Abstract
In slope stability research a ground water level increase is often the
critical factor for failure. High ground water levels (or more properly
stated: high pore water pressures) reduce the internal strength of the
slope. It is recognised for quite some time that fast infiltration of
precipitation towards the (perched) ground water table can induce high pore
pressures and thus instability within formerly stable slopes. However,
deeper located landslides are affected on the long term by a slow but
distinct ground water table rise, which may take place a significant time
after the occurrence of rainfall. From the above it is clear that
hydrological insight in natural slopes susceptible to landsliding, is more
than appropriate for the long-term risk assessment in case of land use or
climate change.
The objective of this thesis is to analyse and quantify the hydrological
processes that play a role in landslides within clayey slopes. The following
questions are addressed:
- What can hydro- and geochemistry add to our knowledge of a
hydrological system in a clayey slope?
- What processes dominate the ground water recharge in unstable clayey
slopes and how can the ground water recharge be quantified?
- What is the consequence of a land use or climatic change with
respect to unstable clayey slopes?
The study of the potential use of hydro- and geochemistry in refining the
hydrological knowledge of a site is described in the second part (chapter
3). Analyses have been made to cation exchange capacity and exchangeable
cation compostion with NH4Ac and NaCl method. It is concluded that
geochemistry is a potentially valuable technique for e.g. landslide
reserarch, but is recognised that still a lot of work has to be done before
this technique can be applied in engineering practice.
The hydrological analyses of the Beline study area at Salins-les-Bains shows
the importance of the role of the unsaturated zone in deep-seated
landslides. A methodology is presented to model state-dependent ground water
recharge. This is basically a precipitation time series that is rescaled as
a function of the state of the unsaturated zone. The latter can be
calculated on basis of the results of an unsaturated zone model, soil
moisture content or even be approximated using a sinusoidal function. The
results of the Beline case study showed that clear improvement of the
modelling of ground water level fluctuations can be obtained with this focus
on the input series.
It was made plausible that the Beline slope suffers from creep displacement
process. The changing ground water conditions as a result of changes in
climate or land use have two important consequences for the creep
displacement at the Beline slope. Acceleration of the displacement will
occur because of an increased ground water level. Probably more significant
is the impact of prolonged periods of high ground water level. This
prolonged period of movement is for slopes, which encounter creep features,
probably the most important factor for catastrophic failure. In that respect
a long-term change in vegetation pattern has much more influence on a clayey
slope system than a short-term change in climate input.
critical factor for failure. High ground water levels (or more properly
stated: high pore water pressures) reduce the internal strength of the
slope. It is recognised for quite some time that fast infiltration of
precipitation towards the (perched) ground water table can induce high pore
pressures and thus instability within formerly stable slopes. However,
deeper located landslides are affected on the long term by a slow but
distinct ground water table rise, which may take place a significant time
after the occurrence of rainfall. From the above it is clear that
hydrological insight in natural slopes susceptible to landsliding, is more
than appropriate for the long-term risk assessment in case of land use or
climate change.
The objective of this thesis is to analyse and quantify the hydrological
processes that play a role in landslides within clayey slopes. The following
questions are addressed:
- What can hydro- and geochemistry add to our knowledge of a
hydrological system in a clayey slope?
- What processes dominate the ground water recharge in unstable clayey
slopes and how can the ground water recharge be quantified?
- What is the consequence of a land use or climatic change with
respect to unstable clayey slopes?
The study of the potential use of hydro- and geochemistry in refining the
hydrological knowledge of a site is described in the second part (chapter
3). Analyses have been made to cation exchange capacity and exchangeable
cation compostion with NH4Ac and NaCl method. It is concluded that
geochemistry is a potentially valuable technique for e.g. landslide
reserarch, but is recognised that still a lot of work has to be done before
this technique can be applied in engineering practice.
The hydrological analyses of the Beline study area at Salins-les-Bains shows
the importance of the role of the unsaturated zone in deep-seated
landslides. A methodology is presented to model state-dependent ground water
recharge. This is basically a precipitation time series that is rescaled as
a function of the state of the unsaturated zone. The latter can be
calculated on basis of the results of an unsaturated zone model, soil
moisture content or even be approximated using a sinusoidal function. The
results of the Beline case study showed that clear improvement of the
modelling of ground water level fluctuations can be obtained with this focus
on the input series.
It was made plausible that the Beline slope suffers from creep displacement
process. The changing ground water conditions as a result of changes in
climate or land use have two important consequences for the creep
displacement at the Beline slope. Acceleration of the displacement will
occur because of an increased ground water level. Probably more significant
is the impact of prolonged periods of high ground water level. This
prolonged period of movement is for slopes, which encounter creep features,
probably the most important factor for catastrophic failure. In that respect
a long-term change in vegetation pattern has much more influence on a clayey
slope system than a short-term change in climate input.
Original language | English |
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Qualification | Doctor of Philosophy |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 1 Oct 2001 |
Place of Publication | Utrecht |
Publisher | |
Publication status | Published - 1 Oct 2001 |
Keywords
- landslides
- unsaturated soil
- groundwater recharge
- hydrology
- mass movement
- slope stability
- geochemical heterogeneity
- France