Experimental study on proportioning of ultra-high strength similar materials for large similarity ratio model tests

Similar simulation of physical material is a common research method in the field of geotechnical engineering. Selecting appropriate similar materials and determining their proportions is the key to successfully simulating the prototype project. Existing similar materials are mostly developed for similar simulation with small geometric similarity ratio (1∶250-1∶25). These materials generally have low strength (0.2-7.6 MPa), making it difficult to meet the requirements of large similarity ratio model. Therefore, in order to prepare an ultra-high strength similar material with a strength of more than 10 MPa suitable for large similarity ratio model, river sand, barite, gypsum, and cement with different strength grades were selected as the raw materials to prepare the similar materials for model test. A total of 25 different material proportioning schemes were designed with aggregate binder ratio, cement gypsum ratio, barite content, and cement strength grade as the four factors of orthogonal test. Various types of similar simulation specimens were prepared according to the test requirements, and corresponding rock mechanics tests were carried out to obtain the basic physical and mechanical parameters of similar materials with different proportions. The results show that the mechanical parameter variation range of similar materials obtained from the test is relatively large, with compressive strength ranged from 3.017 to 48.179 MPa, which can meet the requirements of ultra-high strength similar simulation under large similarity ratios. By analyzing the sensitivity and influencing law of each factor on the physical and mechanical parameters through intuitive analysis method, it is found that the barite content mainly controls the density of similar materials, the aggregate binder ratio mainly controls the compressive strength, tensile strength, elastic modulus and internal friction angle of similar materials, and the cement gypsum ratio mainly controls the cohesion of similar materials. Using SPSS software to perform regression analysis on the orthogonal experimental results of similar material proportioning, an empirical formula for the proportioning of ultra-high strength similar material was obtained and applied in projects. The formula could provide a theoretical basis for quickly determining the proportioning of cement gypsum sand similar materials.