When Zhi Ruo covered the back of her head she was prepared for the impact. Being in the field for so long, she already knew the impact of bricks and wall falling from such a height. If an unknown and unprepared person like Qing Shan would have faced this impact it would surely have killed him. The first part that those things would have injured would have been his head which would have been injured badly.
On the contrary for a person like Zhi Ruo who was already prepared for the impact, it reduced to the least it could. Except for physical harm there was nothing else that she would get from it. Soon, as expected, the bricks and chunk's of cement landed on Zhi Ruo's back scratching it roughly. Falling from a height of almost ten floors was a big deal, even if the things were light they had the ability to injure anything which comes in contact with them.
