The Effect of Adding High-Density Polyethylene Polymer on the Engineering Characteristics for Sandy Soil

The loose sand is subject to large settlement when it is exposed to high stresses. This settlement is due to the nature of the high drainage of sand, which displays foundations and constructions to a large danger. The densification of loose sandy soils is required to provide sufficient bearing capacity for the structures. Thus soil stabilization is used to avoid failure in the facilities. Traditional methods of stabilized sandy soil such as fly ash, bituminous, and cement often require an extended curing period. The use of polymers to stabilize sandy soils is more extensive nowadays because it does not require a long curing time in addition to being chemically stable. In this study, the effect of adding different percentages of high-density polyethylene HDPE  to the sandy soils' engineering characteristics such as the angle of internal frictions Ø0, shear strength τ, California Bearing Ratio CBR, and permeability k was studied. The results of laboratory tests showed that using of HDPE at percentages  (0.1, 0.3, 0.6, 1, and 3%) led to a decrease in soil permeability by 18% and an increase in both the angle of internal friction, the CBR value, and shear strength about 27.2%, 180.9%, and 38.6 % respectively by adding 1%. HDPE.


INTRODUCTION
High-density polyethylene HDPE is a new category of petrochemical products. It consists of two carbons and four atoms of hydrogen in the base polymer repeat unit. One of the characteristics of polyethylene is that it is highly durable, soft, lightweight, easy to manufacture, cost low, very little absorbency to water, inert chemically (that is, it is insoluble in any of the solvents at room temperature). Still, it is lightly swollen by liquids such as benzene. It has good resistance to acids and bases, the degree of glass transition of polyethylene is very little (-120°C), which gives it flexibility and high resistance to moisture in addition to its electrical insulation properties (Rafiq et al., 2011). Sandy soil contains many geotechnical problems, including high permeability, less shear strength (Bruand et al., 2005), sand dunes (Al-Taie and Al-Shakarchi, 2016), and liquefaction (Al-Taie and Albusoda, 2019). Therefore, it is necessary to stabilize the sandy soil to improve its engineering properties. There are three purposes for stabilizing soil. The first purpose is to improve strength, which increases the bearing capacity of weak soils. The second purpose is to control dust. This is done to remove or mitigate dust generated from the operating equipment during dry climates. Soil waterproofing is the third purpose for soil stabilization and is done to maintain soil strength by preventing surface water from entering. Various additives can be used for stabilization soils, such as calcium chloride, cement, bituminous products, lime (Air Force Manual, 1994), and polymers. Polymers used for soil stabilization must have excellent physical characteristics such as compressive strength, high tensile, good adhesion, flexural, high resistance to chemicals and waters (Palmer, 1995). (Chebet et al. 2019) explained the effect of the polyethylene terephthalate (PET) plastic chips of (2, 4.75, and 5.6mm) sizes, in ratio from 2.5% -20% by dry weight soil on the strength behavior of cape flat sand ( Ø 0 =38.5° and C= 9.4 kPa) and klipheuwel sand (Ø 0 =41.6°and C= 4.8 kPa). The result showed a 25.4% increase in the angle of internal friction Ø 0 , 68% increase in cohesion, 42.5% increase in shear strength at 10% PET for cape flat sand, and 26.6% increase in the angle of internal friction Ø 0 , 187.5% increase in cohesion, and 50.8% increase in shear strength at 12.5% PET for klipheuwel sand. (Talib, 2018) showed that the addition of high-density polyethylene HDPE (2-5mm) size with a ratio of (20, 40, 50, 75, and 100%) to dry weight of sandy soil will affect the properties of sandy soil, such as a decrease in maximum and minimum density of sand about 64% and 60% respectively at 75% HDPE, increase in the angle of internal friction Ø 0 and a large increase in permeability of sand with adding HDPE. (Agbolade and Ojuri, 2015) studied the effect of adding strips of high-density polyethylene (HDPE) waste on the properties of sandy soil. Strips size is (15 × 20 mm, 20 × 25 mm, 25 × 30 mm) in a ratio of (1, 2, 3, 4, and 5%) by dry soil weight. The results showed a 68.54% increase in shear strength, 55.56% increase in the angle of internal friction Ø 0 at 2% HDPE for small size strip (15 × 20 mm), and 61.9% reduction in permeability at 5% HDPE for large size strip (25 × 30 mm). This current research aims to study the effect of adding different percentages (0.1, 0.3, 0.6, 1, and 3%) of high-density polyethylene HDPE to the sandy soils' engineering characteristics, such as the angle of internal frictions, shear strength, California Bearing Ratio, and permeability.

EXPERIMENTAL WORK 2.1 Sandy Soil
The sandy soil used in this research was collected from Najaf Governorate, southern Iraq. The physical properties of sandy soil were tested in the civil engineering laboratories at Al-Nahrain University, as shown in Table 1.

High-Density Polyethylene HDPE
The tests are carried out at Physics laboratories in AL-Nahrain University; the grain size distribution for natural soil and polyethylene polymer HDPE is shown in Fig. 1. Fig. 2 shows the HDPE used in the current study. The chemical and physical properties of HDPE are shown in Tables 2 and 3, respectively.

LABORATORY TESTS 3.1 Permeability Test
The permeability test was conducted on the natural soil according to ASTM D2434. The coefficient of proportionality k (q=kiA) is called "Darcy's coefficient of permeability". Permeability enters all problems involving the flow of water through soil, such as drainage of subgrades, seepage under dams, and backfill.

Direct shear test
The direct shear test for soil is determined according to ASTM D3080. The shear strength of a soil mass is the internal resistance per unit area that the soil mass can offer to resist failure and to slide along any plane inside it. In the direct shear test, a square prism ( 6 × 6 × 2 cm) of soil is laterally restrained and sheared along a mechanically induced horizontal plane while subjected to a normal pressure applied to that plane.

California Bearing Ratio (CBR) Test
The CBR test was conducted on soil according to ASTM D1883. The CBR test is used to evaluate the potential strength of subbase, subgrade, and recycled materials for use in road and airfield pavements. When a cylindrical plunger is made to penetrate the soil at a given rate, the concept of CBR is to establish the relationship between applied load and penetration. The California Bearing Ratio is known as the ratio of applied load to a standard load, expressed in percentage, at specific penetration values. This principle is used in most parts of the world as an essential criterion in flexible pavement design.

RESULTS AND DISCUSSION 4.1 Effect of HDPE on Shear Strength for Sandy Soil
93.6 grams of sandy soil was weighed (depending on the size of the direct shear box and the dry unit weight of the sandy soil) and placed in a direct shear box in the dry state, then 1, 2, and 4 kg loaded were supplied on a sample and tested before and after adding HDPE. Fig. 3 and 4 show the effect of adding polyethylene HDPE on shear strength for sandy soil. An increase in the angle of internal friction was observed upon increasing the polymer ratio, which reached an increase of 27.2% when 1% of HDPE was added.

Effect of HDPE on Permeability for Sandy Soil
The permeability values for sandy soils begin to decrease when adding a polyethylene polymer gradually. After 3% HDPE, the permeability started to rise slightly, as shown in Fig, 5. The small size particles give less permeability and because the grain size of HDPE is smaller than the size of sandy soil grains (it contains more fine particles), as shown in Fig, 1. Therefore, the void ratio is less, and this leads to a decrease in permeability.

Effect of HDPE on CBR for Sandy Soil
The soil was prepared for the CBR test by first the required soil weight, which was 4.5 kg, and then the HDPE was mixed with the dry soil randomly at a moisture content of 5.5%. The sandy soil was compacted in three layers by applying 56 blows distributed on each layer with a hammer weighing 24.5 N at a free fall. A load of 2.5 kg was seated on the last layer. Then the mold was placed under the CBR machine. The penetration plunger was installed at the center of the sample to be in contact with the soil surface. The test was carried out by applying the load through the penetration readings of 0.0, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, and 7.5 mm. In general, the CBR values increase when the polymer ratio was increased, and the maximum increase in the CBR value was given at 1% of HDPE, as shown in Fig. 6. Whereas the presence of this type of polymer, which acts as a filler between the particles of soil, increases the strength of the soil particles. Fig. 7 shows soil molds in the CBR test with adding HDPE. Plate 7. Soil molds in CBR test with adding HDPE.

CONCLUSIONS
This research was carried out to investigate the effect of adding high-density polyethylene HDPE at different percentages to improve some engineering characteristics of sandy soil. The following conclusions may be drawn based on the results of the laboratory tests of this research: 1-Increase in the angle of Internal Friction (Ø 0 ) and shear strength (τ) with increasing HDPE percentage. The maximum increase in the angle of internal friction and shear strength was 27.2% and 38.6%, respectively, at 1% HDPE. 2-The permeability values for sandy soils began to decrease when adding a polyethylene polymer gradually. The optimum decrease in permeability was 18% at 1% HDPE. 3-The CBR values of sandy soil increased when the polyethylene ratio was increased, and the maximum increase in the CBR value is given as 180.9% at 1% of HDPE.