Lateral Support Research Articles

Growth faults and avalanches: Reconstructing Paleoarchean basins in the Pilbara and Kaapvaal cratons

Four new volcano-sedimentary complexes (VSC's), respectively c. 3510, 3460, 3430, and 3320 Ma old, are identified in the East Strelley, Coongan, and Kelly belts of the East Pilbara craton and compared with the extraordinarily complete c. 3450 Ma Buck Reef-VSC in the southern African Kaapvaal craton. The VSC’s reveal an intricate relationship between volcanic deposition, sedimentation, development of syndepositional fault arrays, both extensional and contractional, and magmatism. The geometry and kinematics of these fault systems were analyzed after restoring the tilt of the stratigraphic sequences back to the depositional horizontal. The growth fault arrays are interpreted to have been generated by lack of lateral support of depositional basin margin prisms as known from present-day deltas and passive margins. This ‘basin margin collapse’ scenario for deformation and kinematics of the topmost section of the crust relies on topographic relief combined with vertical crustal oscillation. The relationship between supracrustal collapse and coeval deformation on deeper-seated detachments within the basement of the Pilbara remains as yet unsolved.The restoration corroborates the (semi-)circular basin architecture we proposed in 2017, which preceded, and is unrelated to, the present-day configuration of granitoid complexes and greenstone belts. The new findings also assess an early, syndepositional presence of the east–west Warrawoona Lineament as a major dividing line of as yet unknown structural character between two areas of basin superposition.For the Coonterunah Subgroup a multistorey architecture is established: the Table Top/Coucal-VSC with its near-water level chert top is overlain by regularly bedded Double Bar Basalt. The ensemble is truncated by the newly introduced tectono-stratigraphic Bergamina Unit, interpreted as a mega-avalanche emplaced somewhere between 3496 and 3466 Ma, possibly time-equivalent to the Duffer Fm.The crustal depths of the detachments below the (water-level) tops of all VSC’s identified, in other words the thicknesses of the VSC’s, are used as proxy for determining minimum basin centre depths ranging from 1000 to 3800 m. The greatest depth was reached in the North and South Coongan Basins, where voluminous bimodal volcanism of the Duffer Fm, maximum subsidence and deposition rates resulted in maximum basin margin instability.

Dominant elastoplastic behavior of geocell-reinforced sand subjected to cyclic loading under large-scale triaxial tests

The beneficial effects of geocells on improving the soils' characteristics have always drawn researchers' attention. However, due to the geocell's large scale, more accurate analyses, such as large-scale cyclic laboratory tests, are still needed to determine the soil-geocell system's actual mechanism. In the present research, a series of large-scale triaxial tests are carried out on poorly graded sand samples with 30 cm diameter and 60 cm height reinforced by geocell with heights of 0.6, 1.0, and 1.4 of the pocket diameter and placement depths of 0.05, 0.15, 0.25, and 0.35 of the samples' height under static and cyclic loading conditions. Contrary to common opinion, the results obtained for unreinforced sands showed that the maximum bulge, instead of the middle, occurred at 0.25 of the sample's height from the top surface. Changing the bulging from the middle to the upper part reflects the role of the direction of stress applied and the accumulation of the deformation due to plastic behavior near the load position. On the one hand, the results of static tests revealed that placing geocell at this depth delivers the best performance in controlling the bulging and reducing settlement values due to the predominant lateral support to the sand particles, reducing the localized stress concentrations, increasing internal friction and interlocking, and reducing the likelihood of shear failure. On the other hand, the geocell with moderate height had higher wall rigidity and stability against deformations compared to the geocell with lower and higher height values due to higher soil confinement potential and more resistance against buckling, respectively. Cyclic loading was also performed on geocell-reinforced soils under 110 cycles with cumulative strains ranging from 0.13 to 0.155 %. The cumulative strains for the unreinforced and reinforced soils were 0.196 % and in the range of 0.130–0.154 %, respectively. The best geocell placement depth under cyclic loading mode was at 0.05 of the sample's height, which had a cumulative strain of 0.13 % in 110 cycles and reduced the cumulative strain by about 34 % compared to the unreinforced sample. The presence of geocell in the soil generally led to an increase in the shear modulus and a decrease in the slope of the damping ratio. Further, the shear modulus was reduced by increasing the geocell placement depth.

The speedup of Pine Island Ice Shelf between 2017 and 2020: revaluating the importance of ice damage

Abstract From 2017 to 2020, three significant calving events took place on Pine Island Glacier, West Antarctica. Ice-shelf velocities changed over this period and the calving events have been suggested as possible drivers. However, satellite observations also show significant changes in the areal extent of fracture zones, especially in the marginal areas responsible for providing lateral support to the ice shelf. Here, we conduct a model study to identify and quantify drivers of recent ice-flow changes of the Pine Island Ice Shelf. In agreement with recent studies, we find that the calving events caused significant velocity changes over the ice shelf. However, calving alone cannot explain observed velocity changes. Changes in the structural rigidity, i.e. ice damage, further significantly impacted ice flow. We suggest that ice damage evolution of the ice-shelf margins may have influenced recent calving events, and these two processes are linked.

Deformation Analysis and Optimization of Steel-Tube-Columns Combined-with-Bailey-Beams Doorway Support

As a commonly used support system in highway bridge construction, the deformation of steel-tube-columns-combined-with-Bailey-beams doorway supports is often an indicator for safety and quality control. In this paper, through finite element simulation and theoretical derivation, the main form of deformation of each part of the combined doorway is analyzed, by using the rigid body function of ANSYS. The study shows that when bearing vertical load, the deformation of the combined doorway is mainly caused by the deflection of the Bailey beams; when bearing transverse horizontal load, the deformation of the combined doorway is mainly caused by the rotation of the foundation; when bearing longitudinal horizontal load, the deformation of the combined doorway is mainly caused by the offset bending of the Bailey beams out of the plane. When several loads are applied to the combined doorway at the same time, the deformation in the linear phase follows the superposition principle, and the geometric nonlinearity has little effect on the overall deformation of the structure. The structural deformation caused by different types of loads can be calculated separately, and then the structural deformation under composite load can be calculated by linear superposition, using geometric relationships. The safety and deformation resistance of steel-tube-columns-combined-with-Bailey-beams doorway supports can be effectively improved by choosing reinforced Bailey beams, increasing the width of the foundation, and setting lateral supports between the Bailey beams.

Flexure Hinge Design and Optimization for Compact Anthropomorphic Grippers Made via Metal Additive Manufacturing

Abstract Flexure-based grippers offer an attractive alternative to conventional grippers used in robotics and automation. However, most existing designs appear to suffer from insufficient range of motion, loadability, and support stiffness. This article presents an approach to obtain well-performing flexure hinges for compact anthropomorphic grippers made via metal additive manufacturing. We propose a flexure hinge architecture that achieves a high range of motion despite the challenging combination of a small design space, high Young’s modulus, and limited minimum feature size. Furthermore, we present an optimization procedure to generate suitable tendon-driven designs with high loadability. Using this framework, a flexure hinge with an outer diameter of 21.5 mm and range of motion of ±30 deg is synthesized. For the range of 0–30 deg, simulations show a lateral loadability of 52.5–18.6 N and lateral support stiffness of 12,309–11,130 N/m, determined at a gripper interface located 41.2 mm from the hinge pivot axis. Experiments confirm a loadability of at least 15.4 N and determined a stiffness of 8982 to 9727 N/m for same conditions. The results show that the flexure hinge architecture has large potential for a wide range of applications, while in combination with the optimization procedure, superior designs for tendon-driven grippers can be obtained.

Deformation Characteristics of Pipelines Due to Adjacent Excavation in Riprap Reclamation Strata

The Shenzhen Ma Wan area has special geotechnical conditions, with more than 50% of the area being reclaimed rock formations. Riprap reclamation strata are particularly susceptible to significant deformation upon stress release. To comprehensively comprehend the reaction of existing pipelines to the excavation of an adjacent deep foundation pit within the riprap reclamation strata, an interaction of the soil–pipeline was conducted by encompassing both scaled model tests and numerical simulations based on a cross-sea channel project. Firstly, scaled model tests were performed on a soil–pipeline interaction caused by excavation. Subsequently, the numerical model was verified by comparing the numerical simulation results with the scaled model test results. Then, the internal force, strain of the pipeline, and soil surface deformation under the conditions of a soil layer with riprap were analyzed, and the results were compared with the case without riprap. Finally, the influence of the support structures was analyzed. The results indicated that the presence of the riprap in strata led to a 19% increase in vertical displacement of the ground surface and a 35% increase in the pipeline bending moment compared with the case without riprap in the same strata. The maximum internal force and strain occurred at an inclined angle of 45° in the pipeline section. Furthermore, it was found that the first lateral support after excavation played a pivotal role in controlling the overall deformation of the foundation pit. The changes in stiffness in the lateral support were more sensitive to the horizontal displacement than the vertical displacement of the pipeline. The results provide valuable insights for the design and safety evaluation of engineering projects in riprap reclamation strata.

The effect of humeral head positioning and incomplete backside contact on bone stresses following total shoulder arthroplasty with a short humeral stem.

The use of uncemented humeral stems in total shoulder arthroplasty (TSA) is known to be associated with stress shielding. This may be decreased with smaller stems that are well-aligned and do not fill the intramedullary canal; however, the effect of humeral head positioning and incomplete head backside contact has not yet been investigated. The purpose of this study was to quantify the effect of changes in humeral head position and incomplete head backside contact on bone stresses and expected bone response following reconstruction. Three-dimensional finite element models of 8 cadaveric humeri were generated, which were then virtually reconstructed with a short-stem implant. An optimally sized humeral head was then positioned in both a superolateral and inferomedial position for each specimen that was in full contact with the humeral resection plane. Additionally, for the inferomedial position, 2 incomplete humeral head backside contact conditions were simulated whereby contact was defined between only the superior or inferior half of the backside of the humeral head and the resection plane. Trabecular properties were assigned based on computed tomography attenuation and cortical bone was applied uniform properties. Loads representing 45° and 75° of abduction were then applied, and the resulting differentials in bone stress versus the corresponding intact state and the expected time-zero bone response were determined and compared. The superolateral position reduced resorbing potential in the lateral cortex and increased resorbing potential in the lateral trabecular bone, while the inferomedial position produced the same effects but in the medial quadrant. For the inferomedial position, full backside contact with the resection plane was best in terms of changes in bone stress and expected bone response, although a small region of the medial cortex did experience no load transfer. The implant-bone load transfer of the inferior contact condition was concentrated at the midline of the backside of the humeral head, leaving the medial aspect largely unloaded as a result of the lack of lateral backside support. This study shows that inferomedial humeral head positioning loads the medial cortex at the cost of unloading the medial trabecular bone, with the same occurring for the superolateral position except that the lateral cortex is loaded at the cost of unloading the lateral trabecular bone. Inferomedial positioned heads also were predisposed to humeral head lift-off from the medial cortex, which may increase the risk of calcar stress shielding. For the inferomedial head position, full contact between the implant and resection plane was preferable.

Study on the Stress Distribution and Stability Control of Surrounding Rock of Reserved Roadway with Hard Roof

According to field observation and theoretical analysis, the failure of the 1523103 reserved roadway is mainly affected by the lateral support pressure, rock mass strength, and support mode. With the mining of the 152309 working face, the lateral pressure of coal pillars on both sides of the reserved roadway increases, and since the lithology of the two sides and the floor of the roadway is weak, the reserved roadway experiences spalling and floor heave. Through numerical simulation, the distribution law of surrounding rock stress and the displacement of surrounding rock are obtained after the roof cutting and pressure relief of the reserved roadway with hard roof. According to the cause of surrounding rock failure of a reserved roadway, the combined control technology of roof cutting and pressure relief, grouting anchor cable support, and bolt support is put forward. After cutting the roof and releasing the pressure on the working face, the lateral support pressure of the two sides of the roadway is significantly reduced, the deformation of the two sides of the roadway is small, the maximum shrinkage rate of the section is reduced from 70% to 11%, and the deformation of the surrounding rock of the 1523103 reserved roadway is effectively controlled. The successful control of the surrounding rock in the 1523103 tunnel reduces the number of coal pillars to be installed, improves the coal extraction rate, and is conducive to the sustainable utilization of limited natural resources and the sustainable development of the coal industry.

Seismic performance of an energy dissipating shear key for highway bridges using butterfly-shaped steel plates

Typical small-to-medium-span highway bridges in China are usually equipped with reinforced concrete shear keys in the transverse direction to provide lateral support for the superstructure under design earthquakes. In the 2008 Wenchuan earthquake, a large number of shear keys were severely damaged, resulting in out-of-control consequences of bearing sliding and girder unseating. The deficiency of traditional reinforced concrete shear keys has engendered a sense of urgency in China to develop novel and competent shear keys. As motivated by such a demand, this paper proposes a new kind of energy dissipating shear key (ED shear key) using butterfly-shaped steel plates based on the installation requirements of typical highway bridges in China. Eight full-scale specimens were designed and tested to examine the seismic performance of the ED shear keys under various test parameters. Based on the test results, the failure modes of the ED shear keys were identified and the energy dissipation characteristics were discussed. It was found that the ED shear keys had a stable and considerable capacity of energy dissipation even after buckling occurred to the strips. In addition, the ED shear keys exhibited very good deformation capacity and ductility, with the ultimate drift ratios ranging between 20.4 ∼ 24.3%. According to the identified failure modes of the ED shear keys, an analytical model was finally proposed. The comparison between the experimental and theoretical results demonstrated that the model can well represent the recorded force–displacement skeleton curves. It is expected that the ED shear keys can satisfy the seismic requirements of different highway bridges through adjusting the number of butterfly-shaped steel plates, and the proposed analytical model can be successfully applied to predict the seismic behavior of highway bridges in practical engineering.

Failure mechanism of a Q690 steel tubular transmission Tower: Full-Scale experiment and numerical simulation

The failure mechanism of a Q690 steel tubular transmission tower is investigated through full-scale experiment. The tower is mainly subject to the influence of the wind and the loads from the transmission lines. The displacements and the strains of the key positions as well as the ultimate bearing capacity of the tower are thus obtained. The final collapse is induced by the buckling instability of the compressed main member of a tower leg. A finite element model is established, whose validity is verified by the experimental data. Then, the numerical model is used for further analysis on the structural responses of the tower. It is found that once plasticity occurs at a certain point on the main member, its lateral displacement would be much accelerated, thus amplifying the second-order effect thereof. The horizontal auxiliary members, connected to the bottom of the compressed main member, are initially under tension. While the deformation of the main member is aggravated, they gradually undergo the transition from tension to compression, constituting a lateral support to the main member. This support then enforces the plasticity to develop towards the middle section of the main member, resulting in the final failure at the same location as observed in the full-scale experiment. These findings are crucial for a progressive understanding of the failure mechanism of this type of high-strength steel tubular towers, and they have contributed to the optimization of the design method to prevent the collapse of transmission tower under similar circumstances.

Numerical study on steel plate girders ‐ Intermediate transverse stiffeners axial force

AbstractTransverse stiffeners are used in steel plate girders with slender webs to provide lateral support to the web along the span and thus increase the plate girder shear resistance. Furthermore, transverse stiffeners anchor the tension field, resulting in axial compression in the stiffener. Despite this, it is widely assumed that the design axial force provided by the FprEN 1993‐1‐5 [1] for the transverse stiffeners is significantly greater than that observed in experimental testing and numerical simulations.The results of 550 nonlinear numerical simulations of plate girders loaded in shear up to failure are presented. Shear resistance and axial stiffener forces are evaluated while the effects of a wide parameter range as web aspect ratio and thickness, flange‐to‐web area ratio, and steel grade are investigated. The numerical results are compared to the European standard design values. Finally, a statistical analysis of the set of results is presented.The numerical analyses show that the axial forces installed in the intermediate transverse stiffeners are significantly lower than those specified by FprEN 1993‐1‐5 [1].

Long-term slope instability induced by the reactivation of mass transport complexes: An underestimated geohazard on the Norwegian continental margin

Submarine landslides are significant geohazards, capable of displacing large volumes of sediment from continental margins to deposit mass transport complexes (MTCs) and generate offshore tsunamis. However, the reactivation of MTCs after their initial failure has long been overlooked. By analyzing high-quality three-dimensional seismic reflection data and seismic attribute maps, as well as comparing the geometry of different MTCs, we investigate the development of long-term slope instability and its hazardous consequences on the northwest flank of the Storegga Slide on the Norwegian margin. Our results demonstrate that the reactivation of MTCs can deform both their inner structure and overlying strata, promoting the formation of sinuous channels and local slope failures on the seafloor. These findings further reveal the MTCs that are underconsolidated or comprise slide blocks may remain unstable for a long time after their initial failure, particularly when affected by slope undercutting and a corresponding reduction in lateral support. This study shows that MTC-prone sequences are more likely to comprise regions of continental slopes with long-term instability and recurring marine geohazards.

Lateral cortical notching facilitates dynamization of proximal femoral nailing – A finite element analysis

IntroductionDynamization of proximal femoral nailing by removal of distal interlocking is one of the recommended treatment options for nonunions of femur fractures. However, in certain inter-/subtrochanteric fractures, gliding of the nail along the femoral shaft is blocked by lateral femoral cortical support of the lag screw. For these cases, Biber et al. proposed lateral cortical notching (LCN), in which the supporting lateral bone is removed. This study investigates the biomechanical effect of LCN on gliding of proximal femoral nailing and stress distribution at the bone/implant interface. Materials and methodsIn this finite element analysis a three-dimensional model of an unstable intertrochanteric fracture with proximal femoral nailing without distal interlocking was simulated using the FebioStudio software suite. To simulate LCN, the lag screw hole was lengthened to 15.34 mm at the lateral cortex. Displacement of the nail along the femoral shaft axis and von Mises stress distribution were compared between LCN model and standard implantation model. ResultsDisplacement of the nail along the femoral shaft axis was higher in the LCN model than in the standard implantation model (0.48 mm vs. 0.07 mm). Highest von Mises stresses of 176–178 MPa at the implant and of 52–81 MPa at the proximal femur were detected. Maximum von Mises stresses of the implant were comparable at all sides, except for a reduced von Mises stress at the lateral inferior side in the LCN model (80 vs. 102 MPa). At the inferior lateral screw hole and the anterior/posterior lateral screw hole maximum von Mises stress was reduced in the LCN model (2 vs. 49 MPa and 52 vs. 81 MPa), whereas the maximum von Mises stress at the inferior medial screw hole was higher in the LCN model than in the standard implantation model (53 vs. 27 MPa). ConclusionsLateral cortical notching facilitates gliding of a distally dynamized proximal femoral nail along the femoral shaft axis in intertrochanteric fractures. Additionally, the lack of lateral cortical bone support at the lag screw reduces von Mises stress at the bone/implant interface and thus could lower the risk for implant breakage and peri‑implant fractures.

Parametric Design and Prototyping of a Low-Power Planar Biped Robot.

This study proposes a design approach and the development of a low-power planar biped robot named YU-Bibot. The kinematic structure of the robot consists of six independently driven axes, and it weighs approximately 20 kg. Based on biomimetics, the robot dimensions were selected as the average anthropomorphic dimensions of the human lower extremities. The optimization of the mechanical design and actuator selection of the robot was based on the results of parametric simulations. The natural human walking gait was mimicked as a walking pattern in these simulations. As a result of the optimization, a low power-to-weight ratio of 30 W/kg was obtained. The drive system of the robot joints consists of servo-controlled brushless DC motors with reduction gears and additional bevel gears at the knee and ankle joints. The robot features spring-supported knee and ankle joints that counteract the robot's weight and compensate for the backlash present in these joints. The robot is constrained to move only in the sagittal plane by using a lateral support structure. The robot's feet are equipped with low-cost, force-sensitive resistor (FSR)-type sensors for monitoring ground contact and zero-moment point (ZMP) criterion. The experimental results indicate that the proposed robot mechanism can follow the posture commands accurately and demonstrate locomotion at moderate stability. The proposed parametric natural gait simulation-based design approach and the resulting biped robot design with a low power/weight ratio are the main contributions of this study.

Design of End Casting for Thin Composite Stiffened Panels Subjected to Axial Compression Load

Compression testing of large, thin, stiffened composite panels is complex due to the susceptibility of such panels to premature buckling and failure. Such failures are due to the artefacts of testing, such as, offset at load introduction edges, non-uniform distribution of loads, nature of lateral supports, crushing of panel edges etc. In this paper, a novel approach for compression loading of thin stiffened composite panels is proposed and validated from finite element analysis supported by tests. Compression loading of such panels (less than 2mm thick) is challenging since the edges are susceptible to local crushing. To avoid this, loading edges of the panel were encased in mild steel casing blocks filled with finely grounded aluminium powder mixed with epoxy resin. Coupon level tests were conducted to measure mechanical properties of the interface between composite and casting mixture. Digital Image Correlation (DIC) technique was used in these tests to measure the full field strains and to validate numerical simulations. Further, finite element analysis of the actual composite test panel with end casting mixture was performed which indicated that interface shear stresses and compression stresses at maximum expected load are much lower than allowables obtained from specimen tests. Hence, the Aluminium-Epoxy cast mixture proposed in this study can be used safely to cast edges of large stiffened panels for axial compression tests.

Experimental and Numerical Study on Lateral Resistance of Micropile in Sand

Micropile has been increasingly used not only as a reinforcing material for foundations but also as the foundations themselves. Due to the high slenderness ratio (length/diameter (L/D)) of the micropile, the lateral resistance has frequently been neglected or underestimated. However, field measurements in this study revealed that the lateral resistance of a micropile is considerable. In this study, the lateral behavior and lateral bearing capacity of a micropile were investigated by performing field tests, physical model tests, and numerical analysis. It was found that the lateral resistance of the micropile is highly dependent on the slenderness ratio and the installation condition such as inclination. Particularly, the battered micropile showed higher resistance than the vertical pile. The increase in the lateral support of the micropile was obtained when the micropile was inclined 45° in the direction of the load. Based on the numerical parametric study, a simple evaluation method to determine the lateral bearing capacity of a micropile is proposed.

Vibration responses of the metro station induced by various train operations under unilateral deep excavation

Field noise tests found that the noise induced by train operation under unilateral excavation is more obvious than that without excavation. Therefore, it is necessary to explore the dynamic response characteristics of metro stations under unilateral deep excavation. Based on the Jincheng Plaza Station in China, this study simulates the impact of train vibration on the structure through a 3-D numerical model and verifies its reliability through field-measured results. Considering various train operations, the analysis is carried out from three perspectives, including time-domain analysis, frequency-domain analysis, and vibration acceleration level (VAL) analysis. The results show that unilateral excavation causes the instability of the station structure, which leads to an 80–140% amplification effect on the peak vibration velocity of the station caused by the train load. Secondly, at the location within the excavation area, the longer the train passes, the more significant the vibration amplification effect is. Thirdly, the station vibration induced by the double-sided train operation is the most significant, which makes the amplitude of frequency domain vibration enlarged by 100–140%. Notably, based on the VAL analysis, it shows that the vibration response of the metro station under excavation is the most significant when the center frequency is 40 Hz. In addition, the VAL under unilateral excavation is 4–7 dB larger than that without excavation, and the increase ratio is about 8–13%. Finally, the maximum VAL under excavation reaches 65.8 dB, which exceeds the specified threshold (52.5 dB). For metro stations with both unilateral excavation and train operation, vibration reduction measures and the lateral structural support in the excavation area should be taken to reduce the vibration response, to improve the comfort of passengers and staff.

Performance recovery of locally buckled reduced beam section connections by attaching buckling-restrained components

Reduced beam section (RBS) connections are ductile connections that have been widely used in steel structures. Because of the reduction of web resistance, local buckling usually occurs under large deformations and is associated with decreased strength. In addition, the complex deformation of beams prevents determining the residual strength, hence posing a challenge in postearthquake repairs. In this study, a buckling-restrained system (BRS) including steel channels and a mortar was proposed for deformed RBS regions to provide lateral support on buckled plates so as to recover the connection strength. Two full-scale RBS connections with various cutting ratios were first tested, and then the connection was repaired with BRS loaded again. The test results indicated that the repaired connections were loaded at a drift angle of up to 4% without fracture or strength deterioration. The negative strength increased by approximately 18%, and the maximum strength was similar to that of the original connection, indicating that the column-to-beam flexural strength ratio of the connection did not change. The strain at the heat-affected area also did not increase and rather decreased because of the additional support of the restraint. The dissipated energy capacities of the repaired specimens were approximately 92% and 87% of the values of the original specimens. These results confirmed that BRS provided sufficient lateral resistance and helped recover the connection performance.

Numerical simulation study on the evolution characteristics of the stress induced by mining in deep adjacent working faces

BackgroundThe mining-induced stress in the surrounding rock after coal seam mining is the primary cause of damage and failure of the surrounding rock in the mining area. However, the magnitude and direction of the stress field induced by mining in the overburden strata during the excavation process of deep and adjacent coal seams are not yet clear, and it is difficult to determine how adjacent working faces interact with each other.ResultsIn this study, a large-scale numerical model was built using FLAC3D (Fast Lagrange Analysis Continua) to simulate the sequential mining process of three adjacent working faces (No.1, No.2, and No.3) in Liuzhuang Coal Mine located in southern China. The results showed that the maximum height of plastic zone development after mining in the No.1 working face was 41 m, and the maximum height of plastic zone development was 33.8 m away from the 13 coal seam. It did not affect the top and bottom of the No.3 working face. The development height of the plastic zone on the roof of the No.2 working face after mining was 52m, and the top and bottom plates of the No.3 working face remained intact. The plastic zone of the floor of the No.3 working face after mining was not communicated with the plastic zone of the roof of the No.1 and No.2 working faces. There was a complete rock layer between the two coal seams, and there was not the mutual influence of the mining activities. During the mining process of working faces No.1 and No.2, the range of dynamic pressure influence was extended up to 100m ahead of the working face. During the mining process of the No.3 working face, the range of dynamic pressure influence was 120 m ahead of the working face. The No.1 working face goaf and the mining of No.2 working face had not disturbance to the No.3 working face.ConclusionsAfter the mining of No.1 and No.2 working faces, the stress in the goaf significantly decreased, and the lateral support stress concentration area of No.1 and No.2 working faces had a relatively small impact on the 13 coal seam. Therefore, the No.1 goaf and mining of No.2 working faces had not disturbance to No.3 working face.

Tibial Component Undersizing Is Related to High Degrees of Implant Migration Following Cementless Total Knee Arthroplasty: A Study of Radiostereometric Analysis Data for 111 Patients with 2-Year Follow-up.

A total of 111 patients who underwent TKA surgery with a cementless tibial component were followed for a period of 2 years postoperatively, during which implant migration was assessed with use of RSA. RSA was performed within 7 days postoperatively and after 3, 6, 12, and 24 months. Postoperative radiographs were evaluated for component size and placement in the tibia. The evaluations were performed by experienced knee surgeons who were blinded to the migration data and clinical outcomes. A multivariable linear regression analysis was conducted. Continuous implant migration (i.e., migration occurring between 12 and 24 months postoperatively) had a negative association with tibial component size (coefficient [B], -0.2; 95% confidence interval [CI], -0.33 to -0.08). Subsidence was associated with the absence of posterior cortical bone support (B, -0.7; 95% CI, -1.09 to -0.28), the absence of lateral cortical bone support (B, 0.8; 95% CI, 0.29 to 1.37), frontal-plane varus malalignment (B, 0.6; 95% CI, 0.12 to 1.16), and component undersizing (B, -0.4; 95% CI, -0.06 to -0.68). Posterior tilt was associated only with undersizing (B, 0.6; 95% CI, 0.27 to 1.11). Undersized cementless tibial components are at a higher risk for poor fixation with continuous migration following TKA. Therefore, a higher risk of aseptic loosening should be expected. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.