SOIL INVESTIGATION - Introduction to Soft Soil Geotechnique: Content, Context and Application - page 36

The main purpose is the determination of the subsoil stratification, i.e. the
layering, and to measure the physical and mechanical constitution of stiff and weak
soil layers. In principle, only a limited number of local soil properties can be
measured directly, and most of the required properties must be determined
indirectly, by empirical correlation and additional laboratory testing on carefully
obtained samples. Since soil is heterogeneous by nature and the scale of
heterogeneity (correlation length) differs largely for various properties, a site
investigation provides only limited information and engineering experience plays a
major role in the interpretation of the data obtained.
Figure 3.1a CPT test and schematised soil profile from a boring
In addition to the mechanical and electronic cones, a variety of other CPT-
deployed tools have been developed over the years to provide additional
information. One common tool advanced during CPT testing is a geophone set to
gather seismic shear wave and compression wave velocities.
The Delft continuous sampler is used for obtaining high quality samples of soft
cohesive soils. The system is pushed into the ground using standard CPT
equipment, while the sample being fed automatically into an impervious nylon
sleeve (Fig 3.1b). Next, the sample within the sleeve is inserted into a thin-walled
plastic inner tube filled with a supporting fluid of bentonite. The upper end of the
nylon sleeve is fixed to the top cap of the sample, which is connected through a
tension cable to a fixed point at ground surface. In this manner up to 10m
continuous sampling can be achieved. High horizontal stresses may cause sleeve
breakage.
Ground radar is a non-destructive site investigation technique that uses
electromagnetic waves to visualize the layering of the shallow subsurface. An
emitting antenna radiates an electromagnetic wave front, which is transmitted in
the subsoil. It reflects at inhomogeneities, such as a sand-clay interface, recorded in