My back yard, I have a concrete patio then grass, between the 2 was a fence, I removed the fence and the pole holes, now when I try to fill the holes my dirt disappears after a good rain, I think its somehow seeping down under the cement. How can I fill this hole so I can get rid of this unsafe hole?

im putting down the big square slabs on top of the concrete out the back as its all broken and very unlevel do i need to put a fall in the slabs towards the drain and how do i slab around the drain ie bring the drain up level with patio there is also a sewer drain pipe

We’re wanting to put in a driveway and were intending to put gravel down as the surface material (we are not planning to pave over it). A friend told us that crushed concrete (which is about the same price) is better because it packs harder. Would crushed concrete be a good or better choice for a driveway surface given that it is the same price as gravel? We’re also putting in a retaining wall and will use the leftover gravel...