Percentage passing sieve no 200 = 20% , Liquid limit = 5% and N.P , the classification of this soil according to the AASHTO Method is:a.A-2-6b.Nonec.A-6d.A-2-4

To classify the soil according to the AASHTO method based on the provided parameters, we'll follow these steps:

1. Break Down the Problem

• We need to determine the soil classification using:
  • Percentage passing sieve no. 200 (20%)
  • Liquid limit (5%)
  • Plasticity index (N.P. indicates Non-Plastic)

2. Relevant Concepts

• According to the AASHTO classification system:
  • The primary criteria for classification involve the percentage of fines passing through the sieve no. 200 and the plasticity of the soil indicated by the Liquid Limit (LL) and Plasticity Index (PI).

3. Analysis and Detail

• Percentage Passing Sieve No. 200: A percentage of 20% indicates the proportion of soil particles that are finer than 0.075 mm. In AASHTO classification, if more than 35% of the soil passes through the sieve no. 200, it is classified as A-2-6 or A-6.
• Liquid Limit: The given liquid limit of 5% is quite low. Since the soil is classified as non-plastic (N.P.), this indicates a low liquid limit, leading us to classification categories A-2-4 or A-2-6.
• Plasticity Index: With a non-plastic characteristic (PI = 0), we can eliminate the A-6 category.

4. Verify and Summarize

• Given the percentages and plasticity index, the soil cannot be A-2-6 (as it requires higher plasticity) nor can it be A-6 because of non-plastic nature.
• Therefore, we narrow it down to A-2-4 based on the percentage passing sieve and the non-plastic classification criteria.

Final Answer

Based on the calculations and analysis, the classification of the soil according to the AASHTO method is d. A-2-4.