Maximum Arch Research Articles

An experimental investigation on the arching effect of cohesive materials in trapdoor tests

This study conducted a series of trapdoor tests on low cohesion material at different buried depths, the failure patterns and the variations of soil pressure were investigated, and the development of the arching effect in trapdoor tests was analyzed. The results showed two failure models for soils: when the buried depth ratio was smaller than 2, two rupture surfaces developed obliquely upward from two sides of the trapdoor and merged into one triangular rupture surface; when the ratio was greater than 2, two rupture surfaces developed vertically upward and merged into one tower-shaped rupture surface. As the burial depth increased, the inner boundaries of the soil arch moved upward, and the widths of the inner and outer boundaries expanded. Furthermore, the maximum arching trajectory, obtained by connecting the maximum tangential stress points, was closer to the inner boundary and shifted towards the outer boundary when the trapdoor was lowered. Based on the experimental results, a new composite arch model was proposed to calculate the soil pressure above a trapdoor, it can better describe the development of soil pressure in a trapdoor test.

A systematic review of the explicit knowledge used and evidence base in the process of design and fabrication of orthopedic footwear

BACKGROUND: The design and manufacturing of effective foot orthoses is a complex multidisciplinary problem involving biomedical and gait pattern aspects, technical material and geometric design elements as well as psychological and social contexts. This complexity contributes to the current trial-and-error and experience-based orthopedic footwear practice in which a major part of the expertise is implicit. This hampers knowledge transfer, reproducibility and innovation. OBJECTIVE/METHODS: A systematic review of literature has been performed to find evidence of explicit knowledge, quantitative guidelines and design motivations of pedorthists. RESULTS: 17 studies have been included. No consensus is found on which measurable parameters ensure proper foot and ankle functioning. Parameters suggested are: neutral foot positioning and control of rearfoot motion, maximum arch, but also tibial internal/external rotation as well as a three point force system. Also studies evaluating foot orthoses centering on the diagnosis or orthosis type find no clear guidelines for treatment or for measuring the effectiveness. CONCLUSIONS: A gap in the translation from diagnosis to a specific, customized and quantified effective orthosis design is identified. Suggested solutions are both top-down, fitting of patient data in simulations, as well as bottom-up, quantifying current practices of pedorthists in order to develop new practical guidelines and evidence-based procedures.

Upward soil arching effect under unloading: mechanism, theory and engineering application

Upward soil arching effect under unloading indicates the unloading part moves in a vertically downward direction, generating the arching zone and the loosened zone towards an upward direction. This study presents a summary of definitions, characteristics, theoretical models and engineering applications for the upward soil arching effect under unloading. The evolution of the upward soil arching effect is highly related to the unloading/differential displacement. The characteristics of the upward soil arching effect under unloading are comprehensively interpreted in terms of the normalized height of arching, the minimum soil arching ratio (at which state the maximum arching is developed) and the normalized unloading displacement to reach the maximum arching state. Two deformation-dependent theoretical models are introduced, to appropriately interpret and predict the variation of the soil arching ratio with the normalized unloading displacement (i.e., the ground reaction curve). Using the research findings for the upward soil arching effect under unloading, the settlement of the geosynthetic-reinforced pile-supported embankment as well as the face stability and ground settlement during tunnelling are proven to be precisely predicted and well controlled.

Analysis of the Relationship between Certain Biokinematic and Goniometric Variables of the Linear Smash with Explosive Force Upwards, Forwards, and in Volleyball Shooting

Linear smash, a potent offensive weapon in volleyball, demands complex biomechanical coordination and techniques. This study aimed to identify the biokinematic and goniometric variables of a linear smash and explore their relationship with explosive strength during performance. The research sample comprised 11 female volleyball players from the Sanharib Club. Physical tests measured explosive strength through vertical/forward jumps and medicine ball throws. The biokinematic variables included center of mass elevation/displacement, arch depth, movement time, and velocities. Goniometric variables measured the joint angles during execution. The video analysis software extracted variable values during players' smash attempts. Key findings revealed significant inverse correlations between explosive vertical jump strength and horizontal center-of-mass distance (-0.911) and between explosive medicine ball throw strength and horizontal distance (0.891). Additionally, a positive correlation existed between medicine ball throw strength and shoulder joint angle at the maximum arch (0.82). The vertical center of mass elevation was inversely correlated with the forward jump distance (-0.776). Strong but insignificant relationships emerged between variables such as horizontal speed/medicine ball throw and takeoff-landing distance/jump time. The results highlight the importance of the explosive strength for upward/forward propulsion and proper joint angles for efficient energy transfer during smashing. Recommendations include focusing on correlated variables through targeted training, utilizing joint ranges of motion, and incorporating additional biodynamic factors. This study provides insights into optimizing the linear smash through biomechanical analysis and training interventions.

Investigation of the soil arching evolution in the ground with or without a tunnel

The soil arching effect has been widely observed in geotechnical engineering. Despite extensive studies on this topic, there is still a lack of research on the effect of an existing tunnel on the evolution of the soil arching effect, which is investigated in this study via trapdoor tests. Digital image correlation was used to visualize the displacement and shear information of the sand. The effect of the backfill burial depth was considered. The results showed that the same load–displacement curve characteristics can be obtained with four stages (initial arching, maximum arching, load recovery, and ultimate stages), whether an existing tunnel is present or not. The ultimate soil arching ratio is degraded in ground with a tunnel, and most evident with H/B = 4.0, compared to the results without structures. A shield region was generated above the existing tunnel. A double-groove-shaped displacement was formed in the sand above it in the presence of an existing tunnel; it was symmetrical along the central axis of the trapdoor. The shear band gradually expanded from the inside to the outside as the trapdoor slid downward. New shear bands formed at the tunnel shoulder when the shear band exceeded the trapdoor width range. Two deformation patterns, parallel flow over a tunnel and cross-flow over a tunnel, were identified based on development of shear bands in the sand within the existing tunnel.

The Influence of Construction Methods on the Stability of Tunnels and Ground Structures in the Construction of Urban Intersection Tunnels

The construction of intersection tunnels in urban induces multiple stress redistribution in the surrounding rock, leading to engineering disasters such as instability in rock strata during excavation, disturbance of supporting structures in existing tunnels, and subsidence of ground adjacent buildings. Employing an appropriate construction method is crucial in circumventing excessive stress concentrations and large-scale rock strata subsidence, making it a key aspect of urban intersection tunnel engineering. In this paper, a numerical model for an urban intersection tunnel is developed based on an underground circular road project in a central business district. We conduct numerical simulations of the excavation processes using the full-section method, step method, and center cross diagram (CRD) method, respectively. The findings indicate that while different construction methods do not change the variation trends of surrounding rock stress and displacement, adjacent ground building deformation, and existing tunnel convergence, they affect the variation degrees. The maximum compressive and tensile stresses in the surrounding rock caused by the CRD method are the smallest, which are 3.56 MPa and 0.76 MPa, respectively. The maximum arch subsidence affected the amount, and horizontal convergence affected the amount of branch tunnel #1 caused by the CRD method are the smallest too, which respectively are 1.428 mm and 0.931 mm. The foundation subsidence and overall inclination of the ground building resulting from the three methods are identical. Then, we discuss the construction safety of the three methods and obtain the influence order on construction stability, which is as follows: full-section method > step method > CRD method. It is concluded that the CRD method is the most suitable for urban intersection tunnel engineering in terms of safety. This study could offer valuable insights for selecting construction methods in urban intersection tunnel engineering and provide a foundation for evaluating the safety and stability of tunnel construction.

A two-dimensional experimental study of active progressive failure of deeply buried Qanat tunnels in sandy ground

As an ancient underground hydraulic engineering facility, the Qanat system has been used to draw groundwater from arid regions. A qanat is a horizontal tunnel with a slight incline that draws groundwater from a higher location and delivers it to lower agricultural land. During long-term water delivery, the qanat tunnel has experienced different degrees of aging and collapse, which may result in the significant ground settlement and even disasters. This paper developed a two-dimensional laboratory system to investigate the influence of progressive failure on the stability of deeply buried qanat tunnels. The developed system is fully instrumented with a particle image velocimetry (PIV) system and earth pressure and displacement monitoring. A special cylindrical membrane tube is designed and connected to an advanced pressure–volume controller to simulate the step-wise failure process of the tunnel. Three model tests were conducted on a dry sand considering the buried qanat tunnels at three different depths. Experimental results clearly show the progressive evolution of soil arching effect in the dry sand associated with the progressive failure of the tunnels. The failure of the Qanat ground starts from the vault and develops upwards, which is closely related to the evolution of stress contour at three consecutive stages. Ground surface settlement and volume loss corresponding to three burial depths were compared. A deeply buried qanat tunnel has a small effect on surface settlement. Earth pressure evolution on the 2D plane shows the load redistribution when the qanat collapses. The maximum arch and the initial point of the limit state correspond to a volume loss of 12.5 % and 50 %, respectively. For the collapse of the deep buried qanat tunnel, ground earth pressure evolution can be divided into a stress-increasing region, stress-decreasing region, and no redistribution region. Furthermore, a multi trap-door model considering soil expansion is proposed to describe the progressive failure behavior and its effects.

Thermal performance of CRTS Ⅱ slab track-bridge structure under extreme temperatures: Numerical simulation

Large thermal deformation of CRTS Ⅱ slab track due to thermal effect is harmful to the operational safety of the high-speed railway. In order to explore the thermal deformation of the CRTS Ⅱ slab track under extreme ambient temperatures, the parameters of two bilinear cohesive zone models (CZMs) of vertical interlayer and longitudinal slab interlayer are firstly deduced by the splitting and shearing modelling tests, respectively. Secondly, the transient heat transfer models of CRTS Ⅱ slab track-bridge structure incorporatedwith two CZMs are verified by our previous thermal experimental results. Finally, thermal responses (e.g. temperature distribution, stress, and displacement) of the track structure are calculated under two extreme high temperatures (i.e.50℃ and 60℃) and two low temperatures (i.e.-20℃ and −40℃), respectively. Results show that the heat transfer model could effectively reflect thermal performance of the CRTS II track-bridge structure under extreme high and low temperatures. The internal temperatures and stresses of the track slab rapidly change in two hours and then have a slow change rate, an obvious mutation is found in the stress and displacement response under extreme high temperatures. Furthermore, the maximum arching displacement change from the ends of the track slab under the 50℃ to the middle of the track slab under the 60℃, while both the maximum warping displacement occur at the ends of the track slab under the −20℃ and −40℃, respectively.

Study on Unloading-wet Swelling Mechanism of Upper Arch Deformation of Mudstone Subgrade in a High-speed Railway

Mudstone subgrade may exhibit rather complicated deformation behavior under the coupling effect of unloading and wet swelling caused by subgrade excavation. To study the deformation mechanism of mudstone subgrade, mudstones were sampled from the NO.3 branch tunnel of Badong section of Zhengzhou-Wanzhou High-speed Railway and a series of unloading and wet-swelling tests were carried out on them. We studied the long-term deformation behavior of mudstone subgrade caused by excavation based on a creep test with unloading conditions. The expansion rate of the complete mudstone cylinder samples was extremely low under the wetting and drying cycle, while that of the soil samples after the disintegration of complete mudstone was between 1% and 10% when immersed in water. Excavation unloading damage, groundwater infiltration, long-term creep deformation, dry-wet cycle, and hot-cold alternation catalyzed each other, leading to the aggravation of mudstone disintegration and the obvious increase of expansibility of underwater mudstone after disintegration. The maximum arch deformation of mudstone subgrade can be divided into three parts: the rebound deformation during short-term excavation, the creep deformation related to time and the wet-swelling deformation. Generally, the creep deformation would not converge in two years if support measures were not taken, the wet-swelling deformation could tend to a steady value after a certain period of excavation.

Full-scale model tests of load transfer in geogrid-reinforced and floating pile-supported embankments

Well-designed field full-scale model tests were carried out to enhance the understanding of geogrid-reinforced and floating pile-supported (GRFPS) embankments constructed on medium compressibility soil (MCS). Two comparative test sections of GRFPS embankments with and without pile caps were built over silty clay with medium compressibility for field monitoring, over 25 months. The heavily instrumented embankments produced comprehensive high-quality data. Settlement, earth pressure, and geogrid strain measurements during embankment filling stages and the postconstruction placement stage were conducted. The influence of pile cap installation on the differential deformation and load transfer behaviour of the GRFPS embankment was evaluated. The results demonstrate the installation of pile caps can significantly improve the evolution characteristics of the stress increment ratio on the pile, facilitating a change in load sharing of the pile top from a “softening” feature to a “hardening” feature. The state of the “arching structure” heavily depends on the relative displacement. After the maximum arching is formed, although the subgrade load continuously increases, the arching enters the damage and recovery state, and the transfer of the overburden load increment is largely conducted by the tensioned membrane effect.

Study on the damage evolution of the joint and the arching deformation of CRTS-II ballastless slab track under complex temperature loading

Joint damage has been a severe problem for the longitudinal CRTS-II type ballastless track, which affects vertical stability of the slab track significantly and threatens operation safety of the highspeed railway potentially. This paper presents a refined and detailed finite element model of the CRTS-II track to investigate the damage initiation and evolution of the wide and narrow joint, a pivotal part of the longitudinal CRTS-II track. In detail, a bilinear cohesion model is introduced to simulate the interfacial interaction accurately. And a concrete damage plasticity model is utilized to model the initiation and propagation of the joint crack for comprehensive analysis. The refined model analyzes the joint damage initiation and evolution under complexly extreme temperature load. Then, the influence of joint damages and interface conditions on the slab track upper-arch mechanism are investigated. The results show that tensile damage causes initial cracks inside the narrow joint, then the increase of compressive damage is the leading cause of the final failure of the narrow joint concrete. And the poor quality of concrete tends to cause the wide and narrow joint to be entirely crushed, while the high quality above C30 may cause joint damage intensively, leading to joint concrete fall-block. In addition, the upper-arch on the track slab increases linearly with the joint damage degree. With the interfacial tangential shear strength changing from 0.01 MPa to 1.5 MPa, the maximum arch height of the slab reduces by 4.5 mm.

Interfacial failure and arching of the CRTS II slab track reinforced by post-installed reinforcement bars due to thermal effects

To prevent damage of the China Railway Track System (CRTS) II slab track induced by thermal effects, post-installed reinforcement (PIR) bars between the prefabricated slabs and the concrete base have been utilized in the track. This work presents a study on the interfacial failure and arching of the CRTS II slab track reinforced by PIR bars due to the effects of temperature change. To this end, a novel finite element model of the track was established, in which the non-linear interfacial interaction between the track slabs and the cement asphalt (CA) mortar layer was simulated by a cohesive zone model, the non-linear constitutive material properties of track concrete were represented by a concrete damaged plasticity (CDP) model, and the non-linear bond-slip relationship between PIR bars and track concrete was characterized by non-linear spring elements. Comparison between simulation results and experimental data indicates that the proposed modelling technique is capable of evaluating the performance of the track reinforced by PIR bars. The combined action of insufficient bond strength between PIR bars and concrete, and insufficient bond strength between track slabs and CA mortar layer, was analyzed. Numerical analysis results show: (1) The temperature rise of interface failure between the concrete slabs and the CA mortar layer can be improved by 6 °C after PIR bars installation. (2) The PIR bars are effective in reducing arching displacement of slabs caused by temperature rise in both lateral direction and longitudinal direction of track slabs. (3) Both PIR bond strength and interface bond strength influence the maximum arching displacement of track slabs significantly.

A simple design approach to analyse the piled embankment including tensile reinforcement and subsoil contributions

There is not one generally accepted approach for the design of geogrid-reinforced pile-supported (GRPS) embankments. Relevant mechanisms include arching of the embankment material, but also the effect of geogrid reinforcement and potentially a contribution from the underlying subsoil. This paper presents a simple design approach to identify the contribution of all three mechanisms, in which the contribution of multi-layered geogrid reinforcement is also presented. To validate the theoretical predictions for the effect of geogrid reinforcement and the potential contribution of underlying subsoil, a series of three-dimensional finite element analyses are conducted. It is found that a point of ‘maximum arching’ is increased with the height of embankment. This study also presents that the reinforcement could reduce the ultimate stress on the subsoil. However, this requires significant sag of the reinforcement. It is found that the sag of reinforcement is very sensitive to the span of the reinforcement between piles, but relatively insensitive to the stiffness of the reinforcement. For a case with three layers of geogrid, the upper two grids carry relatively little tension compared to the bottom layer. This in turn leads to an approximate but simple equation of vertical equilibrium which may be of use in design.

Arching in granular soils: experimental observations of deformation mechanisms

Understanding soil arching is an important component of predicting soil behaviour in cases such as the progressive displacements above sinkholes and when predicting loads on buried structures, where the expected deformation mechanisms are used to predict the applied loads. Visual validation of these deformation mechanisms above a void at appropriate stress levels remains limited. Centrifuge tests on dense sand were conducted to allow visualisation of the deformation mechanisms and hence enable a more accurate prediction of the load–displacement curve. The results showed that at the point of maximum arching a triangular failure zone corresponding to the formation of an apparent active failure wedge forms with proposed angles of 45° − ϕp/2 to the vertical. If the soil height is large enough to allow the full formation of this initial wedge, the deformation mechanism progresses to a vertical prism. Otherwise, the soil collapses into the void. A modification of the classical arching theory is required to allow it to be used to more accurately predict the stresses at the point of maximum arching and in the ultimate state with large displacements.

Roof-breaking mechanism and stress-evolution characteristics in partial backfill mining of steeply inclined seams

Steeply inclined seams buried at dip angles of 35–55° are considered hard-excavated seams in the mining industry. A partial backfilling method based on sub-regional features of surrounding rock deformations and failure and support stability was proposed to realize safe, efficient production, to promote sustainable development of coal mining and disaster prevention in western China. Through experiments, calculations, and theoretical analysis, a mechanical model was established, and governing equations for the deflection curve, bending moment, and rotation were deduced. Results reveal the filling percentage, filling ratio, and working-face dip angle as major factors causing roof failure. The degree of roof deformation decreases with increasing filling percentage, filling ratio, and working-face dip angle. With an increase in filling percentage and filling ratio, the range and magnitude of the stress-concentration zone at a T-junction increase, whereas those pertaining to the stress-release zone in the roof decrease. The stress-arch profile of the roof changes from a single peak to double peaks with reduction arch height. Additionally, the maximum arch height shifts towards the centre with increasing moderation of asymmetric features of stress arches. With an increase in working-face dip angle, stress concentration at the coal-wall head T-junction decreases, and a double-peak stress arch develops. Therefore, in order to obtain the best backfill mining effect, a higher filling percentage is preferred; with a maximum filling value of 0.93, the reasonable range for the filling ratio is 1/3 to 1/2 and the reasonable dip angle of the working face is approximately 35°.

3D finite-element modelling of soil arch shape in a piled embankment

Soil arching is a common phenomenon in a piled embankment. A precise soil arch shape is a key prerequisite for developing an analytical model to calculate the soil arching effect. In this study, a three-dimensional (3D) elastic–plastic finite-element model which simulates the formation process of soil arching in a piled embankment was established. The 3D shape of the soil arch in a piled embankment without reinforcements was investigated by the finite-element method. Then, a parametric study on the height of the soil arch was conducted. The results show that the soil arch in a piled embankment is a semi-ellipsoidal shape when ‘maximum arching’ is reached. The height of the soil arch is strongly affected by the clear spacing of the pile cap and the height of the embankment. The height of the soil arch increases gradually with increasing clear spacing of the pile cap. It increases with increasing the height of embankment to a certain value, and then remains constant beyond this critical embankment height. The value of the internal friction angle of the embankment fill has little effect on the height of the soil arch.

Analysis of maximum arching conditions in active plane-strain trapdoors in sand

The trapdoor problem is a useful model to understand the stress distribution around geo-structures. This paper focuses on evaluating the conditions of maximum arching (minimum loads on trapdoors) developing during the lowering of plane-strain active trapdoors in cohesionless granular materials. A parametric study using finite element analysis has been performed to investigate various factors affecting the maximum arching conditions in active trapdoors, with a particular focus on the effect of soil dilatancy. The paper also presents rigorous upper bound limit analysis solutions. Previously published solutions dealing with soil non-associativity have been discussed and compared with the finite element results. The finite element analysis shows that using a Mohr Column model with the associative flow rule and reduced strength parameters, overestimates the load reduction on trapdoors compared with a non-associative model with full soil strength parameters.

Investigation of earthquake angle effect on the seismic performance of steel bridges

In this paper, it is aimed to evaluate the earthquake angle influence on the seismic performance of steel highway bridges. Upper-deck steel highway bridge, which has arch type load bearing system with a total length of 216 m, has been selected as an application and analyzed using finite element methods. The bridge is subjected to 1992 Erzincan earthquake ground motion components in nineteen directions whose values range between 0 to 90 degrees, with an increment of 5 degrees. The seismic weight is calculated using full dead load plus 30% of live load. The variation of maximum displacements in each directions and internal forces such as axial forces, shear forces and bending moments for bridge arch and deck are attained to determine the earthquake angle influence on the seismic performance. The results show that angle of seismic input motion considerably influences the response of the bridge. It is seen that maximum arch displacements are obtained at X, Y and Z direction for 0°, 65° and 5°, respectively. The results are changed considerably with the different earthquake angle. The maximum differences are calculated as 57.06%, 114.4% and 55.71% for X, Y and Z directions, respectively. The maximum axial forces, shear forces and bending moments are obtained for bridge arch at 90°, 5° and 0°, respectively. The maximum differences are calculated as 49.12%, 37.37% and 51.50%, respectively. The maximum shear forces and bending moments are obtained for bridge deck at 0°. The maximum differences are calculated as 49.67%, and 49.15%, respectively. It is seen from the study that the variation of earthquake angle effect the structural performance of highway bridges considerably. But, there is not any specific earthquake angle of incidence for each structures or members which increases the value of internal forces of all structural members together. Each member gets its maximum value of in a specific angle of incidence.

Behaviour of piled embankment without reinforcement

A programme of 20 centrifuge tests was carried out on piled embankments without reinforcement to assess the influence of geometric parameters on surface settlement and on the load transfer mechanism. The three main geometric parameters studied were pile spacing, embankment height and area ratio, which were varied in ranges commonly adopted in practice. The measurements of the forces on the piles allowed assessment of the load transfer mechanisms, and thus the efficiency, which were shown to increase with embankment height and area ratio. Subsoil stress between piles was also assessed and compared with literature data. The centrifuge model test results for stress on the subsoil at the point of ‘maximum arching’ presented good agreement with the method proposed by Hewlett and Randolph in 1988. Measurements of the surface settlements allowed evaluation of the critical height at which surface differential settlements did not occur. The values of critical height obtained herein are in good agreement with recent literature recommendations.

Three-dimensional finite-element analysis of arching in a piled embankment

Piled embankments rely upon arching of the embankment material onto underlying piles, thus potentially significantly reducing load on the soft subsoil that more generally prevails beneath the embankment. Finite-element modelling of a piled embankment in plane strain has previously been reported; the ‘subsoil' was not explicitly modelled, but was represented by a vertical stress acting on the underside of the embankment. This technical note considers extension of this work to three dimensions. The results make particular reference to prediction of the stress on the subsoil at the point of ‘maximum arching' and the height of influence of arching within the embankment.