ABSTRACT;

In order to get a better understanding of the. interrelated factors. leading to the successes and failures with the NATM the author has carried out a basic study from rheological principles. The geological condition, creep and dilatancy and longterm strength properties of rocks are considered important factors. Based on his constitutive equations the author presents a F.E. Analysis; especially the regions of dilatancy creep and the influence of tectonic stress are studied. Various suggestions for the strengthening or tunnels unstable with the time are recommended.

RÉSUMÉ:

Afin d'obtenir une comprehension plus profonde des, facteurs de corelation qui avaint menes aux succes et fiascos de l'ATMM l'auteur a fait une etude fondee sur les principes rheologiques. La condition geologique, le fluage et dilatancy et puissance a long duration de roches sont consideres des facteurs importants. Au fond de ses equations constitutives, l'auteur presente un Analyse d'Elements Finis et especiallement les regions du fluage dilatants et l'influence des tractions tectonics, sont etudies. Plusieurs suggestions pour la fortification des tunnels instabiles avec le temps sont presentees.

ZUSAMMENFASSUNG:

Um ein besser Begriff ueber die zusammenhanqende Faktoren welche nach Erfolge or Katasprophen mit NATM, geleitet haben hat der Verfasser ein grundlegendes studium gemacht auf Grund von rheolo- gische Grundsatzen. Die geologische Bedingung, das Kriechen, die Dilatanz und langzeitliche Festigkeit werden als wichtige Faktoren studiert. Mit Hilfe seiner Material gleichungen hat er eine F.E. Analyse ausgefuehrt. Insbesonders die Machtigkeit der Kriech Dilatant Gebiete und der Einflusz der tectonische Spannungensind analysiert. Verschiedene Vorschlage fuer die Verstarkung von Tunnels instabiel mit dem Zeit sind empholen.

INTRODUCTION

The New Austrian Tunneling Method has been success-fully applied in many tunnels allover the world, In strong tectonic areas, at depths of 1000m under the influence of blast waves from mining operations, as well at low and medium overburdens in weak soils as well as in strong and hard rocks. The. Method has been applied with success to squeezing tunnels in Japan (Otsuka et al 1981). In our country the NATM has also found application in the Jin Jiayan tunnel (Chengdu Railways Bureau 1984), the Nan Ling tunnel (Nanling tunnel experimental station, 1984) at Shallow depth, the instablecgal1eries of the Qing Juan Mine (Tan 1981) and many others.

Despite its many successes however the physics underlying the NATM still needs further clarification. The shotcrete steel web bolts and anchors technique is frequently considered as an omnipotent remedy in complex tunneling. In some cases successes have been achieved, without a pre-analysis. based on basic principles. However in many other cases there was no clear definite result and some failures-technical as well as economical-clearly indicate that the basic philosophy of the method was not fully grasped. Therefore Muller (1978) correctly stressed that the NATM is based on the commentment to certain principles, which have been substantiased by successful use in practice. Thus the engineer must utilize the load bearing capacity of the rock mass to an extent that guarantees an optimum on safety and economy.

In this paper the author will emphasise the importance of geodynamics and rheology in tunneling as it is not yet adequately considered in the NATM.

BASIC FACTORS IN TUNNELING

The author suggests that the following basic factors must be considered:

  1. tectonics, tectonic stress history;

  2. geology of the region (basic state of the rock mass, usually jointed, fissured and cut by weak intercalations);

  3. rheological properties of the rock mass; many complicated fissuring, bulging and failure phenomena occur not earlier than after weeks, months, years and decades;

  4. proper choice of direction of tunnel axis and most feasible tunneling crossection; in order to utilise the load bearing capacity of the surrounding rock mass efficiently, a finite element analysis based on appropriate geological descriptions and constitutive equations must be carried out;

  5. on the basis of the above Ii points to design the strengthening method;

  6. back-analysis+field convergence measurements; improved measures.

GEODYNAMICAL CONSIDERATIONS

Usually a rock-engineering site may cover some square kilometers, but viewed on the scale of the lithosphere it is only a point on the skin of the upper crust. During the tectonic history of hundreds of millions of years the crust was strained, in different manners. It is known that the earth crust is strained continuously at a rate of 10−14 10−16 /sec. In definite parts the straining may be larger than 10−14 /sec and then earthquakes are frequently generated. The present imprints of all these tectonic sequences can be found in:

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