Slide Failure Research Articles

Two-way seismic behaviour of concrete frames with infill walls

The effects of masonry infill walls on the behaviour of reinforced concrete frames are often ignored in seismic engineering. A three-dimensional non-linear finite-element model is introduced in this paper to simulate in-plane and out-of-plane behaviour of masonry infilled reinforced concrete frames. It employs a surface-based cohesive contact model to capture the crack and slide failure mode of the infill wall mortar joints. Comparison with experimental data shows that the proposed numerical model provides good estimates of the strength, deformation and failure modes in both directions. Several two-way numerical tests are conducted to investigate the interaction of in-plane and out-of-plane responses. The tests include sequential out-of-plane and in-plane loading (and vice versa) as well as simultaneous application of both loadings. The results indicate that out-of-plane performance and in-plane strength are significantly decreased by the interaction of loadings in two directions. The out-of-plane loading causes the out-of-plane failure mode, which is often seen in past earthquake events, and before which the in-plane strength is not fully developed. A mathematical expression is proposed for engineering analysis.

Sediment erosion dynamics of a gullied debris slide: a medium-term record

Medium-term post-event sediment flux investigations are rare for headwater catchments and particularly sparse for gullied hillslope failures. Repeat field observation, ground photography and cross section measurements of a debris slide scar at the Wet Swine Gill headwater catchment (0.65km2) in the English Lake District (UK), provide evidence of erosion and deposition dynamics over the medium-term (2002–2014). These data are compared to site topographic and meteorological conditions, to evaluate potential process–response linkages.Rill and gully erosion networks establish soon after the slide failure (1 February 2002); thereafter gully enlargement proceeds rapidly, first by vertical downcutting, prior to lateral expansion and gully wall angle decline. Changes in cross sectional width, depth and area (2002–2013) are characterised by statistically significant (P=<0.05) negative exponential growth models (R2=width: 0.88–0.97; depth: 0.71–0.86; area: 0.87–0.93). Gully walls were dominated by erosion but the gully bed was characterised by episodic sediment production, storage and transfer often leading to temporary deposition. Specific erosion rates on the gully wall exceeded those on the adjacent slide scar by up to 764% (maximum values=wall: −0.0084; scar:−0.0011m2m−1d−1). Upslope contributing (runoff) area and slope gradient are generally important for erosion; although linear regression analysis demonstrates weak or insignificant relationships between meteorological conditions and gully/scar sediment flux. A general conceptual model of slide scar evolution, integrating gully growth and capture, summarises activity at this site. However transferability to locations with terrain characteristics, land management practices and climate conditions different to those existing in the UK uplands remains to be tested. This investigation adds to growing appreciation of the complexities of sediment dynamics in headwater catchments and provides clear evidence for the potential of early management intervention to counter detrimental post-failure sediment erosion; which at this site would have been most effective up to 3–4years following gully initiation.

DEM Analyses of an Uplift Failure Mechanism with Pipe Buried in Cemented Granular Ground

The uplift failure mechanism of buried pipe and its linked soil resistance are key concerns in pipe design. Although the uplift responses of pipe buried in remolded backfill have been discussed extensively, little effort has been spent on pipes buried in cemented ground, a situation that could emerge in practical engineering. This paper aims to eliminate this deficiency through a comprehensive, two-dimensional distinct element method (DEM) study on the failure mechanisms of uplifting pipe buried in loose cemented sand ground with respect to soil bond strength and pipe cover ratio. Two forms of failure mode are identified, namely the global slide failure mechanism and the local flow failure mechanism. Three stages are identified for the global failure mechanism: (1) full mobilization of uplift resistance, (2) postpeak softening with full development of the crack zone, and (3) continual growth of the trapezoid zone with further softening. The local failure mechanism presents with the opposite flow of soils around the pipe, with soils above and below the pipe flowing upward and soils from the two lateral sides of the pipe to the far field flowing downward. With the soil bond strength decreasing or the pipe cover ratio increasing, the failure mechanism gradually changes from the global failure mode found in relatively strongly cemented cases to the local failure mode commonly found in weakly cemented or uncemented cases. A new dimensionless parameter r incorporating both the effects of bond strength and the cover ratio is proposed to identify the uplifting failure modes.

粒子法による河川堤防の進行性すべり破壊に関する解析的検討

粒子法による河川堤防の進行性すべり破壊に関する解析的検討

Treatment Technology for Embankment Landslide Caused by Expansive Soil Foundation Instability

The embankments built on expansive soil foundation with a transverse are prone to crack and slide failure. In this paper, the embankment in a certain section of Bailong highway destroyed due to cracks and rainfall. A group of steel piles and reinforced concrete beams is used to strengthen the toe of slopes, and steel piles and reinforced concrete framework beams is utilized to strengthen embankment slopes, then pressure chemical grouting is used to reinforce soil. The treatment effect is good.

Research Review of Seismic Failure Mode of Abutment and Influence on Deck Fall-Off

Well seismic performance of abutment were safety precondition of whole bridge. According to destroyed multi-span simple beam bridge of Wenchuan earthquake, failure modes of abutment were summarized. On the basis of correlation literature home and overseas, analysis methods of abutment seismic research were investigated. Nether factors should be take into account : soil-abutment interaction, abutment stiffness, bridge span number, pier’s force-displacement curve , bearing stiffness and etc.. Interspace model of seismic analysis were constituted and nonlinear time history adopted, so mechanism of abutment failure modes(strength failure, whole slide and admixture failure )was obtained. Control variables between beam and abutment were discussed. Those variables were keys of research influence on fall-off by abutment failure.

Loss of Composure during Testimony Can Affect Verdict

In the 1980s I participated as an expert for the plaintiff in a case involving slide failure of fill soil in a relatively deep and wide circular excavation. The plaintiff was the general contractor hired by the defendant to excavate the site for the construction of a flood control structure. The excavation was part of a federally funded project that was located in a back-swamp river deposit in the southeastern United States. Because the defendant had made an error in the construction drawings, the plaintiff inadvertently overexcavated a 90-foot-wide 27.432 m section of the circular excavation. The defendant’s error resulted in the plaintiff’s incurring significant additional expenses, which the defendant refused to pay. As a result, the general contractor sought payment through the U.S. Claims Court. The trial was a bench trial, meaning the judge acted as sole determiner of fact. The history of the suit is this: The plaintiff’s initial placement of the fill, done in accordance with construction drawings, slid into the excavation. The defendant ordered the plaintiff to remove the material that slid into the excavation and again place the fill on the slope. The second attempt also failed. At that point, the plaintiff felt that his company was placing the fill properly according to the defendant’s specifications and stopped all work until it could be determined why the fill material was sliding. Eventually, after significant delays, the defendant developed another—and successful—procedure for placing the fill on the slope. When the job was completed, the plaintiff submitted a request for payment. The request included the costs for the extra work for placing the fill on three separate occasions and for the delays associated with work on other construction that had to be interrupted to address the slope repairs. The request for payment for the extra work was denied, so the general contractor decided to seek payment through litigation. In preparation for testimony as an expert witness for the plaintiff, I investigated the site and contractor’s work. My investigation showed that during the excavation process, the surface of the original soil had been disturbed and remolded by the plaintiff, resulting in a marked change in the consistency of the clay soil. Based primarily on examination of the defendant’s onedimensional consolidation test curves, I determined early on that the clay soil on the slide plane was sensitive and resulted in the sliding failure of the fill. The test curves for the subject soil exhibited the concave-inward shape that is typical of sensitive clays. My determinations contradicted the contentions of the defendant’s engineers, who argued that the clay soil on the slide plane was not sensitive and that the failure resulted from the plaintiff’s poor workmanship. But the defendant’s geotechnical engineers had not accounted for the soil’s sensitivity in their slope stability analysis. They had used the undisturbed, unconfined compressive test strength of the soil instead of the remolded strength. This failure to accurately determine the soil’s sensitivity should have weighed the verdict for the plaintiff. However, a different kind of sensitivity—my own—perhaps left a negative mark on the outcome. For the trial, the defendant hired a world-renowned educator and researcher in physical properties and behavior of soils. The expert had previously done considerable research on sensitive soils and produced many publications on the subject, including a popular textbook. The expert agreed with the defendant’s engineers that the soil on the failure plane was not sensitive. Knowing the credentials, experience, and renown of the defendant’s expert far outmatched mine, I carefully reviewed his publications on sensitive soils. When I examined the textbook he had authored, I found a graph that he had developed for estimating a soil’s sensitivity based on three geotechnical parameters. The graph was based on data from many geographical locations. Using the expert’s parameters and the defendant’s own soil data, I found independently that the expert’s graph clearly and demonstrably showed that the soil in question was indeed sensitive. At the trial, the plaintiff’s attorney asked the defendant’s expert if the soil was sensitive. Under oath, the expert stated that it was not. The attorney presented into evidence, for the witness’s consideration, the defendant’s project plans containing numerous soil-boring logs and the results of myriad soil tests. Next the plaintiff’s attorney offered a textbook into evidence and asked the expert if he had authored the textbook, which, he acknowledged, he had. At this point, the plaintiff’s attorney drew attention to a particular graph in the textbook relating to soil sensitivity and asked the expert specifically if the graph was his work. The expert answered that it was. Having established the expert’s published position about iden

A fracture sliding potential index for wellbore stability analysis

Sliding failure along the fractures intersecting a wellbore is one of the major wellbore instability mechanisms. This kind of failure is similar to the slope instabilities, a well-known phenomenon in mining and civil engineering. During drilling operations the drilling fluid can penetrate through fractures and lead to fracture reactivation and wellbore instability. The rock engineering systems (RES), initially introduced in the mining- and civil-related geomechanics problems, is an approach to analyze the interrelationship between the parameters affecting rock engineering activities. In this study, after discussing the sliding mechanism along a fracture in a wellbore during drilling, and identifying all the effective parameters, an interaction matrix is introduced to study the sliding failure mechanism. Thereafter, the interaction intensity and dominance of each parameter in the system is determined to classify these parameters. A systematic approach was used to determine the relative interactive intensity and value of each contributing parameter in the fracture sliding mechanism. As a result, an index is presented to estimate the fracture sliding potential. The results indicate the ability of this method to analyse wellbore instability due to fracture reactivation mechanism. This will assist in finding a better engineering action to mitigate or eliminate potential fracture sliding during drilling. The results show a good agreement with those obtained using Mohr–Coulomb failure analysis and field observations.

Evaluating the significance of event and post‐event sediment dynamics in a first order tributary using multiple sediment budgets

.Investigations of sediment transfer in upland catchments are rarely conducted over a sustained period of time, consequently a full understanding of the changing nature of sediment supply, storage and yield is often lacking. Three recent sediment budget studies from the Wet Swine Gill headwater catchment in the Lake District, Northern England, UK (a 0.65 km2, first‐order tributary), provide evidence of changes in sediment transfer dynamics over the period 2002–2008. The first sediment budget in 2002 describes the impact of a hillslope debris slide and channelised debris flow event, where the former was the dominant budget component. The termination of the debris flow in the Wet Swine Gill channel meant that the vast majority of slide failure material was not transferred to the downstream fluvial system. However, subsequent modification of exposed hillslope sediment by post‐event erosion processes and gully development resulted in ongoing erosion. A second sediment budget (June 2003–January 2004) demonstrated sediment yield downstream of the in‐channel debris slide deposits far exceeds upstream fluvial sediment delivery by two orders of magnitude (c. 4,000 kg and c. 20 kg, respectively). Erosion of sediment from the exposed hillslope failure scar (c. 1300 kg) was less than channel erosion (c. 3300 kg), and sediment transfers from both the hillslope and channel sediment sources are sensitive to high‐magnitude, low‐frequency trigger events including summer thunderstorms, and winter rainfall/ snow‐melt events. However, linear regression analysis only demonstrates weak or insignificant relations between meteorological conditions and sediment yield. A final sediment budget in April 2008 shows the significance of both hillslope (inclusive of gullying) and channel erosion/ transfer processes over the six‐year monitoring period. In this budget, like the first sediment budget, the hillslope system is marginally more dominant, and therefore demonstrates a further switch in the relative significance of hillslope and channel system components. When interpreting such findings the potential uncertainty in the budget components, particularly in the unmeasured residual components, should be considered, as the magnitude of the error can be large.These results suggest that contemporary event and post‐event sediment flux in small headwater catchments are more complex than short‐term investigations would initially suggest. Furthermore there is a clear need for continued, longer‐term monitoring of sediment system dynamics and associated hydro‐meteorological conditions, in order to develop understanding of how future climate change may impact upland sediment systems.

Evidence for debris flow gully formation initiated by shallow subsurface water on Mars

The morphologies of some martian gullies appear similar to terrestrial features associated with debris flow initiation, erosion, and deposition. On Earth, debris flows are often triggered by shallow subsurface throughflow of liquid water in slope-mantling colluvium. This flow causes increased levels of pore pressure and thus decreased shear strength, which can lead to slide failure of slope materials and subsequent debris flow. The threshold for pore pressure-induced failure creates a distinct relationship between the contributing area supplying the subsurface flow and the slope gradient. To provide initial tests of a similar debris flow initiation hypothesis for martian gullies, measurements of the contributing areas and slope gradients were made at the channel heads of martian gullies seen in three HiRISE stereo pairs. These gullies exhibit morphologies suggestive of debris flows such as leveed channels and lobate debris fans, and have well-defined channel heads and limited evidence for multiple flows. Our results show an area–slope relationship for these martian gullies that is consistent with that observed for terrestrial gullies formed by debris flow, supporting the hypothesis that these gullies formed as the result of saturation of near-surface regolith by a liquid. This model favors a source of liquid that is broadly distributed within the source area and shallow; we suggest that such liquid could be generated by melting of broadly distributed icy materials such as snow or permafrost. This interpretation is strengthened by observations of polygonal and mantled terrain in the study areas, which are both suggestive of near-surface ice.

Monitoring and numerical modelling of riverbank erosion processes: a case study along the Cecina River (central Italy)

AbstractRiverbank retreat along a bend of the Cecina River, Tuscany (central Italy) was monitored across a near annual cycle (autumn 2003 to summer 2004) with the aim of better understanding the factors influencing bank changes and processes at a seasonal scale. Seven flow events occurred during the period of investigation, with the largest having an estimated return period of about 1·5 years. Bank simulations were performed by linking hydrodynamic, fluvial erosion, groundwater flow and bank stability models, for the seven flow events, which are representative of the typical range of hydrographs that normally occur during an annual cycle. The simulations allowed identification of (i) the time of onset and cessation of mass failure and fluvial erosion episodes, (ii) the contributions to total bank retreat made by specific fluvial erosion and mass‐wasting processes, and (iii) the causes of retreat. The results show that the occurrence of bank erosion processes (fluvial erosion, slide failure, cantilever failure) and their relative dominance differ significantly for each event, depending on seasonal hydrological conditions and initial bank geometry. Due to the specific planimetric configuration of the study bend, which steers the core of high velocity fluid away from the bank at higher flow discharges, fluvial erosion tends to occur during particular phases of the hydrograph. As a result fluvial erosion is ineffective at higher peak discharges, and depends more on the duration of more moderate discharges. Slide failures appear to be closely related to the magnitude of peak river stages, typically occurring in close proximity to the peak phase (preferentially during the falling limb, but in some cases even before the peak), while cantilever failures more typically occur in the late phase of the flow hydrograph, when they may be induced by the cumulative effects of any fluvial erosion. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Treatment of posterior column fracture in tibial plateau injury

Objective To describe the operative procedures.fracture patterns and clinical outcomes of treatment of posterior column tibial plateau fractures.Methods From February 2005 to August 2006,36 patients with posterior column tibial plateau fracture were operated on.Twenty patients were treated with open reduction and buttress plate fixation via a posterior approach.They were 13 males and 7 females,with a mean age of 38.5(ranging from 29 to 52)years.The other 16 patients were operated on via anterior plus posterior approaches.They were 11 males and 5 females,with a mean age of 37.3(ranging from 27 to 49) yeam. Results All were followed up for an average of 14.5(ranging from 12 to 15)months.All frac- tures got united with an average radiographic bone union time of 15.7(ranging from 11 to 16)weeks and an average full weight-bearing time of 17.6(range from 13 to 21)weeks.The mean HSS(The Hospital for special surgery)score of all these patients at 12 months postoperatively were 83.4(ranging from 68 to 92). There were 1 case of inferior medial genicular vessel injury during the operation,1 wound dehiscence and 1 partial incision necrosis postoperatively which were all eventually healed with conservative treatments.Three cases of numbness within the posterior lower part of the calf occurred postoperatively.No screw toggle,slide, dislodging or fixation failure was found during follow-up.There were no significant differences both between TPA and PA on radiographies and between immediately after operation and 12 months psstoperatively. Conclusion Open reduction and internal fixation with buttress plates via a posterior or anterior plus posterior approaches is appropriate for treatment of posterior column tibial plateau fractures. Key words: Tibial; Fracture; Fracture fixation.internal; Posterior column; Posterior approach

Factors of Caisson Sliding Failures Affected by Damage of Armor Concrete Blocks

Recently, caisson sliding failures affected by large waves have occurred. The damage of the breakwaters in Susami port due to Typhoon 0423 is a typical sliding failure and the caissons were tilted down in the rear of rubble mound. The damage at Fushiki-Toyama port on February 2008 is also another typical sliding failure and concrete blocks were settled down. The present paper describes the factors of their caisson sliding failures affected by damage of armor concrete blocks. It concludes that the caisson sliding failure at Susami port was caused by insufficient weight of the caisson. Even if heavier concrete blocks are placed as armors, the caisson would be slid. The numerical simulation suggests that the caisson sliding failure at Fushiki-Toyama port was caused by the combination of three factors of large wave height, long wave period and duration time.

Research on Formation Mechanism of the Debris Flow on Slope Induced by Rainfall

Based on field investigation and lab tests, rock and soil fracture criterion, and analyses of typical debris flows on slope, the formation mechanism of the rainfall-induced debris flow on slope have been studied by considering its influential factors, kinematics properties, dynamic conditions, and formation and evolution process of the debris flow on slope. The research results indicate that the debris flow on slope is mainly of the type of translational slide failure, which is developed on the steep slope, where gradient is more than 40° with shallow residual soil (thickness is less than 2.0 m). The rainfall is one of the important factors inducing the debris flow on slope. Rainwater penetration makes the residual soil saturate and soften. When water content of the residual soil is more than 28%–30%, the relation curves of cohesion and internal friction angle versus water content show obvious inflexion. That is, when the saturation of the residual soil is more than 75%, the cohesion and internal friction angle both decrease rapidly. The soil on slope will change from stable to destructive. The residual soil will start to form partly mollisol and slip down the slope if it meets persistent rainfall or rainstorm. Further, the sliding soil mass rushes down to create mud slurry-debris flow on slope.

Holocene sedimentary processes in the Andøya Canyon system, north Norway

The Andøya Canyon system is the most pronounced of the ten canyon systems identified on the Norwegian continental margin. None of these canyon systems is linked to any present active drainage area and are interpreted to have been basically non active since the last glacial maximum and the deglaciation period. Our knowledge on these canyon systems is however still limited as no high-resolution stratigraphical or acoustic data sets are available from these areas. The main target for analysing the long term history of the Andøya Canyon has been to study the distal accumulation part of this system in the Lofoten Basin. The Lofoten Basin area is characterized by repeated stacks of extensive turbidite units where the details of the stratigraphical succession can be studied in undisturbed settings. About 3000 km 2 of high-resolution multibeam data (EM300) along with three gravity cores have been collected from the Lofoten Basin area. The analyses carried out on the cores revealed that the predominant process results in single turbidite units interbedded with thin units of hemipelagic sedimentation. The radiocarbon dating revealed that turbidites have been transported through this channel system at least twice during the Holocene. The two uppermost dated turbidite sequences give a maximum age of 7.9 ka 14C BP for the lower sequence and an age of ca. 4.0 ka 14C BP for the upper sequence. The upper sequence is of a similar age as the Trænadjupet Slide failure whereas the lower sequence indicates an age close to the Storegga Slide failure event, taking into consideration the erosive lower boundary of that sequence. The location of the investigated cores, which are far away from both the Trænadjupet Slide and the Storegga Slide, indicate that the instability in these canyon systems during the Holocene period has most probably been influenced by these large-scale failure events. What triggered the release of these turbidites is still not understood, but earthquakes or tsunami waves associated with the mega scale Trænadjupet Slide and the Storegga Slide events are considered to be the most likely mechanism at least during the Holocene Interglacial period.

Austin Dam, Pennsylvania: The Sliding Failure of a Concrete Gravity Dam

Research Article| January 01, 2005 Austin Dam, Pennsylvania: The Sliding Failure of a Concrete Gravity Dam DANIEL F. MARTT; DANIEL F. MARTT 1A.G.E.S., Inc., Southpointe Business Park, 4 Grandview Circle, Canonsburg, PA 15317 Search for other works by this author on: GSW Google Scholar ABDUL SHAKOOR; ABDUL SHAKOOR 2Department of Geology, Kent State University, Kent, OH 44242 Search for other works by this author on: GSW Google Scholar BRIAN H. GREENE BRIAN H. GREENE 3U.S. Army Corps of Engineers, Geotechnical Branch, 1000 Liberty Avenue, Pittsburgh, PA 15222 Search for other works by this author on: GSW Google Scholar Environmental & Engineering Geoscience (2005) 11 (1): 61–72. https://doi.org/10.2113/11.1.61 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation DANIEL F. MARTT, ABDUL SHAKOOR, BRIAN H. GREENE; Austin Dam, Pennsylvania: The Sliding Failure of a Concrete Gravity Dam. Environmental & Engineering Geoscience 2005;; 11 (1): 61–72. doi: https://doi.org/10.2113/11.1.61 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Abstract The Austin Dam, a concrete gravity structure, failed catastrophically on September 30, 1911, less than 2 years after its construction. Several engineering evaluations of the failure have been made since immediately following the disaster. Engineers involved in the construction of the dam recognized early on that the dam failed by sliding on its rock foundation. The dam was constructed on interbedded sedimentary rock, and its foundation was taken to a depth of approximately 4 ft (1.2 m). Although studies of the orientation of the failed blocks of the dam and other site evidence pointed to a sliding failure, no detailed quantitative studies have been done. Recent test pit excavations showed that the critical interface for sliding was a sandstone/shale contact located at a shallow depth below the base of the dam. Stability analyses based on shear-strength tests of the different interfaces of the foundation (concrete/sandstone, sandstone/sandstone, sandstone/shale, and shale/shale) showed that the dam was safe against a bearing capacity failure, but unsafe with respect to sliding and overturning. The lowest factor of safety of 0.6 corresponded to the sandstone/shale interface, as stated above. The major factors believed to have contributed to the failure include low shear strength of the foundation materials, inadequate provisions for reducing the uplift pressure, and weak concrete. The project stands as the sixth worst dam failure in U.S. history in terms of loss of life, and this case history provides numerous lessons with regard to dam safety. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Near-surface geology and sediment-failure geohazards of the central Scotian Slope

The central Scotian Slope demonstrates a complex seafloor morphology superimposed on a regional gradient of 24 across the margin. The west-central Scotian Slope is characterized by a relatively smooth seafloor, but with numerous 1080-m (33260-ft)-high escarpments representing slide failure scars. In the east, the seafloor is highly dissected by canyons. Throughout the region are scars and deposits of sediment mass failures, including retrogressive headwalls, rotational slumps, slides, creep, debris-flow deposits, and turbidites.The complexity of failure styles and triggering mechanisms identified underscores the need for comprehensive site assessments for situating seabed facilities. Critical factors that need to be taken into account include local terrain analysis and shallow subbottom stratigraphy. Slope-stability analysis has shown the surface sediment to be statically stable, except on steep escarpments and canyon walls. There is evidence, however, of sediment failures that approximately correlate to glacial advances (2512, 75, and 130 ka), providing some clue as to potential triggering mechanisms. Sparse, passive-margin, tectonic earthquakes, however, are the likely cause for large-scale, regionally correlated failures and failure escarpments.

The importance of breaching as a mechanism of subaqueous slope failure in fine sand

Large bank failures, comprising up to 106 m3 of sediment, are common features along steep channel banks in estuaries and large rivers that consist of clean, fine sands, and are mostly assumed to be generated by sudden liquefaction of large masses of very loosely packed sand. Another less commonly recognized type of failure is manifested by the gradual retrogression of a very steep wall, steeper than the angle‐of‐repose. Instead of the voluminous surging plastic sediment‐water flow, or hyperconcentrated density flow (sensu Mulder &amp; Alexander, 2001) generated by liquefaction, this type of failure, known as breaching by dredging companies and hydraulic engineers, produces a sustained quasi‐steady, turbidity current. To date, sedimentologists have not recognized the process of breaching as such. In this paper, it is suggested that breaching may be the origin of many thick, massive sand layers known from ancient deposits from various environments, notably in some turbidite successions. Possible differences in the sedimentary structure of the deposits produced by breach failures vs. liquefaction slope failures (=liquefaction flow slides) can be deduced from a knowledge of the sediment transport processes initiated by the failure. A field study is presented on some poorly structured beds in the Eocene Vlierzele Sands in Belgium, which are supposed to have originated from liquefaction failures, but are reinterpreted to be the products of breaching. It is postulated that the local steep slope disturbance required to initiate an active breach can be produced by a small liquefaction slope failure (=liquefaction flow slide failure) or local erosion by river or tidal channel flow at the initial stage of the failure event.

Does the weight of riparian trees destabilize riverbanks?

In contrast to the generally accepted stabilizing effects of riparian vegetation, the surcharge of trees on riverbanks has been widely implicated as a source of bank instability. Fieldwork conducted along the Latrobe River in Victoria, Australia shows that the bank-destabilizing effects of surcharge, due to silver wattle (Acacia dealbata), are minimal. Field observations indicate that it is unlikely that the weight of silver wattles growing on an otherwise stable bank section will directly cause mass failure. Observations of deep-seated failures and silver wattle stands on the Latrobe River indicate that where average-sized slump-blocks support an average number of average-sized silver wattles, the trees represent only 4.1% of the total saturated slump mass. Infinite slope stability analysis indicates a threshold of around 48° where banks become prone to shallow-planar slide failures as they steepen. Where bank sections are inherently unstable and prone to shallow-planar slide failure, the additional weight of the trees may contribute to overall instability. However, manipulation of other stability parameters within reasonable constraints negates the effect of surcharge so it is not possible to demonstrate conclusively a destabilizing influence of silver wattles. Copyright © 2000 John Wiley & Sons, Ltd.

The geomorphic evolution of slopes and sediment chutes on forereefs

Frequent slope failures of the forereef dropoff occur in living coral reefs on the island of Bonaire in the southern Caribbean. Topographic profiles of ten sites were taken perpendicular to shore, followed by an estimation of coral ages (M. annularis) along the topographic profiles. The coral ages were estimated from published rates of growth and sizes of the sampled corals. Comparisons of coral age and adjacent slope angle indicated that the steeper slopes are older and that mass failure of the slope reduces the steepness of the forereef front and destroys the coral community along the disturbed slope. Slopes grow until reaching a critical steepness, after which underwater sliding of the over-steepened forereef front results. In observed slides, the mechanical weakness in the reef structure that facilitates a slide failure was the result of a weak mud and coral rubble layer deposited 2 m below the living coral cover. The remaining slide scarp evolves into a sediment chute that conveys the resulting flow of biogenic sands from the shallow forereef terrace down the forereef edge. Because of the constant flow of sand down these channels, no corals can recolonize the sediment chutes and the chutes become stable topographic features. In addition, these indentations in the forereef front also serve as channels for the vertical density mixing of water of varying salinities and temperatures.