Shear Strength Behavior of Sandy Soil Blended With Coarse Aggregate

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1 Shear Strength Behavior of Sandy Soil Blended With Coarse Aggregate Kesharwani R.S. Research Scholar, Department of Civil Engineering, Jamia Milia Islamia, New Delhi, India. Sahu. A.K. Faculty of Civil Engineering, Delhi Technological University, Delhi, India. Khan. N.U. Faculty of Civil Engineering, Delhi Technological University, Delhi, India. ABSTRACT In Major parts of India and other part in world, alluvial deposits consists of a matrix like soil with inclusions of coarser aggregates of various sizes. Past experience shows that shear tests have been successfully carried out on sample size to maximum particle size ratio of 10. Large sizes granular particles poses the problem of applying the normal pressure. Keeping the above considerations in view, the large size shear box apparatus having box sizes of 30 cm x 30 cm was considered adequate and hence used in the present investigation. The direct shear tests has been carried out on the sand blended with coarse aggregate of various sizes and proportions. To strengthen the sub soil strata, coarse aggregates of 10mm and 20mm sizes were mixed in the sand in various proportions. The soil samples were prepared and tested first without mixing coarse aggregates, then by mixing coarse aggregates in varying percentages by weight starting from 5% to 30%. The Normal pressure of 50,100,150,200,250 & 300 KN/m2 were applied on the sample and shear stress has been recorded for each normal pressure till the failure of the sample. It has been established that the shear strength of soil-aggregate mixture is far greater than the shear strength of soil alone. The bearing capacity of composite soil mass is analyzed based on Terzaghi analysis as per IS The Bearing capacity so obtained is increased by % to % for aggregate mixes of 5 % to 30% of 10 mm size, where as it increases from % to % for aggregate mixes of 5 % to 30% of 20 mm size, KEYWORDS: Soil, Coarse aggregate, Direct shear test, INTRODUCTION The several parts of India such as Punjab, Uttar Pradesh, Bihar and West Bengal have extensive alluvial soil formed by the Indus, Ganges and Brahmaputra rivers, wherever stream meanders alluvial deposits are left behind. An alluvial deposit may generally contain pebbles or boulders. Fine rounded pebbles of varrying sizes can be observed in the old beds of river in Haridwar to Dehradun region of the river Gangas. The Homogeneous stratum in the sub soil system may not pose any difficulty in respect of foundation but regions where the stratum consists of soil-pebble composite, the

2 Vol. 21 [2016], Bund construction of foundations really involves complex problems. For such soils, we should have some means and methods to provide safe and economical foundations hence testing of soil-pebble composite in respect of shearing resistance of the composite mass is essential. An investigation has, therefore, been made in this direction by using the aggregate of different sizes and different proportions. Bearing capacity is a parameter that is evaluated by conducting shear strength test for determining the suitability of any soil type for the use as bearing material. It is evaluated on the basis of types of structure for which either spread, isolated, or raft footing is proposed. The soil should have a bearing capacity greater than the load of the structure to which it is subjected, so that the soil should not fail in shear and the settlement should remain within the safe limits. The dimensions of the proposed footing also depend upon the bearing capacity of the soil. It will be large in cases the soils have low value bearing capacity. The size of footing reduces considerably if the soils have a high value of bearing capacity. To enhance the strength of foundation soil, several techniques like compaction, mechanical/electrical/thermal stabilization, addition of geotextile, geosynthetic, fly ash or randomly distributed discrete fibers are used. In the present study, the variation in the bearing capacity of soil is carried out due to the addition of coarse aggregates. The coarse aggregates are the rock fragments usually restricted to round or sub rounded particles The main aim of the present study is to enhance the strength/bearing capacity of the soil upon which different types of structures rest with the addition of 10mm and 20mm sized coarse aggregates. If the bearing capacity of the foundation soil is comparatively lower, then a massive foundation is required to be provided for the stability of the structures constructed over it which proves to be uneconomical. The review of literature was carried out for the improvement to the sub soil system by various technique. Gopal Ranjan, shamsher Prakash and O.S. Srivastava 1. have carried out large scale in-situ shear tests at different locations on 150 cm x 150 cm size shear box or 70.6 cm x 70.6 cm size shear box depending upon the maximum particle size present in the sample. A ratio of 5 to 6 between the side of the square box and the maximum particle size is usually recommended. To have minimum disturbance, the sample has been slightly trimmed from bigger size blocks left undisturbed after excavation. The shear force is then applied from the adjoining box. The shear and normal displacement were recorded through suitably mounted dial gauges. Tests at different normal loads are carried out to draw Mohr s envelope and obtain the shear parameters. Som and Sahu [2] evaluated the effect of deformation on the improvement of reinforced soil bed using nonwoven and woven type of geo-textile at the compacted fill, artificially consolidated keolinite bed interface and concluded that there is practically no improvement in load carrying capacity with the inclusion of geo-textile till 10mm settlement beyond which the rate of deformation for unreinforced bed is much higher than the reinforced one. To improve the strength of low shear strength and highly compressible kaolin soil, Chakrabarti et al [3] added jute textile. The biodegraded jute was cut into pieces having thickness 1.25mm and was placed over the soft bed of kaolin soil consolidated to 1KN/m3. The results showed that the load carrying capacity of kaolin bed with biodegraded jute textile improved by 25% thereby causing considerable reduction in the pavement thickness. To improve the strength of the silty soil, Shukla, S. K. [4] used bamboo sheets. Unconfined compression tests were carried out on unreinforced and reinforced soil samples prepared at maximum

3 Vol. 21 [2016], Bund dry density corresponding to optimum moisture content. Based upon the data obtained it was concluded that the strength of the soil sample increases with the increase in the number of reinforcing bamboo sheets when placed in horizontal position while it decreases even less than the unreinforced case if the reinforcing bamboo sheets were placed in inclined position, 30 o to 45 o to the horizontal. Nakao and Fityus [5]have performed direct shear test on marginal material using large shear box. The test result shows that the peak & residual effective frictional angles increasing with the particle sizes. Wang et al [6]studied the effects of particle size distribution on the shear strength of accumulation soil. The test result revealed that the angle of shearing resistance increased with the increase in particle size. X.Yu et al [7] performed dierct shear test on rockfill material and observed that the shear strength of granular material depends upon particle shape, size, gradation, relative density and particle strength. Simoni and Houlsby,[8] performed direct shear test and observed that the effect of dilatancy of sand gravel mixture. Farsakh et al [9]studied the effect of moisture content & dry density on cohesive soil using large scale direct shear test. The soil & geosynthetic interaction behavior was also observed. Sridharan et al [10]carried out shear strength studies on soil quarry mixtures. The result shows that the stone dust can be a promising substitute for sand to improve the engineering properties of the soil. A review of the literature reveals that most of the work has been done using either fly ash/geotextile/lime or rice husk ash as a reinforcing material to enhance the strength/bearing capacity of the soil and very few or none studies have been carried out using coarse aggregates as a reinforcing material in the soil to enhance its properties. Hence study is needed to evaluate this aspect too, since in areas where coarse aggregates are available in abundance and procuring of other reinforcing materials proves to be uneconomical, adding coarse aggregate will be a suitable option. Therefore, it is needed to study the effects of coarse aggregates on the strength of soil. Sandy soil: MATERIALS & METHODOLOGY USED The sandy soil used in the study is procured from river basin transported by Stream etc. The different geotechnical properties of soil are summarized in Table-1 and the particle size distribution curve is shown in figure Coarse aggregates: The coarse aggregates obtained in this study are the coarse aggregates used for making plain cement concrete. The different physical properties of the coarse aggregates used are given in table-2. Table 1: Geotechnical Properties of Soil. PARTICULARS VALUES Natural Moisture Content 4.26% Bulk Density KN/m3 Specific Gravity 2.65

4 Vol. 21 [2016], Bund Uniformity Coefficient (Cu) 2 Coefficient of Curvature (Cc) 1.14 Maximum Dry Density (MDD) 17.7 KN/m3 Optimum Moisture Content (OMC) 9.41% Cohesion 0 Angle of internal friction 32o Classification of soil SP Figure 1: Particle Size Distribution Curve. Table 2: Physical Properties of Coarse aggregates. PARTICULARS VALUES Aggregate Crushing Value (ACV) 11.21% Aggregate Impact Value (AIV) 9.86% Specific Gravity (G) 2.64 Water Absorption 2.36 % Fineness Modulus 7.36 Water The Direct Shear tests in the study have been carried out in the laboratory. Therefore, water used for mixing during the preparation of the samples is taken as available in the laboratory which is an ordinary tap water. The various physical properties of water used are given in table-3.

5 Vol. 21 [2016], Bund Table 3: Physical and Chemical Properties of Water. PARTICULARS VALUES ph value 6.87 Dissolved Solids mg/l Suspended Solids mg/l Sulphates mg/l Chlorides mg/l Turbidity * 3.50 NTU Alkalinity mg/l Hardness mg/l EXPERIMENTAL INVESTIGATION Introduction The bulk quantity of sand and aggregates of 20 mm & 10 mm nominal sizes are procured in the laboratory and stored properly. The collected sample of sand and coarse aggregate were characterized in the laboratory. The tests were carried out to determine the physical and chemical properties of the material. The proctor compaction test were performed on the sand to determine the optimum moisture content and maximum dry density of the sand.the coarse aggregate of the 20 mm & 10 mm sizes in various proportion (5% to 30% by weight) is mixed with the sand and the shear tests were performed under optimum moisture condition. Details of Test conducted The details of experimental programs are summarized in Table-4. The tests were performed conforming to Indian standard specifications listed in the reference. Table 4: Experimental Program me MATERIAL DETAILS OF THE EXPERIMENTS Sandy Soil Natural Moisture Contents,.Bulk Density, Specific Gravity, Grain size distribution, Compaction Characteristics Aggregates Aggregate Crushing Value, Aggregate Impact Values, Specific Gravity, Water absorption, Fineness Modulus Water ph, Dissolved Solids, Suspended Solids, Sulphates, Chloride, Turbidity, Alkalinity, Hardness Sand mix with Direct Shear test on Large sized shear box aggregates apparatus

6 Vol. 21 [2016], Bund Direct Shear Test In order to evaluate the shear strength behavior, large sized shear box apparatus as per IS 2720(Part 39/Sec-1)-1977 has been used. Figure 2: Experimental Setup for Direct Shear test Source: IS2720(Part39/Sec-1)-1977 Laboratory Determination of shear strength of soil containing Gravel The unblended sand at optimum moisture content was filled in the box in three layers and compacted to the required density after fixing the two halves of the box. By means of the yoke system and a normal force of 0.5 Kg/cm 2 was applied to the upper half of the box. The incremental horizontal shear force was applied to the upper half of the box, thus causing the sample to shear along the dividing plane of the box. In this test, failure is caused in the soil in a predetermined plane and the shear strength and normal stress are both measured directly. After this the box was emptied. Other samples of the soil was then filled successively in the box in three layers and compacted to the required degree. Constant vertical force of 1.0,1.5,2.0,2.5 and 3.0 Kg/cm 2 were applied to the upper half of the box and increasing horizontal force were applied as before causing the sample to shear along the determined plane. The Normal and constant vertical forces were recorded for unblended sand. The rate of strain was maintained as 0.2 mm per minute. With six sets of normal stresses σ and shear stress τ, obtained above, a relation was plotted taking σ on abscissa and τ on ordinate. The plot was a straight line, the value of C and Ø were obtained as C=0.0 Kg/Cm 2 and Ø= The similar tests has been carried out on the sand mixed with varying percentage of 5% to 30% and the vertical normal load and shearing force were recorded for each case. RESULTS AND DISCUSSION Geotechnical Properties of Soil: The particle size distribution curve obtained by plotting the result of sieve analysis indicates that the soil contains nearly 96.40% particles passing through 4.75 mm IS sieve and larger than 75 micron IS sieve. This shows that the soil falls in the category of sands. Since the uniformity coefficient is 2.1

7 Vol. 21 [2016], Bund and the coefficient of curvature is 1.18, therefore the soil is designated as SP, the poorly graded sand. The tests performed to determine the Atterberg s limits also indicate the non plastic behavior of the soil since it has no plasticity index. The moisture content-dry density curve revealed that due to addition of water, the dry density increases uniformly to a maximum value of KN/m 3 at 9.41% moisture content thereafter the curve shows a declining behavior. On the basis of the results obtained from direct shear test, the angle of internal friction is 36.4 o which shows that there is better mobilization of shear strength through interlocking of soil particles and the soil will fail by local shear failure. Since the value of cohesion is zero, the shear strength in the soil will result from the inter granular friction alone. The geotechnical properties of the soil under investigation are presented in table Physical Properties of Coarse aggregates: The results of sieve analysis of coarse aggregates indicate that about 95% of coarse aggregates passes through 20mm IS sieve and the fineness modulus of these is Therefore, average particle size of the coarse aggregates is 10 mm. Aggregates having impact value 9.86% and crushing value as % shows that the coarse aggregates collected can withstand relatively larger heavy loads. The physical properties of coarse aggregates are shown in Table Physical & Chemical Properties of Water:- The ph value of the water obtained is 7.24 which is greater than 7, therefore, it is alkaline. The presence of sulphate in water affects the durability and strength of mix and chlorides produces efflorescence. The tests on water indicate that the sulphate content in water is 86 mg per liter and chlorides mg per liter, which is in acceptable limits. Table 3 shows the properties of water being used in the study. These properties of water show that the water is potable and is fit for drinking purposes and hence can be used for the present experimentation Direct Shear Test Results: The direct shear tests have been carried out on the soil samples, at OMC, first without adding coarse aggregates in it and then by adding coarse aggregates in varying percentages ranging from 0% to 30% by Weight of the dry soil at a constant optimum moisture content of 9.41%. The constant normal load and shearing force were applied for unblended sand as well as on blended sand and the C & Ø parameter were obtained for various percentage of coarse aggregate. The results obtained are presented in graphical form.

8 Vol. 21 [2016], Bund Figure 3: Shear stress vs Normal stress curve for plain Sand. Figure 4: Shear stress vs Normal stress curve for Sand mixed with 10 mm dia 5% coarse Aggregate

9 Vol. 21 [2016], Bund Figure 5: Shear stress vs normal stress curve for Sand mixed with 10 mm dia 10% coarse Aggregate Figure 6: Shear stress vs normal stress curve for Sand mixed with 10 mm dia 15% coarse Aggregate.

10 Vol. 21 [2016], Bund Figure 7: Shear stress vs Normal stress curve for Sand mixed with 10 mm dia 20% coarse Aggregate Figure 8: Shear stress vs Normal stress curve for Sand mixed with 10 mm dia 25% coarse Aggregate

11 Vol. 21 [2016], Bund Figure 9: Shear stress vs Normal stress curve for Sand mixed with 10 mm dia 30% coarse Aggregate. Figure 10: Shear stress vs Normal stress curve for Sand mixed with 20 mm dia 5% coarse Aggregate.

12 Vol. 21 [2016], Bund Figure 11: Shear stress vs Normal stress curve for Sand mixed with 20 mm dia 10% coarse Aggregate. Figure 12: Shear stress vs Normal stress curve for Sand mixed with 20 mm dia 15% coarse Aggregate.

13 Vol. 21 [2016], Bund Figure 13: Shear stress vs Normal stress curve for Sand mixed with 20 mm dia 20% coarse Aggregate. Figure 14: Shear stress vs Normal stress curve for Sand mixed with 20 mm dia 25% coarse Aggregate.

14 Vol. 21 [2016], Bund Figure 15: Shear stress vs Normal stress curve for Sand mixed with 20 mm dia 30% coarse Aggregate. Pressure Settlement Behavior 78 Nos of tests were conducted on varying sand aggregate mixes with various normal loads. The stresses at failure has been recorded and plotted as given in Fig-3 to Fig-15. From the shear stress and normal stress curves, it is observed that the curves for the soil bed with coarse aggregates follow the same pattern as that of the soil bed without coarse aggregates and there is enhancement in the shear strength parameter with the inclusion of the coarse aggregates in to the soil bed. From the Fig-3 to Fig-15, it can be seen that the angle of internal friction increase with the increase in the fraction of Aggregate. That means the denser is the soil aggregate mixture, the greater is the values of angle of internal friction. The value of Ø is however, affected by initial denseness. With the increase in the Aggregates percentage, there is marked increase in the angle of friction of the composite mass of sand. The increase in the Ø values varies from to for 10 mm dia coarse aggregate mixes of 0% to 30%. The Ø values enhances from to for 20 mm dia coarse aggregate mixes of 0% to30%. Bearing Capacity of Modeled Footing:- The results obtained from the direct shear test for 10 mm & 20 mm coarse aggregate mixes has been applied for safe/ultimate bearing capacity as per clauses5.1 & of IS 6403:1981 for constant sizes of strip footing of 3.0 m at a depth of 1.5 m. The bearing capacity so obtained shows considerable improvement as given in Fig-16 & Fig-17.

15 Vol. 21 [2016], Bund Figure 16: Variation of Safe bearing capacity of sand blended with 10 mm & 20 mm sizes Coarse aggregate for varying Percentage from 5% to 30%. Figure 17: Percentage increase in Safe bearing capacity of sand blended with 10 mm & 20 mm sizes Coarse aggregate for varying Percentage from 5% to 30%.

16 Vol. 21 [2016], Bund CONCLUSIONS The aim of the experimentation performed in the ongoing study was to enhance the bearing capacity of the foundation soil by mixing coarse aggregates in varying percentages. With the further increase of coarse aggregate percentage, the problem of workability was experienced during the experimentation because the coarse aggregates replaces the soil mass with their increase in volume. However following specific conclusions are made from this study: For plain soil the shear parameters obtained are Ø=36.4 o. The Y axis intercepts has been ignored because of nature of sample taken for investigation (i.e. non plastic sandy material). The Ø values varies from o to for aggregate mix of 5% to 30% for 10 mm size aggregate where as it varies from to for 20 mm size aggregate. The shear strength of soil depends both on inter particle forces and friction between the particles. The shear strength increase with the increase in percentage and the size of Aggregate. It has been established that the shear strength of soil-aggregate mixture is far greater than the shear strength of soil alone. The bearing capacity of composite soil mass is analyzed based on Terzaghi analysis as per IS The ultimate bearing capacity has been worked out for a 3.0 m sized strip foundation at a depth of 1.5 m below NGL. The bearing capacity of sand bed alone along with blended material is compared in Fig 16 & 17. The Bearing capacity so obtained is increased by % to % for aggregate mixes of 5 % to 30% of 10 mm size, where as it increases from % to % for aggregate mixes of 5 % to 30% of 20 mm size. REFERENCES 1. Gopal Ranjan, Shamsher Prakash and O.S. Srivastava Geotechnical investigation programmes for cement fectories-1. October 1977, Volume 51, Number 10, The Indian Concrete Journal pp Som, N., Sahu, R. B., (1997), Deformation Behavior of Geo-textile Reinforced Unpaved Road Journal of Indian Geotechnical Conference, Vol. 5 (10), pp Chakrabarti, S., Bhansari, G., Datta, A. (2002) Biodegradation Effects of Jute Geotextile as Soil Reinforcement for Improvement of Load-Settlement Characteristics Proceedings of the Indian Geotechnical Conference, Allahabad,pp Shukla, S. K. (2002) Strength of the Bamboo-Reinforcement Itanagar Silty Sand Proceedings of the Indian Geotechnical Conference, Allahabad, pp T. Nakao, and S. Fityus, "Direct shear testing of a marginal material using a large shear box," Geotechnical Testing Journal, vol. 31, no. 5,pp , J J. Wang, H. Zhang, S. Tang, and Y. Liang, "Effects of particle size distribution on shear strength of accumulation soil, J. Geotechnical and Geoenviron. Eng., vol. 139, no. 11, pp , 2013.

17 Vol. 21 [2016], Bund X. Yu, S. Ji, and K. D. Janoyan, "Direct shear testing of rockfill material," in Soil and Rock Behavior and Modeling, Geotechnical Special Publication, American Society of Civil Engineers, 2006, pp , A. Simoni, and G. T. Houlsby, "The direct shear strength and dilatancy of sand-gravel mixtures," Geotechnical and Geological Engineering, vol. 24, no. 3, pp , Farsakh, M. A., Coronel, J. and Tao, M. (2007). Effect of soil moisture content and dry density on cohesive soil-geosynthetic interactions using large direct shear tests, Journal of Materials in Civil Engineering, ASCE, 19, Sridharan, A., Soosan, T. G., Jose, B. T. and Abraham, B. M. (2006). Shear strength studies on soil-quarry dust mixtures, Journal of Geotechnical and Geological Engineering, 24, Sadanand Ojha and Ashutosh Trivedi.: Shear Strength Parameters for Silty Sand Using Relative Compaction Electronic Journal of Geotechnical Engineering, 2016 (21.09) pp Available at ejge.com. 2. Karimpour Fard, M., Jamshidi Chenari, R., Soheili, F: Shear Strength Characteristics of Sand Mixed with Eps Beads Using Large Direct Shear Apparatus Electronic Journal of Geotechnical Engineering, 2015 (20.08) pp Available at ejge.com. 3. Sadanand Ojha and Ashutosh Trivedi: Comparison of Shear Strength of Silty Sand from Ottawa and Yamuna River Basin using Relative Compaction Electronic Journal of Geotechnical Engineering, 2013 (18.J) pp Available at ejge.com. BIBLIOGRAPHY 1. IS: 2720 (Part 2), "Determination of water content," IS: 2720 (Part III/ Sec 1), "Reaffirmed 2002, methods of test for soils: Part-3, determination of specific gravity, fine grained soils, Bureau of Indian Standards," IS: 2720(Part 4), "Reaffirmed 2006, methods of test for soils: Part-2, determination of grain size analysis, Bureau of Indian Standards," IS: 2720 (Part VII), "Reaffirmed 2003, methods of test for soils: Part-7, determination of water content dry density relation using light compaction, Bureau of Indian Standards," IS: 2720 (Part 13), "Direct shear test," IS: 1498, "Classification and identification of soils for general engineering purposes," IS 1888, "Method of load test on soils," IS: 2386 (Part I), "Reaffirmed 1997, methods of testing for aggregates for concrete: Particlesize & shape, Bureau of Indian Standards," IS: 2386 (Part III), "Reaffirmed 1997, methods of testing for aggregates for concrete: Specific gravity, density, voids ratio, absorption & bulking, Bureau of Indian Standards," 1963.

18 Vol. 21 [2016], Bund IS: 2386 (Part IV), "Reaffirmed 1997, methods of testing for aggregates for concrete: Mechanical properties, Bureau of Indian Standards," ejge