What type of soil often requires more precautions during excavation due to its stability issues?

Clay soil often requires more precautions during excavation because of its properties related to stability. Clay has a high plasticity and cohesion, meaning it can retain significant amounts of water. When wet, clay becomes unstable and may lead to shifting or slumping during excavation activities. This can create unsafe working conditions, making it crucial to monitor moisture levels and take necessary precautions, such as shoring or bracing, to prevent collapse.

In contrast, sandy soil, while it may also pose some challenges, generally drains well and does not experience the same degree of instability as clay when saturated. Gravel tends to have good drainage and stability, reducing the need for special precautions during excavation. Loamy soil, a mix of sand, silt, and clay, is typically less problematic because it has improved drainage and stability characteristics compared to pure clay. Thus, clay soil stands out as the type that necessitates extra caution due to its potential for instability during excavation.