cut-off wall

CUT-OFF WALL DESIGN USING PLAXIS

1. DESIGN OF RIGID CUT-OFF WALL USING P LAXIS 2D Presented by MANISH SHARMA M.TECH (Geotechnical Engg ) 2020PGCEGE12 UNDER THE GUIDANCE OF DR. A. K. SINGH HOD, Department of Civil Engineering NIT Jamshedpur, Jharkhand

2. CONTENT Introduction Literature Review Scope and Motivation Objectives Methodology Illustrative Example Model Validation Result and Discussion Conclusions References

3. INTRODUCTION T he hydraulic structures are built on pervious foundations and water flows through the voids present in the soil from high hydraulic head to lower head. This phenomenon of flow of water, movement of water through the soil is called seepage. C ut-off walls are mainly installed in the subsurface to control horizontal movement of groundwater. Based on the requirement of depth, cut-off wall are mainly of two types Fully penetrating cut-off wall Partially penetrating cut-off wall

4. Location of sheet pile cut-off wall At centre At upstream end At downstream end Types of vertical cut-off wall Rigid cut-off wall Flexible cut-off wall Fully penetrating cut-off wall (blocks seepage) Partially penetrating cut-off wall (lengthens seepage path)

5. Rigid Cut-off Wall There are mainly three types of rigid cut-off wall which are as flows: R. C. C Cut-off Wall Sheet Pile Cut-off Wall Geo-membrane Cut-off Wall Sheet pile cut-off wall It has a long history as it is used for many applications. The steel sheet pile cut-off wall is quite popular, as they are easy to install. Thick steel sheet pile cut-off wall are designed for long life. Fig. 3 Sheet Pile Cut-off Wall

6. AUTHOR OBJECTIVE METHODOLOGY OUTCOME Singh et al. (2006) To design a rigid cut-off wall. The seepage force on active and passive thrusts is calculated by considering limiting equilibrium forces acting on a trial failure wedge. There is approximately 10% between the passive thrust for a rigid cut-off wall of normal length computed by Terzaghi’s method. Mansuri et al. (2013) To introduce the effectiveness of using horizontal drain and cutoff wall in reducing seepage flow from an assumed heterogeneous earth dam Numerical simulation were carried out using SEEP/W software. With increase of the cut off depth, the exit hydraulic gradient reduces and with increase of the horizontal drains length, the seepage discharge increases, but it also reduces piping danger. Shayan et al. (2015) To investigate the effectiveness of measures of cut-off wall, drains and blanket for reducing the uplift pressure and exit gradient A laboratory model and GEOSTUDIO software was conducted for investigating the effects of cutoff wall’s angle on the amount of uplift force, seepage, and exit gradient. I t is observed that the best position of cutoff wall to reduce seepage flow is at the downstream end. LITERATURE REVIEW

7. AUTHOR OBJECTIVE METHODOLOGY OUTCOME Koda et al. (2019) To monitor the cut-off wall and dewatering system as an effective method of contaminated sites reclamation process In this paper two case studies were taken and the two groups were set for performing test. The protection from ground water against leachate is achieved by the containment system consisting of cut-off wall and a periphery drainage mainly. Sivakumar et al. (2019) To analysis deformation of suspended type cut-off wall of diversion structures. Two dimensions model is prepared using FEM software for analysing deformation, stability and ground water flow. With the change in location of cut-off wall, the effect on the analyzing parameter were observed. The lowest and second lowest maximum bending moment in cut-off wall is at upstream and downstream end. And the maximum seepage rate has been observed at middle of dam. Salmasi et al. (2019) Effect of Location and Angle of Cutoff Wall on Uplift Pressure in Diversion Dam Finite element method using SEEP/W model a part of Geo-Studio 2007 software was used When the cutoff wall gets close to down stream heel of dam and when the placement angle gets more then there will be decrease in uplift pressure

8. AUTHOR OBJECTIVE METHODOLOGY OUTCOME Sazzad et al. (2019) To monitor the effect of width, length and position of cut-off wall on the seepage characteristics of earth dam The numerical analysis of the models of the earth dam with cut-off wall using SEEP/W. The location of cut-off wall is most important parameter for performing better and effective performance, the effect of width has negligible effect on velocity and seepage discharge on dam. Arnold et al. (2020) To describe the installation of seepage cut-off wall using cut-off wall using Cutter Soil Mixing. BAUER successfully finished task work and install cut-off wall to a depth of 84 feet deep. The CSM method was proven to be successfully adaptable to the challenging existing ground conditions, easy adjustable wall depths and it also included the replacement of unsuitable organic soils. Chai et al. (2020) Plastic-damage analysis of concrete cutoff wall for a concrete face rockfill dam A 3D numerical model that uses a plastic-damage model for the stress–strain relationship of the concrete was developed to predict the behavior of the concrete cutoff wall. The results indicated that the location of the cutoff wall is a deterministic factor affecting the behavior of the wall.

9. AUTHOR OBJECTIVE METHODOLOGY OUTCOME Angelov et al. (2021) To investigate the efficiency of cut-off wall when it is placed at various angle of inclination. The analysis was done by using PLAXIS 2D. The variations of angles was from to 180 progressively in interval of 30 degrees. The minimum seepage discharge is observed at 60 degrees and least value of uplift pressure was observed at 120 degree. Beiranvand et al. (2021) The investigation was done to reduce seepage from foundation and in dam bodies. A comparatively study was observed between instrument and numerical analysis on seepage rate and pore water pressure of Evesham earth dam. A very good and accurate result of observed data and predicted data for pore water pressure. The sudden drop in pore water pressure was observed at downstream end which indicates the correct functioning of cut-off wall.

10. SCOPE AND MOTIVATION We get some ideas about the working of cut-off wall and the effect of angle of inclination of cut-off wall with respect to dam at various location. We have also studied that most effective parameter which is seepage force in the analysis and design of cut-off wall Scope of the proposed study concludes that the analytical study as presented by S ingh et al. (2006) of rigid cut-off wall can be also analysed and designed using PLAXIX 2D and verification of results can be made.

11. OBJECTIVE To perform the design of rigid cut-off wall using PLAXIS and compare with analytical result given by Singh et al. (2006). The depth of sheet pile cut-off wall will be calculated up-to the required effectiveness. The objective is to develop a model and verified the results, ensuring the depth up to which it will be effective. The various soil parameters and their effect on seepage force acting on various penetrated depth of cut-off wall.

12. METHODOLOGY

13. Illustrative Example An illustrative example is considered to compute seepage force and details are as follows: Top width of dam b T = 5 m, base width b = 65 m, depth of rigid cut-off wall = 8 m, cohesion in foundation soil c 1 = 2 kN/m 2 , c 2 = 12 kN/m 2 , angle of internal friction for foundation is , levee soil , specific gravity G = 2.6 and void ratio e = 0.4. The void ratio and specific gravity of levee soil and foundation soil are taken to be the same for simplicity. Solution: The above problem is solved by PLAXIS 2D. The material property has been defined as dry unit weight of soil and levee is 18.21 kN/m 2 , saturated unit weight of soil and levee is 21.02 kN/m 2 . The depth of cut-off wall is considered 12 m for analysis.  

14. Parameters used in Modelling PARAMETERS VALUE Type of material Plate Material type Elastic and Isotropic EA (kN) 15.5 E6 EI (kN-m 2 /m) 4.51 E5 W (Unit Weight) – kN/m 3 10 Poisson’s ratio (υ) PARAMETERS VALUE Type of material SUBSOIL Material model Mohr-Coulomb Material behaviour Drained Unsaturated unit weight (KN/m 3 ) 18.21 Saturated unit weight (KN/m 3 ) 21.02 Void ratio 0.4 E’ 30.00E3 Cohesion(c) 2 Poisson’s ratio (υ) 0.3 Friction Angle (φ) 30 Angle of Dilatancy (ψ) Groundwater parameter Data Set Hypres Model Van Genuchten Permeability in Horizontal direction (m/day), k x 0.01 Permeability in Vertical direction (m/day), k y 0.01 Interface Reduction Factor ( R inter ) 0.5 Table 1 Parameters used in Cut-off wall Table 2 Parameters used in Foundation soil

15. PARAMETERS VALUE Type of material Fill Material model Mohr-Coulomb Material behaviour Drained Unsaturated unit weight (KN/m 3 ) 18.21 Saturated unit weight (KN/m 3 ) 21.02 Void ratio 0.4 E’ 30.00E3 Cohesion(c) 12 Poisson’s ratio (υ) 0.25 Friction Angle (φ) 15 Angle of Dilatancy (ψ) Groundwater parameter Data Set Hypres Model Van Genuchten Type of soil Coarse Permeability in Horizontal direction (m/day), k x 5.0E-6 Permeability in Vertical direction (m/day), k y 5.0E-6 Interface Reduction Factor ( R inter ) 0.5 Table 3 Parameters used in Levee soil Parameters reference Sivakumar et al. (2019)

16. Fig. 4 Mesh view of Model Fig. 5 Dam with Global Water Table 18 m

17. MODEL VALIDATION The results obtained from the numerical analysis validate with analytical solution and results are good agreement with Singh et al. (2006). When dam base width is 65 m and height is 20 m, the validation of results of seepage force are shown in Table 3.   Depth of cut-off wall Result of Seepage Force (kN/m) for unit width of sheet pile cut-off wall Singh, et al. (2006) PLAXIS 2D 2 35.56 40.83 4 101.09 108.20 6 184.49 213.40 8 283.67 310.40 Table 3 Dam with base width 65 m

18. When dam base width is 85 m and height is 20 m, the validation results for seepage force are shown in Table 4. Depth of cut-off wall   Result of Seepage Force (kN/m) for unit width of sheet pile cut-off wall Singh, et al. (2006) PLAXIS 2D 6 161.76 180 8 248.99 267.40 Table 4 Dam with base width 85 m

19. Fig. 6 Seepage Flow through Dam without cut-off wall RESULT AND DISCUSSIONS

20. Fig. 7 Seepage Flow through Dam by installing Cut-off Wall

21. Different Cases Studies Case 1: Both side slopes as 1.5 Fig. 8 Seepage Force Vs Depth of Cut-off Wall (Slope 1.5)

22. Case II: Side slopes of upstream side and downstream side 2.0 Fig. 9 Penetrated depth Vs Seepage force for slope 2.0

23. Case III: Upstream side slope 2.0 and downstream side slope 2.5 Fig. 10 Penetrated Depth Vs Seepage Force for Upstream Slope 2.0 and Downstream Slope 2.5

24. Case IV: Effect of cohesion and angle of internal friction on seepage force Fig.11 Penetrated Depth Vs Seepage Force Varying Cohesion and Angle of Internal Friction

25. Case V: Side slopes of upstream side and downstream side 1.5 and varying downstream water level Depth of cut-off wall (m) Seepage force (kN/m) for unit width of sheet pile cut-off wall at constant upstream water level and varying downstream water level h 2 = 0 m h 2 = 0.5 m h 2 = 1.0 m 2 34.76 32.92 28.80 4 120.9 112.04 106.6 6 210.9 201.61 184.9 8 289.0 272.4 267.78 10 345.6 318.7 294.4 12 320.1 292.6 276.64

26. CONCLUSIONS On the basis of the results and discussion the important conclusions are drawn as follows: Seepage force is decreasing with increase in base width of dam and levee for height and water level constant. Effectiveness of depth of sheet pile cut-off wall can be ensured and it can be designed . After certain depth for given condition, sheet pile cut-off wall is ineffective. It is obvious that seepage force acting on sheet pile cut-off wall increases with increase in upstream water level. If head difference decreases then seepage force acting on cut-ff wall also decreases. Seepage force is decreasing as the cohesion increases and angle of internal friction decreases of foundation soil. Hence, PLAXIS 2D can be conveniently used for computation of seepage force acting on cut – off wall and accordingly, analyse and design the rigid sheet pile cut-off wall can be performed.

27. FUTURE SCOPE OF STUDY On the basis of literature review and analysis through software, the value of seepage force has been calculated and rigid cut-off wall is designed. This study can be used for future study for below cases: An investigation can be done on multi-layered soil, with different soil parameters (c &  ). The effect of Geo- sheet can be used in place of cut-off wall is also a new scope of study.

28. REFERENCE Athani , S. S., Solanki, C. H. and Mohapatra, B. G. (2016), : “Strains induced around cut-off walls of earth dam under full reservoir and drawdown conditions” , International Association of Lowland Technology, 297 – 304. Beiranvand , B. and Komasi , M. (2021), : “An Investigation on performance of the cut off wall and numerical analysis of seepage and pore water pressure of Eyvashan earth dam” , Iranian Journal of Science and Technology, Transactions of Civil Engineering, https://doi.org/10.1007/s40996-021-00613-y Evans, J. and Ruffing, D. (2021), : “ Design and specification considerations for cut-off walls” , DF-I45 conference. Evans, J. C. and Daniel, D. E. (1993), : “ Vertical cut-toff walls”, Geotechnical Practice for Waste Disposal, Chapter 17, 430 – 454, Chapman & Hall, London. https://doi.org/10.1088/1757-899X/471/14/04/2021 Jesmani , M., Mehdipour , I. and Ajami , A. (2011), : "Comparison between 2d and 3d behaviour of sheet piles by finite element method" , Kuwait Journal of Science and Engineering, Volume 38 (2B), 1–14. Koda , E., Miskowska , A., Sieczka , A. and Osinski , P. (2019), : “ Cut-off walls and dewatering system as an effective method of contaminated sites reclamation process ”, Material Science and Engineering, 1 – 8.

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