| Aiming at the compression-torsion fracture of Cretaceous water-rich and muddy weakly cemented sandstone commonly encountered in shaft construction in the west of our country and its induced engineering environment coupling effect,with the support of“The present situation and countermeasures of well construction technology in the western region” and“The research and engineering application of frozen shaft lining design in the Western Region”,on the basis of X-ray CT compression-torsion test,the paper presents a new method of 3D printing(3DP)of weakly cemented Shaly sandstone in the west of China,the research reveals the law and mechanism of the influence of water environment on the formation and evolution of 3DP sandstone compression-torsion fracture.The results are of great significance to enrich the structural mechanism of the Cretaceous compression-torsion fractures in the western region of our country.Taking ceramsite sand and chlorite powder as base material,furan resin as binder,weak cementation is realized by controlling the content of binder,and muddy inclusion is realized by controlling the content of binder and chlorite powder,finally,3DP sandstone with 0.6% effective mud content was prepared.The matrix particles in argillaceous 3DP weakly cemented sandstone mainly play the role of framework supporting and filling,and the framework supporting particles are mainly composed of φ≥70μm particles,the filling particles are mainly composed of a small amount of φ≤70μm fine particles and some unbonded φ＞70μm particles.The density and porosity of Shaly 3DP sandstone are lower than the upper limit of the original rock due to the different composition of cement,preparation process and compactness.Although the tensile strength and internal friction angle of argillaceous 3DP sandstone are slightly higher than the statistical lower limit range of the original rock,its compressive strength and cohesion,the softening coefficient,Poisson’s ratio and elastic modulus are in the lower and upper limits of the original rock respectively.The ceramsite sand particles are nearly round,which is more consistent with the high degree of roundness of matrix particles induced by deposition.The grain azimuth distribution of shaly 3DP sandstone is anisotropic in both horizontal and vertical planes.The compressive-torsional fracture system in Shaly 3DP sandstone specimens is composed of through-fracture,which is maintained from axial load to failure and from synchronous compressive-torsional to failure path,the compression-torsion fractures are concentrated at the tip.With the application of water pressure,the dip angle of compression-torsion fracture of argillaceous 3DP sandstone samples increases.The fracture morphology is characterized by high angle single inclined fracture,“Y” type fracture and nearly vertical fracture.Based on fine measurement of real-time X-ray CT images,the argillaceous 3DP sandstones were measured from the initial time to the end of the experiment,the axial strain increases or decreases by 9.0% and the radial strain increases by 28% and decreases by 55% after initial isotropic consolidation,respectively,the results show that the effect of strengthening and weakening of 3DP weakly cemented sandstone samples is enhanced with different time of applying water pressure.The torsional moment causes the large and small principal stresses to rotate on the plane of the middle principal stress method.The relative direction relationship between the principal stress axis and the compressive-torsional fracture in the argillaceous 3DP weakly cemented sandstone specimen is changed by the time of applying hydraulic pressure and the path of compressive-torsional fracture. |
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