Testing of creep phenomena on soft rock

Abstract

Creep test involves deformation of material with time under a constant stress. Hence, for proper conducting of the creep test it is highly important to maintain, i.e. constant control the stress applied to a specimen. Namely, impact of the compression on the extent of deformation is distinctively non-linear; therefore the stress level or eventual variations of stress over time largely affect the increment of time-dependent components of deformation. Therefore, it is necessary to ensure that variations of stress are kept within limits of ±1% during the creep test the duration of which sometimes may last for several years. This paper presents structure of the dead-weight creep apparatus for maintaining constant stress over long time interval (day, week or year) with a capacity of 750kN and 1500kN, as well as for measuring of force and deformations at creep test. The creep tests have been conducted on marl specimens in duration of up to one year. The creep test results are presented for the uniaxially compressed prismatic specimens of dimensions 15x15x40cm and biaxially compressed plate models of dimensions 60x60x10cm, with circular opening at centre.