When is water jetting most appropriate as an aid to pile penetration, and what is the main caution?

1. Jetting is best in clean sands to loosen the soil at the tip; stop jetting before final bearing so the pile can seat and develop capacity
2. Jetting is required in stiff clay because water cuts clay faster than a hammer
3. Jetting should continue through the last foot of driving so the pile never sees hammer energy
4. Jetting is used only on H-piles driven to rock and has no effect on sandy soils