Principal Compressive Stress Research Articles

Anisotropic microplane constitutive model for coupling creep and damage in layered geomaterials such as gas or oil shale

An anisotropic constitutive model for coupling creep with damage of shale and other anisotropic geomaterials under complex loading paths is formulated. The material damage is described by a previously developed spherocylindrical microplane model, which can simulate not only the stress-induced incremental anisotropy but also the inherent material anisotropy. Like material damage, the creep must be expected to be anisotropic as well. The creep responses of shale with inherent transverse isotropy are first separately constructed for the loading by compressive principal stress oriented either (i) parallel or (ii) normal to the bedding planes, and (iii) for shear stress along the bedding planes produced by the differences of the bedding plane inclination angle. This leads to three elementary linear creep models, which are mathematically formulated based on a continuous retardation spectrum of generalized Kelvin chain. These three creep responses are combined with the spherocylindrical microplane model. This leads to a general anisotropic constitutive creep model for arbitrary three-dimensional applied loading and arbitrary loading path. To achieve high numerical efficiency, a fully explicit numerical algorithm for the microplane constitutive model and finite element analysis is then formulated. Short-time (two-day) creep tests of shale cylinders with multilevel deviatoric stress and various inclinations of bedding planes relative to the axial compressive load are conducted. The numerical simulations by the microplane model are compared with the results of laboratory creep tests. The comparisons demonstrate a linear dependence of creep on the stress and verify the applicability of the anisotropic microplane model for creep and damage. Extensions to multi-year time ranges are in principle possible but will necessitate further calibration and verification.

Hydrospheric modulation of stress and seismicity on shallow faults in southern Alaska

Shallow (≤40 km), low magnitude (M≥2.0) seismicity in southern Alaska is examined for seasonal variations during the annual hydrological cycle. The seismicity is declustered with a spatio-temporal epidemic type aftershock sequence model. The removal of aftershock sequences allows detailed investigation of seismicity rate changes as water, snow and ice loads modulate crustal stresses throughout the year. The GRACE surface loads are obtained from the JPL global land and ocean mass concentration blocks (mascon) solutions. The stress changes at a depth of 10 km are calculated using a 1D spherical layered Earth model. To evaluate the induced seasonal stresses of ∼10 kPa, we use >30 yr of earthquake focal mechanisms to constrain the tectonic background stress field orientation and assess the seasonal stress change with respect to the principal stress orientations. The background stress field is assumed to control the preferred orientation of faulting, and stress perturbations are expected to increase or decrease seismic activity on the faults. The number of excess earthquakes is calculated with respect to the background seismicity rates for discrete stress intervals. The results indicate a ∼25% increase in regional seismicity rates that correlate with a ∼3-month time lag following failure-encouraging annual mean-normal-stress, differential stress, and least principal compressive stress. No immediate earthquake rate variations are observed in this region-wide analysis. The correlation with a 3-month time lag suggests increased mobility of preexisting fluids at seismogenic depths is varying the pore pressure within fault zones to modulate the seismicity rates throughout the seasonal loading cycle.

Shear strength of RC beams with stirrups using an improved Eurocode 2 truss model with two variable-inclination compression struts

The shear strength of reinforced concrete beams with stirrups can be assessed with strut-and-tie models based on the truss analogy. The Eurocode 2 formulation exploits such a possibility with a variable-angle inclination of the compression struts that is determined through the lower-bound theorem of plasticity. This approach tends to underestimate the shear capacity of lightly shear-reinforced beams where the concrete contribution, which is neglected in this formulation, is more significant. Based on this consideration but adopting an identical theoretical framework without adding a concrete contribution explicitly, this paper presents an upgrade of the EC-2 truss model incorporating two variable-inclination compression struts, whose inclination angles are determined through equilibrium conditions and the theory of plasticity. In this model, the upper compression strut may have lower inclination than the lower compression strut, which is mechanically motivated by the increase of shear stresses observed in the upper portion of the beam, in the neighborhood of the crack tip, following the trend of the principal compressive stress direction. This improved truss model enables the construction of a wider class of statically admissible solutions compared to the EC-2 single-strut approach. Closed-form expressions are derived for a variant of this model in which the two compression struts extend equally for half of the inner lever arm, which allows a simple and compact formulation for practical design purposes. Based on comparison with the well-established ACI-DafStb databases including more than 200 tests, the proposed model leads to values of the shear strength that are in very good agreement with experimental results and more accurate than the values obtained from the EC-2 procedure, despite the relatively comparable simplicity.

The relationship between stress changes and strong earthquakes since 1900 around the Bayan Har block in northern Tibet, China

A 3D viscoelastic finite-element model of the Qinghai-Tibet Plateau, including the Bayan Har block, is established in this article. This model takes into consideration differences in the regional geological structure, the main active fault zone, the active tectonic block (hereafter referred to as a block) and boundary fault zone, the irregular topography and layered lithospheric structure, and the seismic velocity structure of the crust and mantle. Moreover, the present tectonic background stress field in the research area is reconstructed using the constraints of the observed values for the rate of crustal horizontal movement and the direction of maximum principal compressive stress. On these bases, the historical strong earthquake sequences with Ms ≥ 7 that have occurred around the Bayan Har block since 1900 AD are simulated. Based on the Coulomb failure stress and equivalent stress data, the relationships between stress evolution and strong earthquakes, the interactions between strong earthquakes are investigated. In addition, we have also explored the changes in stress on the Longmenshan fault zone before and after the 2008 Wenchuan earthquake, as well as the relationships between stress evolution and regional seismicity. The results show that the occurrence of strong earthquakes around the Bayan Har block may be related to the increase in the total stress in the source area. The influence of long-term tectonic stress loading on strong earthquakes cannot be ignored. The 2008 Wenchuan earthquake induced an increase in stress in the southern section of the Longmenshan fault zone, indicating that the 2008 Wenchuan earthquake has an obvious promoting effect on the 2013 Lushan earthquake. The seismicity of the Bayan Har block and its adjacent areas may be affected by the regional total stress state.

Investigation on shear strain of reinforced concrete membrane panels subjected to pure shear

Hsu recently conducted a shear test on nine reinforced concrete panel elements subjected to applying pure shear using a shear testing device. Modern truss models (i.e. modified compression field theory and a rotating angle softened truss model) are used to perform a complex nonlinear analysis through a trial and error method based on a double loop. This analysis is conducted by employing equilibrium conditions, compatibility conditions, and a ductile stress–strain relationship of a reinforced concrete membrane panel in a biaxial state. In this study, an effective algorithm that uses a revised Mohr compatibility method based on the failure criteria of struts and ties is proposed. This algorithm is used to improve the convergence rate in the analysis of shear history, which was performed in the experiment of Hsu. The result of the analysis indicates that the shear strain energy in a state of extended shear strain is influenced by the relationship between principal compressive stress and strain (crushing failure).

Experimental and Numerical Study into 3D Crack Growth from a Spherical Pore in Biaxial Compression

A series of specimens made from transparent casting resin, each with a spherical pore at the centre of specimen were tested in a polyaxial stress state with different stress ratios ($$ \sigma_{x} /\sigma_{y} $$) between the lateral (the intermediate principal stress, $$ \sigma_{x} $$) and the axial (the major principal stress, $$ \sigma_{y} $$) loads, and the minor principal stress ($$ \sigma_{z} $$ ) was equal to 0, i.e., biaxial compression. The experimental results revealed the dramatic influence of the intermediate principal stress on the mechanics of 3D crack growth from a spherical pore. In uniaxial compression, the initial spherical pore produces several differently oriented wing cracks which are relatively short, smaller than the pore diameter (referred to as wing crack wrapping). In biaxial compression even with relatively low intermediate principal stress, a large wing crack is formed growing to an extent sufficient to split the specimen. The threshold for the intermediate principal stress separating these two regimes of wing crack growth is found to be 8.5% of the major principal stress. The results obtained from finite element method modelling show that with the intermediate principal stress above this threshold the directions of most of the secondary principal stresses (tensile) along the lateral surface of the initial pore are roughly perpendicular to the intermediate principal compressive stress direction. For the intermediate principal stress below the threshold, the directions of the secondary principal tensile stresses near the lateral surface of the initial pore are distributed in radial directions with respect to the initial pore. Results of numerical modelling also show that when transition is made from spherical pore to oblate pores, this threshold increases.

Integrated Interpretation of Microseismic and Petroleum-Engineering Data for Comparison of Gas Production in Two Interfering Adjacent Wellpads in the Horn River Basin, Canada

SummaryWe present an integrated interpretation of microseismic, treatment, and production data from hydraulic-fracturing jobs carried out in two adjacent wellpads in the Horn River Basin, northeast British Columbia, Canada.We conclude that poor correlation coefficients (R2) in crossplots of normalized production rate vs. the product of stimulated reservoir volume (SRV) and porosity and total organic carbon (TOC) (SRV×ϕ×TOC) indicate pressure interference between wells or wellpads. Good correlation coefficients in the same crossplots indicate lack of interference.The SRV×ϕ×TOC product reflects the hydrocarbon pore SRV because there is a relationship between TOC and hydrocarbon saturation in shales (Lopez and Aguilera 2018). Our results suggest that natural-fracture networks have an important effect on well connectivity and on the spatial distribution of microseismic data. Connectivity between wellpads occurs through a network of pre-existing natural fractures, which are approximately perpendicular to the least principal compressive stress in the area.This conclusion is supported by data analysis from Wellpads I and II in the Horn River Basin. Wellpad I includes eight wells that were drilled and fractured in the Muskwa and Otter Park formations (four wells in each formation) in 2010. Wellpad II includes three wells drilled and fractured in 2011 in each of the three shale formations, Muskwa, Otter Park, and Evie. There is a 1-year interval between fracturing on the first and second wellpads.The data analysis includes evaluation of magnitudes, b-values, moment-tensor inversion (MTI), and the spatial and temporal distributions of three-component microseismic events recorded during more than 200 stages of fracturing by multiwell downhole arrays. We analyzed Gutenberg-Richter frequency/magnitude graphs for each fracturing stage, and with proper integration of b-values, fracture-complexity index (FCI), MTI information, and treatment data, we distinguished hydraulic-fracturing-related events and events associated with slip along the surface of natural fractures. The results are compared with 5- and 4-year gas-production data in Wellpads I and II, respectively.Identification of natural fractures and information about interactions between hydraulically fractured wells are both essential for optimal well placement and completion, reservoir characterization, SRV calculation, and reservoir simulation. This study presents a distinctive insight into the integrated interpretation of microseismic events and production data to identify the activation of natural fractures and interference between the hydraulically fractured wells. The methodology developed in this study is thus related to production engineering, but examines it from the point of view of microseismic data.

In situ stress states at KURT, an underground research laboratory in South Korea for the study of high-level radioactive waste disposal

The Korea Atomic Energy Research Institute Underground Research Tunnel (KURT) is an underground research laboratory in South Korea, built for investigations into the geological disposal of high-level radioactive waste. We characterize in situ stress states at KURT using data from a series of hydraulic fracturing (HF) tests and borehole image logs to depths of ~700 m in two boreholes. The tensile fractures induced by HF tests, plus several borehole stress indicators (e.g., drilling-induced tensile fractures and borehole breakouts) measured from image logs, consistently indicate an ESE–WNW oriented maximum horizontal principal compressive stress (SHmax). This site-scale SHmax orientation varies slightly from the regional-scale SHmax orientation, likely reflecting a local stress perturbation resulting from a fault network that traverses the site. Estimated magnitudes of the minimum horizontal principal compressive stress (Shmin), determined either from the shut-in pressures recorded during HF tests or from stress indicators on image logs, are comparable to the vertical stress, indicating that the stress regime at the KURT site straddles the boundary between strike-slip and reverse faulting. The depth-dependent trend in estimated SHmax magnitudes deviates at ~500 m depth, which we attribute to variations in the distribution of natural fractures in the granitic rock mass. This depth-dependent variation in SHmax magnitudes has implications for the slip stability of pre-existing fractures at the site. That is, at shallow depths, SHmax lies within the Coulomb stress limit for optimally oriented fractures and faults with a frictional coefficient of 0.6, whereas at greater depths, SHmax exceeds this limit, meaning that pre-existing fractures at shallow depth are more susceptible to slip reactivation. Our stress estimation results suggest that the site-scale stress state is strongly coupled with characteristics of natural fractures, emphasizing the importance of detailed geologic and stress data for subsurface utilization and its stability evaluation.

Stimulation of subchondral bone cyst healing by placement of a transcondylar screw in the equine medial femoral condyle

To predict the bone formation stimulus of a transcondylar screw across an equine subchondral bone cyst (SBC) in an equine medial femoral condyle (MFC). Finite element modeling (FEM) of an equine MFC with a 2 cm3 SBC under several transcondylar screw conditions. The right stifle of a yearling thoroughbred without stifle disease that had been euthanized for reasons unrelated to this study and donated to the University. The FEM was derived from computed tomography of a yearling thoroughbred and analyzed in ABAQUS v6.14. The transcondylar screw was modeled as a 4.5-mm stainless steel cylinder. The region of interest was the centrodistal MFC, and bone stimulus was calculated. The stimulus threshold for bone formation (BFT) was >60 MPa and is presented as the percentage of total bone surface area (BFA) and frontal plane maps. Principal compressive stress vectors were also determined. Tested variables were daily cycles, load, and screw compression and position. At 750 cycles and 900-N load, <3% of the BFA exceeded the BFT. Increases in BFA > BFT occurred proportionally with load, screw compression, and daily cycles (steps). Compressive stress was oriented vertically on the SBC surface without a screw but aligned with the long axis of well-placed lag screws. Screw placement through the void also increased the number and magnitude of compressive vectors. This model predicted that a transcondylar lag screw across an MFC SBC increased surface BFA stimulation and reoriented the compression vector. Increasing screw compression, load, and steps per day increased the bone formation stimulus. This study provides evidence that supports the use of a lag screw thorough an MFC SBC to promote bone formation.

State-of-the-art in nonlinear finite element modeling of isolated planar reinforced concrete walls

A number of finite element modeling approaches for reinforced concrete (RC) structural walls have recently become available for both research purposes and design applications. Five conceptually-different state-of-the-art finite element models for RC walls are described and evaluated in this paper, including models based on either a fixed-crack or a rotating-crack approach for simulating the biaxial behavior of concrete under plane-stress state, models characterized with either a single- or a multi-layered representation of the wall cross-section, and models with or without consideration of various individual failure mechanisms (e.g., buckling of reinforcement, out-of-plane instability). Modeling approaches were validated against experimental data obtained for five benchmark RC wall specimens, all with rectangular cross-sections, yet are differentiated by a range of salient response characteristics (e.g., aspect ratio, axial load, failure mechanism), in order to assess the capabilities of the models in representing the response of isolated planar walls under uni-directional lateral loading, as well as to identify future research directions. Results presented suggest that the models considered in this study can all capture the lateral load at yield and the peak lateral load capacity of the wall specimens with ±10% accuracy, while the initial stiffness and yield stiffness can be overestimated as much as 3.0 and 1.8 times, respectively. All models can capture nonlinear shear deformations and interaction between flexural and shear responses under cyclic loading, where the analytically-predicted flexural and shear deformations are within ±30% of the experimentally-measured values. Moderate differences between the predicted crack orientations and distributions are noted between the models, and the model results for the magnitudes of principal compressive stresses in concrete and the extent of stress localization are comparable. All models can capture the nonlinear distribution of vertical strains measured along the base of the walls, where the magnitudes of the predicted tensile and compressive strains are within ±50% of experimentally-measured strains for most models. Although some of the model formulations proved to be successful in capturing the experimentally-observed strength loss mechanisms for individual wall specimens, none of the models were capable of comprehensively simulating all of the strength degradation mechanisms observed during the tests.

Structure and emplacement of the Coastal Deccan tholeiitic dyke swarm in Goa, on the western Indian rifted margin

Mafic dyke swarms, when controlled by a regional stress field, are emplaced perpendicular to the minimum principal compressive stress direction. However, mafic dyke swarms may also exploit pre-existing structural fabric in their host rocks. Distinguishing between the two scenarios is important for correct geodynamic understanding of magmatic events. Continental flood basalt provinces such as the Deccan Traps of India represent huge fissure eruptions produced by swarms of mafic dykes. The Coastal dyke swarm of the Deccan, along the western Indian rifted margin, is one of its three major dyke swarms. We present a field study of the Goa dykes, part of the Coastal swarm. The dykes are typical dolerites and basalts exposed in Proterozoic-age basement; lava flows which these dykes may have once fed have been stripped away by erosion, though exposed in the Western Ghats escarpment ~ 100 km to the east. The Goa dyke swarm contains 60 dykes, some of which form larger multiple-injection dykes. The dykes are short compared to typical (kilometers or tens of kilometers long) dykes in flood basalt provinces such as the Deccan or Iceland, and range in length from ~ 15 to ~ 220 m and in thickness from 3 cm to 20 m. Most dykes are vertical and the others dip steeply in various directions. Their structural attributes and internal features (such as vesicular zones and columnar jointing) provide clues to the processes of magma flow and solidification in the dykes. Field measurements yield an average crustal dilation of 8% due to dyke emplacement. Calculations of magmatic overpressures and magma chamber depths generally yield unrealistic values owing to the low aspect ratios of the dykes. Based on comparisons between the dyke trends and the host rock joint trends, we consider that a few of the Goa dykes were emplaced along pre-existing fractures, but the orientations of the great majority of the dykes reflect contemporaneous stress fields. Based on crosscutting relationships, we infer that the regional minimum horizontal compressive stress (σ3) changed over time from a ~E-W orientation to a ~NE-SW orientation and finally to a ~N-S direction.

Episodic stress and fluid pressure cycling in subducting oceanic crust during slow slip

Slow slip events are part of a spectrum of aseismic processes that relieve tectonic stress on faults. Their spatial distribution in subduction zones has been linked to perturbations in fluid pressure within the megathrust shear zone and subducting oceanic crust. However, physical observations of temporal fluid pressure fluctuations through slow slip cycles remain elusive. Here, we use earthquake focal mechanisms recorded on an ocean-bottom seismic network to show that crustal stresses and fluid pressures within subducting oceanic crust evolve before and during slow slip events. Specifically, we observe that the retrieved stress ratio, which describes the relative magnitudes of the principal compressive stresses, systematically decreases before slow slip events in New Zealand’s northern Hikurangi subduction zone, and subsequently increases during the evolution of each slow slip event. We propose that these changes represent the accumulation and release of fluid pressure within overpressured subducting oceanic crust, the episodicity of which may influence the timing of slow slip event occurrence on subduction megathrusts. This work contributes an improved understanding of the physical driving forces underlying slow subduction earthquakes, and a potential means by which to monitor stress and fluid pressure accumulation in such regions. Stress cycling in subducting crust before and during slow slip events is due to accumulation and release of fluid pressure, according to analysis of small earthquakes in the Hikurangi subduction zone.

Extensional Structures in the Ophiolites from Cuba and China: New Constraints to Slowly‐Spreading Ancient Oceanic Lithosphere

AbstractA group of low‐angle normal faults developed in banded gabbro of Moa Ophiolite, Cuba. The dark gabbro was cut into puddings by several normal faults, while light gabbro was just swelling in layer thickness. In Hongliuhe ophiolite at eastern segment of South Tien Shan Suture Zone in China, the extensional deformation concentrates on fine cumulus gabbro which is typically mylonitized. Abundant structural features were discovered in HLH ophiolite such as S‐C foliation, C’ foliation, extensional crenulation cleavage, small toughness normal fault, low‐angle normal faults and high‐angle normal faults. According to the above tectonic phenomenon from the ophiolite belts in Cuba and China, we will get the conclusion: the maximum principal compressive stress (b1) is vertical to cumulus bedding, and the maximum tensile stress (b3) is paralleling to cumulus bedding. Considering of the above evidence, the extensional tectonic event should developed at mid‐ocean ridge. Due to seafloor spreading, the maximum tensile stress is paralleling to cumulus layer, and extensional tectonic is kept in cumulus gabbro. In this way, normal faults developed in dark gabbro, while brittle‐ductile extensional developed in light gabbro. A large number of domes, folds paralleling to ocean ridge and detachment faults represented by low angle normal fault were discovered near ocean ridge in Indian Ocean and Atlantic Ocean. In this way, materials from deep oceanic lithosphere (e.g. gabbro, mantle peridotite) outcrop at the crust surface of ocean basin. The above evidences from China and Cuba are consistent with extensional tectonic and metamorphic core complex from slowly and super‐slowly spreading Indian Ocean and Atlantic Oceanic lithosphere based on ODP. Therefore, extensional deformation in the ophiolite belt is of significant meaning for clarifying the formation process and mechanism of ancient oceanic basin.

Seismicity evaluation of Mongton area of Salween in Myanmar

The area of Mongton is located in the central part of main stream of Salween. There has a straight-line distance of 200 km to the border of China’s Yunnan Province and 90 km to the border of Chiang Mai Province of Thailand. There are two earthquake concentrating regions of destructive earthquakes within this area. It reflects the collision between the Indian plate and the Eurasian plate. The main regional seismic activity characteristics are summarized as follows in accordance with the spatial-temporal distribution characteristics of the seismic activity and the estimated future seismic trend of the area under analysis: (1) There are 132 times of destructive earthquake occurrences of M ≥ 4.7 that occurred ever since the record within this area. There are 2915 modern small earthquakes of 4.6 ≥ M ≥ 2.0 being recorded within this area totally since 1966. (2) Orientation of axis P of the maximum principal compressive stress of the regional focal mechanism solutions is mainly distributed in the angular domain in the direction of NNE–NE–NEE and under the horizontal action, which indicates that the distribution of the tectonic stress fields within the area is very complicated with the spreading of the earthquake fracture planes displaying a characteristic multi-directionality. (3) This area is located at the intersection of the Himalayan Seismic Belt and the Southwestern Yunnan Seismic Belt; the seismic activities involved display an obvious alternate quiescence and active phenomenon. It will experience a strong seismic activity level similar to that of the previous 100 years in the future 100 years. Large earthquakes are likely to occur within this area.

Stress field modelling of the Late Oligocene tectonic inversion in the Liaodong Bay Subbasin, Bohai Bay Basin (northern China): Implications for geodynamics and petroleum accumulation

The Liaodong Bay Subbasin (LDBS), Bohai Bay Basin, is one of the most petroliferous basins in China. The basin experienced a strong tectonic inversion in the Late Oligocene, which has been proven to have had a major influence on petroleum accumulation. However, the dynamic origin of this tectonic event is poorly understood. In this paper, we present a finite element-based dynamic modelling study of the Late Oligocene tectonic inversion in the basin based on geological, geophysical and geomorphological data with different boundary conditions. We compared the modelling results with actual geological data and concluded that the NE-SW-directed compression model (labelled with BC-1) is the preferred model, suggesting that the effects of the India-Eurasia collision were the main cause of the Late Oligocene tectonic inversion. The results suggested that the maximum horizontal principal compressive stress direction (σHmax) generally trends EN E-W SW in the whole basin. The majority of the basin features a strike-slip faulting stress regime; the normal fault regimes are limited to the major faults, and the thrust faulting regimes are present only in the northern area of the Liaodong Uplift and Liaozhong Depression. The predicted fault slip rates occurring along the LZ1 fault in the Liaozhong area are significantly higher than those in the Liaoxi and Liaodong areas. Two high shear strain rates belts are present along the major faults in the Liaoxi and Liaozhong areas, indicating that the major faults accommodated the majority of the strain rates. This tectonic inversion play a significant positive role in the accumulation of petroleum in the basin due to the favourable relationship among the high strain rates, the formation of inversion-related traps and the timing of hydrocarbon charging. The high strain rate belts are suggested as the preferred targets for oil and gas exploration.

Biomechanical comparison of implant inclinations and load times with the all-on-4 treatment concept: a three-dimensional finite element analysis

The purpose of this study was to compare the effects of implant inclinations and load times on stress distributions in the peri-implant bone based on immediate- and delayed-loading models. Four 3D FEA models with different inclination angle of the posterior implants (0°, 15°, 30°, 45°) were constructed. A static load of 150 N in the multivectoral direction was applied unilaterally to the cantilever region. The stress distributions in the peri-implant bone were evaluated before and after osseointegration. The principal tensile stress (σmax), mean principal tensile stress (σmax), principal compressive stress (σmin) and mean principal compressive stress (σmin) of the bone and micromotion at the contact interface between the bone and implants were calculated. In all the models, peak principal stresses occurred in the bone surrounding the left tilted implant. The highest σmax and σmin were all observed in the 0° model for both immediate- and delayed-loading models. And the 0° and 15° models showed higher σmax and σmin values. The 0°models showed the largest micromotion. The observed stress distribution was better in the 30° and 45° models than in the 0° and 15° models.

Stress Response and Damage Characteristics of Local Members of a Structure due to Tunnel Blasting Vibrations Based on the High‐Order Local Modal Analysis

Damage characteristics and dynamic stress response of aging masonry structures for blast‐induced ground motion were performed using high‐order local modal analysis method. A complete investigation of damage types and locations of aging masonry buildings due to tunnel blasting vibration were performed by on‐site survey. A typical 2‐storey aging masonry building located above a tunnel was selected for dynamic response analysis. The experimental dynamic characteristics of the structure were determined by using the operational modal analysis (OMA) method. Finite element models for the masonry structures were updated by modifying material parameters based on OMA results. The first five natural frequencies of the updated finite element models ranged from 8.80–24.99 Hz, and the first five modes were global modes. The sixth to twentieth natural frequencies ranged from 26.10–36.34 Hz, and the sixth to twentieth modes were local modes whose deformation was greater than the global deformation. Since the principal frequencies of the tunnel blast vibration were mostly higher than the natural global modes’ frequencies and were much closer to the natural frequencies of local members, local members experienced more intensive vibrations compared to the main body structure. The principal compressive stress (PCS) and principal tensile stress (PTS) of local members were several times greater than that of the main body structure. Therefore, local members of the masonry building suffered most from the tunnel blasting vibration. Corners due to stress concentration, the contact area between brick and concrete, local members, and precast floor seams are prone to damage during tunnel blasting. With the vibration velocity increasing, the PCS and PTS of local members gradually increase. But, the PTS ratio of local members decreases with the increase of peak particle velocities. The dynamic response analysis result and the damage locations using high‐order local modal analysis method are in accordance with the damage found at the site.

Seismic-Moment Tensor of Earthquakes in Azerbaijan for 2012–2015

Abstract —Seismic-moment tensor solutions for earthquakes in Azerbaijan for 2012–2015 have been calculated with a new method by full waveform inversion of broadband data from modern digital seismic stations and processed statistically. The results are used to model main faulting elements in the region, to correlate the seismicity and fault patterns, and to compile a map of fault plane orientations for large events. The principal compression stress (P) directions are NW to SE in the Zaqatala area and N–S in the Sheki area but then gradually change clockwise toward NE–SW in the Caspian Sea. The directions of principal extension are mainly NE–SW and N–S within the zone where the Kura basin is subsiding beneath the Great Caucasus.

Wing Crack Propagation Simulation Using Scaled Boundary Finite Element Method

Considering the existence of side-face loads, a new scaled boundary finite element (SBFEM) shape function is used to study the problem of wing crack propagation. In the solution of crack contact, the contact interface constraint is introduced by Lagrange multiplier method. The polygon SBFEM remeshing technology is used to simulate the crack propagation problem with single and multiple wing crack. Compared with related experimental and numerical simulation results, the correctness and effectiveness of the new SBFEM shape function in solving the wing crack propagation are verified. It is found that under pressure, the wing crack propagates along the direction of the maximum principal compressive stress during initial expansion, and then the crack opens and gradually expands toward the pressure. Wing cracks only have contact phenomena on the initial crack surface during crack propagation. The contact force gradually decreases from the centre to the sides of the initial crack. The friction coefficient has a great influence on the crack propagation direction.

Strength of massive to moderately jointed hard rock masses

The Hoek-Brown (HB) failure criterion and the geological strength index (GSI) were developed for the estimation of rock mass strength in jointed and blocky ground where rock mass failure is dominated by sliding along open joints and rotation of rock blocks. In massive, veined and moderately jointed rock in which rock blocks cannot form without failure of intact rock, the approach to obtain HB parameters must be modified. Typical situations when these modifications are required include the design of pillars, excavation and cavern stability, strainburst potential assessment, and tunnel support in deep underground conditions (around σ1/σci > 0.15, where σ1 is the major principal compressive stress and σci is the unconfined compressive strength of the homogeneous rock) in hard brittle rocks with GSI ≥ 65. In this article, the strength of massive to moderately jointed hard rock masses is investigated, and an approach is presented to estimate the rock mass strength envelope using laboratory data from uniaxial and triaxial compressive strength tests without reliance on the HB-GSI equations. The data from tests on specimens obtained from massive to moderately jointed heterogeneous (veined) rock masses are used to obtain the rock and rock mass strengths at confining stress ranges that are relevant for deep tunnelling and mining; and a methodology is presented for this purpose from laboratory data alone. By directly obtaining the equivalent HB rock mass strength envelope for massive to moderately jointed rock from laboratory tests, the HB-GSI rock mass strength estimation approach is complemented for conditions where the GSI-equations are not applicable. Guidance is also provided on how to apply the proposed approach when laboratory test data are not or not yet available.