Gen. Grant decided that Vicksburg could not be taken by frontal assault and decided to lay siege to the city. Methodically, his army constructed a line of works around Vicksburg cutting it off from supplies and contact with the outside world. On May 26, they began building thirteen approaches aimed at different points along the Confederate line. The objective was to dig a tunnel under the Confederate line and then destroy it with charges of black powder , allowing the Union forces to breach the defenses.
Around the end of June, Grant's forces, protected by artillery and sharpshooters, neared their objectives. Along the Jackson Road, a mine was detonated beneath the Third Louisiana Redan on June 25. Union forces charged into the crater attempting to break through the breach. After approximately 26 hours of grim hand-to-hand combat, the Federals were finally driven back and the breach sealed.
And they tried the same thing at Petersburg, that didn't work either !