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With the increase of burial depth, complex geological conditions such as high in situ stress, high seepage pressure and weak faults bring many adverse effects to the construction of deep tunnels. Taking Xianglushan Tunnel of Yunnan Water Diversion Project as the engineering background, we conduct a three-dimensional geo-mechanical model test under hydro-mechanical coupling to investigate the excavation stability and the supporting control of a deep tunnel crossing a weak fault. The test results reveal that: (1) The fault has adverse effects on the distribution of physical fields. In the fault, the stress of the surrounding rock is in the plastic state; the displacement and seepage pressure are larger. Accordingly, the contact pressure and seepage pressure of the lining become larger. (2) The distribution of contact pressure and seepage pressure on the lining is uneven. The contact pressure of the lining at the vault and the bottom is generally larger than that at the hance. The largest seepage pressure appears at the bottom, while the smallest at the vault. (3) There is a coupling effect between the stress field and the seepage field in the surrounding rock. The stress field affects the seepage field by changing the deformation of the surrounding rock. The seepage field simultaneously acts to the stress field. Test results obtained in this study will provide an experimental basis for further theoretical studies and engineering designs. [ABSTRACT FROM AUTHOR]

Zonal disintegration is commonly encountered during the construction of tunnels at large depth. To study the formation and evolution mechanism of zonal disintegration in deep tunnels, a geo-mechanical model test is conducted under three-dimensional condition. The results reveal that: 1) with the proceeding of tunnel excavation, the displacements and the stresses around the tunnel present oscillating variation with alternating peak and trough. 2) Four annular rupture zones can be found around the tunnel, where the distance between the outermost rupture zone and the tunnel periphery is approximately 9.6 m. 3) The rupture zone first forms on the sidewalls of the tunnel, and then gradually develops to the interior of the rock mass until a complete ring-shaped rupture zone is formed. 4) The evolution of zonal disintegration is affected by the shape of cross section. The reproduction of zonal disintegration in laboratory can effectively reveal the formation mechanism and develop the control measures. The results obtained will provide important scientific basis for the safety construction of deep underground engineering. [ABSTRACT FROM AUTHOR]

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The microstructure of rock plays a vital role in the deformation and fracturing process when subjected to external loading. Conglomerate, being a pivotal part of unconventional reservoir, is characterized by a distinct composition structure and high degree of heterogeneity. Thus, a proper understanding of the impact of microstructure on the mechanical properties of conglomerate is crucial. We conduct uniaxial and triaxial compression tests on conglomerate samples, accompanied by monitoring acoustic emission events and ultrasonic wave velocity. Experimental results show that: (1) conglomerate fails in tension under uniaxial compression, but in shear fracture or cataclastic flow with volume expanding under triaxial compression; (2) the deformation transforms from brittle to ductile with increasing confining pressure. Two failure modes may exist in the brittle–ductile transition regime, namely, shear fracture and cataclastic flow; (3) the relationship between the mechanical characteristics and average gravel size is consistent with the "Hall–Petch" empirical relationship. The confining pressure required for brittle–ductile transformation reduces with larger average gravel size. Microscopic observation demonstrates that two gravels contacting with each other may fail in Hertzian fractures. Shear slip and rotation of gravel occurs under triaxial compression. We propose a conceptual model to describe the deformation of conglomerate under different confining conditions and compare the deformation properties of conglomerate with sandstone. Highlights: The effects of microstructural and micromechanical properties on the deformation of conglomerate deformation are studied. Both the peak strength and the brittle–ductile transition pressure reduce with higher average gravel size. Discrepancy between gravel and matrix deformation dominates the cracks initiation, while the location of gravel affects the propagation. [ABSTRACT FROM AUTHOR]

An accurate understanding of how water can affect the time-dependent deformation is important to assess the long-term stability of geotechnical projects. Triaxial compression rheological tests with different water contents were carried out to investigate the effects of water content and stress level on the creep strain, creep rate, long-term strength, and creep failure mode. Our experiments show that the time-dependent characteristics of rock are gradually activated with the increase of water content and stress level. The water content and stress level greatly increase the instantaneous strain, creep strain, and the steady creep strain rate, however, shorten the time to dilatancy and the time to failure. The creep curves and the creep rate versus time curves of argillaceous siltstone in the accelerated creep stage show a trend of "brittle-to-ductile" transformation. A modified steady-state creep rate tangent method was proposed and the analysis proves that the long-term strength of the rock decreases continuously with increasing water content. With the increase of water content, the rock exhibits a regularization of the main fracture surface, a gradual decrease of the number of secondary cracks, and a gradual disappearance of the shear slip phenomenon as observed. Our explanation is that since the clay minerals of T3sn argillaceous siltstone are mainly kaolinite, the main softening mechanism of the rock at low water content (0 ~ 1.14%) is the lubricating effect of the bound water film. The softening mechanism of clay-rich siltstone at high water content (1.14–3.35%) is dominated by the hydraulic fracturing action of pore water and Rehbinder effect. Highlights: The triaxial compression creep properties of argillaceous siltstone with different water contents are exposed. A modified steady-state creep rate tangent method for the determination of the long-term strength of soft rocks such as argillaceous siltstone is proposed. The softening mechanism of clay-rich siltstone with different water contents is analyzed and revealed. [ABSTRACT FROM AUTHOR]

In this paper, an experimental study on the dynamic propagation of fractures in granite samples under various injection schemes and initial stress conditions is carried out using a soundless cracking demolition agent (SCDA). Through the combination of acoustic emission (AE) monitoring, stress measurement and fracture morphology observation, the dynamic fracturing process is systematically analyzed. The stress shadowing effect between the two fractures is studied based on the results of stress monitoring and growth of fractures. The experimental results show that SCDA has a strong fracturing capacity and the stress shadowing effect between the boreholes makes the fractures tend to extend toward the direction connecting the two boreholes in the early stage of fracturing, leading to a more complicated fracture propagation mode. The change of stress within the sample can be divided into three stages, which correspond to the initiation of fractures, the initial formation of surface fractures and the stable propagation towards both sides and the lower part of the existing fractures. The fractal dimension of fractures and the roughness of fracture surfaces are quantitatively evaluated. The results show that the initial stress conditions and injection schemes are the key factors affecting the fracturing results. The smaller the side stress coefficient, the stronger the ability to form complex fractures. The optimal injection time interval varies with the selection of evaluation parameters and the fractal dimension of the sample is the highest when the injection time interval is 9 h. Highlights: The dynamic propagation of fractures under various injection schemes and initial stress conditions is systematically studied. The stress shadowing effect in multi-well fracturing makes fracture modes more complicated. The initial stress dominates the formation of complex fractures while the injection schemes also affects the trajectory. [ABSTRACT FROM AUTHOR]

Two methods (i.e., direct tensile test and the Brazilian test) are commonly adopted to measure the tensile strength of rock, but the tensile strengths obtained by the two methods are obviously different. Taking Beishan granite as physical background, this study systematically investigates the discrepancies between the Brazilian test and direct tensile test with the use of three-dimensional Flat-joint model (FJM3D) simulation. Simulation results indicate that the Brazilian disc is under a complex three-dimensional stress state, and produce some shear cracks, which is significantly different from direct tensile test. By assigning different micro parameters to the FJM, the influences of the heterogeneity of the microstructure (particles size and pre-existing cracks) and micro-strength (bond strength) on the direct tensile strength (DTS) and the Brazilian tensile strength (BTS) are investigated. The heterogeneity of particles size, pre-existing cracks, and bond strength have negatively effects on both DTS and BTS, and that the ratio between DTS and BTS decreases with the increase of heterogeneity of pre-existing cracks and bond strength. The statistical analyses reveal that in the Brazilian disc, the contact normal stresses obey the normal distribution, but in the direct tensile specimen, the contact normal stresses obey the log-normal distribution. The three heterogeneities have minor effects on the dip direction of cracks, but significantly affect the dip angle of cracks. The heterogeneity of microstructure affects the local stress concentration, which reduces the tensile strength, and changes the orientation of cracks. [ABSTRACT FROM AUTHOR]

In situ stress and underground water are known to significantly influence the deformation and stability of deep underground caverns. These factors should be considered in the design of excavation and supporting schemes. However, the rock failure mechanism and permeability characteristics under the coupling condition remain largely unexplained. Based on the Xianglushan diversion tunnel in Central-Yunnan Water Diversion Project, we conducted triaxial compression experiments on both intact rock specimens and cracked rock specimens with three confining pressures (11 MPa, 18 MPa, and 25 MPa) and three osmotic pressures (2 MPa, 6 MPa, and 10 MPa). The experimental results show that rock strength can be expressed as a function of confining pressure and osmotic pressure. Osmotic pressure can reduce rock strength, while the effect of confining pressure is opposite. With the increase of osmotic pressure, the initial permeability and the peak permeability increase. Compared with the stress-strain curve, the variation of permeability-strain curve is "hysteretic." For cracked specimens, the stress-strain curve after failure presents a "step down" trend, and the permeability-strain curve appears a "bimodal shape." The failure pattern changes from shear failure to tensile failure as the osmotic pressure increases. With the increase of osmotic pressure, the crack increases gradually and becomes tortuous and rough. The generation and propagation of cracks gradually develop towards vertical load. [ABSTRACT FROM AUTHOR]

Creep properties of interlayered rock mass often encountered in rock engineering, significantly affect the safety and long-term stability of practical engineering. In this study, the theoretical equations of creep strain for interlayered rock specimens when the uniaxial compression loading was applied perpendicular to or parallel with bedding plane were derived. The laws of viscoelastic deformation for soft-hard interlayered rock specimens, soft-soft interlayered rock specimens and hard-hard interlayered rock specimens were also discussed, respectively. The creep deformation characteristics obtained from the numerical simulation and the theoretical analyses were consistent, confirming the correctness of the calculation method proposed in this paper. The results showed that the viscoelastic deformation of interlayered rock specimens was not only related to the volume ratio of rock layers, but it also was affected by the spatial position of the layered structure. In addition, creep properties of hard and soft rock layers were characterized by stable creep model and unstable creep model, respectively. The influences of volume content, number of strips, buried depth, spacing and angle of soft rock interlayer on the creep properties of soft-hard interlayered rock specimens were also analyzed. [ABSTRACT FROM AUTHOR]

Geological disposal at deep burial depths is a widely accepted method for the treatment of high-level radioactive waste, in which an underground laboratory is regarded as an essential facility to connect various aspects of the process. To evaluate the excavation-induced stability of the rock mass surrounding the underground laboratory for deep geological disposal of high-level radioactive waste in Beishan, Gansu Province, true three-dimensional geomechanical model tests are carried out for the first time. A model test loading system is developed with an intelligent numerical control function and automatic excavation apparatuses. The variations in the displacement and stress surrounding the caverns are revealed. The test results indicate that after excavation, (1) the surrounding rock deforms toward the cavern with small displacements less than 3 mm; (2) the radial stress is lower, and the tangential stress is higher; tensile stress is induced in certain parts near the intersection of caverns but at a magnitude lower than the tensile strength of the rock; (3) the excavation-induced perturbation reaches approximately 1.5–2.0 times the cave diameter; and (4) the surrounding rock shows stability after excavation due to the favorable geological conditions and the overall high strength of the surrounding rock. Nevertheless, enhanced support via combined bolting and shotcrete are recommended at the crossing sections. The research results verify the rationality of the design scheme and provide important guidance for the construction of underground laboratories for deep underground disposal of high-level radioactive waste. [ABSTRACT FROM AUTHOR]

During a hydraulic fracturing treatment, sedimentary beddings and preexisting joints in the shale reservoir may cause the deviation of fractures and the diversion of fluid, which ultimately lead to the unexpected fracture patterns. To evaluate the influence of these factors on the fracturing response, a comprehensive study is conducted using the discrete element method simulations. Interactions between the beddings, the preexisting joints and the induced fractures are modeled in a fully coupled manner by idealizing the sedimentary beddings which cause inherent anisotropy as individual horizontal smooth joint and modeling any preexisting joints with continuous smooth joint contacts. The models are first calibrated to reproduce the mechanical properties of the anisotropic rock in field. Results from these simulations indicate that the formation's anisotropy promotes fracture growth along the sedimentary beddings. Joint characteristics (i.e., orientation, aperture, and healing conditions) could have a major impact on the behavior of shale formation during hydraulic fracturing operations. Open horizontal joints play a more important role in the fracture propagation process than the in situ stress under the stress state considered in this study. The healing in the joints creates a barrier for fracture propagation, which might be effective enough to lead to fracture deviation from the preferred orientation. This study reveals the important factors which may influence the hydraulic fracture propagation and thus can serve as numerical basis for the more exhaustive studies in the future, e.g., models with realistic fracture network and more complex injection scenarios. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing in permeable rock is a complicated process which might be influenced by various factors including the operational parameters (e.g., fluid viscosity, injection rate and borehole diameter) and the in situ conditions (e.g., in situ stress states and initial pore pressure level). To elucidate the effects of these variables, simulations are performed on hollow-squared samples at laboratory scale using fully coupled discrete element method. The model is first validated by comparing the stress around the borehole wall measured numerically with that calculated theoretically. Systematic parametric studies are then conducted. Modeling results reveal that the breakdown pressure and time to fracture stay constant when the viscosity is lower than 0.002 Pa s or higher than 0.2 Pa s but increases significantly when it is between 0.002 and 0.2 Pa s. Raising the injection rate can shorten the time to fracture but dramatically increase the breakdown pressure. Larger borehole diameter leads to the increase in the time to fracture and the reduction in the breakdown pressure. Higher in situ stress requires a longer injection time and higher breakdown pressure. The initial pore pressure, on the other hand, reduces the breakdown pressure as well as the time to fracture. The increase in breakdown pressure with viscosity or injection rate can be attributed to the size effect of greater tensile strength of samples with smaller infiltrated regions. [ABSTRACT FROM AUTHOR]

An induction levitation melting (ILM) refining process is performed to remove most microsized inclusions in ultra-low carbon steel (UCS). Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nm remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthening phase. [ABSTRACT FROM AUTHOR]

Fireflies are among the most charismatic insects for their spectacular bioluminescence, but the origin and evolution of bioluminescence remain elusive. Especially, the genic basis of luciferin (d-luciferin) biosynthesis and light patterns is largely unknown. Here, we present the high-quality reference genomes of two fireflies Lamprigera yunnana (1053 Mb) and Abscondita terminalis (501 Mb) with great differences in both morphology and luminous behavior. We sequenced the transcriptomes and proteomes of luminous organs of two species. We created the CRISPR/Cas9-induced mutants of Abdominal B gene without luminous organs in the larvae of A. terminalis and sequenced the transcriptomes of mutants and wild-types. Combining gene expression analyses with comparative genomics, we propose a more complete luciferin synthesis pathway, and confirm the convergent evolution of bioluminescence in insects. Using experiments, the function of the firefly acyl-CoA thioesterase (ACOT1) to convert l-luciferin to d-luciferin was validated for the first time. Comparisons of three-dimension reconstruction of luminous organs and their differentially expressed genes among two species suggest that two positive genes in the calcium signaling pathway and structural difference of luminous organs may play an important role in the evolution of flash pattern. Altogether, our results provide important resources for further exploring bioluminescence in insects. [ABSTRACT FROM AUTHOR]

Covalent probes coupled with chemical proteomics represent a powerful method for investigating small molecule and protein interactions. However, the creation of a reactive warhead within various ligands to form covalent probes has been a major obstacle. Herein, we report a convenient and robust process to assemble a unique electrophile, an α-acyloxyenamide, through a one-step late-stage coupling reaction. This procedure demonstrates remarkable tolerance towards other functional groups and facilitates ligand-directed labeling in proteins of interest. The reactive group has been successfully incorporated into a clinical drug targeting the EGFR L858R mutant, erlotinib, and a pan-kinase inhibitor. The resulting probes have been shown to be able to covalently engage a lysine residue proximal to the ATP-binding pocket of the EGFR L858R mutant. A series of active sites, and Mg 2+ , ATP-binding sites of kinases, such as K33 of CDK1, CDK2, CDK5 were detected. This is the first report of engaging these conserved catalytic lysine residues in kinases with covalent inhibition. Further application of this methodology to natural products has demonstrated its success in profiling ligandable conserved lysine residues in whole proteome. These findings offer insights for the development of new targeted covalent inhibitors (TCIs)., (© 2024. The Author(s).)