How is the required rock support determined using this code?

The support is determined based on the Rock Mass Rating (RMR) calculated as per Clause 4 and Table 1. This classification then guides the required support pressure, bolt length, and spacing using Tables 2 and 3.

What is the purpose of a pull-out test on a rock bolt?

A pull-out test (Clause 8.2.2) is performed to verify the load-carrying capacity of the installed rock bolt, confirming that the anchorage is effective and meets the specified design load.

What are the common types of rock bolts mentioned?

The code covers various types (Clause 6), including mechanically anchored bolts, grouted dowels (rebar), and resin-grouted bolts, each suitable for different rock conditions and support requirements.

How long should a rock bolt be?

As a rule of thumb, bolt length is typically 1/3 to 1/2 of the excavation span. Clause 7.3 provides more specific guidance for different conditions.

IS 14210

: 1995

Code of practice for rock bolting for underground excavations

CurrentSpecializedCode of PracticeGeotechnical · Tunneling and Underground Structures

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This code of practice provides guidelines for the design, installation, and testing of rock bolting systems for supporting underground excavations like tunnels, mines, and caverns. It covers rock mass classification using the RMR system, selection of appropriate bolt types, and quality control procedures to ensure rock stability.

Lays down procedures for design, installation, testing, and maintenance of rock bolts used for supporting underground excavations.

Quick Reference Values

RMR range for 'Good' Rock61 to 80

RMR range for 'Very Poor' Rock< 20

Typical grout water-cement ratio0.4 to 0.5

Minimum 28-day grout compressive strength25 MPa

Pull-out test load requirement1.5 times the design load

Torque for 20mm mechanically anchored bolt200-250 Nm

Key Formulas

L = 2 + 0.15B — Bolt length (L) for large cavern with span (B) > 20 m (Clause 7.3)

L = B/2 to B/3 — Rule of thumb for bolt length (L) based on excavation span (B)

Practical Notes

The Rock Mass Rating (RMR) system detailed in Table 1 is fundamental to the entire design process in this code; accurate geological investigation is therefore paramount.

Pull-out tests (Clause 8.2) are mandatory and should be performed on a specified percentage of production bolts (typically 1-2%) to verify design assumptions and installation quality.

For grouted bolts, ensuring complete grout encapsulation without air voids is critical for corrosion protection and achieving the desired bond strength and long-term performance.