Which device is commonly used to repair a cracked water main?

The split-sleeve clamp is the correct answer as it is specifically designed for the purpose of repairing cracked water mains. This device involves a sleeve that wraps around the damaged section of the pipe, and it is secured tightly using bolts. This creates a supportive and sealing effect that helps to restore the integrity of the water main while preventing leaks. It is an effective and reliable method to repair cracks or holes in a variety of pipe materials.

Other options, while important in plumbing and water systems, do not serve the specific function of repairing a cracked main in the same effective way. Pipe joints are used to connect sections of pipe but are not designed for damage repair. Expansion joints are meant to accommodate movement and thermal expansion in piping systems but do not repair damage. Gasket seals are used to prevent leaks at joints and fittings but are not viable for repairing major cracks in water mains.