Engineering geology aspects for design and classification - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 27

Also non-cohesive and cohesive soil types with more than 30 % cobbles of over 0.01 m³
to max. 0.1 m³ volume.
Class 7: Difficult to excavate rock. Rock types, which have internal, minerally bonded
coherence and high joint strength and which are only slightly jointed or weathered, also
densely consolidated, unlettered slate, conglomerate beds, slag heaps of ironworks or sim-
ilar. Also cobbles with a volume of over 0.1 m³.
DIN 4022, Part 1 - “Subsoil and groundwater; Naming and description of soil types and
rock” [55] is valid for the uniform description of soil types. A soil type is assigned to a soil
group according to DIN 18196, “Earthworks and foundations - Soil classification for civil
engineering purposes” [57]. This latter standard applies to earthworks and has the aim
of combining soil types (loose ground) into groups with approximately similar material
composition and similar soil physical properties.
Soil mechanics parameters. In order to be able to describe the condition of a soil layer
or soil sample, the following parameters have to be determined in addition to the grading
distribution and plasticity:
ρ Density of the soil (mass of a damp sample related to the total volume of the sample)
or weight density γ of the soil, if it has to be regarded as a load or loading for construc-
tion purposes.
ρ s Grain density (density of the solid grain material).
n Pore volume (Volume of the pores between the grains of the solid mass related to the
total volume of a sample).
w Water content (ratio of the mass of water in the soil m W to the mass of a dry sample).
w L Liquid limit.
k f Permeability coefficient.
I p Plasticity index.
In special cases, the air and oil permeability may have to be determined.
If the effective stress in the soil mass is changed by external loading, the shape changes
and the state of the soil changes. Since the soil can only resist slight tension forces, only
the compression and shear loading in the subsoil are normally of significance. The com-
paction (squeezing) caused by the application of compression loading is characterised by
the stiffness modulus E s . Shear loading exerts a relative displacement between the indi-
vidual soil particles, the magnitude of which depends on the shear strength of the soil. The
shear strength of a soil is a combination of friction angle φ and cohesion c .
For preliminary design, M. Kany [102] recommends the values given in Table 2-3.