Unified Rock Classification System

Abstract
The Unified Rock Classification System (URCS) provides a reliable and rapid method of communicating detailed information about rock conditions pertinent to design and construction of civil engineering projects. The URCS consists of four fundamental physical properties: 1) weathering, 2) strength, 3) discontinuities and 4) density. A general assessment of rock performance is then based on a grouping of the four key elements to aid in making engineering judgments. These individual properties are estimated in the field with the use of a hand lens, a 1 -pound ballpeen hammer, a spring-loaded “fish” scale and a bucket of water. Each property is divided into five ratings which convey uniform meaning to engineering geologists, design engineers, inspectors and contractors as well as contract appeal board members. Subjective terminology, such as “slightly weathered, moderately hard, highly fractured and lightweight,” varies widely in meaning, depends on individual and professional experience, and cannot be quantified with any reliability. The URCS is not intended to supplant existing geologic classifications but it does offer a suitable alternative to ambiguous descriptive terminology.

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