Effects of near-surface environmental conditions on instability of an unsaturated soil slope

2004 ◽  
Vol 41 (6) ◽  
pp. 1111-1126 ◽  
Author(s):  
James A Blatz ◽  
Nelson J Ferreira ◽  
James Graham
Keyword(s):  
Unsaturated Soils ◽  
Field Investigation ◽  
Soil Suction ◽  
Soil Slope ◽  
Flux Boundary Condition ◽  
Near Surface ◽  
Cause Of Failure ◽  
Seepage Modeling ◽  
The Right ◽  
Mechanism Of Failure

In 1999, after a period of extensive rainfall, two shallow slope failures developed in the right-of-way of Provincial Road 259 near Virden, Manitoba. The rainfall caused dissipation of soil suction in the near-surface soil, thereby reducing shear resistance and triggering failure. A research project was initiated between the Geotechnical Group at the University of Manitoba and the Manitoba Department of Highways and Transportation to assess the mechanism of failure. The project included a field investigation program, laboratory testing program, and advanced numerical modeling to identify the cause of failure. The results demonstrate that the rainfall resulted in dissipation of the suction in the soil slope, resulting in a reduction in the soil shear strength that triggered shallow failures. The dissipation of the soil suction has been modeled using a time-dependent seepage model that accounts for the flux boundary condition that existed at the ground surface.Key words: slope stability, unsaturated soils, laboratory tests, soil suction, seepage modeling, flux boundary.

Simulating transient infiltration in unsaturated soils

1998 ◽  
Vol 35 (6) ◽  
pp. 1093-1100 ◽  
Author(s):  
J R McDougall ◽  
I C Pyrah
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Flow Model ◽  
Unsaturated Flow ◽  
Surface Region ◽  
Infiltration Rate ◽  
Soil Suction ◽  
Wetting Front ◽  
Near Surface ◽  
Unsaturated Hydraulic Conductivity

Transient responses to various infiltration events have been examined using an unsaturated flow model. Numerical simulations reveal a range of infiltration patterns which can be related to the ratio of infiltration rate to unsaturated hydraulic conductivity. A high value of this ratio reflects a prevailing hydraulic conductivity which cannot readily redistribute the newly infiltrated moisture. Moisture accumulates in the near-surface region before advancing down through the soil as a distinct wetting front. In contrast, low values of the ratio of rainfall to unsaturated hydraulic conductivity show minimal moisture accumulation, as the relatively small volumes of infiltrating moisture are readily redistributed through the soil profile.Key words: numerical modelling, infiltration, unsaturated soil, soil suction, groundwater.

Soil Strength Reduction Method Induced by Variation of Water Content

2012 ◽  
Vol 170-173 ◽  
pp. 847-852
Author(s):  
Peng Ming Jiang ◽  
Zhong Lei Yan ◽  
Peng Li
Keyword(s):  
Slope Stability ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Strength Reduction ◽  
Actual State ◽  
Soil Slope ◽  
Simple Method ◽  
The Common ◽  
The Stability

As the complexity of unsaturated soil theory, and it must have a long test period when we study the unsaturated soils, so the conventional design analysis software does not provide such analysis, so we can imagine that such a slope stability analysis does not accurately reflect the actual state of the slope. Based on the known soil moisture content，this paper use the soil water characteristic curve and strength theory of unsaturated soil to calculate the strength reduction parameters of soil which can calculate the stability of the soil slope when using the common calculation method. It is noticeable that this method can be extended and applied if we establish regional databases for this simple method, and these databases can improve the accuracy of the calculation of slope stability.

Field Investigation of a New Recharge Approach for ASR Projects in Near-Surface Aquifers

Ground Water ◽  
2015 ◽  
Vol 54 (3) ◽  
pp. 425-433 ◽  
Author(s):  
Gaisheng Liu ◽  
Steven Knobbe ◽  
Edward C. Reboulet ◽  
Donald O. Whittemore ◽  
Falk Händel ◽  
...  
Keyword(s):  
Field Investigation ◽  
Near Surface

Measurement of Soil Suction and Soil-Water Characteristics of Bentonite-Sand Mixtures

2010 ◽  
Author(s):  
Pan Hu ◽  
Qing Yang ◽  
Maotian Luan
Keyword(s):  
Soil Water ◽  
Vapor Phase ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Phase Method ◽  
Soil Suction ◽  
Compacted Bentonite ◽  
Water Characteristics ◽  
Wide Range ◽  
High Level

The soil-water characteristic curve (SWCC) is a widely used experimental means for assessing fundamental properties of unsaturated soils for a wide range of soil suction values. The study of SWCC is helpful because some properties of unsaturated soils can be predicted from it. Nowadays, much attention has been paid to the behaviours of highly compacted bentonite-sand mixtures used in engineering barriers for high level radioactive nuclear waste disposal. It is very important to study the various performances of bentonite-sand mixtures in order to insure the safety of high-level radioactive waste (HLW) repository. After an introduction to vapor phase method and osmotic technique, a laboratory study has been carried out on compacted bentonite-sand mixtures. The SWCC of bentonite-sand mixtures has been obtained and analyzed. The results show that the vapor phase method and osmotic technique is suitable to the unsaturated soils with high and low suction.

scholarly journals Observed Boundary Layer Wind Structure and Balance in the Hurricane Core. Part I: Hurricane Georges

2006 ◽  
Vol 63 (9) ◽  
pp. 2169-2193 ◽  
Author(s):  
Jeffrey D. Kepert
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Tropical Cyclone ◽  
Radial Profile ◽  
Lower Altitude ◽  
Near Surface ◽  
Wind Structure ◽  
The Right ◽  
Tropical Cyclone Boundary Layer ◽  
Upper Boundary

Abstract The GPS dropsonde allows observations at unprecedentedly high horizontal and vertical resolution, and of very high accuracy, within the tropical cyclone boundary layer. These data are used to document the boundary layer wind field of the core of Hurricane Georges (1998) when it was close to its maximum intensity. The spatial variability of the boundary layer wind structure is found to agree very well with the theoretical predictions in the works of Kepert and Wang. In particular, the ratio of the near-surface wind speed to that above the boundary layer is found to increase inward toward the radius of maximum winds and to be larger to the left of the track than to the right, while the low-level wind maximum is both more marked and at lower altitude on the left of the storm track than on the right. However, the expected supergradient flow in the upper boundary layer is not found, with the winds being diagnosed as close to gradient balance. The tropical cyclone boundary layer model of Kepert and Wang is used to simulate the boundary layer flow in Hurricane Georges. The simulated wind profiles are in good agreement with the observations, and the asymmetries are well captured. In addition, it is found that the modeled flow in the upper boundary layer at the eyewall is barely supergradient, in contrast to previously studied cases. It is argued that this lack of supergradient flow is a consequence of the particular radial structure in Georges, which had a comparatively slow decrease of wind speed with radius outside the eyewall. This radial profile leads to a relatively weak gradient of inertial stability near the eyewall and a strong gradient at larger radii, and hence the tropical cyclone boundary layer dynamics described by Kepert and Wang can produce only marginally supergradient flow near the radius of maximum winds. The lack of supergradient flow, diagnosed from the observational analysis, is thus attributed to the large-scale structure of this particular storm. A companion paper presents a similar analysis for Hurricane Mitch (1998), with contrasting results.

Subsurface Investigation

2015 ◽  
pp. 744-795
Keyword(s):  
Field Tests ◽  
Field Investigation ◽  
Soil Parameters ◽  
Near Surface ◽  
Ground Investigation ◽  
Geophysical Techniques ◽  
Vertical Profiling ◽  
Sample Recovery ◽  
Subsurface Investigation ◽  
A Site

A good knowledge about a site including its subsurface conditions is very important in its safe and economical development. It is therefore an essential preliminary to the construction of any civil engineering work. This chapter outlines the objectives of site characterization and the general objectives of geotechnical investigation. It discusses the phases of field investigation and the stages of a full exploratory program including methods of sample recovery and field tests and sampling methods. Geophysical techniques can contribute very greatly to the process of ground investigation by allowing an assessment, in qualitative terms, of the lateral variability and vertical profiling of the near-surface materials beneath a site. Some of these geophysical techniques are discussed in the chapter. Laboratory examination/verification and testing should be made of representative portions of the samples to establish appropriate soil parameters. Some soil parameters may be estimated by correlations. The results of the subsurface investigation and related testing, together with interpretations, discussions, and foundation recommendations, are usually presented in the form of a detailed soil report.

scholarly journals The effect of hygroscopicity on sea-spray aerosol fluxes: a comparison of high-rate and bulk correction methods

2012 ◽  
Vol 5 (5) ◽  
pp. 6285-6321
Author(s):  
D. A. J. Sproson ◽  
I. M. Brooks ◽  
S. J. Norris
Keyword(s):  
Relative Humidity ◽  
Eddy Covariance ◽  
High Rate ◽  
Sea Spray ◽  
Original Form ◽  
Near Surface ◽  
Sea Spray Aerosol ◽  
Flux Corrections ◽  
Counting Statistics ◽  
The Right

Abstract. The eddy covariance technique is the most direct of the methods that have been used to measure the flux of sea-spray aerosol between the ocean and atmosphere, but has been applied in only a handful of studies. However, unless the aerosol is dried before the eddy covariance measurements are made, the hygroscopic nature of sea-spray may combine with a relative humidity flux to result in a bias in the calculated aerosol flux. "Bulk" methods have been presented to account for this bias, however they rely on assumptions of the shape of the aerosol spectra which may not be valid for near-surface measurements of sea-spray. Here we describe a method of correcting aerosol spectra for relative humidity induced size variations at the high frequency (10 Hz) measurement timescale, where counting statistics are poor and the spectral shape cannot be well represented by a simple power law. Such a correction allows the effects of hygroscopicity and relative humidity flux on the aerosol flux to be explicitly evaluated and compared to the bulk corrections, both in their original form and once reformulated to better represent the measured mean aerosol spectra. In general, the bulk corrections – particularly when reformulated for the measured mean aerosol spectra – perform relatively well, producing flux corrections of the right sign and approximate magnitude. However, there are times when the bulk methods either significantly over- or underestimate the required flux correction. We thus conclude that, where possible, relative humidity corrections should be made at the measurement frequency.

Retrogressive slope failures at Beaver Creek, south of Saskatoon, Saskatchewan, Canada

1977 ◽  
Vol 14 (3) ◽  
pp. 288-301 ◽  
Author(s):  
M. D. Haug ◽  
E. Karl Sauer ◽  
D. G. Fredlund
Keyword(s):  
Stability Analysis ◽  
Soil Properties ◽  
Field Investigation ◽  
Slope Failures ◽  
The South ◽  
River Bank ◽  
South Saskatchewan River ◽  
Rest Condition ◽  
Mechanism Of Failure ◽  
Rate Of Movement

Active landslides are occurring along the banks of the South Saskatchewan River at Saskatoon. A field investigation and stability analysis indicated that a multiple retrogressive mechanism is valid in explaining the failures at Beaver Creek, 28 km south of Saskatoon. Computations indicated that lateral pressures ranging from the active to something greater than the at-rest condition tend to support the successive blocks but are not high enough to stabilize the slides. It was assumed that the rate of movement of the blocks varies and probably increases downslope. Valuable information was obtained about the soil properties in the area and the mechanism of failure that seems to apply over a long section along the river bank south of Saskatoon.

scholarly journals Generation of Subsurface Anticyclones at Arctic Surface Fronts due to a Surface Stress

2017 ◽  
Vol 47 (11) ◽  
pp. 2653-2671 ◽  
Author(s):  
Liam Brannigan ◽  
Helen Johnson ◽  
Camille Lique ◽  
Jonas Nycander ◽  
Johan Nilsson
Keyword(s):  
Mixed Layer ◽  
Surface Stress ◽  
Ekman Transport ◽  
The Arctic ◽  
Near Surface ◽  
Geostrophic Flow ◽  
Unstable Surface ◽  
Surface Cyclone ◽  
Ekman Flow ◽  
The Right

AbstractIsolated anticyclones are frequently observed below the mixed layer in the Arctic Ocean. Some of these subsurface anticyclones are thought to originate at surface fronts. However, previous idealized simulations with no surface stress show that only cyclone–anticyclone dipoles can propagate away from baroclinically unstable surface fronts. Numerical simulations of fronts subject to a surface stress presented here show that a surface stress in the same direction as the geostrophic flow inhibits dipole propagation away from the front. On the other hand, a surface stress in the opposite direction to the geostrophic flow helps dipoles to propagate away from the front. Regardless of the surface stress at the point of dipole formation, these dipoles can be broken up on a time scale of days when a surface stress is applied in the right direction. The dipole breakup leads to the deeper anticyclonic component becoming an isolated subsurface eddy. The breakup of the dipole occurs because the cyclonic component of the dipole in the mixed layer is subject to an additional advection because of the Ekman flow. When the Ekman transport has a component oriented from the anticyclonic part of the dipole toward the cyclonic part then the cyclone is advected away from the anticyclone and the dipole is broken up. When the Ekman transport is in other directions relative to the dipole axis, it also leads to deviations in the trajectory of the dipole. A scaling is presented for the rate at which the surface cyclone is advected that holds across a range of mixed layer depths and surface stress magnitudes in these simulations. The results may be relevant to other regions of the ocean with similar near-surface stratification profiles.

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