Standard Penetration Resistance in Very Stiff Clays

Standard penetration resistance (N-value) is a measure of the resistance of soil to penetration by a standard sampler driven by a standard weight falling from a standard height. The N-value can be used to estimate soil properties such as shear strength, bearing capacity, and settlement. In very stiff clays, the N-value falls within a certain range, as explained below.

Definition of Very Stiff Clays

Very stiff clays are soils that have a high shear strength and low compressibility. They are typically classified as CL-ML soils according to the Unified Soil Classification System (USCS). These soils have a plasticity index between 15 and 40 and a liquid limit between 50 and 90.

Range of Standard Penetration Resistance

The standard penetration resistance in very stiff clays falls within a specific range, as shown below:

- Option A: 2 and 4 - This option represents soft to medium clays, which are much less stiff than very stiff clays. Therefore, option A is incorrect.
- Option B: 4 and 8 - This option represents stiff to very stiff clays, which are closer to the correct range but still too low. Therefore, option B is incorrect.
- Option C: 8 and 15 - This option represents very stiff to hard clays, which are too high for very stiff clays. Therefore, option C is incorrect.
- Option D: 15 and 30 - This option represents very stiff to hard clays, which is the correct range for very stiff clays. Therefore, option D is correct.

Conclusion

In conclusion, the standard penetration resistance in very stiff clays lies between 15 and 30. This range is higher than that of softer clays but lower than that of harder clays. Understanding the properties of soil is crucial for geotechnical engineering, as it affects the design and construction of foundations, retaining walls, and other structures.