0 (0000) 0 0 ISBN 0-9780479 AES-ATEMA 2013 Fourteen International Conference on Advances and Trends in Engineering Materials and their Applications (Toronto, Canada: August 05 09, 2013) Dynamic Behavior of Black Cotton Soil Stabilized with Enzyme Dr. I.R. Mithanthaya 1* Dr. A.U. Ravi Shankar 2, Dr. N. Bhavanishankar R 3 1 Professor, Dept. of civil Engineering, NMAMIT, Nitte, Karkala-574110, India (E-mail: mith9999@yahoo.com) 2 Professor, Dept. of Civil Engineering, NITK, Surathkal,, Mangalore 575 025,India (E-mail: aurshankar@yahoo.com) 3 Professor, Dept. of civil Engineering, NMAMIT, Nitte, Karkala-574110,India (E-mail: raonbs@yahoo.co.in) Abstract The Black Cotton (BC) soil is abundantly available in North Karnataka (India).To improve its properties the soil has to be stabilized either mechanically or chemically to improve the geotechnical properties of such type of soils. Enzyme soil stabilization is one of the methods of soil stabilization. Various experimental investigations have shown that there is much improvement in Atterberg limits, CBR and UCS strength when stabilized with Enzyme.In recent past many Enzymes have come to the market which can be used as Stabilizing agent. One such stabilizing agent (Product A )is used in the present investigation to improve the soil properties for using it as sub base material in the pavement. The effect of enzyme on black cotton soil in terms of Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), Compaction and permeability have been studied. It has been observed that the enzyme treated soil showed significant improvement in terms of UCS, CBR with longer curing period. Since the CBR test results show that the increase in CBR value is more than 100%, fatigue behavior of enzyme stabilized soil also has been studied to find stress variation for repeated load condition. The experimental investigation shows much improvement in its fatigue behavior for BC soil.suitability of this stabilized soil as sub base material for the flexible pavement design has been
investigated. Keywords: Enzyme, California Bearing Ratio, Fatigue life, Unconfined Compressive Strength (UCS) Maximum dry density (MDD), Optimum moisture content (OMC) 1. Introduction Engineers are often faced with the problem of constructing on soils, which do not possess sufficient strength to support the loads imposed upon them either during construction or during the service life of the structure. In many parts of India, soils consist of high silt contents, low strengths and minimal bearing capacity. The performance characteristics of soils are generally attributed to the nature and quantity of the fines present in the material. For better performance of structures built on such soils, the performance characteristics of such soils need to be improved. The poor engineering performance of these soils has forced engineers to attempt to improve their engineering properties of such soils. There are various methods that could be used to improve their performance. These methods range from replacing with a good quality soil to methods that involve complex chemical stabilization. The choice of a particular method depends mainly on the type of soil to be improved, its characteristics and the type and degree of improvement desired in a particular application. Stabilization of soils is an effective method of improving their properties. The objectives of any stabilization technique with respect to road engineering are to increase the strength and stiffness of soil, improve workability and constructability of the soil and reduce its Plasticity Index. For any given soil a stabilization method, using suitable stabilizing agents, may be more cost effective rather than removing and replacing the whole material. Availability or financial considerations may be the determining factor on which a stabilizing agent is selected. Soil improvement by mechanical or chemical means is widely adopted. In order to stabilize soils for improving strength and compressibility, a number of chemical additives, both inorganic and organic, have also been used. Recently enzymes have emerged as a new chemical for soil stabilization. Enzymes are organic, and liquid concentrated substances which are used to improve the geotechnical properties of soil. Due to variation in clay content the black cotton soil abundantly available in North Karnataka region does not satisfy the requirements of soil (Liquid Limit 25% and Plasticity Index 6%) to be used for construction purpose. An attempt has been in this investigation to find the improvement in its geotechnical properties and also its fatigue behavior when stabilized with enzyme. 2.0 Literature review A comprehensive study of the enzyme soil stabilizer product and its effectiveness on sub-base and sub-grade soils was conducted by Lacuoture and Gonzalez (1995). 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. The Palm Oil Research Institute of Malaysia conducted field studies on improvement on plantation roads. Enzyme was used to treat 27.2 km of the road, which was having serious problems during the monsoon season or after heavy downpour. 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 continued exposure to heavy rainfall. No surface damage was observed, thus requiring no repair works to the road section. Enzyme stabilization can convert the road to an all weather road that has minimum destruction in hot and wet season (Brazetti et.al & Murphy et.al, 2000). The field experiments were conducted in Brazil to study the use of enzyme as the enzyme stabilizer for road construction on selected soils namely sandy clay, silty clay, sandy silt, plastic and non-plastic clay, sandy loam, loam mixed with clay, soil mixtures with pieces of recycled pavement. The field stretches were periodically tested using DCP (Dynamic Cone Penetrometer) equipment. After the evaluation it was concluded that the enzyme stabilization is a good technique for the effective and economic solution for pavement construction. The effectiveness of enzyme treatment was evaluated on the basis of statistical measurement of change in CBR, Shear strength, soil stiffness and soil modulus (Andrew et.al, 2003). A comprehensive study of one type of commercially available enzyme and its effectiveness on clay type soil collected from Kerala. The results of tests on the soils treated with the enzyme was observed and recorded and compared with test results on the untreated samples for the period of 8 weeks ( Isaac et. al, 2003). It was found that in all soil types considered, the CBR value has increased by addition of enzyme, which proved its suitability as a stabilizing agent. The increase in CBR was of the order of 136 to 180 times that of the original value. Enzyme is useful for clay soil and had increased in CBR by 700%. An experimental investigation was conducted to assess the suitability of enzyme as soil stabilizer on five types of soils with low clay content to very high clay content. Laboratory tests were conducted to determine the engineering properties of soil and strength characteristics of soil with and without stabilization using enzyme.
In the cases of highly clay soils, the effect of stabilization improved the CBR and unconfined compression strength (Manoj et. al, 2003).A study has been conducted and concluded that the enzymes require some clay content in the aggregate material in order to create the reaction that will strengthen the material. The successful enzyme stabilization could be achieved with as little as 2% clay in the aggregate material but best result seems to be achieved with 10 to 25% clay. It was reported that after one week, two week, three week, and 14 week periods CBR of the treated soil was found as 37%, 62%, 66% and 100% respectively where as it was 28% for untreated soil ( Bergmann et. al, 2000). Repeated load test was conducted on a sub base soil subjected to 1,000 to 100,000 repetitions, to verify the general trend of deformation. The effect of various factors including moisture content, density, deviator stress, confining pressure, load frequency, freeze and age were investigated to determine their individual contributions to deformation accumulation. Test results also suggest that main contributors to the accumulation of permanent deformation are moisture content, deviator stress (Qiu et. Al. (1999).Moishmith et. al, (1975) found that permanent deformation and log of the number of load applications have a linear relationship e p = AN b where e p is permanent plastic deformation, N is number of load repetitions and A & b are material parameters (Regression coefficients). This equation is widely accepted in practice, especially for cohesive subgrade soils. Improved method of analysis for pavements with stabilized layers has been suggested by Lutfi Raad et.al, (2000). The method incorporates the bimodular properties (i.e., tensile modulus different from compressive modulus) of the stabilized layers and the stress dependent behavior of granular and subgrade soils. This method was used to predict stresses, resilient strains, and deformations using a finite element representation of pavement structures. The method also was used to study the behavior of cement and lime stabilized layers under repeated loads. 4.0 Experimental Investigation To assess the suitability of enzyme as soil stabilizer for black Cotton soil, laboratory tests were conducted to determine the geotechnical properties and strength characteristics of black cotton soil with and without adding enzyme. The black cotton soil samples considered for study were first tested for Index and compaction
properties immediately after mixing and samples were then tested for CBR and Unconfined Compressive Strength (UCS), with stabilization and without stabilization for a curing period of 0 week, 1 week, 2 weeks, 3 weeks, 4 weeks 6 weeks and 8 weeks. All the tests were performed as per relevant I.S. Codes. 4.1 Materials Used & Tests Conducted The materials used for the tests include the black cotton soil, and enzyme. The black cotton soil obtained from field was tested in the laboratory for evaluating the properties like specific gravity, grain size distribution, consistency limits, CBR, compaction characteristics unconfined compression strength and permeability. The results are tabulated in Table 1. All the tests were performed as per relevant IS codes. Sl. No. Table 1 Geotechnical Properties of Virgin soil Property 1 Specific gravity 2.45 Value 2. Grain Size distribution Gravel (%) 2.57 Sand (%) 11.91 Silt (%) 42.42 Clay( %) 38.56 3. Consistency limits Liquid Limit (%) 68.00 Plastic Limit (%) 41.62 Plasticity Index (%) 26.00 4. IS Soil Classification MH 5. Engineering Properties IS Standard Compaction Max dry density, γ dmax (kn/m 3 ) 17.0 OMC (%) 18.0 IS Modified Compaction Max dry density, γ dmax (kn/m 3 ) 17.5 OMC (%) 16.0 6. CBR, % IS Light Compaction (at OMC) 16.0 7. IS Light Compaction (Soaked) 1.0 IS Modified Compaction(at OMC) 22.0 IS Modified Compaction (Soaked) 2.0 Unconfined Compressive strength a) IS Light Compaction (kn/m 2 ) 189 b) IS Modified Compaction (kn/m 2 ) 242
Table 1 indicate that more than 50 percent of soil is retained on 75 micron I.S. sieve and therefore grouped under coarse grained soil as per I.S. classification. Further the test results indicate that the value of liquid limit is 68 per cent and plasticity index is 26 per cent. These results indicate that the soil is of low compressibility and it is classified as silty sand with clay content of 38%. Under standard and modified compaction the MDD was found to be 17.0 kn/m 2 and 17.5 kn/m 2 respectively and OMC was found to be 18 % and 16.0 % respectively. The CBR values of black cotton soil at OMC for standard and modified compaction was found to be 16 % and 22 % respectively and at soaked condition it was found to be 1 % and 2 % respectively. For standard and modified compaction the unconfined UCS of black cotton soil was found to be 189 kn/m 2 and 242 kn/m 2 respectively. which also depends upon per/m 3 of soil. In the present experimental investigation four dosages were considered to study the variation in geotechnical properties of the black cotton soil ( see Appendix 1) 4.3 Consistency Limits Liquid limit and plastic limit of soil mixed with different dosage of enzyme were determined immediately after mixing. The results are shown in table 2 Table 2 Consistency Limits of treated soil Dosage of Enzyme Black cotton soil LL (%) PL (%) PI 0 68.00 41.62 26.00 1 61.32 42.59 19.00 2 59.49 44.70 15.00 3 57.71 45.95 12.00 4 55.73 46.73 10.00 4.2 Description of the enzyme used The commercially available enzyme is used in this study. This product is an organic nonbiological enzyme formulations supplied as liquid. Enzymes are natural organic compounds which act as catalysts. Their large molecular structures have active sites, which assist bonding and interactions. Most of the research studies carried out been done based on the dosage recommended by the suppliers. Sunil Bose, et.al, (2003) used the optimum dosage of enzyme based on optimum CBR value of treated soil 4.4 Compaction Tests Light and Modified Compaction tests were conducted according to relevant IS codes (IS: 2720(Part8)-1980) to evaluate Maximum dry density (MDD) and Optimum Moisture Content (OMC) immediately after mixing and the results are tabulated in Table 3. Table 3 Compaction test results
Curing Period (week) First A. Author, Second A. Author, Third A, Author Dosag e of Enzy me Modified Compaction MDD OM (gm/c C m 3 ) (%) Standard Compaction MDD OM (gm/cm 3 C ) (%) 0 1.75 18.00 1.70 18.0 1 1.95 14.13 1.66 17.34 2 2.06 12.91 1.75 13.40 3 1.91 14.72 1.69 15.33 prepared and kept in desicator to retain moisture of the sample so that reaction between soil particle and enzyme may be continued. The test results are tabulated in Table 4 and it is clear from the table that, UCS strength for dosage 2 is optimum and further increase in dosage decreases the UCS value. Hence CBR test has been conducted for this optimum dosage only. Table 4 UCS Values for soil treated with enzyme 4 1.90 15.25 1.70 24.20 4.5 Unconfined Compressive Strength Tests Enzym e dosage 1 (MDD =1.95 gm/cc) (OMC =14.13 %) Enzyme dosage 2 (MDD=2.0 6 gm/cc) (OMC=12. 91%) UCS(kN/ m 2 ) Enzym e dosage 3 (MDD= 1.91 gm/cc) (OMC= 14.72% ) Untrea ted:242 Enzyme dosage 4 (MDD=1. 90 gm/cc) (OMC=1 5.25%) 0 251 296 255 220 1 292 376 272 245 2 342 412 293 288 3 355 488 310 302 4 452 565 322 342 6 523 654 407 398 8 589 756 512 495 4.6 California Bearing Ratio Test The test was conducted at both unsoaked and soaked condition for standard and modified compaction (IS2720(PART16)-1979). Unsoaked and soaked CBR test results for the original soil samples are tabulated in Table 1 and from the unconfined test result it is found that enzyme dosage 2 is optimum for black cotton soil. The CBR tests were conducted with enzyme dosage 2 for the curing period of zero, one, two, three, four, six and eight weeks. Unsoaked and soaked CBR test results are tabulated in Table 5 and the variatio variation of CBR results for different curing periods are graphically presented in Fig 1. Table: 5 Unsoaked and Soaked CBR test results on treated soil Unconfined compressive (UCS) strength of black cotton soil stabilized with different dosages of enzyme for one, two, three four and eight curing weeks were evaluated. The specimens were
Curing Period (week) Black cotton soil MDD = 2.06 gm/cc OMC = 12.91 % Unsoaked CBR (%) Soaked CBR (%) 0 23.60 4.00 1 33.00 5.00 2 46.65 6.30 4 75.00 9.60 6 86.50 11.60 8 95.60 11.50 Fatigue life of a specimen is defined as the total number of load repetitions that can be sustained by the specimen just prior to its failure, under a specified loading, frequency and stress level. To investigate the performance of enzyme stabilized soil under fatigue, the enzyme stabilized specimens were exposed to the repeated loading in the laboratory. For this purpose the laboratory experiments were conducted in a fatigue testing apparatus and the specimens were subjected to many numbers of repeated loads. Cylindrical specimen with 3.8 mm diameter and 7.6 mm height is used for testing. 5.2 Effect of Enzyme Content on Fatigue Life Fig.1 Variation of CBR 5.0 Fatigue analysis The unconfined compression test results indicate that the increase in UCS value and it is more than 200% as compared to untreated soil. Also there is considerable increase in CBR value from 2% to 12%, the fatigue behavior of stabilized soil also studied. Fatigue tests have been conducted on soil samples with different dosages of enzyme to determine its response for repeated loading condition. The fatigue tests were conducted at frequency of 2 Hz on stabilized soils at various stress levels. The soil samples are treated with different dosage of enzyme viz 1, 2, 3 & 4 were tested. 5.3 Effect of curing period on fatigue life To bring out the effect of curing period on the fatigue life of enzyme stabilized soil, experiments were carried out on stabilized soil samples cured for different time periods. The results of the experiments are plotted as curing period v/s fatigue life. 5.4 Effect of Stress Level on the Fatigue Limit 5.1 Laboratory Fatigue Testing The Fig. 4 presents the effect of stress level on
fatigue life of enzyme stabilized soil specimens. The stress level is started from 30% of UCC strength and extended up to a loading amplitude of 80% beyond which the fatigue life of the stabilized specimens were negligibly small. It is observed in Fig. 4 that at lower stress level of 30% the specimens exhibit a high fatigue limit of more than 15,000 loading cycles and with further increase in stress level, the fatigue life of stabilized specimen reduces considerably in a exponential manner and beyond about 80% stress level, the increase in fatigue life is small. Further, it is observed that the fatigue life at any stress level increases as the curing period increases. 6.0 Chemical analysis The soil stabilizer was first tested to determine their chemical composition and mode of action indicates that it contains high concentrations of sodium and silicon, which suggests that it acts like cement by forming hydrated calcium silicate when added to soil. The enzyme also contains a high concentration of protein, and appears to contain active enzymes based on standard enzymatic activity test. 7.0 Correlation between fatigue life and unconfined compressive strength Considering the different stress level, UCS for different curing period and the corresponding fatigue life the correlation between the fatigue life v/s UCS strength the equation has been generated for black cotton soil. This equation has been generated for stress levels 30% to 80% and it is found that the correction coefficient (R value) varies in between 0.84 to 0.86. Stress level 30% 40% 50% 60% 80% 9.0 Conclusions For 4% enzyme Black cotton soil Correlation equation Fatigue=287.8 UCS Based on the tests conducted and the analysis of test results, the following conclusions are drawn which are applicable only to materials used and test conditions adapted in the study. R² value + 6182 0.85 Fatigue=214.8 UCS + 3425 0.85 Fatigue=170.8 UCS - 278.7 0.86 Fatigue=126.6 UCS - 119.2 0.84 Fatigue=92.68 UCS - 3157 0.85
1. Enzyme stabilization has shown marginal improvement in some engineering properties of black cotton soil such as specific gravity, consistency limits. This may be due to chemical constituent of the soil which has low reactivity with enzyme. 2. Unconfined compressive strength increases with the increase in dosage of enzyme and at optimum dosage ie, at dosage 2 the increase in UCS value is more than 250% as compared to untreated soil 3. CBR test results indicate that at enzyme dosage 2, the increase in CBR value is 6 times that of original soil. 4. The fatigue limit of the stabilized soil initially increases up to dosage 2 and further increase in enzyme dosage, decreases the fatigue life of the stabilized soil. 5. The fatigue limit of stabilized soil increases as the stress level decreases 6. Regression analysis results indicate that the unconfined compressive strength and fatigue life of stabilized soil specimen mainly depend upon the enzyme dosage, curing period and stress level. The fatigue limit of the stabilized soil increases initially with curing period up to 4 weeks. With further increase in curing period there will be no change or marginal change in the fatigue life. References 1. Dhinakaran, C. and Prasanna K.R. (2007): Bioenzyme soil stabilization in road construction, Everyman s Science, Vol.XLI No.6, pp.397-40. 2. Andromalos, K.B., Hegazy,Y.A. and Jasperse, B. H. (2000): Stabilization of Soils by Soil Mixing, Proceedings, International Conference on Soft Ground Technology, ASCE, Noorwijkerhout, Netherlands, pp, 194-205. 3. Gireesh, B.G. (2008): study on geotechnical properties of laterite and black cotton soils with Bioenzyme as a stabilizer, M.Tech. Thesis, National Institute of Technology, Srinivasanagar, Karantaka, India. 4. Hitam, A. and Yusof, A. (1998): Soil stabilizers for plantation road, Proceedings, National seminar on Mechanisation in Oil Palm Plantation,, Selangor, Malaysia, pp.124-138 5. Manoj, Sunil, B. and Sikdar, P.K.(2003): Bio-Enzyme for stabilization of soil in Road construction a cost effective approach, Proceedings, Indian Roads Congress seminar on integrated Development of Rural and Arterial Road Networks for Socio-
Economic development, New Delhi,India,pp.123-136. 6. Isaac, K. P., Biju and Veerararagavan, A. (2003): Soil stabilization using Bio-Enzyme for Rural Roads Proceedings, Indian Roads Congress seminar on Integrated Development of Rural and Arterial Road Networks for Socio- Economic development, New Delhi,India,pp-98-123.