A composition and a sustainable method thereof for achieving a significant improvement in unconfined compressive strength and shear strength of clayey soil

Abstract

A composition and a sustainable method thereof for achieving a significant improvement in unconfined compressive strength and shear strength of clayey soil The present invention relates to the field of strengthening of clayey soil in hilly areas for achieving better quality of construction. The invention provides a composition for achieving a significant improvement in unconfined compressive strength and shear strength of clayey soil present naturally in hilly areas, comprising 1% nano lime and 1% recycled 5mm strips of polyethylene terephthalate recycled from PET bottles added to clayey soil with 28 days of curing, characterised by an increase in unconfined compressive strength by up to 454%. A sustainable method (200) of treatment of the soil is also provided. The invention is applicable in construction of roads and buildings. Ref Fig 9B

Description

FIELD OF THE INVENTIONThe present invention relates to a composition of materials added to clayey soil toimprove its strength. More particularly, the invention relates to a composition of nanolimeand recycled PET strips from plastic bottles, to increase the unconfined compressivestrength and shear strength of clayey soil.BACKGROUND OF THE INVENTION AND THE RELATED PRIOR ARTClayey soil exhibits properties that render any construction weak. To work on theenhancement of its properties, experiments were conducted.The effect of nano-materials and biopolymer on the engineering properties of the soilwith different additives like biopolymer, nano-lime, nano-silica, nano-silica andbiopolymer were investigated and comparative result was concluded with thenanomaterials and the other additives (Firmansyah et al. ,2024).The lime stabilization for low-plastic clay subgrade soil have been studied in the past.The findings include a decrease in plasticity index, with the liquid limit and the plasticlimit, the maximum dry density (MDD), while the optimum moisture content (OMC)increases due to the flocculation of soil particles (Utami, 2014).In the past, some attempts have been made in this direction and the same are providedhere as prior art:CN Appl. No 201811478336.3 published 14 / 5 / 2019Carbon nano tube building filler and using method thereofThe invention discloses carbon nano tube building filler and a using method thereof, andbelongs to the technical field of building filler. The carbon nano tube building fillercomprises the following compositions: clayey soil, quick lime, granite crushed stone,coarse sand, gravelly soil, gravel soil, cobbly soil, clay, fine sand and carbon nano mixingballs. The using method thereof comprises the following steps: washing crushed stoneimpurities, heating and pre-treating crushed stones, grinding and dispersing the crushedstones, mixing the stones, adding a filler auxiliary, and filling by the building filler.Multiple components in the building filler can be bonded and fixed, filling characterchange of the filler caused by different characters of shearing strength, compressivedeformation and compatibility and the like of forming components in the filler is reduced,and the shearing strength and compressive deformation resistance of the buildings arereinforced, thereby a building potential safety hazard caused by an external environmentchange is reduced.The inventors in the above-mentioned application have used carbon nano tubes primarilyas building fillers. There is no use of nano-lime or PET material.The problem:In geotechnical practice, clay soil is considered as a problematic soil due to its low shearstrength capacity. It is known to undergo significant volumetric changes due to its shrinkswell-behavior, thus making it highly compressible. Due to the small particle size andhighly cohesive nature, clay soil has poor drainage which often leads to water-loggingand furthermore to weakening of foundations.Roads built in hilly areas are based on natural clayey soil which is weak in unconfinedcompressive strength and shear strength, and displays swelling properties.The weak soil poses significant challenges due to its susceptibility to landslides and poorstructural integrity. This leads to early failures on the roads.Whereas, researchers have conducted studies in the past with different additives, but theproblem has not been fully mitigated.The present invention solves the problem by enhancing the unconfined compressivestrength and shear strength of the clayey soil, besides reducing the swelling.SUMMARY OF THE INVENTIONThe present invention pertains to a composition of nano-lime and recycled Polyethyleneterepthalate (PET) strips and a sustainable method of addition thereof for achieving asignificant improvement in unconfined compressive strength and shear strength of clayeysoil with applications in road building and construction in hilly regions. A compositionof 1% Nano Lime with 1% of 5mm of recycled Polyethylene terephthalate (PET) resultsin 454% increase in the Unconfined Compressive Strength (UCS) value of clayey soil.The roads built on the said treated clayey soil last longer without much deformation.OBJECTS OF THE INVENTIONThe primary object of this invention is to provide a composition of nano-lime and PETstrips to be added to clayey soil so as to improve its strength.Another object of the invention is to provide a method of the addition for a high efficacyof the mixture.BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS AND TABLESFigure 1: Illustrates variation of stress strain curve in UCS test of soil+1%NL+0.5%10mm WP at different curing daysFigure 2A: Illustrates variation of stress strain curve in UCS test of soil+1%NL atdifferent curing daysFigure 2B: Illustrates variation of stress strain curve in UCS test of soil+2%NL atdifferent curing daysFigure 3A: Illustrates variation of stress strain curve in UCS test of soil + nano-lime for0,7,14 and 28 days of curingFigure 3B: Illustrates variation of stress strain curve in UCS test with soil+0.25% 5mmWP at different curing daysFigure 4A: Illustrates variation of stress strain curve in UCS test of soil+0.5% 5mm WPat different curing daysFigure 4B: Illustrates variation of stress strain curve in UCS test of soil+1.0% 5mm WPat different curing daysFigure 5A: Illustrates variation of stress strain curve in UCS test of soil+0.25% 10mmWP at different curing daysFigure 5B: Illustrates variation of stress strain curve in UCS test of soil+0.5% 10mmWP at different curing daysFigure 6A: Illustrates variation of stress strain curve in UCS test of soil+1.0% 10mmWP at different curing daysFigure 6B: Illustrates UCS value of soil + waste plastic strips for 0,7,14 and 28 days ofcuringFigure 7A: Illustrates variation of stress strain curve in UCS test of soil+1%NL+0.25%5mm WP at different curing daysFigure 7B: Illustrates variation of stress strain curve in UCS test of soil+1%NL+0.5%5mm WP at different curing daysFigure 8A: Illustrates variation of stress strain curve in UCS test of soil+1%NL+1.0%5mm WP at different curing daysFigure 8B: Illustrates variation of stress strain curve in UCS test of soil+1%NL+0.25%10mm WP at different curing daysFigure 9A: Illustrates variation of stress strain curve in UCS test of soil+1%NL+1.0%10mm WP at different curing daysFigure 9B: Illustrates UCS value of soil + 1%NL+ waste plastic strips for 0,7,14 and 28days of curingFigure 10: Illustrates UCS value of soil + 2%NL+ waste plastic strips for 0,7,14 and 28days of curingFigure 11: illustrates A method of addition of Nano Lime and Recycled Plastic strips ofpolyethyleneTable 1: Illustrates UCS of soil, soil-nano-lime for different curing daysTable 2: Illustrates UCS of soil- WP mixture for different curing daysTable 3: Illustrates UCS of soil-nano-lime-waste plastic strips mixture for differentcuring daysDETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THEACCOMPANYING DRAWINGSFor the purpose of promoting an understanding of the principles of the present disclosure,reference will now be made to the various embodiments and specific language will beused to describe the same. It will nevertheless be understood that no limitation of thescope of the present disclosure is thereby intended, such alterations and furthermodifications in the illustrated system, and such further applications of the principles ofthe present disclosure as illustrated therein being contemplated as would normally occurto one skilled in the art to which the present disclosure relates.It will be understood by those skilled in the art that the foregoing general descriptionand the following detailed description are explanatory of the present disclosure and arenot intended to be restrictive thereof.Unconfined compressive strength tests were conducted by the inventors to analyse theimpact of nano-lime (NL) and waste (recycled) plastic strips (WP) on the shear strengthof clay soil. Addition of nano-lime, plastic strips, and a combination of both increasedthe UCS value. The parent soil was amended with nano-lime (1% and 2%) and wasteplastic strips (0.25%, 0.5% and 1%). Two aspect ratios were considered for the plasticstrips (5mm x 2.5mm, and 10mm x 2.5mm). The effect of the addition of nano-lime andwaste plastic strips in different proportions was observed by conducting UCS test. Asignificant enhancement in the soil's strength characteristics was observed with theincorporation of 1%NL and 1% 5mmWP. This combination resulted in a remarkable454% increase in the Unconfined Compressive Strength (UCS) value. The substantialimprovement in the strength characteristics demonstrates the suitability of these additivesfor use as a subgrade layer in heavily trafficked roads, meeting relevant engineeringstandards.Nano-lime contributed to strength gain through pozzolanic reactions, formingcementitious compounds that bind soil particles together. Waste plastic strips enhancedstrength by acting as reinforcement, increasing internal friction, and improving loaddistribution within the soil. It enhances the flocculation of the soil matrix producing adenser and stronger structure. While plastic strips provided mechanical reinforcement tothe soil which improved the tensile strength of the soil sample. With the combination ofboth the additives, clay soil was able to improve its compressive as well as tensilestrength effectively. In the initial test, the combination of nano-lime and waste plasticstrips resulted in a synergistic effect, further increasing the UCS of the soil, indicatingthat the chemical and mechanical stabilization mechanisms complement each other toachieve greater strength enhancement.The optimum results of the soil mixed with nano lime and plastic strips were obtainedfor the soil sample mixed with 1% nano-lime and 1% plastic strips of dimension 5mm x2.5mm.- Smaller strips gave better results compared to larger strips because of the weakshear planes produced by the larger strips, which resulted in uneven stressdistribution.The invention pertains to a composition and a sustainable method of soil improvementusing nano materials and at the same time utilizing the waste plastic bottles in increasingthe soil strength. Overall, the results suggest that higher nano-lime content combinedwith an optimal percentage of plastic strips improves the strength properties of the soilby enhancing particle bonding and ductility. These findings support the use of nano-limeand plastic reinforcement in construction applications to improve soil stability,durability, and load-bearing capacity.a) Experimental setupb) Mission: the properties of clayey soil that can be enhanced by the use of nanolimeand plastic wastes by Unconfined Compressive Strength test. The weak soilposes significant challenges due to its susceptibility to landslides and poorstructural integrity. By leveraging the sustainable method of aims to enhance thesoil's compressive strength, thus contributing to safer and more stable soilstructures. The test series involved soil, nano-lime, waste plastic strips (PET)blends with different proportion mix of lime (1% and 2%) with the waste plastic(PET) bottle strips (0.25%,0.5% and 1%) of dimensions: 5mm x 2.5mm and10mm x 2.5mm.c) The study also aims to explore the individual effects of addition of differentproportions of nano-lime and waste plastic strips to be used for the stabilisationof clayey soil. The nano-lime taken as 1% and 2%, and waste polyethyleneterephthalate plastics strips as 0.25%,0.5% and 1% with the soil. The mixproportions were tested for their unconfined compressive strength test at differentcuring days of 0, 7, 14 and 28 days. The effect of short-term and long-term wasaimed to be observed.UCS tests were carried out for various mix proportions across different test series. Theinitial series involved soil, nano-lime, waste plastic strips blends. The waste plastic stripstaken were of dimensions: 5mm x 2.5mm and 10mm x 2.5mm. Following that, the secondseries comprised of soil-nano-lime- waste plastic strips combinations. The primary aimbehind the inclusion of small additive percentages was to evaluate its impact on thecompressive strength properties of the mixes. The tests were done for differentcombinations of mixes of soil (S) with nano lime (NL) and waste plastic (WS). The mixinclude S+1%NL and S+2%NL in the first set of experiment, S+0.25%WP, S+0.5%WPand S+1%WP for the second set of experiment, S+1%NL+0.25%WP,S+1%NL+0.5%WP, S+1%NL+1%WP, S+2%NL+0.25%WP and S+2%NL+0.5%WPfor the combined effect.(b) Results and analysesClay soil amended with nano-limeThe UCS was initially conducted for the parent soil after the compaction test as per theprocedures given in IS: 2720 Part X-1991. The dry soil sample was passed through 425-micron sieve and mixed with the optimum amount of water content. The soil mixturewas then filled into the mould and compacted. Samples were made for 0,7,14, and 28days curing. The samples were then tested according to the curing days and the maximumshear strength of the samples were noted. The same procedure was done for a mixture ofsoil and nano-lime, where the nano-lime was amended in percentages of 1.0%, and 2%.The results obtained from the unconfined compression tests are given in Table 1. Theresults shows that there is increase in strength of soil when the nano lime is mixed withthe soil. It increases from 130 kPa to 297 kPa for 0 days while it increases to 566 kPa for28 days curing with the maximum strength in 2% nano lime mix.Figure1. illustrates the stress strain curve from the UCS test when 1% nano-lime wasadded to the soil samples cured for 0, 7, 14, and 28 days. As the curing period increased,the strength of the soil also improved, reaching a maximum of 533 kPa after 28 days.The highest UCS value was recorded for the soil mixed with 2.0% nano-lime and curedfor 28 days, reaching 566 kPa shown in figure 2. This represents an increase of 310% instrength compared to the parent soil sample cured for the same duration. Figure 3 showsthe comparative values of UCS obtained for all the mixes after specific curing period.With increasing curing period, the UCS value also tends to increase. This is because ofthe moisture redistribution and gradual settlement of the soil sample. In the presence ofsoil stabilisers, increasing curing period enhances the bonding and interaction betweenthe soil and additives, thus improving the physical and chemical processes. Whenamended with nano-lime, there is a significant increase in UCS value. This is becausenano-lime particles have higher ability to flocculate and agglomerate the soil matrix dueto its small particle size (Govindasamy et al., 2017). This improves particle bonding, fillsvoids, and reduces porosity, resulting in a denser and stronger soil structure. As a result,the soil's load-bearing capacity improves, leading to higher UCS values.Clay soil amended with waste plastic strips (PET)The tests for soil and waste plastic strips mixtures were also done in a similar way as perthe procedures given in IS: 2720 Part X-1991. The plastic strips used were of 5mm X2.5mm and 10mm X 2.5mm and were amended with the soil in percentages of 0.25%,0.5% and 1%. The soil samples were then cured for 0, 7, 14 and 28 days. The resultsobtained from the UCS test are as shown in Table 2The UCS results show that the unconfined compressive strength values increase with theaddition of waste plastic strips. The optimum value of the UCS was obtained as 151kPafor the mix of soil and 1.0% 5mm plastic strips which marks a net increase of 10%. Theincrement observed in 5mm plastic strips is more than the increment observed in 10mmplastic strips. This is because larger strips result in broad, unconsolidated weak shearplanes (Kassa et al., 2020). Thus, it can be seen that size is an important factor for shearstrength.The increase in UCS values can be attributed to the property of the plastic strips to act asreinforcement within the soil. Soil is brittle in nature. When plastic strips are mixed withthe soil, it promotes ductile behaviour (Vismaya et al., 2016). The reinforcementprovided by the strips distributes the applied load more evenly, resist deformation, andrestrict the movement of soil particles under stress. This reinforcement effect improvesthe ductility and tensile resistance of the soil, reducing crack formation and enhancingoverall strength. As a result, the soil can bear more load before failure, leading to anincrease in UCS.Clay soil amended with nano-lime and waste plastic strips (PET)After the soil was mixed with nano-lime and waste plastic strips separately, the sampleswere made for both the additives mixed together with the soil. Both the additives hadthree percentage mixture so the total combination was 9 mixtures. The experiments wereconducted as per the procedures given in IS: 2720 Part X-1991. The UCS results obtainedfor the mixes are shown in Table 3.For the first set, the nano-lime content was kept constant as 1.0% and the samples weretested with varying plastic strips content. The strips with dimensions with 5mm x 2.5mmdimensions were used first and then 10mm x 2.5mm dimensions plastic strips were used.The UCS values for the mix S+1.0%NL+0.25% 5mm WP can be seen for different curingdays. The value increased from 305 kPa with 4.0% strain to 561 kPa with 4.9% strainwhen kept in curing for 28 days, which is a net gain in strength of 307%. This shows thatcuring promotes proper moisture redistribution which is crucial for increasing UCSvalue. While it is seen that for 1% nano-lime and 0.5% 5mm WP, the UCS valuedecreased from 584 kPa with 4.5% strain to 491 kPa with 5.1% strain from 7h day to 28thday of curing. This can be attributed to the unconfined condition during the testing whichcauses the soil to slip along the plastic strips due to increasing compressive strain(Saravanan et al., 2020). Also, the increased interaction between the plastic strips becauseof more overlapping of plastic results in a reduction of soil plastic interaction (Vismayaet al., 2016). This leads to a reduction in UCS value. However, when the soil was mixedwith 1.0% NL and 1.0% 5mm WP, a gradual increment in the strength can be witnessedfrom 344 kPa in 0 days to 764 kPa in 28 days with a strain of 5.6%. This mixture had thehighest strength gain of 454% compared with the parent soil. This is because nano-limeenhances bonding between soil particles, while plastic strips provide tensile strength andprevent sudden failure. Together, they produce a denser, more cohesive and reinforcedsoil matrix.For the second set, nano-lime content was taken to be 2.0% and the plastic strips weretaken as varying quantities. As earlier, 5mm strips were tested first and then 10mm strips.The result exhibited an increase in UCS values with increasing curing period with a gainof 79.8% and 69.2% respectively. Increasing and decreasing pattern which can be due tothe overlapping of plastic strips and slippage of soil over the strips. For the case of 10mm,all the mixes displayed an incremental behaviour. When nano-lime comes in contact withwater, it leads to pozzolanic reactions which helps to produce cementitious compoundswhich act as binding gels. This decreases the porosity by filling up the micro-pores aswell as nano-lime. This attribute helps to enhance the compressive strength of the soilsample. The plastic strips in the soil sample act as reinforcement in the soil which helpsto increase the resistance of the soil to the applied forces. This enhanced the ductility ofthe soil and subsequently increase its tensile stiffness. Comparing the results obtained forboth 5mm and 10mm, it can be stated that smaller strip content and size produces moreUCS value, thus making them crucial factors for maximum strength gain. The maximumstrength gain was witnessed for soil mixed with 2% NL and 0.5% 5mm WP, a gradualincrement from 394 kPa in 0 days to 718 kPa in 28 days of curing showing an increaseof 420%.From the above test, it was seen that with addition of the nano lime and waste plastic incombination increases the strength of the soil and the optimum mix is obtained at the mixof S+1.0%NL+1.0% 5mm WP where the gain in strength is around 454% that of parentsoil.Table 1. UCS of soil, soil-nano-lime for different curing daysTable 2. UCS of soil- WP mixture for different curing daysTable 3. UCS of soil-nano-lime-waste plastic strips mixture for different curing daysConclusion:Key findings include:i. Unconfined Compressive Strength (UCS) Improvement: The UCS of the soiltreated with nano lime and waste plastic strips increases and is effective for soilstabilisation.ii. Effect of nano lime: With the addition of nano lime, the UCS increases up to310% compared to untreated soil, using 2% nano lime at 28 days of curing.iii. Effect of WP Addition: With the addition of waste plastic strips, the UCS valuesaw a maximum increase of around 9% with 1% 5mmWP at 28 days of curing.iv. Optimal Conditions: The best performance was observed S+1.0%NL+1.0%5mm WP at 28 days of curing with an increase in 454% with respect to the parentsoil.USE CASES:Construction of roads and buildings in hilly regions

Claims

1. A composition for achieving a significant improvement in unconfined compressive strength and shear strength of clayey soil present naturally in hilly areas, comprising: 1% nano lime and 1% 5mm strips of polyethylene terephthalate recycled from PET bottles added to clayey soil with 28 days of curing, characterised by an increase in unconfined compressive strength by up to 454%2. A method (200) of addition of Nano Lime and Recycled Plastic strips of polyethylene terephthalate for significant enhancement of strength of clayey soil, the method involving steps: (201): measure and identify the area and depth of clayey soil to be treated, calculate the volume; (202): sprinkle 1% by weight of nano lime across the area chosen; (203): distribute 1% by weight of 5mm strips of polyethylene terephthalate across the area chosen; (204): spray the optimum water over the area chosen and allow curing for 28 days; (205): The clayey soil is ready for use for construction.