Distribution Characteristics And Time-space Effect Of Internal Force For Prestressed Anchor

This paper aims to study the distribution of force along the prestressed anchor in the excavation of foundation pit. A filed experiment is carried out to investigate mechanical behavior of anchor through a comprehensive reconstruction project in Xining railway station, theoretical and numerical simulation analysis is taken, and gets some meaningful research results.1. The test obtains the distribution of axial forces and frictional forces in time and space. The results show that, if unanchored, there will be a point on the anchored part where the axial force of the anchor is zero, and the axial force increases at first,then decreases, the frictional forces is negative before the zero area, and it is positive after the zero area. If anchored, the axial force and the frictional forces decreases steadily along the anchored part, the maximum value locates at the forepart of the anchor section, the minimum value locates at the end of the anchor section.2. Compared with the measured data and numerical simulation analysis, the development of potential slip plane is analyzed, potential slip planes of slope moves deeper inward due to the effects of anchor. At the same time, the exit of the slip plane moves upwards from the foot of the slope, and locates at about one third the height from the bottom of the pit.3. The paper discusses the relation of free part and anchoring part of the prestressed anchor.On one hand, prestressed anchor with longer free length has better mechanical performance, however one with certain length that is enough to prevent potential slip of slope is more economic and reasonable. On the other hand,the anchoring length of anchor,which provides sufficient anchoring force, is better to be short so that the anchor is economic and efficient.4. Based on P-Y curves of poll-out test and the perfect elastic-plastic model, the paper gives a new simple practical method to calculate frictional resistance which is proposed by Phillips, the method can be well reflect distribution characteristics of frictional resistance when compared with measured result.5. The prestress loss of anchor is about30%to40%, it occurs mainly in the process of anchor and three to four hours after anchor, the contact is not density, anchorage retraction, waist beam deformation, soil creep will certain effects the loss of prestress in the anchored progress, bolt and waist beam stress relaxation is the main reason for the loss of prestress after anchored, and within3-4hours after locking,it will be basically stability.This test provides a certain value of reference for the design of anchor, and lays a good foundation for improving the bolting theory.