7.
Geology and Hydrogeology
7.3
Glacial Soils
7.3.1 Gravels
Thick gravel deposits occur within the constraints study area,
mainly along the major river crossings. The main gravel areas
identified are as follows:
-
Gravel deposits along the River Nore south of Kilkenny City.
The major gravel aquifer within this area is designated
G-3 on Figure 5A
- Gravel
deposits along the River Barrow.
These
materials do not present problems for road construction, provided
the road alignment is kept above the water table. Generally,
gravels provide good formation for pavement construction and
are generally suitable for reuse. Water bearing sand and silt
layers where encountered can be problematic.
7.3.2 Clayey Till Glacial tills dominate much of the constraints
study area. These glacial deposits are mainly deposits of
the 'Midlandian' ice sheet with the coarse fraction dominated
by cobbles and boulders of limestone with lesser proportions
of sandstone, slates and shales.
The depth of till occurring within the constraints study area
is not known, and is likely to vary. Depths of 0m to 5 m were
reported in the vicinity of Thomastown . Elsewhere the depth
of the till is likely to vary considerably.
The
geotechnical properties of Irish glacial tills are well-documented
These soils are generally well graded, variable with gravel
lenses, with quite an absence of clay minerals. The clay fraction
(rock flour) typically amounts to about 15% and the fines
fraction (clay and silt) is about 30 to 40%. The glacial tills
are generally over-consolidated, and therefore are of a low
compressibility. These soils are usually firm to stiff, however
due to their low plasticity they are very susceptible to softening
and deterioration in wet weather, especially if heavily trafficked.
When the clayey tills are kept dry, they present relatively
little difficulty to road construction.
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