Shear strength and dilative characteristics of an unsaturated compacted completely decomposed granite soil

2010 ◽  
Vol 47 (10) ◽  
pp. 1112-1126 ◽  
Author(s):  
Md. Akhtar Hossain ◽  
Jian-Hua Yin
Keyword(s):  
Shear Strength ◽  
Normal Stress ◽  
Matric Suction ◽  
Water Retention Curve ◽  
Direct Shear ◽  
Normal Stresses ◽  
Soil Water Retention Curve ◽  
Strength Data ◽  
Decomposed Granite ◽  
Completely Decomposed Granite

Shear strength and dilative characteristics of a re-compacted completely decomposed granite (CDG) soil are studied by performing a series of single-stage consolidated drained direct shear tests under different matric suctions and net normal stresses. The axis-translation technique is applied to control the pore-water and pore-air pressures. A soil-water retention curve (SWRC) is obtained for the CDG soil from the equilibrium water content corresponding to each applied matric suction value for zero net normal stress using a modified direct shear apparatus. Shear strength increases with matric suction and net normal stress, and the failure envelope is observed to be linear. The apparent angle of internal friction and cohesion intercept increase with matric suction. A greater dilation angle is found at higher suctions with lower net normal stresses, while lower or zero dilation angles are observed under higher net normal stresses with lower suctions, also at a saturated condition. Experimental shear strength data are compared with the analytical shear strength results obtained from a previously modified model considering the SWRC, effective shear strength parameters, and analytical dilation angles. The experimental shear strength data are slightly higher than the analytical results under higher net normal stresses in a higher suction range.

Shear strength characteristics of two saprolitic soils

1996 ◽  
Vol 33 (4) ◽  
pp. 595-609 ◽  
Author(s):  
Julian K-M Gan ◽  
D G Fredlund
Keyword(s):  
Shear Strength ◽  
Characteristic Curve ◽  
Matric Suction ◽  
Coarse Grained ◽  
Triaxial Tests ◽  
Direct Shear ◽  
Strength Behavior ◽  
Decomposed Granite ◽  
Insight Into ◽  
Completely Decomposed Granite

The saturated and unsaturated shear strength behavior of an undisturbed, completely decomposed fine ash tuff and an undisturbed, completely decomposed granite from Hong Kong were studied using direct shear and triaxial tests. The completely decomposed fine ash tuff is a fine- to medium-grained saprolite. The completely decomposed granite is a coarse-grained saprolite. Results show that matric suction increases the shear strength of both soils. The extent of the increase is the shear strength with matric suction is related to the soil-water characteristic curve for the soil and to the amount of dilation during shear. The effect of matric suction on the shear strength was more pronounced for the fine- to medium-grained completely decomposed fine ash tuff than for the coarse-grained completely decomposed granite. These studies on the saprolitic soils provide insight into the understanding of the shear strength of unsaturated, coarse-grained soils. Key words: saprolites, shear strength, matric suction, triaxial, direct shear, coarse-grained soils.

scholarly journals Study on Water Characteristic Curve and Shear Characteristics of Typical Unsaturated Silty Clay in Shaoxing

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Ruiqian Wu ◽  
Youzhi Tang ◽  
Shaohe Li ◽  
Wei Wang ◽  
Ping Jiang ◽  
...  
Keyword(s):  
Shear Strength ◽  
Internal Friction ◽  
Unsaturated Soil ◽  
Direct Shear Test ◽  
Shear Test ◽  
Characteristic Curve ◽  
Friction Angle ◽  
Matric Suction ◽  
Silty Clay ◽  
Direct Shear

In order to probe into one simplified method to predict the shear strength of Shaoxing unsaturated silty clay, the test method combining unsaturated soil consolidation instrument and conventional direct shear instrument is used to study the shear strength, and the method is compared and verified with the results of equal suction direct shear test. The research results show that the soil water characteristic curve fitted by the measured data points and VG model has obvious stage characteristics in the range of 0~38 kPa, 38~910 kPa, and 910~10000 kPa. The shear strength of unsaturated soil measured by consolidation meter combined with conventional direct shear test is in good agreement with that measured by equal suction direct shear test in the range of 0~500 kPa. The results show that the shear strength, total cohesion, and effective internal friction angle of soil increase slightly with the increase of matric suction in the range of 0~38 kPa. When the matric suction increases from 38 kPa to 500 kPa, the shear strength and total cohesion force of the soil have similar stage characteristics with the SWCC, which first increases and then tends to be stable, while the effective internal friction angle changes slightly. Finally, taking the air-entry value as the demarcation point, an improved model of unsaturated shear strength is proposed by analyzing the error value. Compared with the measured value, the absolute value of relative error is basically kept in the range of 5%~10%, which is close to the measured value.

scholarly journals Effect of gypsum content on unsaturated engineering properties of clayey soil

2020 ◽  
Vol 9 (1) ◽  
pp. 84
Author(s):  
Mohammed N J Alzaidy
Keyword(s):  
Shear Strength ◽  
Clayey Soil ◽  
Engineering Properties ◽  
Water Retention Curve ◽  
Shear Strength Parameters ◽  
Swelling Potential ◽  
Soil Water Retention Curve ◽  
Strength Parameters ◽  
Gypsum Content ◽  
Vapour Diffusion

Many of gypsum soils have existed in arid and semi-arid lands. It is considered one of the most problematic soils because of its complicated and unpredicted behavior when exposure to moisture. Extensive researches have been conducted in Iraq to observe the behavior of such soil and to suggest safety restrictions for the collapse and set practical precautions for the structures. This study investigated the effect of gypsum content on some unsaturated engineering properties of a clayey soil. Three different proportions of gypsum (0%, 5% and 20% by weight of the parent soil) were added and tested. The samples have been subjected to swelling potential test, soil water retention curve (SWRC), vapour diffusion and shear strength parameters. It is observed that gypsum content has a significant influence on SWRC, whereas, soil that has high gypsum content made SWRC with higher variables represented by air entry values and residual state. On the other hand, an increase in gypsum content led to a reduction of swelling potential and shear strength parameters. The results of vapour diffusion indicate that gypsum content could modify the microstructure in an unsaturated state and reduce the vapour diffusion through the soil.  

scholarly journals Effects of inclusion of granulated rubber tires on the mechanical behaviour of a compressive sand

2020 ◽  
Vol 57 (5) ◽  
pp. 763-769 ◽  
Author(s):  
W. Li ◽  
C.Y. Kwok ◽  
K. Senetakis
Keyword(s):  
Particle Size ◽  
Shear Strength ◽  
Mechanical Behaviour ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Rubber Content ◽  
Filling Materials ◽  
Rubber Particles ◽  
Decomposed Granite ◽  
Completely Decomposed Granite

Drained triaxial shearing tests were performed on a well-graded compressive sand (completely decomposed granite, CDG) and its mixtures with granulated rubber tires to investigate the effects of rubber size and content on their mechanical behaviour. Three sizes of rubber particles, GR1, GR2, and GR3, were used with size ratios to CDG (D50,rubber : D50,CDG) of 0.9, 3.5, and 7.2, respectively, and the rubber content ranged from 0% to 30%. The results show that for CDG–GR1 mixtures, the strength decreases with increasing rubber content, while for CDG–GR2 and CDG–GR3 mixtures, the strength decreases only at 10% rubber content and then increases markedly with increasing rubber content. The increase of strength is mainly because the inclusion of large rubber particles widens the particle size distributions of the mixtures, resulting in denser packings. The denser packings also lead to a decrease in compressibility. At larger size ratio and higher rubber content, the CDG–rubber mixtures show higher shear strength and lower compressibility than pure CDG, which indicates the CDG–rubber mixtures are very suitable to be used as filling materials.

scholarly journals Numerical Analysis for the Progressive Failure of Binary-Medium Interface under Shearing

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Rihong Cao ◽  
Wenyu Tang ◽  
Hang Lin ◽  
Xiang Fan
Keyword(s):  
Shear Strength ◽  
Bond Strength ◽  
Normal Stress ◽  
Strength Ratio ◽  
Normal Stresses ◽  
Stress Increase ◽  
Tensile Cracks ◽  
Medium Interface ◽  
High Bond ◽  
High Bond Strength

Binary-medium specimens were fabricated using the particle flow code, and the shear strength, dilatancy, and failure behavior of the binary-medium specimens with different bond strength ratios (0.25, 0.5, 0.75, and 1.0) under different normal stresses were studied. Numerical results show that the bond strength ratio and normal stresses considerably influence the shear strengths of binary-medium interface. Shear strength increases as the bond strength ratio and normal stress increase. The dilation of interfaces with high bond strength ratios is more evident than those of interfaces with lower bond strength ratios, and the curves for the high bond strength ratio exhibit remarkable fluctuations during the residual stage. At increased normal stress and bond strength ratio, the peak dilation angle shows decreasing and increasing trends successively. In this study, the specimens exhibited three kinds of failure modes. In mode II, the sawtooth experienced shear failure, but some tensile cracks appeared on the interface of the binary-medium. In mode III, no sawtooth was cut off, indicating tensile failure on the interface. At a low bond strength ratio, damage or failure is mostly concentrated in the upper part of the model. Failure parts gradually transfer to the lower part of the model when the bond strength ratio and normal stress increase. Furthermore, evident tensile cracks occur on the interface. When the bond strength ratio reaches 1.0, the failure mode of the specimen gradually transforms from sheared-off failure to chip-off failure. The number of microcracks in the specimens indicates that the lower the bond strength ratio, the more severe the damage on the specimens.

scholarly journals Effect of Rock Particle Content on the Mechanical Behavior of a Soil-Rock Mixture (SRM) via Large-Scale Direct Shear Test

2019 ◽  
Vol 2019 ◽  
pp. 1-16
Author(s):  
Longqi Liu ◽  
Xuesong Mao ◽  
Yajun Xiao ◽  
Qian Wu ◽  
Ke Tang ◽  
...  
Keyword(s):  
Shear Strength ◽  
Normal Stress ◽  
Large Scale ◽  
Direct Shear Test ◽  
Shear Test ◽  
Volumetric Strain ◽  
Direct Shear ◽  
Stress Strain ◽  
Particle Content ◽  
Rock Particle

The mechanical strength of the landslide deposits directly affects the safety and operation of the roads in the western mountainous area of China. Therefore, the research is aimed at studying the mechanisms of a landslide deposit sample with different rock particle contents by analyzing its characteristics of the stress-strain behavior, the “jumping” phenomenon, the volumetric strain, and the shear strength parameters via a large-scale direct shear test. Stress-strain results show that stress-strain curves can be divided into 3 different stages: liner elastic stage, yielding stage, and strain-hardening stage. The shear strength of SRM behaves more like “soil” at a lower rock particle content and behaves more like “rock joints” at a higher rock particle content. Characteristics of the “jumping” phenomenon results show that the “intense jumping” stage becomes obvious with the increasing rock particle content and the normal stress. However, the lower the rock particle content is, the more obvious the “jumping” phenomenon under the same normal stress is. Volumetric strain results show that the sample with a lower rock particle content showed a dilatancy behavior under the low normal stress and shrinkage behavior under the high normal stress. The dilatancy value becomes smaller with the increasing normal stress. The maximum shear stress value of the rock particle content corresponds to the maximum value of dilatancy or shrinkage. We also conclude that the intercept of the Mohr failure envelope of the soil-rock mixture should be called the “equivalent cohesion,” not simply called the “cohesion.” The higher the normal stress and rock particle content are, the bigger the equivalent cohesion and the internal friction angle is.

Shear strength of unsaturated soil interfaces

2009 ◽  
Vol 46 (5) ◽  
pp. 595-606 ◽  
Author(s):  
Tariq B. Hamid ◽  
Gerald A. Miller
Keyword(s):  
Shear Strength ◽  
Unsaturated Soil ◽  
Characteristic Curve ◽  
Matric Suction ◽  
Direct Shear ◽  
Direct Shear Tests ◽  
Strength Failure ◽  
Suction Control ◽  
Failure Envelopes ◽  
Fine Grained Soil

Unsaturated soil interfaces exist where unsaturated soil is in contact with structures such as foundations, retaining walls, and buried pipes. The unsaturated soil interface can be defined as a layer of unsaturated soil through which stresses are transferred from soil to structure and vice versa. In this paper, the shearing behavior of unsaturated soil interfaces is examined using results of interface direct shear tests conducted on a low-plasticity fine-grained soil. A conventional direct shear test device was modified to conduct direct shear interface tests using matric suction control. Further, the results were used to define failure envelopes for unsaturated soil interfaces having smooth and rough counterfaces. Results of this study indicate that matric suction contributes to the peak shear strength of unsaturated interfaces; however, postpeak shear strength did not appear to vary with changes in matric suction. Variations in net normal stress affected both peak and postpeak shear strength. Failure envelopes developed using the soil-water characteristic curve (SWCC) appeared to capture the nonlinear influence of matric suction on shear strength of soil and interfaces.

On the Hypothesis of Effective Stress in Consolidation and Strength for Unsaturated Soils

2012 ◽  
Vol 256-259 ◽  
pp. 108-111
Author(s):  
Seboong Oh ◽  
Ki Hun Park ◽  
Oh Kyun Kwon ◽  
Woo Jung Chung ◽  
Kyung Joon Shin
Keyword(s):  
Shear Strength ◽  
Soil Water ◽  
Effective Stress ◽  
Unsaturated Soils ◽  
Water Retention Curve ◽  
Triaxial Tests ◽  
Residual Soil ◽  
Soil Behavior ◽  
Soil Water Retention Curve ◽  
Soil Water Retention

The hypothesis on effective stress of unsaturated soils is validated by consolidation strength results of triaxial tests for the compacted residual soil. The effective stress can describe the unsaturated soil behavior, which was defined from shear strength or from soil water characteristic curves. Since the effective stress from consolidation agrees with that from the shear strength, the effective stress from soil water retention curve could describe the unsaturated behavior consistently on both consolidation path and stress at failure. The effective stress can describe the entire unsaturated behavior from consolidation to failure.

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%.

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