The effect of waste marble powder and phosphoric acid on the shear angle and cohesion value of expansive soils

. In general, the expansive clay soil is a problematic soil due to the impact of climate change, during the rainy season the soil expands, and during the dry season the soil shrinks and cracks. Of these problems, it is necessary to carry out soil stabilization in order to determine the mechanical properties of the soil using the Waste Marble Powder (WMP) and Phosphoric Acid (PA) chemicals. To improve soil characteristics, tests were carried out with a mixture of 2.5%, 4%, 5.5% and 7% WMP, while Phosphoric Acid was a fixed percentage of 4% for the expansive soil. Curing periods of 3 days,7 days, and 14 days were also conducted in this study. According to the test results, the increase in the shear angle value, from originally 6.45° changed to 29.81° which increased by 21.64% of the percentage of the original soil, while the soil cohesion value, from originally 0.37 kg/cm 2 changed to 2.25 kg/cm 2 which increase of 16.44% in the curing period of 14 days. This increase is caused by chemical reactions that occur as a result of chemical elements, especially calcium (Ca) and potassium (K) contained in marble powder waste, and the mineral phosphorus (P) contained in phosphoric acid chemicals.


Introduction
An expansive soil is a type of soil that is able to expand and contract significantly due to changes in water content.This soil property can lead to damage to building structures and other infrastructure, as well as potential erosion of agricultural land.In order to reduce the impact on vast soils, expansion and cushioning research is very important, one of the methods used is soil stabilization.
One method that was explored in this study is the use of waste marble powder and phosphoric acid as a soil improver.Marble powder waste generated during marble processing can reduce the physical and mechanical properties of the soil due to its mineral composition, such as calcium (Ca) and potassium (K), which make extensive soil hard and difficult to work with expand.Meanwhile, phosphoric acid can be used as a chemical liquid to change soil chemical properties such as pH and ion concentration.
In this context, this study aims to investigate the effect of waste marble powder and phosphoric acid on two important parameters of the engineering properties of extensive soils, namely the shear angle ( o ) and soil cohesion value (kg/cm 2 ).The shear angle is the maximum angle in the resistance plane at which the soil will begin to experience internal displacement.The cohesion value measures the internal strength of the soil, caused by the forces of attraction between soil particles.These two parameters are very important for evaluating the resilience potential of the soil after mixing with marble powder waste and phosphoric acid.
We hope that this study will provide useful information on the effect of these materials on the mechanical properties of vast soils.The results of this study may contribute to the development of sustainable and effective methods of soil stabilization to reduce the risk of damage due to changes in the volume of vast soils.In this study, laboratory testing of soil mechanics was carried out with a mixture of waste marble powder 2.5%, 4%, 5.5% and 7%, while phosphoric acid was a fixed percentage of 4% for an extensive soil with a curing period of 3 days.7 days and 14 days.From these percentages, study the change in shear angle ( o ) and soil cohesion values (kg/cm 2 ) after treatment with waste marble powder and phosphoric acid.Thus, this study is expected to provide new insight into the potential application of industrial wastes and chemicals in the sustainable management of vast soils.

Literature review
The subgrade layer has an important role in the foundation support system in a construction.Poor subgrade properties can result in cracking and collapse of construction due to settlement and landslides.This can be caused by low particle binding, extreme slope, excess water, extreme slope dimensions, and overload [1].A settlement can cause damage to buildings or affect the serviceability of a building during its construction [2].The main causes are soils that tend to be compressible, potential for excessive swelling, low levels of shear strength, permeability, carrying capacity, and lack of particle bonding under conditions of high water content [3].This poor soil property needs to be corrected by strengthening, replacing the soil area, or mixing it with other reinforcement materials [6].The results of the UU and CU triaxial tests show that if the sampling point is farther from the centre of the column, the value of φ is greater, while the value of c is smaller.So the farther from the centre of the column, the soil has a large frictional force with small interparticle adhesions, so the soil is more unstable [4].The main objective of this brief report is to calibrate the triaxial cell WF11001/ SN:100257-9 in order to be able to measure with reasonable accuracy the change in volume of the test object during the test in case of partially saturated or dry material, if there is no transducer in the soil sample [5].
Base on [6] states that the test object is inserted in a thin rubber sheath and placed in a glass tube.The test object is pressed by cell tension (σ3), which comes from the liquid pressure in the tube.Air can sometimes be used as a medium for the application of cell tension (confining pressure).The stresses acting on the test object are denoted σ1, σ2 dan σ3.σ1 is called the major principal stress, σ2 is called the intermediate principal stress, and σ3 is called the minor principal stress.The stress resulting from the difference between σ1 and σ3 or (σ1 -σ3) is called the deviator stress or stress difference.For triaxial testing in order to know soil parameters such as: Internal shear angle (o), Cohesion (c) ( o ), Strain (ε), Stress (σ), Modulus young (E') and Mohr's Circle (τ).

Soil expansive
Clay soil mostly consists of microscopic (very small) submicroscopic particles (cannot be seen clearly with an ordinary microscope [7].Other minerals that are commonly found are Illite and Kaolinite.A characteristic of soil depends on the percentage of dominant material, at a certain level, it may cause the soil to have really good behavior or really poor behavior.An expansive soil has mostly microscopic and sub-microscopic material size (<0.002mm or 2 microns), and its particle size may vary between >100 mm -<0.001 mm [8].Mechanical stability involves stabilizing soil by adding initial soil with soil from another area that has better physical properties.On the other hand.Chemical stabilization combines elements between one material and another with the aim of obtaining new elements in the material [7].
Table 1 illustrates the classification of Gedebage soil as soft clay with a high plasticity index based on prior studies.Due to its high PI and physical characteristics, gedebage soil is also classified as expansive clay soil.This type of soil expands when there is an excess of water present and fissures when water shrinks.It falls into the fair to poor subgrade category according to AASHTO, and the fat clay or high plasticity (CH) category according to USCS [9].Soil shear strength parameters are needed as a material for the analysis of soil bearing capacity, load on retaining walls and slope stability.Mohr, in [10] proposes a theory that material failure occurs due to a combination of critical conditions between normal stress and shear stress.The relationship between normal stress and shear stress is expressed by Equation 1and Figure 1

Waste Marble Powder (WMP)
The cost of Waste Marble Powder (WMP) is comparatively low.WMP is produced by cutting marble, which is anticipated to replace chalk as a cost-effective soil stabilizer.Nevertheless, research on waste powder marble This material stabilizer, which is currently quite limited, improves soil cohesion, fills soil pores, and stabilizes soil.The origin of WMP is Padalarang, located in Bandung Barat Regency.Waste Marble Powder (WMP) has a specific gravity of 2.79 and is finely white in color.The marble powder waste has extremely fine grains; all 100 percent of the granules pass through sieve number 200, which has a 0.08 mm diameter.Calcium oxide (CaO) has the largest mineral concentration on WMP, according to the mineral characteristics test conducted by Polytechnic Manufacture Bandung (POLMAN), as seen in Figure 2 and Tabel 2 below.

Phosphoric Acid (PA)
Phosphoric acid is a clear, fluid that evaporates quickly and doesn't smell.Because sour phosphate interacts quickly to produce bound aluminum compounds with soil, perhaps the acidity of the phosphate will diminish the water content of the soil and the level of development on it.Both organic and inorganic phosphate are present in soil.Calcium, Iron, Aluminum, and Fluorine are the form solution compounds in organic form.Phosphate organic matter is derived from microorganisms and plants and is composed of phospholipids, phytin, and sour nucleic acid [11].Expanded clay is crucial for soil rehabilitation because it stabilizes the soil.The deep mineral cations in the soil combine with the addition material chemistry fluid sour phosphate to generate a new compound that forms a hard layer that doesn't dissolve in water.To determine the standard specifications for the substance phosphoric acid (H3PO4) used in products, refer to Table 3.

Shear strength (Triaxial test)
One way to determine the parameters of soil shear bond strength (c) and internal shear angle (Φ) is a triaxial test.In a triaxial test, a soil sample is loaded along all three axes (Cartesian axis) with compressive loads σ1, σ2 and σ3.The purpose of this test is to simulate real field conditions, namely that a soil element bears a compressive load from above (vertically), consisting of the load of the soil above it or the overburden pressure and other loads (σ1), as well as the soil pressure from the radial direction, which compresses (compresses) the earth elements (σ2 and σ3).Based on [13], Wykeham Farrance triaxial testing equipment is an advanced system that strictly conforms to the most important international triaxial testing standards such as: Unconsolidated Undrained (UU), Consolidated Undrained (CU), Where: σ1 = First Stress (kg/cm 2 ) (σd) f = Deviator stress(kg/cm 2 ) A = Compressed cross section area (cm 2 ) P = Loading (kg)

Methodology
The numerous instances of landslides and subsidence that led to building failures prompted the conduct of this study.This study starts by looking at the physical characteristics of the soil.If it is determined that the soil has undesirable characteristics, stabilization is done to make the soil better.Soil is stabilized by adding WMP and PA to it.In addition, phosphorus acid from the Farma Kimia Store was utilized in this study to facilitate the mixing process.This is because the PA prevents the water from solidifying once the soil mixture is fully blended, which is necessary to seal the soil pores.Subsequently, scientists must also obtain the soil's mechanical characteristics by performing the Undrained.On both the initial and stabilized soil, perform an unconsolidated triaxial test.Additional details are displayed in Figure 4. View details.

Results
Table 1 above displays the findings of the expansive clay property index test that was conducted.
Triaxial testing, which was modified in accordance with the specifications for construction and the properties of the soil, was used to determine the Shear Strength parameter.To ascertain the shear strength of clay soil for immediate construction needs, triaxial UU testing was carried out.The results of the shear strength tests were displayed as Mohr Circle and Stress-Strain graphs.During the test, as the applied load increased, the Mohr Circle grew larger and peaked higher.When the Mohr Circle crossed the collapse line, collapse happened.
Gedebage soil is classified as expansive soil or very poor soft clay, as indicated by its high Plasticity Index in Initial soil in V1 (initial soil) has a very low internal friction angle (j), then increases slightly in the next variation but decreases in the last variation.Based on Table 5, V1 can be classified as a clay with a poor shear angle because it has a cohesion value of 0.45 kg/cm2 and the internal shear angle has a value of 6.45 based on Bowless, 1977, quoted by [14], saying UU triaxial testing of internal shear angles 0 -20 is clay soil, while the soil cohesion increases as the marble powder waste increases and the curing period becomes longer, the soil cohesion value for original soil is initially 0.45 kg/cm2 increasing to 2.62 kg/cm2 at a variation of 7% WMP + 4 %PA with a cooling period of 14 days.
Additionally, the cohesion for each variation also increases, signifying an overall increase in soil strength.Cohesion represents the soil's ability for particle bonding; lower cohesion values indicate weaker interlocking and resistance to loads and forces.V1 (initial soil) exhibits the lowest cohesion value, which gradually increases until V5 (fifth variation).The final soil shear strength is depicted in the Mohr Circle diagrams (Figures 5 to 12           Based on graphs 5 until 20, it shows that the original Gedebage soil initially had low values of shear angle and soil cohesion after stabilizing the soil with variations of Soil+7% WMP+4% PA, the soil is efficient and strong so that it can accept the load from the structure above it and also reduces water content because it is influenced by marble powder waste and phosphoric acid which contains carbon minerals, calcium oxygen, phosphorus and magnesium to cover soil pores and reduce soil water content.

Discussion
The results indicate a significant improvement in the shear strength and cohesion of the soil after stabilization with a mixture of Waste Marble Powder (WMP) and phosphoric acid (PA).The initial shear angle of 6,45° and cohesion of 0,45 kg/cm 2 increased to a shear angle of 29,81° and cohesion of 2,62 kg/cm 2 after stabilization.This suggests that the chosen combination of Waste Marble Powder (WMP) and phosphoric acid (PA) has effectively enhanced the soil's engineering properties.Such findings are encouraging, especially for construction and engineering projects where strong soil mechanics are essential.However, it's crucial to consider environmental, economic, and regulatory aspects when evaluating the feasibility of this stabilization method for broader applications.The increase in the shear strength and cohesion values of the soil after the use of a mixture of marble powder waste and phosphoric acid is closely related to chemical reactions in the soil.Chemical processes occurring when this mixture is applied to the soil have altered its properties, resulting in a significant improvement in its mechanical characteristics.These chemical reactions may include changes in the soil's minerals, an increase in pH, the formation of new chemical bonds, and the soil's ability to retain moisture.

Conclusion dan recommendation
-Gedebage soil has poor soil properties, as evidenced by very high plasticity index values, low friction angles and low cohesion.-Stabilization can correct bad soil behaviour; in this research, it can increase the shear strength of the soil at an optimum level of 7% WMP and 4% PA (Variation 5) with a curing period of 14 days.-The test results show that during the stabilization process, the internal friction angle (φ) value increased from 6.45° to 29.8°, and the cohesion value (c) increased from 0.45 kg/cm2 to 2.62 kg/cm2.This indicates that the clay underwent positive changes during stabilization, with significant increases in shear strength (φ) and cohesion (c).The results of this stabilization make Gedebage expansive clay stronger in terms of resistance to pressure and shear, approaching the properties of normal clay.-More mixture variations need to be carried out in further research to obtain the most appropriate percentage of stabilization mixture.
) and the stress-strain graphs (Figures 13 to 20) below.The triaxial data result is described in figures 5 to 12 below.The data from each load applied to the sample is represented by the Mohr circle.The soil's capacity to withstand loads increases with its magnitude.The collapse line is shown by the yellow line.When the collapse line reaches the Mohr circle at the surface, the soil collapses.The angle formed by the horizontal line and the collapse line is the shear angle.Additionally, cohesiveness is measured from the lowest collapse line point.

Fig. 16 .
Fig. 16.Stress Strain graph for Initial Soil with 14 days curing period.

Table 1 .
Results on the original soil.

Table 2 .
SEM-EDS waste marble powder test results.

Table 5
from previous tests.This Triaxial Testing also confirms the poor soil strength quality (ϕ = 6,45°).The shear angle and cohesion values are provided below.