Final answer:
The Unified Soil Classification method (C) is widely used and recommended by ASTM standards.
Step-by-step explanation:
The Unified Soil Classification System (USCS) is a soil classification method widely adopted and recommended by the ASTM (option C) (American Society for Testing and Materials) standard. The USCS provides a systematic approach to categorizing soils based on their physical and mechanical properties. It classifies soils into different groups, such as sands, silts, and clays, and their combinations, using a set of symbols and abbreviations.
The USCS has become a standard method for geotechnical engineers, soil scientists, and construction professionals for its simplicity, versatility, and widespread acceptance. This classification system aids in communicating essential information about soil properties and behavior, helping in the design and construction of various civil engineering projects, such as foundations, embankments, and retaining walls.
While the USDA (United States Department of Agriculture) method and the AASHTO (American Association of State Highway and Transportation Officials) method are also used for soil classification, the Unified Soil Classification System is often preferred for its broader applicability and acceptance in various engineering disciplines. Therefore, the USCS stands out as a comprehensive and widely recognized soil classification method in the field of geotechnical engineering and soil science.