Study of soil reinforcement in the east of Mashhad using glass granule

As waste production has increased, these materials have been put to their best use to help reduce pollution. Glass bottles account for more than 5% of municipal waste in Mashhad, according to statistics. This study attempted to look into the impact of using glass granule recycled materials on soil parameters. The impact of adding glass granule materials on the properties of weak soil and the need for improvement in the east part of Mashhad was studied. The dominant soil in the east of Mashhad was determined using samples collected from 54 different locations. Finally, two experimental relations for determining soil strength parameters were presented. The results show that adding glass granule (GG) lowers the optimum moisture content, and CBR testing on the samples revealed that adding GG by 5% water content increases CBR capacity. Adding GG reduces the CBR in saturated conditions with high densities. According to the obtained results, adding 5% of glass granule is the optimal state that increases CBR and adding more than 5% of additive amounts does not have such an effect. Also, by examining the effect of GG on the shear strength of the soil, it was obtained that the addition of GG increases the internal friction angle of the soil by at least 30% and reduces adhesion by about 40%, as determined by a direct shear test. Adding glass granule in cyclic CBR has no effect in low cycles and has a negative effect in high cycles.


Introduction
Reinforced soil is now widely used as one of the most appropriate and cost-effective methods for increasing soil strength, in the field of urban construction to strengthen soil beneath foundations and as a road substructure [1]. Because changing the soil of the site is too difficult and expensive, improving the properties of poor soil can be a good solution. To improve the soils properties, various materials and methods are used, including fibers, geogrids, geosynthetics, geopolymers, and even microbially induced methods [2][3][4][5]. The use of waste materials to improve soil resilience creates better conditions for the project, economically and environmentally. Glass granule (GG) is one of the commercially neglected recyclable materials, with billions of tons being buried in landfills worldwide. According to estimates from municipal waste companies, glass bottles account for roughly 2%-5% of the dry waste produced in Mashhad [6,7], which is a significant amount. For example, in the United States, about 11 million tons of glass entered the municipal waste stream in 2001, but only 2.4 million tones (22%) were recovered and recycled. The remainder was thrown away in landfills. Besides, roughly 850,000 tons of glass are used in Australia each year, but only 350,000 tons (40%) are recycled [8]. As a result, even the most advanced countries in the material recycling business can only recycle 20%-40% of used glass material, leaving the rest to be buried in landfills. On the other hand, biodegradation of glass takes around 450 years; so, this longduration stresses the importance of reusing recoverable materials such as glass. Recycled glass is made out of a variety of colored glass pieces gathered from municipal and industrial waste streams, and it is frequently mixed with a variety of detritus such as food scraps, plastic and metal caps, pottery, paper, and soil [9,10].
Various researchers have tried to improve the engineering properties of soils by repurposing waste materials and removing them from the environment and geopolymers have been shown to be useful in stabilizing problematic soils in recent studies [11,12]. Glass residue, which is high in silica, noncrystalline, and amorphous, is one of the most recent materials utilized to make geopolymers. There are two places where glass residue exists. Glass debris (e.g., bottles, windows, and doors) is crushed to get the necessary granulometry for concrete aggregate [13] and fine-particle-size powder for soil stabilization [14] or brick manufacture [15]. The appropriate residue of cutting and tillering glass sheets in the presence of water is the second source. The dust formed during the glass cutting technique is mixed with water until it settles. As a result, thin layers build over time at the bottom of the container where the mixture (water + glass) is gathered. Finally, the sedimentation process produces hard clods of glass granule. These clods are then collected and crushed to produce recycledglass granule as a final product. This glass granule is also a byproduct of discarded glass slurry used in the manufacture of ophthalmic lenses [16].
Recycling glass granule wastes for geopolymer manufacture is a new approach that has been studied in recent construction projects. The use of milled glass in concrete manufacturing and as an aggregate in layers of pavement bases is considered possible, despite the fact that it has been rarely researched in the process of soil stabilization [17]. Recent research has demonstrated that coffee grounds (CG) stabilized with slag and fly ash (FA) can be used as a road subgrade material without causing environmental damage to the surrounding soils and waters [18,19]. Arulrajah et al [20] investigated the use of GG as a supplementary filler material in wasted CG geopolymers, using slag and FA as precursors for inducing geopolymerization in GG-CG blends at a concentration of 30 wt%. The authors concluded that a 70% Na 2 SiO 3 and 30% NaOH alkaline liquid ratio was utilized to optimally induce geo-polymerization in the blends, resulting in a Unconfined Compressive Strength (UCS) value of 10 MPa after 28 days of curing. They also discovered that GG-CG, FA, and slag are alternate construction materials that help ensure the construction industry's long-term viability [20,21]. According to Suksiripattanapong et al [22] a 70:20:10 CG:RHA:Slag mixture with a 90-day curing time at 50°C generated a unconfined compression strength (UCS) of 2 MPa, indicating that such materials can also be used on the pavement [22]. The viability of utilizing a geopolymer based on the GG to improve the mechanical behavior of clay soils was next examined by others [23]. They employed a low-plasticity clayey soil mixed with various percentages (0%-25%) of GG and NaOH as an alkaline activator, which was made with various concentrations of NaOH (1, 2, 3, 4, 5, 6, 7, and 8 M, M = Molar) and then added to the soil-GG mix. The authors looked at the effects of different curing temperatures (25°C and 70°C) and curing times (7, 28, and 91 days) on UCS. They found that all specimens stabilized with a geopolymer had higher UCS values and greater NaOH concentrations than the unstabilized soil samples. When the specimens were cured for 91 days, the UCS values were maximum, indicating that a rich silica supply (in an amorphous phase), such as glass granule, was needed for greater soil stabilization and the production of a geopolymer gel [23]. Calcium carbide residue (CCR) as an alkaline activator for GG-clay blends and looked at the impacts of various parameters such CCR content, glass granule content (0-25 percent), starting synthesis temperature, and curing duration. By increasing the CCR and GG contents to the optimum amounts of 7% and 15%, respectively, the UCS of CCR-GG specimens increased dramatically [24]. The authors also found that as the starting synthesis temperature climbed from 25°C to 70°C for both curing durations (7 and 28 days), the UCS values of geopolymeric specimens increased. For the 28-day curing interval, however, the influence of a high initial synthesis temperature on the UCS of the specimens was less effective [24,25].
This study looks into the laboratory evaluation of the effect of soil reinforcement using GG in the east part of Mashhad. The influence of these materials on problematic soils in urban contexts such as road construction has been studied using the direct shear test and the impact of these materials has been determined by using CBR testing in static and cycling circumstances.

Experimental program
There were two stages to the experimental program. The soil and glass granule (GG) waste were subjected to characterization tests in the first stage. The soil granulometry curve, Atterberg limits, and specific gravity were obtained in agreement with ASTM C136, ASTM D 4318-98, ASTM D 1557, respectively [26][27][28]. The soil granulometric curve was plotted using a pycnometric experiment and a hydrometer test based on ASTM D4546 and ASTM D422-63 standards, respectively [29,30]. The glass residue granulometry curve was obtained using sieve analyzers, and the GG specific gravities were found using the Archimedes and balloon approach [31]. Furthermore, the CBR test was carried out according to ASTM D: 1883-87 and AASHTO T: 193-81 standards to assess the reinforced concrete by GG in the subgrade of a road or other paved area [32,33].
The effect of adding GG on soil properties was explored in the second stage, and an equation for predicting the shear strength of fine-grained soil reinforced by glass shards was proposed.

Soil properties
The use of waste materials produced in each geographical area for the soil of the same area is one of the goals of this study. Thus, soil resistance parameters such as adhesion, internal friction angle, and grain size were examined in 54 points of the east part of Mashhad, and it was discovered that about 68% of the samples with a tolerance of 0.08% had soil parameters similar to clayey soil named No.36 [34]. So this was chosen as the criterion of the experiments and this sample has been considered as the index soil of the zone of Mashhad. All samples were collected at a depth of 1 m.
The pycnometric tests were conducted twice on materials according to ASTM D4546 standard, and the specific gravity of the soil grains was 2.63, according to the data and findings of the pycnometric experiment. Grain size distribution of the soil was determined on the desired soil using the sieve analysis of fine and coarse aggregates standard procedure ASTM C136. Sedimentation determines the grain size of silt and clay particles that are less than sieve No. 200, so the hydrometric test was carried out on the materials passing through sieve No. 200. Grain size distribution has been provided based on the findings of sieve analysis and hydrometric studies, as shown by the curve in figure 1. It should be noted that glass granule has been used and we have shown the percentage passing through the sieve to be clear about the degree of crushing, glass granules have not been used.
The examined soil is silty clay, which is classified as CL-ML in the Unified Soil Classification System (USCS) based on grain size distribution, hydrometric tests, and Atterberg limits. Table 1 shows the test findings of the soil sample characterization conducted following the experimental description.

Additive/stabilizer
To combine shards of glass with soil, you must first add shards of glass of a specific size to the soil. The glass used in this study was derived from scrap glass collected from soft drink bottles and municipal waste.
The wastes were crushed using the ASTM C131-89 [35] standard procedure in a Los Angeles abrasion machine with 12 steel balls to acquire GG, and then they were kept in different containers based on their diameters. Figure 2 shows a crushed glass granulation diagram. Furthermore, the findings of studies using

Standard proctor tests
The soil sample was subjected to standard Proctor tests, and the soil was treated with various amounts of glass granule. Following that, the maximum dry density and optimum moisture content for untreated soil and soil treated with various amounts of GG (5%, 10%, and 15%) were determined. For the selected cases, figure 3 shows that as the water content increases, the dry density increases until it reaches the optimum moisture content, after which it declines. Figure 3 also shows how the maximum dry density varies with the percentage of GG. The optimal moisture content of materials is reduced when the proportion of GG is increased. In addition, adding 5% by weight of GG reduces the ideal moisture content by around 2%. When it comes to specific gravity, adding GG always raises the maximum dry specific gravity, and the rate of increase is nearly constant which is align with the outcome of the other scholars [13,15,23].

California bearing ratio test (CBR)
California bearing ratio (CBR) tests were carried out following ASTM D1883-16 [36] to investigate the CBR strength of GG treated and untreated soil for use as a pavement subgrade and subbase.
The GG additive and water content were added to the soil based on the maximum dry density after the specimens were made and compacted at optimum moisture content. To reduce experimental errors, three repetitions were carried out.
To obtain complete results, soil samples with various percentages of glass (5,10 and 15%), different densities, and different percentages of moisture (up to optimum) are loaded at this stage. The soil samples are packaged and stored for a maximum of 24 h after reaching the desired moisture content before CBR compaction. According to British standards in BS 1377 [37], the molded clay was compressed using the compaction method with a hammer with a weight of 2.5 kg with fall height of 300 mm compresses soil samples into five equal layers. Then the samples are kept in the mold for 24 hours after compaction to equalize their moisture. The outcomes are depicted in figure 4.
According to the findings, increasing the CBR with waste materials increases the soil strength, and this material can be used to improve the soil properties of the sampled soil (CL-ML). As a result, adding about 5% by weight of glass waste will positively impact CBR, increasing it by 20 to 60%, which is inversely related to the increase in soil density. According to the obtained results, adding 5% of glass granule is the optimal state that increases CBR and adding more than 5% of additive amounts does not have such an effect.
The samples were also subjected to CBR cyclic test in order to determine the effect of adding GG to the soil in road construction projects, which yielded the result as shown in figure 5. It should be noted that adding glass granule has no effect at high hammer blows (56 blows), so the curve is smoothed. According to the obtained results, adding 5% of glass granule is the optimal state that increases CBR and adding more than 5% of additive amounts does not have such an effect.
The outcomes show that adding GG increases the soil strength in the initial cycles; however, increasing the resistance of the treated samples at the initial cycles is not significantly different from the untreated sample. While using GG has a negative effect on soil resistance in high cycles; this can indicate the crushing of GG due to cyclic loading and the loss of its curative effect on the soil. Adding glass granule in cyclic CBR has no effect in low cycles and has a negative effect in high cycles.

Direct shear test
To determine the shear strength of treated soil, direct shear tests were performed in accordance with ASTM D3080 ( figure 6). Despite the fact that the direct shear test is one of the most straightforward methods for determining shear strength, the predetermined fracture plane is regarded as a technical issue [38]. Because dune sand particles were rounded and uniform in size, the impact of this issue could be overlooked to some extent. The direct shear strength tests were conducted by applying a constant strain rate of 1.06 mm/min to soil samples placed in standard shear boxes until the soil failed or a maximum horizontal displacement of 10 mm was reached.
The effect of adding GG on the resistance parameters was investigated at this stage of the research. Determine the amount of shear stress at overheads of 49, 98, and 147 kPa, and examine the performance in zero, 5, 10, and 15% of the GG, as well as the effects of changes in internal friction angle and adhesion with a direct shear machine for different percentage of GGs is evaluated. The effect of different soil densities on these parameters was also investigated with the test sample consisting of soil compacted with 30, 10, and 56 hammer blows to determine the effect of soil density. In this case, the specific gravity of soil at 5% moisture for 10, 30, and 56 hammer blows of the CBR test sample is equal to 18.5, 19.3, and 20.3 (kg/cm3), respectively. Figure 7 shows the effect of adding GG to the soil at various densities on the internal friction angle of the soil, and figure 7 depicts the effect on soil adhesion.
As shown in figure 7, increasing the amount of GG increases the internal friction angle of the soil by about 45 percent at low density, and the rate of this increase decreases at high densities to about 30 percent.
As shown in figure 8, the increasing amount of GG reduces soil adhesion by about 40%, with the effect being more noticeable at higher densities.

Analysis of shear strength results of soil reinforced with GG
In order to provide a relationship in estimating the shear strength of fine-grained soil east of Mashhad reinforced with GG, an analytical study was performed based on laboratory results under the influence of GG and soil density. According to studies, a quadratic relationship with three coefficients is established between the internal friction angle of the soil and the percentage of GG. The coefficients of this relationship also have a linear relationship with density (soil-specific gravity). Based on this, the following experimental equation can be presented to estimate the internal friction angle of the soil: In the equation (1), the amount of friction angle is measured in degrees, G is the weight percentage of GG, and the amount of specific gravity is measured in kilotons per cubic meter.  According to studies, soil adhesion and the percentage of GG have a linear relationship with two coefficients. This relationship's coefficients also have a linear relationship with density (soil-specific gravity). Based on this, the following experimental equation for estimating soil adhesion can be presented: In the equation (2), the amount of adhesion is measured in kilopascals, G is the weight percentage of GG, and the amount of specific gravity is measured in kilotons per cubic meter.

Conclusion
The purpose of this study was to look into the impact of using GG materials on soil parameters. It was looked into incorporating these materials into the required Mashhad improvement soil. The dominant soil in Mashhad's east was determined using samples collected from all over the city's east. Two experimental relationships were presented based on laboratory results. In the unified system, the soil is silty sand with a liquid limit of 25 and a plastic limit of 21, and it is designated as CL-ML. It also has a grain density of 2.63. Its optimum moisture content is around 12%, which is reduced when glass waste is added. The following are some of the most significant findings of this study: • In general, increasing the percentage of GG lowers the materials' optimal moisture content. In addition, adding 5% by weight of GG reduces the optimal moisture content by about 2%. Based on this, the optimal GG weight percentage for achieving optimal humidity is at least about 5%. When it comes to specific gravity, GG generally increase the maximum dry specific gravity.  • Adding GG to material in any situation increases the material's CBR capacity. Depending on the looseness or compactness of the soil and the percentage of GG added, this increase will range from 5 to 40%. However, it can be said that adding 5% by weight of GG is the optimal and desirable amount, both economically and in terms of increasing CBR productivity.
• According to the results of static tests in saturated conditions, the addition of GG to high-density soil reduces its bearing capacity. The addition of GG in saturated conditions to less dense soils, on the other hand, increases productivity by at least 30%. The effects of the number of loading cycles and the percentage of GG on medium-density soils were also investigated by conducting four tests under repeated loading conditions.
• Based on the findings, using GG for fine-grained soils is not recommended in situations where repetitive loading is likely. Furthermore, by examining the effect of sample saturation in both static and repetitive loading modes, it can be concluded that the value of the load-bearing ratio in the saturated mode is significantly lower than in the optimal moisture state. When GG is added to high-density saturated soils, the load-bearing capacity is reduced by about 25%.
• Increasing the GG increases the internal friction angle of the soil by about 30%, which increases the internal friction angle of the soil by about 45% when the density of samples is decreased. The amount of soil adhesion decreases by about 40% when the weight percentage of GG is added, which increases the effect on soil adhesion by increasing soil density.
In general, the presence of GG in fine-grained soil causes the soil particle status to change to granular soils, and thus the soil resistance parameters shift to granular soils. Because friction has more significant effect on the strength and bearing capacity of soil than adhesion, it can be stated that increasing and decreasing the angle of friction and adhesion in soil with GG compared to the reference soil results in greater bearing capacity.