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Gabion Retaining Walls with Alternate Fill Materials

IGC 2009, Guntur, INDIA

GABION RETAINING WALLS WITH ALTERNATE FILL MATERIALS

K.S. Beena Reader, School of Engineering, Cochin University of Science and Technology, Cochin–682022, India. E-mail: [email protected] P.K. Jayasree Lecturer in Civil Engineering, College of Engineering, Trivandrum–695 016, India. E-mail: [email protected]

ABSTRACT: Although have been used from ancient times, it is only in the last few decades that their wide spread use has lead them to become an accepted construction material in Civil Engineering. Gabion retaining walls are mass gravity structure made up of strong mesh containers known as gabion boxes, filled with stone. Considering the cost and scarcity of quarry stones, the replacement of it with some other cheaper material will make the construction more economical. This aspect is studied here. Considering the specific gravity, , cost and availability, quarry and red was selected as the fill material. Model gabion retaining walls were constructed for the purpose in which, different combinations of quarry dust, and coarse were taken as the filling material. Analyzing the lateral deformations of various cases, it can be concluded that a 50%–50% combination of alternative material and aggregate will perform better than the coarse aggregate alone, considering the cost of construction.

1. INTRODUCTION dry stone gravity mass wall made of gabion boxes. They are cost effective, environmental friendly and durable structures. Retaining walls, one of the major geotechnical applications, Because of these reasons gabions are widely used now days are mainly used in the case of highways and railways to all over the world. The gabion walls are used for a variety of support the soil at different levels. In some places they may applications like retaining earth and water, highway even be used to support water, coal, dumped wastes etc. protection, fall protection etc. Based on the stability, the retaining walls are classified into Gravity wall, Mechanically stabilized earth wall and Semi From the economic studies conducted so far [Lee et al. (1973), gravity wall. The gravity relies on its own Collin (2001), Koerner et al. (2001)], it can be seen that the weight for its stability. The mechanically stabilized earth MSE walls with gabion facing and reinforcement wall uses the principle of introducing reinforcements into a is very cost effective. Indian railways in 1999 conducted a granular backfill through mechanical means such as metal cost comparison study between gabion and RCC walls. As strips and rods, geotextile strips and sheets or wire grids. the height of wall increases the expense of gabion wall is Semi gravity retaining walls are those in which the size of the observed to be less when compared to RCC walls. But it is section of a gravity retaining wall is reduced by the introduction quite obvious that the stone filling used in gabions increase of small amount of reinforcement in the back fill. the cost of construction if the quarry stone is not locally Nowadays, a new type of construction named as gabion available. In such circumstances, there arises the need of an retaining wall is gaining momentum as substitute to the alternate material for the filling of gabions boxes. Alternate conventional retaining walls. This work deals with such a material should be such that it is locally available, and, gabion system which resists the lateral pressure by gravity provides the same stabilizing gravity force to the facing as loading as as by the friction and interlocking between provided by the stone fill. Although, soil filled box gabions the reinforcement and the back fill which is commonly are used in practice, they do not offer the same stabilizing referred to as MSE type gabion retaining walls. force as that of stone filled type. In this work, the possibility of replacement of the stone filling with a of stones The cost effectiveness can be further increased if we use and the easily available cheap waste material like quarry dust locally and cheaply available materials as fill material. An and red soil are thought of. The use of quarry dust will also exploration in this direction is also needed. Hence laboratory help to solve many of its disposal problems. investigation on model retaining wall using materials like quarry dust and red soil, which are easily available in the While using the quarry dust and red soil as a fill material, locality at lower cost, is proposed. there is a possibility of the leakage of the material through the voids of the stones and through the mesh of the gabion boxes. Hence the fill material, which is a mixture of stones, 1.1 Scope of the Present Study quarry dust, and red soil, should be contained inside the Gabion retaining wall system is an emerging technique in the gabion boxes with geotextile linings. Thus the facing system of retaining walls construction. It is a flexible type of used here is the same as that of the soil filled type gabion

472 Gabion Retaining Walls with Alternate Fill Materials walls and the gabion system proposed here can be considered boxes. It is used alone and in combination with coarse as a modified form of soil filled gabion walls. For the studies aggregate also. This quarry dust was obtained from a quarry on such a system, a model gabion retaining wall with coarse near Edayar in Ernakulam district of Kerala. Red soil was aggregate, quarry dust and red soil as filling material was also tried as fill material. It is used alone and in combination constructed in laboratory. Loading tests were conducted in with coarse aggregate. Tests were conducted according to IS the gabion system with different percentages of coarse specifications to find out physical properties of sand, quarry aggregate, quarry dust and red soil as filling material. Thus dust and red soil are reported in Table 2. the determination of optimum combination of coarse aggregate and quarry dust, coarse aggregate and red soil Table 2: Physical Properties of Fill Materials filling material, which resists the earth pressure, ensures stability as well as allows sufficient drainage, was the object Property Sand Quarry Red of the study. dust soil Uniformity co-efficient Cu 3.3 10.9 6.9 Co efficient of curvature C 1.05 1.05 1.51 2. EXPERIMENTAL INVESTIGATION c Effective size D10(mm) 0.255 0.034 0.34 The experimental studies were carried out on a model gabion Angle of internal friction φ 38 39 45 wall constructed in the laboratory Specific gravity G 2.529 2.639 2.71 of School of Engineering, CUSAT. In this project, the physical properties of the material used for the construction, like sand (backfill), coarse aggregate, quarry dust, red soil, 2.1.3 Steel Wire Mesh and steel mesh were obtained and the behavior of a model In field, actual gabion boxes are made with double twist or gabion retaining wall is studied. A parametric study was also tripple twist hexagonal wire mesh. For the model gabion box, conducted with different material combination to study the steel mesh with square opening of was used. The wire advantages of locally available materials. diameter of mesh was 1.17 mm and size of square mesh are 12 mm × 12 mm. Tensile strength of mesh was obtained by 2.1 Materials Used conducting tension test on steel mesh using universal testing The materials used for the construction of model gabion machine and found to be 22.4 kN/m, with a breaking load of walls were coarse aggregate, sand, quarry dust, red soil, steel 1.75 kN. mesh and accessories. The details of the physical properties of materials are discussed below. 2.1.4 Geotextile Thermally bonded non woven type geotextile was used on 2.1.1 Coarse Aggregate the back face of the wall to prevent the entry of back fill sand The stone filling of size 20 cm–30 cm in an actual field into the boxes as well as on all faces of each box to prevent gabion wall was replaced with coarse aggregate having size the escape of quarry dust and red soil through the mesh 20 mm–40 mm in the model studies to conform to the opening of the boxes. Terram 1000 obtained from proportion of the size of the mesh opening in the prototype Meccaferri. Pvt. Ltd. was used in this study. The properties and the model. Coarse aggregate for this purpose was of geotextile provided by the suppliers are: Tensile strength = collected from a quarry near Kothamangalam in Ernakulam 8 kgN/m, Elongation = 28%, Pore Size = 150 μm, Mass per district of Kerala. The properties of coarse aggregate were Unit Area = 1.25 N/m2, Permeability = 100mm/s found out using different test in the laboratory according to IS specifications and are shown in Table 1. 2.2 Construction of Model Gabion Wall Table 1: Physical Properties of Coarse Aggregate The model gabion wall was constructed in a test tank of size 1 m × 1 m × 1 m. The height of the wall was 0.6 m. Sixteen Uniformity coefficient C 1.577 u number of gabion boxes each of 0.25 m long, 0.15 m wide Coefficient curvature Cc 1.284 and 0.15 m high were used to retain the back fill. The boxes Effective size D10 13 mm were fabricated by stitching steel mesh panels to get the Fineness modulus 4.25 required shape of the gabion box. Four such boxes were Flakiness index 18.185 stitched one beside the other to form a layer such that they Elongation index 19.546 behave as a single unit. The boxes were filled with filling 3 Crushing value 22% material at an average of 16 kN/m . After filling the Specific gravity G 2.852 boxes, top cover was closed and tightly connected to the sides of the gabion boxes using the steel wires. Geotextile was placed behind the boxes in each layer, in order to avoid 2.1.2 Fill Materials the entry of granular back fill into the boxes. Then sand was used as the backfill for model gabion wall. backfilling was done up to the height of the boxes. The Quarry dust was used as fill material in the model gabion backfill sand was compacted in each layer to get an average

473 Gabion Retaining Walls with Alternate Fill Materials density of 16 kN/m3. Each layer of the fill was compacted to The gabion boxes were filled with the fill material at an get the same density by controlling the weight of soil and average of density 16 kN/m3. For all the cases, the gabion thickness of layer. After leveling the backfill, the next layer boxes were given a lining of geotextile (Terram 1000) to of gabion boxes was placed above the first layer and they prevent the escape of the fine materials through the steel were stitched with steel wires and the procedure was mesh openings. For case 2, lower half of each box was filled continued up to the required level. Four layers of boxes each with quarry dust and upper half with coarse aggregate. For of height 0.15 m were placed one above the other to complete case 4 and 5, a core was made to fill the quarry dust and red the construction. The layers were also interconnected using soil in it and the coarse aggregate was filled on the two sides steel wires such that the entire wall behaves as a single block. of the core. The study was conducted to check the stability of Markings with small metal strips were made on the front face gabion walls with quarry dust and red soil as an alternative to of the selected boxes at the center for taking deformation quarry stones inside the gabion boxes so as to reduce the cost measurements with dial gauges. of construction of gabion walls using locally available material. After the construction of the wall using gabion boxes, loading is done using hydraulic jack and lever arrangement. The loading pattern used is of two-point loading action on a 3. RESULTS AND DISCUSSION 25 mm thick and 0.2 m wide strip placed over the sand Load tests were conducted on the model retaining wall in backfill parallel to the gabion wall. Each time the load was order to obtain the lateral deformations and bulging applied by pumping oil into the piston with the help of characteristics of the model gabion wall for different fill levers. Load is applied in increments of 3 kN. After applying combinations. each increment, the load was kept constant the deformations stabilized. Prior to next increment, lateral deformations were measured using dial gauges. The 3.1 Load Deformation Studies photograph of the loading setup used in the experiment is The model gabion retaining wall was constructed and loading shown in Figure 1. was done using hydraulic jack and lever arrangement. Each time the load was applied by pumping oil into the piston with the help of levers. After applying each increment, the load was kept constant till the deformations stabilized. Lateral deformations were measured at different points using dial gauges.

3.1.1 Lateral Deformation The variation of the lateral deformation against the load applied shown by dial gauges fixed at the top layers is shown in Figure 2. From the figure it can be seen that as the load applied increases, lateral deformation also increases. The lateral deformation seems to be less for the combination 50% red soil and 50% coarse aggregate. The coarse aggregate alone showed more lateral deformation may be because of Fig. 1: Experimental Test Set Up the large voids present in the boxes. From the conducted tests, when compared with 100% coarse aggregate, for a lateral deformation of 5 mm, it is seen that the load carrying 2.3 Parametric Study capacity increases by 31.32% (average) for 50%–50% The experimental studies were conducted on model wall combinations of red soil and coarse aggregate (as core), using five different filling materials inside the gabion boxes. 16.55% (average) for 50%–50% combination of quarry dust The combinations were varied by percentage volume of the and coarse aggregate (as core) and 18.5% (average) for 50%– 50% combination of quarry dust and coarse aggregate (as gabion box because in the actual field practice this is the layer). usual filling pattern. The six different cases adopted for the study were When comparing 50%–50% combination of quarry dust and red soil along with coarse aggregate (as core), the load 1. Coarse aggregate alone carrying capacity for 50%–50% combination of red soil and 2. 50% coarse aggregate and 50% quarry dust (as layer) coarse aggregate increases with 13.12% (average) for a 3. Quarry dust alone lateral deformation of 5 mm. While comparing 50%–50% 4. 50% coarse aggregate and 50% quarry dust (as core) combination of quarry dust and coarse aggregate (as core and 5. 50% coarse aggregate and 50% red soil as core) as layer), there is not much variation for the loading capacity 6. Red soil alone for the lateral deformation of 5 mm.

474 Gabion Retaining Walls with Alternate Fill Materials

Load (kN) When comparing, it has been noted that 50%–50% 0 1020304050 combination of red soil and quarry dust along with coarse 0 aggregate (as core), the lateral deformation at the top of the retaining wall, is reduced by 11.84% for 50%–50% 2 combination of coarse aggregate and red soil (as core). Similarly, it is seen that the 50%–50% combination of quarry 4 dust and coarse aggregate (as core and as layer), the lateral deformation at the top of the retaining wall is reduced by 0.92% for 50%–50% combination of quarry dust and coarse 6 aggregate (as core). From the test result, it is observed that, there is not much variation for bulging pattern of 50–50 8 combination of coarse aggregate and quarry dust (as core and as layer). 10 Lateral Deformation(mm) 4. SUMMARY AND CONCLUSION 12 Gabion retaining walls with base extensions are very good alternative to expensive RCC walls. They incorporate basic 14 50-50QD+CA (as layer) principles of gravity retaining walls and mechanically 100%QD reinforced earth walls. The economic studies conducted by 16 100%CA Indian railways gives a good comparison between gabion 100%Red soil 50-50 Red soil+CA(as core) and RCC walls, as the height of wall increases the expense 50-50QD+CA(as core) of the gabion wall is observed to be less when compared to Fig. 2: Load Vs. Lateral Deformations RCC walls. The percentage cost savings by gabion is of the order ranging from 30% to 60%, since less time is required for the construction. In the construction of RCC walls, as the 3.1.2 Bulging Patterns work involves cost of , sand, aggregate, shuttering Studying the bulging pattern it was observed that, the first etc. it becomes more expensive. layer from the top experienced the maximum bulging than In order to reduce the cost of construction further, and to the lower layers at failure. As the percentage of quarry dust reduce the use of rubbles in gabion boxes, alternative and red soil increases the bulging is observed to increase. materials are proposed as filling. Here laboratory The bulging is found minimum for coarse aggregate. Figure investigations are conducted on model gabion walls using 3 shows the bulging patterns of different gabions in a single locally available and cheap materials like quarry dust and red figure for a particular load 24 kN which corresponds to soil. The materials were tried in layers as well as in core. minimum load at failure. The minimum bulging is observed From the result of different test and analysing the lateral for the 50%–50% combination of coarse aggregate and red deformation, it can be concluded that a 50%–50% soil (as core). Comparing the lateral deformation at the top of combination of alternative material and aggregate will the retaining wall, for 100% of coarse aggregate and 50%– perform even better than the course aggregate alone, where 50% combination of red soil and coarse aggregate (as core), as the cost of construction can be drastically reduced. the lateral deformation is reduced by 30.11% for 50–50 combination of red soil and coarse aggregate (as core). ACKNWOLEDGEMENT 50% QD + 50% The authors express their gratitude to Kerala State Council 60 CA ( as layer ) for Science and Technology for their financial assistance for 50 100% QD the study. 40 100% Red soil REFERENCES 30 Collin, J.G. (2001). “Lessons Learned from a Segmental 20 50% Red soil + Retaining Wall Failure”, and , 50% CA ( as Wall HeightWall ) ( cm 19, 445–454. 10 core ) 100% CA Koerner, R.M. and Soong, T.Y. (2001). “Geosynthetic 0 Reinforced Segmental Retaining Walls”, Geotextiles and Geomembranes, 19, 359–386. 024650% QD +50% CA ( as layer ) Lee, K.L., Adams, B.D. and Vagneron, J.M.J. (1973). Wall Deformation ( mm ) “Reinforced earth retaining walls”, ASCE Journal of and Engineering Division, Vol. Fig. 3: Bulging Patterns at 24kN Load 99, No. SM10, October 1973, pp. 745–764.

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