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The mechanical and hydraulic behaviors of rock fractures are strongly dependent on the properties of the surface morphology. In this study, a sandstone fracture surface is taken as the research object. The morphological properties of the fracture surface characterized by parameters Z2s, Z2, and SRv are analyzed under the different sampling windows and profile lines. The results show that the large sampling window is more conducive to obtaining stable values of the morphology parameter Z2s. The coefficient of variation (CV) and the percentage of variation (PV) are proposed to determine the stable values of the morphology parameter Z2s, which is defined as a representative elementary surface (RES). It is confirmed that there is a RES with a size of 220 mm in the study region. The large sampling window generates a long correlation length of the morphology parameter Z2s. The differential sensitivities of the morphology parameters Z2 and SRv are compared under the different profile lines. It is found that the parameter Z2 can better describe the random variation properties of the surface morphology, while the parameter SRv is more suitable for describing the spatial structural variation properties of the surface morphology. The findings of this work are of great significance for investigating the size effect and anisotropy of rock fracture permeability. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Meta-learning has been widely applied to solving few-shot reinforcement learning problems, where we hope to obtain an agent that can learn quickly in a new task. However, these algorithms often ignore some isolated tasks in pursuit of the average performance, which may result in negative adaptation in these isolated tasks, and they usually need sufficient learning in a stationary task distribution. In this paper, our algorithm presents a hierarchical framework of double meta-learning, and the whole framework includes classification, meta-learning, and re-adaptation. Firstly, in the classification process, we classify tasks into several task subsets, considered as some categories of tasks, by learned parameters of each task, which can separate out some isolated tasks thereafter. Secondly, in the meta-learning process, we learn category parameters in all subsets via meta-learning. Simultaneously, based on the gradient of each category parameter in each subset, we use meta-learning again to learn a new meta-parameter related to the whole task set, which can be used as an initial parameter for the new task. Finally, in the re-adaption process, we adapt the parameter of the new task with two steps, by the meta-parameter and the appropriate category parameter successively. Experimentally, we demonstrate our algorithm prevents the agent from negative adaptation without losing the average performance for the whole task set. Additionally, our algorithm presents a more rapid adaptation process within re-adaptation. Moreover, we show the good performance of our algorithm with fewer samples as the agent is exposed to an online meta-learning setting. [ABSTRACT FROM AUTHOR]

For various rock engineering, injection of fluids into rock fractures through boreholes is quite common. It is of great significance to investigate the characteristics of radial flow (RF) in rock fractures for these activities. In this study, macroscopic and mesoscopic characteristics of RF in rough rock fractures were investigated and compared with those of unidirectional flow (UF) by theoretical analysis, tests and simulations. An equation for nonlinear RF was derived for rock fractures according to conservation law of mass and Izbash's law. Four scanned rough rock fracture models were established and used to experimentally investigate the macroscopic flow characteristics in both UF and RF. Numerical simulations were performed to clarify the mesoscopic differences in fluid pressure distributions and the flowlines of RF and UF in rock fractures. The parameters of hydraulic aperture and equivalent width for RF were obtained and correlated to those for UF. A method to calculate fracture roughness coefficient of fractures for RF related to the flow direction was proposed. The characteristic parameters, i.e., critical Reynolds numbers for the flow transition from linear to nonlinear flow, effective hydraulic apertures and non-Darcy coefficients, were obtained for the UF and RF based on the test results. It was indicated that the fracture roughness plays a critical role in the macroscopic and mesoscopic characteristics of both RF and UF. According to the test results, the macroscopic characteristic parameters for RF are related to those for UF, and the nonlinearity of RF was stronger than that of UF at a specified flow rate, which was consistent with the mesoscopic characteristics observed in the simulation that the distribution of water pressure, flow velocity and the streamlines in RF were more non-uniform than that in UF. The study results were useful to describe the RF characteristic in rock fractures with the characteristic parameters for UF, which have been investigated extensively in literature. Highlights: A nonlinear flow equation for radial flow in rock fractures was derived to describe the relationship between the hydraulic head and flow rate. The differences and relations between radial and unidirectional flow were studied from macroscopic and mesoscopic aspects. The parameters of hydraulic aperture and equivalent width for radial flow were obtained and correlated to those for unidirectional flow. The effect of fracture roughness on radial and unidirectional flow was related to the flow direction and was incorporated in the Forchheimer equation. [ABSTRACT FROM AUTHOR]

Reinforcement learning has a demand for massive data in complex problems, which makes it infeasible to be applied to real cases where sampling is difficult. The key to coping with these few-shot problems is knowledge generalization, and related algorithms are often called few-shot reinforcement learning (FS-RL). However, there lacks a formal definition and comprehensive analyses of few-shot scenarios and FS-RL algorithms. Therefore, after giving a uniform definition, we categorize few-shot scenarios into two types. The first type pursues more professional performance, while the other one pursues more general performance. In the process of knowledge transfer, few-shot scenarios usually have an obvious tendency to some type of knowledge. Based on this, we divide FS-RL algorithms into two types: the direct transfer case and the indirect transfer case. Thereafter, existing algorithms are discussed under this classification. Finally, we discuss future directions of FS-RL from the aspect of both theory and application. [ABSTRACT FROM AUTHOR]

Fracture surface morphology, mechanical and hydraulic properties are related to fracture size. One of the core issues in the size effect is the representative elementary surface, which determines the size of the test specimens in the laboratory and facilitates the application of test results to the field. In this study, the size effect on surface morphology and permeability of rock fractures is investigated, and the representative elementary surface size for the surface morphology and the permeability was determined based on the asperity height data of fracture surfaces obtained by 3D laser scanning in the field. The roughness of fracture surfaces varies significantly at small fracture surface sizes. As the fracture surface size continues to increase, the fracture surface roughness tended toward a relatively stable state. The critical size for fracture surface roughness stability in the study, which is called the representative elementary surface, is 300–400 mm. The size effect on the permeability of rock fractures was investigated, and the results show that fracture permeability tended toward a relatively stable state with increasing fracture size, which was the same as the fracture surface roughness. The representative elementary surface size for fracture permeability is less than 100 mm in the study, which is also less than that for fracture surface roughness with the same coefficient of variation. This result indicated that a lower coefficient of variation might provide the best estimate of the representative elementary surface for fracture permeability compared with the fracture surface roughness. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Deep Q Network (DQN) is an efficient model-free optimization method, and has the potential to be used in building cooling water systems. However, due to the high dimension of actions, this method requires a complex neural network. Therefore, both the required number of training samples and the length of convergence period are barriers for real application. Furthermore, penalty function based exploration may lead to unsafe actions, causing the application of this optimization method even more difficult. To solve these problems, an approach to limit the action space within a safe area is proposed in this paper. First of all, the action space for cooling towers and pumps are separated into two sub-regions. Secondly, for each type of equipment, the action space is further divided into safe and unsafe regions. As a result, the convergence speed is significantly improved. Compared with the traditional DQN method in a simulation environment validated by real data, the proposed method is able to save the convergence time by 1 episode (one cooling season). The results in this paper suggest that, the proposed DQN method can achieve a much quicker learning speed without any undesired consequences, and therefore is more suitable to be used in projects without pre-learning stage. [ABSTRACT FROM AUTHOR]

The phenomenon that the rock deformation increases with time at a state of constant stress is termed as creep behavior of rocks. The creep behavior and creep constitutive model of rock are important for understanding and analyzing the time-dependent geological movements and predicting the long-term stability of underground facilities in rock engineering. Two sets of triaxial creep tests were conducted on mudstone and diabase specimens, and one set of uniaxial creep test was conducted on sandstone specimens to investigate the creep behavior of rocks subject to different stress-strain loading histories. The creep behaviors of the three types of rocks were analyzed, and the creep strain versus time and creep strain rate versus time relations were obtained. The applicability of conventional time-dependent creep constitutive model in describing the creep behavior under complex conditions was discussed. Based on the internal state variable theory, an internal state variable creep constitutive model for the rock creep property was proposed, in which the irreversible axial strain was considered as the internal state variable. The fitting of test data into the strain-dependent hardening law showed that it was capable of describing the creep behavior of rocks experienced complex stress-strain loading histories. [ABSTRACT FROM AUTHOR]

The inter-cavern containment property assessment is one of the critical issues of the underground water-sealed oil storage facility and its result determines whether the mixing of different oil products occurs or not. In this study, an inter-cavern containment property assessment method combining discrete fracture network analysis with graph theory was proposed. In the method, the discrete fracture network analysis is adopted to obtain the distribution of the hydraulic head in the rock mass and the graph theory is used to determine the hydraulic connectivity between the two adjacent caverns. The influences of cavern spacing, liquid level differences, water curtain pressures, and geometric parameters on the inter-cavern containment property were investigated based on the assessment method. The results indicated that the inter-cavern containment property could be guaranteed by increasing cavern spacing (d), water curtain pressure (P), or decreasing liquid level differences (Δh), fracture trace length, and linear density. To compare the influence of different factors on the inter-cavern containment property, a parameter p was defined to represent the connectivity of fracture networks between caverns according to the connected relations in graph theory. By comparing changed connectivity parameter p, the influences of cavern spacing, liquid level differences, and water curtain pressures on the inter-cavern containment property were ranked as follows: Δh > d > P. Based on the Huangdao underground oil storage caverns, the inter-cavern containment properties were discussed. The result showed that the cavern spacing should be greater than 40 m, the water curtain pressure should not be greater than 130 kPa and the liquid level difference should be less than 12 m to ensure inter-cavern containment properties, which can offer good guidance for the design and operation of caverns. [ABSTRACT FROM AUTHOR]

Rock mass is typically in contact with ground water for a long time in engineering projects. The hydro-physical–chemical effects between ground water and rock mass are important. A series of uniaxial creep tests were carried out on dry sandstone, saturated sandstone subjected to distilled water, and other five altered sandstones subjected to chemical solutions with different ion concentrations and pH values. The hydro-physical effects were studied by comparing the creep behavior of dry sandstone and saturated sandstone samples, and the hydro-chemical effects were explored by comparing the creep behavior of sandstone samples subjected to five different chemical solutions. Based on the internal variable theory, an internal variable creep model was proposed, in which the irreversible strain was considered as the internal variable. The fitting between the test data and the internal variable creep model indicated that the internal variable creep model was efficient to describe the creep properties of sandstones under complicated hydro-physical–chemical effects. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

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. Highlights: A 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. [ABSTRACT FROM AUTHOR]

In order to improve the production capacity and efficiency of orebodies, the stope span enlargement with the overhand drift-and-fill mining method based on the pre-stressed expandable pillar support technology is developed by numerical simulation and on-site industrial test. The results demonstrate that compared with the natural pillar support, the vertical deformation of stope roof increases approximately 10 mm, and the stress release and plastic failure of stope roof slightly increase under the pre-stressed expandable pillar support. However, relative to no support, the expandable pillar support can effectively limit the vertical deformation (about 13 mm), stress release and plastic failure of stope roof. The farther the monitoring point is from the stope center or support position, the smaller the vertical deformation and stress release of stope roof will be. In general, the expandable pillar support technology can realize the "yielding support" to stope roof. With the stope span enlarging, the load on the bar-shaped natural pillar is immediately transferred to the adjacent expandable pillars, and the closer the distance is between the expandable pillar and the mining area or the stope center, the greater the bearing stress increment on the expandable pillar will be. The maximum bearing load on pre-stressed expandable pillars does not exceed 700 kN. Deriving from the industrial test, the support design of pre-stressed expandable pillars by the traditional pressure arch theory is conservative. The actual load on the support body is 1/6 times or less than the rock mass weight of stope roof within a semicircular area, and the load bearing area is equivalent to a parabolic shape with large opening. After the on-site industrial test is completed, the stope and expandable pillars are visually safe and stable. From the perspective of technical benefits, the stope span enlarges from 3 to 9 m, the ore production capacity increases from 30 t/day to 90 t/day, and the ore recovery rate improves by 30%. In terms of economic benefits, the profit of test stope is 77026 US$. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

One of the most important issues in the construction of underground water-sealed oil storage caverns is the assessment of their containment properties. These properties depend on the hydrogeological condition and also engineering characteristics of the caverns. Conceptual hydrogeological model for assessing the containment properties of underground water-sealed oil storage caverns was developed. Empirical, numerical and experimental methods for assessing the containment properties were summarized. A principle for the selection of assessment methods was proposed for engineering application. It was proposed that the selected assessment method should be appropriate for the investigation stages, the research objectives and the parameters which have been determined. A five-stage flowchart for the assessment of containment properties of underground water-sealed oil storage caverns was developed. The set of assessment methods was applied to a pilot underground water-sealed oil storage facility in China. Empirical methods, fracture network method and field test methods were presented for the assessment of the containment properties of the cavern, while the other methods were introduced in previous studies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Silicon photonics has become very popular because of their compatibility with mature CMOS technologies. However, pure silicon is still very difficult to be utilized to obtain various photonic functional devices for large-scale photonic integration due to intrinsic properties. Silicon-plus photonics, which pluses other materials to break the limitation of silicon, is playing a very important role currently and in the future. In this paper, we give a review and discussion on the progresses of siliconplus photonics, including the structures, devices and applications [ABSTRACT FROM AUTHOR]

The hydro-mechanical behavior of a pilot underground crude oil storage facility in a granite host rock in China was analyzed using the finite element method (FEM). Characterization of hydro-mechanical behavior of the rock mass was performed using laboratory test, field monitoring, back analysis of field measurements and permeability tests. FEM numerical analyses were used to assess the hydro-mechanical behavior of the granite to study several design and construction issues. The containment properties of the storage facility were investigated without and with the water curtain system. Results showed that the stored oil would leak into rock mass if a water curtain system is not provided, whereas the containment property of the facility will be maintained when a water curtain system is in place. On the influence of cavern excavation sequence, it was indicated that the excavation of the caverns from left to right is a better choice than right to left for the containment property of the facility. On the influence of permeable condition, it was found that the extent of plastic zones, horizontal convergence and crown settlement under permeable condition are lower than those under impermeable condition due to the different stress paths in the rock mass experienced during excavation. [ABSTRACT FROM AUTHOR]

Scientific site selection is the first step in constructing underground water-sealed petroleum storage depots, but no uniform standard and code for such activity has been established. Therefore, the main objective of this study is to propose an evaluation method for the site selection of an underground water-sealed petroleum storage depot. The first large underground water-sealed petroleum storage depot being built in China served as the background of this study. The following 12 indexes were used as evaluation factors based on comprehensive evaluation criteria and specifications for key project site selection: geographic structure development feature, topographic feature, lithostratic formation feature, crustal stress, strength of rock mass, joint development feature, hydrogeological conditions, long-term water sealing conditions, environmental/ecological vulnerability, regional stability, technical and economic conditions, and meteorological and hydrological conditions. The weight back analysis and power coefficient methods were also used to evaluate the site selected for the first underground water-sealed petroleum storage depot project. Petroleum site classification models based on the two aforementioned methods were established and used to verify the feasibility of the evaluation criteria and methods, and the evaluation results show the grade of the site selected for the underground water-sealed petroleum storage depot in Huangdao, China is good. The study results may be used as a reference for the site selection of future underground water-sealed petroleum storage depots. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Heteroepitaxy of InP on Si by epitaxial lateral overgrowth (ELOG) using a thin seed layer of InP as starting material is investigated, with special attention given to the effect of the surface morphology of the seed and the mask layers on the quality of the ELOG layers. Chemical mechanical polishing (CMP) has been used to improve the morphological and optical quality of InP grown by hydride vapor-phase epitaxy (HVPE) using ELOG. Two approaches have been investigated: polishing the InP seed layer on Si before depositing the SiO2 mask and polishing the SiO2 mask after its deposition on the unprocessed seed layer. For polishing the InP (seed)/Si, a two-step process with an aluminum oxide- and sodium hypochlorite-containing slurry as well as a slurry based on sodium hypochlorite mixed with citric acid was used. For SiO2 mask polishing, a slurry with colloidal silica as an abrasive was employed. In both cases, the SiO2 mask was patterned with double line openings and ELOG carried out in an HVPE reactor. Morphology and crystal quality of the resulting ELOG layers were studied with atomic force microscopy (AFM) and room-temperature panchromatic cathodoluminescence (PC-CL) in situ in a scanning electron microscope (SEM), respectively. The results show that, whereas both polishing approaches result in an ELOG InP layer with good morphology, its surface roughness is lower when the InP (seed)/Si is subjected to CMP prior to deposition of the SiO2 mask, than when only the SiO2 mask is polished. This approach also leads to a decrease in the number of defects generated during coalescence of the ELOG layers. [ABSTRACT FROM AUTHOR]

Optical frequency combs emerge as a promising technology that enables highly sensitive, near-real-time spectroscopy with a high resolution. The currently available comb generators are mostly based on bulky and high-cost femtosecond lasers for dense comb generation (line spacing in the range of 100 MHz to 1 GHz). However, their integrated and low-cost counterparts, which are integrated semiconductor mode-locked lasers, are limited by their large comb spacing, small number of lines and broad optical linewidth. In this study, we report a demonstration of a III-V-on-Si comb laser that can function as a compact, low-cost frequency comb generator after frequency stabilization. The use of low-loss passive silicon waveguides enables the integration of a long laser cavity, which enables the laser to be locked in the passive mode at a record-low 1 GHz repetition rate. The 12-nm 10-dB output optical spectrum and the notably small optical mode spacing results in a dense optical comb that consists of over 1400 equally spaced optical lines. The sub-kHz 10-dB radio frequency linewidth and the narrow longitudinal mode linewidth (<400 kHz) indicate notably stable mode-locking. Such integrated dense comb lasers are very promising, for example, for high-resolution and real-time spectroscopy applications., Competing Interests: The authors declare no conflict of interest.