Employees were tasked to change out the bad idlers on the p-11 and the p-5 belts. They were on the last idler for the p-11 belt and were going to stage the lifting bar with the come-a-long. While EE was carrying the bar and the come-a-long EE stepped on the soft mud and the concrete causing EE to slip and fall backwards onto the ground landing on EE's left side.