Growing needs for modern transportation and utility networks have increased the demand for a more extensive and elaborate use of underground space. As a result, more underground projects have to be completed in a variety of ground conditions, including weak water bearing soils and soft rocks. Significant technological advances have rendered these projects possible, but have also given rise to new challenges as many of these projects have to be completed in difficult conditions, with very strict environmental constraints, particularly in urban areas where the potential impact of tunneling on existing structures is a major concern. This report addresses the main aspects of tunneling and underground works performed in soils and soft rocks. A summary is presented of the main features related to construction techniques, ground investigations, design methods, and instrumentation and monitoring practices, as well as of some of the more recent advances in these fields.
Significant progress has been made in the area of soft ground tunneling over the past thirty years, partly because of advances in computer technologies. The scope of increasing difficult project conditions to be addressed requires that the best use be made of these technologies, as well as of lessons gained from past experience and current observational records.

This lecture deals with tunnelling under squeezing rock conditions. Following an outline of the main factors influencing squeezing, the definition of this type of behaviour, as proposed by ISRM (International Society for Rock Mechanics) in 1995, is given. An overview of the methods used for identification and quantification of squeezing is presented, along with the empirical and semi-empirical approaches presently available in order to anticipate the potential of squeezing tunnel problems. A brief historical retrospective is reported on the excavation and support methods used in Italy in order to cope with squeezing conditions at the end of 1800, when the first railway tunnels were excavated.
Based on the experiences made and lessons learned in recent years through important tunnelling works in Europe, an attempt is made to trace the state of the art in modern construction methods, when dealing with squeezing conditions by either conventional or mechanised excavation. The closed-form solutions available for the analysis of the rock mass response during tunnel excavation are described in terms of the ground characteristic line and with reference to some elasto-plastic or elasto-visco-plastic stress-strain models for the rock mass. Also described are the equations for the support characteristic lines.
Then, the use of numerical methods for the simulation of different models of behaviour and for design analysis of complex excavation and support systems is considered, also including three-dimensional conditions near the advancing tunnel face.
Finally, a brief discussion on monitoring methods is given, in conjunction with a short description of a case study.

The complex variable method for solving two dimensional linearly elastic problems is used to obtain several fundamental analytical solutions of tunneling problems.
The method is used to derive the general mathematical representation of problems involving resultant forces on holes in a half-plane. Such problems are encountered in geomechanics during the excavation of tunnels. When tunnels are excavated the removal of the weighted material inside the tunnel causes the ground under the tunnel to rebound. This in turn causes a resultant force, referred to here as the buoyancy force, to act on the tunnel until the stresses return to a state of equilibrium. The mathematical representation derived in this thesis shows that the displacements will usually be unbounded at infinity in solutions of two-dimensional problems involving resultant forces acting on holes in a half-plane.

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