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Received Dec 23, 2017; Accepted Feb 11, 2018
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1. Introduction
Many rocks involve moisture [1]. Moisture has multiple effects on a rock, such as softening and lubrication [2, 3]. Moisture-dependent rheological deformation is found in many rock masses [4, 5], where the long-term effect of moisture aggravates the rheological properties of rocks [6], causes changes in the physical properties and microstructure of rocks, and, in turn, results in rock strength reduction or damage [7, 8]. A significant example of this effect is that of the rock mass in the Three Gorges Reservoir Area [9]. According to incomplete statistics, approximately 69% of the reservoir area suffered rockslide hazard during the impoundment of the Three Gorges Reservoir [10, 11], which is closely related to the rheological effect under water-rock interaction of the mudstone formation.
Rheological mechanical characteristics have attracted extensive research. For instance, Lipponen et al. [12] studied the effect of water on the long-term stability of the tunnel surrounding the rock. Okubo et al. [13] performed a long-term creep test on aqueous tuff. A triaxial creep experiment was conducted on limestone under saturated condition [14]. A creep constitutive model was proposed to describe the deterioration of the hydraulic properties of sandstone [15]. The mechanism of creep damage under water-rock interaction of red-bed soft rock was also clarified [11]. Despite numerous rheological constitutive models for multiple types of rock [15, 16, 17], a special model for mudstone, considering moisture content, is still required.
This paper aims to develop a new rheological constitutive model of mudstone, which allows the incorporation of the effect of moisture. First, the laboratory triaxial rheological tests are conducted on the mudstone specimens collected from the interlayer in the Three Gorges Reservoir Area. Both dry and saturated conditions are considered. Based on these test observations of stress-strain, a rheological constitutive model, namely, the HKCV model, is then developed. Finally, the developed model estimates are compared with the laboratory test observations and the existing model estimates.
2. Test Equipment and Method
2.1. Test Equipment
The triaxial rheological test equipment is a rock triaxial rheometer (Figure...