters to study their effects on the hydraulic fracturing process. The results show that changes in rock mechanical properties as well as fluid parameters could lead to significant changes in the hydraulic fracture propagation

Effect of thermal history on the properties of bentonite

PublishedJournal ArticleThis is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this record.© 2016, Springer-Verlag Berlin Heidelberg.The effect of thermal history on the properties of bentonite was studied through a number of experimental tests. The desired thermal history was created on samples of bentonite by keeping them at a fixed temperature (50, 100, 150, 200 and 250 °C) for a specific duration (3, 7, 14 and 30 days). Standard compaction, Atterberg limits, free swelling and swelling pressure tests were carried out on the samples on the dry side of optimum, optimum and wet side of optimum of the compaction curve with desired thermal history. In addition chemical tests were carried out on the flooding water at the end of the swelling test. The results showed that the changes in compaction characteristics were not considerable but the Atterberg limits, free swelling and swelling pressure of the soil were changed due to the thermal history in comparison with the soil without any thermal history. The magnitudes of free swelling and swelling pressure were dependent on the location of prepared sample on the compaction curve. In addition, the changes in Atteberg limits and swelling parameters (amount of free swelling and swelling pressure) were functions of magnitude of temperature and duration of time that the sample experienced the temperature in its temperature history. The effects of temperature and also duration of exposure of the soil to temperature was discussed with the aid of the Diffuse Double Layer (DDL) theory. It was found that the temperature may change the gradation of soil due to cementation of particles as a result of formation of some salts and oxides that help to paste the particles together and change the properties of the soil

An analytical solution for reliability assessment of pseudo-static stability of rock slopes using jointly distributed random variables method

PublishedReliability analysis of rock slope stability has received considerable attention in the literature. It has been used as an effective tool to evaluate uncertainty so prevalent in variables. In this research the application of the jointly distributed random variables method for probabilistic analysis and reliability assessment of rock slope stability with plane sliding is investigated. In a recently published paper, the authors showed the dependency of the numerator and denominator of the safety factor relationship and argued that, as a result of this dependency, the method could not assess the reliability correctly. In the current research the authors present a new approach to solve this problem. In this approach, using the basic relations in this method, the safety factor relationship is obtained directly without separation of its numerator and denominator. Furthermore, in addition to friction angle of sliding surface, apparent cohesion, depth of water in tension crack, and earthquake acceleration ratio, in the present work the unit weight of rock is also considered as a stochastic parameter. The results are compared with the Monte Carlo simulation. Comparison of the results indicates good performance of the proposed approach for assessment of reliability. The new results of parametric analysis using the jointly distributed random variables method show that the friction angle of sliding surface is the most effective parameter in rock slope stability with plane sliding

Effect of cement on treatment of a clay soil contaminated with glycerol

This is the author accepted manuscript. The final version is available from American Society of Civil Engineers via the DOI in this record.An investigation into the behavior of a contaminated clay soil and its treatment was carried out through a program of experimental tests. The contaminated soil samples were prepared with different percentages (3, 6, and 9%) of a glycerol solution with 40% concentration. The samples were prepared as mixtures of clean or glycerol-contaminated soil with different cement contents (3, 6, and 9%). Atterberg limits and unconfined compressive strength (UCS) tests were conducted on the samples. The results showed that Atterberg limits are reduced by adding glycerol or cement or adding glycerol to soil-cement. Both the strength and stiffness of the contaminated soil are reduced by increasing the degree of contamination. The results of treated soil showed that adding cement to contaminated soil increases the strength and the amount of increase in strength is dependent on the percent of cement, curing time and degree of contamination. Based on scanning electron microscopy analysis, it was found that the presence of glycerol prevents the interaction between soil and cement

Properties of Clay Soil and Soil Cement Reinforced with Polypropylene Fibers

This is the author accepted manuscript. The final version is available from American Concrete Institute via the DOI in this recordRandomly reinforced cohesive soils can be used as construction material in many civil engineering projects. These materials may be subjected to compressive, tensile or flexural stresses in their life. The presence of stabilizing agents or fibers may affect their resistance against various loads. In this work a clay soil was reinforced randomly at four different lengths of fiber ((10, 15, 20 and 25 mm) [0.394, 0.591, 0.788 and 0.985 in]) with fiber inclusions of 0.5 and 1%. Reinforced soil-cement samples were also prepared with 8 and 10% cement and reinforced similar to the soil. Unconfined compressive and tensile strength tests were carried out on the prepared samples. The results show that the compressive strength is increased with fiber length up to about 10 mm (0.394 in). When length of fiber is larger than 10 mm (0.394 in), the compressive strength is still increased but with a slow rate. The results for the reinforced soil-cement samples indicate that for a given fiber and cement content increasing the length of fiber has no significant effect on the strength of the sample. The tensile strength of reinforced soil is increased by increasing the fiber inclusion and length of fiber. For the reinforced soil-cement samples the tensile strength is increased with increasing fiber content, length of fiber, percent of cement and curing time

Three dimensional simulation of seawater intrusion in a regional coastal aquifer in UAE

Published13th Computer Control for Water Industry Conference, CCWI 2015In this study the vulnerability of the Wadi Ham aquifer, located in the Fujairah Emirate of the UAE, to seawater intrusion (SWI) is assessed using a 3D finite element (FE) model. The numerical model is developed based on available hydrogeological data in real scale. By simulation of the aquifer for the next 10 years and by maintaining the current rates of pumping (in year 2015), the progress of seawater intrusion in year 2025 is followed by further depletion in freshwater storage of the Wadi Ham aquifer. In order to control this problem, the model is subjected to a management strategy involving surface recharge of the aquifer with treated wastewater

Effect of Quality Electrolyte Fluid on Removing MTBE from a Clay Soil Using Electrokinetic Technique

This is the author accepted manuscript. The final version is available from ASCE via the DOI in this recordMethyl tertiary butyl ether (MTBE) is a chemical product and the most commonly used gasoline oxygenate. It is characterized as a pollutant for soil and water that has effects on human health. Research on the remediation of soil polluted with MTBE is relatively rare. This paper presents the results of laboratory experiments to study the feasibility of using the electrokinetic technique to remove MTBE from a clay soil. Tests are conducted on a clay soil contaminated with MTBE in a special apparatus, using different quality of electrolyte and direct current (DC) or alternating current (AC) electricity. The results of the tests reveal that, under laboratory conditions, MTBE can be removed from soil using the electrokinetic technique. The efficiency of remediation is dependent on the quality of electrolyte and type of applied electrical current

Models for predicting the seepage velocity and seepage force in a fiber reinforced silty soil

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Randomly reinforced soil is used in hydraulic projects such as temporary canals, earth dams, stream restoration and so on for controlling seepage. This paper presents an investigation into the effect of random reinforcement on the seepage velocity and seepage force in a silty soil. Experimental tests were carried out on randomly reinforced samples with two types of fiber at different lengths and percentages. The results show that the random reinforcement of soils with fiber is an effective technique in controlling the seepage velocity and seepage force. Regression models were developed based on the experimental data for determination the seepage velocity and seepage force. The proposed models include the length of fiber, fiber content of soil and hydraulic gradient. Comparison between the model predictions and the experimental results shows that the proposed models can satisfactorily predict the seepage velocity and seepage force for a randomly reinforced silty soil. Analysis of the results of the proposed models shows that the seepage velocity increases with increasing the hydraulic gradient but decreases with increasing fiber length and fiber content. In addition the seepage force increases with increasing the fiber length and fiber content of the soil