The primary role of instrumentation is providing information with the following objectives:
I. Safety - or warning of trouble (particularly instability) in time to take corrective action.
II. Monitoring - of selected features:
Does a hazard exist?
To what extent is situation getting worse?
What remedial measures are needed? To what extent were remedial measures effective?
Establish confidence in completed project.
Assure adequate safety without wasting money.
Provide data sufficient to make initial decisions.
Treat ground conditions properly, without overkill. This paper outlines the techniques used on four underground projects by addressing each of the above noted objectives. The case histories include:
A 25m diameter multiple drift soft ground tunnel.
An underground hydroelectric powerhouse in unstable ground.
Pilot tunnel and 15m diameter multiple drift main bore tunnel in squeezing ground.
A twin highway tunnel project in sedimentary rock, where instrumentation reduced the initial support cost by 25 percent.
This paper is dedicated to the memory of Howard B. Dutro, who passed away on October 7, 1989. Boward's career as an Engineering Geologist spanned 35 years and included minerals exploration Work, blasting consulting, and various leadership and management positions at Terrametrics, Inc., Where he specialized in the development of rock mechanics instrumentation apparatus and techniques. Few other men have had such an impact on the geotechnical industry, and Howard will be remembered and missed by his many colleagues and friends.
Advances in underground excavation and support technology have tended to outstrip the state of the art in the prediction of geologic conditions ahead of the face. It has been necessary to evaluate tunneling conditions as they are encountered, and adjust tunneling procedures accordingly. It is in this area of timely identification and evaluation of unforeseen rock and soil mass conditions, that field (in-situ) instrumentations can help improve both the safety and economy of the underground opening during construction, as well as the overall performance of the completed structure.
Field instrumentation can be used in the applications listed below. In many of these, it is the only means by which reliable numerical information may be obtained.
Identification of rock and soil mass properties, such as strength, deformation, anistropism, and resistance to some types of alteration.
Observation of the state of stress in the masses, including residual stress and redistributed stress.
Observation of the response of the rock or soil masses to disturbances by construction and operation of the structure.
Measurement of the reaction of the man-made structure to conditions imposed by the geologic mass, and to conditions during subsequent operation.
Observation of the behavior of associated or adjacent structures or services either affected or at risk as a result of tunnel construction.
Recognition of hazards, either actual or incipient.
