Centrifugal test on the mechanical characteristics of existing prestressed anchor bolts in highway widening.

To study the stress characteristics of existing prestressed bolts and slope stability during secondary excavation in a slope reconstruction and expansion project, five slope centrifugal tests were conducted. Tests focused on prestressed bolt-reinforced bedding slope with anchoring angles of 10°, 20°, 30°, 45°, and 60° during the excavation phase. The test results showed that the horizontal displacement at slope top increased slightly during the excavation of rock and soil masses in the upper slope part, while during the excavation of slope foot, such displacement increased rapidly. The bolt axial force in the anchorage section decreased along the anchoring depth. The peak axial force in the free section decreased significantly with the progress of excavation, and the axial force distribution in the free section presented a monotonically decreasing pattern. The anchoring angle significantly impacted the attenuation amplitude of axial forces in the anchorage section, while having insignificant effect on the distribution of axial forces. With the increase of anchoring angle, the cumulative horizontal displacement at slope top first decreased and then increased, while the earth pressure in slope first increased and then decreased, suggesting the presence of an optimal anchoring angle for the prestressed bolt.It is suggested that graded excavation should be adopted for the secondary excavation of slope engineering. Moreover, it is recommended to appropriately reduce the rate of excavation when working on the top and foot of the slope. Additionally, the design of the anchoring angle should consider various factors, including slope slope, rock formation, and the dip angle of the weak surface.