Which type of soil is described as being very difficult for the HYEX to excavate?

Caliche is a type of soil that consists of hardened natural cement, which means it tends to be very compacted and difficult to penetrate. When excavating with a hydraulic excavator, such as the HYEX, this type of soil poses several challenges. The hardness of caliche requires more power and specialized tools, such as rock-breaking attachments, to effectively break apart the material.

In contrast, other soil types, such as sand, clay, and limestone, have different properties that affect their excavation. For instance, sand is much more manageable as it is loose and easy to displace, while clay can be sticky and challenging but still allows for some degree of penetration and movement. Limestone, while hard, can sometimes be excavated with standard equipment if it is not too deeply embedded. Thus, caliche stands out as particularly tough for hydraulic excavators to handle due to its dense and cement-like characteristics.