Felicity deployed the shuttles from Absolution with Terraforming arrays equipped, and allowed them to race around the perimeter of the Alliance camp. Each pass dug the trenches a little deeper, and the high speed made them harder to target with light arms fire from the ground, should there be any more enemy forces close to their position.
Putting Mecha into trench lines was a bit nostalgic for Max. He hadn't used trench warfare tactics in a long time, but building a wall that was thousands of kilometres long wasn't feasible after the first attacks started.
Trenches were easily cleared by the Mecha if they were collapsed or filled, but walls were difficult to rebuild. The earthen fortifications that had been made with the displaced dirt would have to be enough to defend the front lines from attack.