Thixotropic Hardening of Fao Clay

Abstract

Fao region is characterized by weak soft silty clay to clayey silt thick layer which extends to a depth of about 20 m. The construction of some structures on such soils may needs piles. During the installation of driven piles, the soil geotechnical properties are exposed to significant changes result due to shearing under large shear strains. These changes significantly decrease the shear strength of the virgin soil due to the destruction of soil structure caused by remolding. The degradation of shear strength is usually followed by strength regaining which is called “Thixotropy”. In this study, the thixotropic effect on Fao clay was investigated. Many disturbed and undisturbed soil samples were brought from Fao region. Some of the soil samples were thoroughly remolded in the laboratory in its natural water content and molded as direct shear specimens. More than 180 specimens were prepared and tested over 36 weeks in order to accurately assess the percentage of strength regaining with time passing. The results show that soil remolding causes about a 45 % reduction in shear strength in comparing with the shear strength of the intact soil. This reduced percent in shear strength was almost fully regained after 25 weeks due to thixotropic effect.

Evaluation Method for Thixotropy of Clay Subjected to Unconfined Compressive Test

“…In engineering practice, according to sensitivity, the structure of clay can be divided into three categories: low sensitivity (1 ≤ S t ≤ 2), medium sensitivity (2 < S t ≤ 4), and high sensitivity (4 < S t ), among which the limit value of sensitivity S t is 2 and 4. Referring to the Huo et al (2016); 3 Skemption and Northey (1952); 4 Kamil and Aljorany (2019).…”

“…Further studies by Kruyt (1952) indicated that thixotropy generally exists in clay-water systems. Under the influence of the thixotropy of soil, the strength and deformation characteristics of soil show strong time dependence Al-Janabi and Aubeny, 2019;Kamil and Aljorany, 2019;Ruge et al, 2019;Alam et al, 2020). Thixotropic evaluation of soil is one of the key problems in safety evaluation of foundation engineering under long-term load.…”

Unconfined compressive strength and pore structure evolution law of structural clay after disturbance

“…and studied the change rule of mechanical properties of reconstituted clays with specific water content over time, finding that the shear strength and yield stress of reconstituted clays increased significantly after 90 d compared to the initial moment. According to Kamil and Aljorany's (2019) study on the thixotropy of 180 soil samples, the strength of the soil decreased by 45% following reconstitution, and after 25 weeks of standing, the strength of the soil recovered to the strength of the undisturbed soil caused by the thixotropic effect. Under the influence of thixotropy, the strength and deformation characteristics of soil show strong time dependence (Ruge et al, 2019;Alam et al, 2021;Tang et al, 2021b).…”