"Smashing through the barricades" is one of the more confusing parts of the main quest in Old Vizima during Chapter V. Which barricades can be smashed and how to proceed through them depends on the path Geralt has chosen at this point in the game. His choice of actions and allies also branches.
If Geralt has chosen the Scoia'tael path, his main allies are Zoltan, Toruviel and Yaevinn. He is met by Zoltan upon entering Old Vizima and fights his way through to the field hospital while gathering some refugees. Later, he must smash through the barricades with Zoltan to help Toruviel and Yaevinn who are busy fighting the Order. Although Yaevinn is only spied from a distance in a cut scene during the run of the barricades, he does appear later.
If Geralt has chosen the Order path, his main allies are White Rayla and Siegfried, but he does have the support of the Order. He is met by White Rayla upon entering Old Vizima and fights his way through to the field hospital while trying to beat Rayla's record for the most squirrel tails gathered. Later, he must smash his way through the barricades with Siegfried to help White Rayla as she and her men are busy fighting the Scoia'tael.
If Geralt has chosen the neutral path, his main allies are Triss, Zoltan and Shani. He is met by two nurses upon entering Old Vizima and fights his way through to the field hospital while keeping the nurses safe from both the Order and the Scoia'tael. Later, he must smash his way through the barricades with Shani to help her get to the swamp cemetery to help the refugees. Triss shows up later. Also note that with this path, only the "back" door of the field hospital is usable. The "front" door (by the notice board) is locked for this path.
The first map shows the relative locations of the barricades. All the barricades are present, irrespective of the path Geralt has chosen. The difference is which ones he can actually "Aard" his way through and which ones become "fixed" (and therefore not aardable).