Rock Mass Hydraulic Conductivity Estimated by Two Empirical Models

Abstract

Listen

Translate article

Undertaking engineering tasks such as tunnel construction, dam construction, mine development, the abstraction of petroleum, and slope stabilization require the estimation of hydraulic conductivity for fractured rock mass. The understanding of hydraulic properties of fractured rock mass, which involves the fluid flow behaviour in fractured consolidated media, is a critical step in support of these tasks. To obtain hydraulic properties of fractured rock mass, double packer systems can be adopted (NRC 1996). They can be used to determine the hydraulic conductivity in a portion of borehole using two inflatable packers. Although this type of test can directly measure the hydraulic parameter, costs of the testing are fairly high. Several studies (Snow, 1970; Louis, 1974; Carlsson & Olsson, 1977; Burgess, 1977; Black, 1987; Wei et al., 1995;) have proposed the estimation of rock mass hydraulic conductivity using different empirical equations, which were based on the concept that rock mass permeability decreases with depth, as shown in Table 1. These empirical equations provide a great feature for characterizing rock mass hydraulic properties quickly and easily. However, the applicability of these equations is very limited because depth is not the only significant variable on the prediction of rock mass permeability. Hydraulic properties of rock mass may vary with geostatic stress, lithology and fracture properties, including fracture aperture and frequency, fracture length, fracture orientation and angle, fracture interconnectivity, filling materials, and fracture plane features (Lee & Farmer, 1993; Sahimi, 1995; Foyo et al., 2005; Hamm et al., 2007). Thus, a more applicable empirical equation for estimating hydraulic conductivity of rock mass possibly must include the aforementioned factors. This chapter proposes two empirical models to estimate hydraulic conductivity of fractured rock mass. The first empirical model was based on the rock mass classification concept. The study developed a new rock mass classification scheme for estimating hydraulic conductivity of fractured rocks. The new rock mass classification system called as “HCsystem” based on the following four parameters: rock quality designation (RQD), depth index (DI), gouge content designation (GCD), and lithology permeability index (LPI). HCvalues can be calculated from borehole image data and rock core data. The second empirical model was simply based on results of borehole televiewer logging, flowmeter logging and packer hydraulic tests. Three borehole prospecting techniques for fractured rock mass hydrogeologic investigation were performed to explore various hydrogeologic characteristics, such as fracture width, fracture angle, flow velocity and hydraulic