Pullout Experimental Study On Inserted Foundation

During the three decades lately, a number of experimental study used to resist horizontal and vertical loads of spread foundations are carried out worldwide. However, according to the existing research fruits, both the applicability and credibility of the proposed formula on bearing capacity, which derived from many theories of uplift foundations, is restricted. In view of soil mechanics, the uplift mechanism is more complicated than any other soil engineering problems. Factors such as uplift behavior of soil, crack development, filled soil quality and progressive failure are shown having greatly influenced on pullout behavior. In this paper, based on the model test of inserted foundation, the uplift mechanism, of inserted foundation, which has been applied widely in transmission tower, is studied and discussed deeply. And then, some useful results are obtained.The principal contents are listed as following:Firstly, the investigation state of inserted foundation is presented generally in the paper. The development of uplift bearing capacity theories is summarized, including the significance of the investigation about the anti-pulling mechanism.Secondly, the basic principle of the model test is discussed. A pullout loading test equipment is designed, and then, a great deal of tests and data-gathering apparatuses are introduced, including the examination approaches and processes.Furthermore, the results of laboratory tests, totally 57 small-scale specimens, are presented that it is a much complex process that load being transferred from inserted angle steel to concrete foundation. Besides the concrete strength, factors that tensile force on angle steel, material properties and stress distribution of the whole foundation have influence on the foundation design, too. Bond stress in the state of bond-slip should be adopted in the foundation design. In addition, the test results also demonstrate that bond-slip response between angle steel and concrete foundation in tension could be reflected with the displacements between angle steel and concrete, because bond stress is obviously decreasing with the cross section shrinking, that is effects of Poisson's Ratio. For the obvious yield point of angle steel, the critical frictional resistance could be regarded as ultimate pullout capacity. The test results of inserted foundation with shear fastening apparatus showed that the interaction between bond stress and shear fastening apparatus is very great, however, they couldn't be superposed in principle.To the end, the features of load, load-transferring and construct of insertedfoundations are analyzed. And then, the four basic models of failure of inserted foundation are expressed, in details this paper focused on three methods of cone of earth solution, Liu Wenbai's, Charles's of interpretation. Aimed at these methods of ignores the base soil normal force, the analysis method of pullout bearing capacity of inserted foundation is amended. Finally, the four methods results are compared.