Decks, Patios, Porches and Docks - Filling gap under concrete patio slab

We have a concrete patio off the back of our house. House sits on a steep slope, and the rains this year have eroded a good portion of the slope back to the slab, to the point where there is actually a gap under one corner of the slab. It's about 3" deep, I'd guess, and goes around 4" in under the slab. We are going to be regrading the slope with soil this weekend, then planting spreading evergreens and ground cover to help stabilize the slope. We're at odds as to what to do about the gap. Is it better to fill it in with gravel, then pack in the soil around it, or fill it with a mixture of gravel and soil, to provide a more solid base. Or is filling it in with soil sufficient?

I'd appreciate any responses ASAP, 'cuz we're doing this today & tomorrow, and this issue just came up! Thanks in advance!

Use gravel under the slab. Any dirt would be bad news and would just wash out avain. A mixture of gravel and soil only looks like a solid base.

Make sure you have the grade around the slab starting at about the slab level and sloping downward gradually. your previous slope must have been far to steep and soil had no stability.

Like Dick said, don't use dirt under the concrete.

Regrade the area around the slab so that it fairly level for the first foot of so, then let it start falling. Adding a small retaining wall with interlocking Keystone blocks or something similar to maintain the slope would be a big help.