There are several issues to deal with.
- Does the meaning of "expanse" include the concept of solidity?
- Regardless, did the Hebrews and the author of Genesis view the expanse as a solid dome?
Compare the Hebrew raqiya` which means expanse, it is derived from raqa` which means to spread out. A question is raised whether the word, while meaning expanse, also implies solid. Ocean means a large body of water. Oceans are blue and wet and large. The word "ocean" carries the meaning "large" though this is not what it primarily means. "Ocean" does not carry the meaning "blue" even though they are normally that colour.
In Genesis the expanse separates, thus a solid object may be in view. Compare divider which is usually an object that separates several items. However a road can have a divider that is solid (barrier wall) or non-solid (a large space between the opposite lanes). Rivers divide up tracts of land. So even though most dividers are solid, it is difficult to claim that solidity is part of the meaning of the word "divider". The Hebrew raqiya` does not need to correspond to English "divider" or "expanse". But the existence of a solid raqiya` does not intrinsically imply that part of the meaning of raqiya` is solid. It may be consistent with it, but does not prove it. There are biblical reasons to suspect that raqiya` was not thought of as solid and I will come back to this.