Cohesive Soil Subgrade Reaction Calculator
As per IS 2911 (Part 1 / Section 2 - Clause C-2.2)
p / y = K
K = (k₁ / 1.5) × (0.3 / B)
K = (k₁ / 1.5) × (0.3 / B)
Calculation Results
Soil Consistency:
Interpolated k₁ Value:
× 10³ kN/m³
Lateral Soil Modulus, K:
× 10³ kN/m³
| Soil Consistency | Unconfined Compression Strength qᵤ (kN/m²) | Range of k₁ × 10³ (kN/m³) |
|---|---|---|
| Soft | 25 – 50 | 4.5 – 9.0 |
| Medium Stiff | 50 – 100 | 9.0 – 18.0 |
| Stiff | 100 – 200 | 18.0 – 36.0 |
| Very Stiff | 200 – 400 | 36.0 – 72.0 |
| Hard | > 400 | > 72.0 |
Explanation of Calculation
This calculator evaluates the Lateral Soil Modulus (K) for cohesive soils as per IS 2911 Clause C-2.2.
The lateral soil resistance is represented by:
p / y = K
Where:
- p = lateral soil pressure
- y = lateral pile deflection
- K = lateral modulus of soil reaction
The modulus of subgrade reaction is calculated using:
K = (k₁ / 1.5) × (0.3 / B)
- k₁ = Terzaghi’s modulus of subgrade reaction obtained from plate load test
- B = pile diameter or width in meters
Interpolation Method
For intermediate values of unconfined compressive strength (qᵤ), the calculator performs linear interpolation between IS 2911 table values.
k₁ = k₁a + [(qᵤ − qᵤa)/(qᵤb − qᵤa)] × (k₁b − k₁a)
This gives smoother and more realistic values instead of abrupt jumps between soil categories.
Important Notes
- For qᵤ less than 25 kN/m², IS 2911 recommends taking: k₁ = 0, indicating negligible lateral resistance.
- Smaller pile diameter results in higher K values.
- Final units of K are expressed in: kN/m³ × 10³.
- This calculator is intended for preliminary geotechnical design checks.
- Interpolation has been incorporated for intermediate qᵤ values.
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