Germination

Combinatorics

Geology

Brittleness

Creep

Composite material

Geotechnical engineering

Materials science

Imbibition

Mathematics

Botany

Biology

Saturation (graph theory)

Rock Mechanics and Rock Engineering

The presence of water greatly influences time-dependent rock deformation. An understanding of how water can affect the time-dependent mechanical behavior of rock is important when assessing the long-term stability of geotechnical projects. While the previous studies have performed brittle creep experiments on oven-dry or fully-saturated rocks, we report here on a study designed to better understand brittle creep at different levels of saturation. We performed brittle creep experiments on oven-dry samples of red sandstone (Hunan province, China) and samples of the sandstone pre-immersed in water for different durations (from 2 to 8 days). These samples were deformed at a constant stress in one of either two conditions: dry or submerged in water. Before performing creep experiments, we first performed a series of water absorption and constant stress rate experiments to guide the stresses required for our creep tests and to assist with their interpretation. Our creep experiments show that immersion in water greatly increased the minimum creep strain rate and greatly shortened the time-to-failure when compared to the dry state. In detail, the minimum creep strain rate and time-to-failure increased and decreased, respectively, as pre-immersion duration increased from 4 to 6 days, but did not change as the duration was further increased to 8 days. We attribute this to the saturation of microcracks between 4 and 6 days (i.e., water imbibition was complete, or close to completion, following 6 days). We also show that oven-dry samples deformed at a constant stress underwater fail at stresses much lower than oven-dry samples deformed under dry conditions, due to the imbibition of water during deformation. Samples pre-immersed in water, but deformed in the dry condition were characterized by lower strain rates and longer time-to-failure than those pre-immersed in water and deformed underwater. Our explanation for this is that, due to the availability of water, crack tips can remain hydrated when the sample is deformed underwater, thus increasing the efficacy of stress corrosion cracking. The relationships and data provided herein inform on the long-term stability of engineering structures.

The Influence of Water Saturation on the Short- and Long-Term Mechanical Behavior of Red Sandstone