Shear strength characteristics of an unsaturated expansive clay

2006 ◽  
Vol 43 (7) ◽  
pp. 751-763 ◽  
Author(s):  
Tony LT Zhan ◽  
Charles WW Ng
Keyword(s):  
Shear Strength ◽  
Manganese Oxides ◽  
Matric Suction ◽  
Strength Characteristics ◽  
Water Volume ◽  
Silty Clay ◽  
Expansive Clay ◽  
Direct Shear ◽  
Peak Shear Strength ◽  
Direct Shear Tests

The shear strength characteristics of an expansive clay from China were studied by performing suction-controlled direct shear tests on both natural and compacted specimens. The tested soil was a silty clay with intermediate plasticity and medium expansion potential. A modified direct shear apparatus with a newly developed water volume indicator was used for this laboratory study. The experimental results clearly show that the dilatancy of the expansive clay increases with an increase in the applied suction for both the natural and compacted specimens. Matric suction contributes to the shear strength of the expansive clay via two different mechanisms: the contribution of capillary force to interparticle normal stress, and the effect of suction on soil dilatancy. As a result of the second mechanism, the contribution of suction to peak shear strength for the clay is more significant than that to post-failure shear strength, particularly at a high suction range. The contribution of suction to post-failure shear strength for the natural specimen is basically consistent with that for the compacted specimen. The higher peak shear strength and dilatancy for the natural specimen are related to the cementation effect of the iron and manganese oxides. The contribution of suction to shear strength for the compacted expansive clay is more significant than that for a compacted kaolin at suctions less than 100 kPa.Key words: expansive clay, matric suction, shear strength, dilatancy, direct shear test, water content.

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.

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.

Analyses on the Differences of the Consolidated Quick Direct Shear Strength Index of the Silty Clay

2011 ◽  
Vol 71-78 ◽  
pp. 1907-1910
Author(s):  
Tian Yun Liu ◽  
Ai Min Liu ◽  
Zhi Fa Yu
Keyword(s):  
Shear Strength ◽  
Friction Angle ◽  
Soil Samples ◽  
Silty Clay ◽  
Direct Shear ◽  
Strength Index ◽  
Shear Tests ◽  
Direct Shear Tests ◽  
Before And After ◽  
Different Levels

It is found that great differences exist in the consolidated quick direct shear strength index of the silty clay based on several consolidated quick direct shear tests with different rate of shear. In this letter, the changes of the water-content coefficients of the soil samples before and after the tests are analyzed. The results indicate that the drain consolidation phenomenon exists during the consolidated quick direct shear tests. Different rates of shear are corresponding to different levels of drain consolidation, and then the strength index is different. Furthermore, the reason of the fact that the friction angle of the silty clay relatively increases with different rates of shear, while the cohesive strength decreases relatively is explained.

scholarly journals Mechanical Properties and Micro Mechanism of Nano-Clay-Modified Soil Cement Reinforced by Recycled Sand

2021 ◽  
Vol 13 (14) ◽  
pp. 7758
Author(s):  
Biao Qian ◽  
Wenjie Yu ◽  
Beifeng Lv ◽  
Haibo Kang ◽  
Longxin Shu ◽  
...  
Keyword(s):  
Shear Strength ◽  
Void Ratio ◽  
Soil Mass ◽  
Direct Shear ◽  
Test Results ◽  
The Sustainable Development ◽  
Direct Shear Tests ◽  
Soil Cement ◽  
Nano Clay ◽  
New Material

To observe the effect of recycled sand and nano-clay on the improvement of the early strength of soil-cement (7d), 0%, 10%, 15% and 20% recycled sand were added. While maintaining a fixed moisture content of 30%, the ratios of each material are specified in terms of soil mass percentage. The shear strength of CSR (recycled sand blended soil-cement) was investigated by direct shear test and four groups of specimens (CSR-1, CSR-2, CSR-3 and CSR-4) were obtained. In addition, 8% nano-clay was added to four CSR groups to obtain the four groups of CSRN-1, CSRN-2, CSRN-3 and CSRN-4 (soil-cement mixed with recycled sand and nano-clay), which were also subjected to direct shear tests. A detailed analysis of the modification mechanism of soil-cement by recycled sand and nano-clay was carried out in combination with scanning electron microscopy (SEM) and IPP (ImagePro-Plus) software. The test results showed that: (1) CSR-3 has the highest shear strength due to the “concrete-like” effect of the incorporation of recycled sand. With the addition of 8% nano-clay, the overall shear strength of the cement was improved, with CSRN-2 having the best shear strength, thanks to the filling effect of the nano-clay and its high volcanic ash content. (2) When recycled sand and nano-clay were added to soil-cement, the improvement in shear strength was manifested in a more reasonable macroscopic internal structure distribution of soil-cement. (3) SEM test results showed that the shear strength was negatively correlated with the void ratio of its microstructure. The smaller the void ratio, the greater the shear strength. This shows that the use of reclaimed sand can improve the sustainable development of the environment, and at the same time, the new material of nano-clay has potential application value.

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.

scholarly journals Strength Tests and Numerical Simulations of Loess Modified by Desulfurization Ash and Fly Ash

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 512
Author(s):  
Zhi Cheng ◽  
Xinrong Cheng ◽  
Yuchao Xie ◽  
Zhe Ma ◽  
Yuhao Liu
Keyword(s):  
Shear Strength ◽  
Fly Ash ◽  
Power Plants ◽  
Utilization Rate ◽  
Direct Shear ◽  
Test Results ◽  
Mass Ratio ◽  
Direct Shear Tests ◽  
Strength Tests ◽  
Actual Test

Desulfurization ash and fly ash are solid wastes discharged from boilers of power plants. Their utilization rate is low, especially desulfurization ash, most of which is stored. In order to realize their resource utilization, they are used to modify loess in this paper. Nine group compaction tests and 32 group direct shear tests are done in order to explore the influence law of desulfurization ash and fly ash on the strength of the loess. Meanwhile, FLAC3D software is used to numerically simulate the direct shear test, and the simulation results and the test results are compared and analyzed. The results show that, with the increase of desulfurization ash’s amount, the shear strength of the modified loess increases first and then decreases. The loess modified by the fly ash has the same law with that of the desulfurization ash. The best mass ratio of modified loess is 80:20. When the mass ratio is 80:20, the shear strength of loess modified by the desulfurization ash is 12.74% higher than that of the pure loess on average and the shear strength of loess modified by fly ash is 3.59% higher than that of the pure loess on average. The effect of the desulfurization ash on modifying the loess is better than that of the fly ash. When the mass ratio is 80:20, the shear strength of loess modified by the desulfurization ash is 9.15% higher than that of the fly ash on average. Comparing the results of the simulation calculation with the actual test results, the increase rate of the shear stress of the FLAC3D simulation is larger than that of the actual test, and the simulated shear strength is about 8.21% higher than the test shear strength.

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