Evolution of the factor of safety following excavation in clay

2009 ◽  
Vol 46 (5) ◽  
pp. 487-493 ◽  
Author(s):  
J. S. L’Heureux ◽  
S. Leroueil ◽  
J. F. Laflamme
Keyword(s):  
Pore Pressure ◽  
Factor Of Safety ◽  
Clayey Soil ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soil Mass ◽  
Eastern Canada ◽  
Soft Clays ◽  
Clay Deposits ◽  
The Difference

Numerical analyses have been performed to study the evolution of the factor of safety following the excavation of a cut in clay. The analyses consider variable thickness of the clayey soil deposit under the excavation. The results show that, for a given clayey soil, there is a relation between the time for full dissipation of excess pore-water pressure from the soil mass following the excavation and the geometry of the cut (Htot/Hexc). The analytical results agree reasonably well with pore pressure measurements made in excavations in clay deposits from eastern Canada. This suggests that time to reach full pore pressure equilibration following the excavation of a cut in homogenous clayey soil deposits can be predicted when knowledge of the coefficient of swelling–consolidation is available. Lastly, results obtained in the present study show that 50% of the difference between the short- and long-term factors of safety may be lost at values as low as about 8% of the time to reach equilibration of pore pressures. This means that the time during which one can rely on the short-term strength of the clayey soil following the excavation may be relatively short, especially for soft clays.

Monotonic and dilatory pore-pressure decay during piezocone tests in clay

1998 ◽  
Vol 35 (6) ◽  
pp. 1063-1073 ◽  
Author(s):  
S E Burns ◽  
P W Mayne
Keyword(s):  
Pore Pressure ◽  
Pore Water Pressure ◽  
Soil Mechanics ◽  
Water Pressure ◽  
Cavity Expansion ◽  
Coefficient Of Consolidation ◽  
Soft Clays ◽  
Fine Grained ◽  
Cavity Expansion Theory ◽  
Pore Pressure Response

During a pause in cone penetration in fine-grained soils, pore-water pressure dissipation tests are performed to evaluate the coefficient of consolidation. For standard piezocones with shoulder filter elements, soft clays and silts show a monotonically decreasing response with time; however, dissipation tests performed in heavily overconsolidated silts and clays show dilatory behavior, with the pore-pressure behavior increasing from the initial measured value to a maximum, and then decreasing to hydrostatic values. This paper presents a theoretical framework which combines cavity-expansion theory and critical-state soil mechanics with an analytical solution to the radial consolidation equation. The method is able to describe the pore-pressure response curve for dissipation tests performed in soils which demonstrate either monotonically decreasing or dilatory pore-pressure behavior.Key words: cavity expansion, consolidation, piezocone, pore pressure.

scholarly journals Pengaruh Beban Kendaraan sebagai Beban Terbagi Rata terhadap Deformasi Geogrid sebagai Perkuatan Embankment

2012 ◽  
Vol 8 (1) ◽  
pp. 31
Author(s):  
Adhe Noor Patria
Keyword(s):  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Vertical Displacement ◽  
Soil Mass ◽  
Vehicle Load ◽  
Surcharge Load ◽  
The Difference ◽  
High Level

<p>Soft soil such as clay was sensitive soil. Public contructions built in this kind of soil would face some problemssuch as long period consolidation time, unstable embankment slope, not easily compacted and high level settlement. Some solution that could be suggested were the usage of vertical drain, or the usage of geosynthetics material such as geogrid combined with floating  piles.Analysis was carried out by using plaxis version 7.2. soil for embankment and embankment foundation was modelled in plane strain. Also geogrid andfloating piles were modelled in palne strain too. Surcharge load on top of embanknet were variated, they were 20, 35 and 50 kPa. The simulation was carried out in staged contruction mode.Final vertical displacement in geogrid due to 50  kPa vehicle load as surcharge load and long term load period (in this case excess pore water pressure was small) was -0,9062 m for  rigid embankment and -1,4206 for interface embankment. The difference occured due to slip at the interface of geogrid and soil. It  leaded to adding soil mass supportd by geogrid, furthermore the deflection of geogrid became bigger.</p>

The Test Study to the Changes of Excess Pore Water Pressure during Precast Pile Construction

2012 ◽  
Vol 193-194 ◽  
pp. 1010-1013
Author(s):  
Shu Qing Zhao
Keyword(s):  
Pore Water ◽  
Clayey Soil ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Excess Pore Pressure ◽  
Soil Pressure ◽  
Excess Pore Water Pressure ◽  
Test Study ◽  
Excess Pore

The construct to precast pile in thick clayey soil can cause the accumulation of excess pore water pressure. The high excess pore pressure can make soil, buildings and pipes surrounded have large deflection, even make them injured. Combining with actual projects, this paper presents an in-situ model test on the changes of excess pore water pressure caused by precast pile construct. It is found that the radius of influence range for single pile driven is about 15m，the excess pore water pressure can reach or even exceed the above effective soil pressure, and there are two relatively stable stages.

Type of Slope Failure Identified from Pore Water Pressure and Moisture Content Measurements

2015 ◽  
Vol 744-746 ◽  
pp. 690-694
Author(s):  
Muhammad Rehan Hakro ◽  
Indra Sati Hamonangan Harahap
Keyword(s):  
Moisture Content ◽  
Pore Pressure ◽  
Slope Failure ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Failure Process ◽  
Small Scale ◽  
Content Increase ◽  
Sudden Increase ◽  
Model Slope

Rainfall-induced landslides occur in many parts of the world and causing a lot of the damages. For effective prediction of rainfall-induced landslides the comprehensive understanding of the failure process is necessary. Under different soil and hydrological conditions experiments were conducted to investigate and clarify the mechanism of slope failure. The failure in model slope was induced by sprinkling the rainfall on slope composed of sandy soil in small flume. Series of tests were conducted in small scale flume to better understand the failure process in sandy slopes. The moisture content was measured with advanced Imko TDR (Time Domain Reflectrometry) moisture sensors in addition to measurements of pore pressure with piezometers. The moisture content increase rapidly to reach the maximum possible water content in case of higher intensity of rainfall, and higher intensity of the rainfall causes higher erosion as compared to smaller intensity of the rainfall. The controlling factor for rainfall-induced flowslides was density of the slope, rather than intensity of the rainfall and during the flowslide the sudden increase in pore pressure was observed. Higher pore pressure was observed at the toe of the slope as compared to upper part of the slope.

scholarly journals Integrated Simulation Modeling Approach for Investigating Pore Water Pressure Induced Landslides

2022 ◽  
Author(s):  
Sahila Beegum ◽  
P J Jainet ◽  
Dawn Emil ◽  
K P Sudheer ◽  
Saurav Das
Keyword(s):  
Pore Water ◽  
Factor Of Safety ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Simulation Models ◽  
Integrated Simulation ◽  
Hill Slope ◽  
Slope Factor ◽  
The Stability ◽  
The Hill

Abstract Soil pore water pressure analysis is crucial for understanding landslide initiation and prediction. However, field-scale transient pore water pressure measurements are complex. This study investigates the integrated application of simulation models (HYDRUS-2D/3D and GeoStudio–Slope/W) to analyze pore water pressure-induced landslides. The proposed methodology is illustrated and validated using a case study (landslide in India, 2018). Model simulated pore water pressure was correlated with the stability of hillslope, and simulation results were found to be co-aligned with the actual landslide that occurred in 2018. Simulations were carried out for natural and modified hill slope geometry in the study area. The volume of water in the hill slope, temporal and spatial evolution of pore water pressure, and factor of safety were analysed. Results indicated higher stability in natural hillslope (factor of safety of 1.243) compared to modified hill slope (factor of safety of 0.946) despite a higher pore water pressure in the natural hillslope. The study demonstrates the integrated applicability of the physics-based models in analyzing the stability of hill slopes under varying pore water pressure and hill slope geometry and its accuracy in predicting future landslides.

Downslope movements at shallow depths related to cyclic pore-pressure changes

1993 ◽  
Vol 30 (3) ◽  
pp. 464-475 ◽  
Author(s):  
K.D. Eigenbrod
Keyword(s):  
Pore Water ◽  
Slip Surface ◽  
Pore Water Pressure ◽  
Limit Equilibrium ◽  
Water Pressure ◽  
Ground Surface ◽  
Soil Mass ◽  
Passive Resistance ◽  
Pressure Changes ◽  
Timber Piles

Slow, shallow ground movements in a slope near Yellowknife caused excessive tilting of timber piles that supported an engineering structure. To avoid damage to the structure, the pile foundations had to be replaced by rigid concrete piers that were designed to resist the forces of the moving soil mass. Downhill movements were rather slow and, during an initial inspection, were indicated only by soil that was pushed up against a series of piles on their uphill sides, while gaps had formed on their downhill sides. No open cracks or bulging was observed on the slope. A stability analysis indicated that the slope was not in a state of limit equilibrium. To obtain a better understanding of the creep movements in the slope and their effect on the rigid concrete piers, extensive instrumentation was carried out after the construction of the piers. This included slope indicators, piezometers, thermistors, and total-pressure cells against one of the concrete piers. In addition, a triaxial testing program was undertaken in which the effect of cyclic pore-water pressure changes on the long-term deformations of the shallow clay layer was investigated. From the data collected in the field and laboratory, it could be concluded that (i) tilting of the original timber piles was caused by downslope movements related to cyclic pore-water increases; (ii) the lateral soil movements increased almost linearly with depth from 2 m below the ground surface, with no indication of a slip surface; and (iii) the pressures exerted by the moving soil mass against the rigid concrete piers within the soil mass were equal to the passive resistance activated within the moving soil mass. Key words : soil creep, slope movements, soil pressures, pore-water pressures, freezing pressures, permafrost, cyclic loading.

scholarly journals Mechanical response and pore pressure generation in granular filters subjected to uniaxial cyclic loading

2018 ◽  
Vol 55 (12) ◽  
pp. 1756-1768
Author(s):  
Jahanzaib Israr ◽  
Buddhima Indraratna
Keyword(s):  
Cyclic Loading ◽  
Pore Pressure ◽  
Pore Water ◽  
Mechanical Response ◽  
Pore Water Pressure ◽  
Axial Strain ◽  
Water Pressure ◽  
Internal Erosion ◽  
Excess Pore Water Pressure ◽  
Excess Pore

This paper presents results from a series of piping tests carried out on a selected range of granular filters under static and cyclic loading conditions. The mechanical response of filters subjected to cyclic loading could be characterized in three distinct phases; namely, (I) pre-shakedown, (II) post-shakedown, and (III) post-critical (i.e., the occurrence of internal erosion). All the permanent geomechanical changes such, as erosion, permeability variations, and axial strain developments, took place during phases I and III, while the specimen response remained purely elastic during phase II. The post-critical occurrence of erosion incurred significant settlement that may not be tolerable for high-speed railway substructures. The analysis revealed that a cyclic load would induce excess pore-water pressure, which, in corroboration with steady seepage forces and agitation due to dynamic loading, could then cause internal erosion of fines from the specimens. The resulting excess pore pressure is a direct function of the axial strain due to cyclic densification, as well as the loading frequency and reduction in permeability. A model based on strain energy is proposed to quantify the excess pore-water pressure, and subsequently validated using current and existing test results from published studies.

Studying the Geotechnical Properties of Clayey Soil Contaminated by Kerosene

2020 ◽  
Vol 857 ◽  
pp. 383-393
Author(s):  
Mahdi O. Karkush ◽  
Amer G. Jihad
Keyword(s):  
Shear Strength ◽  
Water Content ◽  
Contaminated Soil ◽  
Fine Particles ◽  
Clayey Soil ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Chemical Characteristics ◽  
Coefficient Of Consolidation ◽  
Plastic Containers

This study focuses on investigating the impacts of kerosene on the physical, mechanical, and chemical characteristics of clay soil. The soils specimens are contaminated artificially with six ratios of kerosene (5, 10, 20, 30, 40, and 50) % calculated according to the dry weight of soil. The artificial contamination includes air drying of the disturbed soil, then placed in plastic containers and mixed with the field water content and the specified concentration of kerosene to ensure getting homogenous contaminated soil specimens. The contaminated soil specimens left for 30 days in plastic containers covered by nylon sheets to control the water content and prevent volatility of contaminant. The results of tests proved that different ratios of kerosene have different impacts on the engineering and chemical characteristics of soil specimens. The specific gravity, percentages of fine particles, optimum water content, the initial and final void ratio, coefficient of consolidation, swelling index, permeability, the undrained shear strength, effective shear strength parameters, and the rate of reduction of initial pore water pressure are reduced significantly with increasing the content of kerosene in soil. Generally, the concentration of kerosene less than 10% has slight impacts on the studied characteristics of soil specimens.

An effective stress model for creep of clay

1995 ◽  
Vol 32 (5) ◽  
pp. 819-834 ◽  
Author(s):  
Mohammed M. Morsy ◽  
D.H. Chan ◽  
N.R. Morgenstern
Keyword(s):  
Finite Element ◽  
Pore Pressure ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Surface Model ◽  
Interpolation Technique ◽  
Stress Integration ◽  
Integration Algorithms ◽  
Double Yield

An effective stress constitutive model to study the problem numerically of creep in the field is presented. A double-yield surface model for the stress–strain–time behaviour of wet clay is described. The model adopts the concept of separating the total deformation into immediate and delayed components. The yield surfaces employed are the modified Cam-clay ellipsoid and the Von Mises cylinder inscribed in the ellipsoid. The proposed numerical scheme incorporates the pore pressure based on field observations into a finite element analysis. An interpolation technique is used to determine the pore pressure at every element. A field example is presented to illustrate the interpolation technique procedure. The scheme not only avoids the complexity of making predictions of pore-water pressure, but also allows the analysis to be carried out in terms of effective stresses based on the actual observed pore pressure. Two stress integration algorithms based on the implicit calculation of plastic strain are implemented and tested for the double-yield surface model. A numerical simulation of stress-controlled drained creep tests confirms the numerical procedure. Key words : constitutive equations, creep, finite element, stress integration algorithms, effective stress approach, pore-water pressure.

scholarly journals Boulder Pickup by Tsunami Surge

2019 ◽  
Vol 13 (05n06) ◽  
pp. 1941006
Author(s):  
Samuel Harry ◽  
Margaret Exton ◽  
Harry Yeh
Keyword(s):  
Pore Water Pressure ◽  
Initial Conditions ◽  
Scale Effects ◽  
Traditional Approach ◽  
Water Pressure ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Flow Conditions ◽  
The Difference ◽  
The Impact

Study of boulder transport by tsunamis is challenging because boulder size, shape, and composition vary greatly; furthermore, flow conditions, topography, and initial conditions are generally unknown. To investigate the mechanism of boulder pickup, experiments of tsunami-like flow past spherical boulders partially buried in a sediment bed are conducted. The experiments are performed in a large centrifuge facility to reduce scale effects and the corresponding dynamic similitude is discussed. The traditional approach to determine boulder pickup is adapted for the case of a half-buried spherical boulder. The adapted model predicts that the boulders are transported, but does not accurately predict the timing of pick up. To investigate the difference in pickup timing, two physical phenomena are discussed: pore-water-pressure dissipation in the soil, and the impact of the free-surface flow on hydrodynamic forces. For a spherical shaped boulder, vertical forces (i.e. buoyant and lift forces) are critical for the initiation of boulder pickup. It was found that spherical boulders that are three-quarter buried in the soil are not transported, even when exposed to flow conditions that would otherwise predict transport.

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