PULLOUT BEHAVIOR OF PRECAST CONCRETE ASSEMBLY SPREAD FOUNDATION

The precast concrete assembly spread foundation for Qinghai-Tibet AC750kV/DC±400kV grid interconnection project in a frozen soil area was tested under pullout loading. The mechanical co-working properties for the different structural parts of the foundation were analyzed based on the monitoring results of their displacement and stress. Under an uplift load, the displacement of the ring flange connecting the column and the bottom slab and the joint seam of the two consolidated bottom slabs conformed with that of the top plane of the foundation. Three stages of the elastic, elastic-plasticity and failure were observed according to loading-displacement curves of the foundation. Moreover, the stress of the connecting anchor bolts and channel beams increased with the tension load. Under a designing load, all connecting anchor bolts and channel beams were in elastic stress status. Because of the structural characteristic of the assembly foundation, the gaps among the assembly parts, the discrepancy of the nut screwing up and the mismatching tolerance existed during consolidating. Therefore, under the tension load and the dead weight of the soil above the foundation, the two edges which were parallel to the joint seam of two consolidated foundation slabs had a tendency to down warping. And the displacements of all angular measuring points were less than the displacement of the top plane of the foundation. The displacement and the stress of the different connected parts redistributed until the new balance developed. As a result, the different connected parts of the precast concrete assembly foundation co-operated to carry the tension load. All structural parts foundation had good entirety. And the earth cone method can be adopted to determine its ultimate uplift bearing capacity.