Let's puzzle this question….
Below is a reference image proposing a 2 pipe outline formation. Possibilities: 1. What if the mating pipe disconnected and shifted? (this "shifted" & "disconnected" pipe end mating section would have filled the circle area next to the existing pipe). Possibility 2. What if there were 2 pipes, side by side?
Possibility #1 - If accurate, the mating outline should have a curve arc left in the concrete void. But the concrete void has an irregular curve arc (realm of possibility that the end was fractured, leaving a non-smooth arc).
Possibility #2 - 2 complete pipe runs were placed adjacent to each other. Although this goes against the single run drain & longitudinal collection design, stranger things could have happened…. This case would mean that all of the surrounding drain rock must have existed in the blue outlined hatch line area (best estimate).
In order for #2 to match the image, the missing CS area of the rock would have to be puzzled out (also, an answer on how someone kept their job when the foreman saw this…2 pipes vs single pipe construction design). #1 becomes less of a possibility as the volume of the void extends deeper under the concrete. Thus the "disconnected" end would have had to have been shoved beyond the pipe mating intersection. The irregular arc also casts doubt on #1.
So far the best fit is a single drain with "pushed drain rock forming the adjacent hump". Why? Look to the "widening" of the plastic to the left. It is following the original pyramid or "tent" design, albeit irregular from concrete pour forces. Also, the combined volume of the blue outlined area plus the 2nd proposed drain pipe area best fits the total cross-section area of a symmetrical pyramid "tented" design for any original placed rock…… (side note: I find this photo very interesting as it looks like a natural break apart of the concrete slab. For the original drain rock to be present means there was no hard scouring of water after it broke - so where did this piece of evidence come from?).
