The Effect of Matric Suction on the Shear Strength of Unsaturated Sandy Clay

Abstract

The shear strength parameters of the soil is the key engineering property required for the design of geotechnical structures and stability analysis. The shear strength of an unsaturated soil is controlled by matric suction. This research examined the effect of matric suction on the shear strength behavior of sandy clay using a series of experimental tests in the laboratory. The contact filter paper method was used to measure matric suction and the SoilVision knowledge-based system was used to give an approximation of the entire soil water characteristic curve (SWCC). The shear strength of the unsaturated sandy clay was examined using a series of unconsolidated undrained (UU) triaxial tests to identify the relationship between shear strength, cohesion, internal friction angle, and matric suction. The result shows that the shear strength of the soil increases as matric suction increases. It was found that when the matric suction is smaller than air entry value (AEV), the shear strength of the soil increases as matric suction increases and the increment is linear because the soil is in saturated conditions. At a certain matric suction value (on soil samples occurred at 40-600 kPa matric suction values), there is a significant increase in the shear strength of soil associated with the inter-particle force produced due to negative pore water pressure. Furthermore, at a high matric suction, the relationship between shear strength and matric suction tend to be stable as in a low water content, the matric suction is not transmitted effectively to the contact point of soil particles.

Characterization of lateritic soil based on literature and lab testing

“…In regard to Figure 9, the shear strength envelope is not horizontal due to the unsaturated condition of the specimens, i.e., the specimens were prepared using optimum water content leading to the 79% degree of saturation. The results are supported by the previous investigations in which the shear strength based on the UU test increased with the increase in suction [89,90]. Moreover, the results are consistent with previous results in which the deviator stress increased with increasing confining pressure [91].…”

Relationship of Rainfall Intensity with Slope Stability

“…Similar findings were found by Latief & Zainal [9] via the numerical method that the dry condition shows the second highest factor of safety value after groundwater level 0.5 m below ground level. This can be treated as the optimum increase in soil suction because some researchers [12][13][14][15][16] conclude that the increase in pore pressure does not always reduce the shear strength of soil. Besides, soil cohesion and internal friction angle increase as the soil suction increases.…”

Deformation and Strength of Unsaturated Loess—Hydraulic Coupling Effects under Loads

“…Wong [18] estimated the change in matric suction during the shear process by measuring matric suction before and after a UU test and using a soil water characteristic curve (SWCC) with equilibrium soil suction, explaining the characteristics of the undrained shear strength of compacted clay. Pujiastuti [21] measured the matric suction using the filter paper method and conducted a series of UU tests to measure the shear strength of unsaturated sandy clay, obtaining the relationship between shear strength, cohesion, internal friction angle, and matric suction. Therefore, utilizing UU tests to examine unsaturated soils and predict variations in matric suction throughout the shearing process based on the soil-water characteristic curve is a viable approach.…”