I have no idea what it could be. I see the possibility that the great pyramid has large voids that are filled with sand and debris caused by stone cutting is a valid hypothesis given the sand found when the French team bored into part of the pyramid in the 80s. Using sand and rubble to fill in voids would expedite the construction process so that the 20-30 year construction make sense. That also would be a progression of the attempt to stack blocks on a mound of sand and rubble to build a pyramid, which failed in the fifth dynastic attempts.
I have no idea what it could be. I see the possibility that the great pyramid has large voids that are filled with sand and debris caused by stone cutting is a valid hypothesis given the sand found when the French team bored into part of the pyramid in the 80s. Using sand and rubble to fill in voids would expedite the construction process so that the 20-30 year construction make sense. That also would be a progression of the attempt to stack blocks on a mound of sand and rubble to build a pyramid, which failed in the fifth dynastic attempts.