Friction Stabilizers (Split Sets) in Mines – DGMS Standards, Components & Properties

⚙️ DETAILED NOTES

1️⃣ Introduction

Roof and side support is a critical safety requirement in underground mines. One of the most widely used support systems today is the Friction Rock Stabilizer, commonly called the Split Set Bolt. These are simple, mechanical anchoring devices designed to support rock strata by frictional resistance along the bolt length, providing immediate active support.

2️⃣ DGMS Requirement

As per DGMS Technical Circulars and CMR 2017 Reg. 99 & 100 (and MMR 1961 Reg. 99):

Only approved support systems and devices are to be used in underground workings.
Manufacturers of split sets must meet IS 13056:1991 or equivalent international standard.
Every mine must maintain test records and quality certificates for support devices.

3️⃣ Standard Components of Friction Stabilizers

Component	Description
Split Tube (Bolt)	High-tensile steel tube, longitudinally split for compression fit.
Washer Plate	Dome-shaped or flat plate to bear load against rock surface.
Driving Collar	End piece for hammer or impact tool during installation.
Anchorage Length	Full length of tube in contact with rock borehole wall.
Coating/Protection	Galvanized or epoxy-coated for corrosion resistance.

4️⃣ Properties and Performance

Property	Typical Range / Standard
Diameter	33 mm to 47 mm
Length	1.2 m to 3.0 m
Steel Grade	High-tensile (yield ≥ 400 MPa)
Pull-Out Load Capacity	≥ 10 tonnes
Friction Resistance	Continuous over full length
Corrosion Resistance	As per IS 13056:1991
Installation Torque	Not required (drive-in type)

5️⃣ Working Principle

When inserted into a slightly smaller diameter borehole, the split tube compresses and exerts radial pressure on the rock wall, creating frictional resistance. This provides immediate, full-length anchorage and continuous contact between the support and rock, unlike resin or mechanical bolts that anchor only at specific points.

6️⃣ Advantages

Immediate support after installation.
Simple, mechanical, and low maintenance.
Continuous load distribution along bolt length.
Suitable for squeezing ground and poor rock conditions.
Easily combined with mesh or shotcrete for enhanced stability.

7️⃣ Quality and Testing Requirements (DGMS)

Pull test for 5% of installed bolts in each district or panel.
Each batch of bolts must carry manufacturer test certificate (yield, elongation, pull-out).
Bolts must bear manufacturer ID & batch number embossed.
Non-standard or rusted bolts must not be used.
Records to be maintained in Form–IV under DGMS support system guidelines.

8️⃣ Installation Procedure

Drill hole slightly smaller than bolt diameter (e.g., 42 mm for 47 mm bolt).
Insert the split set using driving tool until the plate is tight against roof.
Verify bolt protrusion and ensure washer contact.
Conduct pull test periodically.
Record details (length, load, location).

⚡ QUICK ONE-LINERS

Split sets = friction rock stabilizers.
Work on radial compression principle.
Provide immediate full-length support.
IS standard: IS 13056:1991.
Pull-out strength ≥ 10 tonnes.
No resin or cement required.
Common diameter = 47 mm.
Common length = 1.8 m.
Washer plate = load transfer device.
Used in both coal and metal mines.

🧠 DESCRIPTIVE MODEL QUESTION & ANSWER

Q. Describe the standard components, properties, and advantages of friction stabilizers (split sets) used for strata control in mines as per DGMS guidelines.

Answer:
Friction stabilizers, also known as Split Set Bolts, are steel tubes used as immediate support systems in underground mines. They work on the principle of frictional resistance along the entire bolt length. Components: A longitudinally split steel tube for frictional contact; Washer plate to distribute load on the rock surface; Driving collar for insertion by pneumatic hammer. Properties: Diameter: 33–47 mm, Length: 1.2–3.0 m; Pull-out strength ≥ 10 tonnes; Made of high-tensile steel conforming to IS 13056:1991. Advantages: Provide instant support after installation; Easy and safe to install; Distributes load uniformly along length; Effective in soft or squeezing strata. DGMS mandates that all split sets used in mines must be tested, certified, and approved, ensuring safe roof and side stability in underground workings.

🎯 25 MCQs – Friction Stabilizers (Split Sets)

Q1. Friction stabilizers are also known as:

Solution: "Split set" is the common industry name for friction rock stabilizers.

Q2. Friction stabilizers provide support through:

Solution: Their working principle is based on friction generated by the compressed tube against the borehole wall.

Q3. Standard for friction stabilizers:

Solution: IS 13056:1991 is the Bureau of Indian Standards specification for friction rock stabilizers.

Q4. Split set bolt material:

Solution: High tensile steel is required for the necessary strength and spring action.

Q5. Typical pull-out load:

Solution: A standard split set should offer a minimum pull-out resistance of 10 tonnes.

Q7. Friction stabilizers are installed using:

Solution: They are driven into the hole using impact tools like pneumatic or hydraulic hammers/drifters.

Q8. The supporting action occurs due to:

Solution: The compressed tube exerts outward (radial) pressure against the borehole wall.

Q9. Washer plate purpose:

Solution: The plate spreads the load from the bolt head onto the rock surface.

Q10. Friction stabilizers are used in:

Solution: They are versatile supports used in various underground mining environments.

Q11. Standard length range:

Solution: Common lengths range from 1.2m up to 3.0m depending on strata conditions.

Q12. Support testing required for:

Solution: DGMS guidelines typically require pull testing on a representative sample, often 5%.

Q13. Installation torque needed:

Solution: Unlike mechanical bolts, split sets are driven in and do not require torquing.

Q14. Split sets are most suitable for:

Solution: Their full-length frictional grip makes them effective in fractured or squeezing ground.

Q15. DGMS Regulation for support approval:

Solution: Regulation 99 deals with precautions against roof/side falls, implicitly covering support system approval and usage.

Q16. Split set friction acts:

Solution: The key advantage is the continuous frictional contact along the entire length embedded in rock.

Q17. Bolt corrosion protection:

Solution: Galvanizing or epoxy coating is commonly used to protect the steel from corrosion in mine environments.

Q18. Pull test ensures:

Solution: Pull testing verifies the actual anchorage capacity and performance of the installed bolt.

Q19. Driving collar used for:

Solution: The driving collar is designed to fit the installation tool (hammer/drifter).

Q20. Split set friction depends on:

Solution: The difference between the bolt diameter and the smaller borehole diameter creates the compression and friction.

Q21. Quality records are maintained in:

Solution: Form IV is often designated for recording details of support systems and their testing.

Q22. Friction bolts work immediately:

Solution: The mechanical friction provides immediate support as soon as the bolt is driven in.

Q23. Pull test frequency:

Solution: Testing a sample (like 5%) ensures quality control without testing every single bolt.

Q24. Main function of split sets:

Solution: They are primarily used to support and control the movement of rock strata.

Q25. Manufacturer must emboss:

Solution: Embossing manufacturer identification and batch number allows for traceability and quality control.

🔗 INTERNAL LINKING SUGGESTIONS

Related Topic	Read More On...
Strata Monitoring	Strata Monitoring in Longwall Workings
DGMS Circulars	DGMS Tech Circular No. 02 of 2020
Mine Safety	Safety Features in Crawler/Tyre Mounted Machinery
DGMS Management	Introduction to Mine Management for DGMS Exam

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