ABSTRACT:

To make a better understanding of the meso-surface structure of fractured rocks in influence of the long term behavior of rock mass, two types of rock fractures were induced in sandstone by means of modified shear test and Brazilian split test. The shear creep experiments were performed in the mode of constant normal force with a step-wise increased shear loading force. The morphology of fractured rock surfaces were scanned before, in the mid and after the creep test, respectively. The variation of roughness and waviness of the fractured rock surfaces during creep deformation were analyzed by using of fractal theory. Under consideration of the surface roughness of fractured rock, a modified generalized Kelvin model was established, which presents stable creep behavior with the characters of instantaneous deformation, retard elasticity and plastic deformation. The study shows that the model can nicely describe the creep deformation law of fractured rocks with the influence of the surface roughness, and the predicted results agree well with the experiment.

1 INTRODUCTION

In recent years, with the development of geological engineering projects, the long term mechanical behavior and stability of rock mass have been paid much attention. Griggs (1939) was the first to conduct creep test with limestone, shale and siltstone, which have moderate strength. He pointed out that some amount of creep deformation occurred in rocks when the applied load reached to 12.5%- 80% of the ultimate load only. After nearly 30-years bending creep test on the granite, Ito and Sasajima (1987) found that the granite showed viscous flow without yield. Xu (2005), Yan (2008) and Zao (2009) et al, respectively, conducted shear creep tests for jointed rocks, and obtained the typical shear creep deformation curve of jointed rocks. In addition, they established shear creep models for different types of rock. Chen (2008) carried out creep test on the cylinder silty mudstone with weak interlayer under constant normal stress and step-wise increased shear loading force, and derived a generalized Kelvin shear creep model. Li (2009) made a study on the creep characteristics of the marble's structural surface, and found that creep deformation of rock could be expressed as decay creep and steady creep under the low stress level; they also verified the normal linear shear creep model.

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