Soil slopes under combined horizontal and vertical seismic accelerations

Conventional methods of designing earth structures are based on pseudo-static stability analysis employing a horizontal seismic coefficient. This paper discusses the stability and permanent displacement of a slope subject to combined horizontal and vertical accelerations. A log-spiral failure mechanism is used. It is shown that seismic force has a significant effect on stability and permanent displacement of slopes. The parametric study reveals that vertical acceleration may play an important role on stability and permanent displacement if the corresponding horizontal acceleration is large. © 1997 John Wiley & Sons Ltd.     

Implications of biological and physical diversity for resilience and resistance patterns within Highly Dynamic River Systems

The structure and function of alluvial Highly Dynamic River Systems (HDRS) are driven by highly variable hydrological disturbance regimes, and alternate between resistant, metastable states and resilient, transitional states. These are in turn subject to influences of feedback loops within hydrogeomorphic and biological processes. Here we consider how resistance and resilience largely determine HDRS ecosystem trajectories and how these characteristics can be modified by natural and anthropogenic processes. We review the mechanisms by which biodiversity can affect both resistance and resilience and introduce a conceptual framework that incorporates some unique HDRS characteristics. We suggest that resilient and resistant patterns frequently coexist in the active tract of these river systems, and that this coexistance promotes the return of metastable states after major disturbances. In contrast, highly resistant and poorly resilient patterns dominate at their external boundaries. The loss of these natural dynamics resulting from direct and indirect human impacts causes deviations to resistance and resilience patterns and therefore to HDRS trajectory. We propose that understanding the role of interactions between biological and physical processes that control resistance and resilience is crucial for system restoration and management.     

Spatial distribution of safety factors: Cohesive vertical cut

The objective of the present work is to study the spatial distribution of safety factors in a vertical purely cohesive cut, utilizing the safety map notion introduced by Baker and Leshchinsky (2001). The investigation shows that there exists a zone in the vicinity of the crest in which critical conditions are realized on slip circles with overhanging cliffs. Such mechanisms are stable only if there is sufficient tensile strength to prevent formation of tension cracks. It is shown that the tensile strength required to prevent cracking is of the same order as the mobilized cohesion, and Taylor's classical result is valid only for such conditions. The safety factor of a vertical cut in a zero tensile strength material is approximately 70% of Taylor's value. It is demonstrated that safety maps provide a natural framework for designing remedial measures in substandard slopes. Copyright © 2003 John Wiley & Sons, Ltd.     

Temperature-composition-depth relationship in Rift Valley hot springs: Hammat Gader,northern Israel

The Hammat Gader (El-Hamma) springs constitute a rift valley hot-spring system. The five springs which belong to this complex are distinguished by temperatures of 25, 28, 36, 42 and 50°C and salinities of between 700 and 1400 mg/l. With one exception, the salinity of the spring waters increases with temperature.A model is presented which explains the chemical composition of the individual springs by mixing of an ancient, Ca-chloridic, rift brine with present-day meteoric waters. The water temperatures are dictated by the regional geothermal gradient, which is calculated for the investigated area from deep-drilling data. The model is in good accordance with previously published isotopic and rare-gas data.A model suggested earlier for the Hammat Gader springs is examined, discussed and rejected on geochemical, spatial and hydrogeological grounds.     

Formation and dynamics of vegetated fluvial landforms follow the biogeomorphological succession model in a channelized river

Feedback between hydrogeomorphological processes and riparian plants drives landscape dynamics and vegetation succession in river corridors. We describe the consequences of biogeomorphological feedback on the formation and dynamics of vegetated fluvial landforms based on observations from the channelized Isère River in France. The channel was laterally confined with embankments and mostly straightened. From the beginning of the 1970s to the end of the 1990s, alternate bars were progressively but heavily colonized by vegetation. This context presented an exceptional opportunity to analyse temporal adjustments between fluvial landforms and vegetation succession from bare gravel bars to mature upland forest as the consequence of biogeomorphological interactions. Based on a GIS analysis of aerial photographs (between 1948 and 1996), we show that the spatiotemporal organization of vegetated bars within the river channel observed in 1996 resulted from a bioconstruction and biostabilization effect of vegetation and interactions between bars of varying age, size and mobility. Field measurements in 1996 reflected how a strong positive feedback between sedimentary dynamics and riparian vegetation succession resulted in the construction of the vegetated bars. A highly significant statistical association of geomorphological and vegetation variables (RV of co-inertia analysis = 0.41, p < 0.001) explained 95% of the variability in just one axis, supporting the existence of very strong feedback between geomorphological changes (i.e. the transformation of small bare alternate bars to fluvial landforms covered by mature upland forest, and vegetation succession). Such dynamics reflect the fluvial biogeomorphological successions model, as described by the authors earlier. © 2020 John Wiley & Sons, Ltd.     

Shoreline migration and beach-nearshore sand balance over the last 200 years in Haifa Bay (SE Mediterranean)

Several researchers have investigated morphological changes on the south-eastern Mediterranean coast during the late Holocene. However, very few of these studies include quantitative data covering the last 200 years. In this study, topographical maps, nautical charts and aerial photographs are used to estimate the shoreline migrations and beach–nearshore sand balance over the last 200 years in Haifa Bay, Israel, the northernmost final depositional sink of the Nile littoral cell. The findings reflect two main periods. During the first period, between 1799 and 1928, human intervention along the bay’s coast was negligible, a significant coastal expansion of ∼50 to 150 m (averages of 0.4–1.2 m/year) was measured, and sand accumulation was estimated at ∼70,000 m³ annually in the beach–nearshore area. A dramatic change in the sedimentological pattern was observed during the second period, between 1928 and 2006, following the completion of Haifa Port’s main breakwater (1929–1933). During this period, most of the bay’s coast was in a steady state, with seasonal fluctuations of less than about ±20 m, and slight erosion of ∼7,000 m³ annually. These findings are consistent with previous studies which conclude that from approximately 4,000 years ago until the construction of Haifa Port, sea level remained relatively stable, and a continuous accumulation of Nile-derived sand dried up the Zevulun Plain and shifted the Haifa Bay shoreline westwards to its present location. This long-term trend ceased after completion of the Haifa Port main breakwater.     

A three-dimensional mechanistic-empirical model for geocell-reinforced unpaved roads

Geocell is a three-dimensional geosynthetic product that was originally developed to confine granular bases and minimize permanent deformation of unpaved roads. Many laboratory and field tests have demonstrated the effectiveness of geocell reinforcement in roadway constructions. However, the lack of a well-established design method that can quantify the benefit of geocell reinforcement has greatly limited the application of geocell in roadways. This paper presents the development of a three-dimensional mechanistic-empirical (M-E) model for geocell-reinforced unpaved roads. The constitutive equation for the tangential resilient modulus of the base material was derived under a general three-dimensional condition. Two analytical models were introduced to estimate the compaction- and repeated load-induced residual stresses in the base layer. These analytical models consider the material properties and construction effects in a rational way thus can be used for various situations. Finally, the proposed M-E model was validated against the test results from four unpaved road sections. Comparisons between the calculated results and the test data show that the three-dimensional M-E model effectively simulated the permanent deformation behavior of geocell-reinforced unpaved roads under a large number of load repetitions, given that the unpaved road was stable under a repeated load.     

On the African rift system,theoretical and experimental study

The East African rift system is a product of two separate activities. An ancient process (Precambrian?) resulted in brittle crustal fracture, a deep vertical tensional feature. This defined the principal fracture pattern of the continent. It was initiated by an upward diapiric stress and propagated laterally according to the principles of elastic fracture and bifurcation. Later (Jurassic-Recent) horizontal and vertical multi-stage forces caused tectonic displacements along the ancient fractures and the present rift pattern was derived. As opposed to previous models, the present concept is compatible with many conflicting opinions of previous workers (e.g. indications of tensional versus compressional or vertical forces), and is capable of explaining many moot questions.