ABSTRACT
Penetration rate is a principal measure of full-face tunnel boring machine (TBM) performance and is used to evaluate the feasibility of machine boring and to predict advance rates for excavation. Records of the Culver-Goodman Tunnel in Rochester, New York, are used to show how penetration rate is related to various excavation and support practices and to different levels of thrust and torque applied by a given TBM. Index properties pertaining to rock units in four different tunnels, including the Culver-Goodman Tunnel, are summarized. Correlations between penetration rate and various rock index properties are developed. Correlations with the highest statistical significance are presented, and recommendations are made for estimating TBM penetration rates in sedimentary rocks.
INTRODUCTION
In full-face tunnel boring machine (TBM) applications, the penetration rate is used both to estimate the time required to complete a given tunnel and to evaluate the feasibility of machine boring in a specified geologic environment. The penetration rate establishes an upper bound on tunneling progress from which the advance rate is evaluated through judgments regarding potential sources of downtime and their aggregate effect on machine utilization. Case history studies of full-face TBM projects have generally shown relationships between penetration rate and rock properties for a given job (Tarkoy and Hendron, 1975; Blindheim, 1976 and 1979; Morgan, Barratt, and Hudson, 1979; Jenni and Balissat, 1979). However, correlations between penetration rate and rock index properties over a variety of different jobs employing different machines have shown substantial scatter (Korbin, 1979; Morgan, Barratt, and Hudson, 1979). Korbin (1979) summarized various approaches that have been taken for TBM performance prediction and discussed limitations of these methods. Correlations between penetration rate and intact rock properties must be developed with careful consideration of variations in machine design and operation, contractor practice, and rock mass condition. To investigate how factors related to machine operation, mechanical repair, and support requirements affect penetration rate in different rock types, this paper concentrates on the boring records of the Culver-Goodman Tunnel in Rochester, New York. The quality of the records for this tunnel and the detail with which construction events were recorded permits a comprehensive investigation of contractor practices, mechanical difficulties, and rock property variation. Detailed case histories of this and other tunnels mentioned in this paper have been presented by Nelson (1983), from which additional information about the geology, rock types, and construction procedures may be obtained.
PENETRATION RATE VARIATION IN THE CULVER-GOODMAN TUNNEL
TBM penetration rate during excavation of the Culver-Goodman Tunnel was influenced primarily by two factors: 1) operating levels of thrust and torque, and 2) the rock type present at the heading. The variation in penetration rate caused by each factor is discussed in the following sections.
Construction Project Description
The Culver-Goodman project includes the construction of 8,633 m (28,322 ft) of 5.1 m (16.7 ft) internal diameter tunnel through a sequence of shales, sandstones, and limestones of Ordovician and Silurian age. This tunnel is at an average depth of 46 to 60 m (150 to 200 ft) below the ground surface, and is part of a combined sewer overflow and storage system in the metropolitan area of Rochester, New York, which will be operated by the Monroe County Department of Wastewater Management.
