• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.7
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• pp.35-43
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• 2006

This study was carried out to investigate the liquefaction behaviour and predict deviator stress with matric suction, of unsaturated silty sand. The unsaturated soil tests were conducted using a modified triaxial cell and specimens were prepared using the moisture tamping method. The axis translation technique was used to create the desired matric suctions in the specimen. Undrained triaxial compression tests were carried out at matric suction of 0, 2, 5, 10 and 25 kPa. The specimens were sheared to axial strains of about 20% to obtain steady state conditions. The results showed that liquefaction of silty sand only occurs at matric suction of 0 kPa and 2 kPa. The results also show that at matric suctions of 5, 10 and 25 kPa, the resistance to liquefaction increases. As the suction increases, the undrained effective stress path approached the drained stress path. Also, the predicted and measured maximum deviator stress for unsaturated soils using the effective stress concept showed good agreement as matric suction increases. The deviator stress increase is nonlinear as matric suction increases.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.509-516
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• 2002

Rainfall-induced landslides in a weathered granite soil slope have mostly relative shallow slip surfaces above the groundwater table The pore-water pressure of soil above the groundwater table is usually negative. This negative pore-water pressure(or matric suction) has been found to make a large contribution to the slope stability. Therefore, the variation of in-situ matric suction profiles with time in a soil slope should be understood. In this study, a field measurement program was carried out from June to August, 2001 to monitor in-situ matric suctions and volumetric water contents in a weathered granite soil slope. The influence of climatic conditions on the variation of in-situ matric suctions could be found to decrease rapidly with depth. It could be found that decrement of matric suction induced by precipitation is affected not only by the amount and duration of rainfalls but also by the initial matric suction just prior to rainstorms. The soil-water characteristic from the field monitoring tends toward the wetting path of SWCC obtained from the laboratory test.

• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.5
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• pp.37-42
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• 1998

This study was performed to evaluate the characteristics of volume change is unsaturated clayed soil. The medium-plastic clay was selected and compacted by 50% of Proctor standard compaction energy at 6% higher moisture content than its OMC. A series of isotropic compression tests and triaxial shear tests were performed. The results of the study are summarized as follows. At each matric suction, when the matric suction was increased, the yield stress was increased and slope of volume change was decreased. The more net mean stress was, the less the quantity of volume change was. In shear test, the volumetric strain was much rapidly changed in large matric than in low matric suctions. But the effect of matric suction to volume change disappeared under high net mean stress. At lower deviator stress the more matric suction was, the higher volume change was. But As the matric suction was increasing, the behavior of the unsaturated clayey soil was similar to that of saturated clayey soil. Volume change in the unsaturated clayey soil can be represented as a unique plane in three-dimensional space, which is the axes of net mean stress, matric suction and void ratio.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.143-151
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• 2005

This paper presented a method to estimate the consolidation yield stress of compacted soil with an unsaturated soil mechanics, especially considering the effect of matric suction. Then two kinds of experiments were conducted. One is a series of static compaction tests to monitor the matric suction, and the other is a series of consolidation tests on compacted soil without soaking. The results indicate that it is possible to derive the distribution of matric suction on compaction curves and to hypothesize the changes of the void ratio depending on the matric suction in the consolidation tests. With this experimental results, a new method was introduced to estimate the consolidation yield stress of compacted soil including compaction curves.

• Geomechanics and Engineering
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• v.23 no.4
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• pp.339-349
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• 2020

This study investigates the feasibility of using the results of the UPV (ultrasonic pulse velocity) test to assess the UCS (unconfined compressive strength) of unsaturated soil. A series of laboratory tests was conducted on samples of unsaturated lateritic soils of northern Taiwan. Specifically, the unconfined compressive test was combined with the pressure plate test to obtain the unconfined compressive strength and its matric suction (s) of the samples. Soil samples were first compacted at the designated water content and subsequently subjected to the wetting process for saturation and the following drying process to its target suction using the apparatus developed by the authors. The correlations among the UCS, s and UPV were studied. The test results show that both the UCS and UPV significantly increased with the matric suction regardless of the initial compaction condition, but neither the UCS nor UPV obviously varied when the matric suction was less than the air-entry value. In addition, the UCS approximately linearly increased with increasing UPV. According to the investigation of the test results, simplified methods to estimate the UCS using the UPV or matric suction were established. Furthermore, an empirical formula of the matric suction calculated from the UPV was proposed. From the comparison between the predicted values and the test results, the MAPE values of UCS were 4.52-9.98% and were less than 10%, and the MAPE value of matric suction was 17.3% and in the range of 10-20%. Thus, the established formulas have good forecasting accuracy and may be applied to the stability analysis of the unsaturated soil slope. However, further study is warranted for validation.

• Magazine of the Korean Society of Agricultural Engineers
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• v.45 no.6
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• pp.153-161
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• 2003

The purpose of this paper is to investigate the soil-water characteristic curves for an unsaturated soil. To this ends, a series of suction measured test was conducted on the selected 4 kinds of soils taken from different sites of Korea, using modified pressure plate apparatus. Form the test results, the water contents, degree of saturation and volumetric water contents were analyzed with the suction. And the soil-water characteristic curves of unsaturated soil were drawn from the test results for various factors. The characteristic curves drawn with water content vs matric suction were classified certainly the difference in wet side but were not classified in dry side. The characteristic curves drawn with degree of saturation vs matric suction for unsaturated soil were shown the opposite inclination as compared with the former curve. But the characteristic curve with volumetric water content vs matric suction was described suitably not only in wet side condition but also in dry side. And it was found that the volumetric water contents of loose soil was high at the initial condition but that of dense soil was high at final condition (dry side).

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.4
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• pp.51-57
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• 2006

This study was carried out to investigate the soil water characteristic curve and prediction of void ratio with net stress and matric suction using the linear elastic and volumetric deformation analysis method on unsaturated silty. The unsaturated soil tests were conducted using a modified oedometer cell and specimens were prepared at water content 2 times of liquid limit and required void ratio. The axis translation technique was used to create the desired matric suctions in the samples. It is shown that soil water characteristic curve and volumetric water content were affected significantly by preconsolidation pressure. As a matric suction increases, the reduction ratio of void ratio was shown to considerably small. Also, the predicted and measured void ratio for unsaturated soils using the linear elastic and volumetric deformation analysis showed good agreement as net stress and matric suction increases.

• Smart Structures and Systems
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• v.7 no.4
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• pp.263-274
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• 2011

A reliability-based slope stability assessment method considering fluctuations in the monitored matric suction was proposed for real-time identification of slope risk. The assessment model was based on the limit equilibrium model for infinite slope failure. The first-order reliability method (FORM) was adopted to calculate the probability of slope failure, and results of the model were compared with Monte-Carlo Simulation (MCS) results to validate the accuracy and efficiency of the model. The analysis shows that a model based on Advanced First-Order Reliability Method (AFORM) generates results that are in relatively good agreement with those of the MCS, using a relatively small number of function calls. The contribution of random variables to the slope reliability index was also examined using sensitivity analysis. The results of sensitivity analysis indicate that the effective cohesion c' is a significant variable at low values of mean matric suction, whereas matric suction ($u_a-u_w$) is the most influential factor at high mean suction values. Finally, the reliability indices of an unsaturated model soil slope, which was monitored by a wireless matric suction measurement system, were illustrated as 2D images using the suggested probabilistic model.

• Journal of the Korean Geotechnical Society
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• v.23 no.10
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• pp.57-64
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• 2007

Since matric suction of unsaturated soil was related to soil and ground water contaminations, it is very important to analyze its mechanism that was represented by shear characteristics. In three phases of soil, a little air makes the condition of unsaturated soil on contract or shrinkage surface between water and air. Capillarity and suction in pore of unsaturated soil cause surface tension and surface force so it makes negative pore water pressure and increases effective stress as a result. Therefore, negative pore water pressure in partially saturated soil affects the soil structure and degree of saturation and it is important to evaluate accurately unsaturate flow and behavior. In this study, the shear strength characteristics of the seven sandy soils were investigated using consolidated drained triaxial tests with special emphasis on the effects of the negative pore pressure and the matric suction. These tests involved shearing under either a constant net confining pressure and varying matric suction or under a constant matric suction and varying net normal stress.

• Journal of the Korean Geotechnical Society
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• v.27 no.8
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• pp.31-37
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• 2011

In order to evaluate the effect of matric suction on the strength and deformation characteristics, the unsaturated unconfined compression test is performed for the statical1y compacted silty sand. Specimens used were made under conditions with various initial degrees of saturation. The initial matric suction, matric suction at the peak shear strength and the volumetric deformation during the shear process were measured. From these results, it was found that the initial degree of saturation exerts the influence on the behaviors of suction, peak shear strength and the volumetric deformation. Furthermore, the suction stress($P_s$) which means the apparent cohesion due to matric suction in the unsaturated shear strength could be derived.