Bio-Enzyme Stabilized Lateritic Soil as a Highway Material

Paper No.553 BIO-ENZYME STABILIZED LATERITIC SOIL AS A HIGHWAY MATERIAL† A.U. RAvi ShAnkAR*, hARShA kUmAR RAi** & RAmeShA mithAnthAyA i. *** ABSTRACT The abundantly available lateritic soil in Dakshina Kannada and Udupi districts does not satisfy the requirements (Liquid Limit ≤25% and Plasticity Index ≤6 %) to be used as a base course material in pavements. In order to improve its properties the soil is blended with sand at different proportions unless until it satisfies the Atterberg’s Limits for sub-base course. In recent past many Bio-Enzymes have come to the market which can be used as stabilizing agent. One such stabilizing agent is TerraZyme, which is used in the present investigation to further stabilize blended soil. The effect of enzyme on soil and blended soil in terms of Unconfined Compressive Strength (UCC), California Bearing Ratio (CBR), Compaction and permeability are studied. It has been observed that the enzyme treated soil showed significant improvement in terms of UCC, CBR with longer curing period. 1 INTRODUCTION Soil improvement by mechanical or chemical means is widely adopted. In order to stabilize soils for improving strength and durability, a number of chemical additives, both inorganic and organic, have also been used. Recently Bio-Enzymes have emerged as a new chemical for soil stabilization. Bio-Enzymes are chemical, organic, and liquid concentrated substances which are used to improve the stability of soil sub-base of pavement structures. 1.1 Physical Properties of Lateritic Soils Properties of laterites in Dakshina Kannada (D.K.) District have a specific gravity ranging from 2.40 to 2.65, higher values of specific gravity in lateritic soils are generally associated with soils rich in iron oxides and titaniferous minerals. In-situ dry density is found to vary depending on the chemical composition from 16 kN/m3 to 18.10 kN/m3. However, a range from 25 kN/m3 to 36 kN/m3 has been observed in some laterites (Pavate and Visweswaraiya, 1972)12. The natural moisture content is found to vary from 10 percent to 20 percent and water absorption is around 16 percent. The plasticity characteristics of the lateritic soils are considerably influenced by the amount of clay present in them. This could be interpreted in the light of the genesis, the degree of weathering and the clay mineralogy as well The growth of the population has created a need for better and economical vehicular operation which requires good highway having proper geometric design, pavement condition and maintenance. The highways have to be maintained so that comfort, convenience and safety are provided to the travelling public. The pavements along the national and state highways in the coastal belt of Karnataka are damaged due to the poor strength of soil used and low permeability. Hence, it is necessary to have a proper diagnostic study of the soil to be used as subbase. Cost effective roads are very vital for economical growth in any country. There is an urgent need to identify new materials to improve the road structure and to expand the road network. Commonly used materials are fast depleting and this has led to an increase in the cost of construction. Hence, the search for new materials and improved techniques to process the local materials has received an increased impetus. When poor quality soil is available at the construction site, the best option is to modify the properties of the soil so that it meets the pavement design requirements. This has led to the development of soil stabilization techniques. Since the nature and properties of natural soil vary widely, a suitable stabilization technique has to be adopted for a particular situation after considering the soil properties. * ** *** † Professor, Department of Civil Engineering, National Institute of Technology Karnataka, Mangalore – 575 025, E-mail : [email protected] Post Graduate Student, Department of Civil Engineering, National Institute of Technology Karnataka, Mangalore – 575 025 Associate Professor, Department of Civil Engineering, NMAMIT, Nitte, Karkala-574 110 Written comments on this paper are invited and will be received upto 30 September 2009. Journal of the Indian Roads Congress, July-September 2009 performance and higher resistance towards deformation. non-flammable. for shallow foundations. materials treated with Bio-Enzyme retain higher performance levels and extended life span. fine loam. namely. texture of the soil and the initial void ratio (Gidigasu. TerraZyme named enzyme has been used for stabilization. Enzymes catalyze the reactions between the clay and the organic cat-ions and accelerate the cat-ionic exchange process to reduce absorbed layer thickness. to meet the specified limits of liquid limit and plasticity index and other strength characteristics of soil for airfields and roads as subbase course. These soilstabilizing enzymes catalyze the reactions between the clay and the organic cat-ions and accelerate the cat-ionic exchange without becoming part of the end product 1. on with standard water spraying equipment. The coefficient of permeability of high level lateritic varies from 7 x 10-7 m/s to 16 x 10-7 m/s. formulated using vegetable extracts. facilitates higher soil compaction and increases strength.2 Bio-Enzymes as Soil Stabilizers in Road Construction Bio-Enzyme is a natural. CBR. Therefore. Bio-Enzyme may be used to increase the Maximum Dry Density (MDD) and Unconfined Compressive Strength (UCS) values of a marginal material to achieve specified standards for a base course. but Bio-Enzyme is easy to use as it can be mixed with water at optimum moisture content and then it is sprayed over soil and compacted. sandy loam. The specific as the clay size content. The shear strength parameters. The coefficient of permeability of undisturbed residual laterites soils is considerably influenced by the degree of weathering. rai & Mithanthaya i. non-toxic bio-degradable liquid concentrate that mixes easily in water for application Journal of the Indian Roads Congress.88 kN/m2 to 50. 1.99 kN/m2 and 160 to 300 respectively. to truly improve the soil properties. which is difficult to mix thoroughly. 1976)6. ranges from 98 kN/m2 to 196 kN/m2. non-corrosive liquid enzyme formulation fermented from vegetable extracts that improves the engineering properties of soil.3 Mechanism of Soil Stabilization By BioEnzyme In clay water mixture positively charged ions (cat-ions) are present around the clay particles. brown in colour and smell of molasses. cohesion and angle of internal friction obtained from undrained triaxial shear tests. A Bio-Enzymatic Soil Stabilizer TerraZyme is a natural. Organic enzymes come in liquid form. vary from 5. soil stabilization was tried using locally available river sand and Bio-Enzyme as stabilizer. Among the soil materials stabilized by the Bio-Enzymes in the trials are sandy clay. Lateritic soil was stabilized using variable enzyme dosages and strength of the stabilized soil has been evaluated after curing period of one week. Cation exchange processes can accomplish this. They are perfectly soluble in water. it is necessary to permanently reduce the thickness of double layer. July-September 2009 .4 TerraZyme. The absorbed water or double layer gives clay particles their plasticity. The effect of enzyme on different percentages of sand blended lateritic soil was also studied for a curing period of one week to four weeks.144 Shankar. Lateritic soil considered in the present study has high plasticity index. In some cases the clay can swell and the size of double layer increases. plastic and non-plastic clay. it emphasizes on strength. The tests were carried out to determine the consistency limits. but it can be reduced by drying. and loam mixed with clay. which completely replaces the conventional granular base and the granular sub base. The amount of dilution water depends on in-situ moisture content of soil. sandy silt. Apart from being a concept accepted the world over as a sound and resourceful road building practice. For other types of chemical stabilization. Bio-Enzyme from Australia is a natural. By altering the physical and chemical characteristics of soil. creating a film of water around the clay particle that remains attached or absorbed on the clay surface. So. Bio-Enzyme manufactured in USA and Netherlands also increases the unconfined compressive strength (UCS) and California Bearing Ratio (CBR) of sub-grade soil. chemicals are mixed with soil. The safe bearing capacity (SBC) of laterites with a factor of safety of 3. non-toxic. two weeks. The dosage levels of the Bio-Enzymes vary from 1 to 5 litres for 5 m3 of soil depending on the soil type. non-toxic liquid. soil characteristics. three weeks and four weeks. By utilizing fermentation processes specific micro-organisms can produce stabilizing enzyme in large quantity. unconfined compressive strength and permeability of the soil specimens with and without stabilization using enzyme. These soils are porous and possess medium to high permeability. and product concentration. 1. Bearing capacity of these soils is found to be satisfactory. silty clay. Andrew et al (2003) conducted laboratory scale testing program to evaluate the effectiveness of enzyme treatment on sub grade soil. sandy silt. which was having serious problems during the monsoon season or after heavy downpour. which proved its suitability as a stabilizing agent. TerraZyme acts to reduce the voids between soil particles and minimize absorbed water in the soil for maximum compaction. silty clay.3 and 4. It was found that in all soil types considered. 2 LITERATURE REVIEW 145 Lacuoture and Gonzalez (1995) 9 conducted a comprehensive study of the TerraZyme soil stabilizer product and its effectiveness on sub-base and sub-grade soils. The successful stabilization Journal of the Indian Roads Congress. Laboratory tests were conducted to determine the engineering properties of soil and strength characteristics of soil with and without stabilization with Bio-Enzyme. There is no risk of decay. TerraZyme stabilization can convert the road to an all weather road that has minimum destruction in hot and wet season. the effect of stabilization has improved the CBR and unconfined compression strength. This decreases the swelling capacity of the soil particles and reduces permeability. They require dilution in water before application.2 km of the road. like silty soil to sandy soil. The selected soils were sandy clay. In the cases of highly clay moderate soil. If they are to be stored for long periods of time without losing any of their properties. loam mixed with clay. The increase in CBR was of the range of 136 to 1800 times that of the original value. Isaac et al (2003) conducted a comprehensive study of the TerraZyme and its effectiveness on lateritic soil and clay type soil collected from Kerala. Neither gloves nor masks are required during handling but it can cause irritation to the eyes. sandy loam. No surface damage was observed. The Bio-Enzyme stabilization has shown little to very high improvement in physical properties of soil. Hitam and Yusof (1998)5 of Palm Oil Research Institute of Malaysia conducted field studies on improvement on plantation roads. These features are particularly evident in fine-grained soils such as clay in which the formulation affects the swelling and shrinking behavior. The CBR test appears to be a relatively poor indicator of direct soil strength for testing conditions. This formulation has the ability to change the matrix of the soil so that after compaction the soil loses its ability to reabsorb water and the mechanical benefits of compaction are not lost even after water is reapplied to the compacted soil. July-September 2009 . TerraZyme is specially formulated to modify the engineering properties of soil. Their aroma has no effect. strength.Bio-EnzyME StaBilizEd latEritic Soil aS a highway MatErial weight is similar or equal to that of water. the CBR value has increased by addition of TerraZyme. Manoj et al (2003)10 conducted a study to assess the suitability of Bio-Enzyme as soil stabilizer on five types of soils with low clay content to very high clay content. This little improvement may be due to chemical constituent of the soil. the change is permanent and the product is biodegradable. TerraZyme was treated to 27. it is necessary to maintain a temperature of 550 C. thus requiring no repair works to the road section. The enzymes react with oxidizing agents. soil mixtures with pieces of recycled pavement. The reactions of the soils treated with the enzyme was observed and recorded and compared to the untreated samples for the period of 8 weeks. The sections were then monitored on the surface erosion due to rainwater and wear due to usage. After two monsoon seasons the road was found to be in very good condition in spite of large exposure to heavy rainfall. Once the enzyme reacts with the soil. Bergmann (2000)2 concluded that the Bio-Enzymes require some clay content in the aggregate material in order to create the reaction that will strengthen the material. The variation in properties was observed over a short period only and it was found that in cohesive soils there was no major variation in properties during the early days but the soil showed improved performance progressively. Brazetti and Murphy (2000)3 conducted field experiments in Brazil to study the use of TerraZyme as the bio-enzyme stabilizer for road construction. The pH level is between 4. plastic and non-plastic clay. which has low reactivity with Bio-Enzyme. After the evaluation it was concluded that the enzyme stabilization is a good technique for the effective and economic solution for pavement construction. The application of TerraZyme enhances weather resistance and increases load bearing capacity of soils. soil stiffness and soil modulus.6. The field stretches were periodically tested with DCP (Dynamic Cone Penetrometer) equipment. TerraZyme is useful for clay soil and sand but is less significant to silty soils and clayey and sandy soil had increase in CBR by 700 percent. The effectiveness of enzyme treatment was evaluated on the basis of statistical measurement of change in CBR. without stabilization and with stabilization for a curing period of two-weeks.1 Materials Used & Tests Conducted 4. Value 2.4 percent test results indicate that the value of liquid limit is 35 respectively. Table 1 indicate that more than 50 percent of soil is retained on These results indicate that the soil is low compressible 75 micron IS sieve and therefore grouped under coarse and it is classified as silty sand with 19 percent of gravel. N. sand and TerraZyme (Bio-Enzyme). Journal of the Indian Roads Congress. 5. tests. CBR and permeability tests. 62. All the tests were performed as per IS specifications. on Table 1 Properties of Lateritic Soil S. Cu Co-efficient of Curvature. grain size distribution. kN/m3 b) OMC (%) 11. Property 1 Specific Gravity 2.6 IS Soil Classification SM-GM Engineering Properties 19. 3. grained soil as per IS classification.The sand used for the work was been obtained from the nearby river and was tested in the laboratory for the properties like specific gravity. three-week and fourteen-week periods CBR was found as 37. Cc 3.78x10-8 b) IS Heavy Compaction (m/s) 2. The properties of sand are shown in Table 2. 66 and 100 respectively as compared to 28 percent of untreated soil. Dry Density.50 19. The results are 7. July-September 2009 Consistancy Limits Liquid Limit (%) 35 Plastic Limit (%) 25 Plasticity Index (%) 10 Shrinkage Limit (%) 16.The lateritic soil obtained from field was tested in the laboratory for the properties like specific gravity. all the tests were performed as per relevant IS Specifications.32 kN/m3 and 19. In the above tests TerraZyme named Bio-Enzyme was used for stabilization. laboratory tests were conducted to determine the engineering properties and strength characteristics of lateritic soil and blended lateritic soil with and without stabilization with Bio-Enzyme. 3 EXPERIMENTAL INVESTIGATION To assess the suitability of Bio-Enzyme as soil stabilizer. compaction. vibratory compaction and direct shear 8. tabulated in Table1.45 19 50 29 2 115. The lateritic soil and blended lateritic soil samples considered for study were first tested for engineering properties and samples were then tested for strength parameters such as CBR and unconfined compressive strength. consistency limits. Coefficient of Under light and heavy compaction the MDD was found uniformity (Cu) and coefficient of curvature (Cc) were to be 19. The CBR values of lateritic soil at OMC for percent and plasticity index is 10 percent and it doesn’t light and heavy compaction was found to be 10 percent meet the standards of sub-base course as suggested by and 14 percent respectively and at soaked condition it was found to be 4 percent and 8 percent respectively.87x10-8 .146 Shankar.74 could be achieved with as little as 2 percent clay in the aggregate material but best result seems to be achieved with 10 to 15 percent clay. For IRC: SP:20-2002. three-weeks and four-weeks. Further the OMC was found to be 13. unconfined compressive strength.5 percent and 11. The materials used for the tests include the lateritic soil. It was reported that after oneweek.95 kN/m3 respectively and found out to be 115.74 respectively. two-week.32 IS Light Compaction) Max. Grain Size Distribution Gravel (%) Sand (%) Silt (%) Clay( %) Co-efficient of Uniformity.4 and 0.95 IS Heavy Compaction) Max. kN/m3 a) OMC (%) 13.4 0. Dry Density.40 CBR % IS Light Compaction (at OMC) 10 IS Light Compaction (Soaked) 04 IS Heavy Compaction (at OMC) 14 IS Heavy Compaction (Soaked) 08 Unconfined Compressive Strength a) IS Light Compaction (kPa) 108 b) IS heavy Compaction (kPa) 142 Co-efficient of Permeability a) IS Light Compaction (m/s) 4. 6. grain size distribution. rai & Mithanthaya i. 75 mm sieve and retained on 425 micron is used for adding to the test samples in different percentages. modified Proctor’s test was conducted according to relevant IS Specifications (IS: 2720 (Part-8):1980). CBR tests were conducted on the different soil-sand mixes at soaked condition. 3. The MDD value of the blended soil increased as the percentage of sand increased upto 40 percent and beyond 40 percent the OMC increases and MDD decreases.2. Predetermined quantity of Journal of the Indian Roads Congress. further increase of sand. soil-sand mixes to ensure the specifications specified by MoRTH. the liquid limit and plastic limit values reduced. but the CBR value decreases from 22 percent to 14 percent at 60 percent of sand. The results of these are tabulated in Table 3.13 2 98 trace 0 2 0. When soil is replaced by sand from 10 percent to 60 percent at an increment of 10 percent the variation in MDD and OMC for heavy compaction is tabulated in Table 3. The liquid limit of soil decreased to 25 percent by replacing soil with 30 percent of sand. corresponding to the optimum moisture content was added and the contents were thoroughly mixed.13 17. was added and the contents were thoroughly mixed.786x10-8 m/s and 2.2.1 Compaction Tests Compaction tests were conducted on the soil blend (lateritic soil.83 44º 5´ 0 Zone-II 147 water. These mixes were compacted in the permeability mould and later these moulds were fixed to permeameter then tested. These mixes were compacted in the CBR mould to maximum Proctor’s density. The CBR tests at heavy compaction (soaked) found that CBR increased from 8 percent to 22 percent when soil is replaced by sand from 0 to 40 percent with an increment of 10 percent. The liquid limit decreased from 35 percent to 22 percent and the plasticity index decreased from 10 percent to 3 percent when soil is replaced by sand from 0 to 40 percent at an increment of 10 percent. The results of compaction tests and CBR tests for blended soil with different percentages of sand are given in Table 3. Table 2 Properties of Sand Description Specific gravity Fineness modulus Loose Density( kN/m3) Vibrated Dense Density ( kN/m3) Grain size analysis Gravel (%) Sand (%) Silt (%) Clay (%) Cu Cc Direct Shear Test Angle of internal friction (Ø) Degrees Cohesion ( kN/m3) (c) Grading as per IS: 383-1970 3. On the soil. plastic limit and Plasticity index of lateritic soil and blended soil (sand) is tabulated in Table 3. corresponding to the optimum moisture content by modified Proctor’s test for the mix.865x10-8 m/s to 89.6x10-8 m/s when soil is replaced by 0 to 60 percent of sand.Bio-EnzyME StaBilizEd latEritic Soil aS a highway MatErial light and heavy compaction the unconfined compressive strength of lateritic soil was found to be 86. 3. From the Table 3. The optimum sand content is found to be 40 percent.2 Tests on Blending of Soil The coarse grained soil (sand) collected is sieved and only coarse sand passing through 4. IRC: SP:20-2002. it was found that coefficient of permeability increases with increase of sand content in the soil.87 kPa and 181.865x10-8 m/s respectively 3.sand). The requisite quantity of sand to be replaced for the effective blending of soil is determined in the laboratory by changing the percentage of sand till the desired limits are achieved.2. The results have been given in Table 3. The value increased from 2. Predetermined quantity of water. these samples were kept in water for four days immediately after compaction.3 Permeability Tests Permeability tests were conducted on the different percentage of soil-sand mixes at modified proctor density. July-September 2009 .18 14.64 2. The liquid limit of blended soil decreases with increase in percentage of sand. Consistency limit tests were carried out on soil.4 kPa respectively and coefficient of permeability was found to be 4. For soaked condition. The liquid limit.2 CBR Tests Test value 2. Table 5 Consistency Limits of Soil Treated with Enzyme Dosage 1 1 LL PL PI LL PL PI LL PL PI LL PL PI st Compaction.0 2.39 10. Depending on the soil gradation.9 3.8 24. 14.6 24.60 8 10 14 18 22 20 14 2. Varying quantities of stabilizers can cause different effect in the same soil sample.029 0.5 24.3.6 25.0 ml/kg of Soil 0.0 25. 1.6 24.0 5. to determine the optimum quantity of TerraZyme for best results.0 5.0 4.67 30.5 3.8 24.5 2.5 4. Later these moulds were kept in soaked condition for 4 days and then tested for CBR.4 4.3 28.98 21.87 x10-8 5.5x10-8 18. 3 4 3.4 20. 2. July-September 2009 .59 28.1 Consistency Limits Liquid limit and plastic limit of soil mixed with variable dosage of TerraZyme are tested after 1. CBR and Permeability Test Results MDD CBR Coeff.0 25.0 4.050 Table 3 Consistency Limits.0 20.4 x10-8 89.2 CBR Tests Soil was treated with 4 dosages of enzyme at optimum moisture content.0406 0.0 3.2 28. on clay content and plasticity index of the soil.90 27.44 29 24.3 4. Table 4 Enzyme Dosages Dosage 1 2 3 4 200 ml/m3 of Soil 3. Compaction.35 10.3. Lateritic Sand OMC (kN/ (%) Permeability Soil (%) (%) (%) m3) (Soaked) K (m/s) 100 90 80 70 60 50 40 0 10 20 30 40 50 60 11.2 24.80 28.60 2 3.00 29.0 4. the required dosage of TerraZyme for mixing with soil.148 Shankar.10 11. CBR tests were conducted on each of the soil samples with varying quantity of TerraZyme. rai & Mithanthaya i. Insufficient quantity of TerraZyme may lead to less stabilization of the soil where as excess quantities may result the stabilization ineffective and uneconomical.80 9.9 24. as suggested by supplying company is given in Table 4.8 x10-8 57.2 24.6 x10-8 Treated Weeks 2nd 29.2 25.4 19.3 4.7 4.2 27.0 4. 3. CBR moulds were prepared by modified proctors method and kept in airtight bags for testing on its 7. 21 and 28 days curing.2 21.41 3rd 29.4 x10-8 26.0 30.3 4. The liquid limit and plastic limit of untreated soil is 35 percent and 25 percent.9 25.19 4th 28.61 10.6 25.3 28. Journal of the Indian Roads Congress.6 29.95 11. CBR values of lateritic soil with different enzyme dosages in various curing days are given in Table 6. Both laboratory and field studies conducted in India have shown that soil stabilization with TerraZyme provides such a positive improvements in various soil types that the use of TerraZyme offers a substantial reduction in the construction cost of roads.0 4.0338 0. 3 and 4 weeks of curing.0 20. The results are shown in Table 5. Hence.9 29.75 x10-8 10.3 Stabilization Using TerraZyme (Bio-Enzyme) TerraZyme a bio-enzymatic soil stabilizer improves the engineering properties of the locally available soil for the use of construction of roads.7 24.0 3.7 20. CBR and Permeability Test Results (Blended Soil) Lateritic Soil (%) 100 90 80 70 60 Sand (%) 0 10 20 30 40 Liquid Limit (%) 35 31 28 25 22 Plastic Plasticity Limit Index (%) (%) 25 23 21 20 19 10 8 7 5 3 Dosage calculations are shown in Annex. 3 Unconfined Compressive Strength Tests Unconfined compressive strength of lateritic soil was evaluated by stabilization with variable dosages of enzyme for one.87 2.87 2.63 2. Later these moulds were fixed to permeameter and then tested.67 percent and plastic limit 25 percent to 24 percent for the higher dosage 4 after the curing period of 4 weeks. Effects of variable enzyme dosages on consistency limits of the lateritic soil after one to four weeks of curing were shown in Table 5. Table 7 Coefficient of Permeability of Soil with Enzyme Dosage Treated Weeks 1 2nd 3rd 4th Coefficient of Permeability (K) m/s (x10-8) 1 2. The test results have been given in Table 6. two. Results shows that highest quantity of enzyme that is dosage 4 improves the CBR values to a higher range. 21 and 28 days curing. It indicates that CBR value has improved to a maximum of 288 percent after four weeks of curing in a maximum dosage 4. as period of curing increases the rate of improvement in CBR values also increases.67 4 1. The effect of enzyme dosages on unconfined compressive strength of lateritic soil for a period of one to four weeks of curing is shown in Table 9.63 2. Dosage 2 improves the CBR by 150 percent to 238 percent and Dosage 1 improves the CBR by 113 percent to 188 percent after curing. For chemically stabilized soils the CBR test results may not be realistic. There is little improvement in the consistency limits by treating soil with enzyme.3.91 1.91 1. The specimens were prepared and kept in desecrator to retain moisture of the sample so that reaction between soil particle and TerraZyme may be continued.39 3 1. The four variable enzyme dosages were used for stabilize the lateritic soil.39 2. The test results have been given in Table 7. 14. strength and permeability properties of Lateritic soil during the curing period is shown in Tables 5 to 7. Unconfined compressive strength of the soil was evaluated for untreated soil and treated Journal of the Indian Roads Congress. CBR value of untreated soil is found to be 8 percent where the CBR value of enzyme treated soil after 4 weeks of curing is found to be 31 percent. To substantiate the results UCC tests are conducted on such soils.63 2 2. It shows that dosage 4 improves the CBR by 213 percent after one week of curing and improves by 288 percent after four weeks curing.3.91 1. It was found that liquid limit and plasticity index of treated lateritic soil decreases as the amount of dosage increases st 149 Treated Weeks 2nd 3rd 4th during the curing period. as curing period increases the rate of improvement increases.39 2. Effect of dosages of enzyme on index properties.4 Permeability Tests Permeability tests were conducted on soil treated with enzyme at optimum moisture content.91 1. From the table it is evident that there is gradual improvement in the CBR values of treated soil when compared with untreated one.67 st The effect of enzyme dosages on CBR values of lateritic soil for a period of one to four weeks of curing are shown in Table 8. 3. three and four curing weeks. Liquid limit decreased from 35 percent to 27.67 1. Permeability moulds were prepared and kept in airtight bags for testing on its 7. Enzyme dosage 4 shown slightly higher improvements in liquid limit and plasticity index compare to other smaller dosages and also found that. July-September 2009 .Bio-EnzyME StaBilizEd latEritic Soil aS a highway MatErial Table 6 CBR and UCS Values of Soil Treated with Enzyme Dosage 1 CBR % Untreated 08 1 17 20 21 23 2 20 23 25 27 3 23 25 27 29 4 25 27 29 31 UCS of Soil in (kPa) for Period of Treatment Untreated 142 1 205 272 343 447 2 262 324 398 513 3 330 434 532 716 4 428 513 607 782 3. Dosage 3 improves the CBR by 188 percent to 263 percent.67 1. three and four weeks of curing. It indicates that CBR value improved to a maximum of 300 percent for 10 percent blended soil. where as the value of untreated soil was 2. For the rest of the blending the CBR values are lesser. 4. The test results have been tabulated in Table 8. When more than 20 percent of soil is replaced by sand. 3. It shows that 10 percent of Journal of the Indian Roads Congress.4 Effect of TerraZyme on Blended Soil The CBR values of different percentage of blended soil were studied by treated with enzyme dosage of 200 ml/2 m3 for one.3 Enzyme is found to be ineffective for improving consistency limits. two. Based on the test results it was found that unconfined compressive strength increases with higher dosages for a higher curing period. after one week curing this value increased to 27 percent and after four weeks curing this value was increased to 32 percent.2 The lateritic soil properties have been much improved by stabilizing with enzyme dosage of 200 ml/ 2 m3 of soil. 4.5 The lateritic soil properties have been improved by adding sand. Further addition of sand and enzyme. However. July-September 2009 . From the test results it was found that as sand content increases beyond 10 percent. Compressive strength of the soil was found to be maximum with dosage 4. for 30 percent of blended soil the CBR improves by 175 percent to 275 percent and for 40 percent of blended soil the CBR improves by 163 percent to 250 percent after curing for one week to four weeks. It is observed that CBR value increases with increase in percentage of sand upto 175 percent. The test results are tabulated in Table 6. When CBR value is compared to untreated blended soil there is an increase in CBR value at higher curing periods.150 Shankar. This improvement may be due to chemical constituent of the soil which has low reactivity with Bio-Enzyme. The coefficient of permeability after treating for four weeks with highest dosage is found to be 1. 4. The CBR values are maximum at 10 percent as replaced. The CBR This blended soil is further stabilized by enzyme.5 Test Results on Enzyme Treated Blend Soil The effect of enzyme on CBR values of lateritic soil with variable percentage of sand for a period of one to four weeks of curing are shown in Table 8. as the curing period increases the CBR values of all the blends are increasing further. The higher enzyme dosage 4 is used for treating blended soil. two. Table 8 CBR Values of Blended Soil with Enzyme Soil blend soil-sand % 100-0 90-10 80-20 70-30 60-40 1st 25 27 24 22 21 Treated ( Weeks) 2nd 3rd CBR % 29 30 30 31 29 30 27 28 24 27 4th 31 32 31 30 28 Based on the tests conducted the following conclusions have been drawn which are applicable only to materials used and test conditions adapted in the study.67x10-8 m/s. Tables 8 and 11 give the values of CBR for untreated soil and treated soil with enzyme. Permeability tests were carried out on lateritic soil with different enzyme dosages. 4. Unconfined compressive strength increases from 142 kPa to 782 kPa by treating the soil with enzyme and curing for 4 weeks. Similarly for 20 percent of blended soil the CBR improves by 200 percent to 288 percent.6 The CBR values of the enzyme treated soil blend decreases with increase in sand content. The optimum sand content to replace lateritic soil when further treated with enzyme was 10 percent. consistency limits and CBR values were found to have met the specified limits (LL< 25 percent. rai & Mithanthaya i. three and four weeks of curing with enzyme dosages. the CBR value of lateritic soil increased by 300 percent after four weeks of curing. 4. on blended soil improves the CBR by 238 percent after one week of curing and further improves by 300 percent after four weeks of curing. the CBR value decreases for enzyme treated soils.4 For a higher dosage of 200 ml/ 2 m3 of soil. 4. unconfined compressive strength of the soil increased by 450 and permeability decreases by 42 percent. 4 CONCLUSIONS soil for one. PI< 6 percent and soaked CBR > 20 percent) of sub-base. From the tests it was found that effect of enzyme on permeability characteristics of soil is marginal. 3.1 Bio-Enzyme stabilization has shown medium improvement in physical properties of lateritic soil. therefore it is advisable to first examine the effect of Bio-Enzyme on soil stabilization in the laboratory before actual field trials. there is decrease in CBR values.865x10-8 m/s. paper. 5. (2003). Bulk Density of Lateritic soil = 1. Third Revision. A.0 m3 of soil = 1.D. 12. Pontificia Universidad Jevariana. “Specifications for Road and Bridge Works”. M. Lacuoture.0338 ml of Enzyme For Dosage 3 200 ml for 2.E. MOST (Roads Wing) (1998).97 g/cc Bulk Density = Weight / Volume Weight = Bulk Density x Volume For Dosage 1 200 ml for 3. 30 June 1998.. Hitam. Ca: U. E.97 x 3. Columbia.1. October 2000. and Beaven.0 x 1000 = 5910 kg of soil For 1 kg = 0. Gidigasu. Presented at the IRC Seminar “Integrated Development of Rural and Arterial Road Networks for Socio-Economic Development”. “Soil Stabilizers on Universally Accessible Trails”. The Indian Roads Congress. for enzyme stabilized soils CBR tests are not recommended. New Delhi. (1976). Elsevier Scientific Publishing Company. 32nd Annual Meeting on Paving Brazil. 10. and Yusof.029 ml of Enzyme For Dosage 2 200 ml for 3. Shukla.0 m3 of soil = 1. Bangalore. Chennai for supporting this project by supplying enzymes. T. 6. “Stabilization of Lateritic Soils”. Biju and Veeraragavan (2003).5 m3 to 2 m3 of soil. 4.0 x 1000 = 3940 kg of soil For 1 kg = 0. New York. (1998). and Gonzalez. pp. Brazetti. (1962). “Soil Stabilization Using Bio-Enzyme for Rural Roads” presented at the IRC Seminar “Integrated Development of Rural An Arterial Road Networks 151 for Socio.7 By comparing CBR values of the unblended and blended soil after enzyme treatment it was found that enzyme is not effective for soil containing higher percent of cohesion less soil. “ Lateritic Soil Engineering Pedogenesis and Engineering Principles”. Nicholos.050 ml of Enzyme 2. REFERENCES 1. San Dimas Technology and Development Center.Tolleson. A. India. Brit. R. 8. Sunil and Sikdar.0406 ml of Enzyme For Dosage 4 200 ml for 2. Clare.8 The UCC tests are more realistic than CBR and therefore. P. Isaac. Bose. K. (1995). p. Journal of the Indian Roads Congress. Inc. Shatnawi. 3. Geomatrics. Fadi.S.J. S. Annex-1 Dosages specified by the company for Lateritic soil was 200 ml for bulk volume 3.V and Vishwesswaraiya. “Soil Stabilizers for Plantation Road”. Proceedings of the Symposium on Strength and Deformation Behavior of Soils. Lab. P. R. Sc 29210. 9. Roger (2000).G (1972). “An Evaluation of Strength Change on Sub-grade Soils Stabilized with an Enzyme Catalyst Solution Using CBR and SSG Comparisons”. 4. T. 1970).R.97 x 2. 10. Malaysia. National Seminar on Mechanisation in Oil Palm Plantation.97 x 2.P. “Rural Roads Manual”. “Road Making Materials in Northen Borneo”. New Delhi 5-6 December 2003. ACKNOWLEDGEMENTS The authors are thankful to Mr. July-September 2009 . Technical Report 0023-1202-SDTDC. IRC.. July 2003. 68-78 (Extracted from Gidigasu. Selangor.K. Tech. Pavate. H. IRC:SP:20-2002. 11. M. Apoorva Modi. Andrew. Faculty of Engineering.“ General Usage of Bio-Enzyme Stabilizers in Road Construction in Brazil”. New Delhi. USA. Road Res. K. 7.97 x 3. Department of Agriculture. Avijeet agencies. Bergmann.5 x 1000 = 4925 kg of soil For 1 kg = 0. San Dimas. “Usage of Organic Enzymes for the Stabilization of Natural Base Soils and Sub-bases in Bagota”. A. Forest Service. Vol.5 m3 of soil = 1.Bio-EnzyME StaBilizEd latEritic Soil aS a highway MatErial value of blended soil increased by 300 percent with 10 percent sand with a dosage of 200 ml/ 2 m3 of soil.5 m 3 of soil = 1. and Murphy. New Delhi 5-6 December 2003.Economic Development”. “Bio-Enzyme for Stabilization of Soil in Road Construction a Cost Effective Approach”. 4. (2000). Manoj. Harman and Elahe Mahadavian (2003).5 x 1000 = 6895 kg of soil For 1 kg = 0.