What is the recommended method of burying the deceased in stable soil?

Funeral Rites Part 2: Funeral Prayer, Carrying, and Burial

• Digging a straight trench (Shaqq) and placing concrete slabs on top.
• Digging a chest-deep grave and preparing a side-recess (Lahd) toward the Qiblah wall.
• Enclosing the body in a solid lead coffin.
• Leaving the grave flat and square at the surface.