Most YouTube videos of raised bed construction that I see, anchor the raised bed with posts into the ground. If I'm building a very large raised bed, something on the order of
Is it necessary to anchor the posts in the grounds with concrete pilings?
Yes or no, depending on how you construct it - both materials and details of how it's built.
The simplest way to make such a bed require less structure or in-ground supports is to tie the rather tall, long, sidewalls together at intermediate points, rather than just at the ends. This can be done sub-surface if you want it to look like one long bed, rather than a series of short beds butted up to one another. If the intermediate ties are 30cm/300mm/one foot below the soil surface, they will have little impact on most tillage operations and plant root growth.
Another approach is to make the walls, and the long walls particularly, very strong - reinforced concrete, for example, can easily be made strong enough to hold that much soil without intermediate tie points. It may be costly, but it can certainly be done. Of course, it can also be done "not well enough" and fail/crack.
My personal observation is that every time I've reconfigured my garden beds, they have gotten smaller - this is as much, or more, about garden management as it is about how difficult they are to build. Smaller beds are just simpler to do (weed, plant, harvest, etc.,) and move on to the next bed, than a very large bed. They divide the work and the attention required to manageable chunks; but feel free to learn what works for you, which may be different than what works for me.
No. The soil in the bed will be quite heavy. And you need not drive anything into the ground.
I used my community garden organization's plans for building raised beds. That organization has used those plans countless times for building community gardens. Neither theirs nor mine have blown away. They are extremely solid and unmovable.
