Please help me find the solution.

At a construction site, a contractor plans to make an excavation as shown in the figure below. The water level in the adjacent river is at an elevation of $+20\mathrm{.}0$ m$.$ Unit weight of water is $10\mathrm{.}0$ kN$/$m$^3.$

Please check for hydraulic failure $($piping$)$ under the proposed excavation.

Fig$\mathrm{.}2.$ Cross section of the excavation