Which of the following shall not be assumed to have a presumptive load bearing capacity for foundations?

Which of the following shall not be assumed to have a presumptive load bearing capacity for foundations?

• A. Sedimentary & Foliated Rock
• B. Sandy Gravel
• C. Organic Silt
• D. Crystalline Bedrock

Answer: (C)

Understanding presumptive load bearing capacity means recognizing which ground types are normally treated as capable of supporting foundations without detailed site testing. Organic silt is highly problematic because it is highly compressible, has low shear strength, and can vary with moisture and time, leading to excessive settlement or failure under load. Because of this variability, you cannot presume it has reliable bearing capacity. In contrast, crystalline bedrock is extremely strong and stiff, and coarse-grained soils like sandy gravel typically offer good bearing capacity and drainage, while sedimentary and foliated rocks can also provide solid support when sound and unweathered. So the organic silt cannot be assumed to have a presumptive load bearing capacity, while the others generally can under standard conditions.

Understanding presumptive load bearing capacity means recognizing which ground types are normally treated as capable of supporting foundations without detailed site testing. Organic silt is highly problematic because it is highly compressible, has low shear strength, and can vary with moisture and time, leading to excessive settlement or failure under load. Because of this variability, you cannot presume it has reliable bearing capacity. In contrast, crystalline bedrock is extremely strong and stiff, and coarse-grained soils like sandy gravel typically offer good bearing capacity and drainage, while sedimentary and foliated rocks can also provide solid support when sound and unweathered. So the organic silt cannot be assumed to have a presumptive load bearing capacity, while the others generally can under standard conditions.