Types and formation mechanism of collapse in Tianchi region of Changbai Mountain

Collapse is a disaster in Changbai Mountain area.Based on the present stage of collapse,the anthors summarized three types of collapse and analyzed their formation mechanism.This research makes sense to further study.

Formation mechanism of nanopores in dense films of anodic alumina

Constant-current anodization of pure aluminum was carried out in non-corrosive capacitor working electrolytes to study the formation mechanism of nanopores in the anodic oxide films.Through comparative experiments,nanopores are found in the anodic films formed in the electrolytes after high-temperature storage(HTS)at 130°C for 240 h.A comparison of the voltage-time curves suggests that the formation of nanopores results from the decrease in formation efficiency of anodic oxide films rather than the corrosion of the electrolytes.FT-IR and UV spectra analysis shows that carboxylate and ethylene glycol in electrolytes can easily react by esterification at high temperatures.Combining the electronic current theory and oxygen bubble mold effect,the change in electrolyte composition could increase the electronic current in the anodizing process.The electronic current decreases the formation efficiency of anodic oxide films,and oxygen bubbles accompanying electronic current lead to the formation of nanopores in the dense films.The continuous electronic current and oxygen bubbles are the prerequisites for the formation of porous anodic oxides rather than the traditional field-assisted dissolution model.

Roof collapse mechanism of weak surrounding rock for deep-buried tunnels under high geostress conditions

High geostress,a typical attribute of tunnels located at significant depths,is crucial in causing stress-induced failure and influencing the stability of the tunnel crown.This study developed an analytical method for the failure mechanism that occurs in deep-buried tunnel roofs,taking into account the influence of geostress.The limit analysis theory was utilized for deriving analytical solutions about the geometry of the collapsing surface and the limit supporting pressure.The collapsing surface obtained by the analytical solution was validated by the findings of the physical model test,which shows a high level of agreement with the actual one.An extensive investigation was done to explore the effects of the lateral pressure coefficients,the tunnel buried depth,the geological conditions of the surrounding rock,the long-short axis ratio,and the size of the tunnel profile.The findings indicate that an increase in the lateral pressure coefficient from 0.5 to 1.5 results in a reduction in the height of the collapsing zone by 2.08 m and the width of the collapsing zone by 1.15 m,while simultaneously increases the limit supporting pressure by 18.9%.The proposed upper bound method accurately determines the limit supporting pressure and the geometry of the collapsing surface,which aligns well with the results acquired through numerical modelling and on-site monitoring in actual engineering applications.The proposed analytical method can serve as a reference for similar crown failure issues of deep-buried tunnels.

Geometry and formation mechanism of tension gashes and their implication on the hydrocarbon accumulation in the deep-seated strata of sedimentary basin:A case from Shunnan area of Tarim Basin

With the theoretical and technological developments related to cratonic strike-slip faults,the Shuntuoguole Low Uplift in the Tarim Basin has attracted considerable attention recently.Affected by multi-stage tectonic movements,the strike-slip faults have controlled the distribution of hydrocarbon resources owing to the special fault characteristics and fault-related structures.In contrast,the kinematics and formation mechanism of strike-slip faults in buried sedimentary basins are difficult to investigate,limiting the discussion of these faults and hydrocarbon accumulation.In this study,we identified the characteristics of massive sigmoidal tension gashes(STGs)that formed in the Shunnan area of the Tarim Basin.High-resolution three-dimensional seismic data and attribute analyses were used to investigate their geometric and kinematic characteristics.Then,the stress state of each point of the STGs was calculated using seismic curvature attributes.Finally,the formation mechanism of the STGs and their roles in controlling hydrocarbon migration and accumulation were discussed.The results suggest that:(1)the STGs developed in the Shunnan area have a wide distribution,with a tensile fault arranged in an enéchelon pattern,showing an S-shaped bending.These STGs formed in multiple stages,and differential rotation occurred along the direction of strike-slip stress during formation.(2)Near the principal displacement zone of the strike-slip faults,the stress value of the STGs was higher,gradually decreasing at both ends.The shallow layer deformation was greater than the deep layer deformation.(3)STGs are critical for connecting source rocks,migrating oil and gas,sealing horizontally,and developing efficient reservoirs.This study not only provides seismic evidence for the formation and evolution of super large STGs,but also provides certain guidance for oil and gas exploration in this area.

Genetic mechanisms of high-quality tight siliciclastic reservoirs:A case study from the Upper Triassic Xujiahe Formation in the Yuanba area,Sichuan Basin,China

This study analyzed the petrological characteristics,diagenesis,pore types,and physical properties of the tight coarse-grained siliciclastic sequences in the third member of the Upper Triassic Xujiahe Formation(also referred to as the Xu-3 Member)in the western Yuanba area in the northeastern Sichuan Basin,China,based on the results of 242.61-m-long core description,292 thin-section observations,scanning electron microscopy(SEM),and 292 physical property tests.The types and genetic mechanisms of high-quality tight coarse-grained siliciclastic reservoirs in this member was determined thereafter.The research objective is to guide the exploration and development of the tight coarse-grained siliciclastic sequences in the Xu-3 Member.The results of this study are as follows.Two types of high-quality reservoirs are developed in the coarse-grained siliciclastic sequences of the Xu-3 Member,namely the fractured fine-grained sandy conglomerate type and porous medium-grained calcarenaceous sandstone type.Hydrodynamic energy in the sedimentary environment is the key factor controlling the formation of high-quality reservoirs.These high-quality reservoirs are developed mainly in the transitional zone with moderately high hydrodynamic energy between delta-plain braided channels and delta-front subaqueous distributary channels.The dolomitic debris(gravel)content is the main factor affecting the reservoirs’physical properties.The micritic algal debris and sandy debris in the dolomitic debris(or gravels)tend to recrystallize during burial,forming intercrystalline pores within.In the medium-grained calcarenaceous sandstones,intercrystalline pores in the dolomitic debris are formed at the early diagenetic stage,and a pore system consisting of structural fractures connecting intergranular pores,intergranular dissolution pores,and kaolinite intergranular micropores is developed at the late stage of diagenesis.The formation of intercrystalline pores in dolomite gravels and gravel-edge fractures,a pore system connected by gravel-edge and tectonic fractures,is closely related to the dolomite gravels in the sandy fine-grained conglomerates.

Formation mechanisms and resource potential of carbonate geothermal reservoirs in the Beijing-Tianjin-Hebei plain

Investigating the formation mechanisms of carbonate geothermal reservoirs is of theoretical and practical significance for summarizing the formation pattern of geothermal resources and further guiding their effective exploitation.The Beijing-Tianjin-Hebei Plain(BTHP),predominantly located within the Jizhong Depression and Cangxian Uplift in the Bohai Bay Basin,serves as the primary region for geothermal exploitation and utilization in China.More than 1500 geothermal wells have been drilled therein,with water temperature at the wellhead ranging from 55 to 110°C,single-well flow rate ranging between 80 and 120 m^(3)/h,and cumulative heating area exceeding 100×10^(6)m^(3).However,the exploration and research in the region remain limited overall.As per the previous geothermal and petroleum exploration results and the latest geothermal drilling data,this study comprehensively evaluated the geothermal resources of karst geothermal reservoirs.The results show that two suites of carbonate karst reservoirs,namely the Jxw Formation and the Ordovician strata,have primarily developed in the BTHP,and their formation and evolution can be divided into four stages:the Mesoproterozoic-Early Paleozoic stage with carbonate sedimentation and the development of interlayer karst,the Late Paleozoic stage with the development of direct sedimentary cover,the Mesozoic stage with compressional uplifting and development of buried hill karst,and the Cenozoic stage with regional cover deposition and the modification and finalization of karst geothermal reservoirs.Accordingly,the porosity evolution history of the geothermal reservoirs is composed of three stages,namely a significant decrease followed by a minor increase,a gradual decline,and then a small fluctuation from increase to decrease before slowly rising again.The karstification in geothermal reservoirs can be summarized into quasi-syngenetic karstification,epigenetic karstification,and burial karstification,which can be subdivided into seven subcategories.The carbonate geothermal reservoirs in the study area boast total geothermal resources of 53.821×10^(9)GJ,or 184.155×10^(9)t of standard coal equivalent(tce),and the annual exploitable geothermal resources in the urban area can heat an area of(400‒500)×10^(6)m^(3),indicating great potential of geothermal exploitation.

Formation mechanism and criterion of linear segregation in ZL205A alloy

The experiments and numerical simulation were conducted for ZL205A aluminum alloy cylindrical shell casting. The formation mechanism of the linear segregation produced by the low pressure die casting (LPDC) process was investigated. And the heat transfer of the casting during solidification process was analyzed by simulation technique, resulting from the information of linear segregation obtained by plenty of experiments. The new linear segregation criterion was proposed through the simulation and experimental results. It was found that the melting metal with high Cu contents was feeding the crack shrinkage formed by the tearing under the effect of feeding pressure during the later solidification, which led to the formation of linear segregation. The control methods for the linear segregation were suggested based on the proposed mechanism. Finally, the criterion of linear segregation was confirmed by the production of the actual castings.

Formation mechanism of MgB_2 in 2LiBH_4+MgH_2 system for reversible hydrogen storage

The formation conditions of MgB2 in 2LiBH4 ＋ MgH2 system during dehydrogenation were investigated and its mechanism was discussed. The results show that direct decomposition of LiBH4 is suppressed under relative higher initial dehydrogenation pressure of 4.0×10^5 Pa, wherein LiBH4 reacts with Mg to yield MgB2, and 9.16% （mass fraction） hydrogen is released within 9.6 h at 450 ℃. However, under relatively lower initial dehydrogenation pressure of 1.0×10^2 Pa, LiBH4 decomposes independently instead of reacting with Mg, resulting in no formation of MgB2, and 7.91% hydrogen is desorbed within 5.2 h at 450 ℃. It is found that the dehydrogenation of 2LiBH4 ＋ MgH2 system proceeds more completely and more hydrogen desorption amount can be obtained within a definite time by forming MgB2. Furthermore, it is proposed that the formation process of MgB2 includes incubation period and nucleus growth process. Experimental results show that the formation process of MgB2, especially the incubation period, is promoted by increasing initial dehydrogenation pressure at constant temperature, and the incubation period is also influenced greatly by dehydrogenation temperature.

Microstructures and formation mechanism of headstand pyrocarbon cones developed by electromagnetic-field-assisted CVD

Novel headstand pyrocarbon cones （HPCs） with hollow structure were developed on the surfaces of pyrocarbon layers of the carbon/carbon （C/C） composites at 650-750 °C by the electromagnetic-field-assisted chemical vapor deposition in the absence of catalysts. The fine microstructures of the HPCs were characterized by high-resolution transmission electron microscopy. The results show that the textural features of the HPCs directly transfer from turbostratic structure in roots to a well-ordered high texture in stems. And the degree of high texture ordering decreases gradually from the stem to the tail of the HPCs. The formation mechanism of the HPCs was inferred as the comprehensive effect of polarization induction on electromagnetic fields and particle-filler property under disruptive discharge.

Formation mechanism and organizational controlling of ultra-fine-grain copper processed by asymmetrical accumulative rolling-bond and annealing

The initial copper with large grain sizes of 60-100 μm was processed by six passes asymmetrical accumulative rolling-bond （AARB） and annealing, the ultra-fine-grained （UFG） copper with grain size of 200 nm was obtained, and the microstructures and properties were studied. The results show that there are large sub-structures and also texture component C for the UFG copper obtained by six passes AARB, possessing high strength and microhardness in company with poor elongation and conductivity. Thereafter, the UFG copper was annealed at 220 °C for 35 min, in which the sub-structures disappear, the grain boundaries are composed of big angle grain boundaries, and the textures are composed of a variety of texture components and parts of twins. Compared with the UFG copper obtained by six passes AARB, the tensile strength and yield strength for the UFG copper obtained by six passes AARB and annealing at 220 °C for 35 min are decreased slightly, the elongation and conductivity are improved obviously.

Preparation, formation mechanism and mechanical properties of multilayered TiO_2-organic nanocomposite film

Ti O2-organic multilayered nanocomposite films were deposited on a self-assembled monolayer-coated silicon substrate based on layer-by-layer technique and chemical bath deposition method by a hydrolysis of Ti Cl4 in an acid aqueous solution. The chemical compositions, surface morphologies and mechanical properties of the films were investigated by X-ray photoelectron spectrometer(XPS), scanning electron microscopy(SEM) and nanoindentation depth-sensing technique, respectively. The results indicate that the major chemical compositions of the films are Ti and O. The principal mechanism for the nucleation and growth of the films is homogeneous nucleation, and the layer number of films has great influence on the surface morphology and roughness of the films. In addition, mechanical nanoindentation testing presents a significant increase in hardness and fracture toughness of titanium dioxide multilayered films compared with single-layer titanium dioxide thin film.

Formation of Tianwen-1 landing crater and mechanical properties of Martian soil near the landing site

After landing in the Utopia Planitia,Tianwen-1 formed the deepest landing crater on Mars,approximately 40 cm deep,exposing precious information about the mechanical properties of Martian soil.We established numerical models for the plume-surface interaction(PSI)and the crater formation based on Computational Fluid Dynamics(CFD)methods and the erosion model modified from Roberts’Theory.Comparative studies of cases were conducted with different nozzle heights and soil mechanical properties.The increase in cohesion and internal friction angle leads to a decrease in erosion rate and maximum crater depth,with the cohesion having a greater impact.The influence of the nozzle height is not clear,as it interacts with the position of the Shock Diamond to jointly control the erosion process.Furthermore,we categorized the evolution of landing craters into the dispersive and the concentrated erosion modes based on the morphological characteristics.Finally,we estimated the upper limits of the Martian soil’s mechanical properties near Tianwen-1 landing site,with the cohesion ranging from 2612 to 2042 Pa and internal friction angle from 25°to 41°.

MECHANISM OF MICROBAND FORMATION IN COLD ROLLED INTERSTITIAL-FREE STEEL

The mechanism of the shear band formation in the high cold rolled BCC metal is analyzed. Based on the plastic deformation theory, the shear distribution in the deformed grain is calculated by using the Taylor constraint model and the Bishop ＆ Hill maximum work principle. Results show that when the rolling direction （RD） is parallel to a certain direction of a grain, the large localized shear occurs on one slip plane, thus generating microbands in the grain because of the high localized shear strain. The angle between the RD and the shear band is about 30°. The plate-like structure of the microband is formed because of the dislocation double cross slip. The transmission electron microscope （TEM） observation of the microband in the cold rolled BCC metal confirms the formation mechanism of the microband.

Formation mechanism and crystal simulation of Na_2O-doped calcium aluminate compounds

Calcium aluminate clinkers doped with Na2O were synthesized using analytically pure reagents CaCO3, Al2O3, SiO2 and Na2CO3. The effects of Na2O-doping on the formation mechanism of calcium aluminate compounds and the crystal property of 12CaO·7Al2O3 (C12A7) cell were studied. The results show that the minerals containing Na2O mainly include 2Na2O·3CaO·5Al2O3 and Na2O·Al2O3, when the Na2O content in clinkers is less than 4.26% (mass fraction). The rest of Na2O is mainly doped in 12CaO·7Al2O3, which results in the decrease of the crystallinity of 12CaO·7Al2O3. The crystallinity of 2Na2O·3CaO·5Al2O3 is also inversely proportional to the Na2O content in clinkers. The formation processes of 2Na2O·3CaO·5Al2O3 and 12CaO·7Al2O3 can be divided into two ways, which are the direct reactions of raw materials and the transformation of CaO·Al2O3, respectively. The simulation shows that the covalency of O-Na bond in Na2O-doped 12CaO·7Al2O3 cell is weaker than those of O-Ca and O-Al bonds. The free energy of the unit cell increases because of Na2O doping, which results in the improvement of chemical activity of 12CaO·7Al2O3. The leaching efficiency of Al2O3 in clinker is improved from 34.81% to 88.17% when the Na2O content in clinkers increases from 0 to 4.26%.

Review of collapse triggering mechanism of collapsible soils due towetting

Loess soil deposits are widely distributed in arid and semi-arid regions and constitute about 10% of land area of the world.These soils typically have a loose honeycomb-type meta-stable structure that is susceptible to a large reduction in total volume or collapse upon wetting.Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils.For this reason,collapse triggering mechanism for loess soils has been of significant interest for researchers and practitioners all over the world.This paper aims at providing a state-of-the-art review on collapse mechanism with special reference to loess soil deposits.The collapse mechanism studies are summarized under three different categories,i.e.traditional approaches,microstructure approach,and soil mechanics-based approaches.The traditional and microstructure approaches for interpreting the collapse behavior are comprehensively summarized and critically reviewed based on the experimental results from the literature.The soil mechanics-based approaches proposed based on the experimental results of both compacted soils and natural loess soils are reviewed highlighting their strengths and limitations for estimating the collapse behavior.Simpler soil mechanics-based approaches with less parameters or parameters that are easy-to-determine from conventional tests are suggested for future research to better understand the collapse behavior of natural loess soils.Such studies would be more valuable for use in conventional geotechnical engineering practice applications.

Reservoir characteristics,formation mechanisms and petroleum exploration potential of volcanic rocks in China

Characterized by complex lithology and strong heterogeneity, volcanic reservoirs in China developed three reservoir space types： primary pores, secondary pores and fractures. The formation of reservoir space went through the cooling and solidification stage （including blast fragmentation, crystallization differentiation and solidification） and the epidiagenesis stage （including metasomatism, filling, weathering and leaching, formation fluid dissolution and tectonism）. Primary pores were formed at the solidification stage, which laid the foundation for the development and transformation of effective reservoirs. Secondary pores were formed at the epidiagenesis stage, with key factors as weathering and leaching, formation fluid dissolution and tectonism. In China, Mesozoic-Cenozoic volcanic rocks developed in the Songliao Basin and Bohai Bay Basin in the east and Late Paleozoic volcanic rocks developed in the Junggar Basin, Santanghu Basin and Ta- rim Basin in the west. There are primary volcanic reser- voirs and secondary volcanic reservoirs in these volcanic rocks, which have good accumulation conditions and great exploration potential.

Application of General Shear Theory to the Study of Formation Mechanism of the Metamorphic Core Complex:A Case Study of Xiaoqinling in Central China

: The kinematic vorticity number and strain of the mylonitic zone related to the detachment fault increase from ESE to WNW along the moving direction of the upper plate of the Xiaoqinling metamorphic core complex (XMCC) and the geometry of quartz c-axis fabrics changes progressively from crossed girdles to single girdles in the same direction. Therefore, pure shear is dominant in the ESE part of the XMCC while simple shear becomes increasingly important towards WNW. However, the shear type does not change with the strain across the shear zone, thus the variation of shear type is of significance in indicating the formation mechanism. The granitic plutons within the XMCC came from the deep source and their emplacement was an active and forceful upwelling prior to the detachment faulting. The PTt path demonstrates that magmatism is an important cause for the formation of the XMCC. The formation mechanism of the XMCC is supposed to be active plutonism and passive detachment. Crustal thickening and magmatic doming caused necking extension with pure shear, and magmatic heating and doming resulted in detachment extension with simple shear and formed the XMCC.

Formation Mechanism of the Changxing Formation Gas Reservoir in the Yuanba Gas Field,Sichuan Basin,China

In a very gentle platform-margin paleogeographic environment, platform-margin reef flat facies carbonate reservoir rocks were developed in the Changxing Formation of Yuanba field. Later weak structural evolution and diagenetic evolution caused the Changxing Formation to form lithologic traps, with good reservoirs such as dissolved bioclastic dolostone and dissolved pore dolostone. The Changxing Formation gas reservoir is a pseudo-layered porous lithologic gas reservoir under pressure depletion drive, with high H2S and moderate CO2 contents. This paper predictes that the conducting system for the Changxing Formation gas reservoir is possibly composed of the pores and microfractures in the Changxing Formation reservoir, the top erosional surface of the Changxing Formation, as well as the micropores and microfractures in the underlying formations. The Changxing Formation reservoir has experienced 3 hydrocarbon charging stages. This paper suggests that diffusion is the major formation mechanism for this gas reservoir. In the Middle and Late Yanshanian, the Yuanba area entered the major gas charging stage. The gas migrated mainly through diffusion and with the assistance of seepage flow in small faults and microfractures from the source rocks and the other oil-bearing strata to the Changxing Formation carbonate reservoir rocks, forming lithologic gas pools. In the Himalayan Epoch, the lithologic traps were uplifted as a whole without strong modification or overlapping, and were favorable for gas preservation.

Study on Gel Formation Mechanism of Konjac Glucomannan

The transformation of molecular conformation after gelatinization of konjac glucomannan is characterized by means of GC, GPC, FT-IR, DSC, XRD and TEM. The results showed that the molecule of KGM had no branch, the monose composition and connecting type of the molecular chain had no change, the transformation of molecule weight was little, and its drying powder sample formed an evidently new crystalline region. The hollow double helix structure of KGM in hydrosol changed from stretch chain into intercross and entwisted after gelatinization. The gelatin formation mechanism of konjac glucomannan is thereby expounded.