# The soil profile at a construction site is shown in the figure (not to scale). Ground water table (GWT) is at 5 m below the ground level at present. An old well data shows that the ground water table was as low as 10 m below the ground level in the past. Take unit weight of water, γw = 9.81 kN/m3 .The overconsolidation ratio (OCR) (round off to two decimal places) at the mid - point of the clay layer is ________.

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## Answer (Detailed Solution Below) 1.18 - 1.26

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CT 1: Ratio and Proportion
2140
10 Questions 16 Marks 30 Mins

## Detailed Solution

Concept:

$$Over\;consolidation\;ratio = \frac{{Effective\;stress\;in\;past}}{{Effective\;stress\;in\;present}}$$

Calculation:

Given;

dry)sand = 17.5 kN/m3

sat)sand = 18.5 kN/m3

sat)clay = 17 kN/m3

Let,

Effective stress at the center of clay layer in past = σc'

σc' = (17.5 × 10) + (18.5 - 9.81) × 5 + (17 - 9.81) × 4 = 247.21 kN/m2

Effective stress at the center of clay layer in present = σ'

σ' = (17.5 × 5) + (18.5 - 9.81) × 10 + (17 - 9.81) × 4 = 203.16 kN/m2

$$OCR=\frac{\sigma'_c }{\sigma' } = \frac{{247.21}}{{203.16}} = 1.22$$

OCR = 1.22
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