Swelling behavior of volcanic rocks under cyclic wetting and drying

• Volcanic swelling rocks were tested under cyclic wetting and drying.
• The swelling stress increased only after the rock was allowed to deform.
• Indirect estimations showed a decrease of strength and stiffness after cycling.
• A swelling potential function is proposed and evaluated.
• Conventional testing may underestimate the long term swelling and mechanical behavior of these rocks.

The swelling behavior of rocks can be affected by cyclic wetting and drying. This issue is of practical importance for the design and construction of underground structures in which the surrounding swelling rock mass could be subjected to moisture fluctuations. The present work investigates the cyclic swelling behavior of volcanic rocks from the Central Andes of Chile. The specimens were tested under oedometric conditions measuring the axial swelling stress and strain. The results indicate that the wetting and drying cycles have an impact on the swelling potential and that this occurs only after the rock is allowed to deform during the wetting phase. In addition, indirect estimations with the needle penetration test showed a decrease of strength and stiffness. This implies that conventional testing procedures may underestimate the long term swelling behavior and overestimate the mechanical parameters of these rocks.