Initial Compression Stage Research Articles

Analogue sandbox modeling of orogenic wedge front faulting: Roles of inherited fault zones and topographic loading

Earthquakes reported in the frontal belts of active orogenic wedges such as the 2013 Mw6.6 Lushan and 1999 Mw7.6 Chi-Chi earthquakes, highlight the importance of loading exerted by mountainous topography and inherited fault zones. However, their effects on formation and activation of these wedge front fault systems remain poorly understood. This study presents three sets of sandbox experiments in which topographic loading and geometry of inherited faults were first separately investigated, then explored jointly. Experiments show that smaller topographic loading favors gentle-dipping wedge front thrusts, while larger topographic loading promotes the development of steep wedge front faults. Introduced as zones of frictional weakness, all inherited faults promote deformation localization, though the steep ones are characterized by buttressing nearby rather than direct slip on themselves. When the two factors were tested integrally, four major deformation modes arose, including (1) direct reactivation; (2) fault truncation in the initial stage of compression; (3) stacking of small thrusts against the inherited fault and possible truncation in a later evolutionary stage; (4) behavior as a fossil structure. These modes show differences not only in first-order deformation styles, but also in the distribution of secondary structures, defining a basic framework and providing new guides for the interpretation of complex wedge front fault systems and their activities, in areas such as the Longmen Shan (eastern Tibet), the Tian Shan and the western margin of the Taiwan orogen.

Deformation behavior of high-entropy oxide (Mg,Co,Ni,Cu,Zn)O under extreme compression

Following the discovery of high-entropy alloys, high-entropy oxides have gained considerable interest due to their unconventional structural characteristics and versatile functional properties for promising applications. Via synchrotron radial x-ray diffraction in a diamond anvil cell, the mechanical strength and deformation behavior of a typic high-entropy oxide (Mg,Co,Ni,Cu,Zn)O with a rock-salt structure under extreme compression has been investigated in situ. This compound in a polycrystalline state shows a large elastic anisotropy at the initial compression stage and then gradually becomes isotropic at around 21.4 GPa, similar with the behavior of MgO. Based on the lattice strain order conversion and texture evolution under compression, a dominant slip system transition from {100}<011> to {110}<1–10> is proposed in this high-entropy oxide. This work deepens our understanding on the role of chemical disorder in the mechanical properties of entropy-stabilized oxides, which would be indispensable to the design of advanced structural ceramics with optimal strength-to-ductility ratio.

Statistical damage constitutive model for the two-component foaming polymer grouting material

Abstract Two-component foaming polymer (TFPU) grouting material is increasingly used in civil engineering. Its compressive strength is key to achieving the desired enhancing effect. The constitutive model of TFPU grouting material is a theoretical basis to evaluate the strength performance, which, however, is not fully understood. Here the uniaxial compression experiment of TFPU samples of different densities (0.11–0.53 g·cm−3) was conducted. Based on the stress–strain curves, the damage evolution equation of each sample was obtained by function fitting, followed by the establishment of statistical damage constitutive model. The model was simplified to a universal function with density as the argument. Results show that the stress–strain curves contain the initial compression stage, linear elastic stage, yield stage, yield plateau stage, and strain hardening stage regardless of the varied density. The variation laws of the damage with strain conform to the form of first-order decay exponential function. The theoretical stress–strain curves are in good agreement with the experimental ones, indicating that the statistical damage constitutive model can well reflect the mechanical behavior of TFPU grouting material. With this constitutive model, the mechanical properties of TFPU grouting material can be obtained according to the density alone, which is more convenient for practical engineering applications.

Effects of particle size on the particle breakage of calcareous sands under impact loadings

Particle breakage of calcareous sands under impact loadings, closely related to marine and geotechnical engineering, has attracted a great deal of attention. This paper presents the results of a study on the effect of particle size on particle breakage characteristic of calcareous sands that underwent different degrees of particle breakage. Calcareous and quartz sands of four different particle size (i.e., 5.00–2.00 mm, 2.00–1.00 mm, 1.00–0.50 mm and 0.50–0.25 mm) were subjected to impact loadings with different input energies. By defining particle size distribution (PSD) using fractal methods, it is found that the PSD evolution of quartz sands is similar to that of calcareous sands. Compared with quartz sands, the particle size related fractal behavior of calcareous sands is more easily affected by the initial particle size. The compressibility of calcareous sands is greater than that of quartz sands. The volumetric deformation of the above two kinds of sand can be divided into three typical stages: initial compression stage, failure stage and stability stage. Unlike calcareous sands, quartz sands can reach the stability stage at a low input energy. For calcareous sands or quartz sands, the breakage sensitivity of fine particles is more significant than that of coarse particles. This could be attributed to their different coordination numbers. Particles with smaller coordination numbers undergo larger impact loadings, resulting in the higher breakage sensitivity than particles with larger coordination numbers. Finally, an empirical model for estimating the degree of particle breakage by volumetric deformation is proposed.

WITHDRAWN: Fracture evolution of fiber-reinforced backfill based on acoustic emission fractal dimension and b-value

To investigate the fracture evolution process of fiber-reinforced backfill, uniaxial compression tests were conducted on different fiber types of reinforced backfills. The fracture evolution law of the fiber-reinforced backfill is explored by analyzing the trend of acoustic emission (AE) fractal dimension and b -value with time during the fracture of the backfill. The results show that both amplitude time series values and RA (rise time/maximum amplitude) time series values have good fractal characteristics, but the amplitude time series values have better fractal characteristics compared to RA time series values. In the whole stress change process, the value of the RA correlation dimension ( D ) is relatively small, but at the occurrence of a major event, the reduction and fluctuation of the RA D is larger than the amplitude D . Compared with the fiber-free backfill, the fiber-reinforced backfill has a more pronounced symmetry in the amplitude D and RA D curves and a denser distribution after the peak, and its AE b -value is smaller. At the initial compression stage, there are more small-scale cracks and the D values are large and densely distributed; at approximately 75% or 90% of the peak stress, the D values drop; at the residual deformation stage, the D values rise and fall steeply. The results of the study provide a theoretical basis for the stability control of fiber filling in mines.

Experimental Study of the Compression Stress of Artery Tissue in Bipolar Electro-surgery Modality

Bipolar vessel sealing (BVS) is an advanced hemostasis technology applied in the electro surgery, and the technology could be further improved for the aim of reducing the lateral thermal damage and increasing the sealing burst pressure. Since the BVS is operated under the tissue compression state, the vessel sealing performance could be influenced by the compression stress variation, which is rarely studied. Therefore, in this work, the compression stress of bovine arteries was studied with different parameters as compression ratio, feeding speed, electrode width and vessel size using a self-made experimental apparatus. The experimental result shows that the vessel tissue compression stress presents the viscoelastic characteristics, and generally, the stress increases very rapid and decreases slowly under a compression state, and compression stress displayed significantly different with lower compression ratio and higher compression ratio, the stress at 40% compression ratio was much higher than that under 30% compression ratio. The compressive stress decreased with the increase of compression feeding speed, i.e. the stress at a high compression speed was smaller than that at a low feeding speed. Moreover, smaller tool width and smaller vessel diameter caused a greater stress at the initial stage of compression. It was found that the elastic modulus of a small diameter vessel tissue was larger than that of a large diameter vessel tissue by the analysis of compression data, which might be the one of the reasons for the lower burst pressure for large vessel size.

Pressure-induced transparency of MgO, Al2O3, AlN, and cBN ceramics at room temperature

The in situ axial X-ray diffraction patterns of four ceramic powder samples (MgO, Al2O3, AlN, and cBN) that were compressed in a diamond anvil cell under uniaxial non-hydrostatic conditions were recorded. The microscopic deviatoric stress as a function of the pressure was determined from the X-ray diffraction peak broadening analysis: the curves increased approximately linearly with the pressure at the initial compression stage and then levelled off under further compression. Pressure-induced transparency was observed in all of the samples under compression, and the pressure at the turning point on the curves of the microscopic deviatoric stress versus pressure corresponded to the pressure at which the samples became transparent. Analysis of the microstructural features of the pressure-induced transparent samples indicated that the compression caused the grains to fracture, and the broken grains bonded with each other. We demonstrated that the ceramics’ pressure-induced transparency was a process during which the grains were squeezed and broken, the pores were close between the grains, and the broken grains were re-bonded under compression.

ACOUSTIC EMISSION AND DAMAGE CHARACTERISTICS OF ANTHRACITE UNDER DIFFERENT CONDITIONS

Acoustic emission (AE) can be used to observe the process of coal fracture propagation. Based on a press and acoustic-emission platform, the damage and acoustic-emission characteristics of anthracite with different loading rates, water amounts and sizes were studied. The results show that there is less acoustic emission in the initial compression stage of coal; acoustic emission is more active in the transition from elastic deformation to plastic deformation, which is manifested in the following aspects: the faster the loading rate, the higher is the number of acoustic-emission events; the peak count of acoustic emissions of a saturated-coal sample is significantly lower than that of a natural-coal sample. Coal samples and large coal samples emit even more sounds. Based on the normalization of acoustic-emission counts, the relationship between damage variables and stress-strain is studied, and it is characterized by an initial slow increase, followed by a rapid increase; however, different factors have a great influence on the damage-characteristic curve. The research results have a certain guiding significance for the coal and rock disaster prediction.

Twinning and twin intersections in γ grains of Ti-42.9Al-4.6Nb-2Cr

A nanoscale observation utilizing the transmission electron microscopy (TEM) device was presented to investigate the hot deformation behavior of β-solidifying γ-TiAl alloy (Ti-42.9Al-4.6Nb-2Cr, at.%) with duplex structure, and elucidate twinning and twin intersections in γ grains. Results showed that twinning is tightly linked to twin intersections in γ grains. At the initial stage of isothermal compression, faults in two directions with the acute angle of ∼70° intensively formed in γ grains. With the proceed of isothermal compression, faults paralleling to each other gradually evolved into twins in the lateral direction, which is helpful to accommodate the atomic plane misfit. And dislocations piled-up advantageously promote longitude twinning in γ grains. Once faults in all directions evolved into twins, various twin intersections phenomena would be observed in γ grains.

Experimental Investigation on the Correlation between Dynamic Ultrasonic and Mechanical Properties of Sandstone Subjected to Uniaxial Compression

Ultrasonic wave velocity is effective to evaluate anisotropy property and predict rock failure. This paper investigates the correlation between dynamic ultrasonic and mechanical properties of sandstones with different buried depths subjected to uniaxial compression tests. The circumferential anisotropy and axial wave velocity of sandstone are obtained by means of ultrasonic wave velocity measurements. The mechanical properties, including Young’s modulus and uniaxial compressive strength, are positively correlated with the axial P wave velocity. The average angles between the sandstone failure plane and the minimum and maximum wave directions are 35.8° and 63.3°, respectively. The axial P wave velocity almost keeps constant, and the axial S wave velocity has a decreasing trend before the failure of rock specimen. In most rock samples under uniaxial compression, shear failure occurs in the middle and splitting appears near both sides. Additionally, the dynamic Young’s modulus and dynamic Poisson’s ratio during loading are obtained, and the negative values of the Poisson’s ratio occur at the initial compression stage. Distortion and rotation of micro/mesorock structures may be responsible for the negative Poisson’s ratio.

Experimental Study on the Relationship between Compression Stability and Deformation Localization of Viscous/Brittle Rock‐Like Materials

Rock‐like materials often exhibit irregular failure deformation under long‐term service conditions, and the deformation and failure of asphalt and concrete materials is a serious problem that leads to subgrade failure. In this study, two different viscous/brittle rock‐like materials were prepared by the in situ loading and optical speckle synchronous monitoring test method, and the evolution characteristics of the deformation field were studied during compression. The formation process of the compression deformation localization of rock‐like materials and their relationship with stability were analyzed. A quantitative description of the compression deformation stage and localization characteristics of the viscous/brittle rock‐like materials is presented. The results can be summarized as follows. At the initial stage of compression, the deformation localization zone of viscous/brittle rock‐like materials begins to expand from the middle area to the surrounding area. Preliminary results of the deformation localization of the linear elastic deformation stage were obtained. The failure cloud image is completely formed at the peak, which is consistent with the failure physical map. The deformation process of compression can be quantitatively described using the deformation localization characteristics of rock‐like materials.

Experimental Study on Hydro-mechanical Behaviour of Anisotropic Columnar Jointed Rock-Like Specimens

Columnar jointed rock masses (CJRM), characterized by regular arrays of polygonal prisms or columns, are exposed in the dam foundation of the Baihetan hydropower station and pose a challenge to the stability of the project. To understand the hydro-mechanical behaviour of Baihetan CJRM, triaxial compression experiments are carried out on artificial CJRM specimens with regular arrays of hexagonal columns, which are similar to the actual CJRM. Based on the experimental results, mechanical and hydraulic behaviour of CJRM is studied. It is found that the compressive strength of CJRM varies in a typical U-shape with the joint inclination angle. Three failure modes associated with the angle of joint inclination are observed. The evolution of permeability with stress exhibits distinct phased characteristics: initial compression stage, linear elastic stage, yield stage, and strain-softening stage. The results of this study provide helpful information for the design and construction of the Baihetan project involving CJRM.

Deformation of Tianjin soft clay and corresponding micromechanism under cyclic loading

The deformation of soft clays under cyclic loading is controlled by microfabric changes. Cyclic triaxial tests, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were conducted to investigate the deformation and the corresponding micromechanism under cyclic loading. The correlations between the microparameters and deformation of Tianjin soft clay are discussed. The deformation increases linearly in the initial compression stage (number of cycles, N &lt; 500), at a decreasing rate in the later shearing stage (N &lt; 5000), and eventually stabilizes when the cyclic stress ratio (CSR) is 0.30. The probability entropy of both the soil particles and pores have a weak correlation with the deformation on the whole, reflecting a fluctuation within a small range in the initial compression stage. The correlations between the median pore diameter, median particle diameter, and specific surface area and the deformation are validated by using the gray correlation method. More specifically, the specific surface area and the deformation are highly correlated in the initial compression deformation stage. The median pore diameter and median particle diameter are highly correlated with deformation in the later shearing deformation stage.

Effective Stress Law for the Permeability and Pore Volume Change of Clayey Sandstones

AbstractThe influence of confining and pore pressures on permeability and pore volume change was studied in two clayey sandstones. The coupling effect is characterized by the effective stress coefficients κ and β, respectively. Hydrostatic compression of a porous rock typically involves an initial nonlinear stage of elastic crack closure and a subsequent linear stage of pore deformation. To elucidate the influence of microcracks on the behavior, we measured the effective stress coefficients in these two stages separately. Our data show that the coefficients κ for permeability of both clayey sandstones are uniformly greater than 1, in agreement with published data and theoretical prediction for a microscopically inhomogeneous assemblage. Our data show that the presence of microcracks may homogenize the pore space, as reflected by a significantly lower κ value during the initial stage of nonlinear compression. We obtained some of the first measurements of the effective stress coefficient β for pore volume change in sandstones, which show values close to but uniformly less than 1. Synthesizing our sandstone data, recently published data on limestones, and theoretical analyses, we propose to define in the β‐κ space two fundamentally different regimes for the effective stress behavior. A comparison of our data with Berryman's model, the clay shell model, and clay particle model indicates apparent discrepancies, which we propose to resolve with a dual equivalent‐channel model based on the spatial partitioning of clayey and clay‐free pore volumes.

Investigating Toppling Failure Mechanism of Anti-dip Layered Slope due to Excavation by Physical Modelling

The failure mechanism of anti-dip layered slopes is essentially different from that of dip layered slopes. Therefore, it is important to investigate the failure mechanism of anti-dip slopes due to excavations. In this study, slope instability induced by mining excavation at the Changshanhao open-pit mine in Neimenggu province, China, was used as a case study. Based on the similarity ratio theory, a physical model was built to investigate the failure mechanism of the anti-dip layered slope under excavation. The physical model was monitored by various monitoring equipment including static strain data acquisition equipment, infrared thermal camera, and digital speckle displacement field measurement equipment. The evolution characteristics of the multi-physics fields including displacement field, strain field and temperature field of the physical model during the excavation were comprehensively obtained. According to the deformation characteristics of the anti-dip layered slope during excavation test, the failure mechanism can be divided into four stages: initial compression stage, crack generation stage, crack propagation stage and formation of sliding surface stage. The deformation characteristics of the slope at each stage were analyzed and compared with those of the anti-dip slope in the field. The comparison verified the rationality and accuracy of the physical model experiment, and provided a deeper understanding of the failure mechanism of anti-dip layered slope under excavation through the comprehensive monitoring data. The results of this work can be used as a reference for the follow-up reinforcement and treatment of similar anti-dip layered slopes.

Compaction effects on permeability of spherical packing

PurposeThe purpose of this paper is to investigate the evolution of the permeability of spherical packing during cold compaction by pore-scale modeling.Design/methodology/approachThe discrete element method (DEM) is used to generate spherical packing structure under different compressive pressures and the Lattice Boltzmann method (LBM) is adopted to calculate the permeability of each spherical assembly.FindingsIt is found that the decrease of the porosity is the main reason of the reduction in permeability in the initial compression stage, but its influence becomes insufficient in the late compression stages. Besides, two empirical formulas are obtained, which describe the relation between the permeability and the equivalent mean diameter and the variation of normalized permeability with compressive pressure, respectively.Research limitations/implicationsIn this study, the authors study the spherical particles and ignore the non-spherical effects. Besides, the classical contact model, the linear-spring-damping model, is used in DEM, so the plastic deformation cannot be considered.Originality/valueThe DEM and the LBM are well combined to study the compaction effects on permeability of spherical packing. Two simple expressions of the spherical packing structure with uniform diameter distribution are given for the first time.

Mechanical Characteristics and Failure Mechanism of Siltstone with Different Joint Thickness

The mechanics of rock mass is significantly affected by joints, but many existing studies of jointed rocks make simplifications that do not consider the joint thickness. To further study the influence of joint thickness on rock mechanics (mechanical properties, failure mechanism, damage model, etc.), we fabricated jointed siltstone specimens with different joint thickness (5, 10, 15, and 20 mm) and the specimens were subjected to uniaxial compression tests. The effects of joint thickness on the uniaxial compression strength (UCS), the strain at UCS, the elastic modulus, and the stress‐strain curves were thus analyzed. For the stress‐strain curve, with rising joint thickness, the upper concave in the initial compression stage intensified, the slope of the stress‐strain in the elastic stage decreased, and the sudden stress drop after peak strength became more obvious. Both the peak compression strength and the elastic modulus gradually decreased with rising joint thickness, but a positive correlation was found between the strain at UCS and the joint thickness.

Mechanical Behavior and Energy Evolution of Sandstone considering Slenderness Ratio Effect

To study the influence of slenderness ratio effect on the mechanical behavior, acoustic emission properties, and energy evolution of sandstone, the uniaxial compression tests coupled with acoustic emission technology are carried out at different slenderness ratios D (0.5, 1.0, 1.5, 2.0, 3.0). The results show that a logarithmic function relationship is observed between the peak strength, the peak strain, and the elastic modulus with slenderness ratio. The failure patterns of the tested sandstone varied significantly with the increasing slenderness ratio. When the slenderness ratio, D, is lower than 1.5, complex failures and multiple shear planes are formed, while simple failures and single shear planes are generated at D larger than 1.5. Besides, the AE ringing counts are more obvious with a higher slenderness ratio, D, at the initial compression stage due to the greater body volume and more defects in the sandstone. The energy evolution curves and energy ratio distribution curves can be divided into four stages, corresponding to the stress‐strain curves.

Measurement of water permeation through membranes from extremely high hydraulic pressure to atmospheric pressure

The performance of electrochemical hydrogen compressors (EHCs) with polymer electrolyte membranes which work in the presence of water is affected by the flooding; however, the water permeation through the membranes from the high-pressure side (dozens of MPa) to the low-pressure side has never measured. In this study, a method to measure the permeation from the high hydraulic pressure side (2–20 MPa) to the atmospheric pressure side is shown, using EHC cells and a water hydraulic pump. By this method, liquid-liquid permeation (LLP) and liquid-vapor permeation (LVP) were measured. The higher the hydraulic pressure was, the more the water flux was, and the increase in the permeation was large for LLP. It is considered that the electro-osmotic drag accumulates water on the cathode at low pressure during the initial stage of the electrochemical hydrogen compression and then the permeation from the cathode to the anode exceeds the electro-osmotic drag as the cathode pressure increases, which causes the decrease in the performance by flooding.

Seismic characteristics and strontium isotope ages of the Middle Miocene Ngrayong Formation in the Madura Strait Basin: Implications for the paleogeographic reconstruction of East Java

East Java, on the southeastern margin of the Sundaland Shelf, is an ideal and pilot location to study paleogeographic changes due to the interactions of the Eurasian and the Indian-Australia plates. Many studies have been conducted; however, some issues remain poorly understood, such as the initial compression stage and associated paleogeography of East Java. Here, we report newly acquired high-resolution seismic data and drilling wells in the area of the Madura Strait. We systematically reconstruct a three-dimensional model on the paleogeography of East Java in the Middle Miocene in combination with others’ results. Different depositional environments and characteristics of the related lithofacies observed on both sides of the Middle Miocene volcanic arc imply that weak subaerial and subaqueous volcanism existed in East Java. The extensive Ngrayong fining in the southward clastic sequences, located north of the mentioned volcanic arc, were deposited in a bathyal marine environment, which showed an oversteepening slope and basinal characteristics with outer neritic to bathyal facies within the present-day Kendeng Zone and Madura Strait area. This differs from the northern region of the present-day Rembang-Madura Inversion Zone and the northern offshore region of East Java, which were deposited in a transitional and neritic marine environment. We identified two new turbidite fans showing opposite source directions based on 3D seismic data within the Madura Strait area. Four controlling factors contributed to the formation of the Ngrayong turbidite fans, including the paleotopography of the underlying Kujung Formation, short-term intense regional tectonic events, high rates of sediment supply and occasional volcanic activity.