2.3 Underground Ground Support Systems & Excavation Design

PRC Mining Engineer Licensure Examination Philippines

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1 Chapter 1: Surface Mining Methods & Pit Optimization

1.1 Surface Mining Unit Operations & Method Selection 1.2 Bench Geometry, Slope Stability & Geotechnical Pit Design 1.3 Cut-Off Grade Optimization & Lerchs-Grossmann Pit Limits

2 Chapter 2: Underground Mining Methods & Strata Control

2.1 Underground Mining Method Classification & Selection 2.2 Rock Mechanics, Stress Analysis & Strata Control 2.3 Underground Ground Support Systems & Excavation Design

3 Chapter 3: Materials Handling, Equipment & Mine Economics

3.1 Drilling, Blasting & Explosives Engineering 3.2 Mine Loading, Haulage & Materials Handling Systems 3.3 Mine Capital (CAPEX), Operating Costs (OPEX) & Financial Evaluation

4 Chapter 4: Mine Safety, Ventilation & Philippine Mining Laws

4.1 Mine Ventilation Network Analysis & Environmental Quality 4.2 Philippine Mine Safety Rules, Health & Disaster Prevention 4.3 Philippine Mining Act of 1995 (RA 7942), DAO 2010-21 & Mining Ethics

5 Chapter 5: Physical Geology, Mineralogy & Philippine Deposit Types

5.1 Structural Geology, Tectonics & Ore Controls 5.2 Igneous, Metamorphic & Sedimentary Ore Mineralogy 5.3 Major Philippine Ore Deposit Models

6 Chapter 6: Mineral Exploration, Geophysics & Core Logging

6.1 Geochemical & Remote Sensing Exploration Techniques 6.2 Geophysical Exploration Methods in Mining Geology 6.3 Diamond Drilling, Core Logging & QA/QC Protocols

7 Chapter 7: Geostatistics, Resource Estimation & PMRC Code

7.1 Ore Body Block Modeling & Spatial Variography 7.2 Inverse Distance & Ordinary Kriging Grade Estimation 7.3 Philippine Mineral Reporting Code (PMRC 2020) & Resource Classification

8 Chapter 8: Comminution, Sizing & Physical Mineral Separation

8.1 Crushing, Grinding & Bond Work Index Calculations 8.2 Particle Screening, Hydrocyclone Classification & Sizing 8.3 Gravity Concentration & Magnetic/Electrostatic Separation

9 Chapter 9: Froth Flotation & Extractive Hydrometallurgy

9.1 Froth Flotation Chemistry, Reagents & Cell Kinetics 9.2 Leaching Technologies (Heap, Agitation & Tank) 9.3 Precious Metal Recovery: CIP, CIL, Merrill-Crowe & Electrowinning

10 Chapter 10: Process Plant Flowsheets & Environmental Tailings Management

10.1 Metallurgical Plant Flowsheets & Pulp Mass Balances 10.2 Tailings Storage Facility (TSF) Design & Dam Safety 10.3 Acid Mine Drainage (AMD) Mitigation & Environmental Protection (EPEP/FMR/DP)

11 Chapter 11: 2025 PRC Blueprint, Prospecting Tools & Exploration Decisions

11.1 Official 2025 TOS, Three-Paper Structure & Exam Strategy 11.2 Prospecting Instruments, Base Maps & Surface Geological Mapping 11.3 Integrating Direct and Indirect Evidence for Exploration Decisions

12 Chapter 12: Mine Infrastructure, Sustainable Development & Climate

12.1 Power, Water, Drainage & Support-Facility Selection 12.2 Sustainable Development, Progressive Rehabilitation & Community Impact 12.3 Mining, Climate, Reforestation, Coal & Energy-Transition Minerals

13 Chapter 13: Mine Valuation, Financial Analysis & Due Diligence

13.1 Time Value of Money, Future Value & Present Value 13.2 Financial Statements, Mine Economics & External Price Drivers 13.3 Exploration Provenance, Technical Review & Legal Due Diligence

14 Chapter 14: Mine Organization, Communication & Accountable Leadership

14.1 Line and Staff Functions in a Mining Organization 14.2 Communication With Superiors, Peers & Subordinates 14.3 Authority, Responsibility, Delegation & Safety Accountability

15 Chapter 15: Philippine Mining Law, Indigenous Rights & Professional Ethics

15.1 Legal Hierarchy, Mineral Tenure & Compliance Analysis 15.2 Constitutional Participation, IPRA, FPIC & Ancestral Domains 15.3 RA 4274, Professional Scope, Ethics & Document Integrity

16 Chapter 16: Applied Mathematics & Mine Surveying

16.1 Engineering Mathematics for Safe, Efficient Mine Decisions 16.2 Survey Control, Instruments, Traverses & Error Adjustment 16.3 Topographic Maps, Underground Set-Out & Survey Timeliness

17 Chapter 17: Feasibility Studies, Data Quality & Project Decisions

17.1 Scoping, Pre-Feasibility & Final Feasibility Study Maturity 17.2 Data Accuracy, Assumption Control & Go/No-Go Decisions 17.3 Multidisciplinary Integration, Interfaces & Independent Review

18 Chapter 18: Mining Computer Applications, Digital Control & Global Developments

18.1 Computer Functions, Office Applications & Data Governance 18.2 Geological Modeling, Mine Planning, Scheduling & Valuation Software 18.3 Real-Time Control, Critical Minerals & Regional Mining Developments

19 Chapter 19: Earth Systems, Geologic Time & Philippine Hazards

19.1 Solar-System Origin, Earth Interior & Atmospheric Layers 19.2 Rock Cycle, Landforms & the Geologic Time Scale 19.3 Philippine Tectonics, Geologic Hazards & Mitigation

20 Chapter 20: Metallurgy, Foundry Practice & Assaying

20.1 Extractive, Physical & Adaptive Metallurgy Principles 20.2 Foundry Materials, Casting, Solidification & Defects 20.3 Sampling, Fire Assay, Cupellation, Parting & Assay Calculations

21 Chapter 21: Solid–Liquid Separation, Environmental Law & Mine Ecology

21.1 Thickening, Filtration & Solid–Liquid Separation 21.2 Philippine Air, Water, Waste & Hazardous-Substance Controls 21.3 Mine Ecology, Closure, Tailings, Waste & Community Livelihood

2.3 Underground Ground Support Systems & Excavation Design

Key Takeaways Explain This Topic AI

Ground support systems are categorized into primary (installed immediately post-excavation for safety) and secondary (installed for long-term reinforcement or under dynamic conditions), operating as active (pre-tensioned) or passive (reinforcing upon rock movement) elements.

Rock-bolt selection depends on mechanical behavior: mechanically anchored bolts can be tensioned, ordinary full-column resin-grouted rebar is generally passive unless deliberately tensioned, and friction bolts mobilize load through borehole contact and deformation.

Shotcrete acts as a continuous structural skin, enhancing joint shear strength and preventing rock unravelling, with fiber-reinforcement (steel or synthetic) significantly increasing post-crack flexural toughness and energy absorption.

Backfill engineered for underground stopes — including hydraulic fill, paste fill, and cemented rock fill (CRF) — provides regional ground stability, reduces surface subsidence, and maximizes mineral recovery by allowing pillar extraction.

Pillar design can screen average stress with Tributary Area Theory and estimate strength with a calibrated empirical relation, but acceptance depends on geology, extraction geometry, failure mode, scale, variability, consequence, and the project-specific reliability target—not one universal FoS.

Last updated: August 2026

2.3 Underground Ground Support Systems & Excavation Design

Quick Answer: Ground support systems stabilize underground excavations by reinforcing the rock mass and supporting surface blocks. Support elements are divided into primary (installed at the face) and secondary (installed for long-term or dynamic duty) systems, operating via active (pre-tensioned) or passive mechanisms. Rock reinforcement hardware includes mechanically anchored bolts, resin-grouted rebars, friction bolts (Split Sets, Swellex), cable bolts, fiber-reinforced shotcrete, and steel arches. Mine pillar design can combine Tributary Area Theory for stress screening with empirical strength formulas calibrated to the relevant deposit. Required reliability or Factor of Safety is selected from failure mode, database applicability, geometry, variability, consequence, and current design criteria; 1.5–2.0 is not a universal statutory range.

Primary vs. Secondary Ground Support & Support Mechanics

Underground ground support systems prevent roof falls, rib spalling, and major collapse by modifying rock mass behavior or catching detached rock blocks:

Primary Ground Support: Installed immediately after blasting and mucking at the active face. Its objective is to preserve workplace safety, prevent unravelling of loose key blocks, and maintain excavation boundary geometry.

Secondary Ground Support: Heavy-duty support installed later in long-term excavations (shaft stations, main haulage drives, permanent crusher chambers, stope intersections) or in high-stress/dynamic ground. Includes long cable bolts, thick fiber-reinforced shotcrete, and heavy steel arches.

Support Function Mechanics

Active Support: Applies an immediate compressive pre-load to the rock mass upon installation. Pre-tensioning compresses joint planes, increasing normal stress and friction resistance along potential shear surfaces (e.g., pre-tensioned resin bolts, expansion shell anchors).

Passive Support: Provides no initial load upon installation. Load develops only as the surrounding rock mass undergoes deformation and displacement toward the excavation void (e.g., untensioned grouted rebars, Split Sets, timber props, standing steel sets).

• Rock Reinforcement Hardware
• 1. Mechanically Anchored Expansion Shell Bolts

Mechanism: A point-anchor bolt. Rotating the bolt forces a threaded wedge into an expandable serrated shell, gripping the borehole wall at the deep end.

Characteristics: Provides immediate active pre-tensioning upon installation. However, susceptible to loss of tension under blast vibration or rock anchorage slip; un-grouted steel is highly vulnerable to corrosion.

2. Resin-Grouted Rebar Bolts

Mechanism: Full-column encapsulated steel rebar. Two resin cartridges (fast-set resin at the anchor end, slow-set resin along the shank) are inserted into the borehole. Spinning the rebar breaks and mixes the chemical resin cartridges.

Characteristics: Provides stiff, high-capacity, full-column reinforcement and can protect steel from groundwater when encapsulation is complete. Ordinary resin-grouted rebar is generally passive unless installed with an intentional tensioning system; bond and installation quality require testing.

3. Friction Bolts: Split Sets & Swellex

Split Sets (Friction Stabilizers): High-strength C-shaped steel tube with a longitudinal slot driven into an undersized borehole. Frictional resistance along the full length resists rock movement (1.0–1.5 tonnes per meter of embedment). Highly yieldable under ground convergence.

Swellex Bolts: Folded steel tube inserted into a drill hole and expanded hydraulically using high-pressure water (~300 bar). The expanded tube presses against the borehole wall to provide immediate frictional load transfer; capacity and deformation performance depend on hole condition, installation pressure, corrosion, and pull testing.

4. Cable Bolts

High-strength steel wire strands (single or multi-strand, birdcaged or bulbed to increase bond shear strength) installed at project-specific lengths and grouted to a verified design. Essential for stabilizing large open stope roofs, hanging walls, and wide drive intersections.

Surface Support & Standing Support Systems

Rock bolts reinforce the interior rock mass, but surface elements are required to prevent loose rock fragments from falling between bolt pattern grids:

Shotcrete: Pneumatically projected concrete applied wet-mix or dry-mix at 50–150 mm thickness. Acts as a continuous structural membrane, filling open joints, sealing rock against air/moisture weathering, and locking key blocks. Fiber-reinforced shotcrete (FRS) incorporates steel or macro-synthetic fibers to provide post-crack flexural toughness and energy absorption (E700–E1000 Joules rating under panel testing).

Wire Mesh: Welded wire mesh or flexible chain-link mesh secured against the rock surface using bolt bearing plates. Retains fractured rock spalls.

Steel Sets & Yielding TH Arches: Standing structural support for severely broken, squeezing, or fault-damaged ground. TH (Toussaint-Heintzmann) Yielding Arches consist of overlapping sliding steel segments clamped with friction shackles, allowing controlled yield under heavy convergence without structural buckling.

Mine Backfill Technologies

Backfilling empty stopes provides regional ground stability, prevents major wall sloughing, reduces surface subsidence, and permits maximum ore extraction by enabling pillar recovery.

Backfill Type Tailings / Aggregate Material Binder Content Pulp Density (% Solids) Transport Mode Primary Advantage

Hydraulic Fill Classified tailings (slimes removed) 3%–6% Cement (optional) 65%–72% Solids Gravity slurry pipeline Fast placement, free-draining

Paste Backfill Tailings blend selected by testwork Binder and solids set by strength and rheology tests High-solids, non-settling target Pump selected for rheology Reduced segregation and bleed when properly designed; strength is not automatically uniform

Cemented Rock Fill (CRF) Waste rock from development 4%–8% Cement slurry Solid rock + slurry Haul truck / Jammer High early compressive strength (2–5 MPa)

Pillar Design & Stress Analysis

Pillars are unmined rock columns left between excavations to support overlying strata.

1. Tributary Area Theory

Assumes each pillar supports the entire weight of the rock column directly above it plus half the span of adjacent rooms ( w o w_o w o ​ ). For a regular grid of square pillars of width w p w_p w p ​ :

Extraction Ratio ( R R R ): R = 1 − w p 2 ( w p + w o ) 2 R = 1 - \frac{w_p^2}{(w_p + w_o)^2} R = 1 − ( w p ​ + w o ​ ) 2 w p 2 ​ ​

Average Pillar Stress ( σ p \sigma_p σ p ​ ): σ p = σ v 1 − R = γ z ( w p + w o w p ) 2 \sigma_p = \frac{\sigma_v}{1 - R} = \gamma z \left( \frac{w_p + w_o}{w_p} \right)^2 σ p ​ = 1 − R σ v ​ ​ = γ z ( w p ​ w p ​ + w o ​ ​ ) 2

2. Obert-Duvall Empirical Pillar Strength Formula

Obert and Duvall formulated pillar strength S p S_p S p ​ based on pillar width-to-height ratio ( w p / h p w_p / h_p w p ​ / h p ​ ): S p = S 0 ( 0.778 + 0.222 w p h p ) S_p = S_0 \left( 0.778 + 0.222 \frac{w_p}{h_p} \right) S p ​ = S 0 ​ ( 0.778 + 0.222 h p ​ w p ​ ​ )

where S 0 S_0 S 0 ​ is the unconfined compressive strength of a cubic rock specimen ( w / h = 1.0 w/h = 1.0 w / h = 1.0 ).

3. Factor of Safety ( F o S FoS F o S ) F o S = S p σ p FoS = \frac{S_p}{\sigma_p} F o S = σ p ​ S p ​ ​

A preliminary design may use a range such as 1.5–2.0 in a stated context, but no universal factor is guaranteed or required by this equation alone. Acceptance criteria must reflect the calibrated pillar-strength method, variability, design life, failure consequence, interaction, monitoring, and controlling standard.