The Seahawks’ $8 million gamble failed.

Luke Joeckel made it five games before hitting the shelf again. He’s out at least a month, and it could be a lot longer. He’s just the latest big-money addition that hasn’t turned out for Seattle.

In eight offseasons in charge of the Seahawks, John Schneider has paid 11 outside veterans at least $4.8 million a year. For a variety of reasons, just two of them — Michael Bennett and Cliff Avril — have turned out to be worth it.

Unless Joeckel returns for the final five or six games and helps steady the offense through the playoffs, he will end up joining the likes of Sidney Rice, Zach Miller, Robert Gallery, Matt Flynn, Percy Harvin, Cary Williams and Jimmy Graham as big-money busts.

Not all of those were bad gambles, of course. Miller, Gallery, Flynn and Graham all looked like good additions — failing because they were misused (Miller, Graham) or suffered unexpected injuries (Gallery, Flynn).

As for Joeckel, it’s hard to fault Schneider. The GM was desperate for better veteran linemen than he signed in 2016; and, after missing out on T.J. Lang, he overpaid Joeckel on the bet that the former No. 2 overall pick would rebound from a knee injury that limited him to four games last season.

As with most of his veteran moves, Schneider unfortunately lost the bet.

With Joeckel out for at least a month (Pete Carroll hinted it could be longer), the Seahawks are on to their fourth starting line since August — which is about par for their season course.

Since Russell Wilson became quarterback in 2012, the Seahawks have averaged six starting lines per season. They are technically on their third now, with benched right guard Mark Glowinski competing with rookie Ethan Pocic to fill Joeckel’s left guard spot. You could call it the fourth, though, if you count George Fant’s preseason injury. It’s the kind of inconsistency that has doomed this unit to perpetual poor performance.

Joeckel’s play had been considered no better than average by outside observers, although he seemingly had improved from Week 1 to Week 5. He had committed no penalties and had given up two sacks.

“You could argue that he’s been the most consistent solid guy for us through five games,” Tom Cable said, confirming that an average player is the best the Hawks have right now.

The Seahawks’ line is no better than it was in 2016, ranking 27th in run blocking and 21st in pass protection, per Football Outsiders. In 2016, the unit was 26th and 25th.

Just one team has been stuffed behind the line more often than Seattle’s 29 percent. In 2016, just two teams were stuffed more than Seattle’s 23 percent.

The Hawks rank 15th in the NFL in rushing at 109.2 yards per game, but Wilson’s scrambling has beefed up those numbers. (They ranked 25th at 99.4 ypg last year, when Wilson played hurt for most of the season.)

The only good game the line has had was against Indy: 132 yards on 27 runs by tailbacks. In the four other games, Seattle’s tailbacks averaged just 3.1 yards per carry and did not eclipse 100 yards. And it’s not like they were running against brick walls — none of the defenses they have faced are ranked in the top half of the league against the run.

Now the Hawks are going to platoon Glowinski and Pocic at left guard and see which one emerges. Glowinski struggled there last season and then was benched for Oday Aboushi at right guard after two games this season. Suffice to say this is not an upgrade.

With Rees Odhiambo struggling at left tackle (30 QB pressures allowed, per PFF), the left side of the line could be a catastrophe for the next few games. That is why the Hawks brought in Branden Albert for a workout and reportedly have had talks with Houston about Duane Brown and Buffalo about Cordy Glenn.

Wilson has been sacked three times in all but one game and has been hit 44 times. It would help if the Hawks could run, but Pete Carroll said they really need a lead to be able to do that right now.

After running backs gained just 39 yards on 19 carries in a 16-10 win over the Rams in Week 5, Carroll said, “I wish we had gotten ahead a little bit more so we could have really pounded it a little bit more and see if we could make some more yards with it. … We need to do better. I really want to keep pounding away until we get better at it. We will make progress there.”

It’s hard to believe that, especially with the Hawks losing the Joeckel bet and already on their third (or fourth) starting quintet this season.