Utilization of lime,slag and fly ash for improvement of a colluvial soil in New South Wales,Australia

In Australia, colluvial soils form large terrains which are often subjected to considerable erosion and mass movement. This study presents a laboratory evaluation of the improvement effected by hydrated lime, milled blast furnace slag and fly ash on a fine grained (erosive) colluvial soil in New South Wales, Australia. Geotechnical tests were conducted to determine the compaction and consolidation characteristics and the compressive and shear strength properties of the blended and natural soil specimens. The effect of these additives on the Atterberg limits and pH levels is also investigated. As large amounts of fly ash and steel slag are produced in New South Wales, it is economically attractive to utilize these industrial by-products for ground improvement rather than employing conventional methods such as lime treatment. This study demonstrates that for the colluvial soil tested, milled slag is the most effective in terms of improving the internal friction angle of the treated soil, while lime is the most suitable for achieving the optimum compressive strength. Non-pozzolanic fly ash is found to be inappropriate as a soil improving agent. The cost of ground treatment using the various additives is also estimated and compared.     

Erosion rates in the southern oregon coast range: Evidence for an equilibrium between hillslope erosion and sediment yield

The relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes. In landscapes containing hillslopes crenulated by alternating topographic noses and hollows, estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows. Hollows act as local traps for a portion of the colluvium transported down hillslopes, and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area. Analysis of colluvial deposits in nine Oregon Coast Range hollows has yielded average colluvial transport rates into the hollows of about 35cm³cm^?1yr^?1 and average bedrock lowering rates of about 0.07 mm yr^?1 for the last 4000 to 15000 yr. These rates are consistent with maximum bedrock exfoliation rates of about 0.09 mm yr^?1 calculated from six of the hollows, supporting the interpretation that exfoliation rates limit erosion rates on these slopes. Sediment yield measurements from nine Coast Range streams provide similar basin-wide denudation rates of between 0.05 and 0.08mm yr^?1, suggesting an approximate steady-state between sediment production on hillslopes and sediment yield. In addition, modern sediment yields are similar in basins varying in size from 1 to 1500 km², suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape.     

Slope process change and colluvium deposition in Swaziland: An SEM analysis

Electron microscope analysis of sixty samples taken from six colluvium sites in Swaziland has shown that the quartz grains exhibit marked edge abrasion in the uppermost beds of exposures. This edge abrasion is lacking in the lower beds in all sections examined and indicates slope process change during colluvium deposition. A model of slope evolution is provided, in which slope erosion progressively brings about more channelling and causes greater surface roughness because of the exhumation of more core stones and differentially weathered rock. This roughness causes increased edge abrasion.     

Quaternary colluvium in west-central Anatolia: sedimentary facies and palaeoclimatic significance

The Quaternary colluvial aprons in Lake Eğirdir area, Taurus Mountains, consist of steep coalescent fans, up to 17–20 m thick and 350–450 m in plan-view radius, and the sedimentary succession comprises four lithostratigraphic divisions. The basal red–brown colluvium consists of a chaotic, bouldery fan-core rubble covered with bedded, openwork to matrix-rich gravel, whose deposition is attributed to rockfalls and cohesive debrisflows, with minor grainflows and sheetwash processes. The middle part of this division contains interbeds of early Pleistocene tephra. The overlying light-grey colluvium consists of bedded gravel with numerous palaeogullies and its deposition is attributed to waterflow, rockfalls and cohesive debrisflows. The younger, medium-grey colluvium consists of stratified pebbly sand interspersed with cobble/boulder gravel and its deposition is attributed to sheetwash processes accompanied by rockfalls and wet snowflows/slushflows. A bulk-pollen radiocarbon date indicates Late Würm age. The youngest, yellow–grey colluvium consists of bedded, mainly pebbly and openwork gravel, whose deposition is attributed to dry grainflows, rockfalls and minor cohesive debrisflows. Based on the sedimentary facies assemblages and available isotopic dates, the four colluvial divisions are correlated with the following stages of the region's climatic history: (1) the latest Pliocene to Early Pleistocene stage of warm–humid climate with pronounced phases of drier conditions; (2) the Late Pleistocene stage of colder climate, with alternating phases of higher and lower humidity; (3) the last glacial (Würm) stage of coldest climate; and (4) the Holocene stage of warm semi-arid climate. It is concluded that colluvial depositional systems bear a valuable proxy record of climatic changes and regional geoclimatic differences.     

Late Pleistocene tectonic-geomorphological development within a passive margin — The Cariatá trough, northeastern Brazil

Studies on the geomorphological evolution of the South American passive margin have been based on the pediplanation model, which predicts that its morphology is a response to regional uniform uplift and concomitant development of erosion surfaces. We combined remote sensing, geological mapping, lithostratigraphic and facies analyses, and luminescence dating in the Cariatá trough, northeastern Brazil, in order to determine how brittle tectonics and climate influenced colluviation and the shaping of local landforms in the Quaternary. Our work indicates that Cariatá is an asymmetrical trough  40 km long,  25 km wide, 250–550 m deep, and delimited by ENE–WSW-trending faults to the north and south. We recognized an ENE–WSW-oriented compression related to a strike-slip faulting regime, which corresponds to the present-day stress field in the region. This faulting event led to the deposition of colluvial fans, shed from adjacent uplifted crustal blocks, in a tectonically controlled depression. The colluvial succession is  45 m thick and presents two facies assemblages that filled the southern and, in particular, the northern borders of the trough: non-cohesive debrisflow and mudflow deposits. Optically stimulated luminescence dates of the sedimentary infill yielded ages at 224–128 ka and 45–28 ka, dominated by debrisflow and mudflow deposits, respectively. These ages may be over-estimated due to poor bleaching of colluvium, but they and our field data suggest that the margins of the trough were tectonically uplifted and eroded twice in the Late Pleistocene. The spasmodic colluvial accretion reflects the occurrence of high-magnitude, low-recurrence episodes probably associated with climate shifts in a semi-arid hillslope system. It follows that the present-day low-lying piedmont in which the Cariatá trough occurs is a juxtaposition of surfaces of various ages. This trough may have counterparts across the region. These conclusions do not corroborate the application of the cyclical pediplanation hypothesis in the area.     

Landslide hazard of slopes of sewage treatment plant lagoons constructed in colluvium deposits

A landslide occurred in colluvial deposits at one of the lagoons of Wadi Es-Sir Sewage Treatment Plant Project (under construction) in Jordan. This paper summarizes the geotechnical investigations conducted at three lagoon sites in the project area including the failed lagoon. Results of stability analyses are presented along with recommendations to stabilize the slided lagoon and surrounding areas.     

Coincidence and spatial variability of geology,soils, and vegetation,mill run watershed,Virginia

The Mill Run watershed is a structurally-controlled synclinal basin on the eastern limb of the Massanutten Mountain complex of northwestern Virginia. Bedrock contacts are obscured by coarse sandstone debris from exposures near basin divides. Colluvium blankets more than half the basin, masking geomorphic surfaces, affecting vegetation patterns, and contributing to the convexity of the alluvial, terrace, pediment and erosion surfaces. Examination of the bedrock geology, geomorphology, soils and vegetation shows distinct distributional correspondences. Vegetation is strongly interdependent with geomorphology, bedrock geology, and soils. On convex colluvial slopes, mixed hardwood forests are most common. In concave coves and deep gorges, mixed hardwoods are replaced by conifers. In thin colluvium, in poorly developed soils, and on blockfields, chestnut oak is singularly prevalent. Conifers dominate shaley bedrock areas. Soils and surficial sediments have a major effect on near-surface hydrology. During wet seasons, cemented horizons in the subsurface cause temporary saturation in the superjacent horizons; lateral movement of soil-water effectively eliminates a vertical component of ground-water recharge. Vegetation is strongly dependent on water availability and thus reflects the distribution of subsurface barriers and sediment-soil fades changes.     

The ‚loess’︁ section at Borden,Kent, SE England

A 5.3m profile originally described as loess with a buried interglacial soil is reinterpreted from petrographic evidence and thermoluminescence dating as a Holocene colluvial accretionary soil. Mineralogical analyses of coarse silt (16–63 μm) fractions suggest that most of the silty colluvium was derived from weathered Thanet Beds upslope, though some loess was incorporated during the final depositional phase. Thin sections show that clay illuviation occurred penecontem-poraneously with deposition of colluvium. Thermoluminescence properties suggest partial optical bleaching of the grains during rapid deposition, which is consistent with a Holocene colluvial origin.     

Aggregate stability and colluviation in the Luxembourg ardennes; an experimental and micromorphological study

To obtain a better understanding of the colluvial deposits in two catchments in the Luxembourg Ardennes, structural aggregates from forest and farmland soils were subjected to the impact of falling water drops. The changes that the aggregates underwent and the material eroded from them were studied in thin section. Predictably, forest aggregates were more resistant to water-drop impacts than those from farmland. Farmland aggregates tended to slake upon wetting and to break down into many micro-aggregates having a size-frequency distribution similar to that of the micro-aggregates in the undisturbed soil. The forest aggregates were eroded slowly under water-drop impact, losing material from their surfaces or occasionally shearing into several smaller equally resistant aggregates. The size-frequency distributions of the break-down products differed from the micro-aggregates in the untreated aggregates or original forest soil, probably because of bonding by organic material. The differing composition of the aggregates points to the importance of oriented clay and planes for the lack of stability of the farmland aggregates. It can be concluded that agricultural colluvium is probably largely deposited by processes other than splash and that splash is an important process, but not the only one, in the formation of colluvium under forest.     

The deposition of stony colluvium on clay soil as a cause of gully formation in the Rif Mountains,Morocco

V-shaped gullies are formed on slopes in the Rif Mountains where stony colluvium covers a truncated Luvisol in finegrained, early pleistocene slope deposits. The colluvium resulted from large-scale deforestation of summit areas in recent times. A number of properties related to the response of soil material to rainfall were investigated. Colluvium has a high infiltration capacity compared to the Luvisol. Consequently, the deposition of colluvium reduced overland flow and erosion by surface wash. Gully-forming processes on the other hand were activated by the superposition of permeable over impermeable material.