A Simplified Direct Shear Testing Procedure to Evaluate Unsaturated Shear Strength

Abstract

The work in this paper presents a simplified and expedient procedure to evaluate unsaturated shear strength using conventional direct shear testing with tensiometer-measured suctions. Two types of residual soils are utilized in this testing program. These are classified as elastic silt (MH) and silt (ML) and were obtained from a test site in Greensboro, North Carolina. Unsaturated triaxial tests were performed to provide reference values for comparison with the measured values from the proposed direct shear testing approach. Both single stage and multistage triaxial tests were performed, and an insignificant difference in the peak stress from both approaches was found. The total cohesion intercept was used to represent the strength contribution of the matric suction in order to normalize the effect of the confining pressure. The applicability of the simplified expedient procedure in assessing shear strength of residual soils used herein was demonstrated based on the total cohesion intercepts obtained from both testing approaches. The results from the proposed approach were very similar to those obtained from the unsaturated triaxial compression tests.

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

“…Oberg and Sallfors [32] presented a formula for calculating the shear strength of unsaturated soils in combination with soil saturation and matric suction. Tang et al [33] discussed the feasibility of using conventional direct shear instrument combined with the initial soil-water characteristic curve of 0 pressure to estimate the strength of unsaturated soil. This paper conducted three experiments, respectively, for the unsaturated soil consolidation test, conventional direct shear test, and equal suction direct shear test.…”

“…This paper conducted three experiments, respectively, for the unsaturated soil consolidation test, conventional direct shear test, and equal suction direct shear test. The unsaturated soil consolidation test can obtain soil-water characteristic curve, which describes the relationship between matric suction and water content of soils and reflects the waterholding capacity of soils under suction [33]. The conventional direct shear test is to obtain the shear strength of the soil with different water contents, which reflects the relationship between the different water content and the shear strength; the equal suction direct shear test can directly obtain the shear strength of the soil under different matric suction states.…”

Osmotic Oedometer Using Sodium Chloride Solution and Reverse Osmosis Membrane

“…This method is usually used for unsaturated soil characterization for soil suctions between 0 and 1,500 kPa (Fredlund and Rahardjo 1993). The axis-translation technique has been applied in geotechnical testing using triaxial apparatus (Ho and Fredlund 1982;Rahardjo et al 1995;Thu, Rahardjo, and Leong 2006;Goh, Rahardjo, and Leong 2014), direct shear apparatus (Gan, Fredlund, and Rahardjo 1988;Nam et al 2011;Chen et al 2013;Tang, Borden, and Gabr 2018), and oedometer (Matyas and Radhakrishna 1968;Kassiff and Shalom 1971;Delage, Vicol, and de Silva 1992;Delage and Cui 2008a;Nowamooz and Masrouri 2008;Ajdari, Monghassem, and Reza Lari 2016;Derfouf et al 2020). The other method uses salt solutions.…”

Suction and strength of unsaturated soils

“…The shear strength parameters of unsaturated soils have been investigated using modified triaxial and direct shear apparatuses (Ho and Fredlund 1982, Fredlund et al 1987, Gan and Fredlund 1988, Escario et al 1989, Rahardjo et al 1995, Kato et al 2011, Schnellmann et al 2013, Tang et al 2018.…”

“…The axis translation technique has been applied in geotechnical testing using triaxial apparatus (Ho and Fredlund 1982, Rahardjo et al 1995, Thu et al 2006, Goh et al 2014, direct shear apparatus (Gan et al 1988, Nam et al 2011, Chen et al 2013, Tang et al 2018) and oedometer (Matyas and Radhakrishna 1968, Kassiff and Shalom 1971, Delage et al 1992, Delage and Cui 2008, Nowamooz and Masrouri 2008, Ajdari et al 2016, Derfouf et al 2020).…”