1. Add some soil at the bottom.

2. Add some soil in the ground.

3. Add some on the floor.

4. Add some soil in the hole.

(Are the sentences grammatical?)

All are correct, yes, but the meanings would be clear only in context, I think.

Yes, all four sentences are grammatically correct. However, the meaning of each sentence differs slightly depending on the context. Let's analyze each sentence:

1. "Add some soil at the bottom." - This sentence suggests adding soil to the bottom of something, but it doesn't specify what that something is. Additional information is needed to understand the complete meaning.

2. "Add some soil in the ground." - This sentence suggests adding soil into the ground, which could indicate activities like gardening or landscaping. It is a general statement and lacks specific details.

3. "Add some on the floor." - This sentence implies adding soil directly to the floor, which might be unusual and typically not desired. More context is necessary to fully understand the intention behind this statement.

4. "Add some soil in the hole." - This sentence indicates adding soil into a hole. Again, it lacks specific information about the type of hole or the purpose behind filling it with soil.

In summary, while the sentences are grammatical, their intended meanings are not entirely clear without further context.