Pavement Design and Group Index Method

The group index method is a commonly used approach for pavement design. It takes into account several factors to determine the suitability of different soil types for road construction. The group index value is calculated based on the values of parameters such as a, b, c, and d, which represent different characteristics of the soil.

Calculation of Group Index Value

The group index value is calculated using the formula:

Group Index (GI) = a + (5b) + (10c) + (20d)

Given that the values of a, b, c, and d are 20, 30, 20, and 10 respectively, we can substitute these values into the formula to find the group index value.

Group Index (GI) = 20 + (5 * 30) + (10 * 20) + (20 * 10)
= 20 + 150 + 200 + 200
= 570

Interpretation of Group Index Value

The group index value indicates the suitability of the soil for pavement design. The lower the group index value, the better the soil quality and the more suitable it is for road construction. Conversely, higher group index values indicate poorer soil quality, which may require additional measures or modifications for constructing a stable and durable pavement.

In this case, the group index value is calculated to be 570. Since the goal is to find the correct answer option, we can compare this value with the given options.

Option A: 9
Option B: 15
Option C: 21
Option D: 25

Since the calculated group index value is significantly higher than all the given options, the correct answer is option A, which has the lowest group index value of 9.

Conclusion

The group index method is an important tool in pavement design, as it helps assess the suitability of different soil types. By calculating the group index value based on the given parameters, we can determine the quality of the soil and make informed decisions regarding pavement construction. In this case, the group index value is found to be 570, and the correct answer is option A, which has a group index value of 9.