Uniaxial Compressive Strength of Rock (UCS)(IS 9143:1979)
Determination of the unconfined compressive strength of intact rock cores per IS 9143 — the single most used rock design parameter, feeding rock mass classification, foundation bearing and pile socket design.
What is the Uniaxial Compressive Strength Test of Rock?
Uniaxial Compressive Strength (UCS) is the stress at which an unconfined cylindrical rock specimen fails under axial load. It anchors practically every rock engineering calculation in Indian practice — allowable bearing pressure on rock, pile socket friction and end bearing, rippability, and the strength ratings inside RMR and Q classification. IS 9143:1979 (Reaffirmed) is the Indian method; note this is the rock test, distinct from the unconfined compression test on soil per IS 2720 (Part 10) — a common point of confusion in investigation reports.
Global Lab prepares NX/54mm and other core sizes to the standard L/D ratio with ground ends, controls the moisture state (dry or saturated as specified), loads at the standard stress rate to failure, and reports UCS with failure mode photographs. Point-load index correlations are available where only irregular samples exist.
How the Uniaxial Compressive Strength of Rock (UCS) is Conducted
- 1
Core Selection & Logging
Intact core lengths are selected, logged and photographed; weathering grade and discontinuities are noted. - 2
Specimen Preparation
Specimens are cut to the standard L/D ratio; ends ground flat and parallel within IS 9143 tolerances; dimensions measured. - 3
Conditioning
Specimens are tested air-dry or after saturation, as the design brief requires, with moisture state recorded. - 4
Axial Loading to Failure
Load is applied at the standard stress rate on a calibrated frame until failure; peak load is recorded. - 5
UCS Computation & Classification
UCS is computed from peak load and cross-section; the rock is classified by strength grade for RMR/Q use. - 6
Reporting
UCS values, failure photographs and moisture state are issued via Autovity QLMS.
Applicable Test Standards
| Standard | Title | Scope | Type |
|---|---|---|---|
| IS 9143:1979 | Method for the Determination of Unconfined Compressive Strength of Rock Materials (Reaffirmed) | Test Method | Indian Standard |
| IS 8764:1998 | Method for Determination of Point Load Strength Index of Rocks (Reaffirmed) | Correlation Method | Indian Standard |
| ISRM SM | ISRM Suggested Methods for Rock Characterization, Testing and Monitoring | Supplementary Practice | International |