Abstract: A type of variable cross-section anchor is proposed for the binary layered foundation with upper soil and lower rock that is widely encountered in transmission line engineering. Its principle is to increase the cross-sectional area of the anchor in the overlying soil layer to fully utilize the bearing capacity of the soil and rock. To examine the performance of the proposed anchor, the load-bearing capacity improvement mechanism of the variable cross-section anchor is discussed through a combination of field tests and numerical simulations, and the effect of different factors on the bearing performance is investigated. The results indicated that compared with uniform section anchor, the uplift, downward, and horizontal bearing capacities of the variable cross-section anchor are increased, and the horizontal bearing performance is improved significantly. The thickness of covering soil on the sites has a significant impact on the uplift bearing capacity of the anchor, while the influence on the downward and horizontal bearing capacity is less. The terrain slope of site has a great influence on the horizontal load-bearing performance of the anchor, and the two are negatively correlated. Furthermore, under the “uplift + horizontal” loading, the group anchor foundation with variable cross-section anchor exhibits higher bearing capacity than the one with uniform section anchor and the traditional composite foundation, and also has the advantages of small excavation volume and more suitable for slope terrain. This study can provide technical support for the application of this new type of foundation.

Key words: transmission line, tower foundation, rock bolt, soil-rock combination foundation, numerical analysis