Potential Slip Plane Research Articles

The use of deep counterfort drains as an effective method of stabilizing cuttings constructed in overconsolidated clays

Abstract Slope failures in cuttings constructed in heavily overconsolidated clays often occur after a period of 20 to 30 years due to the gradual dissipation of negative pore pressures and the effects of water ingress into the slopes. These slope failures are often stabilized with the installation of deep counterfort drains, which reduce the pore water pressures on the potential critical slip planes and act as a reinforcing element in the slope. Counterfort drains are normally designed using empirical methods. However there is little published data on drain performance. This paper summarizes the findings of a research project undertaken by Mouchel on behalf of the Highways Agency to assess the performance of counterfort drains installed in two highway cutting slopes that have been monitored over a number of years. The study has shown that measured pore water pressures can exceed the theoretical pressures, due mainly to what is believed to be the poor performance of the counterfort drains and that the apparent improved slope stability may be primarily due to the reinforcing effect of the drains within the slope. Further studies are required to determine the effects of construction techniques and materials used on the performance of counterfort drains before the efficiency of the existing empirical design methods can be fully assessed.

On the Bumps and Curves in the Microband Boundaries in a Channel-Die Compressed Goss-Oriented Ni Single Crystal

The crystallographic alignment of microbands in a Goss oriented single crystal was investigated by two and three dimensional electron back scatter diffraction. The microband boundaries were found to be curved instead of being perfectly flat interfaces, and the overall alignment closely matched a potential slip plane. The bumps and curved were created during subsequent deformation and, thus, deviates the microband boundaries from crystallographic nature.

Plastic deformation of wadsleyite: IV Dislocation core modelling based on the Peierls–Nabarro–Galerkin model

In this paper, we determine dislocation core structures and Peierls stresses of wadsleyite, a high-pressure mineral present in the Earth mantle. We use a Peierls–Nabarro model combined with a finite-element method in which we introduce two-dimensional generalized stacking fault energies. Several potential slip planes of wadsleyite are considered. The results show that dislocations in this mineral can exhibit complex dislocation cores with linear or non-collinear dissociation and even three-dimensional dislocation cores. The calculation of the Peierls stresses gives information on the potential activity of slip systems governing the plasticity of wadsleyite. Our study confirms experimental observations that ½〈1 1 1〉{1 0 1} is the easiest slip system in this structure at high-pressure and that [1 0 0](0 1 0) is the second easiest. Both these easily slip systems have dislocations that dissociate into collinear partial dislocations. In contrast [0 1 0] dislocations with very large Burgers vector (11.2 Å) are stabilized by complex dissociations involving four partial dislocations.

Effective grouting area of jointed slope and stress deformation responses by numerical analysis with FLAC3D

To study the grouting reinforcement mechanism in jointed rock slope, first, the theoretical deduction was done to calculate the critical length of slipping if the slope angle is larger than that of joint inclination; Second, the numerical calculation model was founded by FLAC3D, so as to find the stress and deformation responses of rock mass in the state before and after grouting. the analysis results show that the range between the boundary of critical slipping block and the joint plane that passes the slope toe is the effective grouting area (EGA). After excavation, large deformation occurs along the joint plane. After grouting, the displacements of rock particles become uniform and continuous, and large deformations along the joint plane are controlled; the dynamic displacement can reflect the deformation response of slope during excavation in the state before and after grouting, as well as the shear location of potential slip plane. After grouting, the dynamic displacement of each monitoring point reaches the peak value with very few time steps, which indicate that the parameters of the joint plane, such as strength and stiffness, are improved; the stress field becomes uniform. Tensile area reduces gradually; whole stability of the slope and its ability to resist tensile and shear stress are improved greatly.

Burgers vector determination in deformed perovskite and post-perovskite of CaIrO 3 using thickness fringes in weak-beam dark-field images

The thickness-fringe method [Ishida et al. , Philosophical Magazine 42 (1980) 453] for complete determination of the character of a dislocation Burgers vector has been performed in CaIrO 3 perovskite and post-perovskite deformed at high pressures and high temperatures. By selecting several main zone axes and determining the number of terminating thickness fringes at the extremity of a dislocation from a wedge-shaped thin-foil specimen in weak-beam dark-field transmission electron microscope (TEM) images, the Burgers vectors were unambiguously determined. The results demonstrate that [1 0 0] screw and edge dislocations on the (0 1 0) slip plane are dominant in the post-perovskite phase. Curved [1 0 0] and [0 1 0] dislocations and straight 〈1 1 0〉 screw dislocations on a potential (0 0 1) slip plane were identified in the perovskite phase as well as a high density of {1 1 0} twins. Low-angle tilt boundaries consisting of different groups of parallel edge dislocations on the {1 1 0} and (0 0 1) planes indicate diffusion-assisted climb in perovskite at high temperatures. The differences in dislocation microstructures could be due to activations of limited numbers of slip systems for post-perovskite and of a large number of multiple slip systems for perovskite, which may result in the strong crystallographic preferred orientation (CPO) in post-perovskite and the lack of CPO in deformed perovskite.

Landslides: a question of balance

The impression given in some textbooks is that a landslide can be generated by increasingthe weight of an unstable block or adding water to a potential slip plane. Thisdemonstration, which might easily be adapted as a student investigation in physics atadvanced level, was an attempt to rectify such oversimplifications and explain to studentsthe mechanics of mass movements.

Crystal morphology and dislocation microstructures of CaIrO3: A TEM study of an analogue of the MgSiO3 post‐perovskite phase

Polycrystalline CaIrO3 phase, synthesized in a cubic‐anvil type high pressure apparatus at 4 GPa and 1473 K, has been investigated using transmission electron microscopy (TEM). Individual crystallites have a platy crystal habit elongated parallel to the crystallographic a‐axis, which is the direction of the edge‐shared octahedral chain. The dislocations with Burgers vectors b = [100] and 〈u0w〉 nucleated in the CaIrO3 phase during the synthesis experiments. The potential slip plane could be (010), the most likely having with the (010)‐layered structure of IrO6 octahedrons. The crystal morphology and dislocation microstructures of CaIrO3 should provide important constraints for the discussion of the deformation behaviour and polarization anisotropy of the post‐perovskite phase in the lowermost mantle.

Vegetation Succession and its Consequences for Slope Stability in SE Spain

The effect of land abandonment as a result of changing land-use policies is becoming more and more important throughout Europe. In this case study, the role of vegetation succession and landslide activity on steep abandoned slopes was investigated. The influence of vegetation succession on soil properties over time, as well as how developing root systems affect soil reinforcement was determined. The study was carried out in the Alcoy basin in SE Spain, where the marl substratum is prone to landsliding along steep ravines. The bench-terraced slopes have been abandoned progressively over the last 50 years and show various stages of revegetation. The study was carried out at two scales; at the catchment scale long-term evolution of land-use, vegetation succession and slope failure processes were investigated. At a more detailed scale, vegetation cover, soil properties and rooting effects on soil strength were determined. Results showed that the soil has changed over a period of 50 years with respect to soil properties, vegetation cover and rooting, which is reflected in the activity of geomorphological processes. Vegetation succession progressively limits surface processes (sheet wash and concentrated overland flow) over time, whereas slopes affected by mass wasting processes increase in number. The spatial heterogeneity of infiltration increases over time, leading to increased macro-pore flow towards the regolith zone, enhancing the potential risk of fast wetting of the regolith directly above the potential plane of failure, as was concluded from rainfall simulations. In situ experiments to determine soil shear strength in relation to rooting indicated that roots contributed to soil strength, but only in the upper 0.4 m of the soil. Most failures however, occur at greater depths (1.0–1.2 m) as anchorage by deeper roots was not effective or absent. The observed initial increase in mass wasting processes after land abandonment can therefore be explained in two ways: (1) the limited contribution of anchorage by root systems at potential slip planes which cannot counterbalance the initial decline of the terrace walls, and (2) the fast transfer of rainfall to the potential slip plane by macro-pores enhancing mass movements. However, after approximately 40 years of abandonment, mass wasting processes decline.

Observation and Simulation of Root Reinforcement on Abandoned Mediterranean Slopes

The mechanics of root reinforcement have been described satisfactorily for a single root or several roots passing a potential slip plane and verified by field experiments. Yet, precious little attempts have been made to apply these models to the hillslope scale pertinent to landsliding at which variations in soil and vegetation become important. On natural slopes positive pore pressures occur often at the weathering depth of the soil profile. At this critical depth root reinforcement is crucial to avert slope instability. This is particularly relevant for the abandoned slopes in the European part of the Mediterranean basin where root development has to balance the increasing infiltration capacity during re-vegetation. Detailed investigations related to root reinforcement were made at two abandoned slopes susceptible to landsliding located in the Alcoy basin (SE Spain). On these slopes semi-natural vegetation, consisting of a patchy herbaceous cover and dispersed Aleppo pine trees, has established itself. Soil and vegetation conditions were mapped in detail and large-scale, in-situ direct shear tests on the topsoil and pull-out tests performed in order to quantify root reinforcement under different vegetation conditions. These tests showed that root reinforcement was present but limited. Under herbaceous cover, the typical reinforcement was in the order of 0.6 kPa while values up to 18 kPa were observed under dense pine cover. The tests indicate that fine root content and vegetation conditions are important factors that explain the root reinforcement of the topsoil. These findings were confirmed by the simulation of the direct shear tests by means of an advanced root reinforcement model developed in FLAC 2D. Inclusion of the root distribution for the observed vegetation cover mimics root failure realistically but returns over-optimistic estimates of the root reinforcement. When the root reinforcement is applied with this information at the hillslope scale under fully saturated and critical hydrological conditions, root pull-out becomes the dominant root failure mechanism and the slip plane is located at the weathering depth of the soil profile where root reinforcement is negligible. The safety factors increase only slightly when roots are present but the changes in the surface velocity at failure are more substantial. Root reinforcement on these natural slopes therefore appears to be limited to a small range of critical hydrological conditions and its mitigating effect occurs mainly after failure.

Deformation microstructure and orientation of f.c.c. crystals

The effect of crystallographic orientation on the microstructural evolution in f.c.c. metals with medium to high stacking fault energy is analyzed. This analysis is based on a literature review of the behaviour of single crystals and polycrystals supplemented with an experimental study of cold-rolled pure aluminium. It is generally observed that all crystallites subdivide during deformation into cell blocks and cells bounded by rotation dislocation boundaries. In general the boundaries have a macroscopic orientation with respect to the geometry of the specimen. A crystallographic analysis shows that dependent on the crystallographic orientation of the crystal the subdividing boundaries may be nearly parallel to slip planes or they may have a non-crystallographic orientation. This difference is discussed on the basis of an analysis of potential slip planes identified by a Schmid factor analysis

Limiting equilibrium and liquefaction potential in infinite submarine slopes

Abstract Stability evaluation of submarine slopes is hampered by the difficulty of making field measurements. Owing to the scarcity of detailed field data, stability is commonly assessed by assuming homogenous infinite slopes with steady seepage. For these conditions, it is necessary to measure only the slope angle, friction angle, cohesion, and pore pressure at some distance into the sediment to evaluate stability. Depth of submergence is irrelevant since it is the gradient of pore pressure in excess of hydrostatic that affects stability. The boundary conditions at the slope surface differ for submarine and subaerial slopes, and lack of appreciation of this difference has resulted in some confusion in the marine slope‐stability literature. Submarine slopes have a constant head rather than constant water pressure along the slope surface. For a condition of steady seepage in infinite submarine slopes, constant head is also required on all subsurface planes, including potential slip planes, that parallel the slope surface. As a consequence, submarine slopes with steady seepage always undergo Coulomb failure prior to liquefaction. However, if slope angles are low, submarine slopes are close to a liquefied state when failure occurs. Examination of available data shows that conditions close to those required for liquefaction are necessary for Coulomb failure in many continental shelf areas. This favors long landslide runouts and flow of sediment subsequent to failure.

Analysis of Deformation Mechanism of Particulate Material at Particle Scale

ABSTRACT In this paper the shearing mechanisms for particulate material are investigated at the particle scale. Then, the coefficients in the basic equation of Markov process, which has been explained in the previous paper (Kitamura, 1981), are quantitatively evaluated by introducing the concepts of the potential barrier and the potential slip plane. It is revealed that these concepts play important roles for the investigation of shearing process of particulate material at the particle scale. The values of these coefficients can be obtained by using the energy transferred into or out the particulate material, the initial void ratio, the grain size distribution, the coordination number and the frictional coefficient.

Mechanism of Deformation of Particulate Materials as Markov Process

In this paper, the micrometric approach which can establish the constitutive relations of particulate materials such as sands is described. In this approach the motion of particles in particulate materials is assumed to be a Markov Process which is one of the well-known stochastic processes. This assumption is reasonable because the irregularities of the particles in both size and shape, and the complicated fabric of particulate materials are considered to prohibit the deterministic approach to the motion of individual particles in the particulate materials.First, the Markov Process is explained briefly and the basic equation of the Markov Process is derived. Secondly, the Markov Process is applied to the mechanical behaviors of particulate materials, and the concepts of potential berrier and potential slip plane are introduced in order to determine the coefficients in the basic equation of the Markov Process. Thirdly, the strain of particulate materials is derived by averaging the motion of particles. Finally, the stress-strain relationship obtained from the micrometric approach is compared with the result of the drained triaxial compression test on Toyoura Sand. It is shown that this approach is very valuable in order to analyse the various mechanical behaviors of particulate materials comprehensively.

Crystallographic and fractographic studies of hydrogen- induced cracking in purified iron and iron- silicon alloys

Crystallographic and fractographic studies have been carried out on hydrogen charged purified iron and on iron-silicon alloys with silicon contents up to 3 pct. The specimens could be cracked by cathodically charging with hydrogen even without the application of an external stress. An experimental technique was developed which enabled the exposure of the fracture surface formed purely by hydrogen charging, and to contrast this with an adjacent mechanically induced fracture surface. In the case of purified iron, hydrogen induced cracks are found to occur on potential slip planes whereas in the case of iron-3 pct silicon, the crack follows the observed cleavage plane. Intermediate silicon content alloys showed transitional behavior. In agreement with the variation of crack plane in the alloys, the fracture surface appearances was also drastically different, reflecting the change in intrinsic toughness with alloy content. The observed transition from slip plane cracking to cleavage plane cracking was found to occur near a silicon content of 0.7 pct. The observed behavior is discussed in terms of how the intrinsic toughness of the ironbased lattice affects how hydrogen-induced cracks are formed.

Strengthening mechanisms and brittleness in metals

The basic strength of the various crystalline engineering materials depends in a sensitive way on the imperfection structure which exists in the nature and arrangement of the atoms composing them. For example, nominally pure aluminium is observed to have a tensile yield strength at room temperature varying between ∼ 100 psi , fora single crystal produced in the laboratory, and ∼ 8,500 psi , for a fine-grained polycrystal containing a finer dislocation substructure. The yield strength may be increased to ∼ 90,000 psi by going to the strongest aluminium alloy. These values compare with an estimate of the limiting theoretical yield strength of 830,000 psi for a perfect single crystal with a potential slip plane at 45° to the tensile axis. Pure iron crystals containing dislocations have a yield strength of 1,500 psi . Extremely fine-grained (eutectoid) steel wires exhibit tensile yield strengths as high as ∼ 605,000 psi . Essentially perfect iron crystal whiskers have shown a tensile strength of 1,800,000 psi and this value compares favourably with a limiting theoretical strength of ∼ 2,060,000 psi . The foregoing values apply at room temperature and at reasonably slow strain rates, on the order of 10 −2 min −1. The values for iron change more with temperature and strain rate than do those for aluminium. Iron can be induced to fail by brittle cleavage and aluminium, thus far, cannot. These last-mentioned differences are characteristic of the body-centred cubic crystal structures as compared with the face-centred cubic ones, respectively. The general priciples underlying such ranges in strength levels and behaviour may be formulated in terms of the atomic architecture.