Abstract:Due to the excessive development speed， the rotation mechanism is often damaged by collision with the limit device when it is deployed to a predetermined form. For example， when the Falcon 9 rocket produced by SpaceX is deployed in the folding leg， too large a corner speed may lead to the destruction of the pin hinge of the leg. Installing a damper can slow down the speed of the mechanism and improve the safety of deployment， which is the premise and guarantee of the stable landing of the rocket. The traditional displacement damper cannot adapt to the speed， and there is a risk of sticking when applied to the mechanism development. However， the traditional high-pressure oil damper easily causes leakage and failure under high-speed operation. As a new type of velocity damper， eddy current torque damper can be used to slow down the angular speed of the mechanism. It has the advantages of no external power supply， no working fluid， and strong durability. However， due to the low relative motion speed between the permanent magnet and the conductor plate， its energy dissipation efficiency is not high， which limits its application in engineering. To enhance the performance of traditional composite tube eddy current dampers， a composite tube eddy current torque damper with the optimized magnetic circuit is proposed in this paper. Compared with traditional composite tube eddy current dampers， the damper proposed in this paper has litter magnetic leakage and a smaller installation volume. In addition， the working speed of the damper is increased by adding a gear accelerating device to further improve the energy consumption performance. The finite element model of the eddy current torque damper was established based on COMSOL analysis software， and the effects of air gap， conductor tube thickness， and back iron thickness on the torsional damping coefficient were analyzed. At the same time， considering the installation space size， the formula for calculating the eddy current damping force is derived， and the formula for estimating the eddy current torque damping coefficient of the composite pipe is proposed. The prototype of a large speed discharge eddy current torque damper and the principle verification device of the expansion mechanism are manufactured， and the impact retarding performance is tested. The results show that for the specific damper parameters， reasonable values of the thickness of the permanent magnet and conductor plate can obtain high torsional damping coefficients. The damping coefficient estimation method presented in this paper can accurately describe the mechanical properties of a velocity amplifier eddy current torque damper in the damping linear section. Using a prototype damper weighing about 12 kg， the final kinetic energy dissipation efficiency of the test development mechanism can reach 41.6% under the most unfavorable working conditions， which has a strong energy dissipation efficiency advantage.

Abstract:Rubber concrete is concrete formed by using rubber particles as additional aggregates， and its unique physical properties and strengthening effects have led to its increasing popularity and application in civil engineering. To study the feasibility of rubber concrete as a pile cap in the pile-bearing low embankment system， this paper prepared rubber concrete specimens with different rubber particle sizes and volume content， carried out a series of static compressive tests and hysteresis test under cyclic loading， and obtained mechanical property indexes such as compressive strength， hysteresis dissipation， damping loss factor， dynamic modulus of elasticity etc.， and their changing rules with rubber particle size and volume content. It is found that with the increase of the volume content of rubber particles， the compressive strength and dynamic elastic modulus of rubber concrete specimens gradually decrease exponentially to a critical value， which is related to the size of rubber particles. The smaller the particle size， the lower the strength and dynamic elastic modulus. The hysteresis energy consumption and loss factor show a quadratic trend with the rubber particle content， increasing first and then slightly decreasing， and reaching a peak at around 8% to 10% of the rubber particle content. Compared with the loading amplitude level， the influence of particle size on energy consumption is relatively small.

Abstract:To study the effects of buffer layers on the mechanical and deformation characteristics of the pile-slab wall structure supporting expansive soil slopes， the combined pile-slab wall-buffer layer ［including polystyrene foam （EPS） buffer layer and bagged gravel buffer layer］ supporting structure of a railway expansive soil slope in Dangyang， Hubei Province was taken as the object. Through a field test， the change laws of soil moisture， pile displacement， earth pressure behind the inter-pile slab， and pile and inter-pile slab bending moment of the combined supporting structure under the climate environment were analyzed. The interaction mechanism of the expansive soil slope-buffer layer-pile-slab wall combined supporting structure and its synergistic mechanical and deformation relationship were revealed under different buffer layers. The research results show that compared with the bagged gravel buffer layer， the EPS buffer layer can effectively reduce the lateral swelling pressure， with a maximum reduction rate of 69% obtained by this test. Meanwhile， the EPS buffer layer can rapidly respond to the change of swelling-shrinkage behavior of expansive soils caused by the climate environment and then dynamically improve the distribution of total lateral earth pressure behind the slab， while the bagged gravel buffer layer is relatively weak in response to the climate environment. A stable and coordinated interaction can be formed between the expansive soil slope-EPS buffer layer-pile-slab wall structure， which can reduce the influence of swelling characteristics of expansive soils on the bending moment of inter-pile slabs.

Abstract:The design of connections is the foundation for ensuring the cooperative work of both materials in timber-concrete hybrid structures. To investigate the mechanical performance and failure modes of timber-concrete bolted connections， this study selected Cross-laminated timber （CLT）-concrete bolted connections and Spruce Pine Fir （SPF）-concrete bolted connections as experimental subjects， and designed twenty-seven sets of monotonic loading tests and cyclic loading tests. The typical failure modes of the two types of timber-concrete bolted connections were summarized and compared. The findings reveal that a direct correlation between the bearing capacity of timber-concrete bolted connections and the bolt-yielding mode is observed. Compared to SPF-concrete bolted connections， CLT-concrete bolted connections are more prone to double-hinge failure and exhibit better ductility. Through the analysis of the influencing mechanisms behind the mechanical performance differences， accounting for the impact of steel plates， and introducing the equivalent section of CLT， a mechanical model for the bearing capacity of timber-concrete bolted connections was proposed. The calculated values showed an average error of 12.18% compared with experimental results， indicating good agreement with the experimental values，which provides a reliable reference for the design and application of timber-concrete bolted connections.

Abstract:Four full-scale joints were tested under low cyclic loading to verify the seismic performance of the proposed precast local reactive powder concrete frame beam-column joints. Based on the tests， a calculation method of strength and deformation was proposed according to the connection characteristics of the joints， and a theoretical model of a flat-topped trilinear skeleton curve was constructed. The curve stiffness values of each stage of the test hysteresis curve were obtained by theoretical calculation， and the relationship between the loading and unloading stiffness， as well as the loading drift ratio of the specimen under low cyclic loading， was obtained by fitting. The restoring force model was then established according to the hysteresis rule. The calculation results show that the trilinear skeleton curve and hysteresis curve established by theoretical calculation are in good agreement with the experimental results， which can better reflect the stress characteristics of this kind of connection joints in each stage and provide a theoretical basis for elastic-plastic analysis and seismic design.

Abstract:To study the distortion effect of single-box twin-cell thin-walled box girders with cantilever plates， the distortion differential equation was established based on the plate-beam frame method， and the initial parametric solution of the equation under vertical eccentric concentrated load was derived. The concrete analytical formula of the distortion frame moment of inertia of single-box twin-cell box girder with cantilever plates was also presented. The analysis on the cantilever box girder and simply supported box girders examples was performed using analytical theory. The results show that the analytical solution is in good agreement with the results from existing literature and finite element analysis， which verifies the correctness of the analytical theory. Through the parameter analysis， it can be seen that the greater the thickness of the middle web， the stronger the ability of the twin-cell box girder to resist distortion. The transverse bending moment of the external webs is little influenced by the variation of thickness of the middle web， but the transverse bending moment of the middle web increases with the increase of its thickness. When the thickness of the middle web is equal to that of the external webs， the transverse bending moment of the middle web is approximately twice that of the external webs.

Abstract:In response to the national “14th Five-Year Plan” to vigorously promote prefabricated construction and enhance the energy efficiency of new buildings and to contribute to the achievement of the nation's “dual carbon” target， a prefabricated structural insulation integrated composite sandwich wall panel is proposed. To achieve a fully dry connection for these wall panels， solid concrete frames are positioned around the perimeter of the panels as one of the connectors. The presence of concrete frames creates a significant thermal bridge， which largely determines the thermal performance of the wall panel. Quantifying the effect of the frame ratio on the thermal performance of the wall panel is of great guiding significance for its structural design optimization and practical engineering application. Therefore， six sets of wall panel specimens with varying frame ratios were designed and tested by calibrated hot box method in this study to quantitatively analyze the effect of the frame ratio on the thermal performance of prefabricated wall panels. The experimental results reveal that the presence of concrete frames not only postpones the time to reach a steady state in thermal transmission but significantly reduces the thermal performance of the wall panel. When the frame ratio is 19.94%， 30.85%， 40.95%， 50.26%， and 61.43%， the thermal resistance of the wall panel is reduced by 79.26%， 84.28%， 87.48%， 89.36%， and 91.10%， respectively. To meet the current building energy-saving requirements， the frame ratio of the wall panel should be controlled within 20% in practical engineering applications. Through a comparative analysis of various methods for calculating wall panel thermal resistance with experimental results， it is recommended to use the zone method as the thermal resistance calculation method for wall panels with concrete frames.

Abstract:The ±800 kV ultra high voltage （UHV） long cantilever transmission tower cross-arm structure belongs to a high-level horizontal long cantilever structure sensitive to the vertical seismic effect. It is urgent to conduct vertical seismic fragility analysis research on cross-arm structures. To address this， a framework for vertical seismic fragility analysis， considering multiple performance levels， was proposed for the UHV long cantilever transmission tower cross-arm structure. Firstly， a finite element model was established with the UHV long cantilever transmission tower as the research object， and the vertical dynamic characteristics of the structure were analyzed. Secondly， based on the stress ratio of the main component at the end of the cross-arm structure， multiple performance levels for slight， moderate， and severe damage to the cross-arm structure were established. Finally， a vertical seismic fragility analysis based on a probabilistic seismic demand model was carried out for the cross-arm structure. The analysis results show that the long cantilever transmission tower is significantly affected by higher-order vibration modes under vertical earthquake， and the first three vertical modes that contribute significantly to the vertical response of the structure are the 16th， 26th， and 29th modes， respectively. Under vertical seismic action， the end main component is the main load-bearing member of the cross-arm structure. Compared with considering the strength failure of the main component in tension bending at the end of the cross-arm structure， the failure probability of the cross-arm structure considering the instability failure of the main material in compression bending is significantly higher under the given vertical seismic intensity.

Abstract:To fulfill the requirements for the assembly of building structures， this paper proposes a new type of socketed column-column joints， which uses internal and external sleeves as the splicing members of the upper and lower steel tube columns and is assembled only through high-strength bolts. To study its load-bearing performance under bending-shear action， three specimens were designed and studied by static tests. The load transfer mechanism， failure mode， ultimate bearing capacity， and strain development of the joints were obtained. The finite element models were established， and based on verification of the accuracy of these models， a parametric analysis of the joints was carried out. The effects of the sleeve grouting， the inner sleeve thickness， and the joint length on the ultimate bearing capacity were analyzed. The results show that the inner sleeve near the plate to the first vertical bolt is the key area for load transmission in the joint domain. The sleeve grouting and joint length reduction can retard the joint strain development， but the influence is limited. When the length of the joint and the relative bending stiffness of the inner and outer sleeves are unchanged， sleeve grouting can make the connection force performance better， and the ultimate bearing capacity is increased by 19.3%. When other parameters are unchanged， the greater the length of the node， the greater the level-hold effect. The ultimate bearing capacity is increased by 15.1% as the length of the joint is increased from 300 mm to 600 mm. The greater the thickness of the inner sleeve， the higher the load-bearing capacity safety reserve of the section. The ultimate bearing capacity is increased by 31.4% as the inner sleeve thickness is increased from 8 mm to 12 mm. Based on the finite plastic development strength criterion and level-hold effect， a formula for calculating the flexural capacity of the joints was presented. The accuracy of the calculation formula is verified by comparing experimental results with numerical predictions.

Abstract:To consider the difference in the section rotation angle of the wing flange， web， and composite box girder when calculating the shear stress of a cantilever beam with variable section corrugated steel web， a displacement function was first established based on the rotation angles of the flanges， web， and composite box girder. The energy variational method was used to separate the shear contribution of the flange and web， and the bending moment equivalent was used to further separate the top and bottom flange shear. Secondly， the shear-stress solving program was established based on the stiffness matrix of the beam segment analysis element and the joint load array of the composite box girder with variable section corrugated steel web. Lastly， the study analyzed the shear stress and shear capacity ratio of the top flange， bottom flange， and steel web of the cantilever beam under various loading conditions. The results show that， when compared to the finite element calculation results， the accuracy of the calculation results of the shear capacity ratio of the top flange， web， and bottom flange after considering the difference of rotation angle can be improved by a maximum of 3.48%， 3.43%， and 6.91%， respectively， compared with the existing results of shear stress calculation of variable cross-section. The shear capacity ratio of each component of the cantilever beam depends on the load form. The values of the top flange and bottom flange reach the maximum under the concentrated load of the beam free-end， which is 12.82% of the free end and 60.81% of the fixed end， respectively， and the web shear capacity ratio reaches the maximum under the action of uniform load， which is 78.11% of the free end.

Abstract:Vehicle traveling can cause bridge vibration. As the span increases， bridge non-linearity increases and vehicle-bridge interaction becomes more pronounced. In this paper， a 575m long-span concrete-filled steel tubular arch bridge， Guangxi Pingnan Third Bridge， is taken as the study objective. Pulsation tests and accessibility field tests were carried out on it. Meanwhile， a refined vehicle-bridge coupling finite element model was established. Vehicle-bridge coupling vibration response under different vehicle speeds and vehicle weights was analyzed to explore its response law. Besides， the dynamic coefficient of control sections of the bridge is also calculated and compared with that calculated by the current code to discuss the applicability of the current code to this bridge. The results show that the numerical results are in good agreement with the results of the field pulsation tests， and the trend of the dynamic strain time course curve under different conditions is basically the same as that of the field tests. There is no significant relationship between the dynamic response of the bridge and the vehicle speed within the speed range of 20 km/h to 60 km/h. When the vehicle exceeds 60 km/h， the deflection increases sharply with the speed. The increase in vehicle weight leads to an increase in the maximum dynamic deflection of the bridge and a decrease in the impact coefficient， but the actual total response of the bridge does not decrease. Therefore， the speed and weight of the vehicles crossing the bridge should be strictly controlled to effectively reduce the impact effect of the traffic load on the bridge.

Abstract:The BIM model does not support finite element analysis， and data exchange between the BIM model and the finite element analysis model is difficult. As a result， the forward design process using BIM technology faces issues such as low modeling efficiency and difficulty in modifying models. This makes it impossible to integrate BIM structural design with finite element mechanical analysis， thereby increasing the cost of structural model creation and error correction. Based on the Revit and Midas/Civil software platforms， a set of Revit-Midas/Civil model information conversion programs is designed with the IronPython language in the Dynamo environment. Taking the main bridge of Boshi Bridge as an example， the program automatically realizes the following aspects： 1） It becomes possible for component decomposition in the Revit model bridge， section characteristics calculation， cable， and beam tower elastic connection processing. Then， the processed information was converted into the Midas/Civil language format MCT file， realizing the automatic conversion of the Revit to Midas/Civil model information； 2） The calculation results from the finite element analysis are fed back to the Revit model. The effect information is given a gradient color according to the numerical value， realizing the display function in the BIM model for the results of finite element analysis. This proposed methodology can realize the information conversion between the Revit-Midas/Civil model， which effectively improves the efficiency of BIM forward application and makes up for the lack of BIM technology in bridge analysis.

Abstract:In response to the problem that the current specifications are difficult to reflect the actual bridge safety due to the frequent occurrence of overweight vehicle loads in China， this paper constructed a framework for generating traffic load response considering the impact effect based on measured data from a weight-in-motion （WIM） system. The response of random traffic flow was extrapolated using the compound extreme value theory， and a model for traffic load effect probability that considers the influence of the evaluation benchmark period was established. Moreover， a fatigue reliability assessment method for cable-stayed bridges based on measured traffic flow was proposed. Taking a cable-stayed bridge with the measured data of three mouths from a WIM system as a background， the reliability of the cables was evaluated. The results show that， in the case of using the load probability model extrapolated based on the measured WIM data， the fatigue reliability index of the cables ranges from 3.93 to 6.12， and the reliability index of the ultimate limit state strength for carrying capacity ranges from 7.74 to 11.04. The fatigue reliability index ranges from 4.35 to 6.18 when using the standard load probability model， which indicates that the fatigue reliability is significantly lower than the strength reliability， indicating that the safety of the cables in the assessment benchmark period is mainly controlled by fatigue. Compared with load benchmark periods extrapolated based on measured WIM data， the standard loads will significantly overestimate the fatigue reliability of the cables.

Abstract:To realize the dynamic analysis of expansion joints under traffic flows across bridges， aiming at the large size difference between the main beam and the expansion joint in the bridge-expansion joint system， the complex structure of the expansion joint， and the problem that the conventional modeling approach falls short in balancing detailed analysis with calculation efficiency， a “cross” modeling concept of bridge-joint integration was proposed and a vehicle bridge joint analysis system was established to investigate the influence of dynamic factors of traffic flow on the dynamic response of expansion joints. Firstly， on the basis of clarifying the internal structure of the expansion joint and the movement correlation of the component， the longitudinal division of the bridge element， transverse division of the expansion joint element and multi-point constraint organic connection of the beam expansion joint were proposed. Secondly， a vehicle-bridge-joint analysis program was connected through the program call and preparation of the connection program. Finally， based on the traffic load survey data， the typical traffic flow load conditions were constructed， and the influence of traffic flow dynamic factors such as vehicle weight， speed， and vehicle distribution on the dynamic response of car-joint structure was explored. The results show that： 1） The bridge joint integrated finite element model established based on the “cross” modeling concept not only meets the computational efficiency but also takes into account the detailed components of the expansion joint. 2） There is a significant positive correlation between the vertical displacement of the main beam at the midspan of a cable-stayed bridge and the weight of moving vehicles on the bridge， while the correlation with vehicle speed is weak. The spacing between vehicles in the train decreased from 50 meters to 30 meters， and the maximum vertical displacement at the midspan of the main beam increased by about 34%. The more concentrated the vehicle load on the bridge， the greater the vertical displacement at the midspan of the main beam. 3） The cumulative sliding stroke of the middle beam from the beam end to the fixed end of the expansion joint gradually decreases. Under single vehicle operating conditions， there is a positive correlation between vehicle speed， weight， and longitudinal displacement of expansion joints. There is a negative correlation between the maximum longitudinal displacement of the expansion joint and the distance between vehicles during train operation. The impact of vehicle braking on the dynamic response of the expansion joint is very significant， and the longitudinal displacement response of the expansion joint 1 # beam is 3.97 times that of the normal sports car working condition.

Abstract:To study the wind characteristics at a bridge site in the complex mountainous terrain and their effect on the buffeting response of a long-span bridge， a cable-stayed bridge in a mountainous area was considered as the engineering background. Firstly， the fluctuating wind field characteristics at the bridge site with enough monitoring points were obtained by the large eddy simulation method. Then， the buffeting forces of the bridge were calculated by the fluctuating wind field via the traditional harmonic synthesis method， the type C suggested in the specification， and the large eddy simulation method， and their buffeting responses were compared and analyzed. Furthermore， the effects of non-uniform wind field characteristics at the bridge site on the buffeting response of the bridge were investigated. The results show that the mean wind speeds， wind attack angles， turbulence intensities， etc.， of the long-span bridge in the mountainous terrain， show obvious non-uniformity along the bridge span， and the turbulence intensity ratio， fluctuating wind speed spectra， and coherence function are different from the recommended values in the specification， reflecting the limited applicability of the recommended values in the specification in complex mountainous wind fields. The buffeting response obtained by the fluctuating wind field simulated with the harmonic synthesis method is less safe than that obtained by the fluctuating wind field synchronously monitored by the large eddy simulation method. The buffeting response obtained by the fluctuating wind field simulated by the spectrum suggested in the specification is unsafe in the vertical displacement but conservative in the lateral displacement and torsional displacement compared to the results obtained by the large eddy simulation method. The non-uniform wind speed has significant influences on the vertical， lateral， and torsional buffeting responses of the main beam， and the non-uniform wind attack angles can also affect the torsional response of the main beam. The vertical and lateral buffeting response spectra at the mid-span point under the non-uniform wind speed are obviously higher than those under the uniform wind speed， while the differences of torsional buffeting response spectra at the mid-span point between the non-uniform wind speed and the uniform wind speed are not distinct.

Abstract:The occurrence of geologic hazards often results in widespread failures of road transportation infrastructures， significantly affecting regional transportation activities. To assess the transportation system’s resilience to disasters， this study introduces a method for evaluating the robustness of road networks， considering the influence of geologic disasters. Utilizing historical disaster data， the impact of disasters on road transportation is quantified as the damage probability to network segments. The vulnerability index of road segments is defined based on the damage probability and indicators of the importance of road segments. Employing percolation theory， the study evaluates network robustness from structure and performance perspectives， simulating and comparing changes in robustness indicators under different attack strategies. Structurally， the critical percolation threshold is determined through the connectivity subgraph scale as the robustness index. Regarding performance， overall network accessibility is used to assess performance changes during the percolation process. Results show that the network is most vulnerable to attacks based on road segment vulnerability indicators， with both structural and performance assessments indicating that the primary network components constitute 40%~50% of the overall structure. Meanwhile， the study identifies potential critical road sections using the percolation threshold and the peak of robustness metric changes and proposes a method to distinguish effective critical road sections by comparing their impact on the overall network. The research framework， spanning from robustness assessment to critical section identification， offers insights for evaluating and enhancing the robustness of transportation networks， providing theoretical support for network planning and management.

Abstract:In the field of intelligent transportation systems and urban security， it is crucial to obtain accurate information of vehicles. Vehicle-related information can be directly obtained through visual recognition means such as video or images. However， in low-light environments， the image brightness and contrast decrease， the noise level increases， and the image features are prone to loss. These problems lead to a significant reduction in the detection accuracy of vehicle detection algorithms. Therefore， we propose a vehicle detection method based on low-light image enhancement and an improved object detection algorithm. The low-light image was first enhanced using the image enhancement algorithm ZeroDCE to improve the image brightness. Then， the improved AFF-YOLO object detection algorithm is utilized to perform vehicle detection on the enhanced image. Finally， the proposed method is tested on a vehicle dataset， and the vehicle detection accuracy under different low-light levels is analyzed. The results show that the proposed method can effectively improve the vehicle detection accuracy. Compared with low-light images， mAP@0.5 of the enhanced images improved by 4.9% to 94.7%. As the illumination intensity decreases， the object detection accuracy of the enhanced image improves more significantly. The research results can provide a reference for vehicle detection in low-light environments.

Abstract:The extreme surcharge is an important factor that threatens the safety of shield tunnel structures. Besides， the deterioration of shield tunnel performance caused by reinforcement corrosion may aggravate the risk of structure damage under extreme surcharge. Therefore， an analysis method was proposed to evaluate the fragility of corroded shield tunnels under extreme surcharge. In this paper， a three-dimensional finite element model was established to simulate a corroded shield tunnel under extreme surcharge， taking some typical shallow buried shield tunnels located in soft soil as an example. A large number of numerical calculations were carried out considering the uncertainty on the coefficient of stratum resistance and gravity of soil. Then， the joint opening was taken as the index of fragility， and the fragility curve of the corroded shield tunnel under extreme surcharge was established through a two-parameter lognormal distribution model. This research studied the influence of extreme surcharge and corrosion rate on the fragility of shield tunnels. It showed that the fragility of the shield tunnel increased with the increase of extreme surcharge or corrosion rate of reinforcement； when the surcharge was light， the corrosion rate of reinforcement had a greater influence on the fragility of the tunnel； under the same work condition， compared with the joint located at the top or the bottom of the tunnel， the joint at the waist may have a higher probability of damage.

Abstract:To more reasonably evaluate the bearing capacity of the suspension bridge tunnel-type anchorage （TTA） and explore the failure process of these TTAs under dynamic loads， a numerical model is established using finite difference software. This involves extracting and analyzing the forms of stress and strain distribution on the contact surfaces and comparing them with results obtained under static loads. The research is further extended to establish the impact of various working conditions， examining the anchoring mass and dynamic load parameters that affect the bearing capacity. The results indicate that under dynamic load， the stress and displacement distribution patterns on the rock-anchor contact surface are similar to those under static loads. However， both the amplitude and the rate of increase are significantly higher than in the static load condition. The increase in displacement in the direction of the arch crown and the right arch foot reach 36% and 112%， respectively. At 7 times the amplitude of the static load， the displacement difference between the two reaches a “threshold value” of 0.30 mm. Under dynamic loading， the ultimate bearing capacity of TTA increases with the expansion angle， length， and spacing of the anchor plug. The sensitivity ranking of these geometric parameters from high to low is anchor plug length， anchor plug expansion angle， and anchor plug spacing. The impact of dynamic load frequency on bearing capacity is relatively small. Under dynamic loading， the ultimate bearing capacity of TTA significantly decreases， with an average reduction of about 21%. The sensitivity analysis of TTA bearing performance and influencing factors under dynamic loads provides a reference for the optimal design of TTA ultimate bearing capacity in practical engineering.

Abstract:The visualization physical modeling test plays an increasingly significant role in mechanical mechanism and deformation characteristics of tunnel engineering， and the surrounding rock similar material meeting the transparency and similarity theory is key to ensure the great agreement between the testing results and practical engineering. This paper summarizes the strength property of prepared transparent cemented soil with similar material based on statistical analysis of orthogonal test data， so as to explore the quantitative design method representing the mix proportion of similar material of tunnel surrounding rock. The experiment utilized molten quartz sand， nano-silica， and N-dodecane mixed with 15# white oil as raw materials， designing a 2-factor， 3-level orthogonal test to measure unit weight， internal friction angle， and cohesion. Using the concatenation method， multiple nonlinear regression equations were fitted to describe the relationships between unit weight， internal friction angle， cohesion， and both the particle size of quartz sand and the cement-stone ratio （the mass ratio of nano-silica to quartz sand）. The joint solution of these regression equations was then employed to determine the optimal quartz sand particle size， cement-stone ratio， and geometric similarity constant. The test results indicate that： 1） the ranges for unit weight， internal friction angle， and cohesion of the transparent cemented soil are 16.13~12.53 kN/m3， 27.07°~14.82°， and 31~2.3 kPa， respectively， with shear stress-shear displacement curves displaying both post-peak platform and post-peak drop characteristics；2） T-tests and F-tests reveal that the independent variables in the fitted nonlinear regression equations significantly influence the dependent variables， and the equations are authentic and reliable； 3） Combining the regression equations for specific gravity and internal friction angle， the optimal particle size and cement-stone ratio of quartz sand are calculated， which are then substituted into the cohesion regression equation to finalize the cohesion calculation. This study establishes a novel quantitative design method for determining similar material mix ratios and geometric similarity constants， providing a theoretical foundation and data reference for designing visual physical model tests in tunnel engineering.

Abstract:Accurate prediction of overlying soil pressure is of great significance to the design of tunnel support structures and the selection of excavation methods. Terzaghi’s theory of the soil arch effect is established based on the assumption that the slip plane is vertical， but in practice， the slip plane shows a curved shape due to the formation disturbance. To study the evolution law of slippage surface of cohesive soil layer and the distribution law of loose earth pressure， firstly， the overlying soil pressure after tunnel excavation is calculated by numerical simulation software， and the evolution law of the soil arch effect under cohesive soil is analyzed. Secondly， based on the fracture surface of the tunnel arch， the ellipsoid theory and the circular arc of the principal stress in the cohesive soil layer are used to correct the Terzaghi loose earth pressure. Finally， the theoretical calculation results are compared with the existing experimental data and the finite element calculation results to verify the rationality of the application of the formula in the cohesive soil layer， and to further study the relationship between formation loss rate SL， internal friction angle φ， cohesion c， and tunnel loose earth pressure. The results show that the damage degree of slippage surface in the cohesive soil layer is greater than that in the non-cohesive soil layer. Still， the changes in slippage surface in the cohesive soil layer are the same. When the buried depth ratio of the tunnel is less than 1.5， a triangular slip plane appears. As the buried depth of the tunnel continues to increase， a shear plane is gradually formed inward， and a tower-shaped slip plane is finally formed. The lateral earth pressure coefficient Kv inside the loose zone is different at every location and fluctuates around 1.0， as suggested by Terzaghi. Compared with shallow buried tunnels， the loose earth pressure of deep buried tunnels is more affected by formation loss rate SL. The overlying load of the tunnel in the cohesive soil layer is distributed in a “half gourd shape”， which gradually decreases from near the vault to the arch waist. At the same time， in the formation with a small internal friction angle φ， increasing cohesion c is beneficial to reduce the overlying soil pressure of the tunnel.

Abstract:The morphological characteristics of rock fracture surfaces are key factors affecting their shear slip failure， and normal stress is an important influencing factor on the morphological characteristics of rock shear fracture surfaces. To study the influence of normal stress on the morphological characteristics and roughness anisotropy of sandstone shear fracture surfaces， double-sided shear tests were first carried out on sandstone to obtain shear fracture surfaces under different normal stresses. Then， the shear fracture surfaces formed in the direct shear test were scanned using three-dimensional optical scanning. Finally， the sandstone shear fracture surfaces under different normal stresses were reconstructed in three dimensions. The influence of normal stress on the roughness height indexes for the shear fracture surface was analyzed. Based on the anisotropic parameters， the anisotropic characteristics of sandstone shear fracture surface roughness were studied. The results showed that the expected value， standard deviation， mean of the roughness height， and maximum roughness difference of the sandstone shear fracture surface increased with the normal stress. The roughness of the shear fracture surface exhibited significant anisotropy， decreasing first and then increasing with the increase of the angle between the shear and normal stress direction. When the normal stress was compressive， the shear fracture surface roughness obtained a minimum value at an angle of 75° ~ 90° to the shear direction. The range and anisotropy parameters of the roughness of the shear fracture surface gradually increased with the increase of normal stress， and the anisotropy characteristics of the shear fracture surface were enhanced. The fractal dimension of the sandstone shear fracture surface was a power function of the roughness.