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Pressure head distribution under gravity dam without drain We can calculate Uplift Force under gravity dams by using USBR which assumes uplift pressure under gravity dams is linear. H1=100 m, H2=0 Uplift Force = (H1+H2) 2
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Gravity Dams depend mainly on its own mass to resist the effecting uplift pressure. The effect of uplift pressure can be reduced by using a drainage gallery. The optimum position of the drainage gallery under gravity dam results maximum drain reduction factor. in this study, numerical method (two dimensional finite element) are used to analyze hydr...
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... According to Azizi et al [10], the uplift pressure was decreased by about 66%. El-Razek and Elela [3] and Uday and Hasan [18] determined the optimum location of the drainage gallery underneath gravity dam at which reduction in the uplift pressure was about 54% and 40%, respectively. ...
In hydraulic structures such as diversion or gravity dams constructed on a porous foundation, the difference in water levels between upstream and downstream results in water seepage through the porous soil under the dam. This seepage flow generates uplift pressure under the structure that may cause a crack on the concrete surface of the structure’s floor. In this condition, the exit gradient may exceed the critical value and cause the piping phenomenon. In this study, the effect of the weep hole and cut-off wall on the uplift pressure and the hydraulic gradient under a diversion dam was investigated experimentally and numerically. For this purpose, four weep holes (diameter = 1 cm) were embedded along the longitudinal axis of the stilling basin. The weep holes were examined in single and combined modes. The experiments were conducted in three upstream water heads of 10, 15, and 20 cm. The results showed that in terms of seepage losses, hydraulic gradient, and uplift pressure, the binary combinations of weep holes are better than the other modes. Among the binary combinations, the combination of the two closest weep holes to the dam toe (weep holes 1 and 2) had the most proper performance. In the supplementary experiments, a cut-off wall in two depths (10 and 15 cm) was placed at the dam heel in addition to the best modes of weep holes combination. Overall, the simultaneous use of cut-off wall (especially 15 cm) and weep holes improved the hydraulic condition of seepage phenomenon under the dam.
... The optimum position of the drainage gallery was experimentally obtained to be 0.5B from the heel where B is the base width of the dam. Uday and Hasan (2016), studied the optimum location of drainage gallery under gravity dam using a computer program package "SLIDE V.5.005" and found the optimum location to be 0.167B from the heel of the dam of base width, B. ...
Seepage is a dangerous phenomenon under hydraulic structures and the main cause of failure and damage to dams when neglected and not processed. This study evaluates the numerical effects of the sheet piles' quantity, depth, and spacing beneath a concrete dam with isotropic and homogenous foundations on the seepage rate, pressure head, and exit gradient. The solutions were obtained using SEEP/W code in GeoStudio software 2018 for three configurations using single, double, and triple sheet piles. In addition, SLIDE software 6.02 was examined using single and double sheet piles. Dimensional analysis was applied to draw the dimensionless variables that affect the seepage rate and exit gradient, and all tests were repeated for three different sheet pile depths and distances from the heel of the dam. The findings showed that the seepage rate in all studied configurations reduced when sheet pile depth increased. The position of the sheet pile from the dam's toe significantly decreased the seepage rate in cases using single and double sheet piles, while in cases using three-sheet piles, the position of the middle sheet pile insignificant decreased seepage. It was recognized that when using a single sheet pile, the drop in pressure head increased with depths when the sheet pile was located at the heel and middle of the dam. In addition, in the case of a single sheet pile at the toe or using two and three-sheet piles, the pressure drop decreased as the depths increased. Also, the results showed that the middle sheet pile location in the case of three sheet piles slightly affected pressure reduction. Furthermore, the results showed that using two and three-sheet piles was more effective than using a single one in reducing the exit gradient, while the position of the middle one in the case of using three-sheet piles was insignificant. A nonlinear empirical equation was developed using SPSS 22 program, and the comparison of the seepage rate measured by SEEP/W and SLIDE software versus its quantity calculated from empirical equations showed a good agreement as the determinations (R2) coefficients were equal to 0.9779 and 0.9928, respectively.
This research deals with the effects of the existence of an under drain pipe
beneath the foundation of hydraulic structures, on the uplift pressure, and the exit
gradient downstream of this structure. In order to find the optimum dimensions of
the upstream and downstream cutoffs, bed width of hydraulic structure, location of
under drain (Horizontal and Vertical), and drain pipe diameter, to minimize a
selected relative cost function for a given depth of impervious layer, coefficient of
hydraulic conductivity ratio, and difference between the upstream and downstream
head of water, by using a coupled model of Artificial neural network (ANN) and
Genetic algorithm optimization (GA).
A glass tank experimental model was made using perplex (10mm thickness),
for modeling the hydraulic structure which is a rubber glass. Piezometers for both
sides of the tank were installed in order to measure the piezometric head in selected
locations. The tank was filled with sandy soil with hydraulic conductivity of
0.00022m/sec, which was measured in laboratory by using the constant head
method. Six different geometric cases were experimented the first is without under
drain pipe while the other five cases were with under drain pipe. Results were
recorded to compare with the results of the similar corresponding cases modeled
using the Geo-Studio software. Comparison of the results showed that the head
distribution is close enough with high differences obtained from the six experiments
which are “106 reading", with +6.72% as average difference value between
experimental and Geo-Studio results that indicate over estimation, while 36 readings
with -2.71% as average difference value between experimental and Geo-Studio
results for all experiments that indicate under estimation” hence calibration for the
Geo-Studio modeling results are not required, since it is more likely that the Geostudio
modeling will slightly overestimate head and results in more safe condition .
Numerical (Two dimensional) simulation is carried out using Geo-Studio
Seep/w software, 6050 individual cases were modeled with different variations for
all of the related variables to find each the required volume of the super structure and the required length of downstream protection. For each case the program solves
the seepage equation of the steady-state flow in an anisotropic homogeneous soil.
All data about uplift pressure and exit gradient was transferred to an Excel file to
find the required volume of super structure that satisfies the recommended factor of
safety of 2, against uplift pressure and the required downstream length of protection
against piping according to the recommended factor of safety for piping of 3. This
means a database was created for the required volume of the super structure and the
required length of downstream protection in terms of the head difference, depth of
impervious layer and anisotropy ratio, and assumed length of foundation, depths of
upstream and downstream cutoffs, different drain diameter, and different vertical
and horizontal drain locations. These variables were casted in non-dimensional form
.Then by using (Statistical Procedure for Social science, version 20.0) SPSS program
an Artificial Neural Network (ANN) model was developed to find the relation
between the required volume of the super structure, and the required length of
downstream protection for any given set of the other independent variable. After
many trails used in SPSS program for finding the required ANN model, the highest
correlation coefficient for both relative volume of super structure and relative length
of protection were found as 98.3% and 96% respectively.
A Mat lab program was written for a general optimization model to find the
optimum vertical and horizontal locations of the drain pipe, its diameter, upstream
and downstream cutoff lengths and the foundation length, that minimize a relative
cost function for any given (water head, horizontal to vertical coefficients of
hydraulic conductivities , and depth of impervious layer . The model adopts
constraints of the required factors of safeties against both uplift and piping failures,
in addition to geometrical constraints of the different dimensions of the structure
foundation. The model was casted to allow any constraint limits and any relative
cost combinations selected by the designer. The model was designed to be
implemented easily by any design engineer. Sensitivity analysis was made as usual
practice to find the required GA parameters that ensure stable optimum solution, to
reduce the robustness of the model due to the random selection of the initial assumed
solution set as the GA model adopt. This analysis had shown that for such
experimental engineering problem the required minimum number of population initial assumed solutions is 130000, and a minimum required number of iterations is
3, which gives a stable optimum solution. In addition to that, it was also found that
the position of cross-over that gives the best optimum solution is 5, among the
sequence selected for the variables. It was also found that for such size of initial
solution population and such number of iterations, the mutation process has no
results into more optimum solution, than the reproduction iterations.
Results found indicated that the existence of the under drain pipe in the
foundation has a considerable effect on the reduction of uplift pressure and exit
gradient. The reduction percentage is different for different cases, but generally the
reduction percentage is high.
