Soil shear strength determination methods - State of the art

Soil mechanics as a field of science has been developed for over a century. One of its most important issues is determination of soil strength. Despite passing years, there is still no universal method for determination of soil shear strength. The goal of this paper was to attempt to systematize methods for measurement of soil shear strength and describe the differences between them and where the differences come from. It presents a list of over 20 types of measurement methods, including their basic features such as dimensions or measurement speed. The list contains both standard and prototype methods that can be found in the literature. These methods can be divided into those with forced (direct shear) and with free shear plane (indirect shear), which comprise penetration testing. A comparative review of literature on different measurement methods shows substantial discrepancies, reaching up to few hundred percent, between methods. Cohesion and internal friction angle determined by these methods should not be treated as soil intrinsic properties, as they are affected by a number of factors. These factors-i.e. scale effect, wall effect, strain rate effect, bulldozing effect, shear kinematics, and type of material that the tester is made of-are described in this paper. The most important parameters of the test methods were found to be the geometry, kinematics and speed. The scale effect in soils during shear is discernible up to about 300 cm2 shearing surface; therefore, for most fine-grained soils, it is not necessary to use bigger test devices. Shear speed plays a significant role for cohesive soils, increasing cohesion values threefold or more. The article concludes with guidelines that, according to the authors, should be followed when selecting a method for measurement of shear strength to be applied when determining soil traction properties.

Automated summary

The paper discusses various methods for determining soil shear strength and highlights the significant impact of factors such as measurement speed and geometric parameters. It concludes with guidelines for selecting the most suitable method for accurately measuring soil traction properties.