So far, the belled pier foundation is frequently used in designing a transmission line.
The other aspect involved in uplift behaviour of belled pier is the failure mode in foundations.
Considering the urgent needs of transmission line construction, four groups of model tests were carried out on the belled pier foundations constructed on two-layered soils, coarse-grained saline soil layer above, and conventional coarse soils (CS) layer.
By referencing the detailed design of the South Hami-Zhengzhou transmission line, the test pit and belled pier foundations were designed with a scaling factor of 10%.
Figure 4(c) gives the uplift loading system for the belled pier foundations.
The belled pier foundation with a 100 mm-thick coarse-grained saline soil layer was taken to evaluate the surface feature of fracture during uplift, as shown in Figure 5.
The rectangular coordinate system was set up with the origin at the center of the belled pier and coordinate axis parallel to the brick columns.
This results from the fact that, at relatively lower uplift loads, soils above the bottom board of the belled pier experienced extrusion forces and were compacted.
(2) At higher uplift loads, the displacement of belled pier foundations tends to vary nonlinearly, and the ratio of the uplift load to the ground displacement is significantly lower than that in the first elastic stage, and the deformation of soils includes primarily the plastic deformation, rather than the elastic deformation; in this case, the plastic zone grows in soils at the stresses applied.
At four working conditions considered here, no matter what the coarse-grained soils are crystallized or dissolved, the failure modes for the belled pier foundations all show linear change from the base to the top.
Based on the morphology of the failure planes of the belled pier foundations, we can approximately use two linear relations to describe the failure curves of the two layers at each profile, respectively.
Note that the CSS and CS represent the coarse-grained saline soils and conventional coarse soils, respectively; L and R are the directions considered in both sides of the belled pier. Both values of m and [theta] for each profile approach to the constants, indicating that the profile for the failure cone is approximately identical, which is supposed to happen when filling materials and loads are uniformly distributed in the belled pier foundations.