**5. Field tests and measurements**

Geophysical surveys are primary sources for both qualitative and quantitative data regarding ground conditions, and they form an essential part of many on-site investigations. There are several reasons for this, perhaps the most important of which is that it provides, for design purposes, parameters that represent a more realistic assessment of geotechnical ground conditions than is usually the case with laboratory tests. The samples used for laboratory tests, due to their small size, may not be sufficiently representative of the ground from which they are taken. In particular, it may not have widespread discontinuities, found in rocks or soil masses, which greatly affect the engineering properties of the materials in question. Moreover, the sampling inevitably involves some disturbances in stress conditions and water content of soil and rocks so that the parameters obtained in the laboratory are not fully representative of the conditions at the site [20].
