Experimental Study on the Porosity Creep Properties of Broken Limestone

Shun-Cai Li,Jing-Na Guo,Qiang Li

doi:10.1051/matecconf/20166105001

Shun-Cai Li, Jing-Na Guo + Show 1 more

Open Access

https://doi.org/10.1051/matecconf/20166105001

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Abstract

In the underground engineering, the long-term stability of the surrounding rocks (especially the broken rocks containing water) and the ground settlement resulted from the seepage-creep coupling above goaf have been the important research subjects concerning the deep mining. For the broken rock, its porosity is an important structural parameter determining its creep properties, and the porosity change rate is more superior to describe the creep characteristics compared with the strain change rate at a certain direction. In this paper, MTS815.02 Rock Mechanics Test System is used to carry out the creep experiments on water-saturated broken limestone, and then the time curves of porosity and of the porosity change rate are obtained. By regression, we have got the relation equation between the porosity change rate with the instant porosity and the stress level during the creep. The study indicates that when the stress retains a constant level, the relation between the porosity change rate and the instant porosity can be fitted with a cubical polynomial. The obtained creep relation equation between the porosity change rate and the instant porosity and the instant stress provides a necessary state equation for studying the coupling between the seepage and the creep of the broken rock. Furthermore, the seepage in the broken rock has been verified to satisfy the Forchheimer’s non-Darcy flow according to our previous studies, and its seepage properties, k , β and c a can all be expressed respectively as the polynomial of the porosity, so, by combining with these three state equations we have obtained the four essential state equations for solving the coupling problems of the seepage and the creep for the broken rocks.

Highlights

For the granular material, porosity is a physical quantity which can reflect the creep characteristics comprehensively
We carried out the creep tests on granular limestone saturated by water with MTS815.02 Rock Mechanics Test System [14][15], we got the relations among the change rate of porosity, the instant porosity and the stress level in the creep process
By the MTS815.02 rock mechanics testing system, we carried out the creep experiments on the water-saturated limestone at five levels of stress

Summary

Introduction

Porosity is a physical quantity which can reflect the creep characteristics comprehensively. In the previous literature we can get the creep curve of the axial strain changing with time under each stress level, but the changing rules of porosity in the creep process have not been given directly. This paper argues that the creep characteristics of rock are mainly determined by the current level of porosity and stress. The data of porosity changing can be achieved within a short time under the high porosity and high stress levels. We carried out the creep tests on granular limestone saturated by water with MTS815.02 Rock Mechanics Test System [14][15] , we got the relations among the change rate of porosity , the instant porosity and the stress level in the creep process

Test object and the scheme

The test results

The application of test results in the theoretical analysis and calculation

Conclusions