In the process of excavating seven parallel tunnels at the Jinping II Hydropower Station, several extremely intense rockbursts occurred, killing and injuring construction workers and damaging several ...sets of equipment. Based on the characteristics and mechanisms of these rockbursts, four typical events were selected and their temporal and spatial characteristics were here described in detail. The geological conditions revealed after the rockbursts were surveyed carefully. The responses of support elements were also analyzed. The details documented in each case provide not only an important reference for understanding the development mechanisms of rockbursts but also a basis for the selection and development of rockburst prevention measures in deep hard rock tunnels.
For rock support in burst-prone ground, the wall-rock velocity adjacent to the surface of underground openings is a vital support design parameter, and depends on the seismic source mechanism ...inducing rockburst damage. In this study, to estimate the wall-rock velocity evoked only by rock slab buckling (an important rockburst source mechanism), a comprehensive velocity assessment method is proposed, using an excellent slab column buckling model with a small eccentricity, which relies on a novel compressive or tensile buckling failure criterion of rock slab. The true-triaxial loading–unloading tests and rockburst case analyses reveal that rock mass slabbing induced by high rock stress has major impacts on the evolution and formation of buckling rockburst in deep tunnels. Using a method based on the energy balance principle, the slabbing thickness of intact rock mass is also calculated by an analytical method, which indicates that the slabbing thickness parameter has a nonlinear relation to the following six parameters: uniaxial tensile strength (UTS), uniaxial compressive strength (UCS), normal stress (σ
n
), length of joint (L), friction angle (
ϕ
r
), and joint roughness coefficient (JRC). These proposed models and methods have been quite successfully applied to rockburst and slabbing cases occurring in deep tunnels. These applications show that slab flexure is an important source mechanism invoking high wall-rock velocities and leading to severe rockburst damages in the area surrounding deep tunnels.
Rock brittleness is an essential mechanical property, which plays a significant role in rock classifications and rockburst risk evaluations. To overcome the problems associated with the traditional ...brittleness indexes not comprehensively charaterizing the rock strength and deformation behaviors, this study systematically summarized the existing rock brittleness indexes. Then, a novel brittleness index (BICSS) based on the complete stress–strain curves of rock under different confining pressures was proposed. Its advantages included innovatively considering the characteristic stresses and strains at the stage of crack initiation, the peak points, and residual points. The index also described the stress growth rates from the pre-peak crack-initiation stress to the peak stress points, as well as the stress drop rates from the peak stress to the residual stress points. This study conducted uniaxial and triaxial compression tests of metamorphic sandstone, granite, and gneiss obtained from a deeply buried long-line tunnel group. The aforementioned tests were combined with wave velocity tests and thin-section identification tests using polarizing microscopy techniques. The reliability and applicability of the index were then successfully verified. The results showed that the BICSS could not only quantify and classify the brittleness characteristics of different rock types and characterize the confining pressure inhibition behaviors of rock brittleness, but could also comprehensively express the influences of homogeneity, mineral compositions, and particle sizes on the rock brittleness. Finally, through the parameter sensitivity analysis of the BICSS, the influences of subjective errors in the results of the cracking initiation stress and strain values caused by the different selections during the linear elastic phase could be successfully excluded, resulting in the further verification of the stability of the BICSS.
Aim
Acting as a tumor suppressor, microRNA (miR)‐125b shows aberrant low expression in hepatocellular carcinoma (HCC), and researchers have found that its dysregulation has a close relationship with ...hepatitis B virus (HBV) infection. Here, we investigated the expression profile of this miRNA in the plasma of healthy subjects and patients with chronic HBV‐related liver diseases in order to confirm the feasibility of this circulating miRNA as a differential diagnostic biomarker for HBV‐induced HCC (HBV‐HCC).
Methods
A total of 242 individuals were enrolled in this study. The expression levels of plasma miR‐125b were examined using quantitative real‐time polymerase chain reaction technology.
Results
The levels of plasma miR‐125b were remarkably decreased in HBV‐HCC patients compared to healthy controls and HBV subjects without HCC (all P < 0.001), and the low plasma miR‐125b levels in HBV‐HCC patients were associated with higher prevalence of metastasis (P = 0.021). The receiver–operating characteristic curve analyses indicated that plasma miR‐125b presented a high accuracy (area under the curve = 0.891, 0.958, 0.958) for diagnosing HBV‐HCC cases from healthy controls and patients with chronic hepatitis B and HBV‐related liver cirrhosis, respectively. In addition, our study found that the expression levels of plasma miR‐125b in HBV patients without HCC were higher than those in healthy subjects (P < 0.001); it yielded an area under the curve of 0.691 in discriminating patients with chronic HBV infection who were negative for HCC from healthy controls.
Conclusion
The measurement of plasma‐based miR‐125b holds promise as a diagnostic marker for HBV‐HCC differential diagnosis and for chronic HBV viral infection. Those HBV‐infected individuals with increased risk of HCC would be detected early through monitoring the changes in this circulating miRNA.
Understanding three-dimensional (3D) in situ stress field is of key importance for estimating the stability of large deep underground cavern groups near valleys. However, the complete 3D in situ ...stress fields around large deep underground cavern groups are difficult to determine based on in situ stress data from a limited number of measuring points due to the insufficient representativeness and unreliability of such measurements. In this study, an integrated approach for estimating the 3D in situ stress field around a large deep underground cavern group near a valley is developed based on incomplete in situ stress measurements and the stress-induced failures of tunnels excavated prior to the step excavation of the cavern group. This integrated approach is implemented via four interrelated and progressive basic steps, i.e. inference of the regional tectonic stress field direction, analyses of in situ stress characteristics and measurement reliability, regression-based in situ stress field analysis and reliability assessment, and modified in situ stress field analysis and reliability verification. The orientations and magnitudes of the 3D in situ stress field can be analyzed and obtained at a strategic level following these four basic steps. First, the tectonic stress field direction around the cavern group is deduced in accordance with the regional tectonic framework and verified using a regional crustal deformation velocity map. Second, the reliability of the in situ stress measurements is verified based on the locations and depths of stress-induced brittle failures in small tunnels (such as exploratory tunnels and pilot tunnels) within the excavation range of the cavern group. Third, considering the influences of the valley topography and major geological structures, the 3D in situ stress field is regressed using numerical simulation and multiple linear regression techniques based on the in situ stress measurements. Finally, the regressed in situ stress field is further modified and reverified based on the stress-induced brittle failures of small tunnels and the initial excavation of the cavern group. A case study of the Shuangjiangkou underground cavern group demonstrates that the proposed approach is reliable for estimating the 3D in situ stress fields of large deep underground cavern groups near valleys, thus contributing to the optimization of practical excavation and design of mitigating the instability of the surrounding rock masses during step excavations.
•An integrated approach for estimating the in-situ stress field was developed.•The tectonic stress field direction was deduced according to the regional tectonic framework.•The in situ stress field of large deep underground cavern groups was regressed using 3D numerical simulation.•The regression-based in situ stress field was modified with stress-induced brittle failure observation.
Displacement is vital in the evaluations of tunnel excavation processes, as well as in determining the post-excavation stability of surrounding rock masses. The prediction of tunnel displacement is a ...complex problem because of the uncertainties of rock mass properties. Meanwhile, the variation and the correlation relationship of geotechnical material properties have been gradually recognized by researchers in recent years. In this paper, a novel probabilistic method is proposed to estimate the uncertainties of rock mass properties and tunnel displacement, which integrated multivariate distribution function and a relevance vector machine (RVM). The multivariate distribution function is used to establish the probability model of related random variables. RVM is coupled with the numerical simulation methods to construct the nonlinear relationship between tunnel displacements and rock mass parameters, which avoided a large number of numerical simulations. Also, the residual rock mass parameters are taken into account to reflect the brittleness of deeply buried rock mass. Then, based on the proposed method, the uncertainty of displacement in a deep tunnel of CJPL-II laboratory are analyzed and compared with the in-situ measurements. It is found that the predicted tunnel displacements by the RVM model closely match with the measured ones. The correlations of parameters have significant impacts on the uncertainty results. The uncertainty of tunnel displacement decreases while the reliability of the tunnel increases with the increases of the negative correlations among rock mass parameters. When compared to the deterministic method, the proposed approach is more rational and scientific, and also conformed to rock engineering practices.
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•A probabilistic prediction method of displacement is proposed.•The multivariate distribution function is used to recognize the correlation.•A relevance vector machine (RVM) is used as a surrogate model.•The post-peak parameters are considered to reflect the brittleness of rock mass.•The influence of the correlation on tunnel displacement and reliability is studied.
Holes and inclusions can significantly affect the mechanical properties and fracture modes of brittle rocks. This study adopted digital image correlation (DIC), grain-based model, elastic mechanics ...and complex function theory to investigate the influence of hole shape, filling material stiffness and contact surface properties on the mechanical responses and fracture behaviors of granite. The results demonstrated that the macrocracks included primary tensile cracks, secondary or remote cracks and sidewall slabbing fractures. The uniaxial compressive strength (UCS) and local stress drops during the damage and failure stages changed with the shape of the hole or inclusion. Filling material effectively mitigated the stress concentration around the hole, and enhanced the UCS and elastic modulus. The filling material significantly affected the failure modes of the samples, and the rigid material improved the structural integrity of the damaged samples. Moreover, the friction coefficient of the contact surface and the elastic modulus of the inclusion improved the UCS, but the strengthening effects were limited.
To address the stress–structural failure phenomenon that can be induced by the excavation of a left-side tunnel section of a 610 m crushing station, an unmanned aerial vehicle was used in this study ...to collect the geological conditions and rock mass information of the working face, and important geometric information such as the attitude and spacing of rock mass were extracted. Based on the identified attitude and spacing information, a three-dimensional rock mass structure and numerical simulation model of the 610 m crushing station left-side tunnel section were constructed using discrete element numerical simulation software (3DEC) (version 5.0). The results show that the surrounding rock instability of the left-side tunnel section of the 610 m crushing station is controlled by both the stress field in the contact zone between reddish-brown granite stratum and the gray-black-gray gneiss stratum. The cause of stress–structural failure is that the joint sets (JSet #2 and JSet #3) are most likely to form unfavorable blocks with the excavation surface due to unloading triggered by the excavation. Therefore, stress–structural failure disasters in jointed strata sections are one of the key issues for surrounding rock stability during crushing station excavation. It is suggested to adopt ‘optimized excavation parameters + combined support forms’ to systematically control stress–structural failure after unloading due to the excavation from three levels: surface, shallow, and deep. The stress–structural failure mechanism of deep rock mass is generally applicable to a large extent, so the results of this research have reference value for engineering projects facing similar problems around the world.
Granite exhibits obvious meso-geometric heterogeneity. To study the influence of grain size and preferred grain orientation on the damage evolution and mechanical properties of granite, as well as to ...reveal the inner link between grain size‚ preferred orientation, uniaxial tensile strength (UTS) and damage evolution, a series of Brazilian splitting tests were carried out based on the combined finite-discrete element method (FDEM), grain-based model (GBM) and inverse Monte Carlo (IMC) algorithm. The main conclusions are as follows: (1) Mineral grain significantly influences the crack propagation paths, and the GBM can capture the location of fracture section more accurately than the conventional model. (2) Shear cracks occur near the loading area, while tensile and tensile-shear mixed cracks occur far from the loading area. The applied stress must overcome the tensile strength of the grain interface contacts. (3) The UTS and the ratio of the number of intergrain tensile cracks to the number of intragrain tensile cracks are negatively related to the grain size. (4) With the increase of the preferred grain orientation, the UTS presents a “V-shaped” characteristic distribution. (5) During the whole process of splitting simulation, shear microcracks play the dominant role in energy release; particularly, they occur in later stage. This novel framework, which can reveal the control mechanism of brittle rock heterogeneity on continuous-discontinuous trans-scale fracture process and microscopic rock behaviour, provides an effective technology and numerical analysis method for characterizing rock meso-structure. Accordingly, the research results can provide a useful reference for the prediction of heterogeneous rock mechanical properties and the stability control of engineering rock masses.
Circular RNAs (circRNA), a class of noncoding RNAs, have been found to be involved in various diseases. Here, the expression levels of the circRNA hsa_circ_0001445 in 73 pairs of hepatocellular ...carcinoma (HCC) and adjacent nontumor tissues were investigated by quantitative real-time polymerase chain reaction (qRT-PCR). Our data demonstrate that the hsa_circ_0001445 levels were significantly decreased in HCC tissues (P<0.001) and markedly associated with the number of tumor foci (P=0.014). Furthermore, in vitro approaches showed that overexpression of hsa_circ_0001445 promoted apoptosis and inhibited proliferation, migration, and invasion of HCC-derived cells, suggesting that hsa_circ_0001445 might be involved in the development of HCC. In addition, we found that the plasma hsa_circ_0001445 transcription levels in HCC patients were lower than those in cirrhosis (P<0.001) and hepatitis B (P<0.001) patients as well as in healthy controls (P<0.001). In fact, receiver operating characteristic curve analysis indicated that plasma hsa_circ_0001445 could be a fairly accurate marker to distinguish HCC cases from healthy controls as well as patients with cirrhosis or hepatitis B.
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