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Proper design of special segments under cavity conditions is essential for successfully implementing the upward shield tunneling method. When constructing upward tunnels, the segment structure in the corresponding construction area of the horizontal tunnel is special. To study the internal force distribution on the structure under the worst possible conditions given by the upward shield tunneling method, MIDAS GTS NX software is used to numerically simulate the structure based on the condition of the cavity behind it to determine the most unfavorable radius of the cavity. Moreover, an analysis of the cavity location is conducted. The results demonstrate that when the cavity is located at the bottom of the arch with a radius of 1 m and near the top of the arch with a radius of 0.5 m, the special segment structure is under the most unfavorable combination of stresses. The most dangerous working condition occurs when there is a 0.5 m radius cavity on one side of the arch in the cross‐section of the special segment. [ABSTRACT FROM AUTHOR]

In the health monitoring work of long‐span concrete‐filled steel tube tied arch bridges, finite element models have been commonly employed to indicate the practical stress state, and providing accurate data in real time and efficiently has been confirmed as the weakness of the finite element model. The prediction model is built in accordance with the general regression neural network (GRNN), and the parameters of the GRNN model are optimized using particle swarm optimization (PSO) to build the PSO‐GRNN prediction model, with the aim of modifying the finite element model. A finite element analysis model is built using the Qiuhuli flying‐swallow‐typed tied arch bridge to verify the effect of the PSO‐GRNN prediction model. The model test data are acquired using the horizontal thrust of arch foot, the bulk weight of main beam, and the tension of tied rod as the input variables and using the stress of main arch rib steel pipe, the stress of main arch concrete, and the displacement of mid span as the output variables. As revealed by the results, the average prediction accuracy of the PSO‐GRNN model constructed in this article is 96.706%, 98.531%, and 99.634%, respectively, which are 1.980%, 1.706%, and 0.40% higher than the back propagation (BP) neural network model and 2.262%, 1.632%, and 0.387% higher than the GRNN model. The mean absolute percent error (MAPE), root mean square error (RMSE), coefficient of determination (R2), and Nash‐Sutcliffe efficiency (NSE) coefficient were used to evaluate the prediction performance of the model. The PSO‐GRNN model has the highest fitting accuracy, indicating that the established PSO‐GRNN prediction model can more effectively predict the relevant parameters of concrete‐filled steel tube tied arch bridges and has high accuracy. [ABSTRACT FROM AUTHOR]

The pylon of the Xinshougang Bridge, a welded steel box arch with a variable cross-section, exhibits asymmetrical design and unevenly inclined limb ends. The segmented assembly of this uniquely shaped steel pylon necessitates precise splicing. In this paper, a novel three-point method for segment attitude positioning is proposed based on the local coordinate system. This method facilitates accurate coordinate translation and attitude alignment between the section preparation facility and the construction site. Furthermore, a predictive methodology for segment posture during erection is introduced, aiming to minimize misalignments at the connection interfaces. This approach accounts for potential deviations arising in manufacturing and erection phases. The synergistic application of these methods effectively ensures the precise geometric shape of the bending and twisting steel tower throughout its phased construction. [ABSTRACT FROM AUTHOR]

Because the urban tunnel is an essential knot of urban traffic and an easy blocking point in busy hours, upgrading the urban tunnel was necessary for the city after the tunnel being in service for a long time. However, to demolish the existing tunnel, some problems may be encountered, and these problems include occurrence of longitudinal cracks at the tunnel vault, increase of load due to infrastructure construction over the tunnel, unloading due to excavation of the rock over the tunnel, and uneven load due to asymmetric excavation or construction. To reinforce a cracked tunnel in Chongqing City, China, steel arches were installed to improve its bearing capacity, but some steel arches failed during the excavation of ground over the tunnel. Therefore, the scheme of "steel arch + shotcrete + tube column + transversal horizontal bracing" (hereinafter referred to as SASTCT) was proposed to ensure tunnel safety due to unloading and uneven load during the subsequent construction procedures. Numerical analysis indicated that the SASTCT measure can ensure the safety of the traffic and subsequent construction, which can provide some suggestions for similar tunnel upgrades in the future. [ABSTRACT FROM AUTHOR]

Early tied-arch bridges cannot satisfy the current traffic load demand due to their load grades and maintenance levels. Also, these tied-arch bridges have accumulated structural damage with increasingly prominent safety risks. In order to accurately evaluate the characteristics of tied-arch bridges' structural-influenced lines and identify damage of their arch ribs and suspenders, two analytical solutions are derived and established in this paper for the thrust-influenced lines of parabola and catenary two-hinged arches with a tie beam. A new method and an index for identifying damage of arch ribs and suspenders of tied-arch bridges are proposed. The results of numerical simulation in this paper verified that the proposed analytical solution has good analytical accuracy in practice on those two-hinged nonflat arches. With the use of equivalent thrust-influenced line difference curvature, the effectiveness of damage identification and the verification method were verified on the tie beam, suspender, and arch rib of plane tie arch structure as well as the suspender and arch rib of tied-arch bridges in this research. Furthermore, combining with grey relation analysis, the noise immunity of the proposed index method can be verified. Also, thrust-influenced line recognition based on VMD (variational mode decomposition) is introduced, and a practical process of bridge health assessment based on the quasistatic-influenced line loading of three-axle heavy vehicles is established. Theoretical analysis and numerical verification show that the calculated error of the analytic solution of two-hinged arches with a rise-span ratio greater than 1/8 is less than 9.57%, and the error decreases with the increase of the rise-span ratio. Therefore, it can be applied to the calculation and analysis of tied-arch bridges with a rise-span ratio range between 1/4 and 1/5. With the equivalent thrust-influenced line index proposed in this paper, the damage of suspenders and arch ribs of tied-arch bridges can be accurately located. It has been found that the proposed method is more effective to identify the damage of suspenders than the damage of arch ribs does, showing good noise immunity. In summary, this research has provided theoretical support for arch bridge design and evaluation. Combining with existing bridge-monitoring methods, the new bridge damage identification method proposed in this paper has the prospect of realizing the normal health status assessment of existing tied-arch bridges. [ABSTRACT FROM AUTHOR]

The vertical rotation method is a special option for steel tower construction in fabricated bridge. The tall tower is prefabricated on the ground and then pulled to its designed position using steel wires. Traditional vertical rotation method always uses a taller temporary structure to provide an upward pull force to lift the rotation member; however, the temporary structure would spend much time, cost, and work high above the ground. For instance, the Jinwu Bridge tower's weight was so heavy that the ordinary rotating method was not feasible. Therefore, a relay traction system with two auxiliary struts was employed to rotate the tower. The chief strut was first rotated to an inclined angle of 60° by an assistant strut to decrease the lateral component force of tension. Then, the tower was pulled from horizontal to vertical by the chief strut. Furthermore, a numerical model was established to analyze the mechanical behavior of the inner force, stress, and deformation of the chief strut, assistant strut, and tower. The study identified critical conditions such as the reverse of axial force for the assistant strut, intervention of back cables, and release of cable tension. The relay traction system effectively reduced initial pulling stress, spending less cost and time. Besides, the analysis method can be an innovate reference for other vertical rotating projects. [ABSTRACT FROM AUTHOR]

The existence of giant karst cave can cause collapse and water inrush hazards during the excavation of the karst tunnel, causing serious economic losses. In this paper, based on the FEA software MIDAS, a numerical simulation model for the backfilling of a large karst cave through a large cross-section tunnel was established. The distribution characteristics and change rules of the displacement field, stress field, horizontal support stress, and plastic zone of the tunnel surrounding rock and backfill were explored. The first stage of tunnel excavation leads to a sharp increase in the displacement of the tunnel's surrounding rock and the deterioration of the plastic zone, which should be strengthened and monitored. The tunnel arch, waist, and wall footing areas were prone to stress concentration. The two layers of horizontal support force show a certain regularity, showing a sharp increase and a gradually smooth growth trend. Meanwhile, the site monitoring results for arch settlement and horizontal convergence of the mega cavern tunnel were analyzed. The results show that the numerical calculation results were in good agreement with the values of site monitoring data. The average errors of final crown settlement and horizontal convergence were 8.6% and 15.9%, respectively, which verified the correctness of the numerical modeling method. This project can provide reliable experience for the construction of similar large cavern tunnels. [ABSTRACT FROM AUTHOR]

Due to the influence of the ground stress, mining disturbance, and other factors, the roadway surrounding rock in deep underground engineering such as mines, tunnels, and underground caverns is prone to looseness and deformation with the excavation of roadways. In such engineering, the bolt support is frequently employed to stabilize the surrounding rock. In this work, a part of the anchor and the surrounding rock were taken as a simplified model of the anchorage rock mass, and the laboratory compression test was performed on the similitude model. Then, the FLAC3D software was used to simulate varying numbers of bolts and different lateral pressure conditions, and the peak stress, the maximum principal stress field, and the anchor stress field distribution of the anchorage rock mass were obtained. The influence of bolt pretightening force and row spacing on the stability of surrounding rock was discussed using the combined arch theory. The results show that increasing the number of bolts and lateral pressure in the anchorage rock mass can significantly improve the stress value and distribution range of the maximum principal stress field and the anchorage stress field. The fluctuation of the anchorage stress field at different anchorage distances can be lessened by increasing the number of bolts (bolt density). When the lateral pressure exceeds 3 MPa, the anchorage mechanical characteristics of the anchorage rock mass tend to remain stable. The coverage of the effective anchorage stress field and the thickness of the surrounding rock anchorage composite arch can be increased by increasing the bolt pretightening force and decreasing row spacing, consequently improving the anchorage mechanical characteristics of the anchorage rock mass. The research results can be used as a theoretical reference for choosing appropriate bolt support parameters for the roadway surrounding rock. [ABSTRACT FROM AUTHOR]

The PBA construction method is suitable for urban subway construction in situations with dense traffic and many surrounding buildings and can effectively reduce surface disturbance and control surface subsidence. Based on field-measured data, this study creates numerical finite element models of 3D stratum-structure, studies the influence of each process conversion on the subsidence of the ground surface and the force of the station supporting structure during the construction of the PBA station, and clarifies the optimal construction parameters. The research results show that the consistency between the field monitoring data and the simulation data is more than 80%, which verifies the correctness of the model. It is concluded that the formation of the pile-beam-arch is the main part of the supporting structure and that digging the pilot tunnel and the formation of the beam arch are the control factors of surface settlement. Based on this, the best sequence of pilot tunnel excavation and arch buckle of the two-story two-span station is obtained, and the optimal pilot tunnel excavation scheme of first the middle and then the side, first the upper and then the lower, and the best arch buckle scheme of the synchronous arch buckle on both sides is determined. The results of the research can serve as a guideline when selection the construction parameters for similar PBA stations. [ABSTRACT FROM AUTHOR]

The main objective of the article is to find the optimal ranges of the cardinal topological, shape, and dimensional parameters that fully describe the constructional scheme of pedestrian radial network arch bridges of moderate spans. This task is solved by formulating the global optimization problem and seeking the minimum mass of the whole bridge structure. An optimal bridge scheme was obtained by tuning a large set of interdependent design parameters of diverse character: the topological parameters–the type of hanger arrangement, and the number of hangers; the shape parameters–hanger spread and central section angles, the alteration of these angles, and the arch rise; and the sizing parameters–all cross-sectional dimensions of structural members. Mathematically, this is a constrained mixed-integer global optimization problem solved by a stochastic evolutionary algorithm. Plane light-deck bridges of typical moderate 30, 45, 60, 75, and 90 m spans were optimized. Decisive design parameters and their rational ranges for all spans were revealed. In addition, the effects of some simplifications of the general bridge scheme were shown: using the constant spread and central section angles; imposing certain values on the ratio arch rise/bridge span; bounding the hanger diameters to a given value; and so on. Obtained results clearly indicate that the design recommendations for the lightweight network arch bridges should differ from the recommendations for similar automotive and railway bridges. Our findings are: the optimal ratio of arch rise to the bridge span is 0.20–0.30, the number of hangers is >40 even for the shortest spans, the spread angle between hangers is 30°–40°, and the girder mass amounts to ∼30% of the total bridge mass, while the mass of hangers amounts up to 20% and increases when imposing constraints on the minimal radius at the expense of diminishing arch mass. [ABSTRACT FROM AUTHOR]

In order to study the causes of arch foot cracking, a multiscale numerical simulation method was used to establish the finite element model of Xizha Bridge during the construction stage of the Xiaoqing River restoration project in Jinan by using Midas Civil, and the internal forces under adverse conditions were extracted. On this basis, Abaqus was used to establish the local model of arch foot, and the plastic damage model parameters were introduced to conduct stress analysis. The results show that the anchorage stress of prestressed steel bundle is too high. On the one hand, the stress component produced by the bending of the prestressed steel bundle can squeeze the concrete inside the bending angle, and on the other hand, it will stretch the concrete outside the bending angle, resulting in concrete cracking. There is a tendency of relative displacement between arch rib and arch foot, and the interface surface of arch foot and arch rib is pulled by the displacement of arch rib, resulting in cracking. Arch foot inner bend produces a certain tensile stress, and if this place is not paid enough attention to, insufficient reinforcement will produce large cracks. Finally, it is suggested that concrete cracking can be avoided by arranging enough reinforcement bars under anchor and sealing reinforcement bars, encrypting steel mesh, arranging shear studs, and extending insertion depth. [ABSTRACT FROM AUTHOR]

Taking a concrete-filled steel tube (CFST) arch bridge with a clear span of 400 m as an example, the in-depth analysis of its natural vibration characteristics is carried out by establishing a finite element model. Then, the three-dimensional El Centro recorded wave after amplitude modulation is taken as the excitation wave; the structural response under three kinds of single dimension and four kinds of multidimensional combined excitation and 0∼90° transformation X(longitudinal) + Y(transverse) orthogonal combined excitation is evaluated. The results show that the structure of long-span top-supported arch bridge extends in the longitudinal and vertical dimensions at the same time, and the mode shape density and mass distribution have multidirection and multiangle coupling. With the increase of excitation dimensions, the value and relative ratio of chord axial force increase. The maximum axial force ratio of X + Y to X and Y is 2.1, the maximum axial force ratio of X + Y + Z (longitudinal) to X + Y, X + Z, and Y + Z is 1.4, 1.8, and 1.8; the displacement in X and Y direction under combined excitation is independent and the displacement in Z direction is its coupling term, but the displacement under X + Y + Z combined excitation is only 10% larger than that under X + Z and Y + Z combined excitation. Under the combined excitation of X + Y with a changing angle of 0°∼90°, the axial force variation of the chord at different positions and on the same section of the arch rib has spatial characteristics. The variation range of upper and lower rod axial force varies from 0.63 to 1.35 and from 0.81 to 1.51, respectively, the change trend of displacement in the X and Y directions is relatively consistent, the change of displacement in the Z direction is asynchronous, and the displacement of vault section increases by one time. The seismic response of this bridge type under multidimensional and multiangle excitation shows obvious superposition. [ABSTRACT FROM AUTHOR]

Steel pipe columns are an important component in subway station construction and with stand stress state and internal force during the construction process. Based on the engineering background of Beijing subway, this paper introduces the geological conditions, station structure types, and internal force monitoring of steel pipe columns of 10 subway stations constructed by the PBA method. The field monitoring indicates that the greatest change in the internal force of the steel pipe column occurs during stage 1 (beam, primary support, and secondary lining buckle arch construction stage), no matter pile foundation station or strip foundation station, which accounts for about 60% to 65% of the total axial force. When the left and right spans are not synchronously arched or excavated, the steel pipe column is subjected to uneven forces and bears a large bending moment is produced. When the depth of overburden is between 7 m and 15 m, the internal force of the steel pipe changes positively correlated with the overburden depth. During the construction process, the internal force of the steel pipe varies widely in the silty sand stratum. Also, the steel pipe columns in stations affected by groundwater bears about twice of the axial force compared with other stations are not affected by groundwater. In addition, the construction period is also a factor that affects changes in internal forces. This research is conducive to update the database of the world subway projects and can serve as a practical reference for similar geological condition. [ABSTRACT FROM AUTHOR]

In view of the problem of taking the loose layer as the uniform cloth load while ignoring thickly sticky loose layered arch (TSLLA) of the traditional mining rock overburden structure analysis, combined with the geological conditions of shallow buried thickly sticky loose layer in Shendong mining area, the mechanical model of the mining TSLLA bearing structure is established, the variation law of arch height under different loose layers is analyzed, and the formation conditions of TSLLA are given. The first theory deduced the dynamic evolution mechanism of TSLLA structure advancing. The dynamic evolution of TSLLA structure in 22207 coalface is simulated. The formula for the limit height of TSLLA is derived. A classification method of mining loose layer structure is proposed. The loose layer structure type is divided into load type, arch beam type damage type, and limit arch height type. On this basis, the mechanical model of "arch beam" is constructed. The influence mechanism of the TSLLA on the surface cracks is revealed. The methods and calculation steps for initial surface cracks are presented. The results are verified by the measured data of surface subsidence of the typical thickly sticky layer in Shendong mining area. [ABSTRACT FROM AUTHOR]

Focusing on a constant resistance (CR) cable, using particle flow code (PFC) software, the constant resistance characteristics of the cable are replaced by the servo control of the pallet, and the compressive mechanical properties of rock anchored on the free surface of a tunnel under different constant resistance values (CRVs) are studied. The results show that (1) during the compression failure process of the anchored rock, the stress-strain curve has a "double peak" feature, and the number of cracks has a "step" feature. The mutation point of the number of cracks corresponds to the two peak points of the stress-strain curve. (2) When the constant resistance value of the pallet is approximately 70%-80% of the absolute rigid support strength, the anchored rock has the maximum compressive strength, most stable deformation, maximum pallet energy absorption effect, and minimum number ratio of tensile-shear cracks. The mechanical properties of the CR-anchored rock are the best. (3) According to the different failure forms, the failure types of anchored rock under different CRVs are divided into the overall single-arch collapse type, connected double-arch collapse type, nonconnected double-arch collapse type, and local single-arch collapse type. The research results provide a reference for the design of a CRV and collapse prediction of the anchored surrounding rock. [ABSTRACT FROM AUTHOR]

The 52307 working face with large mining height in Daliuta coal mine is chosen as the research background, where there is the special mining condition in the overburden structure with a buried depth of more than 150 m and only one layer of key structure in Shendong mining area. Using the methods of similarity simulation experiment and theoretical analysis, the overburden movement law based on the arch mechanical model of plane contact block is systematically researched. The research results indicate that before the initial weight, the main key layer appears layered fracture in the mining process, and its lower rock layer becomes a part of the collapse zone. Before the initial weight, the upper key layer forms a "fixed supported beam" structure. When the beam reaches the limit length, shear failure occurs in the middle position; during the periodic weight, the upper key layer breaks into the plane contact block arch structure close to the same size. Relying on the friction between the contact planes, it has a certain displacement but does not collapse completely. The load transmitted from overburden is transmitted to the rear of the gob through the semiarch characteristics of the structure; the sliding instability and rotary deformation instability of the plane contact block arch structure are analyzed. The fracture of the key layer lags behind the mining position of the working face by a certain distance, due to the influence of the fracture angle of collapse zone in the advancing process of working face. The research results provide an important guiding significance for prediction and prevention for dynamic disaster of rock strata in working face with large mining height. [ABSTRACT FROM AUTHOR]

The obvious anisotropy of layered rock mass prevents the built-in constitutive model of commercial simulation software from accurately describing the elastoplastic behavior of the rock mass. In this paper, a transversely isotropic elastoplastic constitutive model (called the AN-MC model) that characterizes the elastoplastic failure behavior of the layered rock mass is developed by introducing the Mohr-Coulomb yield criterion with the tension cutoff in the model based on the transversely isotropic constitutive model and deriving its finite difference scheme. The development and programming of the transversely isotropic elastoplastic constitutive model are achieved on the basis of the secondary development platform of FLAC3D and the VC++ environment. The accuracy and rationality of the proposed constitutive model are verified in terms of consistency of the calculation results of the developed transversely isotropic elastoplastic constitutive model and the built-in constitutive models. In the numerical analysis of the Queerxi tunnel project, the calculation results of the AN-MC model are in good agreement with the field monitoring data. Thus, the deformation characteristics of the tunnel surrounding rock are well characterized. Comparative analysis of the deformation and failure laws of the layered surrounding rock and isotropic surrounding rock indicates that the plastic failure range of the layered surrounding rock tunnel is larger, and the arch foot and waist are prone to plastic penetration failure with butterfly-shaped characteristics. The research results are important for the scientific prediction and precise support of layered rock mass deformation. [ABSTRACT FROM AUTHOR]

In recent years, the construction of a CFST arch bridge has developed rapidly; however, as a kind of structural system dominated by compression, with the increase of material strength and span, the stability of the main arch of the CFST arch bridge has become more and more important. In this paper, the finite element method is used to analyze the hanger force and the main arch stability of the long-span CFST arch bridge. Combined with the Shenzhen Rainbow Bridge project, the axial force of the hanger, the internal force, and stability of the main arch of the arch bridge are studied. In the establishment of the finite element model, considering the actual operation of the arch bridge, the model simulates the interaction between steel pipe and concrete, it studies the large deformation of CFST arch bridges, and the stress distribution and overall stability of the arch bridge are analyzed. The results show that the main deformation of the CFST arch bridge is the vertical displacement of the deck, and the axial force of most members of the upper arch ribs is greater than that of the lower arch ribs. The axial force and bending moment of the lower arch rib near the arch foot are larger, and the compressive stress of the arch foot is greater than that of other positions. The axial force of the suspender of the arch bridge is the largest at both ends of the hanger and the middle hanger, and the axial force of the other hanger is close to each other, and the axial force changes little under the same case. The buckling modes of the arch are mainly the lateral buckling or flexural buckling of the arch rib outside the plane, which indicates that the vertical stiffness of the arch bridge structure is larger than that of the transverse stiffness. The research results make the load-bearing mechanism of the CFST arch bridge more clear and also provide a certain reference for the design and construction of the CFST arch bridge. [ABSTRACT FROM AUTHOR]

The upward shield method in horizontal tunnels has the advantages of small ground space occupation, low construction cost, and short construction period, which expresses substantial economic benefits. The special segments of horizontal shield tunnels corresponding to the upward shield method construction area have special design requirements, and different internal force calculations and analyses should be carried out. To determine the mechanical behavior of the special segment structure of horizontal shield tunnels during the construction of upward shield tunnels, the theoretical calculation formula of the internal force of the special segment structure is deduced based on the average uniform rigidity ring method. Moreover, the bending moment and axial force of special segments are numerically simulated and analyzed using Midas GTS NX software. Finally, the theoretical formula and finite element calculation results are compared and analyzed. The results show that the internal force values of the open segment ring and the adjacent segment ring of the special segment are quite different during upward shield tunnel construction. Furthermore, compared with the arch crown and arch bottom of the segment ring, the stress at the arch waist of the segment ring is the most unfavorable. The stress difference between the open segment ring and the adjacent segment ring may cause unbalanced deformation, leading to damage to the segment ring radial joint. In the design and construction, attention should be given to the shear strength of the segment ring radial joint and the bending stiffness of the ring joint at the arch waist. [ABSTRACT FROM AUTHOR]

Concrete pouring steel tube arch is a critical part in the construction of a long-span concrete-filled steel tube arch bridge. With the adoption of the improved TOPSIS, this study summarized five indicators that controlled the concrete-filled steel tube pouring sequence. The indicators include the vertical displacement of the arch rib, lateral offset of the arch rib, steel tube stress, concrete stress, and elastic safety factor of the arch rib. Furthermore, a comprehensive objective function-rationalization index was proposed, based on which a practical evaluation and determination method for pouring scheme of the long-span concrete-filled steel tube arch bridge was developed. The results showed that a pouring sequence with relatively small stress in the arch rib, advanced alignment, and good stability could be determined using the proposed method. [ABSTRACT FROM AUTHOR]

Aiming at the problems of safety and monitoring beyond the existing experience in the construction of the subway stations with arch cover method in Dalian, China, combined with the real-time monitoring requirements of intelligent construction status, a multi-information construction monitoring system based on digital twin(DT) and Internet of Things(IoT) is proposed, and the digital twin 3D architecture is established. First, on the basis of the IoT monitoring experience of tunnel, the installation plan of the automatic monitoring device of the arch cover method subway station is clarified, and the sensor arrangement is carried out. Then, based on the Revit platform, the establishment of the main structure model of the station and the BIM parametric modeling technology of the sensors are realized, and the monitoring properties of the sensors are expanded. Finally, through the design of the BIM database and in the form of secondary development, a BIM-based construction information visualization monitoring system is established to realize the correlation between the sensor model and the monitoring data and achieve the effect of information visualization query and color change early warning. The system was initially applied at Shikui Road Station of Dalian Metro Line 5 and achieved good results. The system can intuitively reproduce and accurately describe the subway station construction status, which provides an advanced technical means for the informatization and visualization management of the construction of arch cover method subway stations. [ABSTRACT FROM AUTHOR]

In order to solve the problems of insufficient frequency, time-consuming, and labor-consuming of monitoring and measurement in the process of tunnel construction, a tunnel construction monitoring and measurement technology based on Internet of Things is proposed in this paper. This method adopts the basic theory and technology of Internet of Things, analyzes the fit relationship between Internet of Things technology and tunnel construction, uses the comprehensive perception, reliable transmission, and intelligent auxiliary technology possessed by the existing Internet of Things technology system, and has been successfully applied to tunnel engineering. The experimental results show that the contact pressure between the surrounding rock and the initial support on the monitoring and measurement section in the tunnel is zero after the initial support shotcrete is applied. The contact pressure between the surrounding rock and the shotcrete layer at the right arch waist of the left tunnel is the smallest, and the stress in the whole change process is less than 10 kPa. The contact pressure between surrounding rock and shotcrete layer after excavation is divided into three stages. Conclusion. the tunnel construction monitoring and measurement technology based on Internet of Things technology fully realizes the intellectualization and informatization of the construction process, plays a scientific and effective monitoring and early warning role, and reduces the project cost of the whole project, which has a certain engineering value. [ABSTRACT FROM AUTHOR]

At present, the theory of supporting the surrounding rock small structure of gob-side entry driving has been widely used, but there is no specific quantitative analytical formula for the bearing strength and bearing characteristics of the structure. Construct a small structural stress arch mechanical model based on the arch axis equation, and divide the width of coal pillars (fractured zone-plastic softening zone-plastic hardening zone) and small structural stress arch height. According to the relationship between the stress arch height and the size of the roadway, the anchor cable length is determined to be 7.3 m, and the "anchor mesh + ordinary long anchor cable + grouting anchor cable" coordinated support plan is proposed: anchor net support is used for the first support, and long anchor cable and grouting anchor cable are used for the second support. Combined with the supporting parameters, a mechanical model of the surrounding rock composite bearing stress arch is proposed, and the composite bearing stress arch structure is derived using elastoplastic mechanics to obtain the ultimate bearing strength relationship expression. The results show that the ultimate bearing capacity of the haulage gateway of 17236 island working-face in the north of Zhangji coal mine can reach 29.193 MPa after the composite bearing stress arch support. The feasibility of the supporting scheme is verified, and field monitoring showed that the deformation zone of the surrounding rock of the transportation haulage gateway is stable after being supported by the composite bearing stress arch structure, the maximum shrinkage of the top and bottom of the roadway is 287 mm, and the distance between the two sides is 640 mm. [ABSTRACT FROM AUTHOR]

Existence of roof discontinuity surface is one of the extremely important factors causing the asymmetric fracture of roadway roof, especially for large-span soft rock roadway. In this paper, a crack density coefficient (D) is firstly defined by local thresholding-microcell segmentation method and used to analyze the evolution law of D with roof drilling depth (d) (the lower and upper of roof discontinuity are defined as regions I and II, respectively). Then, UDEC numerical simulation is used to investigate the asymmetry evolution law of roof total displacement, maximum principal stress, and crack density with stress release coefficient (α) considering the effect of discontinuity surface. Research results indicate that (1) the roof parameters (D) in regions I and II both show a negative logarithmic function decreasing trend with the increase of drilling depth. When d < 4.5 m, the parameter (D) in region II is about 1.5 times that in region I; when d ≥ 4.5 m, the parameter (D) in region I is almost zero, while the parameter (D) in region II maintains a slight decreasing trend. Roof failure presents asymmetric distribution characteristics along both sides of the discontinuous surface. (2) In the initial stage of open-off cutting excavation, the top left and right corners of roof as well as the bottom of discontinuous surface first occurred the tension-shear failure, and then as the α increases, the two side cracks gradually shift to the middle of roof in regions I and II with the appearance of stress concentration in two top corners. Meanwhile, the direction of maximum principal stress is transformed from "direction approximately parallel to the excavation surface" to "direction perpendicular to the discontinuous surface," of which the location transfers to the deep anisotropically, forming an asymmetric stress loosening zones in the roof of regions I and II. The range of stress loosening zone in region II is significantly larger than that in region I. When the surrounding rock stress is completely released, the roof cracks in region I gradually transition from nonconnected to connected state and form a "quasi-right triangle" loosening zone. In addition, an "isosceles triangle-like" high crack density loosening zone with the roof middle as the axis is also formed in region II. The roadway roof presents a markedly asymmetric caving feature. (3) With the increase of discontinuity surface angles, the roof fracture range gradually decreases in region I and increases in region II as well as the structural features of roof pressure-bearing arch transform from "left-low right-high continuous asymmetric structure" (30°-60°) to "left-low right-high discontinuous asymmetric structure" (90°) to "unilateral partial pressure-bearing arch structure" (120°-150°). Research results can provide an extremely important reference for the optimization and design of support scheme with discontinuity-thick soft rock roof-large span roadways. [ABSTRACT FROM AUTHOR]

Combined with specific engineering examples, the spatial disturbance influence characteristics and laws of the surrounding rock stress in the staggered roadways are analyzed by numerical simulation. This paper concludes that (1) compared with the surrounding rock pressure behavior of the general roadway, the surrounding rock stability of the staggered roadway is relatively poor, showing the characteristics of the local serious roadway rock pressure behavior, such as the intensified destruction of the roadway side, the failure and fracture penetration of the surrounding rock between the roadways, and the relatively serious deformation of the surrounding rock. The reason is that the stress of the surrounding rock at the staggered roadway position is obviously superimposed and disturbed by each other; (2) the influencing factors of the failure and instability of the surrounding rock between interlaced roadways are as follows: the greater the buried depth and the smaller the distance between roadways, the more intense the superposition disturbance of the surrounding rock stress between roadways; the smaller the horizontal azimuth, the greater the influence range of superposition disturbance of surrounding rock stress between roadways; the more unbalanced the original rock stress field, the worse the stability of the surrounding rock between roadways, resulting in the more serious failure and instability of the surrounding rock between roadways; (3) for the staggered roadway layout, increasing the distance between roadways, the closer to the orthogonal layout and selecting the arch section of the lower roadway is conducive to the bearing stability of the surrounding rock between roadways; (4) constrained by the space conditions of staggered roadway, the role of bolt and cable support is limited. Passive support is the key to realize the safety and stability of surrounding rock of staggered roadway, so the control technical scheme of active and passive combined support in staggered roadway position is put forward, the combined support of the upper roadway "bolt + cable + shotcrete + concrete cushion of floor" and lower roadway "bolt + cable + U-shaped steel support passive reinforcement + shotcrete" within the spatial disturbance influence the range of surrounding rock stress in the staggered roadways, and the technical scheme can achieve satisfactory supporting effect. [ABSTRACT FROM AUTHOR]

Profit margins for essential foodstuffs could be a demand rising problem. There are several variables influencing currency fluctuations. For example, the various variables of commodity food prices are climate, crude prices, and so on. Forecasting the fluctuating prices of basic foodstuffs is also relevant even for the government, producers, and customers. The article will use ARCH (autoregressive conditional heteroskedasticity) to forecast the essential food market considering external conditions. The findings agree well enough with the assessment price in the industry by employing two main approaches, ARCH and GARCH (generalized autoregressive conditional heteroskedasticity). For jalapeno, the best result (96.87%) in estimating the cost of employing ARCH is achieved. In the meantime, the best result (99.94%) for the basic food tomato is observed using GARCH. Proportionally, the ARCH is stronger than GARCH, since GARCH is very consistent without disrupting current information. [ABSTRACT FROM AUTHOR]

To study the dynamic response of shallow buried tunnel lining by drilling and blasting method, ABAQUS simulation software was used to establish a tunnel blasting finite element model based on the consideration of in situ stress. Dynamic static coupling numerical simulation was conducted to analyze the vibration response and stress response of tunnel lining. The simulation results were compared and analyzed with field monitoring data to obtain the dynamic response law of tunnel lining. The results show that in the same tunnel lining section, the vibration velocity response in the Y direction is the largest and the vibration velocity response in the Z direction is the smallest. The location of the peak particle velocity of the tunnel lining in three directions appears differently, and the location of the maximum MISES stress appears differently for different excavation sections. The arch shoulder is most affected by horizontal vibration in the X direction, and the vault is most affected by horizontal vibration in the Y direction. The dynamic response at the foot or arch shoulder position away from the lining section of the working face will show the "whip tip effect." A sudden change in MISES stress occurs at the location of the footing in the 315° direction of the liner section, and the liner is not uniformly stressed in this range. [ABSTRACT FROM AUTHOR]

At present, the tunnel construction engineering is increasingly transferring to southwest mountainous areas with complex terrain and geological conditions in China and presents a trend of "large buried depth, long tunnel line, high stress, strong karst, high water pressure, complex structure and frequent disasters." Taking water inrush disaster of karst tunnel fault zone as the research object, an evolutionary mechanical model of rock damage under the coupling action of stress-seepage is proposed in this paper. Besides, based on Comsol Multiphysics numerical software, the tunnel excavation is simulated, and the stress field, seepage field, and rock damage during the excavation are analyzed; thus, the mechanical mechanism of water inrush disaster from tunnel fault in karst area is obtained. The research results indicate that the tunnel excavation is a dynamic construction process, and the construction disturbance redistributes the original rock stress field and changes the state of seepage field. With the increase of excavation steps, the contour distribution of vertical stress ratio near the tunnel face is a circle shape, indicating that the rock mass is obviously disturbed by excavation, and the ratio of principal stress difference of rock mass at arch crown and bottom plate is large. Besides, the fault fissures expand and penetrate under the influence of tunnel excavation disturbance, increasing the permeability of fault zone in karst tunnel. In addition, the water seepage erosion takes away the granular rock mass, and the lithology becomes more weaker, which makes it possible for the occurrence of water inrush disaster in karst tunnel. Therefore, the advanced geological prediction is important in tunnel construction in karst area. The research results can be treated as an important theoretical basis for the prevention and treatment for water inrush disaster of fault zone in karst tunnel. [ABSTRACT FROM AUTHOR]

A common situation found in many old and modern buildings is the annoying floor vibration. Many old buildings suffer floor vibration as no specific design guidelines were employed to limit the situation. In modern buildings, the development of floors of lighter weight, longer span, and less inherent damping is the main cause for the annoying vibration. In this paper, as a novel application, the influence of viscoelastic tuned mass dampers (TMDs) in vibration mitigation of an existing steel joist jack arch floor structure is investigated using finite element (FE) analysis. Results of a free vibration test conducted on the prototype TMDs are used to validate the FE model. The jack arch floor is subjected to the walking loads of different stepping rates of 1.5, 2, and 3 Hz. Various load models that are available in the literature are used to define the dynamic walking load, and the response mitigation is carried out based on the most critical load models. The influence of design parameters such as the excitation frequency, configuration of the individual dampers in the TMD system, and the mass ratio of the TMD system on the vibration mitigation of the floor structure are investigated in detail. Results of this study indicate that the viscoelastic TMDs are effective in vibration mitigation of jack arch floor structures. [ABSTRACT FROM AUTHOR]

Artificial support system takes advantages of self-bearing capacity of surrounding rock mass in roadway support, which is one of the important supporting ideas in modern times. The implementation way of an artificial support system is worthy of deep investigation. In this study, an HLBR hypothesis was proposed with comprehensive consideration of mechanical properties of surrounding rock mass based on the reinforced arch theory and axial variation theory. A model of bearing structure in surrounding rock mass was constructed, and the stress state on the bearing structure was analyzed. It was believed that when the axial ratio (k) of this bearing structure is equal to the lateral stress factor (λ) (which is the optimal axial ratio), the tangential stress on the bearing boundary reaches the minimum and is in uniform distribution. At this moment, the roadway and the supporting structure can make good use of the self-carrying capacity of surrounding rock mass, which is conducive to lowering the stress distribution level of surrounding rock mass. According to prestress diffusion characteristics of bolt, some ways to achieve HLBR were proposed, which were the optimal axial ratio design, difference support and local grouting modification, and finally performance of the original support design in a belt roadway of the mining district IV of a mine in Shanxi Province. A new supporting scheme was provided according to the HLBR hypothesis. In addition, the FLAC3D strain-softening model was modified by C++, which was used to interpret the reasonability of the suggested supporting scheme. The proposed HLBR hypothesis discloses ways to use self-capacity of surrounding rock mass. This study provides a new idea for roadway sectional design and roadway support design, which are beneficial to maintaining the stability of surrounding rock mass in roadways. [ABSTRACT FROM AUTHOR]

The research on the dynamic response and influencing factors of shield tunnel lining under earthquake demonstrates significant engineering value in guiding the design of antiseismic tunnels. In this paper, a nonlinear finite element model of soil-tunnel interaction is established based on FLAC finite difference software, and then Mohr–Coulomb elastoplastic model and dynamic plastic damage model are used to simulate the dynamic characteristics of soil and lining damage of tunnel, and the seismic waves of South Iceland are selected to analyze the residual internal force, dynamic internal force distribution, and the relative deformation of the top and bottom of the arch of the shield tunnel under the earthquake load. Meanwhile, the effects of depth tunnel, lining thickness, and tunnel diameter on the dynamic response of the tunnel are discussed. In addition, the interaction law of horizontal parallel tunnel and the amplification effect on the surface acceleration are also studied. The results show that under the action of a strong earthquake, the bearing capacity of the tunnel decreases sharply, the lining is destroyed, and a large residual internal force appears. When the buried depth of the tunnel is small, the nonlinear effect is more significant, and the R value increases at first and then decreases with the increase in the seismic acceleration. The maximum dynamic bending moment and maximum dynamic axial force of the tunnel lining aggrandize obviously with the increase in tunnel diameter and lining thickness. In particular, the dynamic bending moment has internal force redistribution and deflection under the condition of large tunnel diameter and small lining thickness. Moreover, the interaction of parallel tunnels affects the distribution of internal force and the magnitude of adjacent surface acceleration. [ABSTRACT FROM AUTHOR]

Steel arch bridges with inclined arch ribs under strong wind fields are prone to fatigue damage due to the stress concentration at the position of hanger connections. Therefore, it is essential to perform the wind-induced response analysis for specified shape hangers, such as inclined hangers, to determine the stress distribution and corresponding influencing factors. In this study, wind-induced response analysis for a fatigue-prone asymmetric steel arch bridge with inclined arch ribs is performed by the numerical simulation approach. The investigated bridge hangers' models are established by using the COMSOL Multiphysics software. The wind-induced stress of the bridge hangers under different wind directions is obtained based on the finite element method. The influential factor of the stress distribution of the bridge hangers on both the windward side and the leeward side is discussed. In addition, the stress peaks of the long hanger and short hanger are achieved for further fatigue analysis. This paper provides a reference for determining the critical fatigue-prone position of an asymmetric steel arch bridge with inclined arch ribs. [ABSTRACT FROM AUTHOR]

To reduce the damage of earth penetrators on underground fortifications against blast and fragmentation penetration, a model of underground arch structure with elastic support was established for a modal analysis on the structure subject to penetration and explosion with ANSYS/LS-DYNA software for dynamic analysis. In the process, the effect of spring stiffness coefficient on the dynamic response of the structure was analyzed in terms of pressure, equivalent stress, and peak vertical displacement. The simulation results showed that the elastic support reduced the dynamic response of the structure, while the equivalent stress and pressure of each part of the underground arch structure were reduced, and the peak vertical displacement was increased as the stiffness coefficient of the elastic support was lowered, and the isolation efficiency of equivalent stress and pressure at the arch shoulder was lower than that at other parts. Therefore, reducing the stiffness coefficient of the elastic support alone cannot meet the need for vibration isolation of the arch shoulder, and the type or stiffness coefficient of elastic support should be selected reasonably according to the actual engineering requirements, so as to achieve a good vibration isolation effect. [ABSTRACT FROM AUTHOR]

During the blasting excavation of the large-span tunnels, the instability of the blasting caused the overexcavation phenomenon, making the grille arch difficult to land completely in the primary support of the tunnel, thus forming an arch foot defect. In order to reduce the security issues of tunnel engineering construction and scientifically evaluate the influence of arch foot defects on the force performance of the overall structure of the arch frame, combining the Qingdao Metro long-span hard rock tunnel project, this paper designs two grille arch test sections with arch foot defects and one conventional section to carry out field tests. Combining with FLAC3D numerical simulation, the results of the study were used for analyzing the stress characteristics of arch foot defect grille arch in the primary support of the tunnel. The results indicated that (1) the arch foot of conventional section arch frame is subjected to the force transferred from the upper part and the deformation pressure of surrounding rock within the arch foot range, and the upper transfer force borne by the arch foot mainly comes from the deformation of arch waist. (2) When the arch frame has arch foot defects, the deformation of surrounding rock at the arch foot and the deformation transferred from the upper part mainly depend on the shotcrete, thus resulting in the increase of shotcrete strain. (3) Anchoring bolt and shotcrete can integrate the grid arch with the surrounding rock, thus bearing local loads in the arch crown, arch waist, and shotcrete. (4) The numerical calculation of arch frame with arch crown, arch waist, and arch foot defects claims that the force reduction of the arch frame caused by the arch foot defect was the most obvious, and the calculation results were consistent with the actual project. [ABSTRACT FROM AUTHOR]

The self-bearing capacity of the rock masses has been a hot pot in the research of supporting technology in underground engineering. The pressure arch has been considered the main hypothesis to explain the self-bearing capacity of the rock masses. In this paper, the engineering of the twin-parallel openings in the jointed rock masses was selected as the background of the research. The characteristics of the deformation or the movement of the rock masses above the openings were studied based on the pressure arch theory. The difference between the single opening and the twin-parallel openings has been revealed, and the mechanism has also been illustrated. Besides, the joints' strength, the in situ stress ratio, the distance between the two openings, and the excavation sequence were selected as the variable parameters, and their influences have also been illustrated by the DEM method. [ABSTRACT FROM AUTHOR]

The strong disturbance of upward mining of the short-distance multiseam results in frequent fractures in the coal seam to be mined, jeopardizing the operation safety due to the instability of the surrounding rock of the overlying stope and risks of coal and gas outburst. A lucrative alternative is the downward mining of multiseam, which wide implementation is limited by the lack of reliable data on stress evolution characteristics. In this paper, the evolution, nonlinear interaction, and superposition characteristics of mining-induced stress after multiple pressure relief in the short-distance multi-seam were investigated by the numerical simulation and physical simulation, taking the endowment and mining technology characteristics of group B short-distance multiseam in Pan'er Coal Mine in Anhui Province of China as an example. The numerical and physical models of multiple (2—5 times) mining activities in pressure relief multiseam (with five main coal layers) under downward mining are constructed and implemented with the FLAC3D software and 1 : 100 scaling, respectively. The results showed that a pressure relief arch, which bears and transfers stresses, is formed on the coal seam's roof and floor. In downward mining, the local arch expands to the long arch, which bearing capacity within the influence range of multiple mining disturbances is weak, and the arch structure is prone to instability. If a coal pillar is left in the upper coal seam after its mining, the lower coal seam mining will switch from the large-scale low-stress area under the goaf to the small-scale high-stress area of nonlinear interaction of the multiple mining stresses with the stress under the coal pillar. [ABSTRACT FROM AUTHOR]

In order to study the influence of the softening and swelling of weakly cemented soft rock on the stability of roadway surrounding rock, based on the background of the general return airway in the south wing of Yuwu coal mine, 4 different schemes are designed according to whether the softening or swelling effect of weak cemented soft rock is considered. Based on the numerical simulation program, FLAC3D was used to analyze the distribution characteristics of the shear stress, displacement, and plastic zone of the surrounding rock of the roadway under these 4 designs. On this basis, in view of the geological conditions of the roadway, a new type of "grouting + anchor cable mesh + bottom arch" combined support plan is proposed. The research results show that, under the conventional anchor-net-cable-spraying support scheme, the surrounding rock of the roadway can remain stable without considering the softening and expansion of the weakly cemented soft rock in contact with water and its maximum displacement and plastic zone depth are only 66.9 mm and 2.8 m. When considering the softening and swelling of weakly cemented soft rock roadways, due to the synergistic effect of the two, the maximum displacement of the surrounding rock of the roadway and the depth of the plastic zone will reach 517.4 mm and 6.7 m, respectively, which will continue to increase with excavating along the roadway and lead to ultimately destabilization and destruction. After adopting the combined support of "grouting + anchor cable mesh + bottom arch," the maximum displacement of the surrounding rock of the roadway and the depth of the plastic zone will be reduced by 77.1% ∼ 92.0% and 18.7% ∼ 72.4%, respectively, and they will basically remain stable after excavation of 5 days. [ABSTRACT FROM AUTHOR]

We have analyzed the arch root morphology, nail placement accuracy, degree of arch deformity, and three-dimensional Cobb angle in patients with NF scoliosis by CT 3D reconstruction. Likewise, we have thoroughly examined arch root morphology, nail placement accuracy, degree of arch deformity, and three-dimensional Cobb angle in patients with idiopathic scoliosis by CT 3D reconstruction. The results of the two groups were statistically analyzed and compared to assess the efficacy and other morphological differences between these groups. For this purpose, 276 patients with scoliosis, including 221 with idiopathic scoliosis and 16 with neurofibromatosis scoliosis, were treated in the hospital, which is from May 2008 to December 2016. The 16 patients with idiopathic scoliosis were matched with patients with neurofibromatosis, and the postoperative CT data were reconstructed in three dimensions, and the measurements included arch morphology, arch transverse diameter, arch-rib joint transverse diameter, three-dimensional coronal Cobb angle, and correction rate. The data of the two groups were statistically analyzed to compare the arch morphology, nail placement accuracy, and treatment effect between patients with NF and patients with AIS. Statistical analysis was performed to compare the differences between NF and AIS patients in terms of morphology, nail placement accuracy, and treatment outcome. The results showed that there were more severely deformed pedicles in NF patients than in idiopathic scoliosis, and the difference between them was statistically significant. Of the 142 screws placed in the NF group, 88 screws were in a good position, and the remaining 54 screws were misplaced. [ABSTRACT FROM AUTHOR]

With the development of urban tunnels, more and more studies focus on the antiseismic design of tunnels. Setting up a shock absorption layer is a very effective means in the earthquake resistance of an urban tunnel. In this paper, in order to study the influence of the thickness of a shock absorption layer on the antiseismic effect of the urban shallow buried double arch rectangular tunnel, the Tengzhou–Fenghuang tunnel is used as the research background. Firstly, the model is established by finite element software to analyze the tunnel with 50 mm, 100 mm, and 150 mm thick shock absorption layers, and analyze the tunnel displacement, stress, and safety factors of different models under the action of a seismic wave. Finally, the calculation results are compared and analyzed with those of the model without the shock absorption layer to summarize the thickness of the shock absorption layer suitable for urban shallow buried rectangular tunnels. The results show that the displacement and stress of tunnel lining are significantly reduced, and the safety factor is significantly improved after setting the shock absorption layer. Among them, the tunnel with a 100 mm thick shock absorption layer has the greatest reduction in principal stresses, the greatest increase in safety factor, and the best antiseismic effect, while the construction costs are not high. It is recommended that the urban shallow buried double arch rectangular tunnel be constructed with a 100 mm thick shock absorption layer. [ABSTRACT FROM AUTHOR]

To study the influence of profile shape on the stability of nonhomogeneous slopes, strip mechanical models of slopes with different profile shapes were established following the simplified Bishop method. Three hundred and seventy slope models with different profile shapes and strata sequences were simulated and analyzed with FLAC3D. The results show that slopes with weaker-to-stronger (WtS) strata sequences are, in most cases, more stable than slopes with stronger-to-weaker (StW) strata sequences when all other conditions are the same. Slopes with linear shapes are the most stable. With increasing arch height, the stability of convex slopes decreases, and the stability of concave slopes first increases slightly and then decreases. When the strata sequences are WtS, the factors of safety (FoSs) of slopes with convex and exterior polyline shapes decrease more slowly. However, when the strata sequences are StW, the FoSs of slopes with concave and interior polyline shapes decrease more slowly. The greatest X-displacements are concentrated in the steeper areas of the slopes. For different strata sequences, the higher the rock strength at the steeper position is, the more stable the slope is, and the opposite trend is also observed. For the same strata sequence, the stability of a polyline-shaped slope is always better than that of a curved slope with the same inflection point. [ABSTRACT FROM AUTHOR]

The roadway of S2S2 fully mechanized caving face (FMCF) in Xiaokang Coal Mine is one of the most typical deep-buried soft-rock roadways in China and had been repaired several times. In order to figure out the failure reasons of the original roadway support, the geological conditions were investigated, the surrounding rock stress was monitored, the rib displacement, roof separation, and floor heave were in situ measured, and the performance of the U-shaped steel support was simulated. The above analysis results indicated that the support failure was mainly caused by (1) the unreasonable arch roadway section, (2) the high and complex surrounding rock stress, (3) the failure control of the floor heave, and (4) the inadequate self-supporting capacity of the surrounding rock. For optimizing, the roadway section was changed to circle and a new full-section combined support system of "belt-cable-mesh-shotcrete and U-shaped steel-filling behind the support" was adopted, which could specifically control the floor heave, allow the roadway deformation in control, and improve the self-supporting ability and stress field of the surrounding rock. To determine the support parameters, the selected U-shaped steel support was verified by simulation, and various bolt-cable support schemes were simulated and compared. Finally, such an optimized support scheme was applied in the roadway of the next replacement FMCF. The in situ monitoring showed that the rib-to-rib convergence and roof-to-floor convergence were both controlled within 600 mm, which indicated that the roadway was effectively controlled. This case study has important reference value and guiding function for the optimal design of the soft-rock roadway support with similar geological conditions. [ABSTRACT FROM AUTHOR]

This study presents and evaluates the mathematical model to estimate the mean and variance of single-lead ECG signals in sleep apnea syndrome. Our objective is to use the volatility property of the ECG signal for modeling. ECG signal is a stochastic signal whose mean and variance are time-varying. So, we propose to decompose this nonstationarity into two additive components; a homoscedastic Autoregressive Integrated Moving Average (ARIMA) and a heteroscedastic time series in terms of Exponential Generalized Autoregressive Conditional Heteroskedasticity (EGARCH), where the former captures the linearity property and the latter the nonlinear characteristics of the ECG signal. First, ECG signals are segmented into one-minute segments. The heteroskedasticity property is then examined through various tests such as the ARCH/GARCH test, kurtosis, skewness, and histograms. Next, the ARIMA model is applied to signals as a linear model and EGARCH as a nonlinear model. The appropriate orders of models are estimated by using the Bayesian Information Criterion (BIC). We assess the effectiveness of our model in terms of mean square error (MSE), root mean square error (RMSE), mean absolute error (MAE), and mean absolute percentage error (MAPE). The data in this article is obtained from the Physionet Apnea-ECG database. Results show that the ARIMA-EGARCH model performs better than other models for modeling both apneic and normal ECG signals in sleep apnea syndrome. [ABSTRACT FROM AUTHOR]

The impact of multiple explosion sources on the safety of the underground cavern is enormous. Based on a similarity model test, the finite element software LS-DYNA3D was utilized to analyze the damage evolution and circumferential strain distribution characteristics of the bolt-supported cavern under the seven combinations of concentrated charge explosion sources in three places, including the side of the vault, side arch, and sidewall. The accuracy of the simulation results is verified by comparing them with test results. The research results indicate that the damage of the surrounding rock is mainly caused by the tensile stress wave reflected from the free surfaces and the superposition of the tensile stress wave. The damage of the surrounding rock in the cases of multiple explosion sources is not a simple superposition of that in the cases of a single explosion source. The peak circumferential stress and damage of the surrounding rock in the middle of two explosion sources are significantly greater than that of the cases of the corresponding single explosion source. In the seven cases, the peak circumferential strain of the cavern wall changes from tensile to compressive from the vault to the spandrel. When the explosion occurs on the sidewall, the peak circumferential strain of the floor is tensile. [ABSTRACT FROM AUTHOR]

This paper is based on the condition where layered argillaceous cemented sandstone as an engineering background is met by the No. 207 fully mechanized working face open-off cut (Wanli No. 1 Coal Mine). Through mechanical theory analysis and field practice, the engineering safety problem of the large-span argillaceous cemented sandstone layered open-off cut roof supporting structure was analyzed. The roof caving arch height of the open-off cut roadway in 207 working face was obtained based on the mechanical mechanism of instability and caving of the layered surrounding rock mass roof. The anchor cable suspension and bearing stability of the open-off cut roof were analyzed in terms of the layered beam structure model. Meanwhile, combining with conditions, reasonable and effective support countermeasures and key parameters are proposed for such open-off cut roadway and enhance the actual supporting engineering on-site. These research results could provide engineering reference for an open-off cut roadway with composite roof conditions featured to weak cementation and weak interlayer. [ABSTRACT FROM AUTHOR]

Mining above confined aquifer has become an important task for water inrush prevention in China. To study the failure characteristics of stope floor along the strike, a mechanical model under combined action of mining and confined aquifer was constructed, and the distribution of vertical stress, horizontal stress, and shear stress was obtained. Based on the Mohr–Coulomb criterion, the failure range of the floor is determined and verified by the in situ test. The results indicate the following. (1) Both vertical stress and horizontal stress in the stope floor take the junction of stress increasing area and stress decreasing area as the dividing line, forming two groups of "convex arches" at the solid coal side and the goaf side, respectively. (2) The vertical stress gradient in the solid coal side is significantly higher than that in the goaf side, while the horizontal stress gradient in the solid coal side is similar to that in the goaf side. The shear stress distribution is divided into three regions by the boundary between positive and negative shear stress, which makes the stope floor in this area to show compression shear or tension shear failure. (3) According to the in situ test, the maximum floor failure depth of 41503 working face is 11.38 m, which is quite close to the theoretical calculation result of 9.68 m. (4) Applying the mechanical model to five other coal mines with different mining conditions and stress states, the maximum absolute error between the measured and theoretical values of floor failure depth is 1.1 m, the average absolute error is 0.8 m, the maximum relative error is 8.2%, and the average relative error is 6.5%. The study provides a certain mechanical basis and reference for the floor failure mechanism induced by mining and confined aquifer. [ABSTRACT FROM AUTHOR]

Yelang Lake Bridge is the largest cantilevered single-chamber reinforced concrete arch bridge in China, with a net span of 210 m. In this article, an equation for positioning the height of the formwork before pouring of the arch ring segment was derived, which was suitable for the construction control of the long-span reinforced concrete arch bridge such as the Yelang Lake Bridge. The arch ring segment elevation calculation equation was derived under the two typical working conditions that the concrete pouring of the arch ring segment is completed and the buckle cable and anchor cable tensioning are completed. In addition, two typical working conditions of arch ring segment concrete pouring and cable tensioning were evaluated. Then, a new type of cradle and loading test of the cradle, which meet the requirements of the long segment pouring of the arch ring, were introduced. Finally, the measurement deviation during the construction of the arch segment was analyzed. The linear control results of the arch ring showed that the arch ring segment elevation calculation formula could effectively ensure the accuracy of the arch ring segment construction process under the two typical conditions of completion of concrete pouring of the arch ring segment and completion of the buckle and anchor cable tensioning. The maximum deviation is only 3.1 mm. The line shape after the completion of the arch ring construction was in good agreement with the target line shape, and the deviation between the measured value and the target value was only 2.5 cm, which met the engineering requirements. [ABSTRACT FROM AUTHOR]

In order to explore the stability of coal pillar and the characteristics of roof movement during the process of roadway backfill mining (RBM), the 301 backfilling test working face of Ordos Chahasu coal mine is taken as the background. Based on the expansive pressure arch theory, the evolution process of the stope expansive pressure arch in RBM is studied; by establishing a mechanical model for the stability of coal pillars, the interactions between the height, width, and the maximum number of branches are obtained. When the width and height of the branch are both 5 m, the optimal number of the branches is obtained. Then, by establishing a mechanical model for the subsidence of the immediate roof, the process of the immediate roof subsidence is divided into three stages, namely, the formation stage of the local pressure arch, the merge stage of the pressure arch, and the expansion stage of the pressure arch. In addition, using the numerical method, the alternate bearing process of coal pillars and filling bodies and the change of the maximum supporting stress are studied, and the evolution of the pressure arch bearing structure above the stope and the staged subsidence characteristics of the roof are analyzed. The on-site test showed that the coal pillar has a good stability during the mining process. The maximum stress of the coal pillar is 16.5 MPa, and the maximum stress of the filling body is 9 MPa. The maximum settlement of the immediate roof is 102 mm, indicating that the roof control effect is good. This research will play an important role on engineering practice. [ABSTRACT FROM AUTHOR]

A carbonaceous mudstone tunnel is a type of soft rock tunnel. There is little research on the prevention and control measures for the deformation and failure of carbonaceous mudstone tunnels. In this article, we investigated the construction of the Qiguding carbonaceous mudstone tunnel in Meizhou City, Guangdong Province, China. We monitored and analyzed the deformation and stress characteristics of a section under the original support scheme. The monitoring data showed that this section had large peripheral convergence, vault subsidence, steel arch strain, and concrete strain. The deformations exhibited significant differences in the horizontal and vertical directions, eventually resulting in concrete cracking, steel arch bulging, and distortion in the section. The analysis showed that the primary mechanisms for the failure were the softening characteristics of the carbonaceous mudstone, the plastic rheology, and the shear slip of the rock stratum. Based on a comparative analysis and numerical simulation, we proposed a new support measure called the longitudinal rigid enlarged foundation that consists of a steel arch longitudinal connection system and a locking foot anchor pipe system. Several comparative tests were performed at the tunnel site. The results demonstrated the excellent performance and reliability of the proposed support scheme for the deformation control of the carbonaceous mudstone, providing a reference for similar projects. [ABSTRACT FROM AUTHOR]

For the problems of unreasonable force and large deformation of traditional antislide structure system, three new arch antislide pile-wall structure systems are designed for a loess landslide treatment project in Northern Shanxi province. The working performances of four kinds of antislide structures are numerically simulated and analyzed to realize the optimization of the antislide structure system. The results show that the arch antislide pile-wall structure system is a rigid connection between the piles and cap beam, and the antislide pile, cap beam, and sliding bed soil form a spatial nearly rigid structure. Cap beam can better transfer the bending moment generated by the larger thrust in the landslide middle to the piles with less force on both sides of the landslide, so that the stress and deformation of the whole antislide system tend to be uniform, which makes the antislide system "joint operation." And this structural form increases the overall stiffness and bending capacity and reduces the possibility that the middle pile is destroyed first and loses its working capacity due to large thrust. Compared with the traditional antislide structure system (Model-1), the average displacement of the pile head is reduced by about 60%, and the total control bending moment of the system is reduced by about 6%. The purpose of Model-3 and Model-4 (anchorage arch antislide pile-wall structure system and pull-rod arch antislide pile-wall structure system) is to restrict the deformation of cap beam in both positive and negative directions of x-axis in arch antislide pile-wall structure system, which plays a certain role in coordinating the deformation of antislide structure and better coordinating the stress of each pile. The arch antislide pile-wall structure system (Model-2), anchorage arch antislide pile-wall structure system (Model-3), and pull-rod arch antislide pile-wall structure system (Model-4) can better adapt and adjust the unbalanced thrust between the landslide piles; therefore, they have higher structural robustness than that of traditional antislide structure system. When achieving the management target with a 95% structural reliability probability of the same landslide, the structural robust degrees of Model-1, Model-2, and Model-4 are 0.58, 0.76, and 0.81, respectively. Therefore, the pull-rod arch antislide pile-wall structure system (Model-4) has the best performance among the other antislide structures. These studies lay a foundation for the engineering structural optimization of arch antislide pile-wall structure system. [ABSTRACT FROM AUTHOR]

Cable-supported arch bridges have had many cable break accidents, which led to dramatic deck damage and even progressive collapse. To investigate the dynamic response and robustness of cable-supported arch bridges subjected to cable breaking, numerical simulation methods were developed, compared, and analyzed, and an effective and accurate simulation method was presented. Then, the cable fracture of a prototype bridge was simulated, and the dynamic response of the cable system, deck, and arch rib was illustrated. Finally, the robustness evaluation indexes of the cable system, deck, and arch rib were constructed, and their robustness was evaluated. The results show that the dynamic response of the adjacent cables is proportional to the length of the broken cable, while the dynamic response of the deck is inversely proportional to the length of the broken cable. The dynamic amplification factor of the cable tension and deck displacement is within 2.0, while that of the arch rib bending moment exceeds 2.0. The break of a single cable will not trigger progressive collapse. When subjected to cable breaking, the deck system has the least robustness. The proposed cable break simulation procedure and the robustness evaluation method are applicable to both existing and new cable-supported bridges. [ABSTRACT FROM AUTHOR]