LABORATORY MODEL TESTS TO EFFECT OF DENSITY TO FILL MATERIAL ON THE PERFORMANCE OF A MODEL REINFORCED SOIL WALL

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 7, Issue 3, May June 216, pp , Article ID: IJCIET_7_3_37 Available online at Journal Impact Factor (216): (Calculated by GISI) ISSN Print: and ISSN Online: IAEME Publication LABORATORY MODEL TESTS TO EFFECT OF DENSITY TO FILL MATERIAL ON THE PERFORMANCE OF A MODEL REINFORCED SOIL WALL Sriharsha. Baditala Assistant Professor, Department of Civil Engineering, Assosa University, Assosa, Ethiopia Yohannes Feyissa Beyisho Dean for engineering and technology faculty, Assosa University, Assosa, Ethiopia ABSTRACT The effective functioning of reinforced earth structures is very much dependent on the quality of materials and construction. Many times, due to poor quality of the materials used and poor quality control measures exercised, the density of the reinforced soil fill is not up to the design requirements, leading to underperformance or distress of the reinforced soil walls. Therefore, it becomes necessary to evaluate the level of underperformance vis-à-vis that of relative compaction. In view of this, in the present study, a series of laboratory experiments were carried out on a model soil wall of 3 mm high with vertical face, prepared at different density states of 95%, 8% and 7% of MDD of IS HCT. The wall was subjected to monotonic load applied through a model square footing of size (B) equal to 5 mm on the surface at an offset distance of 1(B). Similar tests were carried out on the soil wall reinforced with a Woven Geotextile in wrap around form; to study the effect of density on the performance of reinforced soil wall. The results indicated proportionality between relative compaction level and performance of soil wall without and with reinforcement. Key words: Reinforced Earth Structures, Density of Soil Fill, Relative Compaction, Offset Distance Cite this Article: Sriharsha. Baditala and Yohannes Feyissa Beyisho, Laboratory Model Tests To Effect of Density To Fill Material On The Performance of A Model Reinforced Soil Wall. International Journal of Civil Engineering and Technology, 7(3), 216, pp editor@iaeme.com

2 Sriharsha. Baditala and Yohannes Feyissa Beyisho 1. INTRODUCTION Tremendous increase in infrastructure development in India during the past decade has increased the reinforced soil applications manifolds. Apart from design, the effective functioning of these reinforced soil walls (RSW), is also dependent on the quality of materials used and the control on quality exercised during construction. Any slackness on these two issues results in low relative compaction, which in turn results in underperformance or distress of the reinforced soil walls. It is a known fact that, remediation of such walls adds to cost and affect project completion schedules. It is therefore necessary to understand the role of in-situ dry density of the reinforced soil fill on the performance of reinforced soil walls, such that, the performance of the reinforced soil fill can be predicted in advance. Essentially, efforts are made in this study, in this direction Review of Literature Considerable research has been carried out on the behaviour of reinforced soil walls. Juran, I. and Christopher, B., (1988), studied the behavior of soil wall reinforced with different materials viz., woven polyester, geo-textile strips, plastic grids, and nonwoven materials. Ho, S.K., and Kerry Rowe, R., (1996), studied the effect of geometric parameters. Vafaeian, M. and Abbaszadeh, R., (28), have studied model studies on soil wall reinforced with three types of cotton papers. They studied the effect of tensile strength of the reinforcement, the number of layers, the vertical spacing, the offset distance of the load applied on the surface and concluded that, the failure surface was found to be an arc of a circle when stiffer reinforcement is used and that for weaker reinforcement was almost a straight line. They also concluded that, the performance of the RSW was better when tensile strength of the reinforcement was higher and number of reinforcement layers was higher. However, limited studies were carried out on the effect of density on performance of RSW, which has been addressed in the present study. 2. METHODOLOGY The methodology includes collection and characterisation of the materials; performing monotonic load tests; analysis and interpretation of test results and drawing observations and conclusions Characterization of Silty Sand The Silty Sand used in this study (locally called as Morum) is collected from Mahaboob nagar district of Telangana state. The index and engineering properties of soil are summarised in Table 1. Table 1 Properties of Silty Sand Parameter Value Gravel sized particles 16.4 % Sand sized particles 78% Fine grained particles 5.6% Consistency Non plastic MDD (IS HCT) 2.3 g/cc OMC (IS HCT) 9.6 % Classification (IS: ) SP editor@iaeme.com

3 Laboratory Model Tests To Effect of Density To Fill Material On The Performance of A Model Reinforced Soil Wall 2.2. Characteristics of Woven Geotextile The woven geotextile used in this study is shown in Fig. 1 and its characteristics are indicated in Table 2 Figure 1 A view of the woven geotextile Table 2 Characteristics of Woven Geotextile Property Value Type of geosynthetic Polypropylene slit film tape woven geotextile Commercial name SKAPS W-25 Mass per unit area 17 (g/sqm) Thickness.425 (mm) Grab Tensile strength 1.11 (kn) Grab elongation 15 (%) Puncture resistance 4.5 (kn) 2.3. Test set up The experimental test set up is shown in Fig 1. The PC controlled Tri-axial test facility is utilised to conduct the model plate load tests. The application of load is by hydraulic control system and the load is measured by an electronic load cell with a sensitivity of 1 kg. The settlement is measured by electronic Linear Voltage Differential Transducer (LVDT) of ± 5 mm range. The PC controlled facility is run by software that enables to give the operating conditions as input. The facility logs the load and settlement observations continuously and provides online display of the progress of the mechanism. Figure 2 A view of the test set up editor@iaeme.com

4 Bearing Pressure (kpa) Sriharsha. Baditala and Yohannes Feyissa Beyisho 2.4. Model test tank & Model footing A model test tank of size 3mmx75mmx6mm is used. The tests are carried out using model footing of size 5 mm such that the width of the tank 3 mm and depth 3 mm, will be more than or equal to 5B, such that the boundary effects are avoided. The model footings are made of 25mm thick aluminium plates with a rough base Scheme of experiments The investigations are carried out systematically as per the scheme of experiments, which includes determining the resistance to the load applied at an offset distance of 1 (B), on the soil wall prepared at three different relative compactions viz., 7%, 85% and 95% ; without and with woven geotextile in wrap around form. 3. RESULTS 3.1. Pertaining to un-reinforced soil wall The results of monotonic load tests on un-reinforced soil wall represented in terms of bearing pressure versus settlement are presented in Fig. 3 and the typical failure is depicted in Fig % relative compaction 8% relative compaction 95% relative compaction Settlement Figure 3 Variation in Bearing Pressure with Settlement pertaining to Unreinforced Soil Wall Figure 4 A view of failure of Unreinforced Soil Wall at 7% relative compaction, with load applied at an offset distance of 1B editor@iaeme.com

5 Bearing Pressure (kpa) Laboratory Model Tests To Effect of Density To Fill Material On The Performance of A Model Reinforced Soil Wall 3.2. Pertaining to reinforced soil wall The results of similar monotonic load tests carried out on soil wall reinforced with woven geotextile in wrapped around form ; compacted at three specified relative compactions; subjected to the load applied at an offset distance of 1. B ; is presented in Fig. 5 and a typical view of failure is shown in Fig % relative compaction 8% relative compaction 95% relative compaction Settlement (mm) Figure 5 Variation in Bearing Pressure with Settlement pertaining to Reinforced Soil Wall Figure 6 A view of failure of the reinforced soil wall at a relative compaction of 7%, with load applied at an offset distance of 1B 4. OBSERVATIONS 4.1. Pertaining to unreinforced soil wall Based on the analysis of test results pertaining to monotonic load tests on unreinforced soil wall, the following observations are made: 1. As it can be seen from Fig. 3, the nature of bearing pressure versus settlement curve, in general is elasto-plastic. A closer examination reveals the fact that, complete failure without considerable plastic deformation was observed specifically at lower relative compaction of 7%. 2. As depicted in Fig. 4, the mode of failure included separation and collapse of plastic zone formed on the unsupported vertical face. The rupture surface was found to be curvilinear akin to a paraboloid. 3. The variation in resistance against applied loads with variation in relative compaction is presented in Fig. 7. It can be seen that, higher the relative compaction, higher is the editor@iaeme.com

6 Bearing Pressure at failure, kpa Bearing Pressure at failure, kpa Sriharsha. Baditala and Yohannes Feyissa Beyisho resistance offered against the applied load. The relationship is well represented by a second order polynomial or by a power equation y =.4636x x R² = 1 y = 4E-25x R² =.9725 y = 6E-5e.1647x R² =.9569 y = 11.96x R² = Relative Compaction, (%) Figure 7 Variation in Bearing Pressure at failure with Relative Compaction pertaining to Unreinforced Soil Wall 4.2. Pertaining to Reinforced soil wall The observations pertaining to the reinforced soil wall are as presented below: 1. The nature of bearing pressure versus settlement curve, for reinforced soil wall, is also elasto-plastic, as seen in Fig. 5. Interestingly, when reinforced, complete failure was not observed even at lower relative compaction of 7%. 2. As shown in Fig. 6, the reinforced soil wall sustained deformation, but not undergone complete failure, as it happened in unreinforced soil wall. 3. As it can be observed in Fig. 8, resistance to the applied load is increasing with increase in relative compaction. The relationship is well represented by 2 nd order polynomial as well as power equation; similar to that for unreinforced soil wall. 18 y = x x R² = 1 14 y = 4E-12x R² = 1 1 y =.3333e.895x R² = y = 59.29x R² = Relative Compaction, (%) Figure 8 Variation in Bearing Pressure at failure with Relative Compaction pertaining to Reinforced Soil Wall 37 editor@iaeme.com

7 Percentage increase Bearing Pressure at failure, kpa Laboratory Model Tests To Effect of Density To Fill Material On The Performance of A Model Reinforced Soil Wall 4.3. Observations pertaining to general comparison The behaviour of unreinforced and reinforced soil wall is compared one-to-one and the following observations are drawn: 1. It is clearly seen from Fig. 9 that, at any relative compaction, a definite increase in resistance offered against the applied load is seen when the soil wall is reinforced Un-reinforced Soil Wall Reinforced Soil Wall Relative Compaction, (%) Figure 9 Comparison of Bearing Pressure at failure soil wall with and without reinforcement 1. The variation of percentage increase in the resistance with relative compaction, is shown in Fig. 1. As established in earlier research, weaker the soil, higher is the percentage increase when reinforced Relative Compaction (%) Figure 1 Variation of Percentage increase in Bearing Pressure at failure due to reinforcement 5. CONCLUSIONS Based on the experimental investigations carried out in this study, the following important conclusions are drawn: 1. This study clearly established that, higher the dry density of the fill material, higher is the resistance offered against the applied loads. This was observed in both Unreinforced Soil Wall and Reinforced Soil Wall editor@iaeme.com

8 Sriharsha. Baditala and Yohannes Feyissa Beyisho 2. A definite increase in resistance to the applied loads was observed when soil wall is reinforced. For the materials used and for the test conditions adopted in this paper, the increase was in the range 449 % to 3827 %. This emphasizes the importance of reinforcement in soil walls. 3. The mode of failure in Unreinforced Soil Wall was consisting of separation and collapse of a zone of soil near the face of wall. This was contained when reinforced. Hence, this study showed that, collapse of soil wall can be effectively contained when reinforced. 4. On the whole, this study clearly brought out the mechanisms of failure of soil walls when subjected to applied loads without and with reinforcement. This study is useful to the designers and practitioners in prediction of the impact of under compaction on the behavior of reinforced soil wall. REFERENCES [1] Ashmawy, A.K. and Bourdeau, P.L., (1995), Geosynthetic Reinforced Soils under Repeated Loading: A Review and Comparative Design Study, Geosynthetics International, 2(4), pp [2] Lee, K. L., Adams, B. D. and Vagneron, J. M. J, Reinforced Earth Retaining Walls, ASCE, Vol. 99, No. SM1, (1973), pp [3] Juran, I. and Christopher, B., Laboratory Model Study on Geosynthetic Reinforced Soil Retaining Walls, J. of Geotech. and Geoenv. Eng., ASCE, 115(5) 1988, pp [4] Vafaeian, M. and Abbaszadeh, R., Laboratory Model Tests To Study The Behavior of Soil Wall Reinforced by Weak Reinforcing Layers, IJE, 21(4) Dec 28, pp [5] Bathurst, R.J., Nernheim, A., Walters, D.L., Allen, T.M., Burgess, P., and Saunders, D.D, Influence of reinforcement stiffness and compaction on the performance of four geosynthetic-reinforced soil walls, Geosynthetics International, 16(1), pp [6] Ho, S.K., and Kerry Rowe, R., Effect of wall geometry on reinforced soil walls, Geotextiles and Geomembranes, 14(1) Oct-1996, pp [7] Binquet, J., and Lee, L.K., (1975), Bearing Capacity Tests on Reinforced Earth Slabs, Journal of Geotechnical Engineering Division, ASCE, 11(12), pp [8] Sridharan, A., Srinivasamurthy, B R., Bindumakhava., and Vasudevan, A K., Reinforced Soil Foundation on Soft Soil, Geotextile Conference, (1988),pp. C53-6 [9] K.V. Maheshwari, Dr. A.K. Desai and Dr. C.H. Solanki, Bearing Capacity of Fiber Reinforced Soil. International Journal of Civil Engineering and Technology, 4(1), 213, pp [1] Machhindra S.Purkar and Sunil Y. Kute, Numerical Modeling of Reinforced Soil Segmental Wall under Surcharge Loading. International Journal of Civil Engineering and Technology, 4(1), 213, pp editor@iaeme.com