Geotechnical characteristics and slope stability on the Ebro margin, western Mediterranean

Baraza, J.; Lee, Homa J.; Kayen, Robert E.; Hampton, Monty A.

doi:10.1016/0025-3227(90)90125-4

Cited by 33 publications

(14 citation statements)

References 14 publications

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“…Therefore, other mechanisms should account for the overconsolidation of the uppermost section of PRGL1. One acceptable hypothesis is the ageing effects related to cementation, bioturbation and physico-chemical changes that have been described in marine environments (Baraza et al 1990;Mitchell 1976;Poulos 1998;Silva and Bryant 2000;Sultan et al 2000).…”

Section: Discussionmentioning

confidence: 99%

Overpressure within upper continental slope sediments from CPTU data, Gulf of Lion, NW Mediterranean Sea

Lafuerza

Sultan

Canals

et al. 2008

Int J Earth Sci (Geol Rundsch)

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Data from in situ piezocone tests (CPTU) and laboratory analyses are utilized for the interpretation of the stress history of Quaternary sedimentary sequences in the upper continental slope of the Gulf of Lion, northwestern Mediterranean Sea. A CPTU based preconsolidation pressure profile referenced to the current effective stress indicates that the deposit is underconsolidated from 12 meters below the seafloor (mbsf) down to at least 150 mbsf. Excess pore pressure below 12 mbsf is further supported by results from oedometer and dissipation tests. Subseafloor pockmarks and indications of free gas in seismic reflection profiles reveal four main overpressure sources (SI-SIV) with overpressure ratios [0.3 at subseafloor depths coinciding with levels where the dominantly silty-clayey sediment contains increased proportions of sand. We relate the excess pore pressure related to free gas due to gas exsolution processes and sea level variations driven by Pleistocene sea level changes. Keywords Stress history Á Preconsolidation pressure Á Overpressure Á Continental slope Á Gulf of LionList of symbols Du excess pore pressure or overpressure, kPa Du CPTU overpressure determined by CPTU, kPa Du LOGS overpressure determined by downhole-logs, kPa Du e equilibrium pore pressure, Du e , kPa Du s excess pore pressure generated by sediment loading, kPa r vo total vertical stress, kPa r 0 vo vertical effective stress, kPa r 0 p preconsolidation pressure, kPa r 0 pa preconsolidation pressures r 0 p obtained following Casagrande's method, kPa r 0 pb preconsolidation pressures r 0 p obtained following Onitsuka's method, kPa k compression index k * adimensional ratio of the overpressure magnitude q w unit weight of the water, g cm -3 / porosity, % D h hydraulic diffusivity, m 2 s -1 e o reference void ratio f s sleeve friction, kPa g gravity, m s -2 N rt cone factor = (q t -r vo )/r 0 p

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Section: Discussionmentioning

confidence: 99%

Overpressure within upper continental slope sediments from CPTU data, Gulf of Lion, NW Mediterranean Sea

Lafuerza

Sultan

Canals

et al. 2008

Int J Earth Sci (Geol Rundsch)

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“…Excess pore pressure (EPP) generation from rapid sedimentation is another factor predisposing the site to failure Haflidason et al 2004;Kvalstad et al 2005a, b) and has been proposed for various slides area off the Norwegian margin (Nyk slide, Lindberg et al 2004; Traenadjupet slide, Laberg et al 2003). Many other continental margins characterized by high sedimentation rates show a record of mass wasting as well, i.e., the Ebro margin (Baraza et al 1990), the Mississipi Delta, Gulf of Mexico (Adams and Roberts 1993), and the Gulf of Alaska (von Huene et al 2001). Hjelstuen et al (2004) have recently estimated a high sedimentation rate (several 10 m/kyr) in the Helland Hansen area at the northern part of the Storegga slide headwall.…”

Section: Introductionmentioning

confidence: 97%

The role of sedimentation rate and permeability in the slope stability of the formerly glaciated Norwegian continental margin: the Storegga slide model

2007

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Despite the gently dipping slopes (ca 1°), large-scale submarine slope failures have occurred on the mid-Norwegian continental margin (Storegga, Sklinnadjupet, Traenadjupet), suggesting the presence of special conditions predisposing to failure in this formerly glaciated margin. With a volume estimated between 2,400 and 3,200 km 3 and an affected area of approximately 95,000 km 2 , the Storegga slide represents one of the largest and best-studied submarine slides of Holocene age known worldwide. Finite element modeling of slope failure indicates that a large (6.5< Ms<7.0) seismic triggering mechanism would not be sufficient to cause failure at more than 110 m below the seabed as observed for the slip planes at Storegga (northern sidewall). This implies that other factors (e.g., liquefaction, strain softening, gas charging, rapid burial) are needed to explain the occurrence of the Storegga slide with a deep surface of failure. In this paper, we discuss the importance of the compaction effect of rapidly accumulated sediments in the slide area. During compaction, sediment grains reorganize themselves, thereby, expelling pore water. Consequently, depending on sedimentation rate and permeability, excess pore pressures might result beneath less permeable sediments. Our modeling and cross-checking illustrate how excess pore pressure generation due to high sedimentation rate could explain the development of layers of weakness, and thus, how such a large slide might have been initiated in deep sediments. Using the highest sedimentation rate estimated in the area (36 and 27 m/kyr between 16.2 and 15 kyr BP), 1D modeling shows excess pore pressure values of around 200 kPa at a depth of 100 m below the seafloor 15 kyr BP and 60 kPa at a depth of 100 m at the time of the slide (8 kyr BP). Excess pore pressure apparently drastically reduced the resistance of the sediment (incomplete consolidation). In addition, 2D modeling shows that permeability anisotropies can significantly affect the lateral extent of excess pore pressure dissipation, affecting, that way, normally consolidated sediments far from the excess pore pressure initiation area.Landslides 4 • (2007) 309

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“…On the European margins, the method was applied to the analysis of the slope stability of the Ebro passive margin in the Western Mediterranean (Baraza et al 1990), on the Atlantic Spanish coasts of the Gulf of Cadiz (Lee and Baraza 1999) and in the North Aegean Sea (Lykousis et al 2002).…”

Section: Methodsmentioning

confidence: 99%

Slope failures and stability analysis of shallow water prodeltas in the active margins of Western Greece, northeastern Mediterranean Sea

Lykousis

Roussakis

Sakellariou

2008

Int J Earth Sci (Geol Rundsch)

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Sediment instabilities are common on the prodeltas of the seismically active continental margins of Western Greece. Sediment failures on the low-angle (0.5°-2°) prodelta slopes manifest themselves as successions of peripheral rotational block slumps restricted to the foresets of the late highstand systems tract (HST). The individual slump blocks are about 80-150 m long and are bounded by growth faults acting as curved slip planes that extend to a mean depth of 10-15 m below seafloor. Shear planes develop in the lower part of muddy and/or gas charged HST foresets. Deeper basal transparent muddy layers of the early HST bottomset, together with the late Pleistocene transgressive systems tract sequences (TST), are mostly unaffected. On the steeper (2°-6°) fan delta slopes of the western Gulf of Corinth debris flows and avalanches with a significant retrogressive component dominate slope destabilisation. Sediment cores taken from landslide scarps and slide planes penetrated gas bubble releasing sediments thereby indicating that failure planes are in the late HST foresets/upper part of the early HST bottomsets gas charged zone. The foresets of the HST prodelta deposits display high water content (30-80%), low bulk density (1.4-1.9 g cm -3 ) and relatively low values of undrained shear strength (3-20 kPa). The water content of the HST distal muddy bottomsets is relatively higher (50-110%) and bulk density relatively lower (1.3-1.7 g cm -3 ) with low values of shear strength (2-10 kPa). The shear strength of the gas releasing sediment layer displays lower values (2-9 kPa) relative to the overlying, post failure, muddy sediments of the late 100-300 years. Slope stability was calculated using the normalised soil parameter (NSP) method under undrained conditions for normally consolidated prodelta sediments. This analysis indicates that instabilities could be induced by critical earthquake ground accelerations of 26.6-29.6% g for the HST foresets and 12.4-14.1% g for the basal transparent layer belonging to the early HST bottomsets. Consequently the early HST bottomsets has to be considered a potentially unstable layer since the regional peak ground accelerations (PGAs) for the next 50 years are expected to range from 19 to 30% g. Moreover, our results show that new glide planes in the prodeltaic sediment bodies of the seismically active continental margins of Western Greece will likely develop from the gas charged sediments of the lower part of the HST foresets to the upper part of early HST bottomsets.

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Geotechnical characteristics and slope stability on the Ebro margin, western Mediterranean

Cited by 33 publications

References 14 publications

Overpressure within upper continental slope sediments from CPTU data, Gulf of Lion, NW Mediterranean Sea

Overpressure within upper continental slope sediments from CPTU data, Gulf of Lion, NW Mediterranean Sea

The role of sedimentation rate and permeability in the slope stability of the formerly glaciated Norwegian continental margin: the Storegga slide model

Slope failures and stability analysis of shallow water prodeltas in the active margins of Western Greece, northeastern Mediterranean Sea

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