Clay Slopes Research Articles

An Investigation on Stability Analysis of Cut Slopes in Clays

When a cut slope is constructed in a saturated clay ground, pore water pressure decreases instantly due to unloading. With time, the ground will expand gradually and the pore water pressure will rise towards long-term state. During this process, air may be absorbed into the slope; consequently, an unsaturated zone appears in the vicinity of the ground surface. In simulating such a swelling process, most existing FE methods neglect the air ingress into the slope and the whole analysis region is assumed saturated. However, this assumption leads to erroneous results, i.e., the factors of safety for assumed slip circles may increase with time; this is discussed in the first half of the text on the basis of illustrative examples. It is inferred that the erroneous results come from the improper assumption of the only saturated analysis. Hence, in the last half of the paper we employ a three-phase saturated-unsaturated model incorporated with an elasto-plastic constitutive relation to take into account the appearance of the unsaturated zone during swelling. This model is applicable not only for saturated problems but also for unsaturated ones. The results indicate that the proposed method can correctly represent the soil behavior of cut slopes, therefore, leading to the conclusion that the only saturated analyses are not adequate for cut slope problems.

Delayed collapse of cut slopes in stiff clay

Delayed failure of railway cutting slopes in stiff clays excavated in the nineteenth and early twentieth centuries has been studied for some forty years. Known failures have generally been deep-seated. More recently failures have been a problem in the slopes of motorway cuttings and embankments, although generally these have been shallow. The average operational strength at failure in these slides has been significantly less than the peak strength, and progressive failure has been postulated as the probable cause of this. Progressive failure can now be analysed using advanced numerical techniques. A series of coupled finite element analyses have been conducted assuming strain-softening soil with properties based on the Brown London Clay, and the results are reported. They show that progressive failure is considerable, and fully explain the observed field behaviour. The delays experienced in the field are also recovered by the analyses. Progressive failure is generated primarily by the high lateral stresses in the soil prior to excavation. The rupture surface generated spreads horizontally from the toe as the soil swells, and differs significantly from the critical surface predicted by limit equilibrium analysis. The average strength on it at collapse is significantly lower than that obtained by back analysis by limit equilibrium methods. It becomes lower as lateral stress increases, but the effect is compensated by the increasing depth of rupture. The roll of the hydraulic surface boundary condition, which is controlled by climate, is important in controlling collapse. The implications of the findings for monitoring and for remedial works in existing slopes is discussed.

Engineering geology of the Agaba-Ras El Naqab highway re-alignment, Jordan

A detailed geological investigation was conducted along the section of highway between Station 00 and Station 88 km of the proposed Aqaba to Ras El Naqab highway in Jordan including the Ras El Naqab Escarpment (Station 75–80 km). The Escarpment area is characterized by soil-rock slope failures, and a complex geological pattern of rock units and faults in a rugged terrain. The geological sequence along the highway alignment consists initially of the Kurnub Sandstones Group and mainly within the Upper and Lower Ajlun Formations. The mechanics of movements associated with the Kurnub Sandstone Group include erosion and toppling of sandstone blocks where undercut. Movements manifested within the Upper Ajlun Formation are due to the opening of joints, formation of gulls, cambering, toppling, sliding, rockfalls and the dislocation of limestone blocks. These slope failures associated with the Lower Ajlun Formation are relatively small while large-scale movements and slips occur within the marl and clay. After extensive slope stability analyses were performed an alignment for the proposed road, including the Escarpment stretch was selected, that also included any special construction considerations. Three locations were selected for the detailed slope stability analyses; initially the critical soil parameters were determined assuming that the slopes are marginally stable. Alternate measures for the stability were then considered and the relative effects on the safety factor were analyzed to determine optimum solutions for locating the proposed road. The recommended alignment is situated adjacent to the existing road and located on the west up to Station 75 + 000 km and from Station 76 + 000 km to Station 79 + 700 km. Between Station 75 + 000 km and Station 79 + 700 km to the crest of the Escarpment the new alignment is located east of the existing road. Design criteria adopted for slopes constructed within the Upper Ajlun Formation include protection of exposed marl and clay slopes, sealing of open joints and fractures within the limestone and minimizing the surface areas of marls and clays in slope faces. Criteria for design of slopes within the Lower Ajlun include those presented for the Upper Ajlun as well as proper design of slope angles, placement of interceptor drains, and specific construction techniques to be adopted where mantle creep is anticipated. Features associated with the Kurnub Sandstones require the installation of surface drainage measures as well as revetment techniques to prevent encroachment of rock-block falls onto the highway or into drainage channels.

Revegetation techniques on clay soil slopes in northern Italy

Several standard techniques currently used in the reclamation and revegetation of former quarry land in Italy's northern Apennine region were compared. The trial site, a 40-degree slope with clay soil, high pH and a little organic matter, was arranged in a randomized block design. The techniques assayed were hydro-seeding+tillage, hydro-seeding on sod, straw mulch+tar, jute mats+tillage+hydro-seeding, jute mats+tillage and a control. Each plot was enriched with equal amounts of chopped straw (120 g m−2), worm compost (140 g m−2) and the fertilizer Biosol® (140 g m−2); the binder Terravest® (36 g m−2) was also used in the three hydro-seeded plots. Ground cover, species, runoff and erosion were compared in each treatment. The overall 3-year data indicate significant differences in the treatments tested. There is a clear distinction between the treatments that promoted good grass cover growth and checked erosion (straw and tar, jute on tilled soil, and hydro-seeding on jute and tilled soil) on the one hand and the hydro-seeded treatments (on sod and on tilled soil), which showed no differences from control, on the other. © 1997 John Wiley & Sons, Ltd.

Revegetation techniques on clay soil slopes in northern Italy

Revegetation techniques on clay soil slopes in northern Italy

Stabilization of Shallow Slope Failures with Lime Piles

Lime piles essentially consist of boreholes filled with lime. They have been used to stabilize slopes in many countries worldwide but have not been adopted as a standard means of stabilization in any country. The literature on the subject makes several claims about the way lime piles stabilize the soil. However, the reported results of experimental work are in some cases contradictory and are too few to facilitate appropriate engineering judgment of the stabilizing mechanisms. Research at Loughborough University, United Kingdom, has investigated the use of quicklime piles in the context of stabilization of shallow slope failures in clay slopes. The stabilizing mechanisms observed in a series of laboratory and field investigations are ( a) increased strength of an annular zone of clay surrounding the pile caused by lime-clay reaction, ( b) clay dehydration, ( c) generation of negative pore-water pressure, ( d) over-consolidation of the soil in the shear plane, and ( e) pile strength. The idea of lateral consolidation of the clay surrounding the pile as a result of physical pile expansion has been shown not to occur in the case of augured quicklime piles sealed with a clay plug at the surface. Data are presented to quantify each of the stabilization mechanisms and advice is given on how to use the data in design. It is concluded that lime piles provide a potentially valuable addition to the techniques available for shallow slope stabilization and are particularly suitable for sites with access problems.

Centrifuge modeling of geotextile-reinforced steep clay slopes

When on-site soil is not granular, substantial cost savings can be achieved if a stable, steeply sloped, reinforced retaining system, backfilled with on-site fill can be sustituted for a vertical retaining wall with granular fill. Centrifuge modeling was used in this work to investigate the failure and prefailure behaviour of 14 reduced-scale geotextile-reinforced steep model slopes of 45, 63.4, 71.6°, backfilled with cohesive soil and constructed on either firm or rigid foundations. The overall performance of model slopes on firm foundations was found to be better than that of similar models on rigid foundations. A stability analysis, using the Bishop simplified method incorporating reinforcement, was found to be a good predictor of the behaviour of models. Key words: reinforced soil, centrifuge modeling, geotextile, retaining structure, slope stability.

The role of lime migration in lime pile stabilization of slopes

Abstract Lime piles, which essentially consist of holes in the ground filled with lime, have been successfully used worldwide for the in situ treatment of failing clay slopes. The literature on the technique does not, however, permit a full explanation as to why lime piles work or how to design them. It is widely reported that migration of the lime from the piles into the surrounding clay provides the major stabilizing mechanism. This paper aims to review the literature on lime migration from piles and to report the results of recent research at Loughborough University to determine migration mechanisms from compacted quicklime piles. Potential applications are then discussed in the light of the findings. Hydroxyl (OH - ) ion migration by diffusion processes in intact clay is shown to be limited by high reactivity to approximately 20-30 mm. Nevertheless hydraulic transport via dehydration cracking or other discontinuities in the clay mass could result in migration extending for far greater distances. Calcium (Ca 2+ ) ion migration, would be expected to occur over distances greater than 1 m in ten years. Thus while full clay stabilization might only occur to a limited degree, modification of the clay is likely to be widespread. Mineralogical changes indicate a strength gain equivalent to that of lime mixed with clay at the initial lime consumption (Eades & Grim 1966) value plus 2% and cured for 28 days.

A visco-plastic model for slope analysis applied to a mudslide in Cortina d'Ampezzo, Italy

Abstract This paper describes a visco-plastic model which, using recorded groundwater levels, is capable of simulating the velocity trend in landslides. It also deals with the phenomenon of shear strength regain that occurs in montmorillonitic clays constituting slopes during periods when landslides are stationary. The model has been validated with long-term observations of a clay slope affected by a mudslide.

The Effect of Raindrop Impact and Sheet Erosion on Infiltration Rate and Crust Formation

AbstractSoil crust formation can result from the beating action of falling drops (structural crust) or the deposition of entrained eroded suspension in shell flow (deposional crust). To determine the relative importance of the two processes, an experiment was carried out with rainfall simulation under laboratory conditions. Clay soil exposed to the beating action of rain drops produced sheet erosion, which was deposited on a layer of clean sand downslope of the same continuous slope. The thin crust that was formed on the two parts of the slope, the clay and the sand, reduced the infiltration rates in time to values of 1 to 5 mm h−1. In comparison with the uniform clay slope, the main difference was the longer time needed to reach the low infiltration rates. Preventing the sand part from any rain impact beating extended the time needed to obtain the low infiltration rates that were nearly the same as those of the clay slope. The results provoke the question is the common theory of compacted crust by rain impact such an important factor?

Softening and Creep of a Compacted Clay Slope

Research Article| January 01, 1996 Softening and Creep of a Compacted Clay Slope* ROBERT W. DAY ROBERT W. DAY Chief Engineer American Geotechnical, 5764 Pacific Center Boulevard, Suite 112, San Diego, CA 92121 Search for other works by this author on: GSW Google Scholar Environmental and Engineering Geoscience (1996) II (2): 255–261. https://doi.org/10.2113/gseegeosci.II.2.255 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation ROBERT W. DAY; Softening and Creep of a Compacted Clay Slope. Environmental and Engineering Geoscience 1996;; II (2): 255–261. doi: https://doi.org/10.2113/gseegeosci.II.2.255 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyEnvironmental and Engineering Geoscience Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.

Physico-chemical effects on the behaviour of a coastal mudslide

Previous work has shown that the type of clay mineral, the valency state of adsorbed cations and the salt concentration of pore-water influences the residual strength of clays. Residual strength can therefore be modified through weathering reactions, clay mineral alterations and fluctuations in groundwater chemistry. This has implications for studies of the seasonal and long-term behaviour of clay slopes. The paper presents results from an investigation of a shallow coastal mudslide on the south coast of England which attempts to isolate the influence of physico-chemical processes on mudslide behaviour. Fluctuations in groundwater chemistry coincided with temporal movement patterns. Low pore-water ion concentrations were apparent immediately before seasonal mudslide reactivation or periods of high activity. Laboratory tests showed that low pore-water ion concentrations resulted in low residual shear strength; higher concentrations observed after movement events led to increases in residual strength. Des travaux antérieurs ont montré que le type de minéral argileux, l'état de valence des cations adsorbés et la concentration en sels de Peau interstitielle influent sur la résistance résiduelle des argiles. Les altérations superficielles du matériau, les altérations des minéraux argileux et toute modification de la chimie des eaux souterraines sont donc susceptibles de modifier la résistance résiduelle. Ceci pent avoir des implications importantes dans l'étude du comportement saisonnier et à long-terme des talus argileux. L'article présente les résultats obtenus sur une étroite pente boueuse en glissement, située sur la côte sud de l'Angleterre. Ces résultats ont permis de mettre en évidence l'influence des processus physico-chimiques sur le comportement de la bone. Les fluctuations de la chimie des eaux souterraines coïncident avec les mouvements temporels. La concentration ionique de l'eau interstitielle devient faible juste avant toute réactivation saisonnière du glissement boueux ou avant toute période de grande activité. Les essais de laboratoire montrent qu'une faible concentration ionique de Peau interstitielle se traduit par une résistance résiduelle faible; les plus fortes concentrations observées après les mouvements du talus favorisent un accroissement de la résistance résiduelle.

Stability of compacted clay slopes using a nonlinear failure envelope

Stability of compacted clay slopes using a nonlinear failure envelope

Surficial Stability of Compacted Clay: Case Study

The factor of safety for surficial stability is highly dependent on the effective cohesion. This study shows that even when triaxial tests are performed at effective pressures as low as 13.8 kPa (2.0 psi), the results may still provide effective cohesion intercepts that are too high. The reason is that the compacted sandy clay behaves as an overconsolidated soil, with effective stress paths bending to the right with low to negative A‐values. As demonstrated by this case study of a surficial failure, the calculated factor of safety was 1.33 using the extrapolated value of effective cohesion of 5.3 kPa (110 psf). An unconfined submerged triaxial test resulted in a lower effective strength envelope, which provided a factor of safety of 0.97 for the surficial failure. There are two factors that can increase the surficial stability of a compacted clay slope: aging and root reinforcement. For the surficial failure, the effect of aging was minor and root reinforcement was not a factor in this case, because the r...

Slow movement investigations in clay slopes : Bertini, T; Cugushi, F; D'Elia, B; Lanzo, G; Rossi-Doria, M Proc 6th International Symposium on Landslides, Christchurch, 10–14 February 1992V1, P329–334. Publ Rotterdam: A A Balkema, 1992

Slow movement investigations in clay slopes : Bertini, T; Cugushi, F; D'Elia, B; Lanzo, G; Rossi-Doria, M Proc 6th International Symposium on Landslides, Christchurch, 10–14 February 1992V1, P329–334. Publ Rotterdam: A A Balkema, 1992

Geogrid Reinforced Clay Slopes in a Test Embankment

A 12 m high geogrid reinforced cohesive soil test embankment with 45 degree side slopes has been built near Devon, Alberta, Canada. The embankment has four test sections: three are reinforced with different geogrids, and one section is unreinforced. The test sections were instrumented with strain gauges and inductance coils on the geogrids) and extensometers, inclinometers and piezometers in the soil. The design, construction and instrumentation of the test embankment is described. Field measurements, taken from the slopes over a seven year period during and after construction, are presented and discussed. The development and the distribution of geogrid strains, soil deformations and pore pressures are presented to show the performance of the reinforced cohesive soil slopes.

Environmental impact of soil erosion under different cover and management systems

Runoff, soil loss and physical chemical composition of surface soil, runoff water and eroded sediment were measured for three erosive rainstorms of the 1988 Autumn-Winter season, on clay soil slopes (Typic Chromoxeret) under different cover and management systems in a locality of Sicily. Four years reconsolidated natural grass-sod ( Avena fatua and Lolium tumulentum), natural grass-sod with implanted forage shrubs ( Atriplex halimus) and natural grass-rod afforested with Pine trees ( Pinus halepensis), reduced significantly runoff and soil loss in comparison with tilled fallow following four years durum wheat cultivation. While differences in runoff and soil loss between reconsolidated systems were not significant, the higher biomass yield (Stringi et al. 1991) and the better soil cover (Chisci et al. 1991) of the Atriplex system, increased O.M. content of the soil and prevented soil erosion under very intense rainstroms of the semiarid Mediterranean area. The comparison of textural and aggregate grain-size composition of surface soil and sediment confirmed that physico-mechanical composition of sediment detached and transported by over-land flow on clayey soils is better estimated by pseudo-textural grain-size composition of surface soil (Chisci et al. 1989) than from textural composition. Soil loss amounts, and O.M., N and P enrichment ratios, combined in a specifically devised Environmental Impact Index (EI), demonstrated the excellent environmental protection value of reconsolidation of arable soils. However, Pinus system was somewhat less efficient than Atriplex and good natural grass-sod systems.

Modelling the risk of progressive slope failure: A new approach

Abstract This paper is concerned with the development of a new, simplified model of progressive slope failure within a probabilistic framework. Moreover, the change in the probability of sliding or overall failure based on ‘conditional’ or observed events can be simulated. Such a simulation can be useful for updating the risk of sliding atvarious stages during the life of a slope. The model requires the definition of an appropriate safety margin representing the event of progressive failure up to a certain position along the slip surface. The probabilities of such events may be calculated if the shear strength parameters are represented by appropriate random fields. In contrast to a previously established progressive failure model, the calculation of joint or bivariate probabilities associated with pairs of events is not required. Therefore, the new model is very convenient for performing the calculations of risk of progressive failure. It works well when compared to the more rigorous bivariate model which has previously been published. The results for an example problem concerning the short-term stability of a slope in saturated clay are compared to corresponding results from the previous, more rigorous model.

Closure to “ Surficial Stability of Compacted Clay Slopes ” by Robert W. Day and Gregory W. Axten (April, 1989, Vol. 115, No. 4)

Closure to “ <i>Surficial Stability of Compacted Clay Slopes</i> ” by Robert W. Day and Gregory W. Axten (April, 1989, Vol. 115, No. 4)

Discussion of “ Surficial Stability of Compacted Clay Slopes ” by Robert W. Day and Gregory W. Axten (April, 1989, Vol. 115, No. 4)

Discussion of “ <i>Surficial Stability of Compacted Clay Slopes</i> ” by Robert W. Day and Gregory W. Axten (April, 1989, Vol. 115, No. 4)