| dc.description.abstract | Fractured rock masses contain discontinuities such as joints, faults, and bedding planes, which may cause their mechanical or engineering behaviors with anisotropies due to the preferred orientations of discontinuities. Nowadays, rating adjustments for orientation in rock engineering practice, such as RSR, RMR, and SMR, provide evaluations of construction quality under various fracture dips (??) and engineering configuration orientations (γ). However, these existing rating adjustments were established based on engineering experiences, which don′t have enough relevant scientific and experimental validations. Additionally, the classifications of ?? and γ in these rating adjustments adopted discrete functions that only provide rough ratings of it. Furthermore, the study of the impact of γ in tunnel excavation is not sufficient, e.g., only three directions of excavation in fractured rock masses were investigated.
This paper provides improved rating adjustments for orientation in tunnel excavation and foundation bearing capacity by analyzing two series of 3D numerical simulations that consist of various ?? and γ. The synthetic rock mass (SRM) framework, using the bonded particle model (BPM) as an intact rock mass coupled with the smooth joint model (SJM) as fracture mechanical behaviors with geometry given by discrete fracture network (DFN), is adopted to construct the 3D synthetic tunnel and foundation rock mass model, respectively, herein. Then, a series of radial displacements of a tunnel under various ?? and γ simulating by step-by-step excavation, and a series of bearing capacity of foundation under various ?? and γ simulating by the bearing capacity test, can be obtained. We optimize the numerical simulation results and existing rock tunnel rating adjustment for orientation to obtain the modified rating adjustment based on the RMR system. Finally, this paper provides the continuous functions of modified rating adjustments for tunnel excavation and bearing capacity, respectively, using multiple regression analysis. According to the simulation and analysis results, the conclusion of this paper can be drawn:
（1） The 3D numerical modeling is necessary for simulating the engineering behaviors of fractured rock due to 3D models can comprehensively present the impacts of ?? and γ on it.
（2） For tunnel excavation simulation, using step-by-step excavation is more reasonable than using one-step excavation, which means that simulating practical engineering problems needed to consider the construction process.
（3） Low-dip fractured rock masses exhibit significant instability under some oblique excavation directions, their radial displacements may exceed the orthogonal and parallel excavation scenarios. Therefore, the rating adjustments for orientation are necessary to consider oblique excavation scenarios.
（4） The proposed continuous functions of modified rating adjustments for tunnel excavation and bearing capacity provide computational convenience and improve the previous rating adjustments′ precision and accuracy.
Illustrative examples of how to employ the proposed rating adjustments are given at the end. | en_US |