Based on available Geological Survey of Ireland (GSI) information
there are relatively few areas of peat within the study
area.
Peat soils are considered to be problematic for construction
work owing to their high organic content, high compressibility
and low shear strength. When loaded, these soils usually
exhibit large immediate and primary settlement followed
by a very pronounced long-term creep settlement. These soils
are also known to exhibit a differential settlement due
to their high variability within the same location. Peat
soils could present problems for embankment stability as
a result of the shear failure of the subsoil during construction.
Special measures for embankment construction are usually
required including piling, excavate-and-replace and preload
with vertical drains, etc.
Alluvial materials are deposited by river action or the
action of melting glaciers. The following major alluvial
tracts cross the constraints study area:
-
Along the basin of the River Barrow from Carlow town to
Goresbridge (AL-2). These soils are poorly drained and
have a slightly peaty clay loam texture. The organic content
can reach up to 20%. The depth of the alluvium is usually
greater than 1m. The depth of the alluvial sands/gravels
occurring in river valleys can typically be 9 m to 12
m.
- Along
the River Nore (AL-3).
These soils are normally consolidated (i.e. they have not
been previously compressed by glaciers) and thus are moderately
to highly compressible, though not as severe as peat soils.
Special measures for embankment construction over alluvial
materials include preloading, with or without vertical drains,
and piling.
Table 7.2 presents a summary of the properties of the soils
discussed in Sections 7.3 and 7.4.
Table
7.2 : Soil Properties within the Study Area
| Soil
Type |
Strength |
Compressibility |
Use
as Earthworks |
| Gravel |
Good |
Low
|
Good |
|
Glacial Till |
Variable |
Low-medium |
Variable
|
| Alluvium
|
Poor
|
High |
Poor |
| Peat |
Very
poor |
Very
high |
Not suitable |
