The Technology of Underground Construction Present and Future

Exploration The technology of underground construction and particularly of tunneling, both now and in the future, starts with knowledge of the properties of the medium surrounding the tunnel. Although we are trying to develop machines that can excavate tunnels independently of the properties of the medium, and although we may achieve some success in this direction, we seem always to be brought up short by a paradox: With increasing sophistication of machines and with increasing complexity of construction jobs, our methods are likely to become more sensitive rather than less sensitive to changes in the medium. I suspect that the need for more precise knowledge of subsurface conditions in advance of construction will increase rather than decrease as time goes by. In the recent anniversary issue of Engineering News Record, Probing the Future, Senior Editor Bill Jacobus prophesies highly sophisticated devices to probe the unknowns of the earth's soil and rock materials. He envisions that "drill holes to obtain borings will give way to rock-melting coring devices". He may be right; it is hard to argue the accuracy of predictions of the future. It seems to me more likely, however, that the rock-melting probe will be simply one more in