Pdf plotting of phreatic line for seepage through earth. Module 2 lecture 10 permeability and seepage 6 topics. For saturated flow, a 2d potential model considers a free boundary problem to laplaces equation with a travelingwave phreatic line generated by a linear. Rainfall and reservoir water level fluctuations are the main external factors of landslides in the three gorges reservoir area. Phreatic seepage flow through an earth dam with an impeding. The position of the phreatic surface influences the stability of the earth dam because of potential piping due to excessive gradient and sloughing because of the softening and weakening of the soil mass as it touches the downstream slope. Mar 10, 2014 line of seepage or prelatic line in earthen dams line of seepage or the phreatic line of saturation line is defined as the line within the dam section below which there are positive hydrostatic pressure in the dam.
As the upper flow line is subjected to atmospheric pressure, the boundary conditions are not completely defined and it is consequently difficult to sketch a flow net until this line has been located. The phreatic surface within a dam can be controlled by properly designed cores or walls. Institute of technology of cambodia dams design tp3 determination of phreatic line and coefficient k. Plotting of phreatic line for seepage through earth dams. On the basis of the boussinesq unsteady seepage differential equation, a new simplified formula for the phreatic line of slopes under the condition of decreasing reservoir water level is derived by means of the laplacian matrix and its inverse transform. Phreatic lines the top flow line of a saturated soil mass below which seepage takes place, is called the phreatic line. Determination of length of a horizontal drain in homogeneous earth dams. Dec 26, 2019 new mathematical models are developed and corresponding boundary value problems are analytically and numerically solved for darcian flows in earth rockfilled dams, which have a vertical impermeable barrier on the downstream slope.
The phreatic surface should be kept at or below the downstream toe. In this video dhananjay has discusses phreatic line. The pore pressure u 2 at point b is equal to the vertical distance between points a and b to the scale of the flow net or the dam section. View determinationof phreaticline andcoefficientk from et 1234 at itc. The first equipotential line epl1 intersects the phreatic line at point a and the trial slip surface at point b. Dam lecture 17 determination of phreatic line in earth dam free download as pdf file. Missouri university of science and technology scholars mine. Pdf study on phreatic line of zoned type earthen dam.
Pdf study on phreatic line of zoned type earthen dam with. Pdf evaluation of phreatic line in homogeneous earth dams with. When seepage emerges along a sloping surface, such as the downstream slope of a dam fig. Pdf on apr 1, 2012, reza ziaie moayed and others published evaluation of phreatic line in homogeneous earth dams with different. Evaluation of phreatic line 619 evaluation of phreatic line in homogeneous earth dams with different drainage systems r. Optimization of earth dams clay core dimensions using evolutionary algorithms marzieh mohammadi1, gholamabass barani2, kourosh ghaderi 3 and sonia haghighatandish 1 1department of water engineering, shahid bahonar university, kerman, iran 2department of civil engineering, shahid bahonar university, kerman, iran. In a homogeneous dam, the phreatic surface may intercept the downstream slope, creating a perennially wet surface condition. Experimental and numerical analysis for earthfill dam. Dam lecture 17 determination of phreatic line in earth dam. In this study, the seepage through earthfill dams was investigated. Phreatic line calculation and stability analysis of slopes. This line separates a saturated soil mass from an unsaturated soil mass. Guanhua sun, a yongtao yang, a shengguo cheng, b hong zheng a. The upstream slopes of most of the earth dams in actual practice usually vary from 2.
The hydrostatic pressure on phreatic line is atmospheric or zero. The top flow line of a saturated soil mass below which seepage takes place, is called the phreatic line. It is defined as an imaginary line within the dam section, below which there is positive hydrostatic pressure, and above there is negative hydrostatic pressure in the dam section. A questionnaire was sent to federal and state agencies, consulting firms, and private consultants experienced in the design and safety evaluation of embankment dams. Indian institute of technology, kanpur 1 nptel advanced. In the case of an existing slope, the phreatic surface can be determined from the subsurface investigation with adjustments for seasonal changes. Phreatic line calculation and stability analysis of slopes under the combined effect of reservoir water level fluctuations and rainfall. In developing this kind of flow net we are solving simultaneously for the flow net and the position of the phreatic line.
Pdf on apr 1, 2012, reza ziaie moayed and others published evaluation of phreatic line in homogeneous earth dams with different drainage system find, read and cite all the research you need on. The properties of the regular parabola which are essential to obtain phreatic line are depicted in fig. Their investigation revealed that the results of this method, compared to the software results, show an average 18 percent difference. Stability analysis of slopes of earth dams soil engineering. The upper surface of this stream of percolating water is known as the phreatic surface. Determinationofphreaticlineandcoefficientk institute. To reduce the risk of dam failure due to wildlife intrusions, this brochure. The chimney drain is the chimney drain is installed vertically with a 1m width and 32 m height. In such case the focus of base parabola is located at the downstream toe of the core, as shown in fig. How to draw phreatic line in dam is often asked in conventional question of mains exam. Home geography water conservation dams earthen dam phreatic line in earthen dam. Phreatic line is also known as the seepage line or saturation line. A wedge of sand and gravel or a perforated pipe in a shallow trench at the bottom of the slope, called a toe drain, can move the phreatic surface down and cure the wet slope problem.
Calculation of the stability of earth dams, transactions of the 2nd. Abaqusstandard this example illustrates the use of abaqus to solve for the flow through a porous medium in which fluid flow is occurring in a gravity field and only part of the region is fully saturated, so the location of the phreatic surface is a part of the solution. Phreatic lines seepage through soil for engineering. Build up one type of material phreatic line or seepage line horizontalblanket slope protection zoned earth dam. Phreatic line calculation and stability analysis of slopes under the combined effect of reservoir water level fluctuations and rainfall guanhua sun, yongtao yang, shengguo cheng, hong zheng 1 abstract. Before drawing the flow net for the earth dam section, it is necessary to plot the phreatic line more accurately. Seepage is the continuous movement of water from the upstream face of the dam toward its downstream face. Hydrostatic pressure acts below the phreatic line whereas atmospheric pressure exists above the phreatic line. Apr 14, 2020 lecture 10 plotting of phreatic line for seepage through earth dams notes edurev is made by best teachers of.
The chimney drain is usually utilized at the downstream side of the impermeable. Pdf evaluation of phreatic line in homogeneous earth dams. This is usually done by the method proposed by casagrande 1937 and is shown in figure 2. This document is highly rated by students and has been viewed 566 times.
Type of material used for dams phreatic line in earth dam phreatic line phreatic line or seepage line is defined as the line within a dam section below which there are positive hydrostatic pressure in the dam. Phreatic seepage flow through an earth dam with an impeding strip. Phreatic line and horizontal drain in earth fill dams. Phreatic line and horizontal drainage in earth fill dams. The position of the phreatic line influences the stability of the earth dam because of potential piping due to excessive exit gradient and sloughing due to the softening and weakening of the soil mass as if it touches the downstream slope or intersects it. Earth dams are generally built of locally available materials in their natural state with a minimum of processing. The hydrostatic pressure on the phreatic line is equal to atmospheric pressure and hence.
May 05, 2017 pdf 7412 k pdf plus 1202 k citing articles. Pdf determination of length of a horizontal drain in. The dam owner is the first line of defense against unsafe dam operations. Upstream face of an earthen dam is phreatic line and. For saturated flow, a 2d potential model considers a free boundary problem to laplaces equation with a travelingwave phreatic line generated by a linear drawup of a water level in the dam reservoir. In this context, the expression of normal stress on the slip surface under seepage forces is deduced, and a procedure for obtaining the. Optimization of earth dams clay core dimensions using. Pdf plotting of phreatic line for seepage through earth dams. A simplified solution for calculating the phreatic line and. In zoned type earth dam, the effect of outer zone on phreatic line is negligible.
For an earthen dam, the phreatic line approximately assumes the shape of a parabola. In the stability analysis of slopes, particularly those related to earth dams, it is necessary to estimate the location of the phreatic surface or the line of seepage. Phreatic lines seepage through soil for engineering youtube. Evaluation of phreatic line in homogeneous earth dams with. As such, the federal emergency management agency fema published this brochure to help the dam owner manage nuisance wildlife and wildlife damages at earthen dams. Determination of length of a horizontal drain in homogeneous. Phreatic line in earthen dam phreatic line is the top flow line which separates saturated zone from unsaturated zone and below which positive hydrostatic pressure exists in the dam section.
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