Failure Angle Research Articles

Strength of partially frozen sand under triaxial compression

To investigate the effect of the pore matrix (i.e., ice and unfrozen water) on the strength of partially frozen sand, a series of triaxial compression tests with internal pore water pressure (PWP) measurements were performed. Both dense and loose saline sand samples were prepared by rapidly freezing the samples and then slowly warming the samples to, and subsequently shearing at the temperature of −3 °C. Test results indicate the temperature only affects the effective cohesion, not the effective friction angle of sand. The pore ice stress was estimated using Ladanyi and Morel’s 1990 postulate on the internal stresses within frozen soil; the stress (hydrostatic) change in pore ice was reflected by an equal change in PWP in the partially frozen loose sand. Based on Ladanyi and Morel’s 1990 concept of internal confinement in frozen sand, a Mohr–Coulomb model that uses effective failure and residual friction angles from unfrozen sand to estimate the strength of partially frozen sand is presented. The proposed model reflects how the pore matrix contributes to the strength of partially frozen sand. For loose sand, the peak strength is enhanced by the internal confinement and cohesion resulting from the pore water (suction) and pore ice, respectively. For dense sand, only pore ice affects the peak strength by incorporating the internal confinement and cohesion.

Experimental study on the shear performance of an anchor cable with a C-shaped tube anchored flat structural plane

To analyse the influence of normal stress (σn) and steel tube strength on an anchor cable with a C-shaped tube (ACC), we selected Q235 steel tubes and Q345 steel tubes as representative ACCs and carried out double shear tests of ACC-reinforced jointed rock masses. Based on the test results, the influence of the steel tube strength on the ACC axial force and shear force under different normal stresses, the characteristics of the shear force-shear displacement curve of the anchored flat structural plane (FSP) in the rock mass, and the ACC failure mode and contribution to the anchored concrete surface shear strength were studied. The test results show that under 2 ~ 10 MPa of σn, the failure angle varies between 28° and 40° due to the bending of the ACC near the structural plane and increases with increasing σn. Compared with Q235-ACC, Q345-ACC contributes more to the shear strength of the structural plane and can better exert its axial force when resisting the lateral shearing action of the structural plane. Additionally, we proved that σn is a main factor affecting the shear stiffness of the structural plane and that the Q345 C-shaped tube effectively improves the shear stiffness of an ACC-reinforced jointed rock mass and can more fully mobilize the anchor cable during shearing ductility in the tangential direction compared to the performance of the Q235 C-shaped tube. The research results can provide a reference for the further application of ACCs to roadways.

Structural Strength Properties of Waste Textile Fiber Reinforced Cementitious Lightweight Composite Mortars

This study aims to investigate the utilization of recycled textile waste fiber (RTWF) as fiber reinforcement in cementitious lightweight composite mortars. The effect of RTWF percentage on cementitious lightweight composite mortar (CLCM) consistency, plastic and dry set density, splitting tensile and compressive strength was measured. In particular, the effect of RTWF percentage on the structural mechanical properties of hardened mortar was examined in detail. Mohr-Coulomb Failure Criterion was used to examine the structural strength properties of composite mortars. Failure angle, internal friction angle, normal and shear strength and cohesion of RTWF reinforced composite mortars were investigated. Three different types of fibers were used including cotton-polyester mixture (Type 1), only polyester (Type 2) and cotton-polyester-acrylic mixture (Type 3). Different percentages of fibers, i.e. 1%, 2%, 3%, 5% and 7%, were added to CLCM. Test results showed reduction in dry set densities compared with the control specimen. It has been determined that the use of 1 % fiber improves the mechanical properties of light mortars. On the other hand, decreasing trend was observed in compressive and splitting tensile strength of mortars with higher amount of fiber usage. When structural strength properties were considered, same trend was kept. However, this research work has unique value from an innovative perspective in terms of evaluation of structural strength parameters.

Finding the right place in Mohr circle space: Geologic evidence and implications for applying a non-linear failure criterion to fractured rock

The ability to relate patterns of brittle rock failure to stress conditions permits geologists to better understand the nature of rock deformation in natural geologic settings. In the field of structural geology, the relationship between shear and normal stress at the time of rock failure, a critical element of any failure criterion, is most commonly assumed to be linear in compressive stress environments. However, derivation and utilization of linear and non-linear failure criteria have been debated and variably invoked in past laboratory, field, and modeling-based analyses. In a study of fractured Jurassic Moab Tongue Member sandstone (Entrada Formation) bordering Arches National Park (Utah), we have documented field evidence for a system of shear fractures whose character and kinematics are best explained by a non-linear failure criterion. This field setting is distinguished by lateral subjacent juxtaposition of a salt-wall diapir (to the northeast) and the fractured sandstone (to the southwest). The shear fracture system reveals conjugate dihedral angles that systematically decrease northeastward reflecting decreasing critical differential stress magnitudes along a non-linear failure criterion, driven by a reduction in mean normal stress closer to the salt-sediment interface. These stress conditions are most likely associated with the mechanical response of the adjacent salt body to tectonic loading. Augmented by experimental rock failure testing, we provide novel field-based evidence that a non-linear failure criterion is most applicable in this natural geologic environment. We also present a pathway to gain insight into paleostress magnitudes utilizing observed failure angles and a geomechanically constrained non-linear failure criterion.

Experimental and Semitheoretical Analyses of Uplift Capacity of Belled Pile in Sand

Although belled piles have been widely applied to structures subjected to large horizontal loads, such as coastal structures, high chimneys, and transmission towers, their uplift capacity characteristics under various conditions have not been investigated in detail. In this study, model tests were performed in circular and half-circular chambers to determine the uplift capacity of belled piles in sandy ground under conditions such as relative density, penetration depth, and pile-tip inclination angle. Furthermore, image analysis was conducted by monitoring the model tests in a half-circular chamber to verify the shape of the failure surface. A semitheoretical model to predict the uplift capacity of belled piles in sandy ground was developed using the pile-tip failure angle and failure surface curve in accordance with the relative density, penetration depth, and pile-tip inclination angle based on the limit-equilibrium equation of a previous conventional pile. The values calculated using the proposed model were in good agreement with those obtained from experimental model tests.

FDEM numerical study on the mechanical characteristics and failure behavior of heterogeneous rock based on the Weibull distribution of mechanical parameters

Rock materials are typically heterogeneous. Traditional digital image processing (DIP) technology and the grain-based model (GBM) method are difficult to apply to engineering-scale problem studies, such as tunnel excavation. Based on the combined finite-discrete element method (FDEM), a random parameter assignment method is proposed to simulate the mechanical properties and failure behavior of heterogeneous rock. The elastic moduli of triangular elements, as well as the strength parameters of quadrilateral joint elements, assigned by this method obey a Weibull distribution. The simulation results of uniaxial compression, triaxial compression and Brazilian disc show that with the increase in the heterogeneity m value, the uniaxial compressive strength, elastic modulus, triaxial compressive strength, equivalent cohesion, equivalent internal friction angle and tensile strength all increase exponentially and approach those of the homogeneous rock sample. In addition, the heterogeneous rock samples mainly shear fail along their corresponding theoretical failure angle under uniaxial and triaxial compression. The simulation results of tunnel excavation indicate that for heterogeneous rock with different m values, the overall fracture morphology of the surrounding rock remains unchanged, and X-shaped conjugate shear failures mainly occur followed by a small amount of tensile failures, which are similar to the homogeneous surrounding rock. However, with the increase in the m value, the failure degree and the maximum fracture propagation range of the surrounding rock decrease exponentially. Moreover, the simulation results of uniaxial compression and tunnel excavation with different element sizes suggest that the random parameter assignment method proposed in this paper is reliable.

The Effect of Pore Pressure on the Mechanical Behavior of Coal with Burst Tendency at a Constant Effective Stress

The mechanical evolution of coal is evident when the pore pressure and the surrounding stress alone influence it. However, the evolution of the mechanical response of saturated coal under the coupling effect of pore pressure and confining pressure needs further investigation. This study identifies the mechanical behaviors of burst tendency dry and saturated coal under the stress condition where confining and pore pressure simultaneously increase but keep the constant difference by conducting a series of triaxial compressions on high burst tendency dry and saturated coal samples. The results show that the elastic modulus (E) and strength (σpeak) of dry coal increase from 3.4 to 4.8 GPa and 78.5 to 92.6 MPa, respectively, and the macro shear failure angle decreases from 64.2° to 56.5° when the confining pressure increases from 9 to 15 MPa. However, these parameters show the opposite evolution law when the pore pressure increases. Furthermore, the E and σpeak of saturated coal decrease from 3.84 to 2.75 GPa and 73.4 to 60.3 MPa, respectively, and the macro shear failure angle of saturated coal increases from 64.7° to 72.4° when the confining pressure and pore pressure increase simultaneously. The coefficient μ is proposed to reveal the evolution of strength at the effective confining pressure. Furthermore, the Mohr–Coulomb failure criterion, including μ, is ameliorated for application in coal under pore pressure conditions. In addition, a model was developed to reveal the effect of a pore-rich layer on the angle of macrocracks, which was confirmed by acoustic emission. The research reveals the mechanical behavior of coal under high pore pressure. Improved Mohr–Coulomb criterion criteria provide new guidance and vision for the analysis of coal instability in high pore pressure coal seams.

Progressive collapse performance of beam-column joint with WUF-B-RW connection after high temperature

This paper studied the progressive collapse resistance of 10 beam-column joints with post-high-temperature through static tests. The size of the ten specimens is the same, and the connection form is bolt-welded connection. Among them, one specimen was at room temperature, and the other nine specimens were treated at 400 °C, 600 °C, and 800 °C and held at the temperature for 30, 60, and 90 min, respectively. The load-displacement curve, deflection curves, and strain development of the critical section of the specimen were studied, and the axial force, bending moment, bending resistance, and catenary mechanism of the specimen were calculated according to the test results. Before and after high temperatures, the failure of specimens is beam-end damage. Temperature only affects the initial position of failure of beam-column joints. The duration time has no noticeable effect on the properties of the steel. Based on the test results, it is found that at the same duration time and different high temperatures, the higher the temperature, the smaller the maximum vertical load and joint rotation angle at failure, and their axial force and bending moment are also weaker. However, there is no difference between the plastic limit rotation angles of the specimens. At the same temperature and different duration, the load-displacement curves of the specimens are very similar. It can be seen that at the same temperature, the duration time has little effect on the mechanical properties of the specimen. At the same time, although the mechanical properties of the specimens were weakened after high temperatures, they still maintained an excellent ability to resist progressive collapse. Even the beam angle of the member with the smallest failure angle was 0.15 rad, more significant than 0.06 rad. The finite element model established by ABAQUS is mutually verified with the test results to prove the accuracy and effectiveness of the finite element model. Based on this model, the expanded parametric analysis is carried out to analyze the influence of hole spacing and hole diameter on the progressive collapse resistance of the specimen after high temperature.

Seismic failure behavior of masonry domes under strong ground motions

General stability and failure behaviors of masonry domes under static loads have been investigated extensively in literature. However, a few studies have been done on the seismic failure behavior of masonry domes under strong ground shaking. This study aims to investigate the seismic failure behaviors and failure angles of masonry domes with support system including drum and buttresses using advanced 3D nonlinear numerical simulations. Four types of masonry domes with thickness-to-span ratios t/R = 0.092, such as a dome with circular drum (Dome A), a dome with circular drum and buttress (Dome B), a dome with dodecagon drum (Dome C), a dome with dodecagon drum and buttress (Dome D), built on historical structures are selected. Three-dimensional solid finite element models of the selected masonry domes are created using isotropic continuum macro modelling technique with homogenized properties. The finite element models are utilized to simulate the seismic behaviors of the masonry domes under three different strong ground motion acceleration records matched according to the target response spectrum with a return period of 475 years in the Turkish Building Earthquake Code. The seismic failure behaviors of four masonry dome models are evaluated by comparing mode shapes, displacements, maximum principal stresses, damage propagation patterns and failure angles. It is determined that the average angle intervals of hoop tension failure regions of Dome A, Dome B, Dome C and Dome D models under strong ground motions vary between 39, 25, 35 and 26 degrees, respectively.

Effects of the embedding of cohesive zone model on the mesoscopic fracture behavior of Concrete: A case study of uniaxial tension and compression tests

The application of the Cohesive Zone Model (CZM) in concrete meso-mechanics solves the nonlinear problem of material crack tip well. At present, the application methods of CZM in concrete mesoscopic models include the bond mechanics characterization of the aggregate-mortar interface transition zone (ITZ) and the characterization of fracture characteristics between material micro-elements. From this, two different numerical models were derived—the combined Finite Discrete Element (FDEM) model and the Cohesive Finite Element (CFEM) model. To evaluate the difference between the two numerical models and the traditional Finite Element (FEM) model in simulating concrete mechanical behavior and crack propagation, a 3D concrete mesostructure modeling algorithm was developed in this study, including innovations in gravitational self-compacting of polyhedral aggregates. After that, the FDEM model and the CFEM model were successfully constructed based on the FEM model. Through uniaxial compression and tensile numerical simulations, it was found that the CFEM model is more in line with the theoretical and experimental mechanisms in the characterization of the static mechanical behavior and fracture process of concrete. The fracture failure angle variable defined by the CFEM model revealed that the compressed concrete material exhibited better strength and toughness due to a higher damage degree and more energy-consuming cracking mechanism. The above findings to a certain extent promote the future development of CZM in the field of concrete meso-mechanics.

Torsional behavior of ultra-high performance concrete (UHPC) rectangular beams without steel reinforcement: Experimental investigation and theoretical analysis

Steel fiber is the main reinforcing fiber of ultra-high performance concrete (UHPC) and could greatly improve its tensile strength and toughness. As a result, steel fiber has a significant influence on the structural behavior of UHPC beams under pure torsion. However, related research in this regard is severely insufficient. To fill in this research gap, this paper presents an extensive investigation to explore the effect of steel fiber property on the torsional performance of UHPC beams without steel reinforcement. A total of 8 UHPC rectangular specimens (including one control beam without steel fibers) were tested under pure torsion until failure. The variables in the specimens included the volume fraction, type, dimension and hybrid effect of steel fibers. The failure modes, torque versus angle of twist curves, torque versus strain curves and distribution of cracks for all specimens were acquired based on the torsion tests. Results show that the addition of steel fibers significantly increased the cracking and ultimate torques of UHPC beams, with maximum increases of 79 % and 159 %, respectively. The volume content, shape and dimension of steel fibers exhibited significant influence on the torsional performance of UHPC beams, including torsional capacity, ductility and cracking pattern. The shape and dimension of steel fibers both affected the post-cracking load-carrying capacity of UHPC beams. The cracking and ultimate torques of the two UHPC beams with hybrid steel fibers were higher than those containing single type of steel fiber, both exhibiting positive hybrid effects. Based on the experimental results of this study, the hybrid use of 1 % end-hooked and 1 % long straight steel fibers is recommended in UHPC beams by comprehensively considering the torsional performance and the cost. Finally, by fully considering the excellent tensile behavior of UHPC, theoretical formulas were proposed for calculating the cracking and ultimate torques of UHPC beams without steel reinforcement based on the Bredt thin-tube theory. Comparison between the experimental and theoretical results on 36 UHPC torsional beams demonstrated the feasibility of the proposed formulas.

Seismic pseudo-static active earth pressure of narrow c-φ soils on gravity walls under translational mode

This study utilises adaptive finite element analysis to investigate the failure mechanisms of narrow cohesive backfill under seismic conditions, and five classical failure modes are summarized. The pseudo-static solution is developed for the case when a narrow cohesive backfill is behind a gravity retaining wall and experiences seismic conditions. Our analytical solution uses the limit equilibrium method, Rankine's theory and the horizontal differential layer method. It considers the effect of soil cohesion, the interface friction angles, backfill geometries, seismic acceleration, the soil arching effect and the effect of shearing forces between adjacent elements on seismic active earth pressure. We propose a new approach that utilises the finite difference method to determine the tension crack depth of the narrow cohesive backfill, and an iterative calculation to determine the critical failure angle of the backfill wedge.

Study on hydraulic fracturing initiation model based on nonlinear constitutive equation

In this article, the nonlinear characteristics of rock deformation were characterized based on the Power-enhanced constitutive equation, and the piecewise nonlinear constitutive equation was established by using the piecewise approximation method. Based on the constitutive equation, an elastic-plastic stress field model around wells was established to analyze the stress field around wells during hydraulic fracturing. The initiation mode of elastic-plastic formation was analyzed and optimized. The results showed that the plastic yield of rock was determined by the in-situ stress field and the initial yield stress. The smaller the yield stress was, the greater the in-situ stress was, and the more easily the plastic yield occurred. Under the combined of rock mechanics parameters and in-situ stress, the tension failure occurred when the wellbore was under elastic state, and there were two failure modes of plastic tension failure and plastic shear failure after plastic state. The initiation directions of elastic tension, plastic tension, and plastic shear failure were the direction of maximum horizontal principal stress, while there was a failure angle between the fracture plane and the maximum horizontal principal stress under the shear failure.

Structural design of the composite blades for a marine ducted propeller based on a two-way fluid-structure interaction method

Compared to metal materials, fiber-reinforced composites have many advantages such as higher specific strength, higher specific stiffness, lighter weight, better damping performance, and better design ability. By reasonably choosing the material and arranging the stacking sequence, the directional stiffness properties of composite laminates can be tailored to match the actual needs. Hence, the effects of the laminate type on the performance of the composite ducted propeller in both hydrodynamic and structural are analyzed in this paper. The two-way fluid-structure interaction (FSI) method is applied to the composite ducted propeller, whose hydrodynamic performance is compared with the metallic one. The efficiency, deformation, stress, failure and pitch angle properties are compared with different laminate types under various working conditions. Moreover, a parameter optimization method is proposed to obtain the most suitable laminate type for the composite ducted propeller with the optimum hydrodynamic performance and structural properties. The research results can provide references for the design of composite ducted propellers.

Failure behavior and dynamic monitoring of floor crack structures under high confined water pressure in deep coal mining: A case study of Hebei, China

The coal mining process may make cracks in the floor to connect the confined aquifers, causing water inrush from the coal seam floor. Through the inclusion theory and compression failure criterion, the failure model of floor crack structures in deep mining is built by adding the additional water pressure. Under the compressive stresses, the additional water pressure in the cracks increases linearly as the mining-induced stress and the mining depth increase. As the confined water pressure rises, the failure strength of the floor crack structures decreases linearly, while the growth length increases nonlinearly. Yet, the failure strength first decreases and then increases as the angle of crack structures increases, and the dominant failure angles of crack structures in the floor range from 30 to 70°. Thus, the various dynamic monitoring technologies of crack structures, such as water-rich area detection, hydrological and micro-seismic monitoring, and failure depth exploration in the floor, are improved on the mining site. And these technologies are combined to establish a reliable early warning system for floor water inrush, and provide a safe guarantee for deep mining under high confined water pressure.

Mechanical characteristics and energy dissipation characteristics of dredged sand concrete during triaxial loading

During the service period, the concrete structures such as water gates, dams and concrete offshore platforms are often in a complex stress state such as triaxial loading. Therefore, it is very necessary to explore the force of concrete with different dredged sand contents under triaxial loading. In this paper, the failure modes of dredged sand concrete under different confining pressures were analyzed firstly. And then the mechanical property was explored. Finally, combined with CT technology, the three-dimensional structure of the fractured sample was reconstructed to realize the 3D visualization and the energy evolution mechanism of concrete triaxial monotonic compression under different confining pressures was explored. The results showed that the residual stress of concrete under triaxial cyclic loading was smaller than that under monotonic loading. According to Mohr-Coulomb failure criterion, the prediction failure angle of the sample is generally 66.1°–77.1°. With the increase of loading times, the energy loss developed more slowly, and the elastic modulus of loading and unloading decreased slightly. The calculation results of the parameterized constitutive equations of concrete under triaxial compression were in good agreement with the experimental results. Concrete was seriously damaged under the condition of low confining pressure and cyclic loading. Before the peak stress, the concrete samples mainly stored elastic energy.

Paper 12: Biomechanical Comparison of Anatomic Restoration of the Ulnar Footprint Versus Traditional Ulnar Tunnels in Ulnar Collateral Ligament Reconstruction

Objectives:Current techniques for ulnar collateral ligament (UCL) do not reproduce the anatomic ulnar footprint of the UCL. The purpose of this study was to describe a novel UCL reconstruction technique that utilizes proximal-to-distal ulnar bone tunnels to better recreate the anatomy of the UCL and compare the biomechanical profile at time zero between this technique, the native UCL, and the traditional docking technique. Our hypothesis was that the biomechanical profile of the anatomic technique is similar to the native UCL and traditional docking technique.Methods:Ten matched cadaveric elbows were potted with the forearm in neutral rotation. The palmaris longus tendon graft was harvested, and bones were sectioned 14 cm proximal and distal to the elbow joint. Specimen testing included: (1) native UCL testing performed at 90° flexion with 0.5 Nm valgus moment preload, (2) cyclic loading from 0.5-to-5 Nm valgus moment for 1000 cycles at 1 Hz, and (3) load to failure at 0.2 mm/s. Elbows then underwent UCL reconstruction with one elbow of each pair receiving the classic docking technique using either anatomic (proximal-to-distal) or traditional (anterior-to-posterior) tunnel locations. Specimen testing was then repeated, as described above.Results:There was no difference between maximum load at failure or valgus angle between the anatomic or traditional tunnel location techniques (34.90 ± 10.65 Nm vs. 37.28 ± 14.26 Nm, P = 0.644) or the native UCL (45.83 ± 17.03 Nm, P = 0.099). Additionally, there was no difference in valgus angle after 1000 cycles across the anatomic (4.58 ± 1.47°), traditional (4.08 ± 1.28°), or native UCL (4.07 ± 1.99°). Anatomic group and the native UCL had similar valgus angles at failure (24.13 ± 5.86° vs. 20.13 ± 5.70°, P = 0.083), while the traditional group had a higher valgus angle at failure compared to the native UCL (24.88 ± 6.18° vs. 19.44 ± 5.86°, P = 0.015).Conclusions:UCL reconstruction with the docking technique utilizing proximal-to-distal ulnar tunnels to restore the anatomic ulnar footprint better recreates the anatomy of the UCL while providing valgus stability comparable to reconstruction with docking technique using traditional anterior-to-posterior ulnar tunnel locations. These results suggest that utilization of the anatomic tunnel location in UCL reconstruction has similar biomechanical properties compared to the traditional method at the time of initial fixation (i.e., not accounting for healing following reconstruction in vivo) while keeping the ulnar tunnels further from the ulnar nerve. Further studies are warranted to determine if an anatomically based UCL reconstruction results in differing outcomes compared to traditional reconstruction techniques.

Respiratory failure and bioelectrical phase angle are independent predictors for long-term survival in acute heart failure

Background. The assessment of long-term mortality in acute decompensated heart failure (ADHF) is challenging. Respiratory failure and congestion play a fundamental role in risk stratification of ADHF patients. The aim of this study was to investigate the impact of arterial blood gases (ABG) and congestion on long-term mortality in patients with ADHF. Methods and results. We enrolled 252 patients with ADHF. Brain natriuretic peptide (BNP), blood urea nitrogen (BUN), phase angle as assessed by means of bioimpedance vector analysis, and ABG analysis were collected at admission. The endpoint was all-cause mortality. At a median follow-up of 447 d (interquartile range [IQR]: 248–667), 72 patients died 1–840 d (median 106, IQR: 29–233) after discharge. Respiratory failure types I and II were observed in 78 (19%) and 53 (20%) patients, respectively. The ROC analyses revealed that the cut-off points for predicting death were: BNP > 441 pg/mL, BUN > 1.67 mmol/L, partial pressure in oxygen (PaO2) ≤69.7 mmHg, and phase angle ≤4.9°. Taken together, these four variables proved to be good predictors for long-term mortality in ADHF (area under the curve [AUC] 0.78, 95% CI 0.72–0.78), thus explaining 60% of all deaths. A multiparametric score based on these variables was determined: each single-unit increase promoted a 2.2-fold augmentation of the risk for death (hazard ratio [HR] 2.2, 95% CI 1.8–2.8, p< .0001). Conclusions. A multiparametric approach based on measurements of BNP, BUN, PaO2, and phase angle is a reliable approach for long-term prediction of mortality risk in patients with ADHF.

Influence of screw head diameter on ex vivo fixation of equine lateral condylar fractures with 5.5 mm cortical screws.

To determine the influence of screw head diameter on equine condylar fracture fixation with 5.5 mm cortical screws. Ex vivo, biomechanical study, blinded, matched-pair design. Fifteen pairs of equine third metacarpal (MC3) bones. Lateral condylar fractures were simulated by parasagittal osteotomies and repaired pairwise by 2 × 5.5 mm cortical screws of 8 mm (standard) or 10 mm (modified) head diameter. Interfragmentary compression at maximum screw insertion torque was measured. The instrumented specimens were pairwise stratified for biomechanical testing under the following modalities (n=5): (1) screw insertion torque to failure, (2) quasi-static axial load to failure, and (3) cyclic axial load to 2 mm displacement followed by failure. Tests (1) and (2) were analyzed for yield, maximum, and failure torque/angle and load/displacement, respectively. Number of cycles to 2 mm displacement and failure was assessed from test (3). Maximum insertion torque was greater, and failure angle smaller, when constructs repaired with modified screws were tested (8.1 ± 0.5 vs. 7.4 ± 0.5Nm; P=.0047 and 550 ± 104 vs. 1130 ± 230; P=.008). Axial yield (7118 ± 707 vs. 5740 ± 2267 N; P=.043) and failure load (12 347 ± 3359 vs. 8695 ± 2277 N; P=.043) were greater for specimens repaired with modified screws. No difference was detected between constructs in the number of cycles to 2 mm displacement. Condylar MC3 osteotomies repaired with modified 5.5 mm cortical screws sustained greater maximal hand torque insertion, smaller insertion failure angle and 1.4 fold greater quasi-static failure forces than constructs repaired with standard 5.5 mm screws. Use of modified screws with larger heads may improve the fixation of condylar fractures in horses. These results provide evidence to justify clinical evaluation in horses undergoing fracture repair.

Active earth pressure against flexible retaining wall for finite soils under the drum deformation mode

A reasonable method is proposed to calculate the active earth pressure of finite soils based on the drum deformation mode of the flexible retaining wall close to the basement’s outer wall. The flexible retaining wall with cohesionless sand is studied, and the ultimate failure angle of finite soils close to the basement’s outer wall is obtained using the Coulomb theory. Soil arch theory is led to get the earth pressure coefficient in the subarea using the trace line of minor principal stress of circular arc after stress deflection. The soil layers at the top and bottom part of the retaining wall are restrained when the drum deformation occurs, and the soil layers are in a non-limit state. The linear relationship between the wall movement’s magnitude and the mobilization of the internal friction angle and the wall friction anger is presented. The level layer analysis method is modified to propose the resultant force of active earth pressure, the action point’s height, and the pressure distribution. Model tests are carried out to emulate the process of drum deformation and soil rupture with limited width. Through image analysis, it is found that the failure angle of soil within the limited width is larger than that of infinite soil. With the increase of the aspect ratio, the failure angle gradually reduces and tends to be constant. Compared with the test results, it is shown that the horizontal earth pressure reduces with the reduction of the aspect ratio within critical width, and the resultant force decreases with the increase of the limit state region under the same ratio. The middle part of the distribution curve is concave. The active earth pressure strength decreases less than Coulomb’s value, the upper and lower soil layers are in the non-limit state, and the active earth pressure strength is more than Coulomb’s value.