I have the following integral. I want to have its value for known value oft(say 10), but I cannot solve it because the inner integral cannot be solved. Is there any way to solve this? I don't know,May be by separation of integrals or some numerical method. I tried Mathematica and it cannot solve it too.

$\displaystyle \int_{0}^{t}\int_{0}^{\tau}\frac{1}{\sqrt{\tau-u} }Erfc(\frac{1}{2\sqrt u})dud\tau$