Yes, i've also read somewhere. But i bet the road will be smooth at your travel time and also there are different routes. Not all of them are under maintenance. Don't worry!

Thanks Miss YoYo, its very comforting to know that. I'm yet to know what the bus schedules are because seems that I can't get it anywhere through the net.

I have found out the related info. in Chinese.
It says:
tickets shall be bought one day before the trip. Passengers can go to two cocah stations of Chengdu: Xinnanmen Coach Station (新南门车站) and Chadianzi Coach Station (茶店子车站). At Xinnanmen, four coaches go to Jiuzhaigou before 08:00 each day. Ticket fare is CNY125. At Chadianzi, four coaches are available at 07:00, 08:00, 09:20 and 10:00 separately. Ticket fare is CNY100.

Hello Miss YoYo, I really appreciate your assistance in getting the information. I was thinking of heading to Jiuzhaiguo on the day I arrived Chengdu itself. Now I know that the tickets must be bought 1 day in advance, is it still possible for me to take a taxi instead to jiuzhaiguo and how much will it cost? I really appreciate your assistance Miss YoYo.