Engineering geology aspects for design and classification - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 26

tion, grain shape and grain angularity. They are resistant to weathering effects. According
to DIN 1054, non-cohesive soils include sands, gravels, cobbles and their mixtures when
the content by weight of the grain fraction smaller than 0.06 mm is less than 15 %, and also
mixed-grained soils with a content by weight of grain sizes < 0.06 mm of 5 to 15 %, unless
the fine-grained content determines the plastic behaviour of the soil.
Cohesive soils. In cohesive soils, the individual particles stick to each other through elec-
trostatic surface forces and form a cohesive mass that can be formed. Their properties,
above all the strength characteristics, are decisively influenced by the water content, grain
size and clay mineral content. Cohesive soils are susceptible to weathering. According to
DIN 1054, this soil category includes clays, clayey silts and silts and their mixtures and
non-cohesive soil with a content by weight of the grain fraction smaller than 0.06 mm
of more than 40 % and also mixed grain soils with 15 to 40 % if the fine-grained content
determines the plastic behaviour.
Organic (organogenous) soils. Organic soils according to DIN 1054 include peat or or-
ganic sludge and anorganic soils with organic contents by weight of animal or plant origin
of more than 3 or 5 % respectively. Depending on the degree of composition, they have a
fibrous, matted or earthy structure and high water absorption capacity.
Soils are also classified in DIN 18 300 “German construction contract procedures (VOB)
- Part C: General technical specifications in construction contracts (ATV) - Earthworks”
[58] with regard to extraction, use and processing into the following classes:
Class 1: Topsoil. Topsoil is the uppermost layer of undisturbed ground, which is particu-
larly rich in micro-organisms and contains humus or clay.
Class 2: Flowing soil types. Soil types, which are of liquid to pasty consistency due to
their water content and do not release the water easily such as mud and silt.
Class 3: Easily excavated soil types. Non-cohesive to slightly cohesive sands and gravels
and their mixtures up to 60 mm grain size, in which there is no or only very slight cohe-
sion due to loam or clay soil types (< 15 % of grain size < 0.06 mm) and with max. 30 %
cobbles of over 63 mm grain size up to 0.01m³ volume.
Class 4: Moderately easily excavated soil types. Mixtures of sand, gravel, silts and clay
with more than 15 % grain fraction smaller than 0.06 mm. Further cohesive soil types of
low to medium plasticity, which are semi-solid depending to water content and contain
max. 30 % cobbles of over 63 mm grain size up to 0.01m³ volume.
Class 5: Difficult to excavate soil types. Soil types in classes 3 and 4, but with more than
30 % cobbles (over 63 mm grain size) up to 0.01m³ volume. Also non-cohesive and co-
hesive soil types with max. 30 % cobbles (over 63 mm grain size) from 0.01m³ to max.
0.1m³ volume and pronounced plastic clays, which are soft to semi-hard depending on
water content.
Class 6: Easily excavated rock and similar soil types. Rock types, which have internal
mineral cohesion, but are heavily jointed, brittle, unstable, foliated, soft or weathered and
comparably solid or cemented cohesive or non-cohesive soil types, for example due to
drying out, freezing, chemical compounds.