$$w_u = 1.25(24.0) + 1.75(10.0) = 30.0 + 17.5 = \mathbf47.5 \text kN/m^2$$
$$Q_u = 1.25 \text (DL) + 1.75 \text (LL)$$ box culvert design calculations pdf fix
Live load + dead load + maximum lateral earth pressure (often the strictest case for side walls). $$w_u = 1