What structural material is listed with a minimum presumptive load-bearing value of 20 tsf?

The structural material with a minimum presumptive load-bearing value of 20 tons per square foot (tsf) is sedimentary rock. Sedimentary rock is generally known for its relatively high density and strength compared to other materials like clay, which typically has a much lower load-bearing capacity.

Understanding load-bearing values is crucial in construction as it helps determine the suitability of materials for specific structural applications. Sedimentary rocks, such as limestone, sandstone, and shale, can provide significant support in construction projects, making them a common choice for foundations and other load-bearing structures.

Granite, while also a strong material, typically has a higher load-bearing value than 20 tsf, positioning it as even more robust for structural applications. Clay, on the other hand, is much weaker and not suitable for high load-bearing applications due to its natural moisture content and structural characteristics. Sandstone can also demonstrate variable strength, but it generally does not consistently meet the 20 tsf criterion compared to sedimentary rock.

In summary, sedimentary rock offers a reliable and strong foundation option within the specified load-bearing value, making it the appropriate answer. Understanding these values can aid construction supervisors in making informed decisions about material selection for various structural elements.