Site Investigation - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 353

13 Site Investigation

13.1 Introduction

The aim of site investigations is to characterize the structure of homogeneous rock mass
units and to elaborate corresponding structural models as described in Section 2.7.2. Be-
cause of the particular importance of discontinuities for the behavior of rock masses the
parameters describing the discontinuities such as orientation, spacing, persistence, rough-
ness, aperture and filling, should be quantified whenever possible.

In this chapter, methods to map rock exposures such as natural outcrops, test pits, drill
cores, boreholes, exploration adits and shafts and the evaluation of the results obtained
from these methods are dealt with.
With regard to a detailed description of some of these methods the reader is referred
to the corresponding suggested methods by the ISRM, and these are compiled in the
so-called “blue book” (ISRM 2007).

13.2 Evaluation of Documents

A fundamental principle in geotechnical engineering is to gather the required information
stepwise, starting from first investigations and proceeding to more detailed investigations in
the design phase as well as during and even after construction (DGGT 1995, ERTC9 1997).
In the initial phase of a project the available documents should be evaluated. Geologic
maps (US) or geological maps (UK), respectively, provide an introduction to the geo-
logical structure of the project area. Geologic maps are usually superimposed over topo-
graphic maps and geological strata obtained from geological mapping and observations
at surface near exposures are represented by colors or signatures.
Geologic maps can be distinguished into general maps at scales of 1:100,000 to 1:1,000,000
and special maps at scales ranging from 1:10,000 to 1:75,000. As an example, the German
special map on a scale of 1:25,000 is subdivided into sheets covering almost the whole
country.
In special geologic maps, more detailed information such as strike and dip of geological
units and the location of exploration drillings are entered. They are supplemented by ex-
planatory booklets that provide information, such as about morphology, formation his-
tory and tectonics, including a detailed description of basement rocks, the overlying rock,
stratigraphic sequence and structural conditions. In addition, they may contain geological
profiles and thematic maps such as structural maps, fracture trace maps, tectonic maps, hy-