The Effect of inclined intermediate Sheet Pile on Seepage Properties Under Hydraulic Structure Using SEEP/W Program

This paper is intended to study the effect of using incline intermediate sheet pile and finding the effect of change for its angle, besides the upstream and downstream piles rest in homogeneous soil layer on the seepage, uplift pressure exit gradient at toe of hydraulic structure using computer program SEEP/W software. From the software test carried out many cases, in beginning, finding the best distance between the three sheet piles then finding the best depth of three sheet piles finally using the angle for incline intermediate sheet pile (θ =30,45,60,90,120,135,150) degree in three cases for first and last sheet piles when the angle of them (θ =30,60,90)degree. Also for each run the quantity of uplift pressure, exit gradient and discharge at toe of hydraulic structure were determined to develop an empirical equations. Depended on the software program tests were carried out with three different value of each following parameter: upstream sheet pile depth, downstream sheet pile depth, intermediate sheet pile depth, upstream sheet pile angle, downstream sheet pile angle and four different value of distance between the sheet piles, then it carried out with seven different value of intermediate sheet pile angle, all of them with using constant upstream head and permeability for soil layer.


Introduction
Hydraulic structures are using to control the flow of water are subjected to seepage under the hydraulic structures adversely affects the safety of the structure resulting in its failure. So, the seepage under hydraulic structures can be considered as one of the most important critical problems in the hydraulic structures safety. The seepage phenomenon (uplift pressure -flow rate -exit gradient of hydraulic structures) is one of the main causes of failure or collapse of hydraulic structures, so it has been reduced using sheet piles under floor of hydraulic structures. For the SEEP/W, it is a finite element software product that design both saturated and unsaturated flow and simulate the actual physical process of water flowing through a particulate medium [1]. Swamee et al ., investigate the affectivity of multiple sheet piles in weir design [2]. Irzooki study the effect of the inclined piles of hydraulic installations on the lift pressure under the structures by using the defined difference method with the relaxation technique in computer programs [3]. Arslan & Mohammad used the experimental and the theoretical study for a pizometric head distribution under the hydraulic structures for upstream, intermediate and downstream sheet piles inclination [4]. Ali study the effect of middle sheet pile on a uplift pressure under hydraulic structure by the finite difference method with the relaxation technique [5]. Teah & Alghazali study the analysis of seepage under hydraulic structures using slide program through single and multi-layers soils and its effect on structures with inclined cut-off at IOP Publishing doi:10.1088/1757-899X/1076/1/012131 2 downstream, at upstream, and at both of them [6]. Rasool study effect of mutual interference piles on seepage properties under hydraulic structures by using finite elements program ANSYS and verifywith the practical results L-SAYED [7]. Jamel research the result of using intermediate sheet piles under the hydraulic structure apron in addition to upstream and downstream piles on non-homogeneous soil layer by using computer program SEEP/W Package and verify with artificial neural network (ANN) [8]. Abbood et al .,study an experimental work by using physical model and numerical model by using Geo-studio software were done to test the effect of using two inclined sheet piles one located at the upstream and the other at the downstream side of the structure through a pervious soils beneath hydraulic structures [9]. Talukdar & Dey study the results of using multiple the sheet piles of different lengths positioned at different distances from the upstream and downstream of a homogeneous earthen dam on the element of seepage and analyze it by using a finite Element modeling in GeoStudio 2007 program using the SEEP/W module [10]. Arshad & Babar investigate and Estimate Using SEEP/W Model and Artificial Neural Network, the Seepage Discharge Through Homogenous Earth Dam with Core, depending on field notes for seepage study, maximum seepage velocity and exit gradient through and under body and earth dam (Case Study: Hub Dam -Pakistan) [11]. Nassralla & Rabea study the effect of sheet pile on seepage characteristics under the hydraulic structure floor through soil consists of two layers by experimentally (Sand Model) and Numerically (Geo-Studio SEEP/W Model) [12]. Irzooki study the quantity of seepage through homogenous earth dam with horizontal toe drain by the computer program SEEP/W (which is a subprogram of Geo-studio) [ 13]. Jamel is using computer software program SEEP/W to Research the result of using double soil layer upstream and downstream sheet pile on discharge, uplift pressure and exit gradient at the toe of hydraulic structure [14]. L Saleh study the exit gradient of seepage under a concrete dam provided with two sheet piles. The results of this study obtained from SEEP/W model were then used to create two neural artificial network (ANN) models [15]. Jassim & Abdulrazzaq study seepage through Al -Wand dam was analyze by using SEEP/W model [16]. Teah & Alghazali study flow net and analyze seepage flow through different porous soil foundation underneath a hydraulic structure by physical model (seepage tank) and Compare of the physical model results with the resulted by Finite element method software (SLIDE 5.0) model [17]. Al Siaede study the stability and safety of small weirs (Teeb weir) using SEEP/W and SIGMA/W packages [18]. In this study and in order to provide the required safety for both piping and uplift pressure due to exit gradient, the designers usually provide sheet pile at the upstream, the downstream sides of the hydraulic structures foundation for homogenously the intermediate sheet pile being necessary. By using SEEP/W will provide information on the amount uplift pressure head, exit gradient and seepage discharge at toe of hydraulics structure.

The Procedure of Design Setup
The object of the SEEP/W model test is to use three different values for each variable effect on the properties of the seepage , which are up stream sheet pile depth(first sheet pile ), downstream sheet pile depth(third sheet piles )(L1=L2=2,3 and 4)m ,intermediate sheet pile depth (second sheet pile )(L2=3,4 and 5)m, the distance between first and third sheet pile =25 m ,the distance between first and second sheet piles (b=5,10,15, 20)m ,angle of first and third sheet pile (1=θ 3= 30,60 and 90) degree, angle of intermediate sheet pile (30,45,60,90,120,135 and 150)degree .For constant up stream head (4.5 m )and permeability of soil (k=10 -4 ) m/sec. The overall runs are (1136) runs. The quantity of inflow discharge exit gradient and uplift pressure at the toe of the hydraulic structure are calculated for each run. The classification for a study group is seen in Figure 1.

Design Variables
The variation of uplift pressure, exit gradient and discharge under the hydraulic structure, depends on the same parameter influences these are: The probable variables that can influence uplift pressure, exit gradient and discharge of the hydraulic structure at a toe are shown in Figure 2.  Figure 2. The analysis of the general section.

Effect The distance of intermediate sheet pile on the variables
In beginning, the following relationships between the variables for cases by using seep/w data with change of site and the distance between the intermediate sheet pile and the terminal sheet piles. Figure 3, shows the relationship of the distance (b (m)) between the first sheet pile and intermediate sheet pile to up lift pressure (P (kPa)) at toe with boundary conditions of constant angle three sheet piles (θ 1,θ 2,θ 3=90º) with constant permeability factor(0.0001 m/sec) .When the second sheet pile have 3m as length and it on the site at (5m,20m) from the first sheet pile the value of pressure is low and when second sheet pile at (10m,15m) form the first sheet pile the value of pressure will increase .And when the length of piles is 4m ,the result of pressure will increase as (0.051 ,0.06,0.065,0.058)% to site of intermediate pile as (5 ,10,15,20) m .while the pile have length 5m the percent of increase in pressure value as (0.11,0.14,0.13,0.12)%. Finally, that mean the hydraulic pressure value decrease when the site of intermediate near the terminal pile and increase when it near the middle of structure.          Figure 7, illustrates the relation of a depth for first pile (L1(m)) to a exit gradient toe of hydraulic in boundary conditions of a constant angle three sheet piles (θ 1,θ 2,θ 3=90º) taken with constant permeability factor . It can be seen from this figure that the pressure will decrease with the rise of depth for piles .When the first pile that have depth =2 m ,the pressure was high value and when the length of first pile =3m the value of exit decrease by approximately (3.23%). Finally, when depth of first pile =4m the value of exit decrease by approximately (7.36 %).       Figure 11. The relation between the discharge and the depth of intermediate pile.

Effect of length of intermediate sheet pile
From Figure 11, the relation will be illustrated the depth of second pile (L2(m)) to discharge of the downstream hydraulic structure (q) with the boundary conditions of the constant angle three sheet piles (θ 1,θ 2,θ 3=90º) with constant permeability factor and the distance between first sheet pile and  Figure 12 illustrated the relation of the depth of first pile (L3(m)) with the pressure with boundary conditions of constant. angle. Three sheet piles (θ 1,θ 2,θ 3=90º) with constant permeability factor and the distance between first sheet pile and intermediate sheet pile (b= 20 m). . In the figure show that a pressure will reduce with rising of depth of piles .when a third pile that have depth =2 m ,the pressure was high value and when the length of third pile =3m the value of pressure increase by approximately (0.1%) . finally, when depth of third pile =4m the value of pressure increases by approximately (0.214%). This indicates the increasing in length of third sheet pile have little effect on value of pressure.     Figure 14. The relation between the discharge and the depth of third sheet pile.    when θ1,θ3=90ẘ hen θ1,θ3=30ẘ hen θ1,θ3=60˚