Xeno tunnels can currently only be destroyed with either C4 or a lot of explosive attacks. The issue I believe is that explosives are a uncommon/rare item, whereas Xenomorphs (with a good burrower) can build a functionally unlimited amount of tunnels. Creating situations where marines may genuinely lose the ability to remove tunnels due to exhausting their explosive supply, or they abandon the idea of destroying them to conserve their limited remaining explosive stock.
My suggestion would be to allow any Marine to click on a tunnel to begin a long (60+ seconds) action that will collapse the tunnel manually. Any interruption will reset the countdown.
The timer being so long would allow any third party to easily interrupt this (such as some alien in the tunnel).
I feel the advantage of this is it would give Marines a way to clear out tunnels reliably, and would feel fair considering xenos do not need to expend any resources to construct one versus marines needing to expend a limited resources to close them. The very long timer would prevent this being abused and ensure if this is done that the marine performing the action would need to be supported by a large group of covering marines, which may even slow down a marine push.
Tunnels have quite long cool down. C4 is not only item you can destroy a tunnel with.
Also imagine facehuggers or, worse, lesser drones interrupting you, just coming out of tunnel. They already do this with current tunnel and C4, with 60 seconds timer it would be even easier.
Destroying tunnels with bare hands sounds extremely cheap, at least you should use a shovel, so being able to break tunnels would cost you inventory space.
Cut it to 20-30 seconds, and require an e-tool. This will require both marines to equip for the job, usually take some slot/storage space, and give more utility to an item that has minimal use outside of standing for three minutes at the FOB filling sandbags you wonāt be bringing into the frontline.