Stress-dependent temperature effect on the swelling behavior of compacted GMZ bentonite

A series of temperature-controlled swelling pressure and swelling strain tests were performed on Gaomiaozi (GMZ) bentonite to study the temperature effects on the swelling behavior. The influence of sample dry densities (for swelling pressure tests) and applied various vertical stresses (for swelling strain tests) were taken into account. Emphasis was put on the stress-dependent properties of temperature effects. Results show that at a certain temperature, there is a unique relationship between the stress level and the void ratio of saturated bentonite specimens for either the swelling pressure or swelling strain tests. This relationship could be defined as “swelling stable line” (SSL), which was bilinear shaped and reflects a stress-dependent swelling behavior of compacted bentonite. This stress-dependent swelling behavior is attributed to the different hydration mechanisms under lower and higher stresses. A comparison of SSLs at different temperatures shows an obvious stress-dependent behavior of temperature effects on swelling properties. These stress-dependent temperature effects on swelling behavior of GMZ bentonite are further confirmed by data collected from literatures on various types (i.e., Ca- or Na-bentonite) of bentonites: regardless of the predominant cations, the elevation of temperature increased the swelling potential in the lower stresses part of SSL, whereas it reduced the swelling potential in the higher stresses part. This phenomenon is related to the influences of temperature on the swelling processes (i.e., hydration, diffuse double-layer repulsion, and separation of elementary layers) under different stress levels.