The standard, accepted, widespread form of burial throughout the generations is what is termed “קבורת שדה,” meaning that the meis placed under the surface of a field or burial grounds. The kever is dug into the ground and the meis is placed under the ground’s surface. Then, the meis is covered with stone blocks, earth, and a top stone, and after some time, a gravestone is placed over the kever. This is the accepted Jewish form of burial.
No coffin. It is preferable to bury a meis directly into the ground, without any barrier between the body and the dirt (רמב''ן, תורת האדם עמ' קי''ז, שו''ע סי' שס''ג ). This is the minhag in Eretz Yisroel, where the body is surrounded and covered with stone blocks.
In a coffin. In places where the authorities do not permit burial without a coffin, e.g., in Chutz l’Aretz, a meis may be buried inside a coffin if the coffin is buried underground, provided that there is some contact between the meis and the ground, e.g., via holes in the bottom or in a coffin without a bottom panel, each place in accordance with its custom (רמב''ן שם ).
Artificial hill. Sometimes there is a desire to add burial spots on a hill’s slope. They build a retaining wall out of concrete and stone at a short distance from the hill. Then, they pour earth in the space created between the wall and the hill, level out the new surface, and prepare it for burial, like any other קבורת שדה area. Since the burial is done in earth that is connected to the sides of the hill, it is considered a standard burial and may be done l’chatchila like any standard burial (שו''ת אג''מ יו''ד ח''ג סי' קמ''ב ).
