Search Results (21)

Upper molar distalization using clear aligners requires optimal force direction and control to ensure effective and predictable tooth movement. This study aimed to evaluate the biomechanical effects of different aligner trimline lengths (trimline ending at the gingival margin vs. 2 mm extended) and attachment designs (no attachment, vertical rectangular, 25-degree beveled vertical, and double horizontal) on maxillary first molar distalization using finite element analysis. A three-dimensional maxillary model was constructed from CBCT data, and eight different aligner configurations were simulated under identical distalizing force. The stress distribution within the periodontal ligament of the maxillary first molar and displacement of crown and root landmarks in three axes were analyzed. The models with no attachments and trimlines ending at the gingival margin exhibited the highest degree of uncontrolled tipping and uneven stress distribution. In contrast, models combining extended trimlines with either beveled vertical or double horizontal attachments demonstrated more controlled bodily movement, reduced palatal root mesial displacement, and more uniform vertical movement. Overall, extended trimlines were associated with increased total distalization and improved force transmission. These findings provide biomechanical insight into optimizing aligner configuration for upper molar distalization and may guide clinicians and manufacturers in improving treatment precision and predictability. Full article

As the core technology for mechanized installation of tunnel folding steel arch frames, snap-fit connection optimization proves critical in enhancing the load-bearing efficiency of support systems and addressing surrounding rock deformation and instability caused by excavation-induced stress redistribution. Addressing the theoretical gaps in existing research regarding snap-fit selection mechanisms and quantitative evaluation criteria, this study adopts a combined approach of numerical simulation and field monitoring verification based on the excavation compensation concept to systematically investigate the load-bearing characteristics of folding steel arch frames with different snap-fit configurations. Key findings include (1) identification of 20 mm as the optimal joint diameter, where the vertical displacements of Type A and B snap-fit connections reached their minimum values of 43.1 mm and 39.2 mm, respectively; (2) demonstration of significant geometric configuration effects on principal stress distribution, with Type B connections exhibiting 4.5% lower maximum principal stress compared to Type A, effectively mitigating stress concentration; and (3) field monitoring data verification, revealing that Type B connections achieved 15.8% lower stress values than Type A at critical crown sections, satisfying yield strength requirements while demonstrating enhanced resistance to surrounding rock deformation induced by excavation-induced geostress redistribution. These results confirm Type B snap-fit connections as superior structural solutions for folding steel arch frames, thereby facilitating the advancement of mechanized installation technology for tunnel steel arch frames. Full article

Current dynamic response analyses of arch dams under an oblique incidence of seismic waves have overlooked the effects of canyon contraction deformation. This study investigated the influence of the incident direction and incident angle of seismic waves on the comprehensive displacements, as well as the damage, of arch dams under canyon contraction conditions. When SV waves are incident obliquely along the river direction, the peak displacements of the dam crest and arch crown beam increase with increasing canyon contraction. The displacement of the dam reaches its maximum when the incident angle is 0°, indicating that the SV wave vertical incidence is the most unfavourable incidence mode affecting the displacement. Dam damage cracking is most severe in the case of a canyon contraction of 60 mm and an incidence angle of 0°. The dam damage cracking index in this case increases only by 7.6% compared to a canyon contraction of 0 mm and an angle of incidence of 0°. However, the change in canyon contraction when a seismic wave is incident obliquely can cause serious damage cracking to the dam. When the SV wave is incident obliquely along the cross-river direction, the dam damage cracking index in this case increases by 110% compared to the case where the canyon contraction is 0 mm, and the incidence angle is 0°. Therefore, it is necessary to comprehensively consider the influences of canyon contraction and the oblique incidence of seismic waves in the seismic design and safety review of arch dams. Full article

Ion erosion has a significant impact on the long-term service performance of lining structures in the subsea tunnel and seriously affects its sustainability. Indoor tests are usually used to study the erosion behavior of lining concrete specimens to reveal the degradation pattern of ion erosion. However, the long-term service performance of lining structures under ion erosion is rarely considered in the industry. In this study, the long-term deterioration characteristics of concrete specimens and subsea tunnel linings are analyzed by using numerical investigations. The long-term diffusion patterns of erosion ions in concrete specimens are evaluated. The effects of ion erosion and water pressure on the stress, deformation, and damage characteristics of the lining structure are examined. The numerical results show that solution concentrations and concrete grades have a significant influence on the ion diffusion in concrete specimens. As the erosion time increases, the rate of ion diffusion gradually decreases due to the decrease in the concentration difference between the inside and outside of the concrete. The service time T has a significant effect on the depth and rate of ion erosion. When T is 10, 50, and 100 years, the depth of ion erosion reaches 25, 63, and 84 mm, respectively, showing a nonlinear increase. As the depth of ion erosion increases, the characteristic parameters reflecting the long-term performance of the lining structure will increase. The maximum tensile stress is 0.98 MPa, and the maximum displacement is 1.59 cm, both of which occur at the arch crown. Disregarding the effects of ion erosion and water pressure, the vertical displacements of the lining structure within the first two years under low loads account for more than 97% of the 100-year displacements. Both ion erosion and water pressure exacerbate the damage deterioration of the lining, in which ion erosion significantly increases the maximum tensile stress of the lining, with a maximum enhancement of 326.09%, and water pressure significantly enlarges the maximum compressive stress of the lining, with a maximum enhancement of 53.23%. However, with increasing depths of ion erosion, the high water pressure will reduce the maximum tensile stress. This study can lay the foundation for further research on the long-term stability of the lining under complex erosion environments. Full article

Dam stability is one of the most essential geotechnical engineering challenges. Studying the structural behavior of dams during their useful life is an essential component of their safety. Terrestrial surveying network approaches are typically expensive and time-consuming. Over the last decade, the interferometric synthetic aperture radar (InSAR) method has been widely used to monitor millimeter displacements in dam crests. This research investigates the structural monitoring of the Lar Dam in Iran, using InSAR and the terrestrial surveying network technique to identify the possible failure risk of the dam. Sentinel-1A images taken from 5 February 2015 to 30 September 2019 and TerraSAR-X (09.05.2018 to 16.08.2018) images were analyzed to investigate the dam’s behavior. The InSAR results were compared with those of the terrestrial surveying network for the period of 1992 to 2019. The Sentinel-1 results implied that the dam on the left side moved over 8 mm/yr. However, the pillars to the left abutment indicated an uplift, which is consistent with the TerraSAR-X results. Also, the TerraSAR-X data indicated an 8 mm displacement over a three-month period. The terrestrial surveying showed that the largest uplift was 19.68 mm at the TB4 point on the left side and upstream of the body, while this amount was 10 mm in the interferometry analysis for the period of 2015–2020. The subsidence rate increased from the middle part toward the left abutment. The geological observations made during the ninth stage of the terrestrial surveying network indicate that there was horizontal and vertical movement over time, from 1992 to 2019. However, the results of the InSAR processing in the crown were similar to those of the terrestrial surveying network. Although different comparisons were used for the measurements, the difference in the displacement rates was reasonable, but all three methods showed the same trend in terms of uplift and displacement. Full article

The soft and fractured strata can cause significant deformation of surrounding rock during tunnel excavation. This study analyzes field monitoring test results and compares numerical simulations from the third bid project of the Dali I section construction within the water diversion project in central Yunnan to address the issue of significant deformation following tunnel excavation in soft and fractured strata. It proposes an optimized support scheme consisting of a densified steel arch and enhanced initial support strength and stiffness. In addition, the research investigates support effectiveness considering varying support strengths and steel arch ring spacing. The study findings indicated the following: (1) The tunnel traverses soft and fractured strata, causing unevenly distributed vertical convergence deformation around the cavern. The maximum settlement occurs at the crown, showing pronounced nonlinearity. (2) The maximum stress in the steel arch is concentrated at the arch crown, measuring −19.02 MPa. The arch remains compressed, with stress decreasing from the crown to the waist. (3) The axial force in the anchor bolt reduces from the crown to the arch’s waist on both sides. As the depth of the rock mass increases, the axial force in each anchor bolt decreases and the tension state is maintained. The maximum axial force reaches 46.57 kN. (4) The maximum displacement decreases from 4.21 to 0.15 cm after the optimized support structure is implemented, demonstrating the optimization scheme’s effectiveness. Future constructions can refer to this scheme and make necessary adjustments based on various terrain conditions to ensure safety. Full article

The tooth impaction of the lower second premolars is an occasional condition but is still seen in clinical practice with a prevalence of 0.6–2.6%. The present case report describes a rare condition of the lower second premolar impaction. An 11-year-old female patient presented with the anteroposterior dental discrepancy, midline shift, and occlusal cant. Intraoral examination revealed the absence of the lower right second premolar with no space available for the eruption. X-ray examination revealed the impaction of tooth #45 in a vertical position, tilting of the adjacent teeth, and two-thirds root length development. The orthodontic treatment plan included space opening using a fixed appliance with a coil spring. The natural eruption of the tooth was expected according to dental age and root development. When the space was opened, no change in the position of tooth #45 was observed. Surgical exposure and active traction were performed. However, the intrusion and tilting of adjacent teeth were observed during the next appointments with no vertical change of tooth #45. Ankylosis was suspected as no tooth movement was recorded. The surgical luxation and osteotomy of the coronal alveolar bone of the impacted tooth were planned for the imminent forced eruption, which was expected due to the young age of the patient. Consequently, the crown of tooth #45 emerged and the bracket was placed. Further traction was planned to use a micro-screw. Following the traction, no vertical displacement of the tooth was observed in the subsequent appointments. Radiographic examination revealed radiolucency in the coronal third of the root. The patient was referred to the endodontist, and CBCT revealed external cervical root resorption in the late reparative stage. ECR in an impacted tooth, mimicking the manifestation of tooth ankylosis, can cause orthodontic treatment failure. Full article

As subsea shield tunnels are becoming increasingly popular, especially in coastal or river cities, the complicated construction environment poses multiple challenges that need to be addressed to ensure their safety and reliable operation. This study presents the results of centrifuge model tests that aimed to examine the impacts of navigable channel excavation and seawall construction on the deformation and forces acting on a subsea shield tunnel. The symmetry of the tunnel structure, as well as the loading and unloading effects from channel excavation and seawall construction in this engineering project, allow for the simplification of the problem. The centrifuge test model included a novel device to simulate the unloading action of channel excavation and the loading impact from seawall construction. The structural response of the tunnel was monitored using an innovative solution, and various parameters such as vertical displacement, opening of the circumferential joint, circumferential bending moment, and longitudinal stress were analyzed. The results reveal that both channel excavation and seawall construction have significant effects on the stress and deformation of the pre-existing tunnel. While the excavation of the navigable channel reduces the load on the tunnel from the overlying strata, resulting in uplifts in the tunnel structure around the excavation area, and the construction of the seawall causes settlement of the tunnel near the loading zone. The unloading effect of channel excavation leads to the opening tendency of the tunnel circumferential joints, while the loading effect of seawall construction has the opposite effect on the tunnel circumferential joints. The excavation of the channel induces tensile stresses on the tunnel crown around the loading zone, while the seawall construction causes significant compressive stresses on the tunnel crown around the loading zone. It is crucial to prioritize safety and ensure the tunnel’s load-bearing capacity through careful design and construction considerations in practical engineering. The study can guide the design and construction of future projects and help minimize the risk of damage to pre-existing structures. Full article

This paper aims to represent the orthodontic treatment of two young patients with skeletal Class I relationship and unilateral impacted canines (case 1 with palatally displaced canine and case 2 with buccally displaced canine). Before starting full-mouth alignment, canines are moved away from the roots of the neighbouring teeth. The protocol involved a surgical phase carried out in order to expose the canine and traction it with TADs (temporary anchorage devices) and an orthodontic phase performed to finalize the alignment. The canines were moved through vertical and distal force vectors by using TADs as well as a cantilever spring. As soon as the crown of the canine was fully visible, digital impressions were taken to start the digital planning of the orthodontic phase. At the end of the treatment, results show a control of the facial aesthetics both from the frontal and lateral perspectives with a harmonious profile. The molar and canine Class I relationship was achieved with the recovery of the impacted canines and the overbite and overjet were normalized. Full article

Cured-In-Place-Pipe (CIPP) rehabilitation technology is widely utilized in pipeline rehabilitation projects and has exhibited favorable results. Nevertheless, the mechanical characteristics of pipelines after CIPP rehabilitation and the effectiveness of CIPP rehabilitation in repairing these mechanical characteristics remain unknown. To address these issues, a three-dimensional numerical model of a corroded concrete pipe before and after CIPP rehabilitation was established in the present study. To authenticate the accuracy of the numerical model, the numerical simulation data were compared with the full-scale test data from prior research, and the comparison outcomes show that the numerical model formulated in this study is reasonable and reliable. To appraise the repair effectiveness of CIPP rehabilitation, the mechanical properties of a corroded pipe, a CIPP-repaired pipe, and a normal pipe under traffic load were computed and compared, and the comparison outcomes demonstrate that the stress in the pipe bell, stress in the pipe spigot, vertical displacement of the pipe crown, and vertical displacement of the pipe invert were reduced by 39.8%, 16.7%, 24.7%, and 24.4%, respectively, after CIPP rehabilitation. Moreover, a series of three-dimensional numerical models were constructed to scrutinize the impacts of factors such as corrosion degree, corrosion angle, and traffic load on the mechanical properties of corroded pipelines before and after CIPP rehabilitation. The findings indicate that the stress on the pipe escalates with increasing corrosion degrees and diminishes with increasing corrosion angles; there are no noteworthy differences between the vertical displacement of the pipe and the von Mises stress of the CIPP liner for diverse corrosion degrees and corrosion angles; the amplification of the traffic load will augment the stress and displacement of the pipe and increase the rotation of the pipe, resulting in a significant upsurge in the stress of the CIPP liner at pipe joints. When the traffic load magnitude rises from 0.7 MPa to 1 MPa, the stress and displacement of the pipe and the von Mises stress of the CIPP liner were increased by 18.9%, 42.3%, and 42.1%, respectively. Full article

With the evolution of modern cosmopolitan cities, subterranean spaces have developed in dense urban environments. Hence, new metro tunnels often intersect with those in operation. The top-priority task of designers is to evaluate the effect of new construction projects. The experience accumulated in this field should contribute to the design of a realistic geotechnical model to simulate long-term displacements in the future. This paper includes a backward analysis of a design scheme developed for a tunnel construction area above an existing tunnel with a 10.3 m diameter, according to the results of geotechnical monitoring performed in PLAXIS 2D. The authors identified the optimum combination of the distance from the tunnel bottom to the lower boundary of the design model, the soil model, and tunnel lining stiffness. The authors derived regression equations describing vertical and horizontal displacements of the tunnel at the stage of excavation to the elevation datum as the excavation pit bottom. These equations can be applied to preliminarily predict the displacements of the tunnel depending on geometrical parameters at the initial design stage. Geometrical parameters include the distance from the tunnel to the excavation pit, the depth of the tunnel from the surface to the crown, the depth of the designed excavation pit, and the distance from the bottom of the excavation pit to the bottom of the tunnel. In addition, the effect of the Muir–Wood coefficient on the vertical displacements of the tunnel was investigated. This work found a reduction in the stiffness of the bearing structure of the tunnel and an increase of 4.8% in deformations on average when this coefficient was considered. Full article

To effectively optimize the mechanical behavior of a traditional anti-slide pile and reduce environmental destruction, a new method for slope reinforcement by a spatial arc crown beam composite supporting structure was proposed. First, a numerical model was validated through lab-scale model test data obtained herein, and then a full-scale numerical model was created for an in-depth understanding of the distribution regularity of displacement along the pile, the soil pressure, the crown beam stiffness, and so on. The results demonstrated that: (1) The spatial arc crown beam is simplified to a two-hinged arch, and the maximum value of the bending moment in the arc crown beam is about one-third of the straight crown beam through theoretical calculation. (2) The spatial arc crown beam redistributes the load sharing among different piles, and the extreme bending moment of other piles varies within 10% along the downhill direction except for the piles at the slope foot. (3) Bending moments are close to zero at the pile end, and the anti-slide pile can be simplified as a vertical beam with one end fixed and the other end hinged. (4) The axial force in the spatial arc crown beam is always presented as pressure, so the crown beam can make full utilization of the compression resistance of concrete. (5) The distribution characteristic of soil pressure in front of the pile at the arch foot is different from that in other positions, and the stable soil at the slope foot provides greater soil resistance for anti-piles. (6) As the crown beam stiffness is above five times the reference value, the axial force of the crown beam tends to be stable, and as the crown beam stiffness increases continually, the maximum value of M_y is −1013.13 kN·m, and the constraining effect of the crown beam is gradually weakened. Full article

In the present paper, a procedure is presented for the evaluation of the safety factor and the limit conditions of masonry arches subject to gravity loadings. The proposed procedure can be considered an extension of Heyman’s method for determining the geometrical safety factor. At variance with Heyman’s method, herein, the analysis of the static safety condition for the arch is performed by means of modified kinematic configurations of the arch obtained by encompassing settlements at the arch constraints. Furthermore, the procedure allows the identification of the critical locations of the hinges in the arch at the limit conditions. Moreover, the present procedure allows the determination of the geometrical vertical displacement that the crown of the arch can accommodate at the safety limit conditions. Finally, the proposed procedure is applied to a real case in order to show its effectiveness. Numerical results are reported and commented on in order to clarify the application of the proposed procedure for the definition of the safety factor of the arched structure and the evaluation of the critical geometrical configuration compatible with the limit conditions of the arch. Full article

The main goal of this paper is to analyze the stress and displacement fields in prosthetic crowns made of zirconium dioxide using the numerical approach of homogenization hypothesis. The simple engineering model is developed and applied in case of vertical forces. The model is a three-dimensional simulation of molars subjected to crushing, mastication, and clenching. Two basic approaches are considered: the single prosthetic crown on a single molar, and the prosthetic bridge on two molars. The distributions of material parameters are determined for the rigid support and the elastic gum structure of the homogenized properties. The crown on a single molar is analyzed in respect of caries, which are represented by weak material parameters. Irrespective of the problem, the maximal stresses are always insignificant compared to the compressive strength for enamel, dentin, periodontium, and zirconium dioxide. In case of caries, the maximal stresses are located at the contact surface caries/crown, whereas the displacement was higher than the same parameter without caries. The stresses inside the prosthetic bridge on two molars were comparable for elastic and rigid support, and located at the same areas. The molar displacement for elastic gum was higher than for the rigid base, and additionally supplemented by the displacement of the supporting structure. Full article

This study aimed to investigate the effects of installing pipe roofings and rock bolts before bench cuts during the excavation of a tunnel. The limited space available during excavation resulted in the formation of triple adjacent tunnels. To solve the issue of narrow spacing between the tunnels, middle posts were added for greater stiffness, and pipe roofings were installed to prevent collapse in tunnel sections with shallow overburden where the rock weathering was significant. PLAXIS 3D 2018, a finite element analysis program, was used to simulate the wall rock displacement during the bench cuts with pipe roofings and rock bolts installed. In addition, the difference between the presence and absence of bias pressure was studied. It was found that, in the absence of bias pressure, the tensile and compressive forces were symmetric from side to side. However, under bias pressure, the tensile force remained unchanged. Moreover, the compressive force under bias pressure was three times greater than without bias pressure and was concentrated at the sidewall of the eastbound tunnel and the crown of the mass rapid transit (MRT) tunnel. The results may be helpful for the design and construction of multiple adjacent tunnels in the future. Full article