Hydrogeology and its effect on slope stability along the coastal aquifer of Nice, France

Stegmann, Sylvia; Sultan, Nabil; Kopf, Achim J; Apprioual, Ronan; Pelleau, Pascal

doi:10.1016/j.margeo.2010.12.009

Cited by 41 publications

(49 citation statements)

References 43 publications

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“…In the case of the Var delta, the peat deposits are interlayered with muddy laminites so only compaction tests on core samples could isolate the contribution of each type of deposit to the overall compaction process. This process might also be influenced by the flow of fresh water in the permeable sandy layers of the Holocene wedge (Stegmann et al, 2011) that is observed here by the presence of numerous freshwater springs on the shelf slope (Guglielmi, 1993;Stegmann et al, 2011). In any case, our results confirm the general trend that Holocene deposits control delta subsidence, with a greater contribution from the superficial layers that are often composed of a large fraction of peat and clay.…”

Section: Deltas and Sediment Compactionsupporting

confidence: 82%

“…6, adapted from the reconstruction work of Dubar and Anthony, 1995;Stegmann et al, 2011), we see that the delta is composed of a Pleistocene basement overlain by Holocene deposits. The thickness of the Holocene superficial strata is maximum offshore by the shelf break (100 m) and decreases landward over a distance of about 4 km: this distance to the shore corresponds to the transition between the Var riverbed and the delta, where the deltaic topset starts to be dominated by gravels as expected for a braided bedload channel.…”

Section: Deltas and Sediment Compactionmentioning

confidence: 89%

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Detailed quantification of delta subsidence, compaction and interaction with man-made structures: the case of the NCA airport, France

Cavalié¹,

Sladen²,

Kelner³

2015

Nat. Hazards Earth Syst. Sci.

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Abstract. River deltas are dynamic coastal systems and their evolutions are closely monitored as it often concentrates vital natural resources for the surrounding areas. Many deltas worldwide experience subsidence due to geological processes (sediment loading and compaction) or human activities (groundwater or hydrocarbon extraction, land reclamation). This causes shoreline erosion or wetland loss which represent serious issues for the population. In this study we investigate the dynamic of the Var delta (France) where reclaimed lands over sea have been built to host the Nice côte d'Azur airport (NCA). Actually, the stability of this infrastructure is a permanent concern since, in 1979, a newly built extension of the runway platform collapsed in the sea, causing important damages. The project of land extension stopped, but the present airport platform is still located on reclaimed land. Factors that can trigger such catastrophic landslide are thought to be linked to the delta activity and the artificial airport platform load. We used, therefore, Envisat InSAR data to measure accurately the ground deformation of the area that includes the Var delta and NCA airport. Combining data from ascending and descending orbits, we estimated the east-west and vertical components of the deformation and obtained very accurate displacement rate (with a 1σ error of 0.25 mm yr −1 ). We found that nearly all the deformation is vertical and impacts the whole Var delta. The Var valley subsides at a very low rate (0.5-1 mm yr −1 ) but downstream the subsidence rate increases and a clear jump is observed at the transition with the reclaimed lands (1-2 mm yr −1 ). On average, the reclaimed lands subside at 3 mm yr −1 . Since the subsidence rate increases in correlation with the sediment thickness, we interpret it as the compaction of the delta quaternary sedimentary wedge. In addition, three areas subside faster (between 5 and 10 mm yr −1 ), with one calling for more attention as it is the largest and overlooks the steep Var canyon. The progressive increase of subsidence rates toward the sea also suggests that the underwater parts of the margins could subside at rates well above 10 mm yr −1 .

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Section: Deltas and Sediment Compactionsupporting

confidence: 82%

Section: Deltas and Sediment Compactionmentioning

confidence: 89%

Detailed quantification of delta subsidence, compaction and interaction with man-made structures: the case of the NCA airport, France

Cavalié¹,

Sladen²,

Kelner³

2015

Nat. Hazards Earth Syst. Sci.

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“…In addition, X-ray scans and visual observations on 957-gc and 926-gc illustrate sub-vertical conduits (piping) with a diameter less than 10 mm, which connect two silt layers. These conduits may be related to overpressure release and fluidization (Kopf et al 2009, Stegmann et al 2011. In low-permeability, fine-grained sediments with kf lower than 1.9*10 -9 m/s ( Table 1), disruption of the sediment structure may be caused when pore pressure, as a result of fluid flow or gas accumulation, exceeds the minimum effective stresses and tensile strength of the material, known as hydro-fracturing (Andersen et al 1994).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Cone penetration testing to assess slope stability in the 1979 Nice landslide area (Ligurian Margin, SE France)

et al. 2015

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In the landslide-prone area near the Nice international airport, southeastern France, an interdisciplinary approach is applied to develop realistic lithological/geometrical profiles and geotechnical/strength sub-seafloor models. Such models are indispensable for slope stability assessments using limit equilibrium or finite element methods.Regression analyses, based on the undrained shear strength (su) of intact gassy sediments are used to generate a sub-seafloor strength model based on 37 short dynamic and eight long static piezocone penetration tests, and laboratory experiments on one Calypso piston and 10 gravity cores. Significant strength variations were detected when comparing measurements from the shelf and the shelf break, with a significant drop in su to 5.5 kPa being interpreted as a weak zone at a depth between 6.5 and 8.5 m below seafloor (mbsf). Here, a 10% reduction of the in situ total unit weight compared to the surrounding sediments is found to coincide with coarse-grained layers that turn into a weak zone and detachment plane for former and present-day gravitational, retrogressive slide events, as seen in 2D chirp profiles. The combination of high-resolution chirp profiles and comprehensive geotechnical information allows us to A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT2 compute enhanced 2D finite element slope stability analysis with undrained sediment response compared to previous 2D numerical and 3D limit equilibrium assessments.Those models suggest that significant portions (detachment planes at 20 m or even 55 mbsf) of the Quaternary delta and slope apron deposits may be mobilized. Given that factors of safety are equal or less than 1 when further considering the effect of free gas, a high risk for a landslide event of considerable size off Nice international airport is identified. . This decrease in shear strength is related to the compressibility of the gas, structural differences according to the gas concentration (i.e. ACCEPTED MANUSCRIPT Highlights An interdisciplinary approach is used comprisntaining morphological, 2D chirp seismic, sedimentological, geotechnical laboratory and in situ datasets. Dynamic piezocone penetration tests (CPTU) provide a powerful, time-and costefficient in situ technique. A large number of coring, static-and mainly dynamic-CPTU tests are used to develop an area-widea regional sub-seafloor strength model near the Nice airport (southeastern France). Detailed 2D finite element slope stability assessments are performed, according to which a.  A potentially tsunamigenic submarine landslide event with a failure depth of >up to 1050 m could may occur.

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“…The types of aquifer determine the migration of groundwater, which is one of the important indicators of lithological character (Stegmann et al 2011;Suzuki & Higashi 2012). The layer of aquifers was directly digitized from the published hydrological map of the Hubei province with a 1:100,000 scale.…”

Section: Geological Factorsmentioning

confidence: 99%

A data-driven approach for landslide susceptibility mapping: a case study of Shennongjia Forestry District, China

Chen

Han

Huang

et al. 2018

Geomatics, Natural Hazards and Risk

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The main purpose of this study was to establish a data-driven approach and assess its potential for shallow landslide susceptibility mapping of the Shennongjia Forestry District, China. For the data processing, Fisher segmenting was used for the classification of topographical factors (gradient, relief amplitude, plan curvature, and normalized difference vegetation index) and the improved Otsu method was used to determine the buffer length thresholds of the locational factors (proximity to roads, rivers and faults). The computations show that these two objective methods help to avoid the uncertainty caused by the subjective judgments and the obtained thresholds are more consistent with actual conditions. Considering the different data types, the locational and topographical factors were evaluated by fuzzy comprehensive evaluation while the geological factors were evaluated by frequency index, and then the three separate evaluations were combined using radar chart analysis. The validation result shows that the susceptibility map based on a datadriven approach has a high accuracy of prediction and this approach will be salutary for risk mitigation and land-use management in mountainous regions.

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Hydrogeology and its effect on slope stability along the coastal aquifer of Nice, France

Cited by 41 publications

References 43 publications

Detailed quantification of delta subsidence, compaction and interaction with man-made structures: the case of the NCA airport, France

Detailed quantification of delta subsidence, compaction and interaction with man-made structures: the case of the NCA airport, France

Cone penetration testing to assess slope stability in the 1979 Nice landslide area (Ligurian Margin, SE France)

A data-driven approach for landslide susceptibility mapping: a case study of Shennongjia Forestry District, China

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