cap4000,
Thanks for the kind words. But a few more comments.
Usually, the structures being underpinned have not needed any temporary shoring. Several times, while underpinning small column footings, I've used temporary shoring but wall footings and large column footings usually don't need this extra support. If you undermine no more than approximately 25% of a column footing at one time, you should not have problems unless there are other non-average conditions to deal with. Walls that do frequently need shoring are walls that were originally common party walls where one of the buildings was removed and there is now nothing to keep the wall from moving laterally, away from the remaining building, due to vibrations, wind, etc. These walls need lateral bracing.
Monitoring is important for all projects. Some projects require additional (excessive?) monitoring. These projects include historic structures, highly ornate structures, and structures whose owners are looking for a lawsuit. If you didn't survey the structure before and during the work, you won't know if you caused the problem or how much of the problem should be yours. Also, pre-construction surveys can discourage frivolous lawsuits.
If you can work pits no closer than 12 feet edge to edge, great. Do it. If the soils are weak or the building has already undergone unacceptable settlements, then work pits farther apart so as not to aggravate the situation. But on most projects, time is of the essence and soils are not weak. The biggest killer to a GC's or CM's schedule is watching a subcontractor underpin a building. As far as they are concerned, all underpinning takes too long. They seem to forget that the purpose of underpinning is to protect people and property.
Writing articles would be very interesting. However, while I am doing that my clients would be waiting for their designs. Most of my work is for contractors who need everything yesterday.
Most engineers never realize that underpinning concrete and drypack are so lightly loaded. Underpinning piers are usually large in size because the worker needs to be inside the pit while digging and a certain bearing area is needed on the dirt beneath the concrete pier. Sometimes, with unreinforced concrete underpinning piers, there is some bending and therefore tension. Adding reinforcing steel into a pier should be a last resort. Usually the pier has a large enough section modulus that the tension stress in the pier is below the allowable.
With respect to having a waiting time for concrete pier shrinkage to occur, remember that most of the concrete shrinkage occurs in the first 12 hours. So, if you pour a pier this afternoon, by tomorrow morning, most of the shrinkage has already occured, the concrete should be stronger than the dirt that was previously there, and the pier should be ready for drypacking. The sooner you get the building resupported (drypacked), the better off you are. Because drypack is relatively dry and placed in a thin layer (about 3 inches), it too will have insignificant shrinkage. Therefore, non-shrink grout is usually a waste of money.
I know you think I am being aggressive, and I know what the few reference books say about underpinning but that's how underpinning is done by companies who do real underpinning for a living, on an everyday basis. Authors generally try not to be too aggressive. They are writing for people who are not experienced. And they don't want readers to get into trouble. Excavators and concrete subcontractors who dabble in shallow underpinning are not real underpinning contractors. A recipe for a problem is to hire an excavator to dig the holes and hire the concrete sub to pour the concrete. When this is done, no one is totally responsible and neither really understands underpinning or its requirements for pit spacing, drypacking, shoring, etc. They know excavating; they know concrete. They just don't know underpinning and don't know that they don't know. Underpinning is a specialty.
Finally, I'm not trying to be aggressive. I want to design it right, build it right, have it perform as intended, be economical, and get the job done ASAP. I can't afford any problems.
Sorry to be so long.