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 be-cause 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 displace-ment,which integrated multivariate distribution function and a relevance vector machine (RVM).The multivar-iate 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 un-certainty 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 determin-istic method,the proposed approach is more rational and scientific,and also conformed to rock engineering nractices.
In this study, true triaxial compression tests were carried out on three types of hard rocks (i.e., granite, marble and sandstone) using rectangular prismatic specimens (50 × 50 × 100 mm
3
) with low ...minimum principal stress
σ
3
, and various intermediate principal stresses
σ
2
. The main purposes were to establish the relationship between the characteristic stress levels (i.e., crack initiation stress, crack damage stress and peak stress) and the corresponding principal stresses and to investigate the brittle fracturing process of hard rocks near excavation boundaries. The test results indicated that the stress–strain curves were primarily characterized by the linear-elastic–brittle behavior. The failure planes of the specimens in the tests were found to be adjacent to the
σ
3
loading surface, and almost parallel to the
σ
1
–
σ
2
plane, which were analogous to the spalling of the surrounding rock. With the aid of scanning electron microscopy, it was shown that cleavage fractures accounted for the majority of the fracture morphology in the sandstone specimens. Two revised methods were developed to determine the crack initiation stress of hard rocks under true triaxial compression, and these characteristic stress levels could be appropriately fitted by utilizing both the parabolic and power functions. Although the power function achieved better fitting results, the parameters in the parabolic function could be associated with the tensile cracks induced during the loading process. The influence of intermediate principal stress on the strength, deformation and failure was significant. In addition, the brittle fracturing process could be illustrated by the crack-induced strains in three principal stress directions.
Circular RNAs (circRNA)are involved in the progression of cancers, and previous study showed that hsa_circ_0001649 expression is down-regulated in hepatocellular carcinoma (HCC).
To explore whether ...hsa_circ_0001649 is a prognostic biomarker for HCC and to investigate the biological functions of hsa_circ_0001649 in HCC.
Hsa_circ_0001649 expression was measured in 77 pairs of HCC and adjacent no-tumor tissues by quantitative Real-Time polymerase chain reaction. Kaplan-Meier curve and Cox regression were used to analyze its prognostic significance for HCC patients. In addition, the hsa_circ_0001649 was over-expressed using a circRNA-forming plasmid in HCC cells, and the biological function of hsa_circ_0001649 was investigated in vitro.
We verified that hsa_circ_0001649 was down-regulated in HCC tissues compared with adjacent non-tumor tissues. In addition, low hsa_circ_0001649 expression was associated with the poor overall survival of HCC patients, and Cox multivariate analysis showed that hsa_circ_0001649 is a novel independent prognostic factor for HCC patients. Furthermore, the in vitro experiments demonstrated that over-expressed hsa_circ_0001649 inhibits the proliferation, migration, and invasion and promotes the apoptosis of HCC cells.
Hsa_circ_0001649 could act as a novel prognostic biomarker for HCC patients. In addition, hsa_circ_ 0001649 might be a potential therapeutic target for HCC.
A convenient and efficient approach to simulate the excavation-induced rock fracturing process from continuity to discontinuity is proposed. The excavation boundary is considered to be an internal ...discontinuity, which is enriched by a Heaviside function. By using partition of unity concept and level set method, the cellular automaton updating rule for elasto-plastic fracturing induced by excavation is developed. The excavation induced rock mass strain localization is described by plasticity. A plastic strain-dependent criterion is proposed to link continuity and discontinuity, by which crack initiation and propagation of rock mass are described. By using the cellular automaton neighborhood information and level set method, the crack propagation path and excavation boundary can be tracked efficiently. The excavation and the induced crack initiation and propagation can be represented and simulated without explicit remeshing. This approach is implemented in a self-developed numerical model, i.e. a rock continuous-discontinuous cellular automaton (CDCA). The reliability and versatility of CDCA in the modeling of excavation-induced crack initiation, propagation, coalescence and block formation in rock mass are well demonstrated. The method helps estimate the onset of stable and unstable failure development, as well as the magnitude of plastic strain before cracking in rocks.
The behavior of rock damage evolution under unloading conditions is of utmost importance for the analysis of the stress-induced failure of overstressed rock masses. In this paper, a new experimental ...approach, the incrementally cyclic loading–unloading pressure test (ICLUP test), is designed to quantify stress-induced micro-fracturing and fracturing under the condition of confining pressure reduction. The experimental results demonstrate that the pre-peak damage and deformation characteristics of marble specimens may be easily quantified by irreversible strains, and two damage stages, namely, the linear steady stage and the nonlinear unsteady stage, which are, respectively, represented as a linear steady rate and a nonlinear unsteady rate of damage evolution, occur along with the increase of unloading damage. The new model is proposed to describe the features of pre-peak unloading damage evolution, and the physical meanings and ranges of its material parameters are explained and analyzed. Furthermore, the evolution of volumetric dilation and elastic parameters which occurs along with the increase of unloading damage is revealed. Also discussed in this paper are the inhomogeneity and initial damage of specimens, as well as related research planned to be performed in the future.
•Spatiotemporal features of stress–structure controlled collapse are presented.•A typical collapse is investigated by field survey, SEM and MS monitoring.•Rock mass fracturing events are mostly ...tensile during this kind of collapse.•MS monitoring can play an important role for the warning of this kind of collapse.
During the excavation of the underground powerhouse in the Baihetan hydropower station, which is currently still under construction, stress–structure controlled collapse has occurred frequently. In order to study the mechanism behind the evolution of this kind of collapse, an in situ experiment involving microseismic (MS) monitoring was carried out in the left main/auxiliary powerhouse. In this paper, the spatiotemporal characteristics of stress–structure controlled collapse are summarized and presented. A field survey, scanning electron microscopy and MS monitoring have been used to investigate a typical stress–structure controlled collapse that occurred during the monitoring period. These methods provided a consistent set of results, namely, that tensile fracturing is the rock-mass fracturing mechanism that is most active during the process of evolution of stress–structure controlled collapse. In addition, the evolution of the microseismicity during the development of the studied collapse was also obtained. The results provide a direct case history that will assist the prediction and support of stress–structure controlled collapse disasters and contribute to excavation of deeply-buried caverns in the field.
Carbon dioxide (CO
2
) sequestration in deep saline aquifers is regarded as a potentially useful method of storing CO
2
due to their large storage capacity. CO
2-
trapping mechanisms in such aquifers ...include solubility trapping, hydrodynamic trapping, structural trapping, and mineral trapping. CO
2
–water–rock interactions occurring in saline aquifers injected with CO
2
are known to play a vital role in these trapping mechanisms. Stress is known to have a significant and positive effect on mineral dissolution, and therefore, pressure solution as a coupled chemo-mechanical behavior could make an important contribution to mineral trapping. Geological storage of CO
2
can also be combined with enhanced water recovery (EWR) from deep saline aquifers, a process referred to as CO
2
–EWR. By exploiting the fluid during CO
2
–EWR, the pore pressure in the reservoir is altered, which could enhance pressure solution between the mineral grains in the reservoir. In this work, the role played by pore pressure in CO
2
mineral trapping from the perspective of pressure solution as a chemo-mechanical coupling process is investigated. To achieve this, seepage–creep tests were performed on sandstone specimens by passing CO
2
–NaCl solutions through them at different pore pressures. Experimental results show that the lower the pore pressure a specimen is subjected to, the greater the amount of carbon trapped in the sandstone. On the basis of this result, a geometrical model is established for pressure solution in the materials used that quantitatively describes the mechanism responsible for pressure solution. Geometrical model is then used to analyze the effects of the various factors affecting the role played by pressure solution in CO
2
mineralization sequestration (mineral type, pore pressure, porosity, and particle size). The results of the analysis are particularly instructive for the evaluation of long-term CO
2
storage in terms of pressure solution. As for CO
2
–EWR, apart from relieving pressure buildup, increasing CO
2
injection, regulating CO
2
migration, and restricting CO
2
leakage, it also enjoys the advantage of enhancing mineral trapping.
•P-wave velocity attenuation index was defined to assess excavation-induced damage.•Changes of elastic modulus, volume, and stress level were reflected in the index.•Elastic modulus deterioration ...index was proposed to identify the loosened zone.
In order to effectively identify the loosened zone around underground openings by using continuum modeling, this paper proposes an index called elastic modulus deterioration index based on the following two steps. First, the response of surrounding rock mass in underground openings as obtained from ultrasonic tests before and after excavation is investigated. Based on the attenuation of the P-wave velocities of the rock mass after excavation compared to the P-wave velocities before excavation obtained from ultrasonic tests, an index (χ) is defined to assess the excavation-induced rock mass damage. Second, by introducing an empirical relationship between the static and dynamic elastic moduli, the index χ is modified to represent the static elastic modulus evolution, volume change, and stress redistribution of the rock mass based on an elasto-plastic numerical model. Furthermore, this study verifies the performance of the elastic modulus deterioration index to identify the loosened zone around underground openings by comparing its predictions with the results from ultrasonic testing of the loosened zones around two tunnels in the Jinping II hydropower station. The comparisons show that the loosened zones as identified by the elastic modulus deterioration index agree well to those from ultrasonic testing. Analysis of the effects of key input parameters and initial shear strength parameters on the elastic modulus deterioration index in identifying the loosened zone demonstrate that: (1) the sensitivity of the index to the key input parameters except the residual static elastic modulus is not significant; and (2) the index has better fault tolerance performance compared to the indices based on plastic zone in terms of the selection of initial shear strength parameters.
Fully grouted bolts are a key component of the support system for underground openings.Although con-siderable effort has been made in the simulation of the reinforcement effect of the fully grouted ...bolts on the rock masses surrounding underground openings,most of the work has limited significance since the structural element approach is used.This study proposes a local homogenization approach(L-H approach)that integrates elastoplastic mechanics,composite mechanics,and analytical approaches with numerical simulation to effectively simulate the reinforcement effect of the fully grouted bolt on deep surrounding rock masses.In the L-H approach,the representative volume of bolted rock mass(RVBRM)with a fully grouted bolt is established based on the original mesh model utilized in the rockbolt element approach.The RVBRM is a regular quadrangular prism with a cross-sectional size equal to the bolt spacing and a length equal to the bolt length.The RVBRM is homogenized by the L-H approach from a unidirectional bolt-reinforced composite into a homogeneous transversely isotropic medium whose mechanical properties are described by a new transversely isotropic elastoplastic model.The L-H param-eters for the RVBRM are obtained using analytical approaches,composite mechanics,and known param-eters of the rock mass and bolt.Using the L-H approach,the reinforcement effect of the fully grouted bolt on the bolted rock specimen and the surrounding rock mass in Jinping Ⅱ Diversion Tunnel#2 with a depth greater than 2000 m is simulated.The results show that the predictions of the L-H approach are more in agreement with the physical model results of bolted rock specimen and provide a more realistic response of the bolted surrounding rock mass.The L-H approach demonstrates that fully grouted bolts with common bolt spacings and diameters substantially enhance the elastic modulus,shear strength,and tensile strength of the rock mass in the direction of the bolt axis.
In tunnel engineering, it is important to understand the influence of schistose structure on the failure strength of chlorite schist. To explore the strength control factors of chlorite schist, this ...paper firstly analyzes the mineral composition and meso structure of chlorite schist of different weathering states. The results show that the mineral composition of chlorite schist is changed during the weathering process, and that chlorite is an anisotropic rock mass. Next, a series of uniaxial compressive tests were conducted on chlorite schist samples with different bedding angles (the angle between bedding plane and loading direction; θ=0°, 15°, 30°, 45°, 60°, 75°, and 90°), moisture conditions (dry and saturated), and weathering states (strongly weathered and weakly weathered). Based on the test data, the authors discussed the change laws of the rock strength with bedding angle, weathering state, and moisture condition. The main results are as follows: Chlorite schist is a low-anisotropy rock mass, whose compressive strength exhibited a V-shaped trend with the growing bedding angle; the schistose structure is the internal cause of the deformation and the anisotropic or transversely isotropic strength of the schist; the schistose structure is reshaped and further damaged by external factors (e.g. water softening and weathering effects) in engineering. The research findings help to improve the rock stability and support design in tunnel engineering.
PDF