kieran1 indicated the proper way to do it. The possibilities for drifting away from vertical for the mast of the rig are very limited : less than 5° usually. The best platform is a horizntal one ( less demanding on swing brakes ).
Depending on the slope, I would try drive from the top with hanging leads. The length of the spuds on the stab section may need to be increased. Also you would start the pile slightly up slope, allowing the pile and leads to walk slightly before biting in. The feasibility of this obviously depends on you geometry and your crane.
The rig will need to be reasonably level. If the block hangs between the cords of the boom it'll work. Driving on a slope is no big deal. The boys will just set the pile uphill a little and hit it. If it gets off too much they will pull it and try agan. What type of ple do you have?
Do not forget that load charts assume the rig/crane is on a horizontal platform. Therefore it is impossible to check the stability if you are working in a slope. I don't know in which country you are working but an accident in these conditions would lead the management of your company, if not yourself, directly in jail.
Rather than cut benches (which the rig would have to traverse over) probably better to raise the levels so that the commencing surface for piling is at the highest level?
Here in the UK, the relevant guidance document is BRE470 - working platforms for tracked plant. This recommends level piling platofrms. Ramps for rig travelling over the plaform should not exceed 1:10.
I've recently looked at a project for a 2km long pipeline with poor ground conditions, where formation of the piling platform is a very large cost, and spoke with a number of rig manufacturers to see what slope a rig could actually operate on.
I was looking at the use of a Soilmec SF50 in CFA mode, and a Juntan PM25 rig in driving mode and both can operate at a slope of up to 3 degrees.
