Fluid Expandable Rock Bolts – Components, Working & DGMS Standards | DGMS Exam Notes

🧾 DETAILED NOTES

1️⃣ Introduction

Fluid Expandable Rock Bolts (FERBs) are one of the most advanced roof support systems used in underground coal and metal mines. They provide immediate, full-length anchorage using pressurized fluid expansion, ensuring safety against roof falls and side collapses.

2️⃣ Objective of DGMS Standardization

DGMS mandates that only approved and tested rock bolts be used in mines to ensure structural reliability, worker safety, and compliance with the Coal Mines Regulations (CMR 2017, Reg. 99 & 100) and Metalliferous Mines Regulations (MMR 1961, Reg. 108 & 109).

3️⃣ Components of Fluid Expandable Rock Bolt

Steel Tube: Seamless tube forming the body of the bolt.
Expanding Slot: Allows radial expansion under hydraulic pressure.
Plug or Sealing End: Ensures fluid tightness during pressurization.
Washer and Dome Plate: Transfers load from roof to the bolt.
Expansion Fluid Inlet Valve: For injecting water at 30–50 MPa pressure.

4️⃣ Properties of Fluid Expandable Rock Bolts (FERBs)

Property	Typical Range / Standard
Material	Cold-drawn seamless steel, yield strength ≥ 500 MPa.
Length	Typically 1.5–3.0 m depending on strata conditions.
Diameter	32–45 mm outer diameter.
Expansion Pressure	30–50 MPa hydraulic water pressure.
Anchorage Type	Full-length radial contact.
Corrosion Protection	Hot-dip galvanized or epoxy coated.
Testing	As per DGMS circular and IS 10208:2023 (Part-1).

5️⃣ Advantages of FERBs over Conventional Bolts

Immediate full-length support — no resin capsule required.
Uniform load distribution along the hole.
Quick installation — 2–3 minutes per bolt.
Reduced maintenance and longer lifespan.
Better performance in jointed and fractured strata.

6️⃣ Testing and Approval

As per DGMS guidelines:

Each new design must undergo pull-out testing, hydraulic expansion testing, and load bearing capacity testing.
Approval under Regulation 99(3) of CMR 2017 or Rule 126 of MMR 1961.
Records must be maintained online under the DGMS Online Approval Portal.

7️⃣ Safety and Maintenance

Never reuse expanded bolts.
Always use calibrated hydraulic pumps.
Conduct weekly visual inspection and load testing (10% sample).
Maintain logbooks for bolt installation, testing, and replacement.

8️⃣ DGMS Legal Reference

CMR 2017 Regulation 99 & 100 – Roof Support and Systematic Support Rules.
DGMS Tech. Circular (2022/2023) – Approval of FERBs for Indian Mines.
IS 10208:2023 – Indian Standard for Rock Bolts, Split Sets, and Expandable Anchors.

⚙️ QUICK ONE-LINERS (DGMS Revision Points)

FERBs are hydraulically expanded supports.
Expansion pressure is 30–50 MPa.
Material: Seamless steel tube, yield ≥ 500 MPa.
DGMS approval is mandatory under Reg. 99.
FERBs provide full-length anchorage.
Resin capsules not required.
Corrosion protection is essential.
Pull-out test confirms anchorage strength.
Approved supplier list maintained by DGMS.
Visual inspection required weekly.

🧮 DESCRIPTIVE MODEL QUESTION

Q. Explain the standard components and mechanical properties of Fluid Expandable Rock Bolts (FERBs) as per DGMS requirements.

Answer:
Fluid Expandable Rock Bolts are hydraulic anchorage systems used for immediate roof support in underground mines. They consist of a seamless steel tube with a longitudinal slot that expands under hydraulic pressure (30–50 MPa) to provide full-length contact with borehole walls. Main components include a steel body, expansion slot, end plug, washer plate, and inlet valve. These bolts are made from high-yield steel (>500 MPa) and provide superior corrosion resistance. DGMS approval is mandatory before deployment, and regular load testing ensures reliability under CMR 2017 Regulation 99.

🧩 25 MCQs (Dynamic Correct Answers A–E)

Q1. The primary function of Fluid Expandable Rock Bolts is:

Solution: FERBs are primarily used as a means of rock support to stabilize roofs and walls.

Q2. FERBs are expanded using:

Solution: High-pressure water is typically used as the expansion fluid.

Q3. Typical expansion pressure for FERBs is:

Solution: The standard operating pressure range for expanding these bolts is 30 to 50 MPa.

Q4. Yield strength of steel used in FERBs should be:

Solution: High yield strength steel (>=500 MPa) is required for the bolt to withstand expansion and rock loads.

Q5. Which of the following is NOT a component of FERBs?

Solution: An electric motor is not part of the bolt itself; a pump (often hydraulic or pneumatic) is used for installation.

Q6. FERBs eliminate the need for:

Solution: Unlike resin bolts, FERBs achieve anchorage through hydraulic expansion, not chemical bonding with resin.

Q7. The DGMS approval for FERBs is mandatory under:

Solution: Regulation 99 deals with support of working places and mandates the use of approved support systems.

Q8. The fluid used for expansion is generally:

Solution: High-pressure water is the standard fluid used for expanding FERBs.

Q9. Typical length range of FERBs:

Solution: Standard lengths typically fall within the 1.5m to 3.0m range for common underground applications.

Q10. Which test ensures bolt’s anchorage strength?

Solution: The pull-out test measures the force required to pull the installed bolt out of the rock, verifying its holding capacity.

Q11. The inlet valve in FERBs is used for:

Solution: The high-pressure fluid (water) is injected through this valve to expand the bolt.

Q12. Expansion occurs due to:

Solution: The injected high-pressure fluid forces the slotted tube to expand outwards.

Q13. The typical outer diameter of FERB is:

Solution: Common diameters fall within the 32mm to 45mm range.

Q14. The fluid pressure is applied through:

Solution: A specialized hydraulic pump is required to generate the high pressures (30-50 MPa) needed.

Q15. FERBs provide:

Solution: The expansion along the entire slotted length provides continuous contact and anchorage within the borehole.

Q16. Corrosion protection of bolts is achieved by:

Solution: Protective coatings like galvanizing or epoxy are applied to prevent rust in corrosive mine environments.

Q17. FERBs are used in:

Solution: These bolts are specifically designed for strata support in underground excavations.

Q18. DGMS circulars related to FERBs are mainly issued under:

Solution: Approval and usage guidelines for support systems fall under the specific Coal or Metalliferous Mines Regulations.

Q19. The expansion process takes approximately:

Solution: The hydraulic expansion process is relatively quick, typically taking a few minutes per bolt.

Q20. Pull-out testing frequency for FERBs is often recommended as:

Solution: Testing a representative sample (often 5% to 10%) is standard practice for quality control. (Note: Original text mentioned 10%).

Q21. FERBs are preferred in:

Solution: Their full-length contact provides better support in jointed or fractured rock compared to point-anchored bolts.

Q22. The most important safety precaution while installing FERBs is:

Solution: Ensuring the hydraulic pump delivers the correct pressure is crucial for proper expansion and anchorage.

Q23. The sealing plug prevents:

Solution: The plug seals the end of the bolt, ensuring the high-pressure water remains inside to maintain expansion.

Q24. FERBs are tested as per:

Solution: IS 10208 is the Indian Standard specifically covering rock bolts, including expandable types.

Q25. DGMS maintains records of FERBs through:

Solution: DGMS is increasingly using online portals for managing approvals and records of equipment like FERBs.

🔗 INTERNAL LINKS

Related Topic	Read More On...
Strata Control	Standard Components of Friction Stabilizers (Split Sets)
Support Rules	CMR 2017 Part 2 - Working & Supervision Rules
DGMS Circulars	DGMS Tech Circular No. 02 of 2020
Underground Safety	Accidents Due to Roof Fall – DGMS Analysis

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