Mining Engineering and Mine Planning
Transforming Underground Stability and Extraction
Three Level Sequential Recovery of Ore Pillars in sublevel stopping: A Geomechanical Approach to Blast Design for Sustainable Underground Mining *O. Barrios1, E. Asencios2, H. Soria2, N. Vásquez1 1Orica Blasting Engineering, Orica Mining Services, Peru, (*Presenting author: omar.barrios@orica.com) 2Colquisiri Mining Company, Mine Planning Department, Peru ABSTRACT Sublevel Stoping (SLS) is a widely used underground mining method for extracting massive ore bodies, high thickness stratiform orebodies, and narrow vein-type orebodies. Its key advantages include high mineral recovery rates—often exceeding 90%—and efficient mechanization of the mining cycle, resulting in improved productivity and reduced operational costs. At the María Teresa mine, operated by Minera Colquisiri, SLS is applied to primary stopes, leaving intermediate pillars (secondary stopes) for later recovery through a descending, retreating sequence. This process involves preparing crosscuts at four access levels and executing radial positive drilling over three secondary blocks. The main technical challenge is achieving recovery above 90% while controlling overbreak and dilution in lateral walls composed of cemented hydraulic fill. These walls are exposed to final openings approximately 60 m in height, 12 m wide, and 15 m long, requiring rigorous geomechanical stability, optimized blast design, and differentiated planning. KEYWORDS Sublevel Stoping (SLS), sequential stope recovery, underground mine design, geomechanics and stability, cemented hydraulic fill, overbreak control, blast optimization, drill deviation measurement, blast vibration monitoring, stope recovery efficiency, sustainable mining infrastructure, retreat mining strategy, World Mining Congress 1. INTRODUCTION Colquisiri Mining Company operates the María Teresa underground mine, located in Huaral Province, Department of Lima, Peru, at an average elevation of 150 m above sea level (approximate coordinates: 11° 21' 45" S, 77° 8' 25" W; UTM Zone 18S WGS84: approximately 8,735,000 m N, 311,000 m E). The operation exploits a volcanogenic massive sulfide (VMS) polymetallic deposit characterized by lenticular ore bodies. The principal mineralized structure currently under extraction is the Sofía D ore body, which supports a daily production rate of approximately 1,600 metric tons of ore delivered to an on-site concentrator plant producing zinc, lead, silver, and copper concentrates. The site operates in close proximity to agricultural land and incorporates full recirculation of process water together with contained tailings management to limit environmental footprint.
Sublevel open Stoping (SLS) with cemented hydraulic backfill is the selected mining method at María Teresa mine. The mining sequence employs a primary-to-secondary stope extraction pattern in a descending and retreating configuration. Secondary stopes act as temporary rib pillars between primary stopes during the initial extraction phase and are subsequently recovered using a multi-level sequential approach that involves access development and drilling from three separate levels. Final secondary stope dimensions reach heights of up to approximately 60 m (spanning multiple sublevels), widths of 12 m, and lengths of 15 m. Consequently, the exposed cemented hydraulic fill (CHF) walls constitute one of the primary bounding surfaces during secondary stope production. This paper presents a practical methodology implemented at the María Teresa mine for the three-level sequential recovery of ore pillars in SLS. The main technical challenge is to minimize instability and failure of the CHF walls exposed during secondary stope extraction, while ensuring optimal fragmentation from the large-scale blasts and achieving effective dilution control. The approach integrates geomechanical stability assessments, optimized ring drill-and-blast designs, drilling quality control measures, blast vibration studies, and 3D post-blast stope surveys. 2. METHODOLOGY The three-level sequential recovery of ore pillars was developed based on a comprehensive understanding of the deposit's natural conditions (geology, geometry, and hydrogeology), the surrounding rock mass response, the performance of drilling and blasting designs, drilling execution quality, blast-induced damage control, and field-measured outcomes in terms of fragmentation and overbreak. To ensure process reliability and validate performance, the implementation followed a structured, five-stage methodology: (1) Geological and Geomechanical characterization (2) Blast Vibration Monitoring (3) Drilling Quality Control, (4) Blast pattern design and simulation and (5) Volumetric surveys of mined stopes. 2.1 Geological and Geomechanical characterization 2.1.1 Local Geology The host rocks consist predominantly of volcanic and subvolcanic sequences of Late Cretaceous age, ranging in composition from basaltic andesite to rhyodacite (calc-alkaline series). 2.1.2 Deposit characteristics The María Teresa deposit consists primarily of lenticular massive sulfide bodies whose longitudinal axes are preferentially oriented N150°E (Figure 1). These orebodies have irregular geometries that grade laterally and with depth into lower-grade veinlet mineralization. One of the largest orebodies contributing to current production is the Sofía D body. It is with approximate dimensions of 700 m along its major axis (N150°E), up to 200 m in width, and vertical thickness decreasing from 70 m in the southwest to only a few meters in the northeast. Along the same N150°E structural lineament, a new mineralized zone exceeding 300 m in length - currently under exploration - has been identified and designated Sofía E.
Figure 1 – Left: Local geological map. Right: Geological sections. The principal economic minerals are sphalerite, tetrahedrite-tennantite (Ag-bearing, with As > Sb), chalcopyrite, and galena. Both the Sofía D and Sofía E orebodies exhibit well-defined vertical zoning, transitioning from Cu-rich (chalcopyrite-dominated) mineralization at the base to Zn–Pb–Ba-rich assemblages toward the top. Mineral reserves are currently estimated at 4.5 million metric tons, with average grades of 1.8 oz/t Ag, 0.82% Pb, 7.6% Zn, and 1.2% Cu. 2.1.3 Geomechanical characterization María Teresa mine has three main structural domains (SD): SD-II, SD-IIIA, and SD-IIIB. The zoning was established using the Bieniawski Rock Mass Rating (RMR) classification system. Within the deposit area, SD-IIIA and SD-IIIB predominate in the mineralized zone, with only minor presence of SD-IVA. In contrast, SD-IIIA is the prevalent domain in both the immediate and distant wall-rock zones (Figure 2). Figure 2 – Geomechanical zoning of Sofia D body (DCR Ingenieros S.R.L. Geomechanical study,2018) 2.1.4. Stope and pillar design parameters Based on the classification of mining geo-conditions, appropriate parameters were selected to determine the stope dimensions. Stope design was performed using the stability chart method
(Figure 3) and complementary stability analysis. In this geomechanical study, the criteria proposed by Nickson et al. (2001) was adopted. Their stability chart incorporates the calculation of the stability number “N,” which makes it particularly suitable for the complex and variable ground conditions encountered at the María Teresa mine. Figure 3 – Sofia D Geomechanical zoning, on the right side the calculated values of “N”. (DCR Ingenieros S.R. Ltda. Geomechanical Study,2018) 2.2 Blast vibration monitoring All blasting operations require precise control to minimize their disruptive effects on nearby structures and the environment. As described earlier, recovery of the secondary stopes at Sofia D employs mass blasting, with radial boreholes drilled in a burden-spacing pattern tailored to the rock mass characteristics. To characterize the propagation of detonation-induced waves and assess their potential impact on exposed CHF walls and overall geomechanical stability, blast vibration monitoring was implemented. Vibration data were collected using seismographs equipped with triaxial geophones, which recorded particle velocity waveforms. Sensors were strategically installed at the undercut level across multiple near-field (typically 10–50 m) and far-field (>50 m) locations relative to the blast source. Measurements of peak particle velocity (PPV) and corresponding scaled distances enabled regression analysis (log-log plot of PPV versus scaled distance) to derive site-specific attenuation constants (K and α) for the ground vibration attenuation law. This followed the widely accepted USBM scaled-distance form: PPV = K . (SD) −α =K . (ඥ D Q)−α (1) Where: PPV: Peak-Particle Velocity (mm/s) SD: Scaled distance D: Distance from the blast source (m) Q: Maximum charge per delay (kg) K: Propagation coefficient
α: Attenuation coefficient (range 0.5 - 2) 2.2.1 Ground vibration attenuation law From the blast vibration monitoring carried out at the María Teresa mine, a set of 75 seismographic records obtained was grouped (Figure 4), from which the following scatter plot was obtained: Figure 4. PPV values registered by the seismographs at María Teresa. Source: Orica Blast Engineering From the graph above, by plotting the trend line of the data distribution with respect to the scaled distance, a general ground attenuation law is obtained: PPV = 1909.83 x( DඥQ )−2.01 This attenuation law has a correlation coefficient (R²) of 0.87, which is acceptable. However, for each peak particle velocity (PPV) value estimated with this model, the probability of not exceeding the established limit will be 50%. This scatter results in moderate correlation in direct fits (R² typically 0.70-0.90) and can cause the fitted attenuation exponent α to deviate from the value that best captures the observed far-field decay. 2.2.2 Seismograph Calibration and Site-Specific PPV Damage Criteria To ensure that the blast design does not exceed the limit established by the standard (USBM RI 8507, 1980), the reliability level of the attenuation law must be increased. A practical and safe way to do this is to shift the curve obtained at 50% reliability upwards, parallel to the line, so that the points located below the line relative to the total number of points are numerically equal to the desired reliability value. Thus, with the 75 seismographic records, statistical analysis was performed to calculate the mean, standard deviation, and standard error. These parameters provided the input to estimate the confidence intervals and find the “K” coefficient at 95% reliability (See Table 6).
Table 2 – Coefficient “K” determined at 95% reliability from the ground attenuation law at 50% confidence. Source: Orica Blast Engineering. Site Law Coefficients Site Coefficient 50 % Confidence 95 % Confidence K 1909.83 4820.30 -α -2.01 -2.01 Standard Error 0.21 Therefore, the 50% and 95% reliability curves were obtained, as shown here: Figure 5. Scatter plot with attenuation laws at 50% and 95% confidence. Source: Orica Blast Engineering. Based on the above, the ground attenuation law is used with a 95% reliability level because, under this constraint, the value of the maximum instantaneous charge (MIC) can be determined, thus avoiding the use of excess charge for the required blasting energy. Therefore, we have the following attenuation law: VPP = 4820.30 x( DඥQ )−2.01 Seeing that the obtained law presents a higher prediction than the first (K95% > K50%), it was validated with the results of the blasting design executed on site. 2.6 Drilling Quality Control The quality of the drilling process significantly influences downstream mining and processing operations, including rock fragmentation and ore recovery rates. Uncontrolled drillhole deviation often results in poor blast performance, excessive overbreak, dilution from adjacent cemented hydraulic fill walls, reduced stope recovery efficiency, potential geomechanical instability in exposed walls and increased operational costs.
2.6.1 Diagnostic Framework and Improvement Evolution Based on the experience during the mineral extraction at the Sofía D orebody, one of the primary challenges during the sequential recovery of secondary stopes was reducing overbreak in the surrounding cemented hydraulic backfill from an initial 18% to 10%. Analysis identified drill hole deviations as a key contributing factor adversely affecting blasting performance and fragmentation uniformity. To address this issue, a comprehensive diagnostic process was implemented using a multi-dimensional assessment framework visualized as a radar chart (Figure 4). The radar chart facilitated a baseline “Current” evaluation of actual performance, direct comparison against a “Base Target” representing optimal operational goals, and assessment relative to a “Risk Threshold” defining the minimum acceptable levels to prevent geomechanical instability or excessive cost overruns. Figure 6. Multi-Dimensional Assessment of Drilling Quality in SLS Production Rings. Initial diagnosis (pre-improvement) identified critical deficiencies in drill hole deviation (scored 4/10), drilling tools (4/10), drill string condition (5/10), and operator performance (4.5/10), with several indicators falling near the Risk Threshold. These findings prompted the implementation of targeted corrective measures, including optimized drill ring patterns, real-time deviation monitoring, and vibration studies to calibrate explosive charges. Improvement was tracked over a six-month period, with post-intervention radar chart assessments showing progressive convergence toward the “Base Target.” For example, the deviation score improved from 4/10 to 8/10, operator performance from 4.5/10 to 7/10, and drilling tools from 4/10 to 9/10. 2.6.2 Drill hole deviation control Implementation of a comprehensive drilling quality control framework at Minera Colquisiri yielded measurable improvements. Initial diagnostics revealed average drill hole deviations of 8–12% across key metrics, resulting in overbreak rates of 18% and recovery efficiencies of 85–90%. Post-intervention, deviations were reduced to 3–5%, overbreak dropped to 10%, and recovery rates exceeded 98% in targeted secondary stopes.
2.7 Simulation and blast pattern design A specialized design scheme is employed for radial (fan-shaped) drilling patterns. The number of drill holes per ring can reach 18 (depending of the level of the section), with their lengths varying according to hole position and the geometry of the ore block to be blasted. The parameters considered to simulate the blast pattern design are: SD-IIIA, drill holes (64mm), Anfo explosive for charge column, explosive density (0.85cartridge emulsion for primer, initiation with electronic detonators, rock density (2.93 gr/cm3), burden 1.53m and spacing 1.45m (Figure 7). Figure 7. Simulation of drilling and blasting for pillar recovery in secondary pits. Blast timing sequences incorporated a 7 ms inter-hole delay within each radial ring, with progressive alternation to control vibration superposition. This delay was calibrated through onsite vibration monitoring (near- and far-field PPV measurements) and post-blast fragmentation assessment (Figure 8). Measured data were iteratively compared against blast simulation software predictions to refine and confirm the timing parameters, ensuring minimal overbreak while maintaining high recovery efficiency. As result an average P80 equal to 7.64in was obtained which satisfy the desired size for the milling plant. Figure 8. P80 determination via image analysis. 2.8 Volumetric surveys of mined stopes Post-blast 3D volumetric surveys were conducted to reconcile the actual mined volume
against the planned stope geometry and quantify overbreak, particularly in the exposed cemented hydraulic fill (CHF) walls. Figure 9 presents an example of isometric view of the surveyed void in stope TJO 017U042U142, segmented by the three sequential extraction levels: • Upper span (Level 059U to Floor of Level 080U): 5,896.9 m³ • Middle span (Level 038U to Floor of Level 059U): 5,649.2 m³ • Lower span (Level 017U to Floor of Level 038U): 5,368.1 m³ The volume calculation was performed using wireframes through a mine planning software. Figure 9. 3D isometric view of post-blast volume survey for stope TJO 017U042U142. These reconciled volumes enabled precise measurement of overbreak in CHF exposures, confirming a reduction from 18% to 10% overall. The survey data supported validation of blast design effectiveness, vibration controls, and wall stability, contributing to the achieved 98% mineral recovery and minimized external dilution. 3. CONCLUSIONS • Implementation of this methodology has delivered measurable outcomes: mineral recovery in secondary stopes reached 98%, overbreak into cemented hydraulic fill was reduced from an initial 18% to 10%, and the economic value added per recovered stope averaged USD 54,000, generating an estimated annual opportunity value of USD 650,000 at current production rates. These results demonstrate that high-recovery pillar extraction can be achieved safely and repeatably in SLS operations bounded by cemented fill, offering a scalable and replicable strategy for similar underground mining projects • Geomechanical characterization and optimized blasting can enable safe, high-recovery stope extraction in underground mining. It aligns with the congress’s theme of Sustainable Infrastructure & Mine Design, showcasing a replicable strategy that balances productivity, stability, and economic value. The integration of blast monitoring tools and design adjustments supports continuous improvement and long-term viability.
• Uncontrolled drill hole deviation can increase operating costs by 5–15% per tonne mined, primarily due to additional mucking, backfilling, and remedial blasting requirements. This challenge is particularly pronounced in secondary stope recovery under sublevel stoping, where retreating sequences across multiple levels expose tall (up to 60 m) and narrow (12– 15 m) openings, necessitating precise geomechanical stability to prevent instability and excessive dilution. • Given the demonstrated effects of drill hole deviation on overbreak, dilution, and overall recovery efficiency, this factor can significantly influence operating costs. Incorporating the quantified cost of percentage deviation per tonne into cost models enables more accurate economic evaluations and supports scalable improvements in drill-and-blast practices. 4. ACKNOWLEDGEMENTS This work would not have been possible without the strong collaboration of Minera Colquisiri at the María Teresa underground operation. The authors sincerely thank the mine management and operational teams for granting operational access to the site, facilitating safe implementation of the sequential recovery strategy, and providing essential support for the extensive field monitoring required for this work. Special thanks are given to the underground crews - drilling, blasting, planning, geotechnical, and survey personnel - for their precise execution and consistent data collection efforts. As Orica Mining Services Peru engineers responsible for the technical development of this paper, the authors also acknowledge the valuable contributions of their colleagues within Orica in blast design development, drill deviation analysis, vibration monitoring and control strategies, and post-blast performance analysis.
5. REFERENCES Henríquez, J., Cortés, H. and Morales, D., (2025). A methodology to define drill and blast designs for drawbells at the Chuquicamata underground mine. Proceedings of the European Federation of Explosives Engineers (EFEE), J. Honkanen et al. 13th World Conference on Explosives and Blasting. Krakow, Poland. 175–182. Mateo, A., Asencios, E. and Oré, B., (2022). Aplicación Del Método Sublevel Stoping Con Relleno Cementado en Minera Colquisiri. Perumin 35 Convención Minera, Arequipa, Perú. 408– 422. Gomez, F., Valencia, J. F. and Ríos, S., (2022). Optimización de las actividades de perforación y voladura en la UM San Rafael mediante la implementación en campo del modelo de rotura y la predicción de cavidades. Perumin 35 Convención Minera, Arequipa, Perú. 171–186. Roy, D., Williams, T. and Preston, C. J., (2019). Transforming Underground Blasting Operations into Primary Crushing Operations. Proceedings of the International Society of Explosives Engineers (ISEE). 45th Annual Conference on Explosives and Blasting Technique. Nashville, Tennessee. Onederra, I. A. (2004). Breakage and fragmentation modeling for underground production blasting techniques. IRR Drilling and Blasting 2004 Conference, Perth, IRR. Player, J. and Perara, V., (2008). A back analysis of dilution and recovery in longitudinal sublevel. 5th International Conference and Exhibition on Mass Mining. Luleå, Sweden: Luleå University of Technology. 575-584. Córdova, E., Gottreux, I., Anani, A., Ferrada, A., and Contreras, J.S. (2021). Blasting and preconditioning modelling in underground cave mines under high stress conditions. Journal of the Southern African Institute of Mining and Metallurgy, vol. 121, no. 2. 71–80. Nong, M.J., Uludag, E., Leeuw, P.J.K. (2025). Using the Aegis underground drill and blast analyser to optimise drill patterns: A case study. Journal of the Southern African Institute of Mining and Metallurgy, vol. 125, no. 9. 533–542 Zhou, X., Zhao, X., Qu, Q., Shi, J. (2023). Stope Structural Parameters Design towards Green and Deep Mining: A Review. Processes 2023, 11, 312
OPTIMIZED GROUND ANCHORS USING GRAPHENEREINFORCED GFRP: A SUSTAINABLE ALTERNATIVE TO STEEL IN MINING GEOTECHNICS *R.R. Huayta1, F.A. Elorrieta2 1President of the Technical Committee CT-100 (Ground Support Systems), APGEO, Perú (*Presenting author: rhuayta@ucm.es) 2ITASCA, USA ABSTRACT Ground anchors are essential for ensuring the stability of slopes and excavations in mining and civil engineering. Steel anchors remain standard practice; however, corrosion susceptibility, high density, and associated maintenance demands may limit long-term performance, particularly under aggressive hydrogeological conditions. This study evaluates an alternative Materials 4.0 approach by assessing graphene-reinforced glass fibre reinforced polymer (GFRP) anchors as a potential substitute for conventional steel reinforcement. A comparative analytical framework based on Eurocode 7 principles and Spanish anchoring guidelines is applied to benchmark a reference Freyssinet 500E steel anchor against graphene-enhanced GFRP profiles. The results indicate that the proposed composite concept delivers comparable global stability levels (FS ≈ 1.5) relative to the steel reference (FS ≈ 1.6), while reducing the required tendon cross-sectional area from 106 mm² to 73 mm² (approximately 31% reduction). In addition, the significantly lower density of GFRP (1.83 g/cm³ versus 7.85 g/cm³ for steel) results in an estimated 75% reduction in material mass per unit length, improving strength-to-weight efficiency and facilitating transport and installation, particularly in constrained mining environments. From a sustainability perspective, conventional steel production is associated with emissions of approximately 1.8 tonnes of CO₂ per tonne of material, highlighting the environmental intensity of traditional reinforcement systems. The reduced material demand achieved through geometric and mass optimization suggests potential embodied carbon advantages at scale. Furthermore, the graphene-enhanced polymer matrix provides corrosion resistance and chemical inertness, mitigating deterioration mechanisms that typically affect permanent steel anchoring systems. Based on this quantitative benchmark, graphene-reinforced GFRP anchors emerge as a mechanically viable and durability-oriented alternative for low-maintenance ground support aligned with contemporary sustainability objectives in mining infrastructure. KEYWORDS Ground anchors; Mining geotechnics; GFRP; Graphene nanoparticles; Durability; Eurocode 7
1. INTRODUCTION Long-term reliability of geotechnical infrastructure is a key determinant of safety and operational continuity in mining, across both large open-pit slopes and confined underground excavations. Ground anchoring systems play a central role in stabilising rock and soil masses, controlling deformation, and enabling excavation advance under demanding stress and hydrogeological conditions. Improving the efficiency of ground support therefore requires solutions that reduce maintenance interventions and logistical constraints without compromising the safety margins demanded by modern design practice. High-strength prestressing steel remains the dominant reinforcement material for anchoring because of its tensile capacity and the maturity of design, installation, and quality-control procedures. However, its long-term performance in permanent applications can be limited by corrosion processes, particularly in aggressive hydrogeological environments where moisture availability and groundwater chemistry may accelerate degradation. In addition, the high density of steel (≈7.85 g/cm³) imposes handling and transport penalties that are especially relevant in constrained underground headings and remote surface installations. These constraints often translate into conservative sizing, additional protection measures, and increased life-cycle management requirements. Although fibre-reinforced polymer (FRP) reinforcements are increasingly explored in infrastructure as corrosion-resistant alternatives, their translation into geotechnical anchoring remains limited by the scarcity of design-oriented quantitative benchmarks within established practice. In particular, evidence is limited on how graphene-enhanced glass fibre-reinforced polymer (GFRP) concepts compare against conventional steel tendons when assessed using acceptance indicators and sizing logic consistent with Eurocode 7 principles and regional anchoring guidance. This gap restricts the ability of practitioners to judge whether nano-enhanced composite anchors can meet stability-driven design targets while offering competitive geometric demand and operational advantages. This study addresses that gap by presenting a quantitative benchmark of graphene nanoplatelet-enhanced GFRP (GNP–GFRP) anchors against a reference prestressing steel system (Freyssi SIOE type) under a consistent analytical framework. Structural efficiency is assessed through global factor of safety (FS) contribution and preliminary sizing metrics, with emphasis on reductions in required cross-sectional area and equivalent diameter. The results provide a design-focused basis to evaluate mechanical feasibility and to define priorities for subsequent numerical and experimental validation, including anchor–ground interaction modelling and long-term bond–slip performance under representative stress and hydrogeochemical exposure. 2. STATE OF ART 2.1 Evolution of Ground Anchoring Systems Ground anchoring systems have played a fundamental role in the stabilization of rock and soil masses in civil, mining, and underground engineering. Their evolution is closely linked to the increasing need to control instability in progressively larger, deeper, and more complex excavations, both at the surface and underground.
The earliest documented applications of rock bolting date back to the mid-19th century (1855–1861), during the construction of the Telemark Canal in Norway, completed in 1863. These early systems consisted of short, mechanically anchored steel bars, typically with diameters of approximately 40 mm, designed primarily to stabilize individual rock blocks on steep slopes. Although rudimentary, these applications marked the first systematic attempt to reinforce rock masses through internal anchorage rather than external retaining structures (Huayta & Carrascosa, 2022). The widespread adoption of ground anchoring techniques occurred in the early 20th century, driven mainly by underground mining. In 1927, mechanical rock bolts were introduced in underground mines in the United States, and in 1947 the U.S. Bureau of Mines formally incorporated rock bolting into mine safety practices to mitigate roof-fall hazards. This institutional endorsement led to a dramatic reduction in fatal accidents and, within five years, annual rock bolt consumption exceeded 25 million units, consolidating anchoring systems as the dominant underground support method. Parallel advances took place in civil engineering, particularly in large hydraulic and transportation projects. A major milestone was the application of prestressed anchoring systems by Eugène Freyssinet in 1939 for the stabilization of the Beni-Bahdel dam in Algeria. Between 1930 and 1960, anchored systems expanded rapidly across Europe, supported by extensive field experience, long-term monitoring programs, and the need to construct infrastructure under constrained urban and geological conditions. During this period, Europe became a global reference in anchored retaining systems, especially for deep excavations, slopes, and dam foundations. From the late 1970s onward, ground anchoring evolved from predominantly temporary solutions to fully engineered permanent systems. In the United States, the Federal Highway Administration promoted the development of standardized design methodologies, acceptance testing procedures, and durability requirements, enabling the routine use of permanent anchors in transportation infrastructure. Similar regulatory frameworks emerged across Europe, incorporating explicit provisions for corrosion protection, grouting techniques, load transfer mechanisms, and long-term performance verification. In the period 2000–2020, the evolution of anchoring systems has been strongly influenced by advances in materials science, numerical modeling, and monitoring technologies. While conventional steel anchors remain widely used, their long-term performance is often limited by corrosion susceptibility, maintenance requirements, and durability concerns in aggressive environments. These limitations have driven research toward advanced anchoring concepts, including composite-based reinforcements, highperformance coatings, and smart monitoring systems. Recent studies highlight the potential of fiber-reinforced polymers, graphene-enhanced composites, and data-driven design methodologies to improve durability, sustainability, and structural efficiency, marking the transition toward a new generation of ground anchoring systems aligned with the principles of Geotechnical Engineering 4.0.
Figure 1 – Timeline of key milestones in ground anchoring systems (1855-Present). 2.2 Classification of Ground Anchors Ground anchoring systems may be classified according to their field of application, as the mechanical role, design objectives, and performance requirements differ significantly between surface and underground environments. Although similar anchoring elements may be used in both contexts, their function within the ground–structure interaction system is fundamentally different. For this reason, ground anchors are herein classified into surface anchoring systems and underground anchoring systems. 2.2.1 Ground Anchors for Surface Applications In surface engineering, including slopes, open-pit mines, retaining structures, and deep excavations, ground anchors are primarily used to enhance global stability and control potential large-scale failure mechanisms. They commonly operate as active systems, where prestressing is applied during installation to provide an immediate stabilizing action and to limit displacements. Surface anchors are typically classified as temporary or permanent, depending on the required service life. Temporary systems are generally associated with staged construction and excavation works, whereas permanent anchors require explicit durability provisions, including corrosion protection and long-term load retention, particularly under aggressive environmental exposure. Common configurations include bar anchors, strand (cable) anchors, and self-drilling anchors, selected according to load demand, ground conditions, and installation constraints. Load transfer in surface anchoring is generally achieved through a bonded grouted length, where axial force is transmitted to the ground via shear mobilization along the grout–ground interface. The governing design intent is to stabilize potential failure surfaces and control face deformations within acceptable operational limits. 2.2.2 Ground Anchors for Underground Applications In underground excavations such as tunnels, shafts, and caverns, anchoring
elements function predominantly as reinforcement components within a broader ground support system. In contrast to typical surface applications, underground anchors often mobilize resistance progressively as the rock mass deforms and stresses redistribute around the excavation boundary. This progressive response is characteristic of passive systems, although prestressing may be adopted in cases requiring enhanced confinement or strict deformation control. Common underground systems include rock bolts, cable bolts, and self-drilling anchors, frequently used together with shotcrete and other support elements. Their performance is governed by anchor–rock mass–boundary interaction mechanisms that control deformation, confinement development, and load redistribution. Installation conditions and long-term durability are particularly critical underground, where high humidity, groundwater chemistry, and complex stress paths may accelerate deterioration mechanisms and affect long-term support capacity. Figure 2 – Conceptual load-transfer and role of anchors in surface vs underground settings. 2.3 Design Implications for Advanced Materials and Numerical Modelling The surface–underground distinction has direct implications for both material selection and modelling strategy. In surface applications, performance is often evaluated through global stability, axial demand, and load transfer efficiency, providing a robust benchmark for quantifying the structural efficiency of alternative reinforcement materials through numerical modelling. In underground excavations, anchors operate within a coupled support system where confinement development, interaction with other support elements, and long-term durability frequently govern performance, thereby amplifying the limitations of conventional steel systems, particularly corrosion susceptibility and maintenance demands. This classification framework therefore motivates the material and modelling choices adopted in this study. The following sections introduce the rationale for advanced reinforcement materials and present the numerical approach used to assess their performance, with quantitative analyses developed for surface slope conditions and underground implications discussed in terms of applicability.
3. MATERIALS FOR GROUND SUPPORT (MATERIALS 4.0) 3.1 Conventional Steel-Based Anchoring Systems Steel reinforcement remains the standard solution for both surface and underground anchoring due to its high tensile capacity, established design procedures, and broad availability. Steel bars and strand tendons are routinely used in grouted anchoring systems in which load transfer is governed by bond mechanisms along the grout–ground interface. Performance is commonly verified through acceptance testing and, for permanent installations, durability provisions and grouting quality control. These practices have enabled the widespread adoption of steel-based anchors in infrastructure and mining applications. 3.2 Key Limitations and Drivers for Innovation Despite their widespread use, conventional steel anchoring systems exhibit limitations that become critical in permanent applications and aggressive environments. Corrosion susceptibility is a primary durability concern and can translate into higher maintenance demands, reduced service life, and conservative design margins. In addition, steel weight affects installation logistics and operational efficiency, particularly in constrained underground settings. Further limitations include uncertainty in long-term performance under complex stress paths and the increasing need for compatibility with modern monitoring systems. Collectively, these constraints motivate the exploration of alternative reinforcement materials and design strategies that improve durability, reduce maintenance requirements, and enhance structural efficiency. 3.3 Advanced Composite Reinforcements and Materials 4.0 Over recent decades, fibre-reinforced polymer (FRP) systems have emerged as promising alternatives to steel reinforcement due to their high strength-to-weight ratios and corrosion resistance. Within FRP families, glass fibre-reinforced polymer (GFRP) is often discussed as a viable option for applications where durability and weight reduction are key priorities. In parallel, Materials 4.0 developments increasingly focus on nanoreinforcement concepts, particularly graphene-based additives, to improve mechanical performance and long-term durability. Graphene is commonly described as a one-atom-thick carbon sheet, while graphene oxide (GO) is a functionalized derivative that contains oxygen groups which improve dispersion in aqueous media (Asim et al., 2022). These characteristics are relevant for cementitious and polymeric systems because dispersion and interfacial bonding strongly condition whether nano-reinforcement translates into macroscopic performance gains.
Figure 3 – Conceptual load-transfer and role of anchors in surface vs underground settings. A diagram illustrating the standard techniques employed for the manufacturing of FRPCs, a) hand-layup, b) spray-layup, c) fila-ment winding, d) compression molding, e) extrusion compound, f) injection molding, g) pultr-usion, h) RTM, i) VARTM. Source: Maiti et. Al., Advanced Sustainable SystemsVolume 6 (2022). 3.4 Why Graphene Matters: Durability and Transport-Controlled Degradation A consistent theme in the infrastructure literature is that graphene-based additives can improve durability primarily by modifying transport-controlled mechanisms. Graphene and GO can act as barrier enhancers and microstructure modifiers, increasing tortuosity and reducing the ingress of aggressive agents that drive deterioration in cementitious and polymeric matrices (Asim et al., 2022). For example, graphene-based nanomaterials have been reviewed as reinforcement options for concrete pavement applications with the aim of improving durability and resistance to exposure-driven degradation (Jayasooriya et al., 2022). This body of evidence supports the rationale that the main value of graphene in civil infrastructure is not only strength gain, but also improved resistance to permeability-driven and chemically driven deterioration. For ground anchoring systems—especially permanent anchors in mining environments—this durability argument is directly relevant. If transport-controlled degradation is mitigated (e.g., moisture and aggressive ion ingress), then life-cycle performance can be improved and maintenance demands reduced. Consequently, graphene-enhanced composites can be framed as a materials route targeting the dominant durability constraints of conventional steel systems.
3.5 Positioning of the Present Study Building on this material evolution, the present work evaluates advanced composite reinforcement concepts for ground anchoring. The assessment is structured to quantify performance under surface slope conditions as a controlled benchmark for comparison, while discussing implications for underground environments where durability and operational constraints are typically amplified. The following section introduces the numerical framework adopted to evaluate mechanical response and performance metrics for conventional and composite-based anchoring solutions. 4. METHODS A permanent anchoring system must be designed to achieve the required factor of safety for a 12-meter-high slope composed of sandy clay with a unit weight γ = 18 kN/m³, effective cohesion c′ = 5 kPa, and effective friction angle φ′ = 28°. The soil exhibits an unconfined compressive strength (qu) of 50 kPa. The compressive strength of the grout at 28 days (fck) is 21 MPa. No groundwater level is detected within the area of interest. It should be considered that the available horizontal space for excavation is 16 meters. The case study is developed in accordance with the technical framework established in the guideline entitled “Guide for the Design and Execution of Ground Anchors in Roadworks,” issued by the General Directorate of Roads under the Ministry of Public Works of Spain. 4.1 Global System Verification Based on a preliminary design model, it is necessary to complete the design and stability verification of each anchor. At this stage, a comparative assessment is performed between calculations using Freyssinet 500E steel bars and the proposed graphenereinforced glass fiber (GFRP) bar system, as presented in Table 4.1. Table 4.1: Ultimate Tensile Strength (N/mm²) and Elastic Tensile Strength (N/mm²) of Freyssinet 500E Steel Anchors and Graphene-Reinforced Glass Fiber (GFRP) Profiles. COMPARISON Ultimate Tensile Strength (N/mm²) Elastic Tensile Strength (N/mm²) Freyssinet 500E Steel 550 500 Graphene-Reinforced Glass Fiber Profiles (GFRP) 800 1000 4.1.1 Calculation of the Factored Nominal Load = 1 = 1.5(30 ) = 45 Being: = Nominal anchor load obtained from the global stability calculation. 1 = Partial safety factor (load amplification factor). = Factored nominal anchor load. 4.1.2 Verification of Tensile Stress in the Anchor STEEL: ≤ 45 ≤ 550000 1.30 = 106 2 Ultimate Limit State
≤ 45 ≤ 500000 1.15 = 103 2 GRAPHENE: ≤ 45 ≤ 800000 1.30 = 73 2 ≤ 45 ≤ 1000000 1.15 = 51 2 Where: = Factored nominal anchor load. = Cross-sectional area of the tendon. = Ultimate tensile strength of the tendon steel. = Yield strength of the tendon steel. = Coefficient depending on the service life of the anchor. = Coefficient depending on the service life of the anchor. 4.1.3 Calculation of Anchor Diameter Where: = Cross-sectional area of the tendon. D = Diameter of the anchor bar. STEEL: = 4 D2 D= ට4 D= ට4(106 2) = 11.6 GRAPHENE: = 4 D2 D= ට4 D= ට4(73 2) = 9.6 4.1.4 Verification of Anchor–Grout Slip = 6.9( 22.5) ⁄ 2⁄3 = 6.9(21 22.5) ⁄ 2⁄3 =6.59 ( . ) ≤ 1,2 Where: = Factored nominal load of each anchor. = Nominal perimeter of the tendon (π·D). = Cross-sectional area of the tendon. = Bond length (bulb length). = Ultimate bond stress between tendon and grout (MPa). = 28-day compressive strength of grout (MPa). 4.1.5 Calculation of Allowable Soil Bond Strength = í 3 = 0.124 1 .65 = 75.2 Where: = Allowable bond stress. í = Ultimate bond stress. 3 =Partial factor depending on anchor type. Elastic Limit State Shear Stress Verification Ultimate Limit State Elastic Limit State
4.1.6 Verification of Pull-Out Failure STEEL: = D + 2 ( ) =11.6 + 2 (20 ) = 51.6 ( . . ) ≤ ≥ ( . . ) ≥ (45 ) 75.2 ( )(0.0516 ) ≥ . GRAPHENE: = D + 2 ( ) =9.64 + 2 (20 ) = 49.6 ( . . ) ≤ ≥ ( . . ) ≥ (45 ) 75.2 ( )(0.0496 ) ≥ . Where: = Nominal diameter. D = Anchor bar diameter. = 20 mm grout cover (each side). = Bond length (bulb length). = Factored nominal load per anchor. 5. RESULTS Graphene-based profiles, due to their lower density compared to steel, are significantly lighter. Furthermore, as chemically inert materials, they exhibit superior resistance to corrosion relative to steel. For geophysical studies, graphene profiles are transparent to EMI/RFI transmissions, whereas steel interferes with such signals. Although graphene itself is a conductive material, graphene-reinforced glass fiber (GFRP) profiles behave as low thermal conductors and are not electrical conductors in the same manner as steel. On the contrary, this characteristic also contributes to improved impact behavior by distributing loads without permanent deformation. The general characteristics of both proposed systems are summarized in Table 5.1. Table 5.1: Summary and Comparative Table of the Main Properties of Both Options. COMPARISON Graphene-Reinforced Glass Fiber Profiles (GFRP) Steel Corrosion Resistance High resistance to chemical agents Prone to oxidation and corrosion Density 1.83 g/cm³ 7.85 g/cm³ Electrical and Thermal Conductivity Non-electrical conductor. Low thermal conductivity Electrical and thermal conductor Strength High strength-to-weight ratio Higher weight for equivalent strength
Impact Resistance Non-deformable. Glass fiber fabric distributes impact loads Possible deformation under impact loading Wave Transparency Transparent to EMI/RFI transmissions Interferes with EMI/RFI transmissions Installation Lightweight for lifting and installation Requires specialized installation equipment Cost Low maintenance and installation cost Low initial cost. Higher longterm maintenance cost compared to GFRP Color and Finish Pigments can be added, allowing a wide range of colors Steel must be painted to achieve color finish The Factors of Safety (F.S.) of both systems do not differ significantly. The upper representation corresponds to the steel anchor system with an F.S. of 1.6, while the lower representation corresponds to the graphene anchor system with an F.S. of 1.5. Figure 5.1 presents the slope stability analysis schemes for both proposed configurations. Figure 5.1: Steel Anchor System – Slope Stability Analysis As shown in Figure 5.1, the steel anchor system achieves a global Factor of Safety (F.S.) of 1.6, with the anchors effectively intersecting the critical slip surface and stabilizing the potential failure mass. The required cross-sectional area for the steel tendon is 106 mm², and the calculated bond length results in ≥3.7 , satisfying the regulatory minimum requirement of ≥3.0 . STEEL
In contrast, the graphene-reinforced GFRP system requires a reduced tendon cross-sectional area of 73 mm² (approximately 31% lower than steel), while maintaining a similar bond length requirement of ≥3.8 . As will be observed in Figure 5.2, the overall stabilization mechanism remains comparable, with the anchors effectively controlling the potential slip surface despite the slightly lower global F.S. of 1.5. Figure 5.2: Graphene-Reinforced GFRP Anchor System – Slope Stability Analysis. The following table (Table 5.2) summarizes and compares the results obtained for both alternatives. Table 5.2: Summary of Design Results for Graphene-Reinforced Glass Fiber (GFRP) Profiles and Freyssinet 500E Steel Profiles. COMPARISON Graphene-Reinforced Glass Fiber (GFRP) Freyssinet 500E Steel Factored nominal load 45 kN 45 kN Tensile verification (required area) 73 mm² 106 mm² Calculated bar diameter 9.4 mm 11.6 mm Anchor–grout slip verification 0.27 m 0.22 m Allowable soil bond strength 75 kPa 75 kPa Pull-out (bulb length) verification 3.84 m 3.7 m Factor of Safety (F.S.) 1.5 1.6 GFRP
6. DISCUSSION AND CONCLUSIONS DISCUSSION The comparative benchmark developed in this study demonstrates that graphene reinforced GFRP anchors can achieve structural performance comparable to conventional steel systems under a consistent Eurocode 7 aligned design framework. The global Factor of Safety obtained for the composite system (F.S. = 1.5) remains within commonly accepted geotechnical design margins when compared to the steel reference (F.S. = 1.6). The difference does not alter the stabilization mechanism nor the geometry of the critical slip surface. The most significant distinction lies in tensile verification and geometric demand. The required tendon cross sectional area decreases from 106 mm² for steel to 73 mm² for graphene reinforced GFRP, representing a reduction of approximately 31 percent. Despite this reduction, the bond length requirement remains nearly identical, with 3.7 m for steel and 3.8 m for GFRP, confirming equivalent load transfer capacity under the same boundary conditions. From an operational perspective, the 75 percent reduction in material density, 1.83 g/cm³ for GFRP compared to 7.85 g/cm³ for steel, suggests potential advantages in transportation, handling and installation efficiency, particularly in constrained underground environments. In addition, the corrosion resistance and chemical inertness of composite reinforcement directly address one of the primary durability limitations of permanent steel anchoring systems in aggressive hydrogeological conditions. Beyond mechanical efficiency, material optimization also has environmental implications. Conventional steel production is associated with emissions of approximately 1.8 tonnes of CO₂ per tonne of material. Therefore, reductions in required steel mass at scale may contribute to lowering the embodied carbon of large anchoring programs in mining infrastructure. While a full life cycle assessment is beyond the scope of this study, the presented benchmark indicates that material efficient composite solutions may support decarbonization strategies without compromising geotechnical safety criteria. Although the benchmark is based on a surface slope configuration, the implications for underground mining applications, where durability, accessibility and lifecycle performance are critical, remain particularly relevant. CONCLUSIONS - Graphene reinforced GFRP anchors demonstrate structural feasibility comparable to conventional Freyssinet 500E steel anchors within accepted geotechnical safety margins. - The composite system achieves approximately 31 percent reduction in required cross sectional area and 75 percent reduction in material density while maintaining similar bond length requirements and global stability performance. - The reduction in global Factor of Safety from 1.6 to 1.5 remains within commonly accepted design limits and does not modify the overall stabilization mechanism under the analyzed conditions.
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