جستجوی مقالات مرتبط با کلیدواژه "نشت" در نشریات گروه "زمین شناسی"

Electromagnetic methods in applied geophysics are advancing rapidly. Since the TDR system has grown, its use has led to innovative applications and comparisons with other previous measurement methods. A TDR system consists of a radar (electromagnetic) receiver and generator, a transmission line, and a waveguide. The electromagnetic pulse generated from inside the conductor cable moves towards the waveguide and is tested through the waveguide into the environment under test. In the last few years, the use of the TDR system to identify water leakage situations has been expanding. In this article, by performing tests on two-strand telecommunication cables as TDR sensors, the ability and accuracy of the time domain reflectometry method in detecting leakage situations has been evaluated. In this research, the two-stranded cable was buried under GC gravel clay material, and by increasing the percentage of soil moisture stepwise at two points, the sensitivity of the TDR method to the changes in moisture around the cable was investigated. Based on the TDR waveforms, the points of reflection coefficient changes are located at the distances of 9.5-9 and 4.5 meters, which is completely consistent with the actual distance of the test points. In this research, TDR moisture meter made by soil moisture company model 6050x1 was used. The results of this research show that the TDR method has the ability to be used as a monitoring system to detect leakage in dams, dikes and other geotechnical structures.

During wet mineral processes in mines, a large amount of wastewater is produced and stored in tailing dams. In Miduk copper mine, Shahr-e-Babak, Kerman, Iran, there are tailing dams and wastewater dams as a result of mineral processing. The wastewater dam normally is constructed in order to separate and to reserve the water content of tailings, and finally, to reuse it for mineral processing. In this study, we have used the geophysical methods (electrical resistivity tomography (ERT) and self-potential (SP)) to investigate the seepage from the wastewater dam of the Miduk copper mine. The ERT surveys show a low electrical resistivity zone (less than 20 Ωm). It can be as a result of a clayey alteration zone or fractured zone. In addition, SP measurements show a positive anomaly in the same area due to the seepage from the dam walls. It can be due to an electrokinetic source origin. The observed natural source in the same zone, confirmed the geological, hydrogeological and geophysical interpretations. These results show the ability of ERT and SP methods to investigate the seepage zones related to wastewater dam walls.

Mining like other industrial activities can affect the environment negatively. Tailing dams have long been associated with mining activities and have formed a major negative impact. Excessive seepage in the foundation of the dam threatens the integrity of the structure. Geophysics has been used intensively in environmental problems, in particular in the study of mine tailings problems. In fact, geophysical surveys especially electrical resistivity tomography (ERT) and self-potential (SP) methods constitute a comprehensive methodology for assessment of anomalous seepage conditions by detecting, mapping and monitoring the zones.

The field survey to detect the seepage in Miduk wastewater dam was composed of a geophysical survey and a hydrogeological study. The hydrological study was performed in order to identify water table, surface water and groundwater quality, and to understand the relation between water collected in dam and water resources. Such a study is very common in environmental geochemical investigations. The ERT survey was carried out along 2 survey lines, called P1 and P2, using the dipole–dipole array with an electrode spacing of 20 m in the survey line P1 that has a total length of 400 m, however, the survey along the survey line P2 has been carried out using an electrode spacing of 5 m. The survey line P2 is 100 m long. A maximum n value of 11 was used for both P1 and P2 ERT profiles. All data were acquired by a WDDS-2 resistivity meter using multi-electrodes cable. The SP survey along SP1 and SP2 survey lines was carried out on the northeast abutment of the dam. The SP measurements were taken using two non-polarizing electrodes (Cu-CuSO4), one electrode was located at the base station as a stationary electrode and the other moving along the desired line at pre-fixed stations. The base-station was chosen at a point convenient for operation but away from the expected anomaly. Electrodes polarization was controlled between measurements using two constant points in the site. In order to identify the water table, in a part of the hydrological study, water depth in 6 observation wells, located downstream of the water retention dam, was measured. In the second part of the hydrological study, hydrochemical investigation was carried out by taking 17 water samples collected from 15 stations. The hydrogeochemical characteristics of water were obtained through physicochemical analysis of the water samples.

The ERT survey shows a low electrical resistivity zone (less than 20 Ωm). It can be the result of a clayey alteration zone or fractured zone. The SP measurements show a positive anomaly in the same area due to the seepage from the dam wall. According to the hydrochemical study, the water type of this area is bicarbonate-chlorate while the water type of one borehole and the dam water sample are both sulfate-chlorate. The obtained information from the survey area confirms the geological, the hydrogeological and the geophysical interpretations

1- Introduction For a dam project in the karstic areas, the most important parameter is the hydraulic conductivity values which are necessary for determining the amounts of leakage from its reservoir and abutments However, secondary porosity and flow networks can cause heterogeneity and anisotropy in karst fields, leading to changes in hydraulic conductivity values and then significant differences in leak calculation values due to scale changes. Limestone formation in a regional scale is generally heterogeneous, and the heterogeneity of hydraulic conductivity (Karami 2002) usually specify the value of heterogeneity in karstic aquifers Kiraly (1975) investigated karstic aquifers and fractures in the Jura Mountains in Switzerland. He reported that the sub-local scale to the well-scale and the great permeabilities on the regional scale are related to karstic conduits and increase hydraulic conductivity. Rovey and Cherkauer (1995) measured the hydraulic conductivities of five hydrostratigraphic carbonate units at different scales and reported that the values of hydraulic conductivities show direct proportionality with the measurement scales. Sauter (2005) studied the various methods, sub-local to regional scales, for determining the permeability in a karstic environment. He mentioned that the various hydraulic conductivities in different scales could be due to the spatial organization and the degree of networking of the drainage system (Sauter 2005). Other hydrological and geological studies have investigated the relationship between scale with values of hydraulic conductivities in fractured rocks (Illman 2007) and sedimentary formations (Chapuis 2010, Galvão et al. 2016). The main objective of this study is an investigation of the scale effect on the amount of water leakage from the reservoir and the dam abutments in the karstic area. We selected the Beheshtabad for the case study of this issue. 2- Methodology Beheshtabad dam is double-arch dam with a height of 180 meters and the reservoir volume of 1050Í106 m3. The dam is situated on the Beheshtabad River with an approximately 33 m3/s flowrate. The right side of the reservoir is in contact with karstic limestone-dolomite of the Sangvil anticline named Jahrom- Asmari Formation with a thickness of about 700 meters. Determining the amount of leakage from the reservoir requires an accurate estimation of the hydraulic conductivity according to the contact scale with the karstic aquifer. The values of hydraulic conductivities have been measured in Jahrom-Asmari Formation of the right-side reservoir using various methods in three scales, sub-local, local and regional scales. We used the Slug and lugeon tests in sub-local scales and conducted simultaneous measurements of spring discharge and boreholes water levels such as pumping wells in the local scale. Also, hydraulic conductivity in the regional scale determined by Recession curve and Darcy method. Finally, the amount of leakage was calculated in different scales and compared based on the hydraulic conductivity values of different scales. 3- Findings The hydraulic conductivity has been calculated on a different scale with a related test for limestone aquifer on the reservoir’s right-side. The values of hydraulic conductivities are not the same in different methods, and it is in the range of 2.1×10-6 to 1.6×10-4 m/s (Table 1). The lowest hydraulic conductivity belongs to a slug test conducted on a sub-local scale, and the highest hydraulic conductivity is for recession curve and Darcy method in regional scale. Also, the spring discharge method and the water levels of boreholes as a pumping well in the local scale estimates the values of hydraulic conductivities. The calculated hydraulic conductivities on the regional scale are about 70 times higher than those for the sub-local scale, which is related to the effect of scale in the karstic environments. According to the results, experiments with a radius of greater than 500 meters will determine the equivalent volume of hydraulic conductivity to the karstic mass region. Table 1. Calculated hydraulic conductivity value using different methods Methods KMIN (m/s) KMAX (m/s) KRE (m/s) PACKER TEST 1.00E-05 1.00E-07 3.20E-06 SLUG TEST 1.10E-06 3.30E-06 2.10E-06 DARCY 1.00E-04 1.30E-04 1.20E-04 RORABAUGH 1.41E-04 3.60E-04 1.60E-04 MILANOVIC 4.10E-05 2.00E-04 8.00E-05 Seep 2D software determined the leakage value for the northern limb to the downstream and southern limb. The amount of leakage varies due to changes in values of hydraulic conductivities. The amount of leakage calculated based on the average reservoir cross-section with a limestone aquifer at sub-local, local and regional scales are 0.3, 3.9, and 5.4 to 8.1 m3/s, respectively. Such differences in the estimation of leakage are related to the scale effects on the heterogeneity of karstic areas. Hydrogeological studies indicate that the Beheshtabad reservoir is contacted regionally with the right-side limestone aquifer; therefore, the leakage amount should be modeled based on the regional hydraulic conductivity. According to the regional scale, hydraulic conductivity varies between 1.1×10-4 to 1.6×10-4 m/s. Therefore, the leakage amount from the dam reservoir will be between 6.3 m3/s and 8.1 m3/s (Fig. 1). Fig 1. Leakage amount based on regional scale hydraulic conductivity 4-Conclusion For determining the amount of dam reservoir leakage in the karstic areas, the most critical parameter is the value of hydraulic conductivity that changes with the measuring scale. When reservoir and abutment of the dam contacted with karst, some methods for determining the regional hydraulic conductivity such as dye tracing, the Darcy method, and the recession curve method are more accurate to estimate the leakage amount. If the reservoir contact is local, the pumping test is more accurate for determining the leakage value. Also, in the sub-local contact scale, lugeon, injection, and slug experiments are more accurate methods in terms of determining leakage amount. In karstic formations, the scale effect is one of the most important factors for reservoir considering in the stage of site selection of the dam. Therefore, the choice of the dam axis can be carried out in places where the reservoir and abutments of the dam are not in contact with the karst network as far as possible. References Chapuis, R.P., 2010. Permeability scale effect in sandy aquifers: A few case studies. Proceedings of the18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris Galvão, P., Halihan, T., Hirata, R., 2016. The karst permeability scale effect of Sete Lagoas, MG, Brazil. Journal of Hydrology 532, 149-162 Illman, W.A., 2006. Strong field evidence of directional permeability scale effect in fractured rock. Journal of Hydrology 319 (1-4), 227-236 Karami, G.H., 2002. Assessment of heterogeneity and flow systems in karstic aquifers using pumping test data. Ph.D. thesis, University of Newcastle Kiraly, L., 1975. Rapport surl’etat actuel des connaissances dans le domaine des caracteres physiques des roches karstiques. In Hydrogeology of Karstic Terrains (eds Burger A and Dubertret L). International Union of Geological Sciences, Series B, 3:53–67 Rovey, C.W., Cherkauer, D.S., 1995. Szxcale dependency of hydraulic conductivity measurements. Groundwater, 33(5), 769-780 Sauter, M., 2005. Scale effects of hydraulic conductivity in karst and fractured aquifers. Geophysical Research Abstracts, Accepted 28 April 2005, https://www.cosis.net/abstracts/EGU05/07748/EGU05-J-07748.pdf

Pressure tunnels in hydroelectric plants are used to convey water to powerhouses. These tunnels are the sources of seepage flow to the rock formation, thus, during the water filling, they will have a low resistance to seepage and, by increasing the internal water pressure of the tunnel, the inflow force will be transferred to the rock mass. In these conditions, the cracks, pores and all other elements of the rock mass are affected by the seepage forces in all directions. This hydro-mechanical interaction affects changing the stresses and displacements of the rock mass around the tunnel and causes modifications in the permeability of rock elements during the water filling. Therefore, changes in stress distribution lead to alterations in the permeability coefficient and redistribution of the seepage field. In these conditions, since the analytical solution of the problem is not possible, the numerical analysis based on the finite element method has been used in this study. In this approach, the rock mass is considered as an equivalent continuum in which the effects of discontinuities are taken into account in its material behavior. High-pressure tunnels under internal water pressure requires reinforced concrete lining to prevent hydro-fracturing. The ABAQUS software is capable of analyzing such as seepage from the tunnel, modeling of the steel bars in concrete, and taking into account hydro-mechanical interaction. Thus, the software is used for numerical analysis.
The pressure tunnel of the Gotvand dam and hydroelectric power plant (HPP) scheme is taken as a case study for the numerical simulation. Pressure tunnel of the Gotvand dam located in the southwest of Iran is taken as a case study for the numerical simulation. Among behavioral models in the software, Mohr-Coulomb failure criterion is considered to describe the rock mass, but the principle of effective stress determines the rock mass behavior. Since the concrete lining of the pressure tunnel will undergo two mechanisms of the cracking due to tension and the crushing due to compression, concrete damaged plasticity model is used to predict the response of the concrete elements. The evolution of the yield surface of the concrete lining is also controlled with tensile and compressive equivalent plastic strains, correspondingly.
In this study, the hydro-mechanical interaction is implemented based on the analysis of the pore fluid/deformation analysis, and the direct-coupled method is used to solve the governing equations of the problem. To verify the proposed model, the elastic behavior of the media is simulated to compare the numerical and the analytical solutions and good agreement is obtained. The numerical analyses are carried out the hydro-mechanical interaction with constant permeability coefficient. When cracks develop in the concrete lining at high water pressure, the properties of the concrete lining change and as a result, the stress dependent permeability of the lining and surrounding rock mass in pressure tunnels should be considered. The coefficient of permeability controls the rate of seepage flow in porous and fractured media. Although permeability represents an original property of the porous media, it can be modified when subjected to the stress variations. Instead of changing aperture, the change in the void space or volume is the typical consequence that results to change the permeability coefficient. In order to bring the model closer to the real conditions and in the validation of the new model, the influence of the permeability coefficient variations of the concrete and rock mass on the deformations and stresses of the model has been added to nonlinear analysis by USDFLD code. Increasing the water head in the tunnel during water filling is also considered with the combination of DLOAD and DISP codes in the model. Since the lining and rock mass have nonlinear properties and complex behavior, for verification of the model in ABAQUS software, the model is simulated with homogeneous, isotropic and elastic behavior. The results of seepage flow on the interface of the concrete lining and rock mass obtained by analytical and numerical solutions indicate that there is a ±5 % difference between them. Then, the results of the elastic behavior of the model show a good agreement with the results of analytical solutions. Therefore, this numerical model has been employed for the nonlinear analyses.
Finally, the optimal thickness of the concrete lining with the appropriate arrangement of the reinforcement in the reinforced concrete linings is utilized to minimize water losses from the tunnel based on the new model. Thus, the results of the analysis with the aim of reducing the water losses from the tunnel indicate that the suitable arrangement of the steel bars in the concrete lining leads to the distribution of micro cracks in the lining, and the reinforcement stress stays at a lower value with high internal water pressure. Based on the new numerical model, it is suggested that the lining should be designed with the thickness of 40 cm and the reinforcement with the diameter of 16 mm and the spacing of 20 cm. The results of the numerical model indicate that to control the seepage outflow from concrete-lined pressure tunnels, the thickness of the lining and the suitable arrangement of the steel bars in the concrete lining play a significant role in preventing excessive seepage from the tunnel.

A tailing dam or confining embankment is constructed to enable the deposited tailings to settle and retain processed water. Tailing dams are susceptible to different kinds of pressures such as water pressure and the load of the tailings themselves. Miduk tailing dam was originally constructed with a fine silty sand layer to retain water covered by coarse grains. It was constructed in stages according to the downstream method, filter and support fill.
Tailing dams and downstream areas must be monitored as they undergo internal erosion, during which, the fine grains in the core of a dam are flushed away by seeping water and, as a consequence, the hydraulic conductivity in the remaining material increases. High velocity flows through the dam embankment can cause progressive erosion and piping. Moreover, the saturation of embankment soils, abutments, differential settlements in foundations, local stress relaxation in the soil and locally increased hydraulic gradient generally reduce soil strengths. The seepage issue in a tailing dam is the cause of reservoir loss to groundwater . Furthermore, it causes environmental problems such as the diffusion of heavy metals, acid drainage and so forth. Reversed water from the tailing dam is particularly important in desert areas.
Resistivity and self-potential (SP) monitoring has been widely applied for solving environmental and engineering problems of embankment dams by studying the changes in the subsurface properties with time. SP changes are caused by water movements through (or under) the dam and resistivity changes reflect the changes in the electrical properties of the dam materials.
Self-potential (SP) is a method where naturally occurring electrical potentials are measured. There are a number of different electro-chemical processes that can create such potentials. The type that is of interest in dam investigations is the so-called streaming potential which is the voltage difference parallel to the direction of flow. The streaming potential is manifested by a shearing of the diffuse layer caused by the hydraulic gradient. The field equipment for SP measurements is simple and inexpensive. It requires a pair of non-polarized electrodes, a high impedance voltmeter and t cables to connect them. Electrode drifts were controlled during SP measurements. Electrode drift is primarily caused by variations in temperature or soil moisture or by contamination of the electrolyte by ions introduced from the soil. Changes in the telluric currents induce substantial changes in the potential distribution in the subsurface, an effect accounted for by making regular measurements of the SP difference between the reference point and the base point within the survey area.
The Resistivity method involves the measurement of the apparent resistivity of soil and rocks as a function of depth or position. The resistivity of the ground is measured by injecting a current with two electrodes and measuring the resulting potential difference with two other electrodes. The readings are usually converted into an apparent resistivity of the sub-surface. From these measurements, the true resistivity of the subsurface can be estimated. The investigated volume can be changed by moving the electrodes. The data are usually inverted to a vertical resistivity section, assuming a 2D geometry perpendicular to the profile. Most commonly, the local variability is minimized, resulting in smooth models compatible with the measured data, meaning that sharp resistivity borders such as the ground water surface is visualized as a smooth transition in such inverted sections.
The principle objective of the present study was to evaluate the electrical resistivity and the self-potential methods used to detect anomalous seepage through mine tailing dams. In this regard, field measurements of resistivity and self-potential were carried out on the downstream grounds of tailing dam so as to identify the SP-responses related to seepage. The hydro-stratigraphy was mapped with the resistivity data (4 profiles of ERT) and groundwater flow patterns were specified with self-potential data (208 SP measurement points). The groundwater flow pattern was controlled by the geological and tectonic history of bedrock and the preferential flow pathway existing beneath the dam.

Gurdian dam with 1450 meters length is including out of the axis of the dam that receives water from the Aras River. Based on geological studies and drilling investigation, river bed in dam site made up of layers of marl and sandstone with interlayer of loose conglomerate of Miocene. Permeability of this sediments vary between 10-11 and 10-3 m/sec. Regarding to dam site specifications is used cut off wall with plastic concrete for over the wall 850 meters length. In fact cut off wall is an impediment under the axis of the dam that caused decrease the seepage amount. Of course the amount of acceptable seepage reduction for this depends on the local geology and characteristics economic value water in the region and the cost all every cubic meters of water. With regard to the conditions of the dam water reservoir of Gurdian, will provide by pumping from Aras river, the cost of each cubic meter water is high, therefore is willing to reduce the seepage amount below 90 percent compared to without cut off wall. Due to this and the underground conditions depth of cut off wall in different parts has been set. The results of seepage analysis indicate that the optimal depth of cut off wall is varied between 5 to 12 meters in different parts. The seepage value from foundation of dam without cut off wall will be 1,898,200 m3/yr and with a cut off wall will decrease to 208,500 m3/yr.

The spreadsheet modeling method is a practical tool for solution of the steady state, confined to the groundwater flow problems.The methodology is simple and includes many of the aspects of general flow condition such as anisotropy, heterogeneity, discharge, recharge, and irregular boundary shapes. The method incorporates numerical solution techniques for large matrices. In addition, since users program the equations in spreadsheet cells manually, the method provides good physical intuition for a groundwater flow problem. This may not always be the case when using commertial software programs. Especially it is a good teaching tool in the classroom for many students because they will understand the solution physically well. Governing equations could be developed for anisotropy and heterogeneous flow conditions. Mathematical treatment of boundary conditions is presented and the sink and sources incorporated into the domain of flow problem. The analysis shows that the solution is sensitive to the selection of the dimension of blocks or cells, node spacing and the number of iteration in spreadsheet program. Finally, advantages and limitations of solution methods are discussed in comparison with other numerical solution techniques. This method offers a number of advantages including, simplicity, accuracy and wide availability of spreadsheets such as Microsoft EXCEL. The method also has a number of limitations such as the necessity for hand programming in which viewed as shortcoming for accuracy and mistakes by handwriting and the speed of convergence of solution due to low order numerical techniques in the spreadsheet