Main Participants: WANG Xiaogang, WANG Yujie, ZHAO Yufei, LING Yongyu, SUN Xingsong, LIN Xingchao, JIANG Long, LIU Lipeng, SUN Ping, DUAN Qingwei, ZHANG Qiang, CAO Ruilang, PI Jin, YIN Tao, NIE Yong

Key words: anchoring technology, sliding resistance and anti-shear, long-term durability

Pre-stressed anchor cable, an important means of slope reinforcement, has been widely used in high slope engineering in fields of water conservancy, hydropower, transportation, etc. The long-term operation behavior of anchor cable is directly related to the safety of engineering operation. Due to the complicated anchoring mechanism, bad occurrence environment, and unclear working behavior of pre-stressed anchor cables, the knowledge of the sliding resistance and anti-shear effects of pre-stressed anchor cables is still limited, and there is no suitable life prediction model, and lack of effective protection and life extension technologies.

In the recent 20 years, with the support of many national, provincial/ministerial and major research projects, the research team has done research focusing on three key problems: how to accurately calculate the anti-sliding effect of anchor cables, how to quantitatively predict the service life of anchor cables, and how to effectively extend the service life of anchor cables. Through theoretical analysis, numerical simulation and indoor field tests, a new type of engineering technology system of slope anchoring has been established, with the mechanical model of sliding resistance and anti-shear effects of pre-stressed anchor cables, long-term life prediction method, monitoring and detecting techniques, as well as life extension technology as the core technologies of the system.

1. Mechanical model of sliding resistance and anti-shear effects of pre-stressed anchor cables in slopes.

·   A large-scale hydraulic servo direct shear test system for anchoring structures (sample size: 1m × 1m × 2m) has been developed;

·   A three-stage failure mode, i.e., anchor cable extrusion and tension, plastic hinge formation, and zoning tension-shear breaking, has been proposed; and

·   A mechanical model of sliding resistance and anti-shear effects of pre-stressed anchor cables has been established.

2. Long-term performance evolution mechanism and life prediction method of anchoring structures.

·   Excavation detection is for the first time carried out for anchor cables of five existing projects, including the Manwan, the Beijing-Zhuhai Expressway, and the old structure of Fengman Dam.

·   Test equipment has been developed to simulate environmental corrosion by full immersion, electrolysis acceleration and dry-wet cycling, with which 2,160 groups of indoor corrosion tests have been carried out.

·   A model of life stage division and a life prediction method of pre-stressed anchor cables have been established.

3. A new type of pre-stressed anchor cable structure and key technologies for cable life extension have been developed.

·   A wedge-shaped inner expansion anchor head and a weak part reinforcement and protection structure with anti-corrosion inner and outer anchor heads have been developed;

·   A new special facility for dynamic adjustment of inner anchor head deformation under excessive stress has been developed.

·   Technology for real-time monitoring of distributed stress deformation and defect detection has been developed.

1. The sliding resistance and anti-shear mechanism of pre-stressed anchor cable has been revealed, and the mechanical model of anti-shear effect of pre-stressed anchor cable has been proposed. With the summary and analysis of the operation state of pre-stressed anchor cable, the major defects of the current design method of slope anchoring have been discovered. Based on the results of indoor model test, numerical simulation and theoretical analysis, the sliding resistance and anti-shear mechanism of pre-stressed anchor cable has been revealed, and the corresponding mechanical analysis model has been established on this basis.

2. The corrosion evolution mechanism of pre-stressed anchor cable and a service life prediction method are discovered. Through the on-site excavation detection of pre-stressed anchor cable, the corrosion characteristics of anchor cable under long-term operation conditions have been found. The corrosion mechanism of anchor cables has been revealed based on the indoor pseudo-environment corrosion test including full immersion, electrolytic acceleration and dry-wet cycling. On this basis, the service life prediction method of anchor cable is proposed.

3. A systematic safety protection concept of pre-stressed anchor cable has been put forward, and the key technology for extending life of pre-stressed anchor cable has been developed. Based on the overview of pre-stressed anchor cable structure system, the concept of "strengthening protection of weak parts, dynamic control of overstressing and whole process real-time monitoring of deformation" has been put forward. Structural measures for strengthening protection of weak parts have been invented, special facilities for dynamic control of overstressing and distributed real-time monitoring technology for stress deformation have been developed, forming a complete set of pre-stressed anchor cable system including structural measures, special facilities and monitoring technology.

The above-mentioned technical system has improved the understanding of the reinforcement effect of anchoring engineering, filled the gap of service life prediction of anchoring engineering, realized the detection and life extension of anchoring, and achieved a breakthrough in slope anchoring technology. The results of this research project have been applied in more than 20 projects, including Three Gorges Project, Jinping I Project and Aertashi Project with satisfactory performance, bringing about important social and economic benefits.

Figure 1. Mechanism of sliding resistance and anti-shear effects of pre-stressed anchor cables in slopes

Figure 2. Mechanical model of sliding resistance and anti-shear effects of pre-stressed anchor cables

Figure 3. Dynamic control device for overstressing of pre-stressed anchor cable

Figure 4. New technology for anchor cable stress and deformation monitoring and defect detection

Figure 5. Fine numerical simulation of the sliding resistance and anti-shear effects of anchor cable in shearing process