A Bending Test for Determining the Atterberg Plastic Limit in Soils

Area of Science:

• Geotechnical Engineering
• Soil Mechanics
• Material Science

Background:

• The standard thread rolling test for determining the plastic limit (PL) in soils is subjective and operator-dependent.
• Existing alternative methods lack the speed, simplicity, and cost-effectiveness of the standard test.
• A previous study introduced a simplified thread bending test to reduce operator interference.

Purpose of the Study:

• To present a refined version of the thread bending test for determining the plastic limit (PL) in soils.
• To enable direct calculation of PL using an equation, eliminating the need for graphical analysis.
• To assess the accuracy and applicability of the new bending test across various soil types.

Main Methods:

• Utilizes soil threads (3 mm diameter, 52 mm length) bent until cracking occurs.
• Measures the degree of bending and associated moisture content.
• Calculates the plastic limit directly from a derived equation, ideally with two experimental points.

Main Results:

• The refined bending test yields PL results comparable to the standard rolling test performed by experienced operators.
• The method demonstrates high accuracy across diverse soil types, including challenging low-plasticity soils.
• Slight discrepancies were noted in high-plasticity cohesive soils, but overall performance is robust.

Conclusions:

• The modified thread bending test provides a reliable, objective, and efficient alternative for determining the plastic limit in soils.
• This method enhances accuracy and reduces operator bias, particularly for soils difficult to test with conventional methods.
• The equation-based approach simplifies PL determination, making it accessible for routine geotechnical analysis.