bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum speed-up in global optimization of binary neural nets
Authors: Liao Yidong , Ebler Daniel , Liu Feiyang , Dahlsten Oscar
Published: November 2020

The performance of a neural network (NN) for a given task is largely determined by the initial calibration of the network parameters. Yet, it has been shown that the calibration, also referred to as training, is generally NP-complete. This includes networks with binary weights, an important class of networks due to their practical hardware implementations. We therefore suggest an alternative approach to training binary NNs. It utilizes a quantum superposition of weight configurations. We show that the quantum training guarantees with high probability convergence towards the globally optimal set of network parameters. This resolves two prominent issues of classical training: (1) the vanishing gradient problem and (2) common convergence to sub-optimal network parameters. We prove that a solution is found after approximately

4

n

2

log

n

δ

N

˜

calls to a comparing oracle, where δ represents a precision, n is the number of training inputs and

N

˜

is the number of weight configurations. We give the explicit algorithm and implement it in numerical simulations.
Lump and new interaction solutions to the (3+1)-dimensional nonlinear evolution equation
Authors: Issasfa Asma , Lin Ji
Published: November 2020

In this paper, a new (3+1)-dimensional nonlinear evolution equation is introduced, through the generalized bilinear operators based on prime numberp = 3. By Maple symbolic calculation, one-, two-lump, and breather-type periodic soliton solutions are obtained, where the condition of positiveness and analyticity of the lump solution are considered. The interaction solutions between the lump and multi-kink soliton, and the interaction between the lump and breather-type periodic soliton are derived, by combining multi-exponential function or trigonometric sine and cosine functions with a quadratic one. In addition, new interaction solutions between a lump, periodic-solitary waves, and one-, two- or even three-kink solitons are constructed by using the ansatz technique. Finally, the characteristics of these various solutions are exhibited and illustrated graphically.
Towards optimizing electrode configurations for silent speech recognition based on high-density surface electromyography
Authors: Zhu Mingxing , Zhang Haoshi , Wang Xiaochen , Wang Xin , Yang Zijian , Wang Cheng , Samuel Oluwarotimi Williams , Chen Shixiong , Li Guanglin
Published: November 2020

Objective. Silent speech recognition (SSR) based on surface electromyography (sEMG) is an attractive non-acoustic modality of human-machine interfaces that convert the neuromuscular electrophysiological signals into computer-readable textual messages. The speaking process involves complex neuromuscular activities spanning a large area over the facial and neck muscles, thus the locations of the sEMG electrodes considerably affected the performance of the SSR system. However, most of the previous studies used only a quite limited number of electrodes that were placed empirically without prior quantitative analysis, resulting in uncertainty and unreliability of the SSR outcomes. Approach. In this study, the technique of high-density sEMG was proposed to provide a full representation of the articulatory muscle activities so that the optimal electrode configuration for SSR could be systemically explored. A total of 120 closely spaced electrodes were placed on the facial and neck muscles to collect the high-density sEMG signals for classifying ten digits (0–9) silently spoken in both English and Chinese. The sequential forward selection algorithm was adopted to explore the optimal electrodes configurations. Main Results. The results showed that the classification accuracy increased rapidly and became saturated quickly when the number of selected electrodes increased from 1 to 120. Using only ten optimal electrodes could achieve a classification accuracy of 86% for English and 94% for Chinese, whereas as many as 40 non-optimized electrodes were required to obtain comparable accuracies. Also, the optimally selected electrodes seemed to be mostly distributed on the neck instead of the facial region, and more electrodes were required for English recognition to achieve the same accuracy. Significance. The findings of this study can provide useful guidelines about electrode placement for developing a clinically feasible SSR system and implementing a promising approach of human-machine interface, especially for patients with speaking difficulties.
Pairwise coexistence of effects versus coexistence
Authors: Stulpe Werner
Published: November 2020

The concept of coexistence of quantum mechanical effects is reviewed. We distinguish between coexistence and pairwise coexistence and give an example showing the non-equivalence the two concepts. A theorem on some closures of sets of pairwise coexistent effects is proved. Some proofs of the well-known fact that any set of pairwise coexistent (mutually compatible) sharp effects is coexistent are considered. In particular, a proof is presented that is based on the statement that every countably complete Boolean lattice of sharp effects is closed in some topology.
Notes on Naimark’s dilation theorem
Authors: Beneduci Roberto
Published: November 2020

After a short review of the main properties of unsharp observables we provide examples of commutative unsharp observables obtained as the projection of sharp observables. In particular, we consider a family of PVMs defined on the tensor product Hilbert space

H
⊗
K

which include the one introduced by Ozawa in his modification of the von Neumann position measurement model and show that their projections onto

H

are commutative POVMs. Then, we make some observations on the concept of Naimark dilation and its connections with the integral representation of commutative POVMs. Finally, we introduce a partial order relation in the set of Naimark dilations, show that there is a minimal element and that it is unique. Minimality is a consequence of the partial ordered structure and coincides with the usual definition of minimal Naimark dilation. In passing, we use Naimark’s theorem in order to prove some well known properties of positive operator valued measures.
What is unsharp quantum reality? A conceptual analysis
Authors: Falkenburg Brigitte
Published: November 2020

In their paper Unsharp Quantum Reality, Paul Busch and Gregg Jaeger explain the conception of unsharp reality in terms of Positive Operator Valued (POV) measures, potentiality, and single-case probabilities. The present paper discusses their conception from a philosophical point of view, focusing on the ontological interpretation of POV measures employed in it and on its relation to Peter Mittelstaedt’s work on the semantics and ontology of quantum mechanics. Busch and Jaeger extend Mittelstaedt’s approach by adding a realistic interpretation of unsharp quantum properties to it. Their account of unsharp quantum reality generalizes Heisenberg’s potentiality interpretation of quantum states. In order to explain the transition from potential to actual quantum properties, they suggest a Ghirardi-Rimini-Weber (GRW) collapse theory. Their approach comes close to recent work on quantum propensities. However, the question remains what unsharp quantum reality means when no measurement takes place, as for example claimed in the quark model of the subatomic constitution of matter.
Two entanglement measures
Authors: Gudder Stan
Published: November 2020

In a previous work we introduced an entanglement number e(ψ) for a vector state ψ. This number relied on the Schmidt decomposition of ψ which may be difficult to compute. We now present a method for finding e(ψ) that is simple and efficient. We show that e(ψ) is continuous in the vector norm. We next extend e(ψ) to an entanglement number e(ρ) for a general mixed state ρ and show that ρ is separable (not entangled) if and only if e(ρ) = 0. We next define a related quantity es
(ρ) ≥ e(ρ) which we call the spectral entanglement number. We argue that es
(ρ) is easier to compute than e(ρ) and that the physical motivation for es
(ρ) is superior to that of e(ρ). It is shown that es
(ρ) is continuous in the operator norm. Although e(ρ) is a convex function, we show that es
(ρ) need not be convex. An open problem is to characterize the states ρ such that e(ρ) = es
(ρ). Many illustrative examples are presented.
Titanium reinforced calcium phosphate improves bone formation and osteointegration in ovine calvaria defects: a comparative 52 weeks study
Authors: Gallinetti Sara , Linder Lars Kihlström Burenstam , Åberg Jonas , Illies Christopher , Engqvist Håkan , Birgersson Ulrik
Published: November 2020

In a 52 week ovine calvaria implantation model, the restoration of cranial defects with a bare titanium mesh (Ti-mesh) and a titanium mesh embedded in a calcium phosphate (CaP-Ti) were evaluated in seven animals. During the study, no major clinical abnormalities were observed, and all sheep presented a normal neurologic assessment. Blood and cerebrospinal fluid analysis, made at termination, did not show any abnormalities. No indentation of the soft tissue was observed for either test article; however, the Ti-mesh burr-hole covers were associated with filling of the calvarial defect by fibrous tissue mainly. Some bone formation was observed at the bottom of the created defect, but no significant bone was formed in the proximity of the implant. The defect sites implanted with CaP-Ti were characterized by a moderate degradation of the calcium phosphate (CaP) that was replaced by mature bone tissue. Calcium-phosphate-filled macrophages were observed in all animals, indicating that they might play a vital role in osteogenesis. The newly formed bone was present, especially at the bony edges of the defect and on the dura side. Integration of the Ti-mesh in a CaP improved bone formation and osteointegration in comparison to a bare Ti-mesh.
Country-scale trends in air pollution and fossil fuel CO2 emissions during 2001–2018: confronting the roles of national policies and economic growth
Authors: Lei Ruixue , Feng Sha , Lauvaux Thomas
Published: November 2020

Fossil fuel (FF) burning, the main energy source of the modern world’s economy, remains the major source of anthropogenic carbon dioxide (CO2) and pollutants in the atmosphere. Based on 18 years (2001–2018) of aerosol optical depth (AOD) data from Moderate Resolution Imaging Spectroradiometer satellite, FFCO2 emissions from the Open-Data Inventory for Anthropogenic Carbon dioxide, and gross domestic product (GDP) data from the World Bank, we found that air quality, FF consumption, and economy are strongly bonded at the continental scale but decoupled at the national level under favorable policies. The comparison of AOD vs PM2.5 and NO2 over urbanized areas shows that the pollutants leading to the AOD load can vary significantly by country. A strong connection between GDP and FFCO2 emissions indicates that economic growth deeply replies on FF consumption in most countries. Meanwhile, air pollution is more associated with the growing trend than the level of development of a country. With more mature technologies and renewable energy, economies can keep growing without compromising their environment and population health.
Spatial patterns of arctic tundra vegetation properties on different soils along the Eurasia Arctic Transect, and insights for a changing Arctic
Authors: Epstein Howard E , Walker Donald A , Frost Gerald V , Raynolds Martha K , Bhatt Uma , Daanen Ronald , Forbes Bruce , Geml Jozsef , Kaärlejarvi Elina , Khitun Olga , Khomutov Artem , Kuss Patrick , Leibman Marina , Matyshak Georgy , Moskalenko Nataliya , Orekhov Pavel , Romanovsky Vladimir E , Timling Ina
Published: November 2020

Vegetation properties of arctic tundra vary dramatically across its full latitudinal extent, yet few studies have quantified tundra ecosystem properties across latitudinal gradients with field-based observations that can be related to remotely sensed proxies. Here we present data from field sampling of six locations along the Eurasia Arctic Transect in northwestern Siberia. We collected data on the aboveground vegetation biomass, the normalized difference vegetation index (NDVI), and the leaf area index (LAI) for both sandy and loamy soil types, and analyzed their spatial patterns. Aboveground biomass, NDVI, and LAI all increased with increasing summer warmth index (SWI—sum of monthly mean temperatures > 0 °C), although functions differed, as did sandy vs. loamy sites. Shrub biomass increased non-linearly with SWI, although shrub type biomass diverged with soil texture in the southernmost locations, with greater evergreen shrub biomass on sandy sites, and greater deciduous shrub biomass on loamy sites. Moss biomass peaked in the center of the gradient, whereas lichen biomass generally increased with SWI. Total aboveground biomass varied by two orders of magnitude, and shrubs increased from 0 g m−2 at the northernmost sites to >500 g m−2 at the forest-tundra ecotone. Current observations and estimates of increases in total aboveground and shrub biomass with climate warming in the Arctic fall short of what would represent a ‘subzonal shift’ based on our spatial data. Non-vascular (moss and lichen) biomass is a dominant component (>90% of the photosynthetic biomass) of the vegetation across the full extent of arctic tundra, and should continue to be recognized as crucial for Earth system modeling. This study is one of only a few that present data on tundra vegetation across the temperature extent of the biome, providing (a) key links to satellite-based vegetation indices, (b) baseline field-data for ecosystem change studies, and (c) context for the ongoing changes in arctic tundra vegetation.
Multi-objective cost optimization for geological risk oriented rail transit route selection
Authors: Yan Gao , Zhiyi Wu , Junyuan Yu , Quan Yuan , Wenlong Li
Published: November 2020

China’s rail transit has entered a period of rapid development, but related safety and risk management fail to match with high-speed construction. The complex and uncertain underground space leads to frequent risk accidents of urban rail transit. As the primary task of rail transit development, the reasonable route selection can not only avoid a lot of geological risks, but also greatly save the duration and cost. In order to guide the rail transit route selection work scientifically and reasonably, the cost problems related to geological risk factors by constructing the objective function of risk assessment, section construction cost and duration are analyzed in this study. Combining with heuristic algorithms such as ant algorithm and particle swarm optimization algorithm, an evaluation method of cost optimization of rail transit route selection for the geological risk are put forward. Taking the geological data of a certain section of a proposed rail transit route in Guangzhou as an example, based on this proposed method, the optimal route selection scheme with relatively low risk, short construction duration and low cost is found, which provides theoretical basis and guidance for the route selection and construction of rail transit, and also verifies the rationality of the application of the cost optimization method for the geological risk to multi-objective engineering management.
Rock stress sensitivity in low-permeability gas reservoirs and its impact on productivity
Authors: Xiong Jian , Wang Haiying , Huang Linlin , Zhang Hui , Liu Xiangjun , Yin Guoqing
Published: November 2020

The relationship between permeability and effective stress could be found using the stress sensitivity test, and the stress sensitivity in the low-permeability gas reservoir was investigated. The productivity model could be deduced and the influences of stress sensitivity on the development of the low-permeability gas reservoirs were also discussed. The results show that the permeability of the core decreases as the effective stress increases and the permeability first quickly declines, then slows. The fitting relationship between permeability and effective stress conforms to the index relationship. The fitting relationship between the stress sensitivity coefficient and permeability accords with the power function relation and the stress sensitivity effect weakens as the original permeability increases. Based on the Darcy flow theory and the original permeability in the reservoir, the productivity model of the well, considering the effect of stress sensitivity, could be presented. The distribution curves of the pressure and permeability in the reservoir are funnel shaped. The pressure and permeability decline quickly as the original permeability or the gas well productivity increases. The stress sensitivity of the permeability in the conglomerate gas reservoir is obvious, indicating that the fluid pressure must be appropriately controlled and the difference in the production pressure should be maintained at a reasonable value during the development process.
A simple approach of calibrating input parallel bond model parameters for DEM simulations of rock behaviour
Authors: Dong Shun , Jia Tong , Fu Fengjiao , Jia Shuaidong , Tang Weiyu , Huang Xin
Published: November 2020

The mineral bonds between grains of rock are usually simulated by parallel bonds in discrete element method (DEM) simulations. The existence of multiple input parameters makes the calibration process tedious and time-consuming. In this paper, a series of parametric studies are firstly conducted by varying the value of each input parameter independently, based on which their distinct influences on the strength and deformation characteristics of simulated specimens are obtained. One-way and multiple-way analysis of variance are conducted to evaluate the sensitivity of macro strength and deformation parameters to the change of input parallel bond model parameters. The order of influence level of these input parameters on the macro behaviour of simulated specimens is obtained and the input parameters with the dominating influences on the macro mechanical properties are identified. Then, empirical correlations between the macro mechanical properties and their dominating input parameters are established separately. These empirical correlations are taken as the basic components in the regression analysis of multiple variables for each macro mechanical property. The regression equations serve as the first estimation of input parameters for the calibration. The adjustment of input parameters is conducted with reference to the partial differentials of the regression equations considering the difference between the simulation results and the experimental data as the increments/decrements. The effectiveness of the proposed calibration approach is validated by simulating a series of triaxial compression tests on mudstone.
Nonlinear seismic responses of the soft rock site for nuclear power plants
Authors: Li Furong , Chen Guoxing
Published: November 2020

With the development of the nuclear power industry, high-quality bedrock nuclear power stations have become scarce. Thus, it is inevitable that nuclear power stations will be built on soft rock sites. This involves the issue of the seismic safety of soft rocks as sites for nuclear power plants. Based on the soft rock site involved in the site selection for nuclear power plants, this paper uses ground motions with different spectral characteristics. Using the DEEPSOIL software for soil layer analysis and the Abaqus finite element software, one-dimensional equivalent linear and nonlinear methods are employed to compare and analyze the characteristics of the nonlinear seismic response of the soft rock site for nuclear power plants. The soft rock site has a significant amplification effect on the input ground motion. The equivalent linear and nonlinear methods have different levels of influence on the acceleration response of the soft rock site. Under the action of far-field earthquakes, surface acceleration and its response spectrum, which were calculated using the abovementioned methods, are relatively close. As the input ground motion intensity increases, the nonlinearity of the soft rock increases, and the amplification effect of the soft rock site weakens. However, the peak ground acceleration of the surface obtained using the two methods gradually differs. Moreover, the nonlinearity is greater than the equivalent linear. Therefore, the nonlinear characteristics of soft rocks should be considered in the site selection and seismic analysis of nuclear power plants.
Characterization and mesosimulation of the triaxial compression failure of rock-like materials
Authors: Wang G , Li X P , Luo Y , Liu T T , Liu X Q , Qu D X
Published: November 2020

The laboratory tests and the numerical simulation of the particle flow code of triaxial compression are conducted to analyze the fractal dimensions of fracture surface, strength properties, energy dissipation, damage patterns, and crack evolution. The following results are obtained. (1) Under low confining pressure, the fracture surface of a brittle specimen is rough, and the angle relative to the maximum principal stress is small. The specimen eventually exhibits a local tensile–shear failure mode. As the confining pressure increases, the strength of the specimen increases, and the yield platform for the stress–strain curve is more obvious. The main fracture surface flattens, and the fracture angle increases as the confining pressure increases. The specimen macroscopically exhibits a shear failure mode. (2) As the confining pressure increases, the trend of transgranular shear failure becomes obvious, and the microfracture surface has a smaller fractal dimension. (3) In the triaxial compression test, energy is stored, dissipated, and released. When the storage limit is reached, the internal elastic strain energy becomes released sharply, and the damage variable increases rapidly. (4) As the confining pressure increases, the number of tensile and shear cracks accumulates in an “S” shape, and the proportion of shear cracks increases gradually.
Pile—soil interactions in frozen soil foundations based on frost heave rate and soil stiffness variations
Authors: Zhou Yalong , Wang Xu , Liu Deren , He Fei , Niu Fujun
Published: November 2020

The frost heave rate and stiffness of soil in frozen soil foundations varies remarkably with the freezing depth under the influence of the freezing-end temperature, temperature gradient, and overburden stress. The stress level of frozen soil increases with increasing frost penetration, leading to greater stiffness and a smaller frost heave rate. In this work, the freezing-end temperature and temperature gradient are introduced to the traditional Takashi model via the frost heave layering method and the overburden stress is modified to establish an empirical prediction model of frost heave rate and stiffness. Analytical solutions of load transfer differential equation of single pile considering stiffness increase and frost heave rate decrease along the frost penetration are derived on the basis of the mechanism of pile–soil interactions. The calculation results are in good agreement with measured values, thus confirming the correctness of the analytical solution. Variations in frost heave rate and soil stiffness with increasing depth are then combined to form four models, and changes in axial force and tangential frost heave force as a function of frost penetration are calculated and analyzed on the basis of these models. Results show that calculation of the frost heave rate and stiffness of soil along the frost penetration depth according to normal values will significantly underestimate the axial force of on the pile.
Deformation Failure Mechanism and Motion Laws of Near-horizontal Thick-layer with Thin-layer Columnar Dangerous Rock Mass in the Chishui Red Bed Area
Authors: Xie J , Yang G L , Qin Y G , Xu X T
Published: November 2020

The collapse of dangerous rock masses, either due to natural causes (such as weathering by rain) or anthropogenic factors (such as engineering construction in the rock area), poses a threat to both life and property. Therefore, investigating deformation failure mechanisms and determining the movement characteristics of the rock masses after collapse can provide practical guidance for conducting linear projects while taking adequate measures to prevent the collapse. In this study, a dangerous rock mass on the right side of the Yuanhou Toll Station of the Rongzun Expressway was used to study the deformation and failure mechanism of near-horizontal and thick layer with thin-layer columnar dangerous rock masses in the Chishui red bed area. A high-definition 3D-surface model was generated by using unmanned aerial vehicle (UAV) tilt photography technology to obtain an aerial image of dangerous rock masses with spatial coordinates in the research area. The three-point method was used to interpret the structural surface of the dangerous rock mass based on the 3D model. A model for the deformation and failure of dangerous rock masses was developed via an engineering geological analysis. We simulated and analyzed the cause of deformation and failure of dangerous rock masses using FLAC3D software. In addition, the motions of rock fall were studied by performing simulations using Rockfall software. From the interpretation of the 3D model of the UAV, the dangerous rock mass developed two sets of dominant structural planes that were nearly vertical and perpendicular to the stratum level, cutting the rock mass into cuboids. Based on the analysis of a stereographic projection, the dangerous rock mass was in an unstable state. The results showed that the dangerous rock mass had a high stress concentration in the middle and lower soft rock, which is likely due to dumping collapse under self-weight and differential weathering. Moreover, rock fall has a 60% probability of causing damage to the road below the rock mass if it collapses, threatening the safety of passing vehicles and people’s lives and property.
Drillability characteristics of formation and evaluation of bit selection for the Zhongtaishan structural strata in Sichuan Basin, China
Authors: Jie Chen , Feiyun Huang , Bin Xiang , Xiangchao Shi , Bo Liu
Published: November 2020

Selecting a suitable bit for a specific formation is very important in increasing the rate of penetration (ROP) and reducing the drilling cost during the drilling process. Drillability and rock mechanical parameters are frequently used to evaluate the resistance of strata to drilling engineering. Based on the drilling well history data for the Zhongtaishan structural strata in the Sichuan Basin, it can be observed that the slow ROP and high drilling cost have become critical factors in restricting the efficient development of tight gas in this tectonic region. Furthermore, a new model for the rock drillability index was established based on the experimental rock drillability data under simulated bottom-hole conditions. Part of the drillability test data was used to verify the accuracy of the model, which can accurately describe the effect of wellbore pressure on drillability. Well history and logging data were also used to calculate the rock mechanics parameters and rock drillability index. In the Xujiahe Formation, characterized by high uniaxial compressive strength (UCS) and drillability index, the Poisson’s ratio of the formation rock was approximately 0.21–0.24, the elastic modulus was 80 GPa–110 GPa, the average value of the internal friction angle increased from 40° to 45°, and cohesive increased from 18 MPa to 36 MPa. The formation drillability index without wellbore pressure ranged from 5–7, whereas that under wellbore pressure conditions ranged from 8–9 with a high Cerchar abrasion index (CAI). Mechanical specific energy (MSE) models were used to optimize the bit quantitatively, and the results demonstrated that the SH633, HJ537GK, I437, and KPMD1642DRT combined drill bits were more suitable for the Da’anzhai, Zhenzhuchong member of Ziliujing Formation, and the 6th, 3rd, and 2nd variables of the Xujiahe Formation respectively.
Relationship between wellbore instability and rock mechanics when drilling in the fault area of Shunbei Formation
Authors: Liu Jingtao , Yu Yang , Ren Pengju , Zhou Zhou
Published: November 2020

The Tarim Basin is one of the most important oil formations in China, and it is prospected to exceed 110 billion barrels. Recently, some fault areas were drilled to achieve high potential oil reservoirs in the Tarim Basin. However, during drilling, wellbore stability is difficult to ensure in the fault areas. Wellbore collapse and lost circulation may unexpectedly occur. Therefore, analysis of wellbore stability according to the formation characteristics of the fault zone is necessary. On the basis of the formation mechanism of the fault zone, the stratigraphic characteristics corresponding to the internal structure of different fault zones were analyzed in this work. As a result of the formation characteristics, the corresponding logging identification methods of the induced fracture zone and sliding crushing zone formed, and the differences in wellbore instability in different internal structures were compared. The formation characteristics and mechanical properties of the sliding crushing zone were characterized by XRD, SEM, linear expansion rate test, rolling recovery test, and other physical experiments. Logging calculations were also conducted to assess the phenomenon of collapse that often occurs in the sliding crushing zone, and the collapse mechanism was analyzed accordingly. In view of the leakage phenomenon in the induced fracture zone, the complex mechanism of the leakage was analyzed, and the traditional minimum principal stress model was modified to obtain the leakage pressure calculation model suitable for the fault zone. Finally, taking the F1 fault zone in Shunbei area as an example, the internal structure of the fault zone was divided by using the summarized logging identification method. The wellbore instability of the different internal structures was compared, and the newly established loss pressure model was applied in the SHBX1 well, thereby proving that the model has a good application effect. The study in this paper provided some mechanisms of wellbore instability based on formation property and rock mechanics in the fault area. In addition, a loss pressure model based on the special formation characteristics was proposed to guide drilling in the fault zone.
Effect of heat exposure on anisotropic mechanical properties of host rock in the Tamusu pre-selected area for high-level radioactive waste disposal in China
Authors: Zhang Haiyang , Liu Jian , Liu Feiyang , Ma Hongsu , Wang Chunping , Zhao Xingguang , Chen Liang
Published: November 2020

As a typical sedimentary rock, clay rock with bedding structure shows clear anisotropy in its mineral composition and mechanical properties. When the clay rock is selected as the host rock for a high-level radioactive waste (HLW) geological repository, its temperature rises because of the continuous release of heat by the HLW. To examine the influence of temperature on the anisotropic mechanical properties of clay rock in the Tamusu pre-selected area for HLW repository in China, a series of direct shear tests in different directions were conducted on the Tamusu clay rock exposed to a range of temperatures. The microstructural characteristics were observed by scanning electron microscopy, and the morphology of the shear failure surfaces was analyzed with the help of 3D laser scanning. The results show that the shear strength parameters of specimens sheared perpendicular to the bedding plane were significantly higher than those of specimens sheared parallel to the bedding plane, and the former specimens exhibited a more rugged failure surface. Strength of both types of specimens increased with the increase in temperature from 30°C to 200°C because of water evaporation and mineral expansion. The mechanical anisotropy was also enhanced by heat exposure. These findings provide key information for the site characterization of the HLW repository, and a reference for the design and construction of underground engineering structures in layered clay rock.
Experimental investigation of the mechanical properties of basalt in the Baihetan hydropower station region in China
Authors: Liu N , Liu Z J , Chen P Z
Published: November 2020

The Baihetan hydropower station is mainly situated in the basalt formations of Mount Emei (Sichuan Province, China). During the excavation process, basalt has shown some special mechanical characteristics. In this study, the deformation and failure characteristics of basalt are investigated via laboratory tests (uniaxial and triaxial compression tests on blocky basalt samples) and field deformation tests (rigid bearing plates applied in situ to columnar jointed basalt). The information gathered is then analyzed to reveal the mechanisms responsible for the failure of basalt. Results show that (1) the stress–strain curves of cryptocrystalline basalt are essentially linear in the pre-peak region and the stress drops rapidly in the post-peak region. The failure mode of the rock changes from being fragmentation-dominated under low–medium confining pressure to fragmentation–shear composite failure under high confining pressure. (2) In the post-peak region, amygdaloidal basalt exhibits brittle mechanical behavior under low confining pressure and ductile behavior under high confining pressure. In terms of failure mode, the basalt transforms from splitting failure under low confining pressure to shear failure under medium–high confining pressure. (3) The deformation moduli measured during field tests with rigid bearing plates are spread over a large range and are influenced by various factors (including column nature, lumpiness, loading direction, unloading-induced relaxation, and stress state). (4) The deformation moduli of the rock masses of Classes II, III1, and III2 successively decrease and exhibit significant anisotropy.
Stability analysis of an expansive soil-embankment slope with a soft interlayer
Authors: Shi Zhenming , Zhao Siyi , Qiao Yafei , He Manchao
Published: November 2020

The soft interlayer in the foundation is one of the most important factors that induce landslide in the expansive soil-embankment slope. The existence of large soft layers significantly reduces the overall stability of the slope, and they have the tendency to further develop into a sliding surface. To investigate the influence of the soft interlayer on expansive soil slopes, taking the high-fill embankment slope with a soft interlayer in the Baoshan area of Yunnan Province as an example, the causes and strength effects of the soft interlayer are analyzed via landslide investigation, laboratory test, and numerical simulation, and the stability and instability mode of the slope are studied. Results indicate the following: ① The soft interlayer is located at the bottom of the weathering layer within the depth of the atmosphere. Its strength is less than that of the expansive soil on both sides. ② The overall stability of the slope and the shape of the sliding surface are controlled by weak interlayers, and its strength greatly impacts the damage scope of the slope. When the strength is high, it appears as a collapse of the fill area, and when the strength is extremely low, it appears as the overall sliding of the slope. Using the residual strength as the calculation parameter of the weak layer reflects well the actual stability and failure mode of the slope. ③ Results of soil layer parameter sensitivity analysis indicate that the internal friction angle of the soft interlayers has the most significant effect on slope stability. Using the lightweight embankment fill can effectively improve the stability factor of embankments.
Strain localization in hydraulic fracturing of granite specimens based on DIC method
Authors: Xing J Q , Zhao C , Zhou Y M
Published: November 2020

Hydraulic fracturing is a crucial and widely-used technology in shale gas exploitation and enhanced geothermal systems, while the fundamental mechanisms of hydraulic fracturing are not comprehensively understood. This paper aims to promote the understanding of strain localization in hydraulic fracturing of granite specimens based on digital image correlation (DIC) method. Through a specially designed pressure enclosure, the hydraulic fracturing processes were captured by a high-speed camera. The strain localization phenomenon, evolution, and coalescence of SLZs in hydraulic fracturing were analyzed. Results show that obvious strain localization occurs before the specimen failure, which gradually develops into a continuous strain localization zone. With the evolution of SLZs, the specimen will be unable to bear the liquid pressure, and macro cracks occur at SLZs. The statistical data in the query region shows that the strain localization in hydraulic fracturing occurs earlier than previously thought, and the evolution of SLZs can be divided into steady, soaring, and fracture stages according to the changing trend. The coalescence of the patchy distribution SLZs occurs frequently throughout the evolution process of SLZs, and the coalescence of SLZs may be the cause of the increasing speed of evolution.
Analysis and test on stress-strain of cement sheath in shale gas wells with hydraulic fracturing
Authors: Liu K , Ding S D , Zhou S M , Tao Q , Liu R G , Gao Y
Published: November 2020

The sealing failure of cement sheath which caused annulus pressure in shale gas wells have significantly affected the safe and efficient development of shale gas. In view of the integrity of cement sheath which is affected by the high fluid pressure in casing during the hydraulic fracturing treatment, an experimental device for testing the integrity of cement sheath is established. In addition, the analytical model for calculating the stress and strain of the well system is established based on parameters of the experimental device. The analytical model for calculating the circumferential strain at outer wall of the steel cylinder is achieved. The error of stress-strain between analytical calculated results and the experimental results is very small. In sensitivity analysis, the parameters which affect the stress on cement sheath interface is discussed. This study has a certain reference value for the design of experiment device and the analysis of sealing ability of cement sheath in shale gas wells.
Influence of water content and maceral composition on the properties of outburst-prone coal: laboratory experiment
Authors: Gong Shuang , Wang Zhen , Zhang Guoqiang , Zhou Lei , Wang Wen , Zhao Yixin
Published: November 2020

We conducted laboratory experiments to investigate the influence of water content and maceral composition on the properties of outburst-prone coal using X-ray diffraction and optical electron microscope. For comparison, two groups of experiments were completed on contrasting coals, namely, outburst-prone and outburst-resistant coals. The complete stress–strain behavior, uniaxial compressive strength, Young’s modulus, and acoustic compressional velocity were measured and correlated with water content. Test results showed that the microhardness and microembrittlement of the outburst-prone coal were higher than those of the outburst resistant coal. When the water content increased to 4%, the uniaxial compressive strengths of the outburst prone and outburst resistant coals decreased by 82.4% and 85.1%, respectively; and their elastic moduli decreased by 90.3% and 86.6%, respectively. The difference between the maximum reflectance and the minimum reflectance of vitrinite was smaller for the outburst resistant coal than for the outburst prone coal. The distribution of maceral composition in the outburst resistant coal was simple, and the primary damage was minimal.
Influence of sidewall size on spalling in deep D-shaped tunnels: An experimental simulation
Authors: Luo Yong , Gong Fengqiang
Published: November 2020

A series of true triaxial compression tests was performed herein on cubic red sandstone samples containing a D-shaped hole with three sidewall sizes to study the influence of sidewall size on spalling in D-shaped tunnels. The initial horizontal stress of the tests refers to the in-situ stress at 500 m depth. The hole axis was arranged along the direction of the maximum horizontal principal stress. The vertical stress was increased to simulate the increasing surrounding rock stress after tunnel excavation. During the test, a self-made monitoring device was used to monitor and record the failure process of the tunnel models in real time. Furthermore, the spalling process of the D-shaped tunnels with different sidewall sizes was reproduced indoors. The failure process and the stress and fracture characteristics of the tunnel models with three different sidewall sizes were then analyzed and summarized. The effect of the sidewall size on spalling in D-shaped tunnels will be discussed in this paper. The results show that the failure of the tunnel models with different sidewall sizes first occurred on the sidewall near the corner then gradually developed upward and axial along the sidewall with the increase of the vertical stress. The width and the depth of the failure zone gradually increased, and a V-shaped notch was finally formed on the sidewall. No failure occurred on the roof and the floor of the tunnel models. The dominant failure modes were tensile failure. The failure forms were mainly spalling occasionally accompanied by slab ejection. The slabs were shaped in thin plates. The vertical stress that caused the initial failure of the tunnel models gradually decreased with the increasing sidewall size. Furthermore, the ability of the surrounding rock to store elastic strain energy decreased. The tensile characteristics became more prominent, and the size of the plate-shaped slabs increased. In the same stress environment, the greater the sidewall size, the larger the failure width and depth on the sidewall, and the more visible the V-shaped failure zone. The stability of deep D-shaped tunnels can be improved, and spalling can be mitigated by reducing the sidewall size. However, the risk of a rockburst will increase. This finding has an important engineering significance for the optimization design of a tunneling cross-section and the prevention of spalling and rockburst in D-shaped tunnels.
Effect of granule size distribution on the compaction property of GMZ bentonite
Authors: Xie J L , Liu Y M , Cao S F
Published: November 2020

In the current concept for disposal of high-level radioactive waste (HLW) in China, a barrier composed of blocks of highly compacted bentonite is constructed around the waste canisters. To develop this technique, uniaxial compaction of full-sized bentonite blocks has been initiated. Many factors affect the quality of bentonite blocks, including water ratio and granule size distribution of the bentonite, compaction pressure and rate, and form geometry. In the present study, compaction tests were conducted using powdered, pelleted, and mixed GMZ bentonite to evaluate the effects of granule size distribution on the integrity and uniformity of the block samples. Results show that high-quality blocks can be manufactured by adjusting the water content of the bentonite to 17%, in spite of different granule size distributions. The compaction in the mixed bentonite was better than that in the powdered and pelleted samples. However, the difference in final density was negligible when compacting at the same pressure. The block uniformity was not improved by adopting different granule size distributions when the height:diameter ratio of the bentonite samples reached 2. Blocks produced by powdered and mixed bentonite were prone to radial cracks when subjected to moisture loss; however, the cracks were healed after moisture redistribution.
Energy storage and dissipation characteristics of red sandstone in triaxial compression tests under constant confining pressure
Authors: Li Liuliu , Gong Fengqiang
Published: November 2020

To investigate the energy storage and dissipation characteristics of rock material in triaxial compression tests under constant confining pressure, a series of triaxial single-cyclic loading–unloading compression tests were conducted on red sandstone specimens under eight confining pressures. Using the method of graphic area integration, the input energy density, elastic energy density, and dissipative energy density of the specimen in axial, circumferential, and total directions were obtained. The results indicate that the input energy density in the axial direction accounts for the largest logarithmic proportion of the total input energy density and that the relationship between all the parameters of the energy density and the unloading level can be described by the quadratic function. In the axial direction, a linear function relationship exists among elastic, dissipative, and input energy densities. In the circumferential direction, a quadratic function relationship exists among elastic, dissipative, and input energy densities. For the total energy parameters of the sample, the relationship of elastic, dissipative, and input energy densities conforms to the quadratic function, providing a new method for the accurate estimation of the energy parameters in the rock under high stress.
Evaluation methods and standards for rock drillability in oil and gas drilling engineering in China: A review
Authors: Shi Xiangchao , Wu Jie , Gao Leiyu , Chen Shuai , Li Gao
Published: November 2020

In western China, 70% of the oil, gas, and geothermal resources are buried in deep formations (more than 3000 m), but the low rate of penetration has become a key factor restricting the development of these resources. Rock drillability evaluation is a basic task for oil, gas, and geothermal drilling engineering design that includes bit design, bit selection, and drilling parameter optimization. Different tests and standards to evaluate rock drillability have been developed worldwide. Against this backdrop, the evaluation methods and standards for rock drillability are reviewed. Various rock drillability tests and classification standards are compared and analyzed. Results show that these methods and standards are inaccurate and fail to meet the design requirements of drilling technology and bit selection in deep and ultradeep drilling wells. In China, micro-drilling test is commonly used to evaluate rock drillability in oil and gas drilling engineering. This method was developed as an oil and gas industry standard and has been used for more than 40 years. However, its results do not reflect the significant effects of high temperature and pressure at the bottom hole on rock drillability and breaking; thus, the results cannot be used in drilling designs. Testing methods and classification standards for rock drillability require innovative developments. This review highlights the following: (1) the classification standards for rock drillability must be refined in the future to meet the requirements of drilling designs in deep and ultradeep wells; (2) efficient and fast rock drillability tests are required to deal with complex and difficult formations; (3) the influence of the real physical environment of the borehole bottom on rock drillability must be further clarified.