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This study proposes a procedure for predicting the required tensile strength of geosynthetics for three-dimensional (3D) geosynthetic-reinforced soil structures (GRSSs) comprised of cohesive backfills subjected to earthquake loadings. This procedure is undertaken using the kinematic approach of limit analysis together with a pseudo-dynamic approach. The influence of cracks is incorporated into the analysis by using a 3D horn-like failure mechanism that includes a vertical crack to characterize the collapse of GRSSs. Two different forms of cracks are considered: cracks forming prior to the collapse of GRSSs (open cracks) and cracks forming simultaneously with the collapse (formation cracks). Based on the work-energy balance equation, the amount of reinforcements needed to maintain the stability of GRSSs is determined. The results of this paper show that the required reinforcements significantly decrease when soil cohesion and 3D effects are considered, whereas accounting for the existence of cracks and seismic forces has an opposite effect. • The required strength of geosynthetics for seismic GRSSs in cohesive backfills is predicted. • The impact of both open cracks and formation cracks is considered. • A pseudo-dynamic approach is used to account for seismic effects. • The inclusion of 3D effects and soil cohesion leads to a significant reduction in the required amount of reinforcements. • Consideration of seismic effects and existence of cracks has an adverse effect. [ABSTRACT FROM AUTHOR]

The natural fracture system exerts a significant influence on the physical and mechanical properties of rock masses. The heat transfer in fractured rock masses is much more complicated than that of intact rock due to the thermal contact resistance induced by natural fractures with varying size, aperture, roughness, and orientation. This work describes a method for determining the representative element volume (REV) of heat transfer and the 3D thermal conductivity tensor of fractured rock masses. The method is based on the element-wise averaging of temperature and heat flux, which can be obtained from a finite element solution to a steady state heat transfer problem with specific boundary conditions. A case study was conducted based on the geological data of a potential area for high level radioactive waste disposal in China. The results indicate that the size of heat transfer REV of the rock masses in the study area is approximately 18 m × 18 m × 18 m. 3D thermal conductivity tensor, the magnitudes and directions of the three principal thermal conductivities, and anisotropy of the fractured rock masses were obtained. Influences of main fracture parameters including density, disc diameter, and thermal contact resistance on the heat transfer characteristics were investigated. The research results in this work can provide a better understanding of the discontinuous heat transfer processes in fractured rock masses and their homogenization methods. [ABSTRACT FROM AUTHOR]

This paper adopts a three-dimensional (3D) rotational failure mechanism to calculate the static and seismic active earth pressure acting on rigid retaining walls within the framework of the kinematic approach of limit analysis. The failure mechanism can be generated through rotating a varying circle defined by two log-spirals, and a plane strain block is inserted into the mechanism for consideration of retaining walls with different widths. Quasi-static representation using the seismic coefficient concept is applied to consider horizontal earthquake effects for the seismic active earth pressure calculation. Two cases with the different points of action of resultant earth pressure are included in this study. In the realm of soil plasticity, the new expressions about 3D active earth pressure are educed from the work-energy balance equation. The critical solution is obtained from an optimization scheme where the maximum of active earth pressure is obtained. Numerical results for different parameters are calculated and presented in the forms of graphs and tables, which may serve as a useful tool for practical application. Compared with existing 2D and 3D solutions, the validity of the proposed method is shown. A parametric study is conducted to investigate the effects of different parameters on the static and seismic active earth pressure under 3D conditions. [ABSTRACT FROM AUTHOR]

The feasibility of developing a geothermal heating system in naturally fractured formations of northern Songliao Basin was investigated. The flow conductivity of reservoir natural fractures was analyzed based on fracture orientations and present stress regimes. A 2D discrete fracture network model was established based on the field geological data and Monte Carlo simulation method. The hydraulic properties of the geothermal reservoir were calculated using a self-developed MATLAB code, which is programmed based on graph-theoretic flow network and hydrologic balance theory. The equivalent permeability of the DFN model, representative elementary volume (REV), and permeability tensor were studied based on the model. Finally, the heat production performance of the geothermal reservoir was numerically investigated. Research results show that the production temperature maintains at a stable level during 30 years of heat production. The system shows high energy efficiency due to the low energy consumption of the injection and production pumps. Research results in this work can provide preliminary understanding of hydraulic property and heat production of geothermal reservoir in the research area. The research methodology can also be applied in the analysis of other geothermal reservoirs. [ABSTRACT FROM AUTHOR]

Convection heat transfer characteristics in a single rock fracture was experimentally investigated in this work. Distilled water was used as working medium for heat transfer in manmade smooth and rough fractures of sandstone and granite samples. The influence of fracture surface roughness on heat transfer intensity was analyzed. During seepage heat transfer process, evolution of samples external surface temperatures was monitored using six resistance temperature detectors to study the local heat transfer characteristics along the flow direction. Subsequently, heat transfer correlations were proposed on the basis of the experimental results. The results indicate that the roughness of rock fracture surface improves the overall heat transfer intensity to a certain extent, whereas lithology has little influence on the heat transfer intensity. For smooth fractures, the local heat transfer intensity decreases with the increase of the distance from the inlet. For rough fractures, evolution of sample external temperatures along the flow direction exhibits strong nonlinear characteristics with multiple peaks. Nu/Pr 1/3 is close to a power function of Re under the experimental conditions in this work. With the increase of experimental temperature, the relationship gradually tends to be linear. [ABSTRACT FROM AUTHOR]

Identifying factors that influence the land surface temperature (LST) of urban forests can help improve simulations and predictions of spatial patterns of urban cool islands. This requires a quantitative analytical method that combines spatial statistical analysis with multi-source observational data. The purpose of this study was to reveal how human activities and ecological factors jointly influence LST in clustering regions (hot or cool spots) of urban forests. Using Xiamen City, China from 1996 to 2006 as a case study, we explored the interactions between human activities and ecological factors, as well as their influences on urban forest LST. Population density was selected as a proxy for human activity. We integrated multi-source data (forest inventory, digital elevation models (DEM), population, and remote sensing imagery) to develop a database on a unified urban scale. The driving mechanism of urban forest LST was revealed through a combination of multi-source spatial data and spatial statistical analysis of clustering regions. The results showed that the main factors contributing to urban forest LST were dominant tree species and elevation. The interactions between human activity and specific ecological factors linearly or nonlinearly increased LST in urban forests. Strong interactions between elevation and dominant species were generally observed and were prevalent in either hot or cold spots areas in different years. In conclusion, quantitative studies based on spatial statistics and GeogDetector models should be conducted in urban areas to reveal interactions between human activities, ecological factors, and LST. [ABSTRACT FROM AUTHOR]

In this paper, the feasibility of generating electricity from EGS (enhanced geothermal systems) by oilfield produced water circulating through reservoir stimulated by staged fracturing technology for horizontal wells is investigated based on the geological data of Xujiaweizi area, located in the Daqing Oilfield, northeast China. HDR (hot dry rock) resource potential assessment is carried out by using volumetric method. Reservoir stimulation is numerically simulated based on the geological data of well YS-1 and field fracturing experience in this region. Geometric dimensions and flow conductivity of the resulting fracture are imported into the hydro-thermal model to calculate the electricity generation potential of the proposed EGS power plant. An EGS design scheme is proposed based on the simulation results. The system is also evaluated from the economic and environmental aspects. The results indicate that HDR resource in Xujiaweizi area is of great potential for development. Through the staged fracturing technology for horizontal wells, electricity generation power of the proposed EGS project can roughly meet the commercial standard. For 20 years of continuous production, power generation from the proposed EGS power plant is economic feasible. Meanwhile, significant reductions in greenhouse gas emissions can be achieved. [ABSTRACT FROM AUTHOR]

In this work, thermal damage effect on the thermal conductivity inhomogeneity of granite was experimentally investigated. To study the influence of different cooling methods, granite samples were heated at different temperature levels (from 100°C to 1000 °C), then cooled in air and water, respectively. Distributed thermal conductivity of granite samples were measured using optical scanning method before and after thermal damage treatment. Besides, some non-destructive tests (open porosity and P-wave velocity) were performed. The results indicate that thermal damage will lead to the decrease of thermal conductivity and the increase of thermal inhomogeneity degree. The decrease degree of thermal conductivity values increases with the treatment temperature. The maximum decrease can be 54.0% (after heated at 1000 °C). When the treatment temperature is higher than the phase transition temperature of quartz (573 °C), the thermal inhomogeneity degree of the damaged samples increased obviously. After heated at each temperature level, the water cooled samples exhibit greater thermal conductivity decrease and greater thermal inhomogeneity factor increase than air cooled samples. This may be attributed to the fact that rapid cooling has extra effects on the damage evolution of rock, which is induced by the high temperature gradient generated when temperature changes occur in a very short time. A thermal damage model was proposed to describe the evolution characteristics of thermal conductivity with treatment temperature. Research results in this work can provide better knowledge to the evolution mechanism of distributed thermal conductivity of engineering rock masses experienced high temperature environment, and the influence of different cooling methods. [ABSTRACT FROM AUTHOR]

This work presents a probabilistic analysis of three-dimensional (3D) seismic active earth pressures acting on rigid retaining walls that are designed to support cohesive-frictional soil masses. The analysis is implemented using sparse polynomial chaos expansions (SPCE) to represent the physical model responses. The deterministic evaluation of 3D seismic active earth pressures is conducted with the application of the kinematic approach of limit analysis combined with a pseudo-static method. All of the input parameters are deemed as random variables. After the SPCE metamodels are determined, the method of Monte Carle simulations is applied to perform the probabilistic analysis of 3D seismic active earth pressures. The effects of uncertainty levels and correlation relationships of input parameters are investigated. Several illustrative examples of the reliability-based design of retaining walls are shown. Results indicate that uncertainties in input parameters possess a notable effect on 3D seismic active earth pressures, suggesting the need to investigate the problem from a stochastic perspective. In most cases, the soil cohesion, internal friction angle, and seismic coefficient are found to be three of the parameters that affect the final response the most significantly. It is also indicated that considering 3D effects and soil cohesion has a favorable effect on increasing the stability of retained slopes. [ABSTRACT FROM AUTHOR]

The active earth pressure evaluation was typically conducted assuming dry backfills and/or two-dimensional collapse mechanisms. In practice, retained slope collapse usually shows a three-dimensional (3D) feature and soils are usually unsaturated. The present work develops a framework for evaluating the 3D active earth pressure under transient unsaturated flow conditions. The framework is implemented by using the kinematic approach of limit analysis, in conjunction with a closed-form solution for the transient unsaturated flow. Based on a 3D horn-like failure mechanism, the active earth pressure coefficient is determined. Results for three hypothetical soils of fine sand, silt, and clay are calculated. It emerges that the inclusion of 3D effects and unsaturated transient flow leads to a smaller active earth pressure coefficient. The 3D effects are mainly influenced by the width-to-height ratio of walls; several certain cases analyzed in this paper show that the difference in the active earth pressure coefficient with and without considering 3D effects can be as much as about 27% when the width-to-height ratio equates to 2, whereas this difference decreases to about 10% and 5% when the ratio reaches to 5 and 10. The contribution of transient flow is mainly affected by the soil types; considering the unsaturated flow effect in clay can approximately reduce the active earth pressure of 67%, whereas this difference corresponds to 34% and 22% in silt and fine sand. The obtained results can help to quantitatively understand changes in the active earth pressure due to 3D effects and the presence of transient infiltration. [ABSTRACT FROM AUTHOR]

• Granites were artificially damaged through cyclic loading and unloading tests. • Temporal and spatial evolution of AE events were obtained. • 2D thermal conductivity images were obtained using optical scanning method. • Influence of mechanical damage on the distributed thermal conductivity was investigated. In this work, influences of mechanical damage and water saturation on the distributed thermal conductivity of granite were experimentally investigated. The samples were artificially damaged using uniaxial cyclic loading and unloading tests, with acoustic emission activity monitored simultaneously. 2D thermal conductivity images were obtained using optical scanning method for both undamaged and damaged samples in dry and saturated conditions. The results indicate that the overall thermal conductivity of the samples decreased after mechanical damage treatment, while the thermal inhomogeneity factor increased. The thermal conductivity difference distribution matched well with the spatial distribution of acoustic emission events. The overall thermal conductivity values increased after water saturation in vacuum condition for both undamaged and damaged samples. Thermal inhomogeneity factor didn't change significantly when undamaged samples were saturated, while thermal inhomogeneity factor of damaged samples decreased to a certain extent when samples were saturated. Research results in this work can provide better knowledge to the evolution mechanism of distributed thermal conductivity of engineering rock masses. [ABSTRACT FROM AUTHOR]

Daqing City in Northern Songliao Basin (China) requires huge amounts of electric power and thermal energy for oil processing and resident support each year. We used actual geological and logging data of deep well YS-2 in Daqing oilfield to investigate electricity generation and heating potential from enhanced geothermal systems in tight rock and naturally fractured formations (3850–4500 m) using different reservoir stimulation methods. We then proposed optimized hydraulic fracturing and heat extraction strategies for each formation. Results indicate that the Yingcheng formation is suitable for the development of HDR (hot dry rock) resources in this region. Heat output in the stimulated naturally fractured formation is obviously higher than that in the tight rock formation. The development of HDR resources in the naturally fractured formation should be prioritized. In middle-low temperature (about 160 °C), tight rock formation still has great potential for heating supply, but the structure has poor capacity for electricity generation because of the low appropriate injection rate resulting from low reservoir temperature. However, when a high temperature reservoir is selected, electricity generation is feasible from tight formation by using gel-proppant hydraulic fracturing combined with horizontal well technology. [ABSTRACT FROM AUTHOR]

• Brittle fracture of deep hard rock was simulated by physical model tests. • The evolution process of brittle fracture in deep tunnels was captured and analysed. • The onset conditions and mechanism of spalling failure in deep tunnels were revealed. • The spalling characteristics were verified by three research methods. Brittle fracture in deep hard rock tunnels in the Jinping laboratory, China, can often endanger the stability of engineering structures. This study describes physical model testing and real-time observations on the evolution process of v-shaped brittle fracture, failure characteristics, onset conditions, and influencing factors in hard rock tunnels. Real-time observations are presented integrated a high-speed camera, acoustic emission system, a digital image correlation, and distributed fiber optic strain sensing technologies. The results show that the process of spalling failure can be divided into two main stages, namely, the instantaneous cracking process in the sidewall surface, and the spalling process of the thin rock chips developing progressively from the excavation boundary to the far field, finally forming stable v-shaped notches. The deviatoric stress of spalling failure in the physical model test satisfies the constant deviatoric stress criterion. The critical strain at spalling failure is consistent with that calculated by the Hoek–Brown strength criterion. Spalling is a form of brittle failure caused by deferential tensile strain. The working face effect is observed in the physical model excavation process. The highest strain caused by overloading occurs near the free surface of the sidewall. The relationship between stress and geometric similarity constants in deep rock engineering is derived. The failure characteristics revealed in the physical model tests are verified by numerical simulations based on cellular automaton theory, which agree well with the experimental results. The research findings can provide theoretical support for the prevention and control of spalling disasters in deep engineering practice. [ABSTRACT FROM AUTHOR]

This paper develops an efficient algorithm that combines polynomial-chaos kriging (PCK) and adaptive radial-based importance sampling (ARBIS) for reliability analysis. The key idea of ARBIS is to adaptively determine a sphere with the center at the origin and radius equal to the smallest distance of the failure domain to the origin, also known as the optimal β -sphere, and only those samples outside the optimal β -sphere have a possibility of failure and thus need to evaluate the limit-state function to judge their states (safe or failure). In the proposed algorithm, both the PCK model and β -sphere are updated adaptively. In each iteration of determining the optimal β -sphere, the PCK model is updated sequentially based on an active learning function, which is used to select the most informative sample from the samples between the last and current β -spheres. Once the stopping criterion is met, the learning process of PCK in this iteration terminates, and the obtained PCK model is then used to determine the next β -sphere. The updating iteration of the β -sphere proceeds until the optimal sphere is found. Five representative examples are revisited, in which the results demonstrate the high accuracy and efficiency of the proposed PCK-ARBIS algorithm. [ABSTRACT FROM AUTHOR]

Prediction of unobserved microRNA (miRNA)-disease associations is one of the most important research fields due to miRNA's roles of diagnostic biomarkers and therapeutic targets for large number of human complex diseases. Thus, the development of effective computational methods for identification of novel miRNA-disease associations would provide a unique opportunity to design better therapeutic interventions. In this study, we presented a novel computational model named Matrix Decomposition and Label Propagation for MiRNA-Disease Association prediction (MDLPMDA) by integrating known miRNA-disease associations, disease semantic similarity, miRNA functional similarity, and Gaussian interaction profile kernel similarity for miRNAs and diseases. Based on the new adjacency matrix of miRNA-disease associations obtained from matrix decomposition through sparse learning method, the model is presented by implementing label propagation process on the constructed integrated miRNA similarity network and integrated disease similarity network, respectively, and then using an average ensemble strategy to combine the two different prediction models. At last, AUCs of 0.9222 and 0.8490 in global and local leave-one-out cross-validation (LOOCV) proved the model's reliable performance. In addition, AUC of 0.9211+/-0.0004 in 5-fold cross-validation confirmed its accuracy and stability. We further implemented case studies to predict potential miRNAs associated with human complex diseases based on different versions of HMDD database. We also carried out case studies on diseases without any known related miRNAs to examine the prediction performance of MDLPMDA. At last, the analysis of the assessment results of cross validations and case studies indicated that MDLPMDA could be an effective method to infer novel miRNA-disease associations. [ABSTRACT FROM AUTHOR]