Mechanical properties of a new high-strength composite shaft lining for the “one drilling and forming process” drilling method in western China

Aiming at the problem of “one drilling and forming process” support for deep and large drilling shafts in water-rich and weakly cemented strata in western China, a new structure of high-strength steel plate-concrete composite shaft lining was proposed. Firstly, based on the similarity theory, the similarity index of the composite shaft lining structure model test was derived using the north ventilation shaft of the Taohutu coal mine in Erdos city, Inner Monglia, as the engineering prototype. The mechanical activation behavior of high-strength steel plate-concrete composite shaft linings was studied by an orthogonal model test with different shaft lining thicknesses, concrete strength grades, and steel plate types. Secondly, the numerical simulation method was used to calculate and analyze the influencing factors and variation rules of the ultimate bearing capacity of the high-strength steel plate-concrete composite shaft lining. Thirdly, based on the results of model tests and numerical calculations, the calculation formulas of the bearing capacity of high-strength steel plate-concrete composite shaft lining and the improvement coefficient of concrete compressive strength were obtained, and the ranges of influencing factors were given, which provides a design optimization method for the engineering application of this kind of shaft lining structure. Finally, the mechanical action effect of the anchor cards in the composite shaft lining structure was analyzed. The results show that in the composite shaft lining structure, due to the high yield strength of high-strength steel plate, it can better produce a composite restraint effect on the intermediate concrete. The compressive strength improvement factor of concrete can reach 2.3−2.6, and the bearing capacity of shaft lining can significantly be improved. Under the same conditions, compared with the Q345 steel plate, the ultimate bearing capacity of high-strength steel plate (Q460−Q620) -concrete composite shaft lining can be increased by about 7.14%−19.46%. And the thickness of the shaft lining can be thinned by 8.18%−19.52%, and increasing the thickness of the inner layer of the steel plate is more helpful to improve the ultimate bearing capacity of the shaft lining. The anchor card in the composite shaft lining structure restrains the inner steel plate so that it does not buckle and destabilize prematurely after reaching the yield stress, and at the same time provides restraint to the intermediate concrete for ensuring that it is in a triaxial compression state. Both of them play a good composite role and contribute to the overall force of the shaft lining structure.