Research Article ANALYSIS & DESIGN OF 44 METER M.S.E. (MECHANICALLY STABILIZED EARTH) WALL BY USING PLAXIS 8.2 1 D. Kishan, 2 Dr. N. Dindorkar, 3 Dr. R. Srivastava, 4* Ankesh Shrivastava Address for Correspondence 1 Asst. Prof, Department of Civil Engineering, MANIT, Bhopal MP INDIA 2 Professor, Department of Civil Engineering, MANIT, Bhopal MP INDIA 3 Director, NIT, Jamshedpur (Jharkhand) 4 Research Scholar, Geotechnical Engineering, Deptt. of civil Engineering, MANIT Bhopal MP INDIA E mail ankesh07vids@gmail.com ABSTRACT Mechanically Stabilized Earth (MSE) Wall has been increasingly used in many Central, state and private projects over the last 20 years. MSE walls are reliable, constructible, and cost effective. However, designing and analysis of MSE all has become a problem for many agencies using them. In this paper a Finite-Element Program PLAXIS is used to analysis and designing of 44 meter 4 tiered MSE wall. Based on the parametric studies it is observed that the top 1 st tiered wall shows the deflection of about 130mm, the total displacement of wall is about 132mm, extreme stresses on to the wall are about 29.69%, and total extreme stresses are about 973. 06 kn/m 2 to the downward direction from the top of the wall. This paper presents the results of investigations to design and analysis of 44 meter MSE wall. 1. INTRODUCTION Soil is an abundant construction material, which has compressive strength and no tensile strength. To overcome this weakness, the soil can be reinforced with materials with high tensile strength. The basic principal of earth reinforcement is the generation of frictional resisting force between the backfill soil and reinforcing element. The reinforcing element can be geosynthetics, metal straps, strips and bars etc. Mechanically stabilized earth (MSE) is a method of reinforcing earthen materials so that they can support their own weight within the minimum space and maximum side slopes. MSE walls are typically constructed using four structural components: 1) geogrid reinforcement 2) wall facing 3) retained backfill and 4) reinforced backfill soil. The facing also plays an important role in the stability of the wall, which includes precast concrete panels, dry cast modular blocks, metal sheet and plates, gabions, welded wire mesh, shotcrete, wood lagging and panels, and wrapped sheet of geosynthetics. 2. PROBLEM STATEMENT The basic need of the infrastructure in civil engineering is continuously increasing to cater the development of nation, and it is necessary that invent new technique to minimize the use of cement concrete in all infrastructural projects and generate a new environmental friendly technique for the construction of various civil engineering structures. Widening of roads in hilly terrains, construction of embankments and foundations on soft soils with minimum utilization of land are the major issues to be addressed during planning and design stages of all major projects. Therefore in the present study the analysis and designing of 44 meters, 4 tiered MSE wall for the widening
of Ghat road has been carried out using finite element program PLAXIS 8.2. 3. OBJECTIVE OF STUDY The main objective of the current study is to determine the alternate method for construction of highway roads in hilly areas. The major tasks performed in this study are as follows 1. To study the fundamental principal and further development of reinforced structures to achive economical designing of the wall. 2. Perform the parametric studies of the various factors that may govern the important parameters of MSE wall like a) The effects of reinforcement. b) The effects of backfill soil. c) The final objective is to compare the total displacement, stresses, strains and axial forces developed in the reinforcing layers as well as in soil. 4. DISCRIPTION OF TIERED WALLS The MSE wall consists of 4 tiered walls each of 11meter height, with effective length of reinforcing layer at 1 st tiered wall from the bottom is of 20meter, 2 nd tiered having 15meter, 3 rd tiered having 12meter and top 4 th having 10 meters respectively. The total numbers of reinforcing layers are 28, in which each tiered wall heaving 7 reinforcing layers of geogrid SR- 2/UX1700. The present study is initially intended to work with concrete modular blocks of size 300mm 300mm in plane with a height of 200mm. uniformly graded sand with different relative density and unit weight was used as backfill and surcharge for each tier. Reinforcing geogrid is used as reinforcing material with minimum vertical spacing is of 80mm and maximum spacing is of 280mm. this spacing is determined by the relevant books and codes. A IRC CLASS-A loading was applied as a moving load on to the wall considering as a worth condition for the movement of the vehicles to the wall. a 300mm 300mm vertical chimney is to be design at the facing side of the wall for the proper drainage of the runoff water. Fig. 4.1 Cross Section-44 m wall
5. FINITE-ELEMENT MODELING The widening of ghat road in hilly areas where other conventional techniques are not applicable accepts the construction of MSE wall has been chosen for this parametric study. This paper based on the construction of the 40 meter soil reinforced wall in Vijayawada (Andhra Pradesh). Fig. 5.1 Finite-Element Modeling of the Soil Wall The reinforced wall is design as per the relevant clauses in BS 8006-1995 and NCMA design manual on design of segmental retaining wall. For the finite element modeling of the wall PLAXIS 8.2 (a finite-element code for rock and soil analysis) has been chosen, and the construction of the wall is carried out safely and economically. The finite element mesh consists of 1276 numbers of 15-node triangular elements to the entire tiered wall and 338 number of 5- node bar element to model the reinforcement (geogrid). The horizontal and vertical boundary conditions are apply for the safe and accurate designing. 6. MATERIAL DATA SHEET There are four major components which constitute a reinforcing soil system. These are the soils, the reinforcement, the draining soil and the facing (skin). In order to design safe and economical reinforced soil structures it is necessary to have detailed characteristics of all four components. The Backfill and Draining Materials High quality backfill material is required for durability, good drainage, and good reinforcement interaction, which can be obtained from well graded granular materials. The back fill soil properties have a great influence on behavior of reinforced soil. The unit weights of materials, in Table 1, provide reasonable values for unit weights of soils in the absence of reliable test results.
Granular Material Gravel Well graded sand and gravel Coarse or medium sand Well graded sand Fine or silty sand Rock fill Table 1- Unit weights of soils γ m : Moist bulk weight (kn/m 3 ) γ sat : Saturated bulk weight (kn/m 3 ) Loose Dense Loose Dense 16.0 18.0 20.0 21.0 19.0 21.0 21.5 23.0 16.5 18.5 20.0 21.5 18.0 21.0 20.5 22.5 17.0 19.0 20.0 21.5 15.0 17.5 19.5 21.0 Table 2- Soil data sets parameters Mohr-Coulomb Backfill soil Draining soil Type Units Undrained Drained γ dry kn/m 3 18 16 γ sat. kn/m 3 20 20 K x m/day 0.00 1.00 K y m/day 0.00 1.00 C ref kn/m 2 10 1 φº 30 30 E ref kn/m 2 6000 1000 ν - 0.3 0.3 Table 3- Modular facing Block Parameter Linear Elastic Modular Block Type Non-Porous γ dry (kn/m 3 ) 24 E ref (kn/m 2 ) 1.05X10 10 Ν 0.15 The facing (skin) element The facing element protects the soil and reinforcing elements from weathering effects and used o keep the backfill soil from flowing. Since the facing is the visible part of the structure, it also controls the aesthetics of the reinforced earth wall. The Reinforcing Element The soil reinforcing element is designed and positioned within the compacted backfill to give
the composite structure tensile strength. The Mesh Data mechanism of soil to reinforcement stress transfer is through the pressure developed due to overburden of the backfill soil on to the The performance of the wall in the software is basically depends upon the mesh data in which the project has been generating. reinforcing elements. Table 4- Geotextile data set Parameter No. Identification EA (kn/m) ν 1 SR-2/UX-1700 64.10 0.00 Table 5- Number, Type of Element, Integrations Type Type of element Type of integration Total no. Soil 15-noded 12-point Gauss 1276 Geogrid 5-node line 4-point Newton-Cotes 338 7. RESULTS Stresses (a) Total Stress=977.77kN/m 2 (b) Cross sectional view Fig. 7.1 Stresses on to the Wall
Fig. 7.2 Depth vs. Stresses The total effective principal stresses are about- shows the total effective stresses on to the wall 973.06 kn/m 2. The stress is increases with the and fig. (b) Shows the cross-sectional view of depth of wall; negative sign shows the the effect of stress on to the MSE wall. downward effect of stresses to the vertical Strain direction. The effective stress on to the top of The maximum strain acting on to the facing of the wall is about-9.39 kn/m 2 and increases with the wall, as the depth is increases the effects of the depth of the wall, and highest stress on to the the strains are also increases up to a certain wall is about-980.66 kn/m 2 located just at the limit. The total strain is of about 29.69%. foundation of facing wall. Above fig. 7.1 (a) (a) Stress-Strain Curve for 1 st Tiered wall (b) Stress-Strain Curve for 2 nd Tiered wall (c) Stress-Strain Curve for 3 rd Tiered wall (d) Stress-Strain Curve for 4 th Tiered wall Fig. 7.3 Stress vs. Strain Curve For Different Tiered wall
Displacement Displacement, in Newtonian mechanics, specifies the change in position of a point in reference to a previous position. In simple terms, it's the difference between the initial position and the final position of an object. Fig. 7.4 presented the load vs. settlement graph for different reinforcing layer, which shows that at a constant loading, as the depth increases the settlement were also increases. Fig. 7.4 Load vs. Displacement Plot for Different Reinforcing Layers (a) (b) (c) (d) Fig. 7.5 Displacement of Facing of Different Tiered Section
Fig. 7.5 (a) shows the displacement plot of 1 st tiered wall, which gives the total displacement of the facing is about 0.18mm, Fig. (b) Shows the displacement plot of 2 nd tiered wall, which gives total displacement, is about 0.15mm, Fig. (c) Shows the displacement plot if 3 rd tiered wall, gives the displacement is about 0.08mm, and Fig. (d) Gives the displacement of top 4 th tiered wall, gives the displacement is about 0.05mm. from the above all the figures state that the maximum displacement of facing is in bottom tiered and top tiered facing represents minimum displacement. 8. CONCLUSION The finite element analysis performed in this study has indicated that geotextile reinforcement may be an effective method of improving the performance of embankments constructed over ghat road. The stabilizing effect of the geotextile was seen to increase as the geotextile modulus increased. The effect was greatest for shallower deposits. The effect of geotextile reinforcement was compared with alternative construction techniques which involved the use of light weight fill or berms alone and in conjunction with geotextile reinforcement. In particular, it was found that the combined use of geotextile reinforcement and light weight fill may be a very effective means of improving the performance of embankments over hilly terrain. 9. REFERENCES 1. AASHTO (American Association of State Highway and Transportation Officials), LRFD (Load and Resistance Factor Design), MSE (Mechanically Stabilized Earth) wall design manual. 2. Abdul aziz A. kamal, pauleen A. lane, and Ali A.R. Heshmati (2005), 13 th ACME conference, Parametric study of reinforced and unreinforced embankment on soft soil. 3. BS 8006-1995 Code of practice for Strengthened/ reinforced soils and other fills. 4. BS 8002-1994 Code of practice for Earth retaining structures. 5. C.Yoo (2002), design of geosynthetics reinforced segmental retaining wall in a tiered arrangement - Use of numerical modeling as a design aid. 6. C.R. Lawson, T.W. Yee & J-C Choi, Segmental block retaining walls with combination geogrid and anchor reinforcements 7. G.L. Sivakumar Babu, professor, department of civil engineering, IIT Bangalore, Use of soil nailing for excavation stability and slope stability improvement analysis of case study. 8. Guangxin Li., yunminchen, Xiaowu tngg Eds.(2008), text book Geosynthetics in Civil and Environmental engineering geosynthetic asia. 9. H.I. Ling, C.P. Cardany, L-X. Sun & H. Hashimoto, Finite Element study of a Geosynthetic-Reinforced soil retaining wall with concrete block facing. 10. Halil Murat Algin professor civil engineering harran university, turkey, settlement analysis of geosynthetic reinforced soil retaining walls at foundation level. 11. IS: 456-2000 code of practice for design of concrete structures. 12. J.Otani, T.Hirai, H.Ochiai, and S.Shinowaki (1998), evaluation of foundation support for geosynthetic reinforced soil wall on sloping ground 13. K. Rajagopal, professor, department of civil engineering, IIT Madras, Design principal of reinforced soil walls 14. NCMA Design Manual for Segmental Retaining Walls, 3rd Edition (2009). 15. PLAXIS 8.2 design manuals a finite element code for rock and soil analysis. 16. P.T. Raju Construction of tiered reinforced soil retaining walls for widening of ghat road to sridurga malleswara swami varla devastanam, Vijayawada. 17. Robert M. Koerner (1990), text book, second edition, designing with geosynthetics. 18. Techfab india industries LTD. (2007), techgrid geogrid reinforced soil walls with welded wire mesh facing to retain the approach to a flyover.