What is one characteristic of clays in regards to excavations?

When considering clays in the context of excavations, one significant characteristic is that they exhibit poor drainage properties and can experience considerable strength variation depending on their moisture content and consolidation state. This is primarily due to the plasticity and cohesion of clays, which can lead to challenges during excavation.

Clays tend to retain water, making them susceptible to changes in the environment, such as rainfall, which can further deteriorate their stability. When excavated, clays can become soft and unstable, presenting risks such as wall failures and cave-ins, particularly if appropriate support systems are not implemented. Therefore, the poor ability of clays to maintain their structure during and after excavation is a critical consideration in civil engineering and excavation practices.

Understanding these properties allows engineers to devise appropriate strategies for excavation, such as shoring and bracing, to manage the inherent risks associated with working in clay soils.