What is the difference between consolidation and curtain grouting?

Consolidation grouting treats the rock mass under a foundation to improve its strength and bearing capacity (Clause 3.1). Curtain grouting creates a narrow, deep, impermeable barrier to cut off seepage, typically under dams (Clause 3.2).

What is a typical starting grout mix?

Grouting typically starts with a thin mix, such as a water-cement ratio of 1.5 to 2.0 by volume, and is progressively thickened based on the rate of grout consumption ('take') by the rock (Clause 4.3).

What is 'grout refusal'?

It's the termination criteria for grouting a stage, defined as when the grout flow into the rock drops below a specified minimal value (e.g., 1 litre/min) for a set duration (e.g., 10-20 min) at the maximum specified pressure (Clause 6.5).

What is the purpose of packers in grouting?

Packers are inflatable or mechanical devices used to seal a borehole at a specific depth, allowing a particular section (stage) of the hole to be grouted under pressure without grout escaping up the hole (Clause 6.2.2).

IS 4990

: 1974

Code of practice for in-situ pressure grouting in rock foundations

CurrentSpecializedCode of PracticeGeotechnical · Tunneling and Underground Structures

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This standard outlines the code of practice for pressure grouting into rock foundations to reduce their permeability and increase their strength. It details procedures for consolidation, curtain, and contact grouting, covering materials, drilling, injection methods, pressures, and control testing for large civil engineering structures like dams and tunnels.

Covers the principles and procedures for pressure grouting in rock foundations to improve strength and reduce permeability.

Quick Reference Values

Typical Grouting Pressure Rule of Thumb0.23 kgf/cm² per metre of depth (or 1 psi/ft)

Lugeon Unit for Permeability1 litre per minute per metre of test section at 10 kgf/cm² pressure

Typical Grout Hole Diameter Range38 mm to 76 mm

Initial Water/Cement Ratio by Volume (Typical)1.5 to 2.0

Grout Refusal Criteria (Example)<1 litre/minute intake over a 10-minute period at final pressure

Practical Notes

The 'Rule of Thumb' for grouting pressure (0.23 kgf/cm²/m) is a starting point; final pressure must be carefully controlled to avoid hydraulic fracturing or lifting of the rock mass.

Water pressure tests (Lugeon tests) conducted before grouting are critical for assessing rock mass permeability and designing the grouting program (mixes, pressures, hole spacing).

Success of grouting is highly dependent on the site geology. Unexpectedly high or low grout 'take' requires immediate investigation and may necessitate changes in the grouting strategy.