Types of Graves in Islam
Question

Is it permissible to fill in soil directly onto the face of the deceased who is buried in the Shaqq? What is the correct way of doing this (i.e., burying the deceased in the Shaqq) if we are forced to adopt this method of burial?
Praise be to Allah.What is a Shaqq?
The Shaqq refers to a trench that is dug in the middle of the grave to suit the size of the deceased, and its sides are built with bricks so that it will not collapse on the deceased, and the deceased is placed in it on his right side facing the Qiblah, then this trench is covered with stones or the like and the ceiling is raised a little so that it will not touch the deceased, then the soil is filled in. 
What is a Lahd?
The Lahd (niche) refers to a place that is dug at the bottom of one of the sides of the grave in the side that is closest to the Qiblah, in which the deceased is placed on his right side facing the Qiblah, then this hole is filled in with bricks behind the deceased, then the dirt is filled in. (See: Ahkam Al-Maqabir fil Shari`ah Al-Islamiyyah, p. 30, by Dr. `Abdullah As-Suhaybani) 
Both the Lahd and the Shaqq are permissible according to scholarly consensus, but the Lahd is preferable, because this is what was done with the grave of the Messenger (peace and blessings of Allah be upon him). 
Muslim (966) narrated that Sa`d ibn Abu Waqqas (may Allah be pleased with him) said, during the illness of which he died: Make a Lahd (niche) for me, and set up bricks behind me, as was done for the Messenger of Allah. 
Ibn Qudamah (may Allah have mercy on him) said in Al-Mughni (2/188): 
“The Sunnah is to make a Lahd in the grave, as was done with the grave of the Prophet (peace and blessings of Allah be upon him).”
An-Nawawi (may Allah have mercy on him) said in Al-Majmu` (2/252): 
“The scholars unanimously agreed that burial in the Lahd and burial in the Shaqq are both permissible , but if the ground is stable and the soil will not collapse then the Lahd is preferable, but if it is unstable and will collapse, then the Shaqq is preferable.”
Ibn `Uthaymin (may Allah have mercy on him) said in Ash-Sharh Al-Mumti` (5/360): 
“But if there is a need for the Shaqq, then there is nothing wrong with it. The Shaqq may be needed if the ground is sandy and it is not possible to dig a Lahd, because when a Lahd is made in sand it will collapse. So a grave hole should be dug and a trench should be dug in the middle of it, and the bricks should be placed over both sides of the hole in which the deceased is placed, so that the sand will not collapse, then the deceased should be placed between these two bricks.”
Should soil be filled in directly on the face or body of the deceased?
The soil should not be filled directly on the face or body of the deceased, whether the grave is a Lahd or a Shaqq, because in the Lahd the deceased is placed in the niche which is dug in the wall of the grave, and the soil is not filled in above him. In the Shaqq, the soil is filled above the roof of the Shaqq, and not directly on top of the deceased. 
For more details, please see the following  answers: 47902 , 12386 , and 82 .     
And Allah knows best.