Investigating Load-Settlement Characteristics of Square Model Footings on Sand Beds Enhanced with Textured Vertical Pultruded Fiberglass Reinforced Helical Piles

doi:10.21203/rs.3.rs-4310084/v1

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Investigating Load-Settlement Characteristics of Square Model Footings on Sand Beds Enhanced with Textured Vertical Pultruded Fiberglass Reinforced Helical Piles

https://doi.org/10.21203/rs.3.rs-4310084/v1

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This article introduces a novel ground enhancement method utilizing textured vertically oriented fiberglass pultruded pipes. These pipes feature a widened bottom toe in a helical shape. The research primarily explores textured prefabricated helical piles, varying in length and cross-sectional area, designed to act as reinforcing bearing elements in sandy soil. The ongoing study includes performing experimental investigations on a laboratory model square footing positioned on sand, with textured PFRH piles installed beneath it. A parametric investigation was carried out to examine the influence of textured PFRH pile slenderness ratio, different states of sand beds, and varying helical plate diameters through laboratory model plate load tests. The findings indicated that placing textured PFRH piles beneath the footing substantially enhanced the settlement characteristics and load-carrying capacity of the structure. There was a noticeable increase in load-carrying capacity with an increase in the slenderness ratio of textured PFRH piles, although the improvement became insignificant beyond a slenderness ratio of 20. In the absence of reinforcement, denser sand exhibited superior bearing capacity for footings. However, in the case of reinforced footings, textured PFRH piles demonstrated the most substantial improvement in medium-density sand. Furthermore, augmenting the helical plate diameter led to an enhanced load-carrying capacity. The study employed multivariate linear regression to establish a robust correlation between experimental and predicted bearing capacity ratios, affirming the reliability of the findings. In summary, this research underscores the significant potential of utilizing textured prefabricated helical piles in fortifying soil foundations, offering valuable insights for optimizing the design and performance of such systems across diverse soil conditions.

Textured pultruded fiber reinforced helical piles

PFRHP’s

Laboratory model square footing

Sand bed

Laboratory model plate load test

Settlement characteristics

Load-carrying capacity

Addressing the settlements of buildings and structures induced by soft soil conditions continues to pose a persistent challenge in geotechnical practices [32, 30]. The challenge becomes more intricate when dealing with foundations built on sloping terrains, soft soils, regions prone to seismic activity, and other adverse geological conditions [46]. Conventional ground improvement methods and materials come with various drawbacks, such as high expenses and impracticality. Additionally, there's a frequent concern about electrochemical corrosion, which can compromise the overall integrity of the overlying construction. Hence, the immediate challenge is to devise practical and efficient approaches to guarantee stable, secure, and cost-effective restoration [33]. Environmentally friendly materials, including geopolymers, expanding resins, bamboo, fiberglass materials, and others, contribute to sustainability. These options comprise eco-friendly geopolymers, expanding resins, natural elements like bamboo, and fiberglass materials, among others [24, 29, 31, 53]. In practical applications, integrating reinforcing elements like micro and helical piles into ground improvement strategies stands out as one of the widely adopted and effective methods for enhancing ground conditions. Various approaches have emerged in this field, with the utilization of horizontal micropiles being among the noteworthy developments [39]. Usmanov's research employed layers of compaction to strengthen weak soils through the application of high-strength geosynthetic materials (HSGM) [45]. A substitute for conventional sand or gravel-type reinforcing piles involves the use of geosynthetic mats encompassing bore pile shapes Shenkman and Maltseva introduced a settlement calculation method based on the reinforcement procedure [38, 41]. Waruwu conducted a study on the underpinnings of natural foundations. [49].

As per Popov, the calculation process should take into account vertically mounted soil-reinforcing devices [27]. To explore soil reinforcing behavior, Sabri employed an expandable polyurethane resin injected into the soil mass through hydrofracturing [29, 31]. Sabri presented an innovative method for calculating the reinforced deformation and strength properties of soils treated with expandable polyurethane resin post-injection. This approach incorporates resin as a solid reinforcing element in vertical orientations [24].

According to Shalenny, regulations do not include references to fiberglass or similar composite materials. Instead, codes stipulate vertical reinforcement using traditional materials such as concrete, geosynthetic-encased columns, steel, and crushed stone [34]. The concept of soil vertical reinforcement offers a practical solution to bolster ground strength and address foundation challenges. This approach involves fortifying the soil by introducing new elements with improved strength characteristics, featuring various shapes and materials, into the soil structure. Numerous studies have delved into the utilization of cement grouting and vertically expanding geopolymers as rigid inclusions [4, 17, 24, 28, 30, 32, 42]. A highly promising avenue in sustainable engineering is the quest for materials suitable for soil strengthening, with the utilization of recycled materials presenting substantial potential for application [22].

The use of fiberglass in diverse contexts, particularly in Fiber Reinforced Polymer (FRP) for geotechnical applications, has experienced notable growth in recent years, influenced by various factors. Several numerical and practical studies have been carried out to evaluate the effectiveness of micropiles in improving soil strength in geotechnical applications [1, 8, 11, 36, 37, 50, 52]. Valez examined the performance of carbon fiber piles in both stabilized and non-stabilized soft soils, along with fiberglass piles [14]. The findings of this study revealed greater adhesion and bearing strength when compared to steel piles. Sirimanna conducted tests on epoxy coating as a potential solution to address delamination issues [16]. Introducing epoxy coating between the shell and core improved cohesion and dynamic load transfer for the driven piles. However, further research is necessary to address the impact of delamination on the bearing capacity of the piles, particularly under lateral and torsional forces. The existing body of research on micropiles as soil-reinforcement elements is insufficient for a comprehensive understanding of the behavior of the studied composite structures in soft soils and their combined effects [22]. Shashkin and Ulitskii emphasized that the majority of existing methods used for settlement calculations show limited correlations with the practical test results observed in extensive experimental investigations [44]. Nurmukhametov introduced a method for calculating settlements in soil reinforced with vertically oriented fiberglass micropiles [25]. A review of the literature highlights numerous advantages associated with the application of fiberglass materials in practical scenarios. Fiberglass micropiles, known for their straightforward installation, cost-effectiveness, and substantial load-bearing capacity in both horizontal and vertical configurations, have become increasingly popular in recent years as a form of vertical soil reinforcement using FRP. However, challenges persist in the utilization of FRP due to insufficient theoretical and practical validation of ground improvement trends with these materials. Moreover, there is a shortage of calculation methods for assessing deformation and strength properties post-reinforcement. Additionally, the connection methods between fiberglass materials and steel or concrete remain underdeveloped and warrant further exploration.

1.1. Objectives

This article aims to propose a soil reinforcement technique involving the vertical installation of texture pultruded fiberglass-reinforced helical piles into the ground. The main goals of the study were:

To analyse the effect of slenderness ratio of PFRH piles.

To analyse the effect of varying diameters of helical blades of PFRH piles on footing.

To analyse at what relative density the stabilisation by the PFRH piles is maximum.

To study MLR analysis for development of a predicted model.

This article proposes a soil reinforcement method that entails vertically installing texture pultruded fiberglass-reinforced helical piles into the ground. The experimental program consisted of two stages: material characterization and experimental setup. During material characterization, the physical and chemical properties of the utilized materials were assessed (refer to Fig. 1).

2.1. Sand

Local river sand sourced from the Jhelum River in the Himalayan region of North India was employed in the testing program. Sand was acquired from the Sumbal region of Bandipora district in Jammu and Kashmir, pinpointed at coordinates 34°11'05.9" N, 74°04'26.6" E, as illustrated in Fig. 2. The assessment of material properties was carried out in accordance with ASTM and Indian standard test protocols. Prior to testing, meticulous cleaning and washing procedures were executed to eliminate any undesirable elements such as tree roots, pebbles, and other debris. The sand used in this study falls within the category of poorly graded sand (SP) as per the Indian Standard Soil Classification System. Figure 3 illustrates the grain-size distribution of the sand, and Table 1 provides a summary of its physical characteristics. All tests were performed following the relevant Codal procedures (ASTM and IS: 1498; IS: 2720).

Table 1

Characteristics of Sand Utilized in the Study.
S.No.	Property	Value
1	D₁₀ (mm)	0.15
2	D₃₀ (mm)	0.20
3	D₆₀ (mm)	0.27
4	D₅₀ (mm)	0.25
5	Coefficient of curvature, C_C	0.95
6	Coefficient of uniformity, C_U	1.82
7	Specific gravity, G	2.67
8	e_max	0.74
9	e_min	0.42
10	Friction angle, ϕ
	At 30% RD	29.65^o
	At 50% RD	35.41^o
	At 80% RD	40.08^o
11	Maximum dry unit weight (kN/m³)
	At 30% RD	15.50
	At 50% RD	16.10
	At 80% RD	17.30
12	Classification of soil type (ISSCS)	SP

In the experimental study, dry sand was utilized, and this dry condition was achieved using the pluviation technique simulating rainfall [5, 6]. The density of the sand under specific conditions is influenced by both the height of pluviation and the rate at which the sand is discharged [21].

To regulate the sand's descent height, adjustments were made to the pluviation tray's position relative to the sand bed. A sequence of experiments, employing different fall heights, demonstrated that enabling the sand to descend consistently through a strainer from heights of 40 cm, 60 cm, and 90 cm yielded relative densities of 30%, 50%, and 80%, respectively. To confirm uniform relative density across the board, samples of sand were gathered in containers with known volumes, strategically positioned at various locations within the tank.

Using this approach, the average dry unit weights attained for relative densities of 30%, 50%, and 80% were 15.5 kN/m³, 16.1 kN/m³, and 17.3 kN/m³, correspondingly.

X-ray diffraction analysis of sandy soil is shown in Fig. 4 and X-ray fluorescence results of sandy soil are shown in Fig. 5 and it can be depicted that the soil contains mainly oxides of silicon, calcium, and aluminum.

2.2. The Investigated Textured Pultruded Fiberglass Reinforces Helical Piles

In laboratory model tests, it is crucial that the dimensions of the reinforcement are in proportion to the dimensions of the footing [20]. Obtaining vertical reinforcement that meets the similarity criteria of experimental models in the laboratory while exerting minimal qualitative and quantitative impact on the outcomes presents a formidable challenge. The materials for fabricating FRP (Fiber-Reinforced Polymer) were procured from "Fibertech Composite Private Limited" in Gujarat, India. Table 2, compiled from data supplied by the manufacturer, delineates the attributes of pultruded fiber-reinforced rods. Figure 6 illustrates the materials utilized in this study.

Table 2

Mechanical Properties of Pultruded Fiberglass Reinforced rods.
S.No.	Physical property	Value
1	Weight / Material length (N/mm)	0.006
2	Ultimate tensile strength (MPa)	637
3	Poisson’s ratio, µ	0.25
4	Longitudinal Modulus of elasticity, E_l (MPa)	4.45 x 10⁴
5	Thermal coefficient of expansion (/˚C)	1.5 x 10^− 6

2.3. Experimental Setup

For the testing procedures, a rigid metal container, measuring 1000 mm × 1000 mm × 1000 mm and fabricated from 6 mm thick steel plates, was utilized. To enhance stability and prevent buckling during the experiments, stiffeners were welded to the plates. This metal tank served as the framework to secure the soil beds in position. Additionally, a 200 mm x 200 mm, 20 mm thick mild steel plate was employed as the model footing.

To reduce the influence of the boundary effect, the ratio between the dimensions of the tank and the dimensions of the footing was maintained at a value greater than four [9]. The bottom of the footing was affixed to a layer of sand using adhesive to create a textured surface [23]. The vertical load was applied concentrically to the footing, situated on the sand, using a loading jack affixed to the loading frame. A calibrated proving ring was employed to gauge the applied load accurately. For measuring the settlement of the model footing, two transducers (CDP-50) were utilized. These transducers were positioned on opposite sides of the model footing and connected to a data logging system (TDS540) from TML Japan, which collected data through static measurement software (TDS-7130v2).

Textured pultruded fiberglass-reinforced helical (PFRH) piles were installed underneath the footing at different relative densities, slenderness ratios, and helical plate diameters. Employing the non-displacement method of installation, the initial step involved filling the tank up to the pile tip. Subsequently, the pile was vertically placed at the center of the tank. The remaining volume of the tank was filled utilizing the pluviation technique, simulating rainfall. Throughout this process, the pile was carefully maintained in a vertical position. To ensure precision, the top surface of the sand bed was meticulously leveled and examined using a spirit level.

The configuration of the test is depicted in Figs. 7and 8.

The settlements of the footing were documented as a dimensionless parameter (s/B), known as the settlement ratio. Here, "s" signifies the plate's settlement, and "B" represents the plate's width. The ultimate load-bearing capacity of the footing, both with textured PFRH piles (qr) and without textured PFRH piles (qur), was derived from the load-settlement curve by identifying the load value corresponding to a relative settlement of 10% of the footing's width (B) [12]. The failure criterion for the footing was established as a settlement of 20 mm for the plate, which has a width of 20 cm, or equivalently, a relative settlement of 10% [18, 19]. Hence, the tests were stopped when the footing settlement reached 20 mm or slightly exceeded it. To facilitate a comparison of the test outcomes, a dimensionless metric called the Bearing Capacity Ratio (BCR), represented as qr/qur, was employed. The BCR signifies the ratio of the footing's bearing capacity with and without the presence of PFRH piles.

3.1. Impact of slenderness ratio of the PFRH piles

The load versus settlement graphs for different l/d (slenderness ratios) of PFRH piles are presented in Fig. 9. These tests were conducted with a helical diameter of 65 mm and a relative density of 50%. Detailed information regarding the model test series, which includes various slenderness ratios for PFRH piles, can be found in Table 3.

Table 3

Details of model test series with varying slenderness ratio of PFRH piles.
S.No.	Type of Reinforcement	Fixed Parameter		Variable Parameter	Load corresponding to 20mm settlement (kN)	Improvement in Load-carrying capacity (%)
S.No.	Type of Reinforcement	Relative Density, RD (%)	Helical Plate Diameter, d' (mm)	Slenderness Ratio, l/d	Load corresponding to 20mm settlement (kN)	Improvement in Load-carrying capacity (%)
1	Unreinforced	50			22
2	Reinforced	50	65	10	34	52
3	Reinforced	50	65	15	37	9
4	Reinforced	50	65	20	41	11
5	Reinforced	50	65	25	43	4

In the case of unreinforced soil, it's important to note that the load corresponding to a foundation settlement of 20 mm is 22.28 kN, which serves as the baseline for comparison. Figure 10 illustrates the graph depicting the relationship between the Bearing Capacity Ratio (BCR) and the slenderness ratio, assuming a helical diameter of 65 mm and a relative density of 50%. The graph reveals that as the l/d (slenderness) ratio increases, the BCR also increases. Specifically, there is a significant 9% improvement in BCR when transitioning from an l/d ratio of 10 to an l/d ratio of 15. However, as the l/d ratio is further raised from 15 to 20, the change in BCR displays minor fluctuations. Nonetheless, the rate of percentage improvement in BCR diminishes as the l/d ratio extends beyond 20 and reaches 25. These consistent trends align with the findings of a study conducted by Sharma [35]. They also noted that once a specific slenderness ratio value is reached, the improvement remains relatively stable. The resistance of PFRH piles to loading is primarily attributed to the skin friction developed along their shafts, and this behavior is influenced by the l/d ratio [5, 35]. As the l/d ratio increases for a specific textured PFRH pile diameter, the frictional resistance also rises, resulting in a more robust confinement effect. Consequently, there is a substantial reduction in the footing settlement, leading to an improvement in bearing capacity. Figure 11 depicts the relationship between BCR and settlement ratio (s/B), while Fig. 12 illustrates the relationship between BCR and settlement (s), both considering varying l/d ratios of the PFRH piles. These graphs clearly demonstrate that as the l/d ratio increases, the percentage increase in BCR decreases for a given settlement ratio. The most significant percentage decrease in BCR is observed when transitioning from an l/d ratio of 20 to 25. This suggests that beyond a certain optimal threshold, increasing the slenderness ratio of the PFRH piles has minimal impact on the load-bearing capacity. The installation of piles at a distance beyond a specific depth from the influence zone of the footing does not significantly affect the load-bearing capacity, and it remains relatively constant [19].

3.2. Impact of Helical Diameter

The load-settlement correlation resulting from tests conducted using textured PFRH piles with different helical diameters, while maintaining a relative density of 50% and a slenderness ratio of 20, is illustrated in Fig. 13. Detailed information regarding the model test series, which encompasses varying helical diameters of PFRH piles, are highlighted in Table 4.

Table 4

Details of model test series with varying helical diameter of PFRH piles.
S.No.	Type of Reinforcement	Fixed Parameter		Variable Parameter	Load corresponding to 20mm settlement (kN)	Improvement in Load-carrying capacity (%)
S.No.	Type of Reinforcement	Slenderness Ratio, l/d	Relative Density, RD (%)	Helical Plate Diameter, d' (mm)	Load corresponding to 20mm settlement (kN)	Improvement in Load-carrying capacity (%)
1	Unreinforced		50		22
2	Reinforced	20	50	25	34	53
3	Reinforced	20	50	45	37	9
4	Reinforced	20	50	65	41	11

The plot clearly shows that as the helical plate diameter of PFRH piles increases, the maximum ultimate load also increases, reaching its peak at a helical diameter of 65 mm. This aligns with the findings of Abdel-Rahim, Kamal Taha, and El din El sharif Mohamed in 2013, which indicate that load-carrying capacities increase with a larger helix diameter [2]. According to Fig. 14, the relationship between BCR and the helical plate diameter of textured PFRH piles reveals that the maximum enhancement provided by the textured PFRH pile is attained at a helical plate diameter of 65 mm when reinforcing the sand. Conversely, for a helical plate diameter of 25 mm, the improvement is minimal, approximately 53% higher than that observed in unreinforced sand scenarios. The diameter of helical piles directly impacts their load-carrying capacity. Larger diameters offer a greater bearing area, allowing the pile to support a higher load without experiencing excessive settlement or failure.

Figure 15 and Fig. 16 display the relationship between BCR and settlement ratio (s/B) as well as BCR and settlement (s), respectively, across varying helical plate diameters of textured PFRH piles. These plots clearly indicate that larger helical plate diameters of textured PFRH piles result in the most significant improvements for each settlement ratio. This observation may be attributed to the pile diameter influencing the surface area in contact with the surrounding soil, thereby affecting the frictional and bonding characteristics between the pile and the soil. Larger diameters provide more surface area for soil interaction, leading to increased skin friction and bonding. Consequently, this enhances the overall load-carrying capacity and stability of the piles.

3.3. Impact of relative density

Figure 17 displays the load-settlement curve obtained from tests conducted at various relative densities of the sand, employing a helical diameter of 65 mm and a slenderness ratio of 20. Comprehensive details regarding the model test series, which encompasses a range of relative densities for the sand beds, are highlighted in Table 5.

Table 5

Details of model test series with varying relative density.
S.No.	Type of Reinforcement	Fixed Parameter		Variable Parameter	Load corresponding to 20mm settlement (kN)	Improvement in Load-carrying capacity (%)
S.No.	Type of Reinforcement	Slenderness Ratio, l/d	Helical Plate Diameter, d' (mm)	Relative Density, RD (%)	Load corresponding to 20mm settlement (kN)	Improvement in Load-carrying capacity (%)
1	Unreinforced			30	13
				50	22
				80	26
2	Reinforced	20	65	30	19	45
3	Reinforced	20	65	50	41	84
4	Reinforced	20	65	80	47	83

The graph clearly demonstrates that as the relative density of the sand increases, the maximum ultimate load also rises, peaking at its highest value when the relative density reaches 80%. Tsukada also noted that the bearing capacity reached its maximum when the sand was in a more compact state [43]. Analyzing Fig. 18, it can be deduced that the relationship between BCR and the relative density of sand indicates that the textured PFRH pile provides its most significant improvement at a relative density of 50% when reinforcing the sand. Conversely, in scenarios with a relative density of 30%, representing loose sand conditions, the improvement is modest, approximately 45% higher than what is observed in unreinforced sand scenarios. These variations in load-bearing behavior can be attributed to the sand's dilatancy characteristics, which are influenced by its relative density [43]. The enhanced shear strength properties of the sand beneath the footing are influenced by the dilatant behavior of the sand. In dense sand, the dilatant deformation behavior leads to increased horizontal stress, thereby enhancing the bearing capacity as it confines the textured PFRH piles within this rising horizontal stress. Conversely, in loose sand, the horizontal stresses may decrease, resulting in reduced confining pressures and, consequently, a decrease in bearing capacity [43]. Figure 19 and Fig. 20 present graphical representations illustrating the relationship between BCR and settlement ratio (s/B) and BCR and settlement (s), respectively, across various relative densities of the sand. These plots clearly demonstrate that the most substantial improvement is observed at the intermediate (50%) relative density of the sand for all settlement ratios. While there is indeed a noticeable enhancement at the denser (80%) state, it is relatively less pronounced when compared to the improvement observed in medium-density sand. This phenomenon can be attributed to the tightly packed arrangement of sand particles in the denser state, allowing less room for particle mobility. Conversely, in the medium-density state, the sand particles are less densely packed, facilitating greater movement. As a result, the confining stress applied by the textured PFRH pile is more prominent in the medium-density state compared to the denser state of the sand.

The multivariate linear regression (MLR) model elucidates the significant interconnection between independent and dependent variables [10]. MLR serves as a statistical technique employed to predict the outcome of a variable (dependent variable) by considering various factors (independent variables). The general equation of MLR model is:

$$Z=A+ A1X1+A2X2+A3X3+ \dots ..AnXn$$

Where, Z is the dependent variable A1, A2, …… An are regression coefficients X1, X2, X3, …… Xn are independent variables A is the intercept on y-axis.

MLR models were constructed using data derived from experimental investigations. The dependent variable for each multiple linear regression analysis was the BCR, while the independent variables included the slenderness ratio (l/d), helical diameter (d'), and relative density (Rd) (refer to Fig. 21). After completing the analysis, the intercept and coefficient values were computed, resulting in the formulation of the following linear regression equation:

$$BCR=0.5756+ 0.0244\left(\frac{l}{d}\right)+0.0056\left({d}^{{\prime }}\right)+0.0066\left(Rd\right)$$

The statistical findings closely align with the experimental results, showcasing a significant relationship, as evidenced by p-values below 0.1 for all dependent variables. Table 6 lists the results of regression analysis. To validate the accuracy of the predicted regression equation, bearing capacity ratios for various combinations of dependent parameters are computed using Eq. 1. The graph illustrating the experimental BCR against the predicted BCR demonstrates a good correlation, with an R² value of = 0.9977 as shown in Fig. 22. Therefore, Eq. 1 proves to be a robust tool for assessing the extent of improvement achieved through the installation of textured PFRH piles beneath footings, particularly in the case of cohesionless soils.

Table 6

Regression Analysis Results
Variable	Coefficients	Value	Standard Error	t-value	P-value
Bearing Capacity Ratio, BCR	Intercept	0.57563	0.28363	2.02948	0.08873
	Slenderness Ratio, l/d	0.02444	0.00902	2.71007	0.03510
	Helical Diameter, d'	0.00563	0.00264	2.13652	0.07652
	Relative Density, Rd	0.00659	0.00295	2.23566	0.06674

The experimental data utilized in this study was obtained through small-scale laboratory testing, offering a valuable method for assessing prototype behavior [13, 15]. Nevertheless, it is essential to recognize that certain discrepancies may exist between small-scale laboratory models and actual prototypes, primarily stemming from scale effects, which can be particularly pronounced in granular soils [7]. The variation primarily arises due to the difference in stress levels between the two scenarios. Additionally, the ratio of the footing size to the size of granular soil particles can also play a role in the observed discrepancies [20]. Stresses experienced in small-scale laboratory models tend to be lower than those encountered in full-scale field tests, resulting in a higher angle of internal friction observed during small-scale testing. This higher angle of internal friction leads to an increased shear strength along the slip line beneath the footing in small-scale tests. Conversely, full-scale field conditions yield a lower shear strength due to variations in stress levels. Additionally, real-world situations often involve neighboring building footings, which introduce stress interactions beneath foundations, a factor that should be taken into account.

Scale effects stemming from differences in footing and soil particle sizes can be neglected when the dimensions of the footing are significantly larger than the size of soil particles. Nevertheless, in 1 g (earth gravity) modeling, variations in stress levels between real footings and small-scale testing introduce scale effects. Despite this, small-scale 1 g models provide substantial value for exploring common behavioral patterns. However, for a comprehensive understanding of design parameters, tests utilizing centrifuge models and analyses based on full-scale field tests are indispensable.

Textured PFRH piles offer a practical solution for enhancing the bearing capacity of sand deposits. The incorporation of these piles beneath the foundation induces soil compaction in the surrounding area, leading to improved load-settlement characteristics. Through laboratory model tests conducted on foundations placed atop sand reinforced with textured PFRH piles, we have examined the impact of various parameters on footing behavior under vertical concentric loading. From these experiments, the following conclusions can be drawn:

The load-carrying capacity is significantly affected by the slenderness ratio of textured PFRH piles. An increase in the slenderness ratio results in a substantial improvement in load-bearing capacity. The increase in load-carrying capacity ranged up to 52%, transitioning from unreinforced soil to reinforced conditions. However, when the slenderness ratio exceeds 20, the enhancement becomes minimal, suggesting the presence of an optimal range for this parameter.

The diameter of the helical plates in textured PFRH piles plays a crucial role in increasing the bearing capacity of footings. An increase in the diameter provides a larger bearing area, allowing the pile to support a higher load without experiencing excessive settlement or failure. The improvement in load-carrying capacity varied up to 53%, shifting from soil without reinforcement to conditions with reinforcement.

The bearing capacity of the footings is influenced by the relative density of the sand. As the sand shifts from a loose state to a denser state, the bearing capacity increases. This is attributed to the heightened confining stresses beneath the footing and around the textured PFRH piles in denser sand conditions. Interestingly, the most significant improvement due to textured PFRH pile installation is observed at a relative density of 50%. Remarkably, the most significant improvement observed through PFRH pile installation is evident at a relative density of 50%, showing an increase to 84%.

The projected BCR (Bearing Capacity Ratio) values closely align with the experimental results, underscoring a strong correlation between the two. This suggests that the established linear regression model effectively predicts the extent of improvement provided by textured PFRH pile installation across various situations.

In summary, this study demonstrates the effectiveness of textured PFRH piles in enhancing the bearing capacity of footings in sandy deposits. Understanding the influence of factors such as slenderness ratio, sand's relative density, and helical plate diameter is crucial for optimizing the design and effectiveness of foundations that utilize textured PFRH piles in geotechnical applications.

Textured PFRH, Textured Pultruded Fiberglass Helical Piles; L, length of the PFRH pile; B, width of the footing; d, diameter of the PFRH piles; d’, diameter of helix; s, settlement of the footing plate; l/d, slenderness ratio of the PFRH piles; RD, relative density of sand; s/B, settlement ratio of PFRH piles; q_ur, ultimate bearing capacity of the footing without PFRH piles; q_r, ultimate bearing capacity of the footing with PFRH piles; BCR, bearing capacity ratio.

Acknowledgements The authors are extremely thankful to the authorities of NIT Srinagar, particularly to Faculty of Geotechnical Engg. Division and supporting staff of the Soil Mechanics laboratory, for helping us execute this project at the institute.

Availability of data and materials All the data was generated through experimental tests performed in the laboratory by the authors.

Author contribution Abdul Hanan Bashir Zargar: Testing, data analysis, and writing - original draft preparation

Dr. Yousuf: conceptualization, methodology, reviewing and editing.

Ethics approval and consent to participate Not applicable

Consent for publication Not applicable

Competing interest The author declares no competing interests

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Investigating Load-Settlement Characteristics of Square Model Footings on Sand Beds Enhanced with Textured Vertical Pultruded Fiberglass Reinforced Helical Piles

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Abstract

Figures

1. Introduction

1.1. Objectives

2. Materials and Experimental Procedures

2.1. Sand

2.2. The Investigated Textured Pultruded Fiberglass Reinforces Helical Piles

2.3. Experimental Setup

3. Results and discussion

3.1. Impact of slenderness ratio of the PFRH piles

3.2. Impact of Helical Diameter

3.3. Impact of relative density

4. Multivariate linear analysis

5. Scale effects

6. Conclusions

Abbreviations

Declarations

References

Additional Declarations

Status:

Version 1