Hydraulic Behavior of Infilled Fractured Rocks under Unsaturated Conditions

Slip along fractures or hydrothermal alternation may lead to formation of weak layers of soils intercalated between the existing rock layers. In this situation, characterization of the behavior of rock fractures requires consideration of a complicated interaction of mechanical properties and geometrical characteristics of the fracture, coupled together with the properties of infill materials. Of the most important parameters which may considerably affect the behavior of an infilled fractured rock are the hydraulic properties of the infill material. These properties reflect the water retention ability of the infill material and determine the meniscus arrangements between the particles. This paper presents a new testing approach to describe the hydraulic properties of an infilled fractured rock under different stress states and saturation conditions. In this regard, a modified triaxial test device was used to establish the characteristic relationship between the degree of saturation and suction referred to as the soil water retention curve (SWRC). The new testing approach incorporates the axis translation technique for suction control, a flow pump for the measurement of infill’s degree of saturation, and the digital image processing (DIP) technique for volume change measurements. Results of this study suggested that variations in hydraulic properties of infilled fractured rock do not always correspond to changes in properties of the infill materials, but can be a result of a complex interaction of several factors, including morphological details of the fracture surface and the thickness and properties of the infill materials.