DGMS Standards for Rigid Steel Props, Chocks & Cogs Used in Underground Mines – Components, Properties & MCQs

🧾 DETAILED NOTES

1️⃣ Introduction

Rigid steel supports such as props, chocks, and cogs are widely used in coal and metal underground mines for roof support, controlling strata movement, and ensuring safe working conditions. DGMS prescribes detailed mechanical and structural requirements to ensure their strength, durability, and performance under load.

These supports resist vertical and lateral loads and are widely used in depillaring, development headings, galleries, and junctions.

2️⃣ Rigid Steel Props – Components

1. Prop Body: Seamless steel tube or thick-walled pipe, high crushing strength. Length varies depending on seam height (1.0 m to 3.0 m).

2. Base Plate: Thick steel plate to distribute load evenly and prevent sinking into floor strata.

3. Cap Plate / Head Plate: Receives load from roof, prevents eccentric loading, typically 150–200 mm wide.

4. Welded Joints: High-quality welds ensuring compliance with IS welding standards.

3️⃣ Chocks & Cogs – Components

Chocks: Stable structures made of fabricated steel sections (I-beams, channels) or timber blocks arranged in layers. They utilize heavy gauge steel Cap & Base Plates and Cross Bracing to prevent lateral movement.

Cogs: Rigid pillar-like structures formed by crosswise stacking of short timber blocks or steel sections. They use a cap piece and packing material, tightened by wedges.

4️⃣ Mechanical Properties (DGMS Recommended)

Property	Requirement
Compressive Strength	Very high (≥ 300–400 kN for steel props)
Yield Strength	250–350 MPa
Buckling Resistance	Must resist lateral deformation
Corrosion Resistance	Coated or painted steel
Fatigue Strength	Withstand long-term cyclic loading

5️⃣ Installation & Maintenance

Props should be installed vertically, with the base secured on a firm floor.
Proper packing is needed between the prop head and the roof.
Cogs must be layered crosswise to prevent shifting, and tightened using wedges.
Regular inspection is mandatory for deformation, rust, and signs of buckling.
Props must not be used if bent or cracked.

⚡ QUICK ONE-LINERS

Rigid steel props provide vertical roof support.
Minimum yield strength of steel ≥ 240 MPa.
Steel chocks used for long-term heavy-duty support.
Compressive strength ≥ 300 kN is expected for steel props.
Must comply with DGMS & BIS support standards (e.g., IS 13224).
Widely used in depillaring operations.
Cap plate distributes the roof load uniformly.
Corrosion-resistant coating (paint/galvanizing) is essential.
Buckling is the major failure risk for props.
Crosswise packing and wedges are used to tighten cogs.

🧠 DESCRIPTIVE MODEL Q&A

Q. Describe the standard components and required mechanical properties of rigid steel props, chocks, and cogs used in underground mines.

Answer:
Rigid steel supports such as props, chocks, and cogs are essential for strata control in underground mines. According to DGMS and CMR 2017, steel props are made of high-strength steel pipes with cap plates, base plates, and locking mechanisms. Steel chocks consist of multiple steel legs connected by frames and braces, while cogs are box-type assemblies built from channels or I-beams. These supports must meet minimum mechanical requirements: yield strength ≥ 240 MPa, compressive capacity ≥ 300–400 kN, high weld quality, corrosion resistance, and dimensional accuracy as per IS standards. All steel supports must be tested at DGMS-approved institutions. Installation must follow the approved support plan to ensure roof stability and worker safety.

🧮 25 MCQs (Dynamic Answers A–E)

Q1. Rigid steel props are primarily used for:

Solution: Rigid props are used to provide vertical support against the load of the roof.

Q2. Standard bearing plate size:

Solution: 150 mm x 150 mm is the widely adopted standard size for square bearing plates in Indian mines.

Q3. Typical tensile strength of roof bolts:

Solution: High-strength steel bolts are required to have a minimum tensile strength exceeding 500 MPa.

Q4. Pull test checks:

Solution: The pull test verifies the integrity of the connection between the bolt, grout (resin/cement), and the rock.

Q5. Resin capsules provide:

Solution: Resin capsules are known for their fast polymerization, providing high anchorage strength almost immediately.

Q6. Bolt threads are used for:

Solution: The threads allow the nut/washer assembly to be securely fastened and pretensioned against the plate.

Q7. Roof bolt torque ensures:

Solution: Applying torque creates pretension in the bolt, which actively compresses the rock strata layers together.

Q8. Friction bolts (Split Sets) are typically used in:

Solution: Friction bolts are often favored in hard rock metal mines where they provide immediate frictional support.

Q9. Yield strength of bolts should be at least:

Solution: The material must have a high minimum yield strength (typically 300–450 MPa) to ensure it resists permanent deformation under load.

Q10. Corrosion resistance is improved by:

Solution: Applying a protective zinc coating (galvanizing) is a standard method to enhance corrosion resistance in humid mine air.

Q11. Bolt anchorage is improved by:

Solution: Resin or cement grout fills the annulus between the rock and bolt, providing the necessary bonding strength.

Q12. Roof bolt accessories include:

Solution: A torque wrench is essential for applying the correct pretension to the bolt.

Q13. Bolt failure may result from:

Solution: Applying a load greater than the bolt's or rock mass's capacity is a direct cause of failure.

Q14. Washer distributes:

Solution: Washers ensure that the compressive load is evenly spread across the bearing plate and surrounding rock.

Q15. Roof bolt length in coal mines (typical range):

Solution: Standard roof bolt lengths typically range between 1.2m and 2.4m, determined by the thickness of the unstable roof strata.

Q16. Fatigue strength helps resist:

Solution: Fatigue refers to the weakening of material under repeated stress (cyclic loading), which bolts must withstand over their life span.

Q17. DGMS requires testing of installed roof bolts via:

Solution: Mandatory pull testing ensures the bolt achieves the required anchorage capacity in the actual mine strata.

Q18. Mechanical bolts use:

Solution: Mechanical bolts anchor by expanding an outer shell against the borehole wall when the nut is tightened.

Q19. Elongation % ensures:

Solution: Adequate elongation ensures the bolt is ductile and can stretch slightly under load instead of fracturing suddenly (brittleness).

Q20. Cement grout is suitable for:

Solution: Cement provides a very strong, permanent anchorage used for long-term stability in main roadways and permanent workings.

Q21. Split set bolt is a type of:

Solution: Split set (or Swellex) bolts are members of the friction bolt family, anchoring through continuous radial contact pressure.

Q22. Bolt rod must be made of:

Solution: The rod material must be high-strength alloy or carbon steel to resist the extreme tensile forces.

Q23. Main danger controlled by roof bolts:

Solution: Roof bolts are used directly for strata control, making the prevention of roof falls their main safety function.

Q24. Bearing plates must withstand:

Solution: The plate transmits the high compressive force created by bolt pretensioning onto the rock surface.

Q25. Roof bolting must be performed by:

Solution: DGMS mandates that installation of support systems be done only by workers who are properly trained and authorized in strata control practices.

🔗 INTERNAL LINKING SUGGESTIONS

Related Topic	Read More On...
Roof Bolting Standards	Revised DGMS Standards for Resin Capsules
Strata Monitoring	Strata Monitoring in Longwall Workings
Alternative Support	Friction Stabilizers (Split Sets)
Testing	Pull Test & Torque Test Methods

🚧 Master Roof Bolting & DGMS Support Standards!

Join Online Mining Exam – India’s 1st Online Mining Academy.

DGMS Technical Notes
Real MCQs & Solved Papers
Complete Coal & Metal Mine Safety Coverage

🌐 www.onlineminingexam.com
📞 9971114020

Download Support System Notes & Practice MCQs Now!

Online Mining Exam