Direct Tensile-Shear Test (DTS) on Unsaturated Kaolinite Clay

Abstract

In this study, constant-water-content direct-tensile-shear (DTS) tests were performed on specimens of kaolinite clay using a new apparatus. Existing studies on strength of clayey soils consider soils subjected to tensile stress, compression-shear stress, or triaxial stress, but only few of them account for combinations of tension and shear. The clay specimens used in this study had an average water content of 15 %. At this water content, the clay is unsaturated, the pore water distribution corresponds to the complete-pendular state, and the soil is subjected to an equivalent effective stress of 400 kPa when external confinement stress is not applied. Each specimen in the DTS test is subjected to an initial tensile stress that is maintained constant while the shear stress is gradually increased until the specimen fails. The results from DTS tests combined with other constant-water-content triaxial compression tests in the same clay produced a failure envelope defined by tensile as well as frictional components. It was found that the Mohr circles derived from the DTS tests are tangent at a common point; this point represents the tensile strength of the material. In other words, the direct shear stress applied produced a tensile failure. These concepts are helpful for understanding and analyzing the behavior of unsaturated soils and other materials subjected to tensile-shear state of stresses, which may lead to formation and/or propagation of cracks. Examples of soils subjected to tensile-shear state of stresses are slopes and desiccating soils and landfill covers.

Correlation between Soil-Shrinkage Curve and Water-Retention Characteristics

“…Hence the shrinkage rate becomes negative (∼ − 0.09) in the adsorption regime. The swelling behavior of Georgia kaolinite is consistent with several previous studies (Vesga 2009;Lu and Kaya 2013). As the matric suction increases, the volumetric water content and void ratio of the soil decreases.…”

“…2 and 5). The slight expansion exhibited by Georgia kaolinite has been previously interpreted as the result of a lack of cation hydration and the existence of capillary water among submicron particles (Vesga 2009;Lu and Kaya 2013).…”

“…5(b) and 6(b)]. Therefore, as the capillary water diminishes, the capillary force at particle contacts releases the soil skeleton without enough constraint provided by physicochemical forces and results in a slight volume swell (Vesga 2009;Lu and Kaya 2013).…”

Closure to “Generalized Equation for Soil Shrinkage Curve” by Pan Chen and Ning Lu

“…The pattern of slight swelling as the Georgia kaolinite specimen approaches the completely dry state is unmistakably a real behavior; it has been reported independently by several other investigators (Vesga 2009;Akin and Likos 2017). Such behavior would lead to a negative soil shrinkage rate that is counterintuitive, but can be physically explained (Vesga 2009;Lu and Dong 2017).…”

Meso‐Experimental Study on Tensile Characteristics of Clay

“…At present, the research achievements on the tensile properties of soils are mostly concentrated on the invention of macroscopic tensile testing devices and related experiment [2,3], and the tensile tests on different soils have been carried out, such as clayey soil [4,5], frozen soil [6], recompacted soil [7,8], reinforced soil [9,10], and unsaturated sands [11]. e stretching methods mainly include direct stretching [12][13][14][15] and indirect stretching [16][17][18].…”