Time-dependent behaviour of some types of rocks is of the “creep” type, in particular in underground works, mining works, and in measuring procedures of rock properties. Tests used for defining material parameters or parameters relevant to defining a failure or behaviour of a material in the plastic state are usually of significantly shorter duration than the creep test. The duration of creep tests may vary from several hours to several years depending on the material being tested and the phenomenon that is the subject of the research. The required duration of the creep test, which provides reliable definition of the time-dependent material parameters of the rheological model, is a theoretical but also practical issue. The theoretical issue relates to establishing criteria for defining the required duration of the creep test. The practical issue relates to minimizing the duration of the creep test from which the necessary material parameters of the rock mass are obtained for correct numerical calculations. This paper proposes criteria for defining the required duration of a rock creep test, based on analysis of the results of unconfined uniaxial compression tests performed on marly rock samples.
Bedding, being a typical feature of sedimentary rocks, is a cause of inherent anisotropy of deformation properties of rock mass. Deformation response, both short‐term and time‐dependent, of certain rock elements near the tunnel opening will depend on the loading/unloading orientation angle to the natural bedding plane. This paper presents results of the triaxial creep tests performed on two cylindrical specimens of marl cut perpendicular and parallel to the natural bedding plane. Equipment and test procedure are also specified.
According to the well-known Jaeger's theory, the minimum possible rock mass shear strength as a discontinuum actually corresponds to the shear strength of rock joints. Since failures in rock masses due to loads caused by civil structures or civil works occur mainly by exceeding their shear strength, the shear strength of rock joints has huge practical significance. Therefore, in this paper it was decided to analyse a factor which can have a very important influence on the shear strength of unfilled rock joints. Namely, the influence of the presence of material bridges and initial joints between them, their number, size, mutual distance and orientation relative to the shearing direction were analyzed using results of laboratory or numerical CNS direct shear tests which were carried out by different researchers around the world. Except for increasing its peak and residual value, the professional public is currently unaware of the impact of this factor on the shear strength of intermittent rock joints. Based on the carried out analysis, appropriate conclusions have been made.
According to the Jaeger's theory, the minimum possible rock mass shear strength as a discontinuum actually corresponds to the shear strength of rock joints. Since failures in rock masses due to loads caused by civil structure and/or civil works occur mainly by exceeding their shear strength, the shear strength of rock joints has huge practical significance in rock engineering. For this reason, in this paper it was decided to analyse one of the factors which have very important influence on the shear strength of rock joints. Namely, natural rock joints are often filled with soft soil material and this infill material may have a significant and often decisive influence on the shear strength of rock joints. As a basis for the conducted analyses were used the results of direct shear tests under constant normal stress which was performed on natural or artificial specimens with horizontal infilled joints by various researchers around the word. Analyses have shown that some basic principles of mechanical behaviour of infilled rock joints during shearing can be reached. The thickness t and mechanical characteristic of the infill material have decisive influence on the peak and residual shear strength of infilled rock joints.
According to the Jaeger's theory, the minimum possible rock mass shear strength as a discontinuum actually corresponds to the shear strength of rock joints. Since failures in rock masses due to loads caused by civil structure and/or civil works occur mainly by exceeding their shear strength, the shear strength of rock joints has huge practical significance in rock engineering. For this reason, in this paper it was decided to analyse one of the factors which have very important influence on the shear strength of rock joints. Namely, natural rock joints are often filled with soft soil material and this infill material may have a significant and often decisive influence on the shear strength of rock joints. As a basis for the conducted analyses were used the results of direct shear tests under constant normal stress which was performed on natural or artificial specimens with horizontal infilled joints by various researchers around the word. Analyses have shown that some basic principles of mechanical behaviour of infilled rock joints during shearing can be reached. The thickness t and mechanical characteristic of the infill material have decisive influence on the peak and residual shear strength of infilled rock joints.
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