A New 3D Printing Method and Similar Materials of the Tunnel-Lining for the Geomechanical Model-Test (2024-05)¶

The preparation of a lining model is an important prerequisite for validating the results of tunnel geomechanical model tests. To respond to the numerous types of complex geological environments, engineers have developed a variety of irregular lining structures with different thicknesses, shapes, and compositions. To address this issue, we propose a novel additive and subtractive 3D printing (AS3DP) method for irregular lining model preparation. First, quartz sand, barite powder, fly ash, and silica fume are used as aggregates, Portland cement and high-belite sulfate-aluminate cement are used as binders, and polypropylene fibers are used as a toughening agent to develop similar 3D-printed materials. The density, compressive strength, elastic modulus, and tensile strength of these materials are tested to analyze the sensitivity and significance of each factor on the material parameters. Second, the additive printing method is utilized to prepare circular lining blanks based on the developed similar material. Afterward, the inner and outer wall surfaces and the upper and lower end surfaces of the lining blanks are polished by subtractive printing. Three circular lining models with an outer diameter of 310 mm, an inner diameter of 260 mm and a height of 300 mm are produced. Third, based on the point load test method, the mechanical properties of the 3D-printed lining models are tested and analyzed. During the loading process, the changes in the displacement curves in the horizontal and vertical directions of the lining model can be roughly divided into elastic deformation and plastic deformation phases. Due to the addition of fibers to the printing material, the lining model does not rupture directly but rather exhibits slow yielding failure in the plastic deformation phase. This property has great potential to meet the performance needs of various types of lining models. Finally, according to the structural parameters of four typical irregular linings of diversion tunnels in the Jinping II Hydropower Station, the corresponding lining models are prepared by the 3D printing method, which establishes the basis for subsequent geological model testing.