Abstract
Two kinds of common tunnel shapes, i.e. elliptical opening and square opening were selected for biaxial compression tests, and the influences of two kinds of opening shapes on the mechanical properties, failure characteristics and failure modes of sandstone were compared and analyzed. The complex variable theory and mapping functions were used to obtain the analytical stress solution around elliptical and square openings. The results show that the stability of the specimen containing an elliptical opening was better than that of the specimen containing a square opening under the same lateral stress. Compared with the elliptical opening, the local damage was formed earlier in the square opening which might be caused by a higher stress concentration around the square opening. The stress distributions around openings were influenced by the opening shape and lateral stress coefficient. The top and bottom of square opening were more prone to tensile fracture, and the distribution range of tensile was larger than that of elliptical opening. When the opening failed, the intensity of square opening failure was weaker than that of elliptical opening. On the basis of the average frequency value and the rise angle value, the failure mode of specimen containing elliptical or square opening was distinguished. It was found that the mixed tension and shear failure dominated the failure of specimens with different opening shapes, and the number of shear cracks in the specimen containing a square opening was greater than that in the specimen containing an elliptical opening. The above method of judging failure mode by acoustic emission signals was well verified by the CT images of damaged specimens.
Highlights
Due to that the sharp increase of the acoustic emission (AE) energy only occurred when the specimen containing an elliptical opening was close to failure, we can predict the instability of elliptical tunnel according to these AE characteristics
In order to investigate the effect of opening shape on rock mechanics, stress distribution, failure process and fracture patterns, elliptical and square holes were machined at the center of sandstone specimens
The main conclusions are as follows: 1. The opening shape has a significant effect on the mechanical properties of specimen
Summary
As the mining depth gradually increases and the development of underground excavation engineering, the studies on the stability of tunnels are more and more extensive and in-depth. When this high compressive tangential stress reaches or exceeds the strength of rock, the rock will be destroyed [4] These failures are often manifested as spalling at sidewalls, tensile fracture in the top and bottom, and even rockburst [3]. The evolution of fractures around holes was studied by Lajtai, et al [13], and the results suggested that the tensile mode dominates the cavities at a low confining pressure, while the position of the compressive stress concentration caused a large deformation under a higher confining pressure. Et al [24] conducted the uniaxial compressive test and studied the spatial-temporal evolution of micro-cracks in the specimen with an inverted U-shaped hole, and the results showed that the failure of hole was dominated by shear cracks. The tangential stress distribution around different opening shapes was analyzed and some suggestions were put forward for the support of tunnels with elliptical and square openings
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
