Barn Question

Hello, I recently purchased a property and have a question on a repair to a barn. I have attached a photo, I am trying to figure
out what to do on the corner of the barn where it looks like erosion has cut under the slab. What is necessary to do to fix and
prevent this?

Put gutter on over hang and run off to opposite end of barn or run out past that end and put down spout on. As far a filling in its going to take 100s of yards of clay that can be packed and brought out several feet.

If the foundation hasn't shifted, I'd form it up and get some concrete poured in that void sooner than later. Maybe even dig it out and flare the outer wall out some. Once the forms are out, back fill and keep an eye on it for future erosion.

If the foundation has cracked and/or shifted, might seek some professional advice and act quickly.

Lots of options , you can form up out about 18 inches or so and order wet concrete and work it back in there might add some steel there to the ground and get buy. Have also watched a man set up and blow sand back under concrete slab once. He used a common yard leaf blower and fed the sand in front of it. There are lots of companies that specialize in foundation repair.

In addition to the other recomendations, which I agree with, I would add dirt to reduce the sharp slope of the grade from the barn. It is hard to tell from the picture but it looks as if the slope is pretty steep.

Thanks everyone for the replies. I do not believe that anything has shifted much yet but will verify. I hope that I can form it up and pour concrete to fill the void. Will get good look at it in the morning and figure out if I need some professional help.

If the yellow eroded foundation is a mortar like material with little aggregate, and is friable (easily loosened by tapping on it, or rubbing it with a crow bar, the answer is to do a replacement of at least that corner back to the right hand side of the open door on the edge of the right edge of the image. To do that will require require supporting the wooden structure on the inside with steel beams and lolly columns so all compression is off of the decomposed portion.
Next operation would be to remove all the material that is now foundation. dig a trench 8 inches below local frost line, and avoid removing any material that will need to be replaced. This means that the bottom of the trench will be undisturbed soil. Form up to the bottom of the wood sill plates (repair wood as needed to create a solid connection), and put anchor bolts about every 36 inches hanging down into the forms at least 8 inches. Pour new stiff concrete into the forms and use a vibration stinger to assure complete filling and contact with the wood. With that cured and the weight put on it you have a real wall with real durability. Follow those same tactics on the lean to making it straight.
Using 6 mill poly, cover the new concrete above intended grade and put a drainage tile (black slotted poly tube) to daylight down hill. Back fill the area with stone over the drain and a layer of gravel on that. I have experience with mortar like material that has had all the cement leached out of it. It cannot be made solid, and will not be reliable. Jim

Would like to see the rest of the barn.

I come late to the table. Dont be nervous about what you see. Ive seen this scenario several times due to animal and weather erosion. Ive dressed many of these back in after the wet spring dries or after manure removal.

First observation is that the foundation looks good and doesnt appear to be separating. Next is if you do not have frost problems dont over think what you have there. If you you poke a frost depth footing in the exposed corner and not the rest of the building you will see unsimilar reaction from that area and the rest of the foundation. My second observation is the old wood siding looks to be in very nice condition and I see a yellow clay looking soil so Im going to guess there is a chance you are in a more arid climate. If in fact the soil is a stable native soil and this barn wasnt moved onto an imported base soil which Im guessing it wasnt that means it has sat in this footprint for a long time and hasnt gone anywhere yet. It looks like the foundation/ slab is a floating slab with no footings so it could be as simple as packing a good binding fill back into that area. It also looks like the grade falls away and would be a challenge to keep any fill up there permanently. If you are looking to house cattle back in the barn then I may suggest an apron slab outside the doors and slab. Maybe even some rock or crushed concrete to dress the slab edge next to the slope. Many old buildings were built this way and many still stand strong.
The farm I grew up on had a bank barn that experienced this same thing each spring on the walk out side. Pa addressed it with an exterior slab poured on top of rocks from the fields to fill similar voids. Our hog barn was similar and was maintained similar.

Number one cause of building damage is poor water removal management. From photo cant see landscaping so cant say any more . Do not have any eves so ,assuming that continues .

I fixed a place like that a few years ago on my son's shop.
Built a form and pushed concrete up under the floor.
Still holding.

I agree with db4600. Fill in with a material that will pack tight and tamp it in the space. I would then build up outside the building to provide a shallow grade out 5-6 feet from the wall. Top with an erosion resistant material if it will have traffic or seed to grass.