Environmental Engineering Reference
In-Depth Information
Problems resulting from loess soils naturally depend on the collapse magnitude.
According to a statistical study by Clemence and Finbarr [CLE 81], damage to
structure starts to be severe when the collapse is higher than 5% (see Table 6.4).
Collapse
Severity of problem
0-1%
no problem
1-5%
moderate trouble
5-10%
trouble
10-20%
severe trouble
>20%
very severe trouble
Table 6.4. Problems with respect to collapse
To build structures on loess, good previous knowledge of sensitive zones is
necessary and various precautions have to be adopted during conception and
construction. Possible collapsible zones should be identified by a geological survey
completed with careful examination of the relevant geotechnical parameters. In this
regard, a high porosity ( n >40%) together with a low plasticity ( I p <5) indicates
significant susceptibility to collapse.
In the case of the loess in Northern France, the layers of collapsible calcareous
loess are covered by a layer of more clayey, plastic and non-calcareous loam that
acts as a protective cover due to higher permeability. When a construction strips this
topsoil (as, for instance, is the case with railways or highways) and exposes the
collapsible layer, it is necessary to take adequate precautions to protect the layer
from any water infiltration during the construction and service life of the structure.
These measures are well-known in areas in which people are familiar with
collapsible soils (see for instance [ABE 79, HOU 95]).
Among the possible solutions are the placement of impervious geosynthetics
above the susceptible layer and paying close attention to specific ways to remove
run-off water. As mentioned by [CLE 81], pre-treatment techniques aimed at either
stabilizing or collapsing the soil deposit can be used prior to construction. These
methods, described in Table 6.5, depend on the depth of the collapsible layer and
support requirements of the facility.
Search WWH ::




Custom Search