Unsteady filtration under maximal draw-off velocities of Tupolang water reservoir

The article presents the results of field studies to determine unsteady filtration in Tupolang dam core. Calculations are carried out for phreatic line curve in the core of Tupolang dam under unsteady filtration for various velocities of reservoir draw-off and water yield coefficient. At the same time it has been established that the increase of velocity and time of water reservoir draw-off leads to the increase of filtration pressure, and the decrease of water yield factor leads to the decrease of filtration pressure. The increase of filtration pressure, in turn, contributes to the increase of the intensity of unsteady filtration of Tupolang dam core.

Influence of speed of filling and draw-off to the filtration regime of Earth-fill dam

To use and manage water resources and carry out protection measures from the destructive effect of water flow, water reservoir hydrosystem construction has greatly developed. The article presents the results of field studies to determine unsteady filtration in the Earth-fill dam core. In the research process, static data from literature review, field study data, and theoretical processing of research results were used. Numerical data processing was carried out with methods of mathematical statistics, and the graphical part was done using Microsoft Excel. Calculations were carried out for phreatic line curve in the core of Earth-fill dam under unsteady filtration for various velocities of reservoir draw-off and water yield coefficient. At the same time, it has been established that the increase of velocity and time of water reservoir draw-off leads to the increase of filtration pressure, and the decrease of water yield factor leads to the decrease of filtration pressure. The increase of filtration pressure, in turn, contributes to the increase of the intensity of unsteady filtration of the Earth-fill dam core.

Sustainable Construction of Earth Dams: Use of Heterogeneous Material from the Dam Site

The volumes of soil required for the construction of an earth dam are usually of importance, so that, consequently, a key aspect to mitigate the negative impacts of dam construction, both from an economic and environmental point of view, is the use of materials in the vicinity of the dam location. However, this is often complicated because the existence of good quality materials with homogeneous properties, necessary for the dam core, is scarce in sites near the dam and their presence in sufficient volume for its construction is not usual. Unfortunately, using and transporting soil with good geotechnical characteristics to construct the core in a faraway location is economically and environmentally unsustainable. Therefore, the possibility of using less suitable material at the dam site as part of the core must be studied. Thus, in the present research the use of a soil of great heterogeneity in its geotechnical properties with a great dispersion of permeability is analyzed. Considering permeability as a random variable, combinations of representative values of heterogeneous soils are analyzed using their mean permeability and coefficients of variation that allow generating different lognormal distribution functions to carry out a Monte Carlo analysis. By maintaining the soil’s global heterogeneity, it was possible to study an unlimited disposition of lifts of different permeability. The statistical formulation allowed the research of the variation of the seepage flows and maximum gradients produced as a function of the variability of their mean permeability, being able to detect the factors with the greatest influence on the generation of high flows and gradients. Thus, it was possible to verify how high gradients were obtained for situations in which the seepage flow rates were moderate and low; the highest maximum gradients were observed in the lowest lifts of the dam core. In addition, based on the results of the Monte Carlo analysis, design charts have been developed for flow rates and maximum gradients, dependent on the mean permeability and the coefficient of variation, which allow judging whether heterogeneous material can be used, under conditions of safety, for the construction of the core of a dam.

Optimized Design of Earth Dams: Analysis of Zoning and Heterogeneous Material in Its Core

To control the seepage in the design of an earth dam, guidelines prescribe a high proportion of fines and high homogeneity of geotechnical characteristics in the material used for the dam core. However, on many occasions there is no material of this nature near the dam placement and, from an economic or environmental point of view, it is not possible to locate and transport material with good geotechnical characteristics close to the dam. This research demonstrated the possibility of using impermeable materials in earth dam cores, as well as soils considered unsuitable according to the classic recommendations and guidelines. For an optimized design, two situations are analyzed here. First, we examined the possibility of using soil with a marked difference in grain size as the core of the dam, each with homogeneous geotechnical properties. In this case, the optimal zoning of up to three types of materials was studied to ensure adequate seepage control. Second, we examined the use of soil with great geotechnical heterogeneity, which presents high permeability dispersion. In such a case, the conditions that would allow its use were studied via the of Montecarlo analysis. By maintaining the soil’s global heterogeneity, it was possible to study an unlimited disposition of layers of different permeability. In the first situation, the results showed that the most effective zoning for decreasing seepage flow corresponded with three vertically set materials. In this design, the most optimized zoning (minimal seepage flow rates) corresponded to the most impermeable soil situated downstream when water heights were under 90% of the height of the dam core. However, for maximum water height, more optimized cases corresponded to the intermediate permeability material located downstream. In the second situation, when heterogeneous materials were used to construct the impervious element of the dams, the Montecarlo analysis indicated that the seepage flow rates were limited to sufficiently low values despite the large dispersion of material permeability. In addition, the highest maximum hydraulic gradients were observed in the lowest lifts of the dam core and for situations in which the seepage flow rates were moderate and low.

The Effects of Grout Curtain Parameters on Uplift and Piping Phenomenon; Case Study: Sattarkhan Dam

Design of earth dams and their issues during and after construction is very important for residents downstream of the dam because of the potential risks and possible breakdowns. In the design of dams, various forces influence the dam body, including uplift pressure and piping phenomenon which should be considered in order to ensure the safety of the dam. Among the measures taken to prevent the washing away phenomenon, the reduction of the output gradient, and the leakage discharge from beneath the hydraulic structures, construction of the grout curtain and installation of the drainage are applicable. Therefore, in order to investigate the effect of various parameters such as the gradient angle of the grout curtain, length, and distance and the number of grout curtains, as well as the length of the drainage on the pressure and output gradient of the numerical models, were considered in current study. For this purpose, the SEEP/W software was used for modeling on Sattarkhan Dam as a case study. The results of the analysis showed that the use of the Qa’im grout curtain at the upstream of the dam has the highest resistance against the pressure and piping phenomenon. The results also showed that increase in the length of the curtain of the water seal increases safety against uplift and piping phenomenon. The use of further spacing between the two grout curtains under the core of the dam led to increase in overall pressure or reduction in safety against uplift pressure. Increase in the length of the horizontal drainage reduced the effects of uplift pressure and output gradient. Results show that period of 70 to 110 degree is appropriate for curtain angle and setting curtain in upstream of dam core with angle of 70 to 80 degree is optimum and economic. A length of 30 m is optimum for curtain. The number of 2 curtains is also optimum. Studying various scenarios of distance of 2 curtains in dam core indicates that distance of 6 m is optimum and also length of 18 m for horizontal drainage is optimum.