Behaviour of Reinforced Soil under Unconfined Axial Compression Loading

This paper pertain the unconfined compressive strength test results of newlydeveloped geomaterial prepared using blast furnace slag, plastic strips cut from used and waste plastic water bottle, EPS beads and locally available soil. The increase in production of slag, plastic waste and their disposal in an eco-friendly manner is a matter of concern. This paper briefly describes the suitability of slag and plastic waste to be used in geotechnical engineering applications as a way to minimize their disposal in the environment and in the direction of sustainable development. The testswere carried by adding EPS beads with different mix proportions. The plastic strips of different aspect ratios 0.05, 0.1, 0.15 and 0.2 were added with different percentages of 0.5 %, 1 %, and 1.5 %. Slag was added in two different percentages of 2.5 % and 5 %.The mix ratio percentages 0.05, 0.1, 0.15 and 0.2 were used in the study. Series of unconfined compression tests were performed on newly developed geomaterial. Test result indicates that compressive strength increases with increase in plastic strips upto aspect ratio of 0.15 and then decreases for aspect ratio of 0.2. The compressive strength values were decreased with increasing mix ratio values. The initial tangent modulus and density of the geomaterial decreased with increasing mix ratio values. Stiffness of the geomaterial increased with increase in slag percentages. Keywords-compressive strength; geomaterial; blast furnace slag; plastic strips; sustainable development;aspect ratio.


I. INTRODUCTION
Over the last few decades there has been a steady increase in the use of plastic products resulting in a astonish rise in plastic waste in the municipal solid waste in major cities of India. Lot of efforts need to be taken to utilize this plastic waste in some or other ways.In India approximately 8 million tonnes plastic products are consumed every year [1]. Out of which 60 % of plastic waste by weight is collected for recycling and 40 % by weight of plastic waste remains uncollected. This 40% plastic is responsible for environmental hazards. According to International Bottled Water Association, sales of bottled water have increased by 500% over the last decade. 1.5 Million Tonnes of plastic are used to bottle water every year.Unfortunately the recycling process is messy and inefficient reported by [2]. Inclusion of these waste plastic bottle strips into the soil causes modification and improvement in the engineering behaviour of soil.Theexperimental studies to know the CBR behaviour of waste plastic strips reinforced stone dust for the effective utilization of stone industries by product in applications of civil engineering was performed by [3]. CBR tests were conducted on plastic strip reinforced flyash to understand the behaviour and to know its suitability in the pavement construction by [4].Experimental studies have conducted by [5] for the utilization of coal combustion by product bottom ash based material reinforced with plastic strips cut from the used and wasted plastic water bottles and EPS beads.
Slag is a by-product generated during manufacture of pig iron and steel. The slag produced at blast furnace during pig iron manufacturing is called blast furnace slag. Around 10 million tonnes blast furnace slag is currently generated in the country as per the report of the Working Group on Cement Industry for the 12 th plan [6].Lot of efforts have been taken and are underway to use this by-product as useful geotechnical material. Many researchers carried out experimental investigations to find the suitability of blast furnace slag in the field of civil engineering applications [7 -12].
The expanded polystyrene (EPS) beads are produced a step before the production of blocks, that is the blocks are made by fusion of beads [13]. They arenon-biodegradable and chemically inert in both soil and water. According to [14] EPS beads are hydrophobic in nature and it has closed cell structure that prevents absorption of water in it. The EPS is a highly compressible material available in different types for specific purposereported by [15]. The mechanical characteristics of light-weight soils consisting of Expanded Polystyrene (EPS), dredged clays, and cement through both unconfined and triaxial compression tests was studied by [16]. They have reported that the strain at failure in triaxial test was 39 % less than that in unconfined compression test.The unconfined compressive strength of the lightweight fillmaterial which was prepared by using soil with Polystyrene Pre-Puff (PSPP) beads and cement increases considerablywith increase in cement to soil ratio [17]. It was reported by [18] that the geomaterial prepared by using EPS beads and bottom ashwas light inweight compared with conventional fill materials and it can be used as a substitute to conventional fill materials on soft soils. The experimental studies to know the behaviour of newly developed construction material under compression loading using stone industries byproduct stone dust and EPS beads was conducted by [19].
The present study mainly focuses on the unconfined compression behaviour of newly developed geomaterial. Series of unconfined compression tests have been conducted on geomaterial specimen of size 38 mm in diameter and 76 mm in height and test results are incorporated in the paper. To prepare the geomaterial, plastic strips and slag were added to soil in percentage of 0.5 %, 1 %, 1.5 % and 2.5 %, 5 % respectively. Different aspect ratios (AR) 0.05, 0.1, 0.15, 0.2 and mix ratios 0.05 %, 0.1 %, 0.15 %, 0.2 % were used in the experimental program.

II. MATERIALS
Four different materials were used to prepare the geomaterial namely blast furnace slag, strips cut from the used and waste plastic water bottles, expanded polystyrene beads and locally available soil. Blast furnace slag was procured from Bhilai Steel Plant, Bhilai, Chhattisgarh, India in moist state. The physical properties of blast furnace slag were given in Table I. X-Ray florescence spectrometer test was performed on blast furnace slag to know the various chemical compounds. Table II gives the chemical compounds of blast furnace slag.Plastic strips which were used in the experimental program were cut from the used and waste plastic water bottles. Four different aspect ratios 0.05 (1 × 20 mm), 0.1 (2 × 20 mm), 0.15 (3 × 20 mm) and 0.2 (4 × 20 mm) were used. Aspect ratio (AR)in the present study is defined as ratio between width and length of plastic strip.  1 shows different sizes of plastic strips used in the experimental program. The density of EPS beads used in the present study is 16 kg/m 3 and they are appeared to be spherical in shape. The diameter of the EPS beads was in the range of 2 to 3 mm.Locally available soil was used in the experimental study. The physical properties of soil were given in Table 3.  III. EXPERIMENTAL PROGRAM The experimental program was planned with an objective to understand and investigate the effect of inclusion of EPS beads, plastic strips cut manually from used and waste plastic water bottles and blast furnace slag in soil and to determine the unconfined compressive strength. Series of unconfined compression tests was carried out in accordance with [20] on newly developed geomaterial. The effect of different mix ratios, aspect ratios, slag and plastic strip percentage on compressive strength, density and initial tangent modulus of newly developed geomaterial was investigated and presented in the paper.

A. Mix Ratios and Preparation of Specimen
In the present study, mix ratio (MR) is defined as the ratio between weight of EPS beads and soil. It was expressed in terms of percentages. The dry weight of the silty clayW b required to make the specimen was calculated using formula W b = γ dmax xV b where γ dmax is the maximum dry unit weight of soil and V s is itsvolume. Volume of dry soil V s was calculated by using the formula V s =V-(V beads +V slag +V strips ) where V is the total volume of the specimen that is 86.2 cc and V beads is volume of beads, V slag is volume of slag and V strips is volume of plastic strips. To achieve the initial mix ratio value of 0.05 %, volume of beads, slag and strips were assumed as 4, 1 and 1 cc respectively. Weight of the beads was calculated by using the formula W beads = ρ beads x V beads, where ρ beads is the density of EPS beads. The weights of plastic strips and slag were calculated based on their percentage taken with respect to soil. Volume of the water to be added was calculated with respect to the dry weight of soilV w = W b x OMC, where OMC is the optimum moisture content. Table IV gives the experimental program.  All the ingredients required for the preparation of the specimen were measured with the help of electronic weighing balance. EPS beads, slag and plastic strips were added to soil as per the calculation and then they were dry mixed. Then all the materials were mixed by adding required quantity of water gradually. This mixture was then put in the mould and compacted. The specimen was then extracted using extractor. The specimen prepared having diameter of 38 mm and 76 mm in height. Fig. 2 shows mixing and extraction of prepared geomaterial specimen.

B. Test Procedure
The initial length, diameter and weight of the specimen was measured and the specimen was placed at the bottom plate of the loading device. The upper portion of the specimen was adjusted in such a manner that it should make contact with the proving ring through a loading plate. The unconfined compressive strength tests were performed with the strain rate of1.25 mm/minute. To complete the experimental program overall 96 specimens were tested and the results are presented in the paper. To check the reproducibility of specimens for each mix ratios one specimen was prepared and tested. Repeatability test results found encouraging to a variation of 4 to 7 %.

IV. RESULTS AND DISCUSSIONS A. Failure Pattern
Under unconfined compressive load, the failure patterns of the prepared geomaterial specimen were observed for different mix ratio values, plastic strip percentages and slag with different aspect ratios. For lower strip percentages bulging failure was observed. The bulging was predominantly at middle portion of the specimen. As the strip content increased, the specimen has not shown considerable bulging during failure. The failure patterns consist of vertical cracks starting from the mid height of the specimen and continued upto bottom of the specimen. Moderate bulging was shown at bottom as if it is getting compressed at bottom during failure. All the specimens were failed at a failure axial strain of 2 % to 7 %. Fig. 3 shows failure pattern of prepared geomaterialat lower strip percentage and higher strip percentage.

B. Dens
For