Movements and failure of cuts and natural slopes constitute an important geotechnical problem that involves a variety of geomaterials in a variety of geological and climatic contexts, and which has a major socio-economic impact in many countries. The paper reviews the state of knowledge in this domain, examining the basic aspects of soil mechanics that are relevant to the context of slopes, the importance of water on slope behaviour, and then the different stages of slope movements: pre-failure, failure, post-failure and reactivation. Finally it is shown how the geotechnical characterisation of slope movements can be used, in particular for assessing risk associated with such movements. Emphasis is put on for the brittleness of soils and its practical implications for the progressive failure developing at the pre-failure stage and on the characteristics of post-failure movements. The influence of other factors such as creep, fatigue, destructuration, partial saturation and infiltration is also considered.

https://www.icevirtuallibrary.com/doi/pdf/10.1680/geot.2001.51.3.197

Natural slopes and cuts: movement and failure mechanisms

This paper presents a theoretical approach in which a Dalton-type mass transfer equation is used to predict the evaporative fluxes from nonvegetated soil surfaces. Soil evaporation tests were conducted in the laboratory on three different soil samples of Beaver Creek sand, Custom silt, and Regina clay. The soil surfaces were saturated and allowed to evaporate to a completely air-dried state. The actual evaporation rate for each soil surface was measured along with the potential evaporation rate for an adjacent water surface. The ratio of actual evaporation to potential evaporation or normalized soil evaporation was then evaluated with respect to drying time, soil-water content, and soil suction. The value of the normalized soil evaporation was found to be approximately equal to unity for all soils until the total suction in the soil surfaces reached approximately 3000 kPa. The rate of actual soil evaporation was observed to decline when the total suction exceeded 3000 kPa. A relationship between the actual evaporation rate and total suction was found to exist for all three soil types which appears to be unique and independent of soil texture, drying time, and water content.

The effect of soil suction on evaporative fluxes from soil surfaces

The time-dependent behavior of soils has been investigated extensively through one-dimensional and triaxial test conditions. Most of the observations in literature have focused on the determination of the time-dependent behavior of clayey soils, whereas the reported experimental studies of granular materials are few. This paper presents an up-to-date review of the various observed time- and rate-dependent phenomena that are known to exist for both clay and sand. The description is carried out separately for creep, stress relaxation, rate dependency, and structuration in laboratory experiments. All of the above-mentioned phenomena are present in both sand and clay. The time-dependent phenomena are more pronounced in clay than sand. However, sand exhibits relatively large deformations at high confining pressures because of grain crushing. Furthermore, the review revealed an essential characteristic situation for soils. That is whether the time-dependent behavior can be characterized as isotach or nonisotach...

Evaluation of Time-Dependent Behavior of Soils

Landslides are caused by a failure of the mechanical balance within hillslopes This balance is governed by two coupled physical processes: hydrological or subsurface flow and stress The stabilizing strength of hillslope materials depends on effective stress, which is diminished by rainfall This book presents a cutting-edge quantitative approach to understanding hydro-mechanical processes across variably saturated hillslope environments and to the study and prediction of rainfall-induced landslides Topics covered include historic synthesis of hillslope geomorphology and hydrology, total and effective stress distributions, critical reviews of shear strength of hillslope materials and different bases for stability analysis Exercises and homework problems are provided for students to engage with the theory in practice This is an invaluable resource for graduate students and researchers in hydrology, geomorphology, engineering geology, geotechnical engineering and geomechanics and for professionals in the fields of civil and environmental engineering and natural hazard analysis

/pdf/hillslope-hydrology-and-stability-58k559e51z.pdf

Hillslope Hydrology and Stability

Different classes of constitutive models have been developed to capture the time-dependent viscous phenomena (creep, stress relaxation, and rate effects) observed in soils. Models based on empirica...

Characterization of Models for Time-Dependent Behavior of Soils

The field observations made during a sloped excavation in a soft sensitive clay are presented. The test site is located in Saint-Hilaire, in a typical Champlain Sea clay deposit, of 30 m depth. The trench was 8 m deep and 60 × 60 m square and its slopes were at 45, 34, 27, and 18° to the horizontal. The induced pore pressures and total lateral stresses have been recorded with vibrating-wire instruments since the beginning of the excavation. The steepest, 45° slope completely failed 1 day after excavating and the 34° slope, 2 weeks after. The piezometer readings have shown that the groundwater regime was modified proportionally to the changes in total stresses; these modifications took place within a time period of 5 months, after which the heads became more or less constant. The total stress cells indicated significant rotation of the principal axes at the toe of the slopes. Stability analyses using the lowest vane strength profile gave minimum factors of safety of 1.15 for the 45° slope and 1.23 for the ...

Behaviour of a test excavation in soft Champlain Sea clay

The objectives of this paper are threefold: (I) to compare the results obtained from constant rate of strain (CRS) and controlled-hydraulic gradient (CHG) consolidation tests with those obtained from incremental loading tests, (2) to compare the experimental data obtained in this study with the results of other investigators, and (3) to determine the possibility of using either CRS or CHG testing or both in geotechnical investigations dealing with soft clays of Eastern Canada. The results of all the consolidation tests yield a unique relationship between preconsolidation pressure and strain rate. Both CRS and CHG tests performed following recommended procedures give values of the preconsolidation pressures which are higher than both those obtained in incremental load tests and those inferred from field studies. Both a simple creep law and a modified equation based on the rate process theory are found to adequately represent the observed soil response.

Controlled-strain, controlled-gradient, and standard consolidation testing of sensitive clays

The exact distributions of gravity stresses are obtained within slopes of finite height inclined at various angles, −β (β = π/2, π/3, π/4, π/6, and π/8), to the horizontal. The solutions are obtain...

Exact determination of gravity stresses in finite elastic slopes: Part I. Theoretical considerations

This paper presents the results of a 3 year monitoring program of the volumetric water content in two clay deposits on Montreal Island. The water content was monitored by means of a neutron depth moisture probe, which was lowered down in a series of 3–6 m deep, permanently installed, aluminium access tubes. These tubes are located at various distances from deep-rooted trees on two experimental sites. On the first site, a two-storey reinforced concrete building, surrounded by four rows of 15–20 m high silver maples, has suffered a differential settlement of over 150 mm. On the second site, a three-storey apartment block, surrounded on two sides by a row of 5–10 m high maples, has suffered a differential settlement of about 50 mm. The paper analyses the volumetric water content variations and compares them with both the rainfall deficits calculated for the period of observation and the elevation profiles of the building foundations. In addition, a comparison is made between the observed damages and a classi...

Foundation problems in Champlain clays during droughts. II. Case histories

Influence diagrams are presented for the gravity stresses arising in excavated finite elastic slopes inclined at various angles, −β (β = π/2, π/3, π/4, π/6, and π/8), with respect to the horizontal. These influence diagrams are calculated for a value of the earth pressure coefficient at rest, K0, equal to 0.50. Several examples are worked out and adequately illustrate the application of the influence charts and of the general solution. Finally, the results obtained from the exact solution are compared with those published in the literature, which were obtained by means of numerical (finite element) and experimental (photoelasticity) methods.

V. Silvestri

Papers

Behaviour of a test excavation in soft Champlain Sea clay

Controlled-strain, controlled-gradient, and standard consolidation testing of sensitive clays

Exact determination of gravity stresses in finite elastic slopes: Part I. Theoretical considerations

Foundation problems in Champlain clays during droughts. II. Case histories

Exact determination of gravity stresses in finite elastic slopes: Part II. Applications