| It is of great importance to reasonably establish the geomechanical model during the study for tunnel excavation and the excavation of rock slope. But whether the geomechanical model is reasonable and efficient or not, it depends on the parameters of rock mechanical properties. Due to various limitations, such as sample drilling, limited funding, time, manpower etc., extensive experiments cannot be conducted generally to obtain such parameters of interest. One alternative is to estimate the rock strength from other properties, such as mineral composition, particle size, shape of mineral particle, directional alignment for mineral particle etc. It is more advantageous compared to the direct testing for rock strength, because other properties like mentioned above can be tested more easily using smaller rock samples. Therefore, based on the information and data from site investigation and laboratory experiments (e.g., test for character and physical mechanics of rock microstructure), this paper delves into the rock strength in the contact zone in Mengtonggou. Through the study and analysis, the results are obtained as follows:(1) Based on the identification of rock slice under microscope and X-Ray diffraction (XRD), geometric parameters of the rock in contact zone are obtained by Petrographic Image Analysis (PIA). These parameters consist of percentage of mineral in rock, the total area of mineral particle, the size of mineral particle, the ratio of long axis to minor axis for mineral particle and shape coefficient of mineral particle.(2) The correlation between geometric parameters and physical-mechanical properties for the rock in contact zone is analyzed using a linear regression, and the results showed:it is not reasonable to estimate the physical-mechanical properties for rock in the contact zone using single factor;(3) Through the analysis regarding anisotropy of the rock in this zone, it is obtained: that elastic modulus of the rock here changes with the variation of the angle of foliation with the curve being "U" pattern and "decreasing" pattern; that the uniaxial compression strength (UCS) varies when the loading direction changes, with curve showing "U" shape, and moreover, the maximum and minimum value of UCS occurred with the intersection angle between loading and foliation direction being90°and30°, respectively; that the sound wave velocity transmitted fastest when parallel to the foliation direction;(4) Correlation degree analysis was conducted for the correlation between geometric parameters and physical-mechanical properties, and the results showed that the ratio of long axis to minor axis for mineral particle plays the most important role in the estimation;(5) Based on the result of correlation degree analysis, the relations between geometric parameters and physical-mechanical properties were analyzed using multiple linear regression and the results suggested:①In the direction parallel to foliation, UCS of sample5,7and11obtained from estimation were similar to that obtained from direct test, yielding a relative error of4.1%,-1.7%and5.2%, respectively; in the direction perpendicular to the foliation, the relative errors are4.9%,1.6%and-1.8%, respectively.②In the direction parallel to foliation, the elastic modulus estimated from regression model showed similar result with UCS, with the respective relative error being6.4%,4.0%and-3.0%; in the direction perpendicular to the foliation, however, the values from different method showed much discrepancy, with the respective relative error of25.5%,-23.3%and9.2%for the3samples (sample5,7and11).③In the direction parallel to foliation, uniaxial tensile strength estimated by regression model was not so close to that from direct tests, and the relative error are-12.7%,23.7%and-8.7%, respectively; in the direction perpendicular to the foliation, the values from different method were much closer to each other, and the relative errors are only3.9%,-0.5%and-0.6%, respectively. |
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