Soil classification must be based on the results of how many analyses conducted by a competent person?

The requirement for soil classification to be based on the results of at least one visual and one manual analysis is grounded in the need for thorough evaluation of soil conditions, especially in construction settings where stability and safety are critical.

A visual analysis allows the competent person to observe physical characteristics such as color, texture, and presence of organic materials, which can indicate how the soil will behave under load and changing environmental conditions. The manual analysis, typically involving testing techniques like sieve analysis or plasticity tests, provides quantitative data about the soil's particle size distribution and plasticity, integral for understanding the soil’s engineering properties.

Together, these analyses provide a comprehensive understanding of the soil's behavior, ensuring that appropriate safety measures and engineering practices can be implemented to mitigate risks associated with excavation and construction activities. This dual approach enhances the reliability of the classifications used in site assessments and during the planning phases of construction projects.