Tunnels excavation - Construction methods and geotechnics

Tunnelling is one of those construction techniques where the interactions between the various aspects of the Civil Engineering trades are particularly numerous. In addition to a sound knowledge of construction materials and their behavior, of the equipment available or to be "invented", of safety imperatives, both for site personnel and with regard to the environment, of regulations, etc., there is an essential player: the field!

In fact, it's "the terrain" that will guide the project, from the design stage, by adapting alignments and profiles as far as possible to the search for "favorable" geology, right through to the construction site, by adapting construction methods to the actual behavior of the terrain.

The purpose of this article is therefore to present the various tunnel construction methods in relation to geological, hydrogeological and geotechnical conditions (hereinafter referred to as "geological conditions").

The first step, of course, is to describe these geological conditions as accurately as possible, and this is the subject of Chapter 1, which presents the main geological factors that can influence the choice of excavation methods, the specific or at least essential reconnaissance methods for tunnel projects, and finally the usual classifications of soils and rocks used in underground work.

Chapters 2 to 3 will then be devoted to descriptions of the construction techniques themselves, from so-called "traditional" methods to mechanized methods using tunnel boring machines, as well as the ground treatment techniques that often accompany the previous ones in particularly difficult projects. In addition to technology, these descriptions will seek to integrate the geological dimension by explaining how or why such and such methods have been developed in response to specific geological problems.

Chapter 6 then looks in more detail at the choice of construction techniques according to the geological conditions anticipated in the design phase, or actually encountered in the construction phase. Finally, Chapter 7 will present some information on the main categories of calculation and dimensioning methods, and more generally modeling methods, commonly used in tunnel studies.