Time-Dependent Behavior of Rock Materials

Abstract

Understanding the geomechanical behavior of a geological model is still an on-going challenge for engineers and scientists. More challenges arise when considering the long-term behavior of rock materials, especially when exposed to environments that enable time-dependent processes to occur and govern overall behavior. The latter is essential in underground projects such as nuclear waste repositories. The lifespan can exceed one million years or other openings where the project’s lifetime and sustainability are the critical design parameter. In such cases, progressive rock mass deformation that can lead to instabilities, time-dependent overloading of support and delayed failure are considered the product of time-dependent phenomena. Understanding and predicting the overall impact of such phenomena aims to achieve design optimization, avoiding dlivery delays and thus cost overruns. This chapter provides more insight into the time-dependent behavior of rocks. Simultaneously, the emphasis is given to investigating and analyzing creep deformation and time-dependent stress relaxation phenomenon at the laboratory scale, and in-depth analyses are presented. This work further develops the understanding of these phenomena, and practical yet scientific tools for estimating and predicting the long-term strength and the maximum stress relaxation of rock materials is presented. The work presented in this chapter advances the scientific understanding of time-dependent rock, and rock mass behavior increases the awareness of how such phenomena are captured numerically and lays out a framework for dealing with such deformations when predicting tunnel deformations.

Time-Dependent Model for Brittle Rocks Considering the Long-Term Strength Determined from Lab Data

“…Table 2. Visco-elastic-plastic rheological models with their associated mechanical analogues; analytical solutions; and stress, strain-time behaviour, modified from [18]. Note that G, K, G K , η K , and η M denote the shear modulus, bulk modulus, Kelvin viscosity, and Maxwell viscosity, respectively, and p, q, t, and ε denote mean stress, deviator stress, time, and strain, respectively.…”

“…The strength of brittle rocks and rock masses is also considered time-dependent, e.g., [8,[13][14][15][16][17][18] where brittle failure at the excavation scale can manifest immediately or after some time due to subdued crack growth and interaction. The lower limit at which these cracks can develop and grow with time is the crack-initiation stress threshold [8].…”

Determination of the Ground Reaction Curve for an Elasto-Plasto-Fractured Rock Mass

“…However, in practical applications, the influence of time is often overlooked [2]. An analysis of the impact of the time factor on the growth of the displacement of rock masses requires the utilization of various rheological models-as discussed, for example, in [3][4][5][6][7].…”