*4.3. California Bearing Ratio*

To obtain the CBR, a static penetration test is performed to obtain the susceptibility of soil against wheel load penetration. According to [42], the CBR value recommended by the RDA is 15% for subgrade in highway construction. In the case of kaolinite, red earth, and sun-dried marine clay, the CBR values increased with an increase in the percentage of granite dust [21]. However, the percentage increase in CBR for a particular dosage of granite dust is more for clay soil due to the change in grain size distribution (Table 6). Soils with high clay content showed a high improvement with granite dust addition.


**Table 6.** CBR characteristics of Granite dust amended soils (Modified after [21]).

This increase in the CBR value is also influenced by the shear strength of the particular soil. In spite of the presence of weak soil, stabilization with granite dust brings the CBR value to the field requirement that helps to reduce the pavement thickness. The increase in the CBR values with the increase in the percentage of granite dust was observed until 50% granite dust addition in the case of black cotton soil [44]. The CBR values of the residual soils increased with an increase in granite dust in soaked and unsoaked conditions [37]. Table 7 shows summary of earlier works related to improvement in CBR characteristics of different soils.


**Table 7.** Summary of works to improve the CBR of the soils with granite dust.

#### *4.4. Shear Strength*

Sun-dried marine clay highly responded to the granite dust addition compared to red earth. The presence of granite dust in clays filled the voids and developed friction among the mixed particles [22]. A significant improvement in the shear strength with the increase in internal friction and a corresponding decrease in the cohesive nature of high-plastic silt was observed up to 60% addition of granite dust as seen in Figure 4.

**Figure 4.** Variation of shear parameters of high-plastic silt with granite dust addition (Modified after [42]).

#### *4.5. UCS and Permeability*

The unconfined compressive strength of lithomargic clay is improved with addition of granite dust content up to 20% and decreased with a further increase in granite dust addition. The coefficient of permeability of lithomargic clay proportionally increased with the addition of granite dust [46].

The wealth of literature summarized reveals that, granite dust enhances the geotechnical properties of silts and clays. High-plastic clays and clayey soils hold poor gradation; thus, the granite dust addition turns the mix into a well-graded complex that yields a high confinement as seen from Figure 5.

**Figure 5.** Change in the particle gradation of clay soil with granite dust addition.

#### **5. Granite Dust as a Substitute for Sand**

Kumar [47] worked on different sub-base materials like flyash, coarse sand, granite dust, and river bed material (RBM). Granite dust was found to have the least resistance to rutting compared to the other three materials used in this study. The RBM has the maximum resistance to rutting. The static and resilient moduli were both higher for the RBM, implying that it had a better performance than the other three materials in the field. The internal friction angle ranged from 26◦ to 39◦, and the specific gravity was nearly close to the specific gravity of river sand, which is required for the fractional sand replacement [36]. From the chemical composition of granite dust, silica/quartz (SiO2) is the predominant mineral that helps give a high shear strength similar to sand. Therefore, practically, granite dust can be used as a substitute for sand. Some previous investigation(s) [31,35,48–50] proved that sand can be partially replaced with granite dust without changing the workability and durability of concrete. Furthermore, the shear strength of sandy soil increases with an increase in the percentage of the granite dust content in sand–granite dust mixes to a certain limit. This work concludes that granite dust is the best source of alternative to save sand availability.

#### **6. Alternate Treatment Methods**

#### *Reinforced Granite Dust*

Sand was earlier referred to as the best backfill material because of its shear strength and permeability characteristics. In view of sustainability, being a cohesion less inert material that can also be used as a backfill due to its bulk utilization, granite dust is also the best substitute for sand [33]. A backfill material should not possess any lateral displacement of facia walls and should be able to resist the settlement due to loading. Granite dust is limited in cohesion property and high density; hence, the concept of granite dust reinforcement has been explored by certain authors. Among several reinforced materials, geosynthetics are considered as the best reinforcing materials due to their workability. Rama Subbarao [51] stated that geo grid reinforcement reduces the shear deformations of granular materials. Reinforced granite dust exhibits a ductile behavior and improves apparent cohesion, but is insignificant in the case of friction. The deviatory stress is the governing factor of shear strength in the case of reinforced stone dust, especially in ductile reinforcements. The EPS geofoam was introduced in granite dust as the load-reduction key. Geofoam is more noticeable for gravelly and sandy fills. The interface shear strength of geofoam–granite dust is highly influenced by normal stress applied [52]. In addition, the presence of geofoam reduces the backfill weight. Reinforced granite dust could be used as a backfill material, even at a lower relative density that reduces facia displacement and vertical settlements [53]. The change in the dimensions of the reinforcement and its location also greatly influence the backfill behavior. Waste plastic strips serve as a reinforcing material for improving the penetration resistance of granite dust. Granite dust is highly influenced by the increase in the density of intruded plastic strips [54]. Earlier works have stated that approximately 1% of plastic strip addition with an aspect ratio of 3 increases the soil CBR. The CBR was improved by the particle interlocking in reinforced layers under

the dry condition (unsoaked) and the sedimentation of fines, in which the coarser particles to the top led to a confinement in the wet condition(soaked) [51].

Backfills and soil walls are some of the bulk applications in geotechnical engineering. The reinforced granite dust material is the best substitute for sand. Being a high-density material, the reinforcement helps reduce the pressure on the facia walls, which consequently leads to the reduction of the horizontal displacement and the vertical settlement due to the interlocking phenomenon (Figure 6). The concept of reinforced granite dust also helps improve the penetration resistance due to the development of a confinement among particles.

**Figure 6.** Mechanism of reinforced granite dust.
