Experimental investigation on soil stabilization technique by adding nano-aluminium oxide additive in clay soil

ABSTRACT In this research article, soil stabilisation is carried out by the latest method: nanotechnology. The stabilizer nano-aluminum oxide is used as a stabilising agent in concentrations of 0.2%, 0.4%, 0.6%, 0.8%, 1%, and 1.2%. Because it is 99% pure and nanoscale, it has a large surface area for analysing the properties and strength of soil tests such as Atterberg's limit, pycnometer, proctor compaction test, California bearing ratio test, and unconfined compressive strength. These tests are done for parent soil and soil with different percentages of nanomaterials. The nanostabilizer addition increases the unconfined compressive strength, California bearing ratio, liquid limit, and optimum moisture content value. One percentage of nano-aluminium oxide is considered an optimum dosage. Beyond the optimum amount, there is a change in soil property. The CBR value, liquid limit, and OMC of soil all go down, so it is recommended to use 1% nano-aluminum oxide to improve sub-grade clay soil.


INTRODUCTION
The land is mostly made of sand, soil, clay, boulders, silt, etc.About 29% of Earth is filled with land and the dirt layer that covers Earth is referred to as the pedosphere.The state of these soil strata varies from location to location.Nowadays, the problem caused by the soil layer can be readily resolved recognition to the development of technologies.The wastelands are considered, and some engineering techniques to rectify the problem are undertaken for that land.The nature of the soil in the pavement region should meet the needed stability characteristics [1].
The most typical method of stabilising soft subgrades involves first removing the soft soil.Then they will be replaced with stronger materials, such as crushed rock.Due to the expensive expense of renewing the materials, numerous types of studies have been conducted to find alternate solutions to this issue [2].For treating the ground with problems such as ground intrusion, changes in the permeability of the soil [3] and sub-grade weakness [4] are adopted, and stabilisation techniques are adopted.When a certain engineering property is absent, there is a need for a certain soil property improvement technique, and that technique is met by the term "soil stabilization.This stabilisation is carried out by adding stabilisers [5].
Soil stabilisation, as it is known in engineering, is a process that turns unusable soil into one of better quality.The creation of an intractable strengthening phase is what causes stabilisation [6].The idea of stabilising dates back 5,000 years.Compared to the original soil, the stabilised soil materials are significantly stronger, more impermeable, and less compressible.In situ stabilisation and ex-situ stabilisation are two common methods for implementing the method [7].The different techniques used in soil stabilisation are mechanical stabilization, chemical stabilization, and the use of geo-synthetics [5].This technique enhances properties such as durability, stiffness (or strength), and the ability to treat soil quickly [8].While undergoing the stabilisation process, clay particle flocculation raises the effective grain size and decreases fluidity, enhancing the matrix's strength [9].Mechanical stabilisation is done by using compacting equipment.The main aim of this technique is to densify the soil by reducing its porosity.Then the chemical stabilisation is followed up by adding any additives.Chemical stabilisation processes are used to enhance the mechanical behaviour of soil [10].In the past, lime and cement were often used, which is also considered a traditional method.When this method is used, a lot of carbon dioxide is released.Aside from these problems, the cement stabilisation process is affected by the ratio of water to cement, the temperature at which the mixture cures, and the specific surface area of the mixture, the presence of contaminants or foreign substances and the presence of additives [1] Other than this traditional method, the following materials are used for chemical stabilization: GGBS, volcanic ash [11,12], fly ash, biomass bottom ash, Phosphogypsum, steel slag, concrete slurry waste [13], fibre and pith of coir, rubber waste, glass, polypropylene fibre, straw of barley fibre,sisalfibre [14], carpet waste, geogrid, geotextile, geocomposite, Chemical soil stabilisation involves modifying the physical-synthetic properties of clay particles so that less water is needed to maintain the static imbalance [15].Apart from these materials recycled aggregate waste [16], plastics, red mud, kaolin waste etc are also nowadays used in civil works like concrete batch preparation and making building materials [17].
In recent days, the emerging technique of nanotechnology has been used in civil engineering applications.The researchers undertook research on soil stabilisation by using nanotechnology techniques [18].This material has an advantage, such as economics, and is available in the best quality.Generally, in soil and rocks, some nanomaterials naturally available are allophane, halloysite, hematite, goethite, imogolite, palygorskite, and smectite [19].Using calcium-based stabilisers, these techniques are carried out globally [17,20].Nanomaterials are used in liquid as well as in powder form.Some of the nano-materials used are nanoclay, nanosilica, nanoaluminum, nanocopper, nanomagnesium, nanogypsum, nanochemicals, nanobentonite, nanocalcined clay [21], multiwall carbon nanotubes, carbon nanofibers [22], nanotitanium dioxide, solutions of silicates [3], nanosoil [20], etc.In addition, certain micro-sized materials can be converted to nanoscale and used as nanoadmixtures.
The mixing of a very small amount of nanomaterial in the soil gives the best result.The addition of less than 0.2% of nanomaterial to sandy clay soil is a great improvement in the properties of the soil [4].The nanostabilizers, in addition to the high clay content of the soil, will decrease the swelling properties of that soil [23].This improvement is due to their smaller size (1 nm and 100 nm) and high surface area [24][25][26].A trace amount of the primary material may actively react with the nanomaterial, changing both its physical and chemical behaviour [27].When there are a lot of nanoparticles, the particles stick together, which hurts the soil's geotechnical properties [28].
In this research paper, the stabilisation of clay soil is carried out by using nanoaluminum oxide.The nano-aluminum oxide is prepared in a laboratory and mixed with soil at various percentages in powder form.The experimental work for soil stabilisation is conducted by separating the work into two different phases.(i) Determination of the geotechnical properties and general properties of stabilizers; and (ii) Determination of the mechanical properties of soil mixed with stabilizers.

Soil
The soil collected is clay soil, which is disturbed while collecting as shown in Figure 1.The sample is collected from the Chunkankadai region, and its properties are discussed in the Table 1.Clay soils are found worldwide, and they will also cause damage to the structure built over them [29].The fraction of the soil that goes through a No. 200 sieve needs to have its particle size distribution determined using a hydrometer study (0.075 mm) as indicated in Figure 2. By using the collected sample, the test is conducted by passing the sample through a 10-number sieve (2 mm) so that the particles larger than 0.075 mm will settle down.At last, sample particle size is identified.

Nano-aluminium oxide
Nano aluminium oxide prepared by combustion synthesis using urea as fuel is used as a stabilizing agent (Figure 3).For the first trial, 50 g of aluminium nitrate powder with an atomic weight of 375.13 and 20 g of urea with an atomic weight of 60.06 are taken, then the combustion process is carried out and the by-product obtained is white in colour.According to various studies, adding nanoaluminum oxide for stabilisation purposes yields better results even when a small dosage is used.The cohesive soil treated with 1% nano-aluminum oxide will have a compressive strength 4.2 times greater than untreated soil [17].

X Ray Diffraction Analysis
The X Ray Diffraction Analysis (XRD) refers to a quick, logical way that reveals the size of unit cells and is mostly used to find out the appearance of crystalline materials.Figure 4 shows the XRD images of nano-aluminum oxide.This XRD shows the polycrystalline and a rhombohedral structure of nano aluminium oxide.

Atterbergs limit
Atterberg's limit is an inexpensive way of finding out the engineering properties of soil.This includes a liquid limit, plastic limit, and shrinkage limit.The phase (solid, semi-solid, plastic, or liquid) of soil can be identified by these tests.The Atterberg limit of soil and soil with different percentages of nano-aluminum oxide stabiliser is given in Table 2.
The liquid limit value drops from 44% to 37%.From this, we can conclude that the liquid limit value decreases when nanoaluminum oxide powder addition increases.Similarly, the flow index, plastic limit, plastic index, shrinkage limit, and shrinkage ratio values also decrease as the percentage of nano-aluminum oxide powder increases.

Standard proctor compaction test
The standard proctor compaction test (IS: 2720 Part 7) is a laboratory technique used to determine the ideal moisture level at which a specific soil type will reach its maximum dry density and become most dense.For virgin soil and soil with varying percentages (0.2, 0.4, 0.6, 0.8, 1, 1.2) of nanoaluminum oxide, the optimum moisture content value and maximum dry density value are determined.Table 3 shows the Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) values for soil and soil with different nano-material percentages.
The optimum moisture content value is at its peak at 0.6% of nanoaluminum oxide, but it will be at a moderate value when 1% of nanoaluminum oxide is added.Beyond 1%, the Optimum Moisture Value drops from 10% to 6%.Whereas the MDD value increases slightly (1.59 to 1.60).

Unconfined compressive strength of soil
The role of the unconfined compressive strength (UCS) test is to determine the strength of the collected sample.Technically, it is defined as the most axial compressive stress a cohesive soil sample can withstand in the absence of any constraining stress.The load per unit area at which a cohesive soil's cylindrical specimen collapses is known as the unconfined compressive strength (qu).The unconfined compressive strength test is done for the virgin sample and then by adding 0.2, 0.4, 0.6, 0.8, 1, and 1.2 percent of nano-aluminum oxide to the sample.
The UCS was done with 2.5 kg of soil that had the right amount of water in it (the "optimum water content").The mixture is divided into three equal parts, each of which is put into the cylinder mould and pressed down with 25 blows.Extra edges are trimmed out, and the initial length and diameter of the specimen are noted.Finally, the specimen is placed in the bottom plate of the unconfined compressive strength apparatus, and the upper plate is adjusted to come into contact with the specimen, eventually setting the load and strain dial gauge to zero.After applying a compressive load, the reading of the load dial gauge noted every 0.5 mm of deformation.After completion of this experiment, the length of the specimen is noted.Table 4 shows the sample's unconfined compressive strength and unconfined cohesion value.
The UCS and cohesion values of soil are 31.5KN/m 2 and 15.75 KN/m 2 .The UCS and cohesion value go up when different amounts of nano aluminium oxide powder are added to the sample.The maximum value of 177 KN/m 2 and 88.5 KN/m 2 are obtained with a 1.2% addition of nano-aluminum oxide stabilizer, because of its binding capacity.

California Bearing Ratio
The strength of the subgrade is measured by a California bearing ratio test.It is defined as the ratio of force per unit area.The standard load for various penetrations is fixed that is given in Table 5.The formula used for determining the California Bearing Ratio (CBR) value is  California Bearing Ratio Value = (Test load) / (standard load) × 100 The graph represents the variations in load vs. penetration for soil and soil with various amounts of nanoaluminum oxide.From this graph, it is known that at the 1% maximum value obtained, there is a sudden drop as shown in Figure 5.So it is recommended to use 1% of nano-aluminum oxide for better sub grade strength.Hence, 1% of nano-aluminum oxide powder is considered an optimum dosage.

Comparison of liquid limit, plastic limit and shrinkage limit
While testing virgin samples, the exact liquid limit, plastic limit, and shrinkage limit of samples are determined.After adding the stabilising agent, the soil properties will changes.Due to these changes, the liquid limit, shrinkage limit, and plastic limit will affect their value, and there will be ups and downs.For virgin soil, the liquid limit  is 44, the plastic limit is 19.59, and the shrinkage limit is 23.5 (Table 2).The liquid limit and plastic limit values keep decreasing at the optimum dosage addition of nanoaluminum oxide [30].The values obtained are 38 and 16.99.The value drops in the liquid limit indicate the amount of water in between the liquid and plastic stages.
The shrinkage limit value increases to 29.32 from 23.5 at optimum dosage as indicated in the Figure 6.In the presence of this amount of water, the fine soil won't change its volume on drying.

Unconfined compressive strength
The increase in compressive strength of soil with nano-aluminum oxide is represented in the Figure 7.For virgin soil, the compressive strength value is 31.5, and after adding oxide at 0.2%, the value slightly increases.These slight variations in the unconfined compressive strength value suddenly increased to the peak at 0.6% (141.9)addition of stabilising agent; after that, there is a gradual increase.At the optimum dosage of 1%, the UCC is 163, and its cohesion is half of that (81.5).The compressive strength increases on adding nano aluminium oxide, this improvement is due to the binding tendency of nano aluminium oxide towards soil and water [31].

Optimum moisture content
The relation between dry density and moisture content is expressed as optimum moisture content.In Figure 8, the optimum moisture content of the virgin soil sample and soil mixed with different percentages of nanoaluminum  oxide is given in the form of a graph.The OMC obtained while testing the virgin soil sample is 12%.After adding the stabilising admixture, the value changes depending on the number of admixtures added [32].The OMC value of 17% was obtained when 0.6% of nano-aluminum oxide was added, whereas when adding 1.2% of nano-aluminum oxide, the very lowest OMC value of 6% was obtained.

CONCLUSION
Thus, from this experimental investigation of soil stabilization technique by adding nano-aluminium oxide additive in clay soil, the following outcomes are identified.
• One percentage of nanoaluminum oxide is considered the optimum dosage.
• When adding nanomaterials, the unconfined compressive strength of the soil sample also increases.
• The liquid limit increases when nanomaterial addition increases; when it exceeds the optimum dosage, the limit drops from 38% to 37%.
• The California Bearing Ratio value also increases simultaneously when the nanomaterial addition increases.But after exceeding the optimum dosage, there is a drop in the California Bearing Ratio value.
• The nanomaterial is in nano size, so it has a high surface area.This fills in the holes in the soil and gives it the important properties it needs.

Figure 1 :
Figure 1: The collected raw material sample of soil.

Figure 2 :
Figure 2: The hydrometer analysis of virgin soil.

Figure 4 :
Figure 4: The X-Ray Diffraction Analysis of nano aluminium oxide.

Figure 3 :
Figure 3: The preparation of the nano-aluminum oxide specimen.

Figure 5 :
Figure 5: The california bearing ratio of various specimens.

Figure 6 :
Figure 6:The comparison of liquid limit, shrinkage limit and plastic limit of the samples.

Figure 7 :
Figure 7: Unconfined compressive strength value of the sample with varying percentages of stabilizers.

Table 1 :
The specific properties of collected soil.

Table 2 :
Values of Atterberg limit of nano aluminium oxide.

Table 3 :
The optimum moisture content and maximum dry density of soil with nano-aluminium oxide.

Table 4 :
The unconfined compressive strength and cohesion value of soil with nano aluminium oxide.

Table 5 :
Standard load for various penetrations.