Ground Classification for Trench, Shaft, and Slope Excavations

Soft ground tunnel/trenchless designers and contractors have used the Tunnelman's Ground Classification system (Heuer, 1974 after Terzaghi, 1950) for over 60 years to describe potential ground behavior for tunneling. Geotechnical baseline reports (GBRs) utilize the Tunnelman's Ground Classification system to baseline ground behavior for trenchless construction. More recently, GBRs are being used to describe soil behavior for shafts and open-cut excavations utilizing the same method. Use of this system for shafts and open-cut construction is outside the original intent of the classification scheme and subsequent modifications. While many ground types behave similarly in tunnels, shafts, and open-cut excavations, there are considerations that are unique to shaft and open-cut excavations. This paper introduces a modified ground behavior classification system for use specifically in describing ground behavior for trench, shaft, and sloped excavations in soils based on the Tunnelman's Ground Classification system. This system provides classification of different ground behaviors, descriptions of the ground behavior, typical soil types associated with those behaviors, and impacts of groundwater on the behaviors. The proposed classification system could be used in not only GBRs, but also incorporated into traditional geotechnical evaluation and recommendation reports which commonly refer to OSHA guidelines for minimum slopes, but do not address ground behavior.