ABSTRACT

Degraded rock samples were prepared to investigate the effect of degradation on the mechanical behavior observed under an uniaxial compression test. The samples of Småland granite were obtained from Äspö HRL in Sweden. The samples were degraded by submerging in 10% saline water (10% NaCl) for 90 days, and axial and circumferential deformations were observed. The behaviors of uniaxial deformations were investigated using an expansion damage model based on the damage mechanics theory. The damage parameters were identified from the stress-strain relation obtained from the mechanical test results. The effect of degradation was inferred by investigating the change in the damage parameters of the degraded rock. Moreover, finite element simulations based on an analytical model of the uniaxial compression test were performed using the damage parameters. As the results, it was inferred that the Småland-granite becomes more expansive material. It is, also, inferred that a localized deformation on surface of sample causes the decrease in stress.

1 INTRODUCTION

To discuss the chemical effect on the mechanical and hydraulic behavior of the rock adjacent to the tunnel wall, Backström et al. (2006) investigated the mechanical properties of chemical degraded sample. The samples were obtained from Äspö HRL in Sweden and preserved in the 10 % salt water, formation water and distilled water for 90 days. Then the samples were subjected to the unconfined compression test.

In this study, a numerical modeling of the chemical degradation of rocks is examined with expansion damage mechanics (Yamamoto et al. 2003). The damage parameters were determined from experimental results. The difference in failure process between sound and degraded rock is investigated by comparing the damage parameters. Moreover, FEM analyses with damage mechanics were carried out using the damage parameters. In this paper, firstly, the results of laboratory tests are briefly reviewed.

2 MATERIAL AND MECHANICAL TEST
2.1 Material

20 samples of Ävrö granite were collected from drill cores, from -450 m in the Äspö Hard Rock laboratory, Sweden by SKB. The samples were submerged in their respective fluids, i.e., 5 samples in saline water, 3 samples in distilled water and 2 samples in the formation water were preserved for 90 days. In addition, 2 samples were submerged in distilled water for 40 days and 3 samples were kept in formation water for 40 days.

2.2 Uniaxial compression test

After submerging in the respective fluids, the samples were experimented by uniaxial compression test. The axial and circumferential deformation was monitored. Table 1 shows uniaxial compressive strength (UCS) of the samples submerged in three different fluids for 90 days. It can be seen that the result of formation water is the mostly similar to the one of saline water. The samples submarged distilled water (as sound sample) and saline water (as degraded sample) are subjected to determination of damage parameter with those stress-strain relation.

3 EXPASION DAMAGE MODEL
3.1 Fundamental concept

In damage mechanics (Lemaitre 1992), the change in mechanical behavior due to the growth of damage (cracks) in material is dealt with.

This content is only available via PDF.
You can access this article if you purchase or spend a download.