Shear-strength characteristics of a residual soil

1995 ◽  
Vol 32 (1) ◽  
pp. 60-77 ◽  
Author(s):  
H. Rahardjo ◽  
T.T. Lim ◽  
M.F. Chang ◽  
D.G. Fredlund
Keyword(s):  
Shear Strength ◽  
Internal Friction ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Residual Soil ◽  
Test Results ◽  
Angle Of Internal Friction ◽  
Slip Surfaces

Shallow landslides in natural residual soils slopes are common all over the world. The slip surfaces associated with these landslides are often situated above the groundwater table. Therefore, it is important to quantify the contribution of negative pore-water pressure to the shear strength of soil. The shear-strength characteristics of residual soil from the Jurong Formation in Singapore were assessed using multistage, consolidated drained triaxial tests. These tests involved shearing under either a constant net confining pressure and varying matric suctions or under a constant matric suction and varying net confining pressures. An extended form of the Mohr–Coulomb equation was used to interpret the test results. The test results show that for matric suctions up to 400 kPa, the angle of internal friction associated with the matric suction, [Formula: see text], is similar to the effective angle of internal friction, [Formula: see text], which averages 26° for the residual soil of the Jurong Formation. The residual soil can maintain a high degree of saturation for matric suctions as high as 400 kPa. Examples involving stability analyses of a residual soil slope with varying pore-water pressure profiles indicate that soil suction contributes significantly to the factor of safety, particularly for shallow slip surfaces. Key words : residual soil, unsaturated soil, matric suction, shear strength, multistage triaxial test, slope stability.

Effectiveness of Capillary Barrier and Vegetative Slope Covers in Maintaining Soil Suction

2016 ◽  
pp. 51-69
Author(s):  
Harianto Rahardjo ◽  
S. Krisnanto ◽  
E.C. Leong
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Numerical Analyses ◽  
Soil Suction ◽  
Vetiver Grass ◽  
Capillary Barrier ◽  
Maximum Rainfall

Capillary barrier and vegetative slope covers can be used to improve slope stability during rainfall by maintaining matric suction in the slope. A study was performed to investigate the effectiveness of capillary barrier system (CBS) and vegetative slope covers (Orange Jasmine and Vetiver grass) in maintaining soil suction. Performance of slopes with and without slope covers was investigated using field instrumentations and numerical analyses. Laboratory tests were performed to measure hydraulic and shear strength properties of the soil, the soils with Orange Jasmine and Vetiver grass root, and CBS materials. Numerical analyses were performed to investigate the variation of pore-water pressure profiles at a selected location and factor of safety during low, high, and maximum rainfall intensities. Pore-water pressures measured in the field were used to calibrate the numerical models. Laboratory test results showed that the presence of root increased the shear strength of soil. Numerical analyses and field monitoring results showed that the slope with covers can maintain negative pore-water pressure better than the original slope. Performance of Orange Jasmine, Vetiver grass, and CBS in maintaining matric suction in the slope is essentially similar during low, high, and maximum rainfall intensities.

scholarly journals Liquefaction, landslide and slope stability analyses of soils: a case study of soils from part of Kwara, Kogi and Anambra states of Nigeria

2016 ◽  
Author(s):  
Olusegun O. Ige ◽  
Tolulope A. Oyeleke ◽  
Christopher Baiyegunhi ◽  
Temitope L. Oloniniyi ◽  
Luzuko Sigabi
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Slope Failure ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Base Material ◽  
Liquid Limit ◽  
Soil Samples ◽  
Landslide Risk ◽  
Angle Of Internal Friction

Abstract. Landslide is one of the most ravaging natural disaster in the world and recent occurrences in Nigeria require urgent need for landslide risk assessment. A total of nine samples representing three major landslide prone areas in Nigeria were studied, with a view of determining their liquefaction and sliding potential. Geotechnical analysis was used to investigate the liquefaction potential, while the slope conditions were deduced using SLOPE/W. The results of geotechnical analysis revealed that the soils contain 6–34 % clay and 72–90 % sand. Based on the unified soil classification system, the soil samples were classified as well graded with group symbols of SW, SM and CL. The plot of plasticity index against liquid limit shows that the soil samples from Anambra and Kogi are potentially liquefiable. The liquefaction screening criteria also revealed that Anambra and Kogi are potentially susceptible to liquefaction, whereas samples from Kwara are not susceptible to liquefaction. Samples from Kogi and Anambra have lower values of MDD and OMC, ranging between 1.64–1.80 g/cm3 and 8.0–12.3 % respectively. These values showed that the samples are granular material with soil having anticipated embankments performance, subgrade and base material as poor-fair, fair-good and good-poor, respectively. The direct shear strength test on the soil samples indicated that the cohesion and angle of internal friction varies between 40 80 kPa and 24–35°. The Coefficient of permeability vary between 8.71 × 10−5 and 1.18 × 10−3. The factor of safety (FOS) values for soils from Anambra, Kogi and Kwara are 1.452, 1.946 and 2.488, respectively. These values indicate stability but care must be taken as the condition at the site shows that the slope is in its state of impending failure. The FOS for dry slope was higher when compared to the FOS values from wet slope. This was due to the effect of pore water pressure on the soil as it reduced the shear strength of the soil. A reduced value of FOS was observed in the model under loading conditions, which indicate that loading is also a contributing factor to the slope failure. It is recommended that proper and efficient drainage system should be employed in these areas to reduce the influence of pore water pressure in the soil.

Shear strength of a compacted residual soil from consolidated drained and constant water content triaxial tests

2004 ◽  
Vol 41 (3) ◽  
pp. 421-436 ◽  
Author(s):  
Harianto Rahardjo ◽  
Ong Boo Heng ◽  
Leong Eng Choon
Keyword(s):  
Shear Strength ◽  
Water Content ◽  
Pore Water ◽  
Volume Change ◽  
Triaxial Test ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Triaxial Tests ◽  
Residual Soil ◽  
Undrained Conditions

Rainfall-induced landslides in unsaturated residual soils can occur slowly under drained conditions or rapidly under undrained conditions. Consolidated drained (CD) and constant water content (CW) tests have been performed to simulate the stress paths followed by soil elements in a slope that fails under drained and undrained conditions. The study was carried out to investigate the shear strength characteristics of soils associated with rainfall-induced slope failures. The soil tested was residual soil from the Jurong sedimentary formation and was reconstituted using static compaction. The test results indicate that the shear strength of the compacted specimens obtained from the CW tests agrees well with the shear strength obtained from the CD tests for the specimens with initial matric suctions less than their air-entry values. The shear strength results from the CD and CW triaxial tests start to differ when the matric suction exceeds the air-entry value of the soil. The CD and CW triaxial tests also indicate that the compacted specimens behave as a normally consolidated soil at matric suctions below the air-entry value of the soil and as an overconsolidated soil at matric suctions above the air-entry value of the soil. Results of the CW triaxial tests show that the relationship between the response of pore-water pressure and the total volume change of the specimen is more complicated than that found in the saturated undrained triaxial tests. In other words, the change in pore-water pressure during shearing is not directly related to the overall volume change of the specimen.Key words: unsaturated soil, compacted soil, residual soil, consolidated drained triaxial test, constant water content triaxial test.

Effect of rainfall on matric suctions in a residual soil slope

1996 ◽  
Vol 33 (4) ◽  
pp. 618-628 ◽  
Author(s):  
T T Lim ◽  
H Rahardjo ◽  
M F Chang ◽  
D G Fredlund
Keyword(s):  
Slope Stability ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Residual Soil ◽  
Soil Slope ◽  
Field Instrumentation ◽  
Pore Water Pressures ◽  
Residual Soil Slope

A slope stability study involving shallow slip surfaces should include the effect of negative pore-water pressures in a slope. A field instrumentation program was carried out to monitor negative pore-water pressure (i.e., in situ matric suction) in a residual soil slope in Singapore. Variations in matric suction and the matric suction profiles under (1) a canvas-convered grassed surface, (2) a grassed surface, and (3) a bare ground surface, in response to rainfalls were investigated. Changes in matric suction due to changes in climatic conditions decrease rapidly with depth. The change was found to be most significant in the bare slope and least significant under the canvas-covered slope. The amount of decrease in matric suction after a rainstorm was observed to be a function of the initial matric suction just prior to the rainstorm. Positive pore-water pressures were observed above the groundwater table, suggesting the development of a perched water table within the slope. These observations are also typical of other regions experiencing high seasonal rainfalls. The field monitoring program presented can be adopted for investigating rainfall-induced landslides in other parts of the world. Key words: matric suction, negative pore-water pressure, field instrumentation, rainfall, residual soil, slope stability.

Conjectures, Hypotheses, and Theories of Drumlin Formation (In memory of Stanislaw Baranowski)

1981 ◽  
Vol 27 (97) ◽  
pp. 503-505 ◽  
Author(s):  
Ian J. Smalley
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Stress Level ◽  
Critical Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Glacial Till ◽  
Forming Process ◽  
Stress Levels

AbstractRecent investigations have shown that various factors may affect the shear strength of glacial till and that these factors may be involved in the drumlin-forming process. The presence of frozen till in the deforming zone, variation in pore-water pressure in the till, and the occurrence of random patches of dense stony-till texture have been considered. The occurrence of dense stony till may relate to the dilatancy hypothesis and can be considered a likely drumlin-forming factor within the region of critical stress levels. The up-glacier stress level now appears to be the more important, and to provide a sharper division between drumlin-forming and non-drumlin-forming conditions.

scholarly journals Field Test Research on Red Clay Slope under Atmospheric Action

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Kaisheng Chen
Keyword(s):  
Internal Friction ◽  
Water Content ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Friction Angle ◽  
Internal Friction Angle ◽  
Red Clay ◽  
Failure Characteristics ◽  
Clay Slopes

By embedding water content sensors and pore water pressure sensors inside the red clay slope on-site in Guiyang, Guizhou, shear tests were performed on soil samples at different depths of the slope under different weather. The changes of water content, pore water pressure, and shear strength index of the slope inside the slope under the influence of the atmosphere were tracked and tested, and the failure characteristics and evolution of the red clay slope were analyzed. It is believed that the depth of influence of the atmosphere on red clay slopes is about 0.7 m, rainfall is the most direct climatic factor leading to the instability of red clay slopes, and the evaporation effect is an important prerequisite for the catastrophe of red clay slopes. The cohesion and internal friction angle of the slope soil have a good binary quadratic function relationship with the water content and density. The water content and density can be used to calculate the cohesion and internal friction angle. Failure characteristics of red clay slopes: the overall instability failure is less, mainly surface failure represented by gullies and weathering and spalling, and then gradually evolved into shallow instability failure represented by collapse and slump. The damage evolution law is as follows: splash corrosion and surface corrosion stage⟶ fracture development stage⟶ gully formation stage⟶ gully development through stage⟶ local collapse stage⟶ slope foot collapse stage.

Infiltration characteristics of two instrumented residual soil slopes

2003 ◽  
Vol 40 (5) ◽  
pp. 1012-1032 ◽  
Author(s):  
Illias Tsaparas ◽  
Harianto Rahardjo ◽  
David G Toll ◽  
Eng-Choon Leong
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Field Measurements ◽  
Residual Soil ◽  
Rainfall Runoff ◽  
Rainfall Events ◽  
Pore Water Pressures ◽  
Soil Slopes ◽  
Pressure Changes

This paper presents the analysis of a 12 month long field study of the infiltration characteristics of two residual soil slopes in Singapore. The field measurements consist of rainfall data, runoff data of natural and simulated rainfall events, and pore-water pressure changes during infiltration at several depths and at several locations on the two slopes. The analysis of the field measurements identifies the total rainfall and the initial pore-water pressures within the two slopes as the controlling parameters for the changes in the pore-water pressures within the slopes during infiltration.Key words: infiltration, rainfall, runoff, pore-water pressure, field measurements.

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