Rapid drawdown in slopes and embankments pinyol 2008. Generally, during the analysis of slope stability under different rainfall patterns, the influence of pore water pressure in. Pore water pressures below the phreatic level of the groundwater are measured with piezometers. Pdf on jan 1, 1985, edward nicholas bromhead and others published pore water pressure manipulation in computerised slope stability analysis find, read. Provided the applied loads do not cause the undrained shear strength of the clay or silt to be exceeded, as the excess pore water pressure dissipates consolidation occurs, and the shear strength of the clay or silt increases with time.
The stability of a soil slope is governed by slope geometries, stress conditions, and soil properties. The effects of pore water pressure have been studied by michalowski 1995 and kim et al. Twodimensional 2d back analysis of slope stability, for failure event in 2011 suggested that the critical pore water pressure distribution can be assigned to. Select whether the effects of the soil water pore pressure should be taken into account when carrying out slope stability calculations type of water influence and for what time level should the calculations be carried out hydrus printout time. Reactivated landslides, pore water pressure, slope stability. This data will be used along with a laboratory testing programme and numerical modelling tools to evaluate the effect of cyclic pore water pressures on the deformation stability of large cuttings in glacial tills in. This is frequently the greatest source of inaccuracy in slope stability work, since the determination of the most critical conditions of pore water pressure for various stages of life of canal is complex and costly. Above this line, pore water pressures are negative and suction is defined as s. Therefore, different stability analysis models should be.
Shear strength tests should be performed on specimens compacted to anticipated placement water contents and densities. The effect of retarded pore water pressure release on slope stability is primarily dependent on the permeability of the soil, the compressibility of the pore water. Slope stability design should be consistent with stateofthepractice design guidelines, including but not. A drawdown of intensity h d takes the free water to a new level m. External water loading, pore pressure changes, and hydrodynamic impact from water flow are factors being either influencing, or completely governing the actual soil properties. The excess pore water pressure cannot be dissipated during a very short period of earthquake duration. Slopew also accommodates the bbar and ru approaches. Transient water flow within soil structures affects porepressure conditions. Rainfallinduced shallow landslides can seriously affect cultivations and infrastructures and cause human losses. Under different rainfall intensity and soil conditions, wetted zone has different porewater pressure forms.
Effects of porewater pressure distribution on slope stability under. Analysis of the slope response to an increase in pore water. Impact of waterlevel variations on slope stability diva portal. The last analysis is a slope stability analysis used to compute the factor of safety when the failure started. Generation of negative excess pore water pressure nepwp due to the excavation of saturated soils under undrained conditions and the dissipation that follows over time may result in different short and longterm slope instability. Pore water pressure uncertainties for slope stability 1 van 31 1 introduction 1. An increase in pore pressure will result in a decrease of effective stress. Hydrological factors affecting rainfallinduced shallow. Guide to geotechnical instruments, 20041124 5 monitoring pore water pressure pore water pressure pore water measurements help engineers to. Testing is done by calculating the slope stability slope of geo structural analysis.
The effective stress principle and basic considerations of slope stability, including design factors of safety, are discussed briefly. Ignoring uncertainties in pore water pressures can thus lead to a serious over or under estimation of slope stability. Ground water flow and deformation within a slope influence each other. Internal causes these which cause failure without any change in external conditions, like increase in pore water pressure. Embankments on soft clay cubzaclesponts experimental. Pdf slope instability due to pore water pressure increase. The nepwp generated due to excavation gradually decreases towards equilibrium or, in some cases, steady seepage. Pdf pore water pressure manipulation in computerised slope.
Dimensionless stability factors for three dimensional slope stability analyses are presented including the 3d effect of the pore water pressure for different values of the slope angle in. Effect of pore water pressure on slope stability to get the effect of soil pore water pressure on slope stability, slope stability calculations were performed which did not occur pore water pressure and slope stability which received pore water pressure. Stability charts for uniform slopes university of michigan. Stability charts for slopes subjected to pore pressure the two effects that must be accounted for in the case of the presence of water are the buoyancy and.
Pore water pressures in three dimensional slope stability analysis. An increase in pore pressure could result from slope saturation by precipitation, seepage, or a rise in the ground water elevation. Methods for the field measurement of pore water pressures are described by ridley et al 2003. The effect of gravity is known, therefore, water is the key factor in assessing slope stability. The magnitude and variation of pore pressures in glacial. Appendix d discusses shear strength value selection. During an earthquake excess pore water pressure u might be generated in the soil near the sliding surface.
An increase of pore water pressure, resulting in a decrease in frictional resistance in cohesionless soils, or swell in cohesive soils. The derivations and effects of seepage forces and rapid. Slope failure is the movement of mass on slope falls, slides, flows landslide. Paper open access effect of pore water pressure on soil. Seepw generated porewater pressures in slopew stability. Etl 11102575 1 sep 11 behavior and failure modes that expanded on the knowledge gained from the performance of the new orleans hurricane and storm damage risk reduction system hsdrrs. The factor of safety and its corresponding critical non. Chapter 4 slope stability universiti teknologi malaysia.
Pore water pressures and slope stability oxford academic journals. A continuous monitoring of unsaturated soil hydrological properties is needed to understand the effects of pore water pressure and water content on shallow landslides triggering and slope safety factor. This paper presents a multidisciplinary approach for the determination of these two factors and for the construction of a reliable model of the subsoil for the slope stability analysis. Height of slip surface positive down from datum y infinite slope. Chapter 10 slope stability analysis nysdot geotechnical page 108 january 21, 2014 design manual 10. However, there is a potential conflict between the engineering requirements of earthwork materials to maintain stability and the moisture requirements to promote and sustain plant growth.
In order to estimate the factor of safety fs for a slope in terms of effective, the pore water pressure must be known. Reactivated landslides, pore water pressure, slope stability, velocity. Rapid drawdown with effective stress geoslope international. Slope stability analyses include static and dynamic, analytical or empirical methods to evaluate the stability of earth and rockfill dams, embankments. Pore water pressures can be defined using piezometric lines, spatial functions, or using the results from other geostudio finite element analyses such as seepw or sigmaw. Therefore, slopes fail due either to increase in stress or reduction in strength.
Effect of negative excess porewater pressure on the. For this reason careful selection of plant species is necessary and more. The effect of retarded pore water pressure release on slope stability is primarily dependent on the permeability of the soil, the compressibility of the pore water, i. Pdf slope stability and porewater pressure regime in. The value of the calculated factor of safety depends on the judgments made in selecting the. The vertical pore water pressure distribution in aquifers can generally be assumed to be close to hydrostatic in the unsaturated vadose zone, the.
Importance of water next to gravity, water is the most important factor in slope stability. There are many publications describing the tests, analyses and experiments carried out at cubzaclesponts. Pore water pressures in the slope are positive below a zero pressure line p w 0. The defined pore water pressure values can be displayed as contours on the geometry to help you see the pwp values. Pore water pressure profiles of the bukit timah granite residual soil slope and the the pore water pressures distributions from seepw were used as input to the slope stability rainfall. Pore water pressure uncertainties for slope stability. Slope stability refers to the condition of inclined soil or rock slopes to withstand or undergo movement.
Slope stability is influenced by many factors, among which are subsoil structure and pore water pressure distribution. Rainfall is the most important factor to induce landslide, of which rainfall pattern is the main influence parameter. Slope analysis and slope design calculations require good information on. Pdf pore water pressures in three dimensional slope. Pore water pressure sometimes abbreviated to pwp refers to the pressure of groundwater held within a soil or rock, in gaps between particles. Introduction on effects of water on slope stability. The stability condition of slopes is a subject of study and research in soil mechanics, geotechnical engineering and engineering geology. Testing of landslide triggering mechanism by pore pressure. Seismic excitation will have at least two effects on slope stability.
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