So we bought our home last July, we never noticed that right in front of the mailbox which is an area with a big patch of dirt and grass is where the mail truck swoops in and delivers the mail, we have tried to refill the hole from the tires with dirt, then with rocks, but each time the tires dig in so much that it's worse now, especially when it rains, two huge puddles. It's now two holes from the tire going in and then out. We are happy and appreciative that we get our mail in a timely fashion but how can we best get that hole to be a flat surface? maybe more dirt? like a hill? help!
Not dirt, ideally. But you can use dirt if you can't get better material.
Better material would be crushed rock, ideally the sort that has all the fine dust from crushing still in it. Rock without fines can also work, but is less ideal.
Biggest problem with "filling a hole" most people have is the fact that you will lose (as you have seen) if you just put stuff in the hole you have. It will be saturated by any standing water, and it will be looser than the hole, and will get shoved back out of the hole easily with traffic.
So, let's look at what you could do differently for the poorest but most available fill - the dirt you have right there. You want to dig out the area of the hole you have to (at least) the full depth of the deepest part of the hole over the whole area of the hole, and somewhat beyond. Then you fill the hole with dirt - but not all at once. Put in an inch or two of dirt, and compact it throughly - don't use a large tamper (ie the common 10x10 square you probably don't own and would be wasting money to buy) - use something like a sledgehammer held head-down, handle vertical, and lifted and dropped over the whole area until it's all compacted. A 2x4 stud (inexpensive) is also effective used the same way (lift and drop on the end.) Then add another inch or two and repeat. In theory a high-heel dance party in high heels you don't mind getting dirty could also work, but it's not one I've tried. Physics says it should work, though.
If you "upgrade" to crushed rock or gravel, you'll want to add a layer of (ideally, but difficult to get in small quantities) geotextile to keep the dirt below from "eating" your rock fill. Probably the closest thing to geotextile commonly available in small amounts is weed-block fabric or filter fabric. The idea is that water should drain through but your rock is not pushed down into the dirt below. Otherwise the tamping is similar.
In both cases you do want to build up slightly, because tamping is good, but not perfect, and also because removing standing water greatly reduces the progression of holes from wheels, while allowing even a small puddle to develop quickly grows as water and dirt splash out. Running your own car smoothly back and forth over the patch (without stopping as the mail-truck does) will also help to compact it. If you do see it starting to puddle, fill it back in sooner rather than waiting for it to get worse (it won't get better by itself.)
There are only a few solutions here.
- Pave the area with asphalt or concrete. Gravel or other rabble will only work short-term.
- Move your mailbox closer to the road and reseed or replant the area.
Option #2 is the way I would go.
Apparently there is a need to clarify option #2 with more detail.
The USPS has guidelines concerning height as well as setback from the road on mailboxes. Before moving the mailbox you should contact USPS to make sure you are in compliance.
Based on your description, "area with a big patch of dirt and grass" and your request for how to repair I assume the problem area is on your property. My suggestion is to move the mailbox closer to the road so that the mail truck can safely use the shoulder of the city/county/state road in compliance with USPS and local traffic regulations.
The other option is the suggestion from Ecnerwal to run a horizontal extension to move the box closer to the shoulder. You'll still need to make sure you are in compliance with USPS regs.