International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 4, April 2014)

Effect of Organic Content on the Index Properties and Compaction Parameters of Soil Purabi Sen1, Mukesh2, Mahabir Dixit3, R Chitra4, Murari Ratnam5 1

Scientist B, 3Scientist D, 4Scientist E, CSMRS, MOWR, Hauz Khas, New Delhi-16 2 Assistant Research Officer, CSMRS, MOWR, Hauz Khas, New Delhi-16 5 Director, MOWR Hauz Khas,New Delhi-16 Central Soil & Materials Research Station, MOWR Hauz Khas, New Delhi-16, India

Abstract— Kalej Khola H.E Project, and Suntaley H.E Projects are located in West Sikkim and east Sikkim respectively. The Kalej Khola H.E Project is located on the river Kalej Khola, a tributary of river Rangit and Suntaley H.E Project on the river Suntaley, a tributary of river Teesta. Both projects envisage construction of approximately 50 m height composite Earth and Rockfill dams with spillway on the right bank and left bank of the river respectively. Installed capacities of proposed surface power house of the two projects are 90 MW 60 MW respectively. In the present study, effect of organic content on index properties and compaction parameters of borrow area soil samples of these two has been investigated. The test results indicate that the organic content significantly alter the geotechnical properties of these samples because determination of moisture content in the samples done through oven drying methods since some of the organic content also get burn up during the oven drying the moisture content determination is often inaccurate in such soils results derived using oven drying always consist of some weight loss due to organic matter apart from moisture content. Therefore it is difficult to arrive at Atterberg limits of the actual soil excluding organic matter. In the present study, it has been shown that Atterberg Limits for oven dried samples can be determined without oven drying the sample and then redetermining the limits. The procedure requires determining the loss on ignition and Atterberg Limits normally of air dried soils. the process results in considerable time saving during the testing .Further prediction of correct results of optimum moisture content and maximum dry density are also possible if somehow the borrow area soil could be heated up to normal oven temperature.

I. INTRODUCTION The State Sikkim is characterised by mountainous terrain as entire state is hilly area. Numerous snow fed streams have carved out into river valleys in south and west of the state. These streams combine into major rivers Teesta and Rangit which flow through the state from north to south. About one third of the state is heavily forested. The hills of Sikkim mainly consist of gneissose rock and half schistose rocks producing generally poor and shallow brown clay soils. Most of the Sikkim is covered with Precambrian rock, which is much younger than the hill. This rock consists of phyllites and schist and are highly susceptible to weathering and erosion and these combined with heavy rainfall causes extensive soil erosion resulting frequent landslides often isolated the rural towns and villages from urban cities1. Centre for Inter-Disciplinary Studies of Mountain & Hill Environment, University of Delhi has done a detailed and extensive study of a large variety of series of soils found in Sikkim in terms of physical look, location, geography, drainage, permeability, grain size distribution, chemical analysis etc. It has been observed that some soil series of East Sikkim and West Sikkim, viz., Goucharan Series, Karporang Series, Chatten Series and Ruben Series contain organic carbon in considerable quantity. The highest reported one is 28.0%.2 Studies on the effect of organic matter on the geotechnical properties of soils revealed that the presence of organic matter has a significant effect on the index and engineering properties of soil3..

Keywords— Atterberg Limits(LL, PL, PI), Co-efficient of Volume Compressibility (mv) , Co-efficient of Consolidation (Cv), Compression index (Cc), , Co-efficient of Permeability(k), Maximum Dry density (MDD), Optimum Moisture Content (OMC), Organic Content, Swelling index(Cs), Shear Strength Parameters(c, c’, , ’)

II. PROJECTS Kalej Khola H.E Project4, is located in West Sikkim on the river Kalej Khola5, a tributary of Rangit and Suntaley H.E Project, is located in East Sikkim on the river Suntaley, a tributary of river Teesta.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 4, April 2014) Both project envisage construction of approximately 50 m height composite dam consisting of Earth and Rockfill Dam with spillway on the right bank and left bank of the river respectively .Installed capacities of proposed surface power house of the of the project are 90 MW and 60 MW respectively. The geotechnical investigations for the above mentioned projects were carried out in order to ascertain the suitability of the borrow area materials to be used as clay core material for the construction of the earth & rockfill dam.

The results of Atterberg Limits results including the soil classifications are presented in Table 1. The liquid lilts values of all the soil samples found to vary from 43.4 to 67.5. base As per IS soil classification in terms f compressibility 7 soil samples out of 10 soil samples 7 soil exhibit high compressibility and the remaining 3 soil samples exhibit medium compressibility. The plasticity index values of the samples indicate that the soil samples in general exhibit low to medium plasticity characteristics. Out of the 10 tested soil samples 7 samples fall under MH (silts with high compressibility) group, 2 soil samples fall under MI (silts with medium compressibility) and the remaining 1 soil sample falls under SM (silty sand) group of as per Bureau of Indian Standard soil classification system.

III. GEOTECHNICAL INVESTIGATIONS A total of ten soil samples were collected from both projects from different borrow areas. The soil samples were subjected to various laboratory tests such as Mechanical Analysis, Atterberg Limits, Standard Proctor Compaction, Specific Gravity, Triaxial Shear Test, One Dimensional Consolidation, Laboratory Permeability, Soil Dispersivity Identification Tests (Pin Hole Tests, SCS Double Hydrometer Tests, Crumb Tests, Chemical analysis of Pore water extract Tests), Chemical Analysis of Soil. All the tests were carried out as per the procedures given in the relevant BIS codes. While carrying out the routine laboratory investigations, it was found that the borrow area material possess organic matter in considerable amount and as such presence of the organic matter influences the physical and the engineering properties of the soil. Therefore, in addition to the routine tests, additional investigations e.g. variation of liquid limit and plastic limit, proctor compaction density, presence of organic matter in the borrow area soil samples at various temperature. The influence of these parameters has been discussed in the following paragraphs. The grain size distributions of all the tested is presented in Fig 1. It is seen from these curves that tested soil samples predominantly possess silt sizes followed by clay sizes. The grain sizes analysis of the soil samples indicate that the clay sizes vary from 13.7 % to 37.4 %, silt sizes from 28.8 % to 70.1 %, fine sand sizes from 2.7 % to 21.0 %, medium sand sizes from 3.4% to 8.2% .The coarse sand sizes are absent in one soil sample and in the remaining soil samples, the coarse sand sizes vary from 0.2% to 4.6%. The gravel sizes are totally absent in 6 soil samples and in the remaining soil samples the gravel sizes vary from 14.1% to 43.7%.

Figure 1 grain Size Distribution Curve

Seven soil samples were subjected to proctor compaction tests as per procedure given in IS 2720: 15. As per procedure, 4.75 mm passing air dried soil samples were taken for the test and in each reading moisture content was determined at 100-110oC.The values of Maximum Dry Density(MDD) and Optimum Moisture Content (OMC) of the tested soil samples vary from 1.12 g/cc to 1.61 g/cc and 21.4% to 41.1% respectively as presented in Fig. 2. From the Standard Proctor compaction test results, it is inferred that the soil samples are capable of achieving low compaction densities and higher OMC values.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 4, April 2014) Table 1 Atterberg Limits Test Results And Soil Classification

Soil No

Liquid Limits

Plastic limits

Plasticity Index

BIS classification

1

43.5

31.0

12.5

SM

2

52.0

33.2

18.8

MH

3

67.5

52.7

14.8

MH

4

59.9

44.6

12.3

MH

5

54.1

41.9

12.2

MH

6

50.6

37.3

13.3

MI-MH

7

43.4

30.6

12.8

MI

8

46.8

31.9

14.9

MI

9

57.2

45.5

11.7

MH

10

51.0

33.2

17.8

MH

LL

PL

PI

Table 2 Loss On Ignition At Different Temperature, Organic Content By Chemical Method And Specific Gravity

Sampl e No

LOI at 80oC (%)

LOI at 110oC (%)

LOI at 550oC (%)

organic content chemical method (%)

Specif ic Gravi ty

1 2 3 4 5 6 7 8 9 10

2.85 5.76 8.45 6.34 5.11 5.02 3.72 4.22 9.53 2.45

4.46 7.59 13.4 9.01 7.93 6.48 5.43 6.41 12.0 4.34

6.85 14.26 22.95 16.84 13.01 12.72 11.82 11.82 20.13 6.75

2.5 6.0 17.7 8.4 7.7 5.4 2.1 4.1 8.9 2.7

2.75 2.69 2.55 2.66 2.73 2.66 2.76

It is seen that the organic content vary from 2.1% to 17.7%. Samples were subjected to both Shrinkage Limit and Free Swell Index tests, however no shrinkage or swelling was observed in samples. To confirm positive indication of organic soil, Atterberg Limit tests on oven dried soil samples were conducted. As per IS code (2720 – 22) “organic silt and clays are usually distinguished from inorganic silts which have the same position on the plasticity chart, by odour and colour. However when the organic content in the sample is doubtful, the material can be oven dried, remixed with water and retested for liquid limit. A reduction in liquid limits after oven drying to a value less than three fourth of the liquid limit before oven drying is positive indication of organic soils6”.he graphical representation of comparative study of Liquid Limits of air dried and oven dried soils are given Fig.3 Similar behaviour was also observed for plastic limit and is presented in Fig 4. The ratio of liquid limit of air dried soil to oven dried soil was found to vary from 0.82 to 0.89 indicating reduction in liquid limit of oven dried soil was less than 25%. Therefore soil could not be classified as organic soil since; the presence of significant amount of organic matter in the soil samples also causes significant changes in the engineering properties of the soils

Figure 2 Result Of Standard Proctor Compaction Test

From the above test results, it is seen that the borrow area materials exhibit relatively high liquid limits, lower compaction density and high OMC which indicate presence of organic matter in the materials. The content of organic matter in soil samples was determined through chemical methods, and oven drying the soil samples at different temperatures .i.e Loss on ignition (LOI) The results of the same are presented in Table -2.

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 4, April 2014) The proctor compaction test was carried out on the air dried and the oven dried soil samples for the sample no 3 and the results of the same for MDD and OMC are presented in Fig. 5.

Dry Density, g/cc

1.3 1.2 1.1 1.0

Oven Dried Air Dried

Figure 3 Liquid Limit Of Soil Samples

It is seen from this graph, that liquid limit of oven dried soil is very close to the liquid limit of air dried soil minus loss on ignition at 1100 C temperature .It is conclude from these results, that determination of liquid limits of suspected organic matter is not required if loss on ignition at 1100 C is subtracted from liquid limit of air dried soil as both values of liquid limit are pretty close at 110oC barring few exceptions. Similar behaviour was also observed for plastic limit as presented in Fig-3.

0.9 15

25

35

45

55

Moisture Content, % Figure 5 Compaction Curve For Sample 3 – Air Dried And Oven Dried Soils

This increase in MDD and reduction in OMC is due to burning of organic matter .These values can be calculated without doing proctor compaction test on oven dried soil and using the Loss on ignition values (LOI). Therefore, the results of dry density and OMC for air dried soil samples and also probable dry density obtained through same analogy as obtained in liquid limit and plastic limits by subtracting loss on ignition values as presented in the figure 6-11.

Figure 4 Plastic Limit Of Soil Samples

In order to study, variation of the loss on ignition at different temperatures, 3 temperatures 80oC, 110oC and 5500C were randomly selected. The 80oC, and 110oC temperatures were obtained in normal oven and for 550 0C muffle furnace was used. The loss on ignitions for these temperatures are presented in Table 3, From these results, it is seen that as temperature increases the loss on ignition increases, however loss on ignition is considerable at 550oC the same might be due burning of only the organic matter but also may be due to change in chemical composition and removal of other type of moisture including adsorbed water.

Figure 6 Compaction Curve For Sample 1

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 4, April 2014)

Figure 10 Compaction Curve For Sample 7

Figure 7 Compaction Curve For Sample 2

Figure 11 Compaction Curve For Sample 9

Figure 8 Compaction Curve For Sample 3

Figure 12 Compaction Curve For Sample 10 Figure 9 Compaction Curve For Sample 6

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International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 4, April 2014) It is seen from the result that as there is improvement in MDD value of the soil if the soil have organic content and soil could be heated. Therefore the practical application of this technique is possible only if we are able to heat the borrow area soil up to the 110oC resulting in burning of organic matter in the field without difficulty. Further, this not only improving MDD values but also determination of MDD values and OMC for heated at so can be determined by LOI...

Predictions of Atterberg Limits for oven dried samples are possible from loss on ignition values and Atterberg Limits normally obtained with air dried soils. Prediction of correct results of optimum moisture content and maximum dry density are also possible if somehow the borrow area soil could be heated up to normal oven temperature.

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IV. CONCLUSION The effect of organic content on index properties, compaction parameters of borrow area soil samples of two HE projects of East Sikkim and West Sikkim has been investigated. The test results indicate that the organic content significantly alter the geotechnical properties of these samples because results derived using oven drying always consist of some weight loss due to organic matter apart from moisture content.

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[5]

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Sikkim, Wikipedia, Geology Ministry of Environment & Forests, Government of India, “Carrying Capacity Study of Teesta Basin in Sikkim”, Volume III, Land Environment-Soil Edil, T.B. “Construction Over Peats Organic Soil” Proc. Conf. on Recent Advances in Soft Soil Engineering, Kuching. CSMRS Report on Geotechnical Investigations on Borrow Area Soil Samples for the Proposed Suntaley H.E. Project, East Sikkim Report No. 3/Soil-II/CSMRS/E/05/2013 CSMRS Report on Geotechnical Investigations on Borrow Area Soil Samples for the Proposed Kalej Khola H.E. Project, West Sikkim Report No.4/Soil-II/CSMRS/E/05/2013