The angles of the I beams probably aren't random, and yes, many bridges have foundations like that. Steel beam piles are used quite often.
There's probably a combination of piles - some straight down, and some leaning away from the roadway. Having the combination of vertical and angled piles makes it even more difficult for natural forces to lift the piles out of the ground, or for them to settle down, since it's easier for a pile to move in the direction of least resistance (straight along its long direction). Having piles at slightly different angles mean that for the foundation to move, one set of piles has to move in a direction that isn't along it's length.
Often, they hammer piles down "until refusal," which means that the giant hammers they use to pound them down can't budge them any more. In other words, unless you dig a giant hole around the whole pile, they aren't moving by any means.
For one of the bridges we built, we used some steel piles to hold up the temporary formwork, and we had planned to pull them out with a bulldozer. We ended up having to cut them off below grade, because the D8 caterpillar couldn't budge them.
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