The soil profile at a construction site is shown in the figure (not to scale). Ground water table $\text{(GWT)}$ is at $5 \text{ m}$ below the ground level at present. An old well data shows that the ground water table was as low as $10\text{ m}$ below the ground level in the past. Take unit weight of water, $\gamma _{W}=9.81 \text{ kN/m}^3$.
The overconsolidation ratio $\text{(OCR)} (\textit{round off to two decimal places}$) at the mid-point of the clay layer is _____________________