PREFACE TO THE SIXTH EDITION

During the few years that have elapsed since the publication of the first edition of this work, the art of tunneling through different soils and especially under large bodies of water, has made considerable progress. During the last ten years, no less than eight subaqueous tunnels involving the construction of sixteen tubes have been constructed for the service of the city of New York alone. The reader will, no doubt, also recall the tunnels under the Boston Harbor, the St. Clair, the Charles and Detroit Rivers in our own country as well as the tunnels under the Thames and the Seine in Europe. Engineers, contractors and workmen have acquired such experience in these difficult underground and under-river construction that the work is now undertaken without any of the fear and hesitation that were associated with the earlier enterprises.

As entirely new methods have been introduced by professional men, it was found necessary to arrange the presentation of the subject in this sixth edition so as to give due prominence to these recent methods.

Besides this, other changes have been made in order to give greater attention to American method of excavating tunnels through rock and loose soil. This will explain the treatment of the crown-bar and also the extensive illustration of the heading and bench method as well as the drift method of driving tunnels which is followed in the United States.

Space has also been given to important tunnels recently built mainly for the purpose of illustrating the various methods discussed in the text and also to bring out more clearly the characteristics of the different methods of tunnel excavation.

The author hopes that these added features will meet the present requirements of engineers and students.

Charles Prelini.

CONTENTS

LIST OF ILLUSTRATIONS

INTRODUCTION

THE HISTORICAL DEVELOPMENT OF TUNNEL BUILDING.

A tunnel, defined as an engineering structure, is an artificial gallery, passage, or roadway beneath the ground, under the bed of a stream, or through a hill or mountain. The art of tunneling has been known to man since very ancient times. A Theban king on ascending the throne began at once to drive the long, narrow passage or tunnel leading to the inner chamber or sepulcher of the rock-cut tomb which was to form his final resting-place. Some of these rock-cut galleries of the ancient Egyptian kings were over 750 ft. long. Similar rock-cut tunneling work was performed by the Nubians and Indians in building their temples, by the Aztecs in America, and in fact by most of the ancient civilized peoples.

The first built-up tunnels of which there are any existing records were those constructed by the Assyrians. The vaulted drain or passage under the southeast palace of Nimrud, built by Shalmaneser II. (860-824 B.C.), is in all essentials a true soft-ground tunnel, with a masonry lining. A much better example, however, is the tunnel under the Euphrates River, which may quite accurately be claimed as the first submarine tunnel of which there exists any record. It was, however, built under the dry bed of the river, the waters of which were temporarily diverted, and then turned back into their normal channel after the tunnel work was completed, thus making it a true submarine tunnel only when finished. The Euphrates River tunnel was built through soft ground, and was lined with brick masonry, having interior dimensions of 12 ft. in width and 15 ft. in height.

Only hand labor was employed by these ancient peoples in their tunnel work. In soft ground the tools used were the pick and shovels, or scoops. For rock work they possessed a greater range of appliances. Research has shown that among the Egyptians, by whom the art of quarrying was highly developed, use was made of tube drills and saws provided with cutting edges of corundum or other hard, gritty material. The usual tools for rock work were, however, the hammer, the chisel, and wedges; and the excellence and magnitude of the works accomplished by these limited appliances attest the unlimited time and labor which must have been available for their accomplishment.

The Romans should doubtless rank as the greatest tunnel builders of antiquity, in the number, magnitude, and useful character of their works, and in the improvements which they devised in the methods of tunnel building. They introduced fire as an agent for hastening the breaking down of the rock, and also developed the familiar principle of prosecuting the work at several points at once by means of shafts. In their use of fire the Romans simply took practical advantage of the familiar fact that when a heated rock is suddenly cooled it cracks and breaks so that its excavation becomes comparatively easy. Their method of operation was simply to build large fires in front of the rock to be broken down, and when it had reached a high temperature to cool it suddenly by throwing water upon the hot surface. The Romans were also aware that vinegar affected calcareous rock, and in excavating tunnels through this material it was a common practice with them to substitute vinegar for water as the cooling agent, and thus to attack the rock both chemically and mechanically. It is hardly necessary to say that this method of excavation was very severe on the workmen because of the heat and foul gases generated. This was, however, a matter of small concern to the builders, since the work was usually performed by slaves and prisoners of war, who perished by thousands. To be sentenced to labor on Roman tunnel works was thus one of the severest penalties to which a slave or prisoner could be condemned. They were places of suffering and death as are to-day the Spanish mercury mines.

Besides their use of fire as an excavating agent, the Romans possessed a very perfect knowledge of the use of vertical shafts in order to prosecute the excavation at several different points simultaneously. Pliny is authority[1] for the statement that in the excavation of the tunnel for the drainage of Lake Fucino forty shafts and a number of inclined galleries were sunk along its length of 3¹⁄₂ miles, some of the shafts being 400 ft. in depth. The spoil was hoisted out of these shafts in copper pails of about ten gallons’ capacity by windlasses.