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The depths of excavation damaged zone (EDZ) and highly damaged zone (HDZ) in rock masses around a tunnel are generally measured by borehole testing. The test results of boreholes with different angles and diameters varied due to the complex structure and anisotropy of such jointed rock masses, therefore, accurately determining the depth of EDZ and HDZ in jointed rock masses is essential to their engineering safety. By investigating columnar jointed basalt in Baihetan Hydropower Station (Sichuan Province, China), a comprehensive method based on the substantial test results has been proposed for determining the depth of EDZ according to HDZ in jointed rock masses. The method is applicable in rock masses where the acoustic wave testing cannot be conducted. The borehole test results in both EDZ and original rock under different drilling conditions were obtained, and revealed that the depth of EDZ was related to borehole angle rather than diameter, while the degree of damage to the original rock in the borehole was more likely to be influenced by the borehole diameter than the angle. The proposed method for determining the depth of EDZ provides a new idea for determining the depth of EDZ in surrounding rocks. Additionally, the data provide an insight into the borehole testing method and a basis for supporting design and stability control of columnar jointed rock masses.

Zonal disintegration refers to the phenomenon whereby fractured zones and intact zones appear alternately in surrounding hard rocks under high stress conditions. In this study, zonal disintegration within hard surrounding rocks of deep tunnels at the China Jinping Underground Laboratory Phase II (CJPL-II) was observed by using a digital borehole televiewer in pre-drilled boreholes. The results revealed that fractured zones within intact high-strength marbles were small and exhibited a higher degree of fracturing, whereas fractured zones within low-strength, low-integrity, marbles showed fewer, yet larger fractures. An evaluation method based on rock mass integrity index using digital borehole televiewer data (RMIBT) has been proposed for the analysis of zonal disintegration process in the deep hard rocks surrounding the tunnels. By using the method we were able to quantify the initiation and evolution of fractures during zonal disintegration. The formation mechanism of the second and third fractured zones induced by the existing fractures was further investigated using numerical analysis. The data provide an insight into the evolution of failures in, and a basis for support design and stability control of, deep engineering works in hard rock.

This paper presents the results of in situ investigation of the internal displacement of hard surrounding rock masses within deep tunnels at China’s Jinping Underground Laboratory Phase II. The displacement evolution of the surrounding rock during the entire excavation processes was monitored continuously using pre-installed continuous-recording multi-point extensometers. The evolution of excavation-damaged zones and fractures in rock masses were also observed using acoustic velocity testing and digital borehole cameras, respectively. The results show four kinds of displacement behaviours of the hard surrounding rock masses during the excavation process. The displacement in the inner region of the surrounding rock was found to be greater than that of the rock masses near the tunnel’s side walls in some excavation stages. This leads to a multi-modal distribution characteristic of internal displacement for hard surrounding rock masses within deep tunnels. A further analysis of the evolution information on the damages and fractures inside the surrounding rock masses reveals the effects of excavation disturbances and local geological conditions. This recognition can be used as the reference for excavation and supporting design and stability evaluations of hard-rock tunnels under high-stress conditions.

Rock mass integrity is regarded as an important index to evaluate rock mass quality. Core drilling technology is one of the effective methods used for this. To overcome the problem of core discing and core breakage from the drilling process, a new evaluation method was proposed: a rock mass integrity index (RMIBT) based on high-definition digital borehole televiewer data. The RMIBT values were obtained by measuring the mass proportions of the length of the rock mass without macroscopic fractures on the borehole wall. Their scoring criteria were determined based on rock quality designation. It was applied in multiple deep rock excavations and therefore proved to be useful, especially where core discing occurs, in specific spatial distributions of structural planes, as well as logging errors from core breakages induced by drilling. In addition, the RMIBT can be used to assess dynamically the integrity of macroscopic rock masses and the evolution of fractures in the excavation damaged zone, thus providing a basis for the evaluation of rock masses in deep rock excavations.

Accurate thermal or mechanical analysis of thin structures has been a challenging task for various numerical methods, due to the exceeding closeness of the two neighboring surfaces. In this paper, the micron-sized interior-like thin structures for steady-state heat conduction is investigated with BEM. Three major difficulties would be encountered during solid analysis of thin structures with BEM: 1) degeneracy of the linear systems of equations; 2) evaluation of singular integrals over distorted elements; 3) evaluation of various orders of nearly singular integrals. To investigate the effect of singular and nearly singular integrals independently, the singularity subtraction technique (SST) and nonlinear distance transformation combined with adaptive subdivision method are employed to deal with singular and nearly singular integrals, respectively. Besides, a conformal mapping procedure aligned with sigmoidal transformation in angular direction is proposed to eliminate the near singularity derived from the distortion of element shape. Several challenging numerical examples with characteristic thickness h = 10 − 3 , including annular disk, hollow sphere and hollow torus examples, are solved with coarse meshes compared to original methods, and some meaningful conclusions have been obtained.

In this paper, the authors present a more efficient and robust implementation of conventional and hypersingular BIEs for potential problems in three dimensions under the framework of boundary face method (BFM). The focus is laid on the accurate evaluation of singular curved surface integrals, and three aspects related are considered simultaneously: (a) the near singularity caused by distorted element shape; (b) the near singularity derived from the angular direction; (c) the singularity in the radial direction. A conformal polar coordinate transformation (CPCT) is employed to eliminate the shape effect of distorted integration cells, which can retain the shape characteristic. Besides, an improved sigmoidal transformation is introduced to alleviate the near singularity in the angular direction. By combination of the two strategies with previous singularity subtraction method, an efficient numerical integration scheme has been obtained for various orders of singularities. Some numerical examples including parallelogram plate, sphere and hollow cylinder examples with coarse meshes are presented to demonstrate the accuracy and flexibility of the proposed method.

Debris flow accumulation has the characteristics of loose and broken, low strength, poor stability and so on. When the tunnel passes through the debris flow accumulation area, it is easy to bring major safety hazards to the construction site. Based on the engineering background of Gangou tunnel crossing debris flow accumulation area in the fourth bid of Jiumian expressway, this paper establishes a numerical calculation model, studies the large deformation characteristics of tunnel surrounding rock in debris flow area, determines the reasonable reinforcement range of tunnel surrounding rock, and puts forward the comprehensive control technology of tunnel passing through debris flow accumulation body combining surface stability and underground reinforcement based on simulation results and field experience. The numerical results show that the deformation of surrounding rock and ground surface can be effectively controlled. The rationality of the proposed control measures is verified by field monitoring, which provides a reference for surrounding rock control of tunnel under type conditions.

Subgrade filling of high-speed railway will cause additional settlement and deformation of existing lines.In this paper,using the finite element analysis platform (Taxis 2D) and considering the settlement of the existing line itself, This paper analyzes the impact of the new and old subgrade lap type and the layer filled this lesson of the new subgrade on the implementation of the existing subgrade. The results illustrate the following points:(1) Compared with different overlapping surface types, different filling those points have a greater impact on the settlement of the existing line; (2) The height of the steps is 0.6m and the width is 1.0m.In the subsequent layered filling construction process, each level The loading capacity of 30cm is more reasonable, which can effectively control the influence of the existing line on the additional settlement of the existing railway. The research results can provide a reference for the optimization of similar roadbed width construction.