Get Isrm Blue Book Pdf

The ISRM (1981) divides the rock strengths from R0 to R6 ing to the UCS of the intact rock, as shown in Table 2. R0 has UCS<1 MPa, R1: 1≤UCS≤5 MPa, R2: 5≤UCS≤25 MPa and R3: 25 ≤UCS≤50 MPa.

Unconfined Compressive Strength (UCS) stands for the maximum axial compressive stress that a cohesive soil specimen can bear under zero confining stress. Unconfined compression test is one of the fastest and cheapest methods of measuring shear strength of clayey soil.

The International Society of Rock Mechanics (ISRM, 1985) has established the basic procedures for testing and calculation of the point load strength index. There are three basic types of point load tests: axial, diametral, and block or lump. The axial and diametral tests are conducted on rock core samples.

The International Society for Rock Mechanics (ISRM) standard terminology for UCS is very low (< 5 MPa), low (5–25 MPa), moderate (25–50 MPa), medium (50–100 MPa), high (100–250 MPa), and very high (> 250 MPa).

In the modern rock mechanics practice, the UCS is estimated from the Point Load Index (Is) using a universal conversion factor (K) equal to 24, following the recommendations of Broch and Franklin (1972).

Considering that UCS is highly important, Engineers often utilize indirect methods, namely the Point Load Test, to obtain the Point Load Index Strength (Is(50)). From this test, the results are correlated in order to predict the UCS value. One of the general correlations is provided by ISRM where UCS=20-25 Is(50).