What type of site investigation involves digging to assess soil conditions?

The correct answer is the type of site investigation that involves digging to assess soil conditions is known as a test pit. This method is specifically designed to provide direct observation of subsurface conditions by excavating a pit to certain depths. Test pits can reveal important information about soil characteristics, such as texture, moisture content, and the presence of rock or groundwater.

This excavation process is critical in construction and geotechnical engineering because it allows engineers and builders to evaluate the suitability of the soil for various types of foundations and to ensure the safety and stability of structures. Test pits can also help identify any potential issues that may not be apparent from surface observation alone.

In contrast, core sampling involves extracting a cylindrical core from the ground at specific depths to analyze soil and rock materials, which may not provide as comprehensive a view of soil layers as a test pit. A geotechnical assessment refers to the overall evaluation of subsurface conditions, but it encompasses various techniques, including test pits and core sampling. Lastly, a site survey focuses on mapping and measuring land features and does not involve the direct assessment of soil conditions through excavation.