Canadian Geotechnical Journal
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An energy approach for assessing seismic liquefaction potential An energy method for assessing liquefaction potential of granular soils was developed based on laboratory tests and observational data obtained in past major earthquakes. Cyclic triaxial and cyclic simple shear tests were conducted and the results show that a unique relation exists between the dissipated energy during cyclic load and the excess pore pressure that eventually led to liquefaction failure. This unique relation has been combined with an energy attenuation equation to develop a criterion for defining the liquefaction potential of a site. Parameters for the criterion were evaluated from 136 sites involved in 13 major earthquakes over the world. A comparison was made between the energy method and the commonly used stress method. The energy method was found to be simpler to apply and more reliable. Key words: energy, earthquake, liquefaction potential, standard penetration test, laboratory cyclic test, excess pore pressure, granular soils, case records.
Canadian Geotechnical Journal - Tập 27 Số 3 - Trang 320-329 - 1990
Ultimate bearing capacity of foundations on layered soils under inclined load The ultimate bearing capacity of footings resting on subsoils consisting of two layers has been investigated for the cases of a dense or stiff layer overlying a weak deposit, and a loose or soft layer overlying a firm deposit. The analyses of different modes of soil failure are compared with the results of model tests on circular and strip footings on layered sand and clay soils.
Canadian Geotechnical Journal - Tập 15 Số 4 - Trang 565-572 - 1978
Remote sensing based assessment of hazards from glacier lake outbursts: a case study in the Swiss Alps Glacier lakes are a common phenomenon in high mountain areas. Outbursts from glacier lakes have repeatedly caused the loss of human lives as well as severe damage to local infrastructure. In several high mountain ranges around the world, a grave uncertainty about the hazard potential of glacier lakes still exists, especially with respect to the effects of accelerating rates of glacier retreat as a consequence of atmospheric warming. Area-wide detection and modeling of glacier lake hazard potentials is, therefore, a major challenge. In this study, an approach integrating three scale levels allows for the progressive focus on critical glacier lakes. Remote sensing methods for application in glacier lake hazard assessment are presented, and include channel indexing, data fusion, and change detection. Each method matches the requirements of a certain scale level. For estimating potential disaster amplitudes, assessments must be made of maximum discharge and runout distance of outbursts floods and debris flows. Existing empirical relations are evaluated and complementary ones as derived from available data are proposed. Tests with observations from a recent outburst event from a moraine-dammed lake in the Swiss Alps show the basic applicability of the proposed techniques and the usefulness of empirical relations for first hazard assessments. In particular, the observed runout distance of the debris flow resulting from the outburst does not exceed the empirically estimated maximum runout distance. A list of decision criteria and related remote sensing techniques are discussed in conclusion. Such a list is an essential tool for evaluating the hazard potential of a lake. A systematic application of remote sensing based methods for glacier lake hazard assessment is recommended.Key words: glacier lake outburst, hazard potential, remote sensing, empirical parameters.
Canadian Geotechnical Journal - Tập 39 Số 2 - Trang 316-330 - 2002
Field hydrological monitoring of a sloping shallow pyroclastic deposit Many mountainous areas in Campania, southern Italy, are characterized by steep slopes covered by unsaturated volcanic deposits. Shallow landslides are frequently triggered by intense and persistent rainfall events, often turning into debris flows that cause huge damage and casualties. Field hydrological monitoring is a useful tool to develop consistent models of slope response to rainfall, in terms of soil suction and moisture, and to define landslide triggering conditions. This is one of the reasons why since 2002 field monitoring is being carried out in Cervinara, around 50 km northeast of Naples. Since October 2009, rainfall height, soil suction and water content at several locations and depths along the slope are automatically being monitored. The data collected help to demonstrate the effectiveness of such a system for better understanding the hydrological processes occurring in similar slopes of Campania, allowing to distinguish between seasonal suction fluctuations, related to long-term meteorological forcing, and short-term response to rainstorms.
Canadian Geotechnical Journal - Tập 53 Số 7 - Trang 1125-1137 - 2016
Effects of layering on triggering mechanisms of rainfall-induced landslides in unsaturated pyroclastic granular soils Rainfall-induced landslides are widespread in shallow layered granular soil deposits. In many cases, slope instability is related to the decrease of suction during rainwater infiltration. However, the contrasts in the unsaturated hydraulic properties of the soils deeply affect the infiltration process, thus influencing slope failure. Coarse-textured soil layers embedded between finer ones may initially confine the process within the overlying finer layers, delaying the infiltration and eventually inducing lateral flow diversion. Nonetheless, depending on the state variables at the beginning of rainfall as well as on rainfall characteristics, the coarser layers may or may not have a positive effect on stability. The results of research based on advanced geotechnical characterization, physical and numerical modeling, and field monitoring have been analyzed to investigate the effects of layering on slope stability.
Canadian Geotechnical Journal - Tập 56 Số 9 - Trang 1278-1290 - 2019
Zeta potential of clay minerals and quartz contaminated by heavy metals Laboratory and in situ test results show that electrokinetic decontamination is a promising subsurface decontamination method. However, it has also been reported that several problems arise, such as reverse flow and pH gradient across the anode and the cathode during the electrokinetic decontamination process. Variation in pH alters the zeta (ζ) potential of soils, which is one of the factors affecting the efficiency of contaminant removal by the electrokinetic method. The magnitude of the ζ potential controls the fluid flow rate, whereas its sign controls the flow direction. However, research on how the ζ potential of soils changes under various chemical conditions is limited. In this paper, the effect of pore-fluid chemistry on the ζ potential of kaolinite, montmorillonite, and quartz powder is determined with NaCl, LiCl, CaCl2 ·2H2 O, MgCl2 ·6H2 O, CuCl2 , CoCl2 , ZnCl2 , AlCl3 , and Pb(NO3 )2 . The test results reveal that the ζ potential of the minerals with alkali and alkaline-earth metals changes according to the diffuse electrical double-layer theory. The hydrolyzable metal ions produce two points of zero charge (PZCs), one of which is that of the soil; and the other, that of hydrolyzable oxide. The ζ potential of minerals with hydrolyzable metal ions becomes increasingly positive and reaches its maximum value at neutral pH. It then decreases and again reaches very negative values at alkaline pH values (pH ∼ 10), depending on ion concentration and the bulk precipitation pH of hydrolyzable metals as hydrolyzable oxides. On the basis of the results of this study, it is recommended that the ζ potential of the soils be determined before electrokinetic decontamination.Key words: alkaline-earth metals, electrokinetic decontamination, heavy metals, zeta potential.
Canadian Geotechnical Journal - Tập 42 Số 5 - Trang 1280-1289 - 2005
Hydraulic conductivity of bentonite-sand mixtures The use of bentonite alone or amended with natural soils for construction of liners for water-retention and waste-containment facilities is very common. The importance of bentonite content in reducing the hydraulic conductivity of liners is well recognised. The study illustrates the role of the size of the coarser fraction in controlling the hydraulic conductivity of the clay liner. It has been shown that at low bentonite contents the hydraulic conductivity of the liner varies depending on the size of the coarser fraction apart from clay content. At a given clay content, the hydraulic conductivity increases with an increase in the size of the coarser fraction. But when the clay content is more than that which can be accommodated within the voids of the coarser fractions, the hydraulic conductivity is controlled primarily by clay content alone. Four different methods of predicting hydraulic conductivity of the liners are presented. Using two constants, related to the liquid limit, the hydraulic conductivity can be predicted at any void ratio.Key words: clays, hydraulic conductivity, liquid limit, liners, void ratio.
Canadian Geotechnical Journal - Tập 37 Số 2 - Trang 406-413 - 2000
Experimental study on swelling characteristics of compacted bentonite Compacted bentonites are attracting greater attention as back-filling (buffer) materials for repositories of high-level nuclear waste. However, since there are few studies about the swelling characteristics of compacted bentonites, it is first necessary to clarify the fundamental swelling characteristics in detail. For this purpose, various laboratory tests on the swelling deformation and swelling pressure of compacted bentonites were performed and the results analyzed. The following conclusions were drawn from the study. (i) The curve of swelling deformation versus time is strongly dependent on the initial dry density, vertical pressure, and initial water content. The maximum swelling deformation, however, is almost independent of initial water content, and the maximum swelling deformation increases in proportion to the initial dry density, (ii) The maximum swelling pressure increases exponentially with increasing initial dry density, whereas the maximum swelling pressure is almost independent of initial water content. (iii) The swelling mechanism of compacted bentonite was considered on the basis of the swelling behavior of swelling clay particles such as montmorillonite. Furthermore, a model of the swelling characteristics and a new parameter (swelling volumetric strain of montmorillonite), which were able to evaluate the swelling characteristics of compacted bentonite, were proposed. Key words : bentonite, laboratory test, nuclear waste disposal, swelling deformation, swelling pressure.
Canadian Geotechnical Journal - Tập 31 Số 4 - Trang 478-490 - 1994
Mineral–water interactions and their influence on the physical behavior of highly compacted Na bentonite Na bentonite is the active component of one of the engineered barriers that are being considered in Sweden to surround the final disposal sites of radioactive wastes from nuclear reactors. It has been chosen because of its low permeability and ion diffusivity and of its self-healing ability through swelling. These properties are due to mineral–water interactions that yield a microstructural pattern with very narrow passages and a low average mobility of interparticle water molecules at high bulk densities.
Canadian Geotechnical Journal - Tập 19 Số 3 - Trang 381-387 - 1982
Collapsibility, composition, and microstructure of loess in China The collapse potential, mineralogy, microstructure, and particle morphology of a loess from the Loess Plateau, China, were characterized by double oedometer testing, X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and image analysis to elucidate the origin of its collapse behavior. Results show that the loess is highly collapsible with a maximum collapse index of 6.7% at a vertical stress of ∼200 kPa. The deposit contains both nonclay (i.e., quartz, albite, muscovite, and calcite) and clay (i.e., two chlorites) minerals. Microstructural, chemical, and image analyses indicate that interparticle calcite and clay cementation and silt particle morphology render the intact soil a metastable structure. Wetting-induced collapse is attributed to both primary and secondary microstructure features. The former is the abundance of weakly cemented, unsaturated, porous pure clay and clay–silt mixture aggregates whose slaking upon wetting initiates the overall structural collapse, while the latter consists of high porosity, unstable particle contacts, and clay coating on silt particles that act synergistically to augment the collapse. A conceptual microstructural model of a four-tiered hierarchy (i.e., primary clay and silt particles, clay aggregates and clay-coated silt particles, clay–silt mixture aggregates, and cemented aggregate matrix) is proposed to represent its structural characteristics and to account for its high collapsibility.
Canadian Geotechnical Journal - Tập 53 Số 4 - Trang 673-686 - 2016
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