Uniaxial Compression Test – Unconfined Compression 


In the uniaxial compression test, a saturated or partially saturated, cylindrical, or prismatic specimen is compressed axially until failure. Lateral deformation is not restraint (σ2/3 = 0). The unconfined compressive strength qu is equivalent to the maximum stress reached. 

The determined stress-settlement diagram allows the derivation of the modulus of elasticity to describe the stress-strain behavior. The test is performed on cohesive soil specimens compliant with DIN EN ISO 17892-7, on binder-improved specimens compliant with TP BF-StB Part B 11.1/3, on rock specimens compliant with DIN 18141-1 or on hardened concrete compliant with DIN EN 12390-3.

Application and Potential 

The unconfined compressive strength qu can be used to calculate the undrained shear strength cu for highly cohesive samples, that is often used to estimate the initial stability of soil. The stress-strain curve can be used to determine the deformation modulus Eu. From this, statements regarding the sensitivity and consistency of the specimen can be derived. For rock specimens, in addition to the compressive strength σU, the deformation modulus E can be determined optionally as tangent or secant modulus up to 50% of the ultimate stress or as average modulus for the linear range. In road construction, unconfined compression tests are part of the suitability test of soil-binder mixtures according to TP StB 11.

Specimen Requirements

 

Tests can be done on undisturbed, reconsolidated, or processed samples. Due to the lack of radial support, the test can only be performed on stable (cohesive) soil samples. The required geometric and granular specifications are based on the type and geometry of the samples. 

Technical Equipment

 

Load frames of various sizes and sensitivity are available in our soil mechanics laboratories. The testing of soils and rocks can be carried out under force application up to 50 kN displacement-, load- or velocity-controlled. 

Weiterführende Informationen

  • DIN EN ISO 17892-7 (2018): Einaxiale Druckversuche an Bodenproben


  • DIN 18141-1 (2014): Einaxiale Druckfestigkeit von Gesteinsproben 


  • Neufassung der Empfehlung Nr. 1 des Arbeitskreises „Versuchstechnik Fels“ der DGGT: Einaxiale Druckversuche an zylindrischen Gesteinsprüfkörpern (2004)


  • Eurocode 7 (DIN EN 1997-2): Kapitel 5.8 bzw. 5.14 für Festigkeitsprüfungen an Boden bzw. Gestein


  • TP BF-StB Teil B 11.1 (2012) bzw 11.3 (2010): Eignungsprüfung bei Bodenverfestigungen bzw. Bodenverbesserung mit Bindemitteln