Search

Fiber-reinforcement is a common feature of many soft biological tissues. The response of fibrous biotissues to applied shear is thus of considerable current interest. We consider here the fundamental deformation of simple shear within the framework of transversely isotropic incompressible hyperelastic materials for fiber-reinforced specimens with a single family of parallel fibers oriented at a general angle to the direction of shear. It is well known that the normal stress effect characteristic of nonlinear elasticity plays a crucial role in maintaining an homogeneous deformation state in the bulk of the specimen. Here we investigate the effects of fiber-matrix interaction on the shear and lateral normal stresses. The inclusion of fiber-matrix interaction stiffens the shear stress response. As regards the normal stress, it is shown that the confining normal traction that needs to be applied to the top and bottom faces of a block in order to maintain simple shear can be compressive or tensile depending on the degree of anisotropy, fiber-matrix interaction and on the angle of orientation of the fibers. In the absence of such an applied traction, an unconfined sample tends to bulge outwards or contract inwards perpendicular to the direction of shear so that one has the possibility of both a positive or negative Poynting effect. It is shown that the fiber-matrix interaction enhances both the positive and negative Poynting effects. The results are illustrated using experimental data obtained by other authors for porcine brain white matter. In particular, it is shown that, for sufficiently small angles of orientation, a transition amount of shear exists at which the normal stress changes character from tensile to compressive with increasing amount of shear. An increase in the degree of fiber-matrix interaction enlarges the range of orientation angles for which this transition can occur and decreases the transition amount of shear. These transition amounts of shear are well within the physiological strain regime. The results obtained here are relevant to the development of accurate shear test protocols for the determination of constitutive properties of fibrous biological soft tissues.

In coastal engineering, the cyclic loading caused by traffic, wind, and waves is superimposed on the initial static shear stress in certain infrastructures such as embankments. In some cases, a por...

A similarity model with a volumetric similarity ratio of 1:100 and a granular flow model for the tunnel were designed. By comparing macroscopic and mesoscopic information (such as fracture process, strain evolution, stress transfer, crack propagation, and stress distribution) of the tunnel models under load, the failure mechanism of the metro tunnel under load was investigated. The result showed that: 1) under the loading path, the instability area of the tunnel is mainly distributed in the straight wall on both sides. When the load is 1.5 MPa, a large number of cracks on both sides of the straight wall run through, resulting in the initial failure of the rock mass; 2) the surface rock mass of arch bottom is under tensile stress and the deep rock mass is under pressure stress, therefore, the fracture does not develop continuously. The surface of straight wall produces continuous development crack under the action of tensile stress; 3) the arch bottom first responds during the stress redistribution of the small-span tunnel; the top and middle parts of the side walls of the running tunnel with greatest potential for damage respond most; 4) in the process of stress redistribution, the peak stress of the deep measuring points of the straight wall is greater than that of the free surface; 5) at the initial stage of loading, tensile cracks account for a high proportion of all cracks found. When the load is 1.5 MPa, the proportion of shear cracks increases to 28%, and when the load is 1.6 Mpa, the proportion of shear cracks increases to 31%. Finally, the tensile-shear effect triggers the failure of the tunnel.

We utilize smoothed particle hydrodynamics (SPH), a Lagrangian particle-based continuum method, to study the initiation and propagation of shear bands or faults in geologic materials over large deformations. We show that SPH is able to capture the formation of shear bands naturally without needing to introduce a heterogeneity or “seed.” In an actively or passively loaded backfill behind a moving retaining wall, we show that shear bands crossing the surface are inclined at an orientation given by the Arthur angle, $$\varTheta _{\mathrm{A}}=45^{\circ } \pm (\psi +\phi )/4$$ , with respect to the principal stresses. Additionally, we conduct simulations to explore the fault propagation problem, where a blind fault in rigid basement rock propagates through an overlying weak layer to reach the surface. Our results demonstrate that the resulting shear band rotates as the blind fault progressively accumulates more slip, initially taking the orientation given by the Roscoe angle, $$\varTheta _{\mathrm{R}}=45^{\circ } \pm \psi /2$$ , then that of the Arthur angle, and lastly, that of the familiar Coulomb orientation, $$\varTheta _{\mathrm{C}}=45^{\circ } \pm \phi /2$$ , in both extensional and contractional setups. Finally, we also evaluate the validity of empirical solutions describing the shear band propagation path and consider the effect of different material parameters on the geometry of the resultant shear bands, as well as on displacement and deformation at the surface. Our results show that SPH deals well with external loadings such as those applied by a retaining wall, or those induced by tectonic movement like in the fault propagation problem.

The microstructure of rock is one of the most important factors that affect its mechanical behaviors. In order to study the effects of grain size on the strength and failure behaviors of granites, a breakable polygonal grain–based discrete-element model is developed to simulate the microstructure of rocks. In the model, mineral grain types, grain size distributions, and mineralogical composition are incorporated, and the intergranular and intragranular cracks are captured in the failure process. Using this method, six kinds of specimen with varying grain size are established, and the effects of grain size on peak strength, deformation properties, microcrack distributions, and macroscopic failure pattern are studied through conducting a series of compressive loading tests. The results indicate that rock strength is inversely proportional to the grain size, while a decreasing tendency in peak strain, an increasing tendency in Young’s modulus, and Poisson’s ratio with the grain size are observed. Meanwhile, an increase of grain size also results in a dramatic rise in crack initiation stress, ratios of shear cracks/intragranular cracks to generated total cracks. Under uniaxial compression tests, rocks consisted of small grains are trend to fracture with a single shear band, while rocks consisted of large grains are trend to fracture with an axial splitting. The failure pattern of rocks under high confining pressure is mainly double shear in a “X” fashion, and the width of fractures increases as the grain size increases. The proposed model provides a reliable method for investigating the influences of grain size on the rock mechanical behaviors in microscopic scale, and the results can be used to predict the macroscopic behaviors of brittle rocks.

The paper presents the results of laboratory studies of the influence of the physical properties of landfill soils on the stability of slopes, namely, the determination of mechanical properties – the angle of internal friction, specific adhesion, and the shear angle of experimental landslide blocks under conditions of different humidity, density and temperature; determination of physical properties – humidity, temperature and density on the fact of shear of the experimental blocks, taking into account the gradual increase in humidity. The results of laboratory tests are processed using the classical statistical method. This made it possible to confirm the reliability of the mathematical model, which includes the solution of individual tasks for assessing the physical properties of landfill soils, and the corresponding methodology developed on its basis for preventing emergencies associated with shear of landfill soils at potentially hazardous burial sites for solid domestic waste.

A structural study on the Adamawa Massif highlights the major structures (faults) of the shear zone as well as the igneous intrusion near Mayo Baleo. Through this study, a comparison on the use of gravity data from the EGM 2008 and terrestrial models was carried out on the basis of gridded gradient data obtained by applying the MAGMAP filtering algorithm on the Oasis Montaj software system. Using the gradients has an advantage in that they contain much information especially on geological structures. The resulting maxima have strong density contrasts, enabling them to be used as tools in explaining geological contacts. Gravimetric lineaments marked by the geometry of the peaks (elongated shape) and the igneous intrusion corresponding to the circular peak were detected on the horizontal gradient maps. Reconciliation with the geology, the slope map and satellite images justifies the presence of the Djohong-Ngaoundal-Dir-Tibati, Tibati-Banyo and Tignere-Banyo lineaments which indicate the underlying Foumban (extension), Tibati and Tchollire-Banyo faults respectively, comprising the shear system residing in the massif underlain by a gneiss-migmatite bedrock. The limitation on the use of gravity data from the EGM 2008 model is manifested through the Djohong lineament correlating with the large mylonitized feature trending NE-SW, defined as a steep relief (27° to 60°), separating the Mbere basin from the upper unit with about 358 m in height difference. This terrain is a small area of relief with morphological units adapted as in the case of the mountainous areas of the West to the use of gravity data from the EGM2008. The other lineaments that are part of the shear zone fault system are not elucidated because they correspond to deep mega structures that the EGM 2008 model resolution cannot attain at depth. The use of this model is suitable for studies of superficial structures which are associated with huge formations such as the volcanic dome of Mayo Baleo, an intrusion of young trachytes with steep slopes (27° to 60°) at an altitude of 2419 m.

Research subject.U-Pb zircon dating, as well as a petrological and geochemical study of pyroxene-amphibole-, pyroxeneamphibole- biotite- and biotite-bearing fenites from the Central Alkaline Band Ilmeno-Vishnevogorsky Complex.Methods.The age of zircons was determined by an ion mass spectrometer (SHRIMP II, Centre of Isotopic Research VSEGEI). The content of REE and trace elements was estimated by secondary ion mass spectrometer methods (CAMECA IMS-4F, Valiev Institute of Physics and Technology RAS).Results.The mineralogical and geochemical (U, Th, REE) features of zircons, as well as fenites, reflect their polygenic-polychronous nature. Most zircon crystals have a metastable matrix and are characterized by averaged REE contents between igneous and hydrothermal types. These crystals are distinguished from magmatic zircons by high LREE contents and low values of Ce anomalies, and from hydrothermal zircons – by differentiated REE distribution spectra. Three ages of zircon were established: 2066–1686 (PR1), 425–404 (S2) and 284–266 (P1) Ma. PR1 zircons reflect the primary features and the degree of changes in the fenite substrate. S2 zircons, limited only to the biotite- bearing fenite, correspond to the age of the miaskite formation process. The P1 zircons clearly reflect the metasomatic process of fenitization initiated by late shear deformations. The temperature of the phenitization processes (based on the Ti content in zircons) was estimated at 630–670°C for S2and ≤ 600°C for P1fenites, respectively.Conclusions.Central Alkaline Band fenites were formed by the metasomatic process of PR1 substrate fenitization in the late stage (P1) of shear strains, which are widely expressed in the Ilmeno-Vishnevogorsky Complex.

En-echelon fractures widely exist in natural rock masses. Although the formation and occurrence features of en-echelon fractures have been extensively studied by geologists, the anisotropic mechanical behavior caused by en-echelon fractures has received little attention. In this study, a set of idealized en-echelon fractures were prefabricated and subjected to direct shear tests. The influence of structural parameters (e.g., fracture angle and persistency) of en-echelon fractures on shear strength, friction and dilation behavior, shear failure structures, and acoustic emission response was comprehensively evaluated. The test results show that the shear of en-echelon fractures involves a cracking stage and a shear-slipping stage. These two stages can be quantitatively described by three shear strength indices and three dilation indices, which present varying degrees of anisotropy under different shear stages and boundary conditions. Also, various types of failure structures evolved from en-echelon fractures can be observed. They essentially depend on different crack types and coalescence patterns of rock bridges and greatly affect the friction and dilation characteristics in the shear-slipping stage. Based on the test results, the anisotropic micro-cracking mechanism was first discussed, and then an idealized vertical slope analysis was performed. Finally, some implications were discussed for the fault structures in field and the deep fault behavior.

This study presents a detailed reconstruction of the state of stress in the crust of the Japan Benioff zone that followed the Tohoku earthquake of March 11, 2011. The stress parameters were found using the method of cataclastic analysis applied to discontinuous displacements based on the identification of a homogeneous selection of earthquake mechanisms around a point of interest. The criteria used to make the selection rely on principles of plasticity theory as extended to cover the case of strain evolving in a cracked medium. The reconstruction used data on earthquake mechanisms from the NIED f-net catalog for the period of observation until June 1, 2018. An analysis of the patterns in the spatial stress distribution derived for six depth levels in the crust showed substantial changes in the state of stress observed in the aftershock area of the Tohoku earthquake in the upper lithospheric layers of the continental slope (0–30 km). The horizontal tensile stresses that appeared immediately after the earthquake are best observed in the uppermost crustal layer (0–10 km). As we go deeper into the earth, this state of stress becomes increasingly less representative. Estimates of the stress magnitudes based on a model of horizontal tension with pure shear showed that the change in the type of geodynamic regime in the upper crustal layer was accompanied by a large change in the level of shear stresses that are directed along the axis of the Benioff zone (the drop was about 90%) and a decrease in the level of maximum shear stresses by nearly 65% relative to its mean value. These results can be explained by a larger contribution into the change of the state of stress due to a quasi-homogeneous horizontal tension compared with that due to pure shear caused by the drop of tangential stresses in the Tohoku source.

Under the temperature range of 200–400 °C and the strain rate of 0.01~1s−1, the microstructure evolution of AZ31B Mg alloy under the new hot constrained compression method compared with single compression test was studied by means of uniaxial compression test and finite element simulation. The effects of strain rate, temperature and constraining material on the equivalent stress and strain, damage distribution, and deformation zone structure of AZ31B Mg alloy are discussed. Results show that, compared with single compression, the stress state and deformation degree of each zone of the specimen is different under the hot constrained compression method. The specimen with constrained compression produces a special deformation zone. Under the condition of constrained compression deformation with the same strain rate and temperature, the degree of structural deformation in each zone has a strong correlation with the ductility of the constrained material. In the macroscopic characteristics of each zone, this correlation is manifested as the increase of equivalent stress and strain, the decrease of the high damage value zone and the disappearance of shear cracking phenomenon. The high damage area at 200 °C has been reduced from 80% to 40%. In the microstructure characteristics of each zone, this correlation is also manifested in the increase of twins and recrystallized grains, and the enhancement of the uniformity of the structure. When the strain increases from 0.2 to 0.7 at 200°C-1s−1, the AZ31B Mg alloy in the HCC-Cu obtains a more uniform grain size distribution and the elongation to fracture increases from 0.22 to 0.56.

A new shear design method for prestressed concrete beams was developed based on the compression zone failure mechanism. The design method uses a sectional design approach, as used in current design codes. In the method, the concrete shear contribution at each design section is assumed to be mainly provided by intact concrete of the compression zone and is determined based on the material failure criteria of concrete considering the compressive normal stress developed by both the prestressing force and flexural action. Design examples using the proposed method were undertaken and the results were compared with the predictions of current design codes. The proposed method was also applied to existing experimental data. The proposed method showed better strength predictions than various current design codes and predicted the strength variation according to main design parameters with reasonable accuracy.

The driving force of backarc extension remains a subject of debate. In this study, we investigate the Kalaqin metamorphic core complex (MCC) in the eastern North China Craton, to determine the driving mechanism of backarc extension related to subduction of the Paleo–Pacific Plate. The MCC records two phases of extensional structures. D1 structures include the NE–SW–striking Louzidian–Dachengzi and Jinshan–Meilin detachment shear zones on both sides of the core complex. These zones originally constituted a single NE–dipping, low–angle, normal–sense detachment shear zone that records deformation temperatures of 500–600 °C. The shear zone seprarted rifted upper crust from locally deformed middle–lower crust. Together, the D1 structures constitute a Cordillera–type MCC associated with magmatism. The MCC was then overprinted by a second phase of extension (D2) that produced a NE–SW–trending horst between rift basins. The interior of the horst was deformed by early normal shear belts and later normal faults, all striking NE–SW. Our U–Pb zricon dating results from deformed and undeformed igneous rocks, together with previous geochronolical data, constrain D1 at 156–150 Ma (Late Jurassic) and D2 at 135–100 Ma (Early Cretaceous). Kinematic and fault–slip data show an evolution from D1 trench–parallel to D2 trench–perpendicular extension with respect to subduction of the Paleo–Pacific Plate. The D1 trench–parallel, NE–SW extension is considered to have resulted from both west–northwestward subduction of the Paleo–Pacific Plate and southward subduction of the Mongol–Okhotsk Oceanic lithosphere, whereas the D2 trench–perpendicular, NW–SE extension took place after closure of the Mongol–Okhotsk Ocean and is ascribed to the subduction of the Paleo–Pacific Plate only.

The proposed site of the Diamer Bhasha Dam in northern Pakistan is situated in an active tectonic zone with intensive seismicity, which makes it necessary for seismic hazard analysis (SHA). Deterministic and probabilistic approaches have been used for SHA of the dam site. The Main Mantle Thrust (MMT), Main Karakaram Thrust (MKT), Raikot-Sassi Fault (RKSF) and Kohistan Fault (KF) have been considered as major seismic sources, all of which can create maximum ground shaking with maximum potential earthquake (MPE). Deterministically estimated MPE for magnitudes of 7.8, 7.7, 7.6, and 7.1 can be produced from MMT, MKT, RKSF and KF, respectively. The corresponding peak ground accelerations (PGA) of 0.07, 0.11, 0.13 and 0.05 g can also be generated from these earthquakes, respectively. The deterministic analysis predicts a so-called floating earthquake as a MPE of magnitude = 7.1 as close as 10 km away from the site. The corresponding PGA was computed as 0.38 g for a maximum design earthquake at the project site. However, the probabilistic analysis revealed that the PGA with 50% probability of exceedance in 100 years is 0.18 g. Thus, this PGA value related to the operational basis earthquake (OBE) is suggested for the design of this project with shear wave velocity (Vs30) equal to 760 m/s under dense soil and soft rock conditions.

The complexity in the shear behaviour of reinforced concrete (RC) beams increases with a decrease in the shear span to effective depth ratio (av/d) because of the increase in the contribution of concrete to the shear resistance of beams. Various models (e.g. numerical models and strut and tie models) for estimating the shear capacity of non-slender RC beams are proposed in the literature, with each having advantages and limitations. In this work, two simpler mechanics-based shear capacity models were considered, one for beams with 1 ≤ av/d v/d v/d range. Knowing the probability density function of the shear capacity and the mean and standard deviation of the shear capacity obtained using a first-order approximation, a characteristic shear capacity equation (Equation 5) is proposed for the design of beams with 1 ≤ av/d v/d

Stress fluctuations caused by stick-slip instabilities are frequently encountered in laboratory shear testings of granular materials. It is not common to observe stick-slips in angular-shaped granular assemblies, although rounded particles are more prone to this type of behaviour. This paper specifically concerns the deviatoric stress fluctuations in the shearing of coarse angular glass granules. A systematic experimental program comprising triaxial compression tests was realized to investigate the effects of particle size, confining pressure, and strain rate on the stick-slip mechanism. Particle size effect was examined by adopting three separate size distributions. In order to understand the influences of testing conditions on the stress fluctuations, the specimens were tested under four different confining pressures and by applying two distinct strain rates. The results showed that both the particle size and confining pressure greatly affected the stress fluctuations whereas the influence of strain rate was unclear.

Earthquake action is multi-dimensional and random. The anti-seismic capability of beam–column joints in reinforced concrete (RC) frame structures under arbitrary horizontal direction loading may be lower than the design capability for unidirectional earthquake actions. To date, detailed calculation methods for the shear capability and shearing performance of joints in RC frames under arbitrary horizontal direction loading have not been reported. For this reason, in this work, the shear mechanism of beam–column joints in an RC frame under arbitrary horizontal direction loading is analysed. This study shows that two oblique compression zones form at the corners of the joint when a synthetic shear force is imposed on the joint, and an oblique compression strut is formed in the core area of the joint, which is different from the shear mechanism of a joint under unidirectional loading. Furthermore, a shear capacity calculation model is established based on the strut-and-tie model. The predicted values of the shear capability in this work are in good agreement with the reported experimental results.

—The stress-strain state before theМ= 7.1 Ridgecrest earthquake in Southern California is analyzed based on spatiotemporal distribution of shear strains calculated in the geomechanical model within local ~100 × 100 km crustal segments at a depth of 3–7 km. In the epicentral zone of the earthquake, starting from three years before the event, a successive series of the time intervals, up to the occurrence of the earthquake, when shear deformations are completely absent and rocks are farthest from ultimate strength—the so-called quiescence zones—are established. The spatial distribution of shear strains in the vicinity of the epicentral zone is analyzed during the quiescence intervals and subsequent bursts of maximum amplitude in the epicentral zone itself. The time intervals of the bursts are called excursions. The successive emergence of maxima in shear strain amplitudes in the epicentral zone and surrounding medium during the excursions corresponds to the situation of a swing when the entire preparation region of a future earthquake is rocking up to the moment of event. Consistency of the obtained results with the existing theoretical models of earthquake preparation is discussed.

This study conducted microtremor testing along six survey lines that cross three typical earth fissures in the Datong basin to determine the dynamic response characteristics of earth fissure sites with regard to the Fourier amplitude spectrum, response spectrum, and Arias intensity. The results show the following. (1) The predominant frequency of an earth fissure site is mainly affected by the thickness and the shear wave velocity of the soil layer and is minimally effected by the presence of an earth fissure. (2) Earth fissures have a pronounced amplification effect on dynamic response. Fourier amplitude, response acceleration, and Arias intensity are high near an earth fissure and decrease with an increase in distance from the earth fissure, tending toward stability at a distance of 20 m. (3) The area that is seriously affected by this amplification is within 6–8 m of an earth fissure, and the general affected area is farther out than this, to a distance of 25 m. (4) New construction should be avoided in an area affected by the amplification, and existing buildings in general and seriously affected areas need to be reinforced to increase their seismic fortification intensity.

This study aims to develop a shear strength model for steel-fibre-reinforced prestressed concrete (SFR-PSC) beams. A dual potential capacity model was adopted to consider the shear-resistant mechanisms of the compression and cracked tension zones at the critical section, and its formulations were modified to address the synergistic effect of prestressing and steel fibres. In the proposed model, the shear demands to be resisted by the cracked tension and intact compression zones, respectively, were estimated based on the equilibrium conditions, and their corresponding potential shear capacity curves were also defined. It is assumed in the proposed method that the shear strength of an SFR-PSC member is dominated by a specific shear-resistance mechanism whose shear demand curve reaches the limit state (i.e. corresponding potential shear capacity curve) earlier than another one. To verify the proposed method, experimental results collected from the literature were compared with those estimated by the proposed model.

Book Chapter in Insights of Geosciences for hazards and education Editor: Florina Chitea ISBN –print 9788-606-537-563-5 ISBN –e-book 9788-606-537-564-2

Geothermal and volcanic areas are prone to earthquake triggering1,2. The Coso geothermal field in California lies just north of the surface ruptures driven by the 2019 Ridgecrest earthquake (moment magnitude Mw = 7.1), in an area where changes in coseismic stress should have triggered aftershocks3,4. However, no aftershocks were observed there4. Here we show that 30 years of geothermal heat production at Coso depleted shear stresses within the geothermal reservoir. Thermal contraction of the reservoir initially induced substantial seismicity, as observed in the Coso geothermal reservoir, but subsequently depleted the stress available to drive the aftershocks during the Ridgecrest sequence. This destressing changed the faulting style of the reservoir and impeded aftershock triggering. Although unlikely to have been the case for the Ridgecrest earthquake, such a destressed zone could, in principle, impede the propagation of a large earthquake. Thirty years of geothermal heat production at Coso in California depleted shear stresses within the geothermal reservoir, which changed its faulting style and inhibited aftershocks from the 2019 Ridgecrest earthquake.

The support system of “the top protection layer and remained pillar” left by gypsum mine easily loses its bearing capacity due to the water-weakening effect, contributing to the geological disasters. In this paper, uniaxial compression tests are carried out to estimate the evolution of mechanical properties with the change of immersion time for gypsum rock. The results show that the uniaxial compressive strength and tensile strength decrease gradually with the increase of immersion time. After that, the energy evolution law of gypsum rock with different immersion time under one-dimensional loading is explored, proving that the input energy, elastic energy, and dissipative energy decrease totally with the immersion time. A damage constitutive model based on the energy dissipation is used to describe the damage characteristics of gypsum rock subjected to the water-weakening effect and uniaxial loading, and the model is verified to be in good agreement with the experiment results. The influence of water immersion on the failure of gypsum rock is discussed from the mesoscopic and macroscopic perspectives, which shows that the meso defects in the rock develop gradually; however, the macro failure has a transition process of “shear to split, and finally to the mix of shear and split”. It can be reached a conjecture by the analysis of experiment results and of previous studies that the water–rock weakening mechanism of gypsum rock may include the special hydrophilic effect of calcium sulfate dihydrate molecular structure, the micro-dynamic response caused by the change of pore water content, and the swelling effect of water-absorbing minerals. This paper has specific research and reference value to understand the damage evolution characteristics of rock under water–rock interaction.

Compression shear failure of rock is a common failure mode in engineering, and there are often complicated seepage phenomena in its shear crack. Due to the anisotropic and irregular rough cross-section on both sides of the natural crack, the experimental study of rock seepage is difficult to operate. In order to study the microscopic seepage characteristics of rock cracks, granite crack specimens were prepared through shear experiments. The data was obtained by scanning the section with laser and imported into MATLAB software to reconstruct the three-dimensional section and crack opening model. In view of the difficulty of observing the microscopic characteristics of rock seepage flow, in this paper, the Reynolds equation of rock fracture flow considering the dynamic effect of boundary is derived, and under the condition of the definition of Reynolds equation theory, based on the advantage of fractal geometry for irregular cross-section, the relationship between flow velocity, permeability and simulation scale is studied by using COMSOL simulation software. The results show that the granite cross-section has a good statistical self-similarity feature, and the fractal matrix mesh covering the fracture surface can well express the feature of the fracture surface; The roughness of the fracture surface has a positive correlation with the fractal dimension. The larger the fractal dimension, the greater the roughness of the fracture surface, which verifies the reliability of the fractal dimension to describe the roughness of the section. There is a positive correlation between the scale-up of the simulation and the velocity of the micro-research points, and the permeability of the model; The feasibility of the fractal percolation model is investigated and the general suggestions for simulating scale are given. Some of the results of this study can be used for reference in the analysis of seepage characteristics of fractures in rough rock mass.

The anchor prestress loss is one of the main factors influencing the stability of deep anchored rock masses, and the shear damage law of prestressed anchored rock masses should be thoroughly studied. To examine the shear law of prestressed anchored jointed rock masses, stress–strain curves of jointed, anchored, and prestressed anchored jointed rock masses of different rock strengths were analysed through laboratory tests, constitutive models, and macroscale and microscale methods. The results reveal that with increasing specimen strength and anchorage mode, the specimen shear strength and tangential stiffness follow the order of prestressed anchored jointed rock mass > anchored jointed rock mass > jointed rock mass. The higher the strength of the rock mass specimen, the greater the resistance to shear deformation of the specimen under the coupling action of the prestressed anchor rod. The smaller the displacement, the greater the shear strength, that is, the smaller the rock. There is no obvious drop in the shear strength of the rock mass, while the drop in the larger rock mass strength curve is obvious. The jointed rock mass deformation mechanism is affected by bolt and prestress application; compared with jointed rock mass, the deformation and failure mechanism of prestressed anchorage jointed rock mass are more complex and changeable, and the prestressed anchored jointed rock mass failure process is mainly divided into elastic rise, yield, and plastic strengthening stages. According to microscopic analysis, the shear failure process is divided into three stages, pore compression, aggregation, and coalescence stages; the prestress to initial prestress ratio at different times is defined as a new damage variable, and the Gurson-Tvergaard-Needleman (GTN) model for mesoscale rock mass analysis is combined with the Weibull distribution of the loss theory to determine the loss and external prestress loss through testing and model fitting analysis. The model accuracy is verified. The method of assessing macro and microscale aspects is applied to accurately describe and qualitatively analyse the shear damage law of anchored jointed rock masses, providing a new research idea for rock mass damage studies.

As a common geological structure, rock joints have a great influence on the mechanical properties and stability of rock mass engineering. The shear constitutive model of the rock joint and its calculation methods have played an important role in theoretical and experimental research. Most of the existing elastic–plastic shear constitutive models of the rock joint are simplified to linear form or only considering hardening behavior, while the shear test results show that the post-peak nonlinear softening curve is the most common form for shear curves. Therefore, based on Barton shear strength criterion, the shear stress softening is characterized by the change of the post-peak joint roughness coefficient (JRC), and an increment elastic–plastic constitutive model reflecting the shear stress softening is established. According to the constraint condition of constant normal stress, the increment model of the normal deformation with shear deformation is obtained. Based on principle of the implicit return mapping algorithm, an algorithm for the shear softening elastic–plastic constitutive model in the stress space is established. The applicability and rationality of the model and algorithm are verified by a large number of the joint shear experiment results under different conditions. The established elastic–plastic constitutive model provides an effective reference for correctly evaluating the shear deformation characteristics of the joint.

An understanding of shear behavior of fractured rocks subjected to different durations of groundwater immersion is essential for practical rock engineering. Direct shear tests were conducted on fractured granite samples after different immersion durations of 1, 3, 6 and 12 months, and the initially dry granite fracture samples were also tested as reference. The results indicate that the peak shear strength, residual shear strength, shear stiffness and dilation at peak shear stress decreased with increasing immersion duration, while the peak shear displacement increased with increasing immersion duration. The shear induced reductions in fracture surface parameter (Z2) and the sheared-off volumes of asperities increased slightly with increasing immersion duration. An empirical function was proposed to successfully describe the evolutions of the shear parameters and the volume of sheared-off asperities with immersion duration. In addition, micro-scale tests including atomic force microscope, X-ray photoelectron spectra, nanoindentation and so on were conducted to reveal the underlying mechanism of immersion-induced weakening of granite fractures, which is attributed to the formation of a thin water layer attached on granite surfaces and the decreasing mechanical properties of asperities.

Aiming at the cyclic impact deformation and failure of tunnel surrounding rock under shear stress, a self-developed rotation-impact simulation test platform was used to determine the number of failures, stress-strain curves, and energy in the process of cyclic impact failure. The failure process of rock under different impact velocities and shear stresses has been systematically studied. Results show that, under the same impact speed, the shear stress will increase with the increase in the rotation speed, but an upper limit will exist. When the rotation speed reaches this upper limit, the shear stress will no longer increase. The presence of shear stress will reduce the number of impacts required for rock failure. When the impact speed is 7.2 m/s, the number of impacts at the maximum rotation speed is 60% of the static state. When the impact velocity is 16.8 m/s, this value is only 33.3%. At the same impact velocity, the stress-strain curves under different rotation speeds do not change significantly, but with the increase in the rotation speed, the slope of the elastic stage of the stress-strain curve gradually decreases, and the corresponding stress of the rock sample decreases when the maximum strain is reached. With the increase in shear stress, the crushing specific energy required for rock failure gradually decreases. The greater the impact velocity, the more obvious the impact of shear stress on energy dissipation. In the tunnel process, when the surrounding rock is subjected to impact loads from different directions, only the axial strain analysis will have certain safety hazards, and timely support and reinforcement work are required.

The formation of geological disasters, such as earthquakes and rock bursts, is a process similar to avalanches. These sudden disasters are closely related to a series of discontinuous cracks. In this study, the relationship between the damage process and the jerk phenomenon (sharp change in stress during loading) of rocks was revealed by evaluating the acoustic emission (AE) characteristics of sandstone under triaxial compression. The results show that most of the AE signals during the loading process were low-energy tensile signals. The aggregation and transfer of these low-energy signals could induce jerks. The proportion of high-energy shear signals was very low; however, the high-energy shear signals could induce the jerk phenomenon. Sandstone failure is a process of local failure and stress concentration transfer within the rock. The forms of gather and transfer are different at each loading step. Overall, the transfer law indicates that the damage area disperses to the edge of the sample and then concentrates to the center. The stress transfer and local damage of rocks are accompanied by a series of jerks. This study provides a better understanding of the rock failure process and provides theoretical support for the prevention and early warning of geological disasters.

The shear behavior of rock is markedly affected by the presence of water. To study the influence of water on the shear behaviors of rock, a series of direct shear tests were conducted on intact sandstone specimens with different water soaking durations (from dried to saturated) under three levels of normal stresses. Before direct shear tests were performed, water absorption experiments were conducted to guide the different levels of water saturation required for the direct shear tests. The influences of water on shear stress-shear strain responses and peak and residual shear strength envelopes were investigated. The results show that soaking duration significantly impairs the peak and residual shear strengths and other shear properties (e.g., cohesion, friction angle and shear stiffness). The reductions in fracture energy and friction coefficient and the chemical and corrosive deterioration are the main mechanisms for the decrease of intact sandstone’s shear strength. A novel observation is that the failure patterns of specimens are sensitive to different water distributions. The results provided in this study reveal that the stability of rock engineering is affected by changes in water levels.

A depletion of high-frequency ground motions on soil sites has been observed in recent large earthquakes and is often attributed to the nonlinear soil response. Here we show that the reduced amplitudes of high-frequency horizontal-to-vertical spectral ratios on soil can also be caused by a smooth crustal velocity model with low shear wave velocities underneath soil sites. We calculate near-fault ground motions using both 2-D dynamic rupture simulations and point-source models for both rock and soil sites. The 1-D velocity models used in the simulations are derived from empirical relationships between seismic wave velocities and depths in northern California. The simulations for soil sites feature lower shear wave velocities and thus larger Poisson’s ratios at shallow depths than those for rock sites. The lower shear wave velocities cause slower shallow rupture and smaller shallow slip, but both soil and rock simulations have similar rupture speeds and slip for the rest of the fault. However, the simulated near-fault ground motions on soil and rock sites have distinct features. Compared to ground motions on rock, horizontal ground acceleration on soil is only amplified at low frequencies, whereas vertical ground acceleration is deamplified for the whole frequency range. Thus, the horizontal-to-vertical spectral ratios on soil exhibit a depletion of high-frequency energy. The comparison between smooth and layered velocity models demonstrates that the smoothness of the velocity model plays a critical role in the contrasting behaviors of horizontal-to-vertical spectral ratios on soil and rock for different rupture styles and velocity profiles. Our results reveal the significant role of shallow crustal velocity structure in the generation of high-frequency ground motions on soil sites.

Ice rises and rumples, sites of localised ice-shelf grounding, modify ice-shelf flow by generating lateral and basal shear stresses, upstream compression, and downstream tension. Studies of pinning points typically quantify this role indirectly, through related metrics such as a buttressing number. Here, we quantify the dynamic effects of pinning points directly, by comparing model-simulated stress states in the Ross Ice Shelf (RIS) with and without a specific set of pinning points located downstream of the MacAyeal and Bindschadler ice streams (MacIS and BIS, respectively). Because ice properties are only known indirectly, the experiment is repeated with different realisations of the ice softness. While longitudinal stretching, and thus ice velocity, is smaller with the pinning points, flow resistance generated by other grounded features is also smaller. Conversely, flow resistance generated by other grounded features increases when the pinning points are absent, providing a non-local control on the net effect of the pinning points on ice-shelf flow. We find that an ice stream located directly upstream of the pinning points, MacIS, is less responsive to their removal than the obliquely oriented BIS. This response is due to zones of locally higher basal drag acting on MacIS, which may itself be a consequence of the coupled ice-shelf and ice-stream response to the pinning points. We also find that inversion of present-day flow and thickness for basal friction and ice softness, without feature-specific, a posteriori adjustment, leads to the incorrect representation of ice rumple morphology and an incorrect boundary condition at the ice base. Viewed from the perspective of change detection, we find that, following pinning point removal, the ice shelf undergoes an adjustment to a new steady state that involves an initial increase in ice speeds across the eastern ice shelf, followed by decaying flow speeds, as mass flux reduces thickness gradients in some areas and increases thickness gradients in others. Increases in ice-stream flow speeds persist with no further adjustment, even without sustained grounding-line retreat. Where pinning point effects are important, model tuning that respects their morphology is necessary to represent the system as a whole and inform interpretations of observed change.

Microstructures, including crystallographic fabric, within the margin of streaming ice can exert strong control on flow dynamics. To characterize a natural setting, we retrieved three cores, two of which reached bed, from the flank of Jarvis Glacier, eastern Alaska Range, Alaska. The core sites lie ~1 km downstream of the source, with abundant water present in the extracted cores and at the base of the glacier. All cores exhibit dipping layers, a combination of debris bands and bubble-free domains. Grain sizes coarsen on average approaching the lateral margin. Crystallographic orientations are more clustered and withc-axes closer to horizontal nearer the lateral margin. The measured fabric is sufficiently weak to induce little mechanical anisotropy, but the data suggest that despite the challenging conditions of warm ice, abundant water and a short flow distance, many aspects of the microstructure, including measurable crystallographic fabric, evolved in systematic ways.

Defects widely exist in rock masses, which have great impacts on the rock mechanical properties. The pre-existing fissures and holes are two common rock defects. In order to study the influence of hole shapes and fissure geometries on the failure modes and mechanical properties of rock masses, the derivatives of kernel functions in the traditional SPH method have been improved by introducing a fracture mark ξ, and a novel numerical method named improved kernel of smoothed particle hydrodynamics (IKSPH) has been developed to realize the simulations of rock fracture processes. The Monte Carlo method has also been introduced into the proposed method to realize the formations of random fissures. The small-scale numerical rock specimens with different hole shapes as well as random fissures are established. The crack propagation processes, the failure modes and the mechanical properties under uniaxial compression are simulated, results show that: ‘Wing cracks’ initiate from the random fissures, whose locations and interaction modes differ according to the geometries of random fissures. For rectangle hole, the crack initiations mainly occur at the upper and lower edges as well as the corners; for circular hole, tensile cracks appear at the 6 and 12 o’clock directions, meanwhile, shear cracks initiate at the 5 and 7 o’clock direction after the tensile crack propagates to a certain extent; for trapezoid and triangle hole, crack initiations mostly appear at the corners of the hole; the length and quantity of pre-existing fissures have greater influences on the mechanical properties of rock masses than the hole shapes and fissure dip angles. The research results can provide guidance for the correct understandings of fractured rock mechanisms. Meanwhile, the proposed method can also provide references for the applications of SPH method into simulations of rock fracture mechanics. At the same time, future research focus should be put on the applications of IKSPH method into engineering practices and developing high-performance IKSPH programming.

Despite their frequent natural occurrence and engineering encounter, heterogeneous rock joints (rock joints with different lithological characters on both sides of the joint surface) have been studied much less systematically. To study the shear behavior and failure mechanism of bolted heterogeneous rock joints, laboratory tests were performed on the heterogeneous rock joints having different joint roughness coefficients (JRC) under different anchorage conditions. The results indicate that shear strength increases with the increase of JRC, showing exponential growth. Under the same roughness, the shear strengths of rock joints from large to small are fully grouted, end anchorage, and without anchorage. The mechanical characteristics of the bolt and joint are poorly matched under the end anchorage condition, which is easy to cause these two to be broken one by one. Under fully grouted, the extrusion force caused by the rock bolt will diffuse around the anchorage agent and will not cause partial continuous damage. The surface damage of heterogeneous rock joints increases with the increase of JRC and presents obvious heterogeneous characteristics. The shear dislocation between the blocks under shear load results in the interaction between the bolt and surrounding media. Under the action of shear force, the bolt body produced both axial and transverse deformation, which leads to breakage of anchorage agent and rock mass. Rock bolt has a significant impact on the shear behavior of the anchorage system, and the damage of the rock bolt to rock mass should be considered in rock engineering reinforcement design.

A micro-meso-scale model is proposed to predict shear deformation and strength of textile-reinforced composites, considering shear non-linearity, strain-rate dependent elastic and visco-plastic beh...

A numerical investigation utilizing the 3D displacement discontinuity method is performed to examine the stress perturbations and induced displacements near a weak fault with arbitrary orientations and dip, assuming zero shear stress and normal displacement. The in-situ stress field near the fault is taken as known and varied with depth. The modelling is constructed based on indirect boundary integral equations. In this work, the fault plane is first modelled as a rectangular plane with negligible thickness between the adjacent surfaces. The fault plane is then divided into numerous rectangular boundary elements with imposed shear singularities on the surface, which is normal to the fault plane to simulate a traction-free scenario. The numerical results of the total induced stresses and displacements are then compared to the existing solutions of a penny-shaped crack for validation purpose. With validated results, the paper moves on to the discussion of various factors that have impacts on the induced stress and displacements, including: aspect ratio which is defined by strike over dip; orientation of the strike on the horizontal ground surface; as well as dip. The boundary integration method with modification is also used to model an elliptical distribution of singularities with inner, corner, and edge elements to accommodate more complex shape of a discontinuity; small differences are observed. Cited as: Chai, Y., Yin, S. 3D displacement discontinuity analysis of in-situ stress perturbation near a weak fault. Advances in Geo-Energy Research, 2021, 5(3): 286-296, doi: 10.46690/ager.2021.03.05

In high-speed impact loading experiments, localized deformation is readily taken place, which may result in differences in assessment of strain, strain rate, and further related deformation behaviors of a material in high rate deformations. In this paper, double-notch shear experiments of pure iron specimens were carried out by an improved split Hopkinson pressure bar (SHPB) device with impact speed ranging 16-64 m/s. The development of shear localization and fracture in shear deformation of the specimens was captured by a high-speed camera. Microstructures of localized shear band (LSB) in the shear zone of the specimens at different strain rate were analyzed by metallographic microscope. The nominal strain and strain rate in the deformation zone and the strain and strain rate in LSB were calculated based on the video frames and metallographic photomicrographs. Fracture strains of the shear bands at different impact speed were obtained. Results show that the deformation process of the specimens at different impact speeds includes uniform deformation, localized formation, microscopic crack, and macroscopic fracture; the formation of the LSB results in the decrease of the effective width of the shear band and causes the strain and strain rate to increase rapidly comparing with the nominal strain and strain rate.

Sliding liquefaction is considered to be the cause of high-speed and long-distance sliding of some homogeneous loess landslides in western China. However, there is still a lack of necessary experimental research and analysis on the effects of sliding liquefaction on these landslides. In this work, the effects of sliding liquefaction on irrigation-induced, high-speed and long-distance loess landslides on the South Jingyang Tableland area in China are studied by performing large-scale ring shear tests and using the sled mode. The results are as follows. (1) There are two kinds of long-runout sliding modes of loess landslides on the South Jingyang Tableland: sliding along the terrace surface and sliding within the saturated terrace alluvium, which is associated with sliding liquefaction. Both sliding modes can lead to long-runout sliding. (2) There are some differences in the inclination of the sliding surface between the two sliding modes. Based on the inclination of the sliding surface, the corresponding sliding mode can be distinguished. (3) Under the two sliding modes, the large shear mechanical properties of the two-layer soil composed of loess and alluvial sandy silt show significant differences. The friction between the loess and dry terrace alluvium increases with increasing normal stress and shear rate, while the friction between the loess and saturated terrace alluvium presents the opposite trend. The results show that the sliding distances under different sliding modes present opposite trends with the change in sliding speed. (4) Based on the test results from the ring shear tests and the morphological characteristics of the sliding surface, the sliding mode and sliding distance of a loess landslide can be identified and predicted.

The composite liner system consisting of geomembrane (GMB) and geosynthetic clay liner (GCL) has been widely used in landfills. Although there have been a lot of studies on the monotonic shear behavior of GMB/GCL composite liner, the dynamic test data are still very limited and consequently, the dynamic shear mechanism is not clear. A series of displacement-controlled cyclic shear tests were conducted to study the shear behavior of GMB/GCL composite liner, including the shear stress versus horizontal displacement relationships, backbone curves, and shear strengths. Hysteretic loops in the shape of parallelogram were obtained and equivalent linear analyses revealed that the secant shear stiffness decreased and the damping ratio increased with the rise in loading cycles. According to the test results, it is generally acceptable to predict the dynamic peak strength of a GMB/GCL composite liner with its static strength envelope. Furthermore, the dynamic softening mechanism and rate-dependent shear stiffnesses were well described by the proposed equations, which also facilitate the accurate modeling of the cyclic shear behavior.

Aim of study: Most sprained lateral ankle ligaments heal uneventfully, but in some cases the ligament’s elastic function is not restored, leading to chronic ankle instability. Ultrasound shear wave elastography can be used to quantify the elasticity of musculoskeletal soft tissues; it may serve as a test of ankle ligament function during healing to potentially help differentiate normal from ineffective healing. The purpose of this study was to determine baseline shear wave velocity values for the lateral ankle ligaments in healthy male subjects, and to assess inter-observer reliability. Material and methods: Forty-six ankles in 23 healthy male subjects aged 20–40 years underwent shear wave elastography of the lateral ankle ligaments performed by two musculoskeletal radiologists. Each ligament was evaluated three times with the ankle relaxed by both examiners, and under stress by a single examiner. Mean shear wave velocity values were compared for each ligament by each examiner. Inter-observer agreement was evaluated. Results: The mean shear wave velocity at rest for the anterior talofibular ligament was 2.09 ± 0.3 (range 1.41–3.17); and for the calcaneofibular ligament 1.99 ± 0.36 (range 1.29–2.88). Good inter-observer agreement was found for the anterior talofibular ligament and calcaneofibular ligament shear wave velocity measurements with the ankle in resting position. There was a significant difference in mean shear wave velocities between rest and stressed conditions for both anterior talofibular ligament (2.09 m/s vs 3.21 m/s; p

The design of multi-storey buildings utilising timber frame walls with partial anchorage often requires an iterative process to calculate the shear capacity of the walls. Partial anchorage, in this instance, refers to the situation where a wall is connected to the underlying structure by fasteners distributed along the base of the wall and where tension forces between the studs and the base are not resisted by tie-down connections. The presented offset force model, evaluating the shear capacity of a single wall element, is a variation of the lower-bound plastic model developed by Källsner and Girhammar. The method allows for a separation of the individual wall height from the height of application of the resultant horizontal force, thereby significantly simplifying the calculation process.

Changes in soil fabric following liquefaction have been studied using various in situ methods that often return inconclusive or conflicting observations. The time–rate variation of stiffness, when observed, is usually not evaluated over significant periods of time, limiting investigations about aging in post-liquefaction regain of stiffness. Even more uncommon is the application of geophysical techniques to evaluate changes in shear wave velocity (V S) as a proxy for small-strain stiffness. This study uses controlled blasting to examine long-term post-liquefaction regain of stiffness following multiple blast events. The multi-channel analysis of surface waves (MASW) technique was used to observe changes in V S of aged deposits at a test site in South Carolina. Blast-induced liquefaction of the target liquefiable layer resulted in significant reduction to its initial small-strain stiffness owing to the destruction of the aged soil fabric. The time-rate variation in V S indicated that the initial small-strain stiffness was not re-established over many months following liquefaction. Following a second blast event, the small-strain stiffness reduced again, but recovered more quickly, similar to previously reported observations of young sand deposits. This study provides a significant basis for interpreting in situ body and surface wave measurements of aged and young sand deposits densified using blast liquefaction.

In discrete element method (DEM) simulations, multi-sphere (MS) clumped and convex particles are two main particle models that are used to study the mechanical behaviours of granular materials. Of interest is the evaluation of the effect of multiple contacts between clumped particles or single contacts between convex particles on the mechanical behaviours of granular materials. In this context, a series of drained triaxial compression tests were conducted on convex true (CT) ellipsoids and MS ellipsoids with aspect ratios (ARs) ranging from 1.0–2.0. The microscale results indicate that at a given AR, the critical friction angle φc changes with the particle type, whereas the peak friction angle φp is nearly independent of the particle type. The anisotropic analysis provides underlying mechanisms of the shear strength evolution from two perspectives. First, the anisotropies of granular materials are essential to shear strength as the deviatoric (q)-to-effective mean (p′) stress ratio can be expressed as the sum of the anisotropies, i.e., q / p ′ ≈ 0 .4 a c + 0 .4 a n + 0 .6 a t , where ac, an and at are the normal contact anisotropy, normal contact force anisotropy and tangential contact force anisotropy, respectively. For all samples, ac and an underpin the shear strength and are influenced by the particle type. The similar φp displayed by the CT and MS ellipsoids does not translate to similar an and ac but similar ac+an for the two particle types. In addition, owing to their larger ac+an, the CT ellipsoids have a higher φc than the MS ellipsoids. Second, there is a satisfactory linear relationship between q / p ′ and ac within strong and non-sliding (sn) contacts a c sn (i.e., q/p′ = k a c sn ), where k is the fitting parameter. Accordingly, in the peak state, the subtle difference in shear strength is attributed to the greater a c sn in the CT ellipsoids than in the MS ellipsoids that is counteracted by the smaller k. However, in the critical state, the greater difference in a c sn between the CT and MS ellipsoids is partially offset by the smaller difference in k, causing a higher φc in the CT ellipsoids than in the MS ellipsoids.

The influence of the number of freeze–thaw (F–T) cycles on the interface shear behaviour of a compacted marine clay (Leda clay)/smooth high-density polyethylene (HDPE) geomembrane is investigated in this paper. Shear tests are performed on samples subjected to various numbers of F–T cycles: zero, one, two, three, five and ten. The test results show that the interface shear strength of the Leda clay/smooth HDPE geomembrane is lower than that of Leda clay. The interface shear strength of the Leda clay/smooth HDPE geomembrane decreases with increasing number of F–T cycles. Furthermore, the interface shear friction angles of the Leda clay/smooth HDPE geomembrane are significantly reduced within the first three F–T cycles. The reduction in strength beyond the three F–T cycles is negligible. The total decrease in the shear strength of the samples that are not subjected to an F–T cycle compared to that of samples subjected to ten F–T cycles is 18·3, 17·6 and 13·6% under a vertical stress of 150, 250 and 350 kPa, respectively.

Pre-stack seismic inversion, well log analysis approach and empirical relations were adopted in this study to better estimate geomechanical properties of Ruby field with minimum error. The use of conventional well log empirical method alone to evaluate geomechanical properties in oil/gas fields sometimes becomes problematic. Geomechanical properties were divided into: elastic moduli [Young’s modulus, shear modulus, bulk modulus and Poisson ratio (PR)] and rock mechanical strength properties (closure stress ratio (CSR), brittleness (BRI) and compressibility). Four geomechanical earth models (CSR, BRI, Young’s modulus and PR) were generated from the inversion analysis to understand the distribution of rock strength properties across the field. The results deciphered high Young’s, shear and bulk modulus in the reservoir zone compared to the cap/seal rocks and a decrease in PR. This implies that, the cap/seal are more ductile and less compressible than the reservoir rocks, indicating that the reservoirs are highly brittle. CSR result reveals high in cap/seal indicating that the cap/seal rock are harder to fracture and has a greater chance to withstand higher compressive stress before failing as opposed to reservoir rocks. The inverted earth model shows that, Young’s modulus and brittleness increase toward the northeastern part of the field, while CSR and PR increase toward the southwestern part of the field. These results suggest that harder, stiffer, highly compressible and easily fractured rocks are found in the northern and eastern part of the field as opposed to the southern to western part of the field that is ductile.

A series of centrifuge model tests were carried out to investigate the performance of geosynthetic-encased stone columns (GESCs) supported embankment under undrained condition. The influence of stiffness of encasement, basal reinforcement and embankment loading on the deformation behavior of GESCs were also assessed. The centrifuge test results reveal that under undrained condition, compared to ordinary stone column (OSC) supported embankment, the settlement of column has reduced by 50% and 34% when columns were encased with high and low stiffness geogrids respectively. Moreover, under identical embankment loading condition, the stress concentration ratio has increased significantly upon inclusion of basal reinforcement in the GESCs supported embankment. In case of OSCs supported embankment, columns experiences bulging in the top portion, inward bending in the central portion and a noticeable shear at the bottom portion. However, when columns were encased with geogrid layer, bulging in the top portion was significantly reduced but the inward bending of columns were noticed. With the inclusion of basal reinforcement, bending curvature of columns increases thereby inducing higher settlement in columns and relatively lesser settlement in surrounding soil. The differential settlement between the encased column and the surrounding soil under embankment loading has been considerably reduced with the inclusion of basal reinforcement.

Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan’an gas field to conduct true tri-axial hydraulic fracturing experiments with water, liquid CO2 and supercritical CO2. CT scan was applied to analyze initiation and propagation laws of hydraulic fractures in carbonate rocks. The experiments show that supercritical CO2 has low viscosity, strong diffusivity and large filtration during fracturing, which is more liable to increase pore pressure of rocks around wellbore and decrease breakdown pressure of carbonate rocks. However, it would cost much more volume of supercritical CO2 than water to fracture rocks since the former increases the wellbore pressure more slowly during fracturing. For carbonate rocks with few natural fractures, tensional fractures are generated by fracturing with water and liquid CO2, and these fractures propagate along the maximum horizontal principal stress direction; while fracturing with supercritical CO2 can form shear fractures, whose morphology is rarely influenced by horizontal stress difference. Besides, the angle between propagation direction of these shear fractures near the wellbore and the maximum horizontal principal stress is 45°, and the fractures would gradually turn to propagate along the maximum horizontal principal stress when they extend to a certain distance from the wellbore, leading to an increase of fracture tortuosity compared with the former. For carbonate rocks with well-developed natural fractures, fracturing with fresh water is conducive to connect natural fractures with low approaching angle and form stepped fractures with simple morphology. The key to forming complex fractures after fracturing carbonate rocks is to connect the natural fractures with high approaching angle. It is easier for liquid CO2 with low viscosity to realize such connection. Multi-directional fractures with relatively complex morphology would be formed after fracturing with liquid CO2.