Application Of 3D Printing Technology On Rock Mechanics And Seepage Tests

The rock mechanics specimens used to be made mainly by two methods:field sampling(raw samples)and mould pouring(rock-like samples).The former method is costly and difficult to be implemented,besides samples by this mean are in lack of representativeness and repeatability.Many problems occurred in the latter method as well,such as time-consuming production cycle,low precision and bubble and precipitate which cannot be ignored.Moreover,a great number of rock mechanics tests are destructive.All the problems make the results of those rock mechanics tests hard to be repeated,leading to confusion in the research.Three-dimensional printing(3 DP)has recently be introduced in the field with advantages of uniformity of printed specimens and custom structure,providing a reasonable approach for problems above.The main conclusions are as follows:1.Specimens made of gypsum by 3D printing have a lower UCS(less than10MPa)and higher failure strain(about 3%),similar to brittle-to-plastic materials.2.The mechanical properties of gypsum powder specimens are influenced by printing angle and postprocessing heating temperature:failure mode of specimens is related to printing angle,single cant shear failure occurred when printing angle is 90°;heating temperature below140? could significantly improve mechanical properties of gypsum powder specimens,moreover the repeatability of test results get better after the improvement of printing angle and postprocessing heating.3.CT scanning and 3D reconstruction could mimic the inner structure of rocks.However,limited by the printing precision and "step effects",only pores with diameter larger than 0.3mm could be mimicked accurately.Permeability coefficients of resin samples are similar to raw rocks,besides permeability coefficient of three dimension could be tested and differences are observed.4.Specimens by 3D printing have similar failure pattern and fracture coalescence with specimens by mould pouring:S mode,propagation of secondary shear cracks lead to a shear crack coalescence in the bridge area when the bridge angle is 45°;W mode,propagation of tensile wing cracks lead to a crack coalescence in the bridge area when the bridge angle is 105°;M mode,a mixed mode of secondary shear cracks and wing cracks when bridge angle is 75°.All the printed specimens have similar mechanical characters which show the 3D printing have great potential in the building of complex geological models.