Model for Prediction of Shear Strength with Respect to Degree of Saturation

2010 ◽  
Author(s):  
Sh. Ma ◽  
M. Huang ◽  
Q. Fan ◽  
X. Zhang ◽  
P. Hu
Keyword(s):  
Shear Strength ◽  
Degree Of Saturation

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.

Influence of degree of saturation on soil nail pull-out resistance in compacted completely decomposed granite fill

2007 ◽  
Vol 44 (11) ◽  
pp. 1314-1328 ◽  
Author(s):  
Li-Jun Su ◽  
Terence C.F. Chan ◽  
Y.K. Shiu ◽  
Tony Cheung ◽  
Jian-Hua Yin
Keyword(s):  
Shear Strength ◽  
Degree Of Saturation ◽  
Interface Shear Strength ◽  
Interface Shear ◽  
Soil Nails ◽  
Soil Nail ◽  
Pull Out ◽  
Decomposed Granite ◽  
Soil Interface ◽  
Completely Decomposed Granite

The nail–soil interface shear strength is a key parameter in the design and stability assessment of soil nailing systems. A number of factors will influence the nail–soil interface shear strength. Among these factors, the degree of saturation (Sr) of the soil is an important one especially for permanent soil nail structures. To study the influence of Sr on soil nail pull-out shear resistance, a series of laboratory pull-out tests have been conducted on soil nails in compacted completely decomposed granite (CDG) fill prepared to different Sr. The tests were conducted using two specially designed pull-out boxes (with same specifications). In the near-saturated tests, a high Sr (about 98%) was achieved using two special features of the apparatus: a waterproof front cap and back-water pressure pipes at the bottom of the pull-out box. Test results showed that the nail–soil shearing plane migrated outwards into the soil when the Sr of the soil increased. Also, peak pull-out strengths of soil nails were strongly influenced by the Sr of the soil. Among the tested Sr, the highest values of peak pull-out shear strength were obtained at Sr values between 50% and 75%.

scholarly journals Regression Equations for Estimating Landslide-Triggering Factors Using Soil Characteristics

2020 ◽  
Vol 10 (10) ◽  
pp. 3560
Author(s):  
Kyeong-Su Kim ◽  
Man-Il Kim ◽  
Moon-Se Lee ◽  
Eui-Soon Hwang
Keyword(s):  
Shear Strength ◽  
Void Ratio ◽  
Soil Characteristics ◽  
Degree Of Saturation ◽  
Geological Condition ◽  
Regression Equations ◽  
Uniformity Coefficient ◽  
Permeability Coefficients ◽  
Triggering Factors ◽  
Geological Conditions

Landslides, which often occur on natural slopes of mountainous areas and artificial slopes around urban areas during summer in South Korea, are mostly caused by localized heavy rainfalls and typhoons. A survey was conducted, and the characteristics of landslide occurrences in different geological conditions—in this case, granite soils in Sangju area and gneiss soils in Yangu area—were analyzed. Soil characteristics in the landslide and non-landslide areas and the surroundings of each geological condition were also evaluated. Triggering factors, namely permeability coefficients (k), shear strength with cohesion (c), and internal friction angle (φ) of soils that are closely linked to landslides around weathered soil layers were extracted based on the examined characteristics and a statistics method. The study used regression analysis to formulate equations to estimate the permeability coefficients and shear strength. Ultimately, the permeability coefficients showed significant results in terms of void ratio (e), the effective size of grains (D10), and uniformity coefficient (cu), while shear strength correlated with the proportion of fine-grained soil (Fines), uniformity coefficient (cu), degree of saturation (S), dry weight density (rd), and void ratio (e).

Vegetation effects on the tensile strength of a partially saturated soil

2021 ◽  
Author(s):  
Alessandro Fraccica ◽  
Enrique Romero ◽  
Thierry Fourcaud
Keyword(s):  
Tensile Strength ◽  
Shear Strength ◽  
Water Content ◽  
Silty Sand ◽  
Degree Of Saturation ◽  
Uniaxial Tensile ◽  
Dry Density ◽  
Partially Saturated ◽  
Soil Shear Strength ◽  
Soil Tensile Strength

<p>Soil tensile strength plays an important role in the hydro-mechanical behaviour of earth structures and slopes interacting with the atmosphere. Shrinkage-induced cracking may be generated by drying/wetting cycles, with consequent faster water infiltration from the top of slopes and reduction of the safety factor. Vegetation roots were proven to increase soil shear strength, but less is known about their effects on soil tensile strength. For this purpose, new equipment has been designed and used to induce plant growth in compacted soil samples and to perform uniaxial tensile tests on the reinforced material. The equipment is composed of two cylindrical moulds linked by a soil bridge in which the tensile crack is induced due to geometrical restraints.</p><p>For this study, silty sand was chosen and compacted at a low dry density (ρ<sub>d</sub> = 1.60 Mg/m<sup>3</sup>) and at a water content w = 15%. After compaction, samples were gently poured with water up to a high degree of saturation (S<sub>r</sub> ≈ 0.95) and low suction (s ≈ 1 kPa). Then, six of them were seeded with Cynodon dactilon, adopting fixed seeding density and spacing. Plants were irrigated and let to grow for three months: during this period, suction was monitored by a tensiometer. Seven fallow specimens were prepared following the same procedure, for comparison purposes.</p><p>When ready, samples were dried in a temperature/relative humidity-controlled room and left in the darkness for three hours, to attain and equalise the desired value of initial suction. Finally, the tensile stress was induced on the soil by a displacement rate of 0.080 mm/min. For each test, suction was continuously monitored by a tensiometer while the water content was checked at the beginning and at the end. Moreover, the void ratio and the root volume and area ratio were assessed close to the crack generated, at the end of each test.</p><p>The hydraulic state affected the soil mechanical response upon uniaxial extension: an increase of strength and a more brittle behaviour were observed as suction was increasing. At the same suction, a higher strength was systematically observed in the vegetated soil. In fact, even at very low suction (i.e. s = 1 kPa), vegetation roots induced a considerable increase in soil tensile strength (i.e. 10 kPa). The soil hydraulic state also affected the root failure mechanism. In wet soil, the roots subjected to tension were stretched and pulled-out whereas in dry soil they experienced a more immediate breakage (i.e. in concomitance with the cracking of the surrounding soil). Some preliminary PIV (Particle Image Velocimetry) analyses showed differences among dry/wet and fallow/vegetated soils. Indeed, a more diffuse strain field was observed in vegetated samples, thanks to the redistribution of stresses induced by the roots.</p><p>Results were successfully interpreted by a well-established shear strength criterion for partially saturated soils, considering the degree of saturation, suction and soil microstructure. An increase of the soil shear strength was observed and correlated to the presence of roots and to their geometrical and mechanical features. Moreover, good consistency was detected with results coming from other equipment.</p><p> </p>

Use of Stiffness for Evaluating Compactness of Cohesive Pavement Geomaterials

2003 ◽  
Vol 1849 (1) ◽  
pp. 11-19 ◽  
Author(s):  
Phillip S. K. Ooi ◽  
Jianping Pu
Keyword(s):  
Shear Strength ◽  
Water Content ◽  
Volume Change ◽  
Degree Of Saturation ◽  
Unit Weight ◽  
Soil Stiffness ◽  
Soil Plasticity ◽  
Dry Unit Weight ◽  
Swell Potential

There has been a recent push toward adoption of in-place soil stiffness as a means of assessing compactness of pavement geomaterials. From a series of low strain GeoGauge stiffness measurements made under controlled laboratory conditions on compacted silts, the variation of stiffness with water content, dry unit weight, degree of saturation, volume change upon wetting, shear strength, and soil plasticity is discussed. In general, the GeoGauge stiffness is not directly related to dry unit weight, and it peaks dry of optimum and decreases upon wetting. Soil specimens with a large stiffness also tend to be stronger, but they also tend to swell more upon wetting, implying that the shrink–swell potential is not optimized if stiffness is. These results help advance the understanding of the role of stiffness in assessing compactness of cohesive geomaterials.

scholarly journals Verification of the Fredlund (2019) Unsaturated Shear Strength Function

Geosciences ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 151
Author(s):  
Thi Phuong An Tran ◽  
Delwyn G. Fredlund
Keyword(s):  
Shear Strength ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Strength Function ◽  
Past Research ◽  
Research Literature ◽  
Reference Points ◽  
Degree Of Saturation ◽  
Anchor Points

There has been a proliferation of equations proposed to describe the unsaturated shear strength envelope going back to the 1970s. However, there have been limited studies to verify the suitability of one unsaturated shear strength equation over another. Most proposed shear strength equations have attempted to relate the shear strength of an unsaturated soil to some aspect(s) of the soil–water characteristic curve (SWCC). Estimation procedures have generally focused on using that of air-entry value (AEV) as defined by the drying (or desorption) branch of the degree of saturation SWCC (S-SWCC). This paper studies the suitability of using two “anchor points” (or reference points) along the drying S-SWCC to estimate the unsaturated soil shear strength function. The anchor points referred to are the air-entry value (AEV) of the soil and the “residual suction point” of the soil defined in terms of the S-SWCC. Shear strength conditions associated with both so-called anchor points are used as “boundary conditions” that should be satisfied when estimating the shear strength function for unsaturated soils. Past research laboratory measurements published in the research literature are used as part of the verification process for this study.

scholarly journals Geo-environmental problem of snow avalanche defensive structures in mudstone zones, Niigata Prefecture, Japan

2002 ◽  
Vol 27 ◽  
Author(s):  
K. Aoyama ◽  
P. Bhattarai ◽  
M. Fukuda ◽  
J. Oku ◽  
T. Sakai
Keyword(s):  
Shear Strength ◽  
Environmental Problem ◽  
Fine Particles ◽  
Clay Fraction ◽  
High Strength ◽  
Particle Size Analysis ◽  
Snow Avalanche ◽  
Degree Of Saturation ◽  
Size Analysis ◽  
Niigata Prefecture

Fence-type defensive structures are very common on highway hillsides in Japan. They are constructed to protect the highway mainly from snow avalanche. Initially, these structures behave well. However, as the time lapses, the foundation of these well designed structures weakens and collapses. The situation is further aggravated by the static load of accumulated thick snow cover behind them. As mudstone is the dominant rock type in the Niigata Prefecture, it is a challenging task for geotechnical engineers to cope with such a severe geo-environmental problem. Although the mudstone exhibits a high strength while it is dry and fresh, it becomes quite unstable after sometime. When it comes in contact with water and atmosphere repeatedly, it starts weathering. Consequently, its shear strength is reduced and cannot resist the imposed shear stress and moment, and ultimately fails. For the laboratory investigation, mudstone blocks of various sizes were collected from the two typical mudstone areas: the Matsunoyama area and Nagaoka area in the Niigata Prefecture. These samples were sub merged and then dried alternately for several cycles. The particle size analysis of the weathered material showed that the proportion of fine particles increased with the degree of weathering. The laboratory tests of these samples exhibited a decrease in shear strength with an increasing degree of saturation. The periodic swelling and contraction of the clay fraction leads to volume change of foundation inducing its further weathering.

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