Assuming that a spindle shape body is made from around rods with rods destruction, and based on upper limit of plastic limit equilibrium in soil body, the problem about stability of deep excavation slopes by anchor and determine of anchor length and anchor spacing is studied.

Attentions are paid to the problems,such as different anchor length,anchor space,shoring obliquity and surface thickness.

Combining the engineering example,the in- fluences of the design parameters,including excavation angle,anchor body diameter,horizontal inclination angle of anchor and spacing between anchors on the anchor length and internal ove.

Based on the research and design of the lock wall of the Three Gorges Project,the action of the dead load and temperature load during construction of the temperature and seepage pressure during operation is analyzd,and the stress of the anchor rod of different free lengths is studied in detail.

The length of this special part of anchor rod is called the anchorage free length.

The unconstrained length of externally prestressed tendon shall be determined in reason,and it shall not be over 12meters,then the frequency of concrete beam is not close to the one of the externally prestressed tendon,so the problem of sympathetic vibration can be avoided effectively.