Field measurements can give information on the global material properties of the rock, the safety of the structure in a particular phase of construction and the effectiveness of particular support measures. Often measurements form the link between theory and engineering practice, in that the observed behaviour can be interpreted with the aid of computations. Using the example of a tunnel in swelling rock it is shown how a structural solution can be based on measurements. The observed behaviour of a prestressed concrete lining for a pressure tunnel is also described.
Durch Feldmessungen können die globalen Materialeigenschaften des Felses, die Sicherheit des Bauwerkes in einer bestimmten Konstruktionsphase sowie die Wirksamkeit einer bestimmten Stuetzmassnahme abgeklart werden. Oft stellen die Messungen das eigentliche Verbindungsglied zwischen Theorie und Praxis dar, indem die beobachteten Daten mit Hilfe von Berechnungen gedeutet werden. Am Beispiel eines Tunnels in einem quellfahigen Gestein wird gezeigt, wie eine konstruktive Lösung aufgrund von Messungen erarbeitet wird. Das beobachtete Verhalten eines vorgespannten Betongewölbes fuer einen Druckstollen wird beschrieben.
Des mesures in situ donnent des informations sur les proprietes globales des materiaux de la roche, sur la securite de la structure dans une phase de construction determinee ainsi que sur l'efficacite d'une mesure de support determinee. Les mesures forment souvent le trait d'union entre la theorie et la pratique, par moyen de l'interpretation par calcul des valeurs observees. La recherche d'une solution constructive sur la base de mesures est expliquee par l'exemple d'un tunnel dans une roche susceptible au gonflement. L'observation du comportement d'une voûte en beton precontraint fait l'objet d'une discussion.
Systematic field measurements and statical computations in the form of parametric studies are established today as recognized, and in many cases indispensable aids for a safe and economic design of underground openings. By means of statical computations an attempt is made to predict the structural behaviour of the opening in an analytical way. The interrelationship between the various factors, for instance rock properties, shape and dimensions of the opening, initial state of stress etc. is clearly seen in the calculated results. But although the latter are already available at the design stage, they are subjected to great uncertainties. Measurements carried out on the structure enable its behaviour to be observed directly, without the actual mechanism, which gives rise to its behaviour, necessarily being illuminated. The measurements are usually carried out during the constructional phase, and, if carefully planned and executed, they can give a true picture of the behaviour of the structure. From these considerations it is clear that computations and measurements complement each other and only when combined are they capable of leading to a correct explanation of structural performance in complex geotechnical situations. Measurements are of greatest interest during construction itself. Completed structures are only observed further in exceptional cases. The practical significance of systematic measurements for a given project depends upon the extent to which the results of the continued observations are able at all to influence the constructional work. This point is illustrated by means of two examples. The first concerns the case of shield tunnelling with lining segments. Here the most important constructional decisions, for instance deciding upon the shield diameter with respect to the anticipated deformations of the lining ring, or designing the ring segments themselves, have to be made well before the start of the construction. The observation of the actual deformations of the tunnel profile, the movements of the surrounding ground or settlements at the ground surface have the function, mainly, of checking the structural behaviour with regard to a satisfactory design and proper execution of the works. In this way shortcomings arising in backfilling the space between the rings and the ground or concerning insufficient support of the tunnel face can be detected. On the basis of careful statical computations a concept is worked out for the excavation sequences both in the cross section and along the axis and for the corresponding support measures. If the measurements indicate a substantial deviation from the anticipated behaviour of the structure, then the most important corrective measures in the construction can still be applied. The above comparison of the two methods of construction restricted itself to the possibilities of influencing the tunnelling process by a proper use of measurements and should in no way be regarded as a general critique of the two methods. Which of the two methods of construction should be applied in a particular case is decided of course by safety and economic considerations. In general the real purpose of field measurements lies in the optimization of the design and execution of underground structures. In other words, the aim is to obtain adequate safety for a minimum of cost expenditure, whereby the manifold influence of the construction time is also included in the costs.