ABSTRACT

The paper is to research the non-linear rheological model of rock. Firstly, a new concept of potential strength is proposed. Then the creep process is divided into numerous instancys, and in every instancy, the instant potential strength can be represented by the instant summit strength to some degree. The instant summit strength is the function of visco-plastic strength. With the development of visco-plastic strain, the damage in rock develops, and the instant summit strength decreases accordingly. When the instant summit strength decreases to be equal to the applied stress, the creep reaches the critical state to the tertiary creep. With the damage going on developing, the instant summit strength changes to be lower than the applied stress, which results in the tertiary creep. Through the instant summit strength, an instant yield function is established, which represents the instant state of the rock. The fluidity parameter is the function of time, applied load, instant strength and the damage in rock. It can be transferred to be the function of time and the instant yield function. So the non-linear fluidity parameter can be established, which includes the linear and non-linear creep properties in a unified form. Based on the parameter and the Nishihara creep model, a non-linear creep model is established, which can also be seen as the generalization of the Nishihara creep model from linear to non-linear. Finally, by numerical calculation, the model is demonstrated to be effective to imitate all the three stages of creep.

1 INTRODUCTION

Hither to now, many works have been done for the creep test and rheological model of rock(TAO Bo,2005, CHEN Yuan-jiang, 2003, HE Kaiping, 2002, Geraldine Fabre,2006, Pierre Be resta,2005), these works are beneficial to establish solid basement of creep theory of rock. As far as the published creep models are considered, most of them deal with the first and the second stage of creep. However, with the development of engineering activity, such as hydropower engineering and mining engineering etc, the third stage of creep is always encountered in practical projects. How to describe the whole process of creep of rock is an urgent challenge.

Now, some works have been done with respect to the non-linear properties and the model of creep of rock. In order to obtain the rule of creep failure of tunnel in high initial stress field, the process of creep failure of surrounding rocks is simulated by FEM(WANG,2005). Chen Weizhong(2007) researches the nonlinear creep damage constitutive model of rock salt and applied the model into practical engineering work. FAN Qingzhong(2007) researches the non-linear creep property of soft rock using laboratory tests.

All the works is helpful in illustrating the creep properties and engineering application. But due to the complex of the problem, much work is still left to do. In this paper, a new concept of potential strength is proposed, then a non-linear creep model is established based on it, and finally a numerical example shows the effectiveness of the model.

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