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Fully exploiting the silicon photonics platform for large-volume, cost-sensitive applications requires a fundamentally new approach to directly integrate high-performance laser sources using wafer-scale fabrication methods. Direct-bandgap III–V semiconductors allow efficient light generation, but the large mismatch in lattice constant, thermal expansion and crystal polarity makes their epitaxial growth directly on silicon extremely complex. Using a selective-area growth technique in confined regions, we surpass this fundamental limit and demonstrate an optically pumped InP-based distributed feedback laser array monolithically grown on (001)-silicon operating at room temperature and suitable for wavelength-division-multiplexing applications. The novel epitaxial technology suppresses threading dislocations and anti-phase boundaries to a less than 20-nm-thick layer, which does not affect device performance. Using an in-plane laser cavity defined using standard top-down lithographic patterning together with a high yield and high uniformity provides scalability and a straightforward path towards cost-effective co-integration with silicon photonic and electronic circuits. Scientists demonstrate an optically pumped InP-based distributed feedback laser array monolithically grown on (001)-silicon operating at room temperature that is suitable for wavelength-division multiplexing applications.

The permeability coefficient of rock mass is a critical parameter for groundwater flow analysis of underground water-sealed oil storages. Based on the site geological investigation, monitoring information, and data statistics, a method of determining representative permeability coefficients of original and grouted rock mass for underground water-sealed oil storage was proposed. Then, the proposed method was applied to the flow field analysis of an underground water-sealed oil storage under construction. The assessment of containment properties, the prediction of water inflow, and the analysis of grouting effect were carried out. For the similar kind of underground water-sealed oil storages, the geometric mean of the tested permeability coefficients was suggested to be the representative value of original rock mass. The relationship between the permeability reduction factors of grouting and the original permeability coefficients was obtained to predict the grouting zone permeability. Based on the proposed method, the representative original permeability coefficient of the storage zone is determined to be 1.96E−03 m/day, and the permeability coefficient of the grouted zone is conservatively suggested to be reduced to 10% of the original value. The predicted results of water inflow and grouting effect by flow simulation were compared with that by engineering analogy and theoretical analysis, which further verified the rationality of the proposed method and the reliability of the flow field analysis. The method of determining the representative permeability coefficients of rock mass and its application can help improve the accuracy of groundwater flow field analysis and offer guidelines for the construction of underground water-sealed oil storage.

The hydro-physical and hydro-chemical interactions between groundwater and a rock mass can lead to changes in the mineral composition and structure of the rock (e.g., generation of voids and dissolution pores and an increase in the porosity), thereby altering the macroscopic mechanical characteristics of the rock mass. Sandstone specimens were saturated with distilled water and five aqueous solutions characterized by various ion concentrations and pH values for several months, and their porosity was measured in real time. Simultaneously, the concentration and pH of each aqueous solution were monitored every 30 days. The results indicate that after immersion in the aqueous solutions for 180 days, the porosity of the sandstone specimens and the ion concentrations and pH of the aqueous solutions tended to stabilize. Then, the immersed sandstone specimens were analyzed in thin section and subjected to computerized tomography scanning. It turns out that the mineral composition and structure of the specimens had all changed to various degrees. Finally, the uniaxial compression tests were conducted on the sandstone specimens to analyze the effects of the hydro-physical and hydro-chemical alteration on the macroscopic mechanical characteristics of the rock (e.g., the stress–strain relationship, elastic modulus, and peak strength). The results of this study can serve as a reference for investigations into theories and applications of water–rock interactions and for research in related fields.

A series of laboratory experiments on water flow through rough fractures was performed using self-designed experimental devices to investigate the effect of fracture roughness on the flow behavior. Nine models of single rough fractures—with three joint roughness coefficients (JRCs) of 0–2, 8–10 and 18–20, and three apertures for each JRC—were prepared using three-dimensional printing technology. In the flow experiments, the values of Reynolds numbers ranged widely from less than 10 to around 10,000. According to the experimental data, the fracture roughness has an obvious influence on the hydraulic properties of fractures. A parametric expression for the Forchheimer equation was proposed to quantitatively describe the influence of fracture roughness on the flow behaviour in the fractures. The relations between the parameters for nonlinear flow (such as critical Reynolds number, non-Darcy effect coefficient and friction factor) and the JRCs were obtained. It was found that the critical Reynolds number decreased significantly from 566 to 67 as the JRC increased from 2 to 20. The increase in fracture roughness causes more extra energy losses and enhances the degree of flow nonlinearity in single fractures.

A method to estimate the representative elementary volume (REV) size for the permeability and equivalent permeability coefficient of rock mass with a radial flow configuration was developed. The estimations of the REV size and equivalent permeability for the rock mass around an underground oil storage facility using a radial flow configuration were compared with those using a unidirectional flow configuration. The REV sizes estimated using the unidirectional flow configuration are much higher than those estimated using the radial flow configuration. The equivalent permeability coefficient estimated using the radial flow configuration is unique, while those estimated using the unidirectional flow configuration depend on the boundary conditions and flow directions. The influences of the fracture trace length, spacing and gap on the REV size and equivalent permeability coefficient were investigated. The REV size for the permeability of fractured rock mass increases with increasing the mean trace length and fracture spacing. The influence of the fracture gap length on the REV size is insignificant. The equivalent permeability coefficient decreases with the fracture spacing, while the influences of the fracture trace length and gap length are not determinate. The applicability of the proposed method to the prediction of groundwater inflow into rock caverns was verified using the measured groundwater inflow into the facility. The permeability coefficient estimated using the radial flow configuration is more similar to the representative equivalent permeability coefficient than those estimated with different boundary conditions using the unidirectional flow configuration.

A series of laboratory tests were performed to examine the fatigue behavior of granite subjected to cyclic loading under triaxial compression condition. In these tests, the influences of volumetric change and residual strain on the deformation modulus of granite under triaxial cyclic compression were investigated. It is shown that the fatigue behavior of granite varies with the tendency for volumetric change in triaxial cyclic compression tests. In the stress–strain space, there are three domains for fatigue behavior of rock subjected to cyclic loading, namely the volumetric compaction, volumetric dilation with strain-hardening behavior, and volumetric dilation with strain-softening behavior domains. In the different domains, the microscopic mechanisms for rock deformation are different. It was also found that the stress level corresponding to the transition from volumetric compaction to volumetric dilation could be considered as the threshold for fatigue failure. The potential of fatigue deformation was compared with that of plastic deformation. The comparison shows that rocks exhibit higher resistances to volumetric deformation under cyclic loading than under plastic loading. The influence of residual strain on the fatigue behavior of rock was also investigated. It was found that the axial residual strain could be a better option to describe the fatigue behavior of rock than the loading cycle number. A constitutive model for the fatigue behavior of rock subjected to cyclic loading is proposed according to the test results and discussion. In the model, the axial residual strain is considered as an internal state variable. The influences of confining pressure and peak deviatoric stress on the deformation modulus are considered in a term named the equivalent stress. Comparison of test results with model predictions shows that the proposed model is capable of describing the prepeak fatigue behavior of rock subjected to cyclic loading.

Hydrogeochemical environment is of critical importance for the environment-friendly operation of underground oil storage caverns. The construction of underground oil storage caverns usually has an impact on the hydro-environment. The characterization and analysis of the hydrogeochemical environment can provide information on the relation between construction and hydro-environment. The quality of water samples was detected and analyzed to determine the chemical type in an underground oil storage cavern in China. The water samples are classified using principal component analysis and cluster analysis. The source and proportion of seepage water into the storage caverns are determined with end member mixing calculation. The results show that the chemical type of groundwater is mainly HCO3 + Cl − Na type, and the two dominant factors affecting the evolution of hydrogeochemical content are rock dissolution and groundwater seepage. All water samples can be catalogued as seepage water, water curtain water, X River water and background water. The water curtain water can fully penetrate into the ground to provide containment for the storage caverns, and the water curtain system has a good performance and can basically cover the project area. Most of the seepage water into the storage caverns comes from water curtain water and X River water, while the proportion of background water is relatively low. The construction of underground oil storage caverns affects the groundwater flow regime by changing the directions of groundwater flow around the caverns. This study showcases the use of hydrogeochemical analysis in depicting the interplay between surface water and groundwater for underground rock engineering.

Macroscopic nonlinear flow, which is closely related to mesoscopic flow structures such as vortices, is an important property of fluid flow and solute transport in rock fractures with a high pressure gradient. Both mesoscopic flow structure and macroscopic nonlinear flow of rock fractures are affected by fracture roughness and aperture. Therefore, the macroscopic seepage process in fractures is studied numerically by directly solving the Navier–Stokes equation. The results demonstrate that the Forchheimer equation can be used to describe the relationship between flow rate and pressure gradient of rough fractures with different apertures. The linear and nonlinear coefficients of the Forchheimer equation increase with fracture roughness and decrease with fracture aperture. Empirical formulas between the linear coefficient, the nonlinear coefficient, the fracture roughness and aperture are established. When the roughness is equal to zero, the empirical formulas can degenerate into conventional cubic law. In additions, the distribution characteristics of the mesoscopic flow structure in rough fractures are also investigated. The results show that the area and kinetic energy distribution characteristics of the mesoscopic flow structure in fractures with different roughness and apertures are similar. The frequency characteristics of the area and kinetic energy of the mesoscopic flow structure in fractures can be fitted with negative exponential and logarithmic normal functions, respectively. The effect of fracture roughness on area and kinetic energy distribution characteristics is significant, but the effect of aperture can be ignored. Empirical formulas between fracture roughness and mesoscopic flow structure characteristics are established for the first time.

Fracture intersections are the main components of fracture networks with significant effects on the distribution of flow velocity and fluid pressure near the intersection. A nonlinear flow model for fracture intersections correlating to geometric parameters of two-dimensional fracture intersections was proposed, which was applicable to different flow patterns in fracture intersections. A total of 68 fracture intersection models were established and simulated. By fitting these calculated results, regression functions in terms of each kind of geometric parameter were obtained to determine nonlinear coefficients. Through independent and comprehensive analysis of the influence of geometric parameters on flow characteristics, the quantitative relationships between the nonlinear coefficients of the fracture intersection flow model and multiple geometric parameters, such as the intersecting angle (θ), aperture (e), and roughness, were obtained. The parametric expressions of nonlinear flow models were verified by flow experiments of typical fracture intersections and simulated cases with complicated combinations of geometric parameters. It was proven that the parametric expressions of nonlinear flow models were capable of describing the nonlinear flow through fracture intersections. The results of this study show that fracture intersections have an obvious influence on the flow characteristics of different flow paths, which indicates that the influence of fracture intersections can enhance the hydraulic heterogeneity of fractured rock and need to be considered in the flow analysis of fracture networks.HighlightsA nonlinear flow model for fracture intersections of two-dimensional fracture intersections was proposed.Quantitative relationships between the nonlinear coefficients and geometric parameters of the fracture intersections were obtained.Flow experiments of typical fracture intersections were carried out.The parametric expressions of nonlinear flow models were verified by flow experiments and simulations of complicated cases.

The matrix–fracture flow transfer is one of the most important characteristics of flow in fractured porous media. Matrix–fracture flow transfer experiments in fractured porous media were carried out using a self-developed experimental device and simulation. The matrix–fracture flow transfer was analyzed in fractured porous media with regular fractures and irregular fractures at different matrix–fracture pressure differences. The matrix–fracture flow transfer rate accounted for 26–72% of the matrix inlet flow rate, and the flow transfer rate presented a nonlinear increasing trend as the matrix–fracture pressure difference increased. We have observed the influence of heterogeneous pressure and inconsistent transfer direction on flow transfer in experiments and simulations. The influence of the heterogeneous matrix–fracture pressure difference increased with increasing fracture aperture and fracture/matrix permeability ratio and decreased with increasing trace length and density. The matrix–fracture flow transfer term obtained in the experiment and simulation was analyzed using the shape factor theory and the genialized transfer model we have previously proposed. In FPM with a regular fracture distribution, the fitting effect of the shape factor model and the generalized model was approximately the same. However, in FPM with irregular fracture distribution, the flow transfer rate predicted by the generalized model was more accurate than that predicted by the shape factor model. The flow transfer rate predicted by the traditional shape factor model may have been overestimated because it ignored the effect of the heterogeneous matrix–fracture pressure difference. The findings of this study can help for a better understanding of matrix–fracture flow transfer to predict groundwater flow field in naturally fractured porous media.Highlights A self-developed experimental device that can simulate the matrix-fracture flow transfer in fractured porous media was designed.The influence of heterogeneous pressure and inconsistent transfer direction on flow transfer in experiments and simulations were observed.Due to heterogeneous matrix-fracture pressure difference, the flow transfer rate predicted by the generalized model was more accurate than that predicted by the shape factor model.