Retrogressive Landslide Research Articles

Discussion of “Use of terrestrial laser scanning for the characterization of retrogressive landslides in sensitive clay and rotational landslides in river banks”Appears in the Canadian Geotechnical Journal: 46(12): 1379–1390.

Discussion of “Use of terrestrial laser scanning for the characterization of retrogressive landslides in sensitive clay and rotational landslides in river banks”Appears in the Canadian Geotechnical Journal: <b>46</b>(12): 1379–1390.

Reply to the discussion by Olsen and Stuedlein on “Use of terrestrial laser scanning for the characterization of retrogressive landslides in sensitive clay and rotational landslides in river banks”Appears in Canadian Geotechnical Journal, 47(10): 1164–1168.

In their discussion about aerial laser scanning (ALS) and terrestrial laser scanning (TLS), Olsen and Stuedlein present some issues than we did not address in our paper (Jaboyedoff et al. 2009a). Our study deals with compact landslide bodies and we had to overcome many related problems, such as shadowing, vegetation, site accessibility, and safety issues. In contrast, Olsen and Stuedlein deal with linear, clean features (coastal cliffs), which enable a completely different way of working. Nonetheless, their remarks are relevant and they were not addressed in our paper because it was beyond the scope of our study. Studies on landslide volumes and mechanisms do not in general need a high accuracy, while it is crucial for landslide movement monitoring. In their discussion, Olsen and Stuedlein give some examples of TLS applications in landslide studies in addition to those highlighted in our article. Most of them relate to coastal erosion and rockfalls in cliffs, and only a few relate to landslides. For the sake of completeness of the literature overview, TLS has also been widely used for

Analysis of a retrogressive landslide in glaciolacustrine varved clay

The largest landslides in Estonia are associated with glaciolacustrine varved clays. One of the recent slope failures, Audru landslide, was chosen for detailed investigation. Landslide morphology was instrumentally measured and the underlying geological setting investigated with eight boreholes penetrating the varved clay. Varve correlation was used to localize the failure zone and estimate the extent of the displaced material within the landslide body. Field measurements and limit equilibrium models displayed a retrogressive complex of three separate sliding events. The first stage of Audru landslide was initiated by the river undercutting and was followed by retrogressive slides that caused partial liquefaction of the landslide body. The influence of the various modeling parameters on the overall slope stability was also investigated.

Research on theory and application of landslide model test

In this paper, a theory of landslide model testing and application in Three Gorges reservoir area were introduced. Based on geo-mechanical model tests, the similarity ratio of similar material parameters, component of similar material and the boundary friction coefficient of the 2D earth landslide model test were derived and stated by theoretical and experimental methods. A model test of the Qianjiangping landslide in Three Gorges reservoir area reveal a two-step trigger mechanism of coexistence between retrogressive landslide and thrust load caused land-slide.

Use of terrestrial laser scanning for the characterization of retrogressive landslides in sensitive clay and rotational landslides in river banks

For more than 10 years, digital elevation models (DEM) produced by light detection and ranging (LIDAR) technology have provided new tools for geomorphologic studies and especially for landslide studies. In particular, terrestrial laser scanning (TLS) provides a great versatility of use. TLS can be used either for monitoring purposes or in an emergency situation that necessitates a rapid DEM acquisition for assessing a hazard. Using three examples we demonstrate the usefulness of TLS for landslide volume quantification, profile creation, and time series analysis. These case studies are landslides located in sensitive clays of eastern Canada (Quebec, Canada) or small rotational slides in river banks (Switzerland).

Complex landslide in the Rječina valley (Croatia): origin and sliding mechanism

This paper discusses the development of the Grohovo landslide on the north-eastern slope of the Rjecina valley, the largest active landslide along the Croatian part of the Adriatic Sea coast. This complex retrogressive landslide was reactivated in December 1996. Thirteen separate slide bodies have been identified. The slide surface is considered to be on the upper flysch bedrock. Monitoring indicated that the magnitude of displacements was very different in time and space. The maximum movements were recorded on the upper part of the slope. The limestone mega-block and separated rocky blocks on top of the slope have also moved, which is not a typical phenomenon of the flysch slopes in the area of Rijeka.

Gravimetric Study Of A Retrogressive Landslide In Southern Italy

Post-failure activity of the December 1993 Senerchia slump-earthflow was characterised by intermittent recession of the headscarp and earthflow movements. The retrogression showed considerable spatial variability, depending on the properties of the geological materials. The retrogressive failures were preceded by intense fissuring of the ground in the crown zone. Two microgravimetric surveys were carried out in order to detect possible spatial-temporal density variations in an area upslope of the headscarp. Although it was not possible to recognise any significant temporal density changes, this surveying revealed the presence of a negative anomaly which coincided with the area of maximum headscarp retreat. The gravity modelling was constrained by borehole information and new headscarp exposures produced by a series of retrogressive failures suggested that the origin of the anomaly might be associated with a hollow in an underlying clay-rich bedrock which had been subsequently filled by coarse colluvium. A possible concentration of groundwater in the hollow and its discharge towards the headscarp area controlled the local slope instability. The results of this study showed that microgravimetric surveys conducted upslope of retrogressive landslides can provide useful information on subsurface lithological heterogeneities that may control the amount and preferential direction of upslope landslide enlargement.

Multiple edifice failures, debris avalanches and associated eruptions in the Holocene history of Shiveluch volcano, Kamchatka, Russia

Investigation of well-exposed volcaniclastic deposits of Shiveluch volcano indicates that large-scale failures have occurred at least eight times in its history: approximately 10,000, 5700, 3700, 2600, 1600, 1000, 600 14C BP and 1964 AD. The volcano was stable during the Late Pleistocene, when a large cone was formed (Old Shiveluch), and became unstable in the Holocene when repetitive collapses of a portion of the edifice (Young Shiveluch) generated debris avalanches. The transition in stability was connected with a change in composition of the erupting magma (increased SiO2 from ca. 55–56% to 60–62%) that resulted in an abrupt increase of viscosity and the production of lava domes. Each failure was triggered by a disturbance of the volcanic edifice related to the ascent of a new batch of viscous magma. The failures occurred before magma intruded into the upper part of the edifice, suggesting that the trigger mechanism was indirectly associated with magma and involved shaking by a moderate to large volcanic earthquake and/or enhancement of edifice pore pressure due to pressurised juvenile gas. The failures typically included: (a) a retrogressive landslide involving backward rotation of slide blocks; (b) fragmentation of the leading blocks and their transformation into a debris avalanche, while the trailing slide blocks decelerate and soon come to rest; and (c) long-distance runout of the avalanche as a transient wave of debris with yield strength that glides on a thin weak layer of mixed facies developed at the avalanche base. All the failures of Young Shiveluch were immediately followed by explosive eruptions that developed along a similar pattern. The slope failure was the first event, followed by a plinian eruption accompanied by partial fountain collapse and the emplacement of pumice flows. In several cases the slope failure depressurised the hydrothermal system to cause phreatic explosions that preceded the magmatic eruption. The collapse-induced plinian eruptions were moderate-sized and ordinary events in the history of the volcano. No evidence for directed blasts was found associated with any of the slope failures.

Slope Evolution Processes of the Choja landslide, Southwest Japan

Landform and geological structure of a landslide slope are deformed from those of original slope by landslide movement. Slope evolution processes of the Choja landslide which have been active for more than five hundred years are examined geologically.Owing to the comparison of the present location of Serpentine in the sliding mass with the original one, the landslide slope was formed retrogressive landslides of three stages (Figs. 9, 13). The movement of the first stage was originated in the middle part of the present landslide slope. The second stage was originated from the boundary between middle and upper part of the slope along the present slip surface, and mass of two retrogressive landslides entered into the landslide slope from. the side slopes. The upper part of the landslide slope began to move in the third stage. Total displacement of the latter two stages are around 300m.The present landslide has correspondent movement to the retrogressive slope evolution, mentioned above. The velocity of surface displacement of the upper slope is larger than that of middle and lower slope. Wide and thin distribution of Serpentine layers in the sliding mass is thought to be formed by ductile deformation around the slip surface, which is shown in the displacement data by borehole inclinometers.

The Hepburn landslide: an interactive slope-stability and seepage analysis

Mechanisms of active landslides are continuous processes involving the dynamics of slope failure interacting with the groundwater regime. This process is simulated in phases by combining stability calculations interactively with a seepage analysis to determine the factor of safety for a dormant landslide near Hepburn, Saskatchewan. The landslide is a multiple retrogressive failure with two parallel slip surfaces at different elevations. The slip surfaces are in originally overconsolidated Cretaceous and Tertiary clays softened by shear from glaciation. An artesian aquifer is present at the base of the slip surface, causing saline springs at the base of the valley slope. A residual effective friction angle of 6.7° with zero cohesion was found to best characterize the shear strength of the clays in the failure zone. Potential nets and head profiles from the seepage analysis illustrate the strong influence of changing topography on the groundwater flow system. The present-day factor of safety for the dormant landslide was estimated to be 1.10. Key words: multiple retrogressive landslides, dormant landslide, seepage modelling, residual strength, artesian conditions, glacial drift, Cretaceous clays.

The Denholm landslide, Saskatchewan, Canada, an update

The lower block of the Denholm landslide has moved 370 m over alluvium deposited by the North Saskatchewan spillway and river during the last 11 500 years at an average rate of 32 mm/year. These values must be considered minimal because erosion of the toe of the landslide is required for the formation of retrogressive landslides. The shear strength for the bedrock clay (shale) of the Lea Park Formation was back calculated to be [Formula: see text] assuming zero cohesion. Key words: retrogressive landslide, clay shale, residual strength, movement rates, geological age, inclinometer.

The Denholm landslide, Saskatchewan. Part I: Geology

The Denholm landslide, whose surface is composed of scarps, ridges, and elongated depressions, is 160 m high, 2000 m wide, and up to 100 m thick. The shear zone is in silty, montomorillonitic clay of the upper part of the Lea Park Formation and Upper Colorado Group unit. The Upper Cretaceous Judith River Formation and the Quaternary Empress, Sutherland, and Saskatoon groups were affected by the landslide. Although these sediments were fractured and gravity faulted by tension when the landslide moved, they can be readily traced through the landslide, particularly the upper part. The scarps (gravity faults), ridges (horsts), and elongated depressions (grabens) are the surface expression of tension resulting from the stretching of beds during the landslide.The movement of the landslide is thought to have started when the North Saskatchewan spillway eroded to the level of the present shear zone about 11 000 years ago (established by radiocarbon dating) and is believed to have stopped in recent time. During this time, it moved about 390 m across the North Saskatchewan River alluvium at an average rate of 35 mm per year. As the landslide moved across the valley, it encountered deposition of alluvium at an average rate of about 2.4 mm per year which resulted in the curved shear zone on the alluvium. Keywords: retrogressive landslide, shale-alluvium, displacement, rate, age.

The Denholm landslide, Saskatchewan. Part II: analysis

A procedure incorporating geological evidence with analytical methods was developed for the back analysis of a multiple retrogressive landslide in Cretaceous clay shale. The slide mass, apparently inactive, extends 2 km back from the toe at the river and is seated on a shear zone 100 m deep at the main scarp. Historical evidence of the slope movement was established from radiocarbon dating of the river alluvium over which the landslide moved. The geometry of the landslide when the factor of safety was near unity was determined from historic and stratigraphic evidence and sensitivity analyses.The stratigraphy of the slide mass showed that the beds are stretched with very little vertical displacement, indicating a mainly translational mechanism along a nearly horizontal shear zone. Apparently movement has taken place at a slow but steady rate over 11 000 years, resulting in a horizontal displacement of 390–430 m at the toe. The landslide, therefore, was analyzed as a series of sliding blocks with a common failure surface retrogressing from the toe up to the scarp. Each successive block was combined and considered to be moving as a single unit. Unknown factors, such as pore-water pressure at failure and the influence of cohesion, were evaluated by sensitivity analyses. The effective angle of shearing resistance required for limiting equilibrium was relatively constant, ranging from 7.6 to 8.7°, assuming the water table to be near the ground surface. For a lower water table, the values ranged from 6.5 to 8.0°. The equivalent values of cohesion required for equilibrium with [Formula: see text] ranged from 42 to 82 kPa depending on the size of the block, suggesting that c′ must be zero for the retrogressive mechanism analyzed by combining successive blocks. Keywords: slope stability, multiple-block, back analysis, residual strength, sensitivity analysis.

On the retrogression of landslides in sensitive muddy sediments: Discussion

Introduction It was with interest that I read Carson's (1977) novel theoretical discussion of the parameters controlling the occurrence of retrogressive landslides in fine-grained sensitive deposits. I t would be extremely useful if we could predict, using only estimates of undrained shear strength and Carson's subsidence ratio, the susceptibility of landslides to retrogression, although it is not immediately apparent how this ratio might be estimated for a slope that has not failed. Although the theory Carson develops may have validity, he makes an implicit assumption about the mode of failure and retrogression that may well be invalid for at least four of the landslides he uses to test his theory. Applicability of his concept of retrogression is conditional upon the absence of buildup of pore-water pressure in permeable strata beneath the clay, a condition he neglects to state until the last page of his presentation. He also waits until the end of his paper to mention that beneath his landslides 1-4 (Table 1, p. 595) in the MaskinongC Valley there are indeed such sandy strata beneath the clay but that their absence in the other two flow slides he studied in the valley provides conclusive that underlying sand strata are not a prerequisite for retrogressive earthflows. Such conclusive evidence at two sites, however, hardly seems to justify ignoring or not investigating geologic data in the other four landslides beneath which buildup of such piezometric pressure in confined sandy aquifers is a very real possibility. Stratigraphic, sedimentological, geophysical, and geochemical investigations in this part of the upper MaskinongC Valley (Donovan 1977) have produced geological data that may well bear on the geotechnical problem but were not presented and only obliquely recognized in the Carson paper. It is the purpose of this note to present some of this geological evidence, which does not invalidate Carson's model but precludes

On the retrogression of landslides in sensitive muddy sediments

The literature dealing with extensive retrogression of landslides in sensitive sediments is reviewed and found to be inadequate in several respects. One obvious deficiency is in the link between supposed retrogressive mechanisms and the morphology of the resultant ‘earthflow’ cavity. Detailed attention is focussed on the origin of linear clay ridges that protrude from the floors of fresh earthflows, and persist for only a short time before being degraded to micro-scale features. The theory of landslide retrogression proposed by Odenstad, after the Sköttorp landslide in Sweden, is discussed, and developed into a model for the prediction of landslide retrogression, and for the explanation of 'flowbowl' morphology. The model, essentially an undrained retrogressive spreading failure, is tested against selected retrogressive landslide sites for which all the necessary information is available; the agreement between nature and theory is good. Some speculation is made regarding the origin of bottlenecked flowbowls, which are viewed as the exception rather than the rule in the sensitive muds of the St. Lawrence Lowlands. Emphasis is directed at the importance of the undrained shear strength of sensitive sediments, and less significance is attached to the actual magnitude of sensitivity of such deposits. Finally, the limitations of the model in very soft sediments, such as found in parts of Norway, are briefly pointed out.

Case record of the slope failure that initiated the retrogressive quick-clay landslide at Ullensaker, Norway

A case record is presented of the slope failure that initiated the retrogressive quick-clay landslide at Ullensaker, Norway. Information concerning the landslide is reasonably complete: initial topography is known, the size of the initial slope failure was witnessed, the approximate location of the slip surface was determined by borings and the water pressures are approximately known from measurements in an adjacent slope. A comprehensive series of drained triaxial compression tests was conducted on undisturbed samples. Effective stress stability calculations of the slope yielded an apparent safety factor of unity. On présente l'histoire d'un cas de rupture de pente qui a déclenché un glissement de terrain rétrograde dans une angile fluide à Ullensaker, Norvège. L'information sur ce glissement est raisonnablement complète: on connait la topographie initiale, les dimensions du glissement initial ont été observées, la position approximative de la surface de glissement a été déterminée par forage, et les pressions d'eau sont connues approximativement par des mesures sur une pente adjacente. Un vaste programme d'essais triaxiaux drainés a été entrepris sur des échantillons intacts. Les calculs de stabilité en termes de contraintes effectives sont donné un coefficient de sécurité égal à l'unité.