Environmental Engineering Reference
In-Depth Information
Figure 3.2.
Example of a complex slide: Peillets slide [DUT 83]
3.2. Slowly moving slopes
3.2.1.
Principal characteristics
The study of slowly moving slopes has attracted the attention of researchers
since the 1960s in particular. Authors, such as Haefeli, Ter Stepanian, Calabresi,
Tavenas, Leroueil, Yen and many others have participated in these developments,
concentrating primarily on creep laws. A synthesis of this work is found in various
publications by the author of this chapter [VUL 86, VUL 88a-c].
All modeling of behavior over time is done by rheological characterization.
Studies of soils (often clays) under laboratory conditions have made it possible to
observe a number of characteristics for specific stress/strain conditions and for time
periods that are often short (one week, for example). A soil sample subjected to a
state of constant deviatoric stress will develop a deformation of the type shown in
Figure 3.3a over time.
It is common practice to define three phases of creep: primary creep (at
decreasing speed), secondary creep (at constant speed) and tertiary creep (at
increasing speed, leading to failure). The three phases are not reached in all cases,
depending on the value of the stress level, the duration of creep test and the soil
type. Some authors have shown the existence of a creep limit expressed in terms of
stress condition, in other words similar to a yield limit (or plastic criterion), below
which the sample will only show primary creep behavior. Similarly, a criterion
analogous to that of plasticity will describe the transition to tertiary creep (see
Figure 3.3b).
