What type of clay has an acceptable relative bearing strength of 1,600 psf?

The correct choice identifies "Firm" clay as the type that has an acceptable relative bearing strength of 1,600 psf. In geotechnical engineering, various types of clay are classified based on their shear strength and compressibility characteristics, which directly influence their bearing capacities.

Firm clay typically exhibits moderate plasticity and cohesion while retaining a sufficient degree of strength to support loads without excessive deformation. A relative bearing strength of 1,600 psf signifies that the clay can safely bear the weight of structures built upon it, making it suitable for construction purposes.

In contrast, soft clay has lower bearing capacity and might require additional support or foundation measures due to its higher susceptibility to settlement. Loose clay also tends to have lower strength and stability compared to firm clay, making it less ideal for supporting structures. Dense clay, while it has a higher bearing capacity than loose and soft clays, might exceed the specified strength of 1,600 psf, indicating that while it is strong, it is not classified under the acceptable range specified for this question.

Thus, firm clay is the correct identification due to its balance of strength and capacity, meeting the specific bearing strength requirements outlined in the question.