scholarly journals Impacts of Unsaturated Conditions on The Ultimate Axial Capacity of Energy Piles

2020 ◽  
Vol 195 ◽  
pp. 04005
Author(s):  
Fatemah Behbehani ◽  
John S. McCartney
Keyword(s):  
Effective Stress ◽  
Unsaturated Soils ◽  
Elevated Temperatures ◽  
Soil Mechanics ◽  
Degree Of Saturation ◽  
Geotechnical Centrifuge ◽  
Axial Capacity ◽  
Coupled Heat Transfer ◽  
Energy Piles ◽  
Unsaturated Soil Mechanics

This study uses concepts from unsaturated soil mechanics to explain changes in axial capacity observed in geotechnical centrifuge experiments on semi-floating energy piles in unsaturated silt heated monotonically to different temperatures. Thermally-induced drying of the unsaturated silt surrounding energy piles was observed during heating using temperature-corrected dielectric sensor readings. An effective stress-based equation for estimating the ultimate capacity was calibrated using the load-settlement curves for a pile at room-temperature, which was then used to estimate the ultimate capacities of energy piles under elevated temperatures using measured changes in degree of saturation near the energy pile. The predicted capacity matched well with the capacity from the experimental load-settlement curves, confirming the relevance of the effective stress principle in unsaturated soils in nonisothermal conditions and the importance of considering coupled heat transfer and water flow in unsaturated soils surrounding energy piles.

scholarly journals Simulation of the thermo-hydraulic response of energy piles in unsaturated soils

2020 ◽  
Vol 205 ◽  
pp. 05002
Author(s):  
Fatemah Behbehani ◽  
John S. McCartney
Keyword(s):  
Heat Transfer ◽  
Unsaturated Soils ◽  
Cumulative Effect ◽  
Degree Of Saturation ◽  
Soil Layers ◽  
Energy Pile ◽  
Axial Capacity ◽  
Coupled Heat Transfer ◽  
Heating And Cooling ◽  
Energy Piles

This paper focuses on the simulation of the coupled heat transfer and water flow in unsaturated soil layers surrounding a solitary energy pile undergoing heating and cooling cycles typical of a field-scale energy pile. The results indicate that heating leads to drying of the soil surrounding the energy pile, which has been shown in previous studies to result in an increase in axial capacity. During cooling, the degree of saturation was observed to recover to the value present before the start of heating initially, however, it will not recover in the following years. Which will lead to a cumulative effect after several cycles of heating and cooling. Heating and cooling cycles lead to an overall reduction in the thermal conductivity of the subsurface, reducing the heat transfer from the energy pile but also leading to greater storage of heat in the subsurface surrounding the pile.

Capillary-based effective stress formulation for predicting shear strength of unsaturated soils

2015 ◽  
Vol 52 (12) ◽  
pp. 2067-2076 ◽  
Author(s):  
Jean-Marie Konrad ◽  
Marc Lebeau
Keyword(s):  
Shear Strength ◽  
Effective Stress ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Adsorbed Water ◽  
Soil Strength ◽  
Liquid Films ◽  
Degree Of Saturation ◽  
Stress Parameter ◽  
Effective Stress Parameter

A number of investigations have shown that the shear strength of unsaturated soils can be defined in terms of effective stress. The difficulty in this approach lies in quantifying the effective stress parameter, or Bishop’s parameter. Although often set equal to the degree of saturation, it has recently been suggested that the effective stress parameter should be related to an effective degree of saturation, which defines the fraction of water that contributes to soil strength. A problematic element in this approach resides in differentiating the water that contributes to soil strength from that which does not contribute to soil strength. To address this difficulty, the paper uses theoretical considerations and experimental observations to partition the water retention function into capillary and adsorptive components. Given that the thin liquid films of adsorbed water should not contribute to effective stress, the effective stress parameter is solely related to the capillary component of water retention. In sample calculations, this alternative effective stress parameter provided very good agreement with experimental data of shear strength for a variety of soil types.

scholarly journals Modelling shear strength of compacted soils

2019 ◽  
Vol 92 ◽  
pp. 15007
Author(s):  
Sam Bulolo ◽  
Eng Choon Leong
Keyword(s):  
Shear Strength ◽  
Unsaturated Soils ◽  
Soil Mechanics ◽  
Published Data ◽  
State Variables ◽  
Compacted Soils ◽  
Earth Structures ◽  
Unsaturated Soil Mechanics ◽  
Coulomb Failure Criterion ◽  
Direct Shear Apparatus

Compacted soils constitute most engineering projects such as earth dams, embankments, pavements, and engineered slopes because of their high shear strength and low compressibility. The shear strength of compacted soils is a key soil parameter in the design of earth structures but it is seldom determined correctly due to their unsaturated state. The shear strength of compacted soils can be better evaluated under the framework of unsaturated soil mechanics. Saturated and unsaturated tests were conducted on compacted specimens using conventional direct shear apparatus under constant water content condition. Tests were conducted at different water contents and net normal stresses. The main objective of this study is to develop a shear strength model for compacted soils. Initial matric suction was measured before the test using the filter paper method. The two-stress state variables together with the extended Mohr-Coulomb failure criterion for unsaturated soils were used to obtain a lower bound model of the shear strength. The model was demonstrated using published data.

Laboratory testing on an unsaturated soil: equipment, procedures, and first experimental results

1999 ◽  
Vol 36 (1) ◽  
pp. 1-12 ◽  
Author(s):  
C Rampino ◽  
C Mancuso ◽  
F Vinale
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Mechanics ◽  
Stress Path ◽  
Matric Suction ◽  
Silty Sand ◽  
Compression Tests ◽  
Water Drainage ◽  
Triaxial Cell ◽  
Unsaturated Soil Mechanics

This paper describes two new apparatuses recently developed at the Università di Napoli Federico II (Italy) in order to test soils under unsaturated conditions. The related experimental procedures and the first results obtained on a dynamically compacted silty sand are also discussed. The devices mentioned are a Bishop and Wesley stress-path cell and a Wissa oedometer, modified to control matric suction and to measure all the stress-strain variables relevant to unsaturated soil mechanics. Specific experimental procedures were established to perform tests under general conditions and were carefully verified during several tests. Using the triaxial cell, isotropic and anisotropic compression stages were carried out under constant suction levels of 0, 100, 200, and 300 kPa. Furthermore, two deviator stages were performed following different stress paths and water drainage conditions. Using the oedometer, an additional suction level (400 kPa) was investigated during compression tests driven up to 5 MPa of vertical net stress (sigmav - ua). This research is a part of a major project in progress at the Dipartimento di Ingegneria Geotecnica of Naples; it is aimed at the experimental analysis of the behaviour of several dynamically compacted soils and at the numerical modelling of boundary problems related to earth structures.Key words: unsaturated soils, equipment layout, silty sand, matric suction.

scholarly journals Effect of Elevated Temperatures on Lateral Earth Pressures in Unsaturated Soils

2020 ◽  
Vol 195 ◽  
pp. 04014
Author(s):  
Sannith Kumar Thota ◽  
Farshid Vahedifard
Keyword(s):  
Effective Stress ◽  
Unsaturated Soils ◽  
Elevated Temperatures ◽  
Earth Pressure ◽  
Effect Of Temperature ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Near Surface ◽  
Earth Pressures ◽  
The Impact

Near-surface unsaturated soils can be exposed to elevated temperatures due to soil-atmospheric interactions under drought events, wildfires, heatwaves, and warm spells, or the heat induced by emerging geotechnical and geo-environmental technologies such as geothermal boreholes and thermally active earthen systems. Elevated temperatures can affect the hydro-mechanical characteristics of unsaturated soils, which in turn can alter lateral earth pressures developed in the backfill soil. The main objective of this study is to quantify the effect of elevated temperatures on active and passive earth pressures of unsaturated soils. For this purpose, the paper presents the derivation of an analytical framework to extend Rankine’s earth pressure theory to account for the effect of temperature under hydrostatic conditions. The equations are derived by incorporating the effect of temperature into the soil water retention curve and a suction stress-based effective stress representation. The proposed effective stress equation considers the temperature-induced changes in the contact angle, surface tension, and enthalpy of immersion. To investigate the impact of temperature on active and passive earth pressures, the proposed method is then used in a set of parametric studies to determine active and passive earth pressure profiles for three hypothetical soils of clay, silt, and sand at different temperatures. Results suggest that elevated temperatures can cause variation in active and passive earth pressures for all the soils considered. The findings of this study can contribute toward analyzing earth retaining structures subjected to elevated temperatures.

An Effective Stress Model for Unsaturated Soils at Elevated Temperatures

2020 ◽  
Author(s):  
Sannith Kumar Thota ◽  
Toan Duc Cao ◽  
Farshid Vahedifard ◽  
Ehsan Ghazanfari
Keyword(s):  
Effective Stress ◽  
Unsaturated Soils ◽  
Elevated Temperatures ◽  
Stress Model

The 1999 R.M. Hardy Lecture: The implementation of unsaturated soil mechanics into geotechnical engineering

2000 ◽  
Vol 37 (5) ◽  
pp. 963-986 ◽  
Author(s):  
Delwyn G Fredlund
Keyword(s):  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Property ◽  
Soil Mechanics ◽  
Geotechnical Engineering ◽  
Characteristic Curve ◽  
Engineering Practice ◽  
Soil Water Characteristic Curve ◽  
Unsaturated Soil Mechanics

The implementation of unsaturated soil mechanics into geotechnical engineering practice requires that there be a paradigm shift from classical soil mechanics methodology. The primary drawback to implementation has been the excessive costs required to experimentally measure unsaturated soil properties. The use of the soil-water characteristic curve has been shown to be the key to the implementation of unsaturated soil mechanics. Numerous techniques have been proposed and studied for the assessment of the soil-water characteristic curves. These techniques range from direct laboratory measurement to indirect estimation from grain-size curves and knowledge-based database systems. The soil-water characteristic curve can then be used for the estimation of unsaturated soil property functions. Theoretically based techniques have been proposed for the estimation of soil property functions such as (i) coefficient of permeability, (ii) water storage modulus, and (iii) shear strength. Gradually these estimations are producing acceptable procedures for geotechnical engineering practices for unsaturated soils. The moisture flux ground surface boundary condition is likewise becoming a part of the solution of most problems involving unsaturated soils. The implementation process for unsaturated soils will still require years of collaboration between researchers and practicing geotechnical engineers.Key words: unsaturated soil mechanics, soil suction, unsaturated soil property functions, negative pore-water pressure, matric suction, soil-water characteristic curve.

Sign in / Sign up

Export Citation Format

Share Document