Rock Mass Classification for Columnar Jointed Basalt: A Case Study of Baihetan Hydropower Station

Abstract

Rock mass classification is important in preliminary design of geotechnical engineering projects. Using the columnar jointed basalt at the foundation of Baihetan Hydropower Station as an example, this paper presents a classification scheme of the columnar jointed rock. Unlike many common rock masses, an obvious characteristic of columnar jointed rock is that it is discontinuous in geometry while continuous in mechanics. Due to the inapplicability of existing rock mass classification systems, a classification scheme, combined with rock mass integrity, weak plane tightness, and permeability, is proposed. The new classification system has five grades with quantitative factors, which takes into account the features of columnar joints. As an easy-to-use scheme and case study, it would be helpful as a reference in the rock mass classification of similar problems.

A Case Study on Tunnel Excavation Stability of Columnar Jointed Rock Masses with Different Dip Angles in the Baihetan Diversion Tunnel

“…According to the geological survey reports, the rock strata at the dam site belong to the Permian Emeishan Formation ( 2 P β ) basalt. Columnar joints are mainly developed in several layers, including Based on the field investigation and geometric characteristics of the drilled rock mass (Figure 3), the CJRM in each rock layer at the dam site of the hydropower station can be classified into three types [31]: The first type of CJRM has slender columns generally between 2 and 3 m long, with an average diameter of 13-25 cm, and a high development density of internal fractures. The rock mass is not completely cut and presents a mosaic structure.…”

“…The third type of CJRM has good integrity, a low joint density, irregular joint development, thick columns between 1.5 and 5 m long, and a diameter of 0.5-2.5 m. This type of rock mass is less affected by weathering and has good quality, and is often not the main focus of engineering research. The first type of rock mass, with poor integrity of the columnar jointed rock Based on the field investigation and geometric characteristics of the drilled rock mass (Figure 3), the CJRM in each rock layer at the dam site of the hydropower station can be classified into three types [31]: The first type of CJRM has slender columns generally between 2 and 3 m long, with an average diameter of 13-25 cm, and a high development density of internal fractures. The rock mass is not completely cut and presents a mosaic structure.…”

Factors Controlling the Hydraulic Fracture Trajectory in Unconventional Reservoirs

“…The propagation of HF is always the focus of field engineers [13][14][15][16][17]. Due to lack of accurate and effective monitoring technology, it is impossible to directly observe the HF propagation process and morphology of underground reservoir [18]. Many scholars have studied the initiation and propagation of HF by numerical simulation method and laboratory-scale fracturing experiments.…”