Point Load Test

The point load test determines an index value for a sample of rock fragments. With a sufficiently large number of tests, it is possible to derive the strength against compression of the tested material. Rock specimens in the form of either cylindrical, cut blocks, or irregular lumps are broken by applying a concentrated load through spherically truncated, conical platens. The test is suitable for solid and brittle rocks with a uniaxial compressive strength above 25 MPa. A defined methodology for point load tests is described by the ‘International Society for Rock Mechanics’. 

Application and Potential

The test is designed to estimate the strength of solid rocks by using fragments when no continuous core can be obtained. A single test results in the point load index iS. From a sequence of at least 10 individual tests, the point load stiffness IS is determined as the mean value. The uniaxial compressive strength σu* can be derived using a conversion factor.

Specimen Requirements

The size of specimens is limited by the space between the two load platens. Specimens between 25 mm and 100 mm with a width of up to 100 mm can be tested. They can have a defined shape (cuboid from cut blocks, cylinder from drill cores) or an irregular shape.

Technical Equipment

Point load apparatus, suitable for field testing.

Further Information

  • International Society of Rock Mechanics (1985): Suggested Method for Determining Point Load Strength. Commission on Testing Methods. Working Group on Revision of the Point Load Test Method
  • Prinz, Helmut; Strauß, Roland (2018): Ingenieurgeologie. Kapitel
  • DGGT (2010): Arbeitskreis 3.3 "Versuchstechnik Fels“ Nr. 5: Punktlastversuche an Gesteinsproben (Neufassung der Empfehlung, Sonderdruck Bautechnik, Aufl. 87/2010, Heft 6)