RECENT DEVELOPMENTS IN SITE INVESTIGATION AND TESTING FOR HARD ROCK TBM PROJECTS
For several recent TBM tunnel projects, unexpected ground conditions have been encountered, causing extra cost, considerable delay, and in some cases major claims. Undoubtedly, insufficient and/or irrelevant site investigation and testing are among the main causes of such incidents. The purpose of this paper is to review the main investigations and tests relevant for hard rock TBM projects, with particular emphasis on the considerable development that has taken place over the last few years. Also, guidelines for defining optimum scope and extent of site investigations and testing are discussed, as well as the importance of adjusting the investigations and tests according to complexity of the ground conditions and project type.
CROSSHOLE SEISMICS INCLUDING GEOTOMOGRAPHY FOR INVESTIGATION OF FOUNDATIONS
Engineering geophysics represents a valuable supplement to other engineering geological investigations. In particular, the cross hole seismic method can rightly be claimed to be unique in providing detailed information of large rock volumes. Assessment of rock mass quality is of current interest in planning and completing rock caverns as well as for foundation purposes. Rock and soil site investigation require site geometries where cross sections can be formed between boreholes and/or exposed surfaces as tunnels or ground surface. To take full benefit of this in-situ site evaluation technique, computerised geophysical tomography should be applied. Interborehole scanning by a defined acoustic source/receiver configuration gives rise to a point by point reconstruction of the seismic velocity field or of the acoustic sound alternation properties in the actual section. Norwegian Geotechnical Institute has experienced the applicability of the cross hole method in dam site evaluation, pre-investigation of ground properties for tunnel projects and for general rock mass descriptions. Obviously, the most useful results are achieved where the client has a well defined problem to solve and where the cross seismic results can be verified, or can be given supplementary interpretations. This paper gives a brief description of the instrumentation. Further, two dam site foundation investigation projects and one main underground highway tunnel project, all taking benefit of cross hole seismic measurements, are presented.
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.