Abstract:As an improved technique of reinforced soil, the geosynthetic reinforced soil-integrated bridge system(GRS-IBS) could reduce the differential settlement at the roadbed-bridge transition section so as to avoid “bridgehead bump” effectively. But at present, GRS-IBS structure is mostly designed with reference to reinforced earth retaining wall, and its design method needs to be improved on account of the difference in bearing characteristics between two structures. Considering this, based on a bridge in Taihang No.1 Tourism Road K43+175 in Shanxi Province, the GRS-IBS was designed referring to the relevant specifications, and a Finite difference numerical model in the same condition was also established by FLAC3D to analyze the abutment deformation, the geogrid tensile force and the panel stress respectively to guarantee the safety of engineering structure. The results show that not only the internal and external stability of GRS-IBS should be validated, but also the bearing capacity and the geogrid tensile force should be checked using the formula recommended by FHWA; the GRS-IBS structure with cast-in-place concrete panel could meet the requirement of relevant specifications for the differential settlement at the roadbed-bridge transition section, but the top of the panel should be reinforced to ensure the safety of engineering structure; the maximum tensile stress of the panel with GRS-IBS structure was located in its lower part, and the reinforcement was suggested on the tension side to avoid concrete cracking.

Abstract:In view of the uneven settlement of ballasted track subgrade, the overall deformation analysis of ballasted track structure is carried out. Based on the coupling method of discrete element method and multi-flexible body dynamic (DEM-MFBD), a simplified 2.5-dimension coupling model of ballasted track is introduced and applied to the study of meso-mechanical properties of ballasted track. Based on the characteristics of the coupling model, the load and stiffness reduction method is proposed. The global stress and deformation of the ballasted track structure under different subgrade settlement wavelengths and amplitudes are calculated and analyzed. At the same time, influence of uneven subgrade settlement on unsupported sleepers is studied. The results show that the increase of subgrade settlement amplitude or wavelength obviously leads to the increase of track irregularity and the outward expansion of the stress concentration position of the ballast bed. The ratio of rail settlement area to subgrade settlement area (S₁/S₀) can reflect the status of unsupported sleepers. It is found that the unsupported sleepers are produced when the subgrade settlement amplitude is 10-15 mm. Therefore, it is suggested that the subgrade settlement amplitude should be controlled within 10 mm, so that the engineering department can control the problems such as unsupported sleepers and track irregularity.

Abstract:For the first time, a bionic root pile imitating mammalian lower jaw molars is proposed, based on the principle of biomimicry and combined with the characteristics of high bearing capacity of mammalian mandibular molars. The bearing performance of bionic root piles and the extrusion effect of sinking piles differ from the conventional conical or flat bottom piles with circular bottom sections. In conjunction with a combination of numerical methods and model experiments are used to explore their bearing characteristics and the role of piles-soil in the pile sinking process. First, the discrete element method (DEM) was adopted for numerical simulation, and it was discovered that the bionic tooth root pile can significantly enhance the bearing capacity of the pile bottom, but was prone to causing soil stress concentration. As for the model test, the particle image velocimetry (PIV) technique based on the transparent soil model test was implemented, and the pile loading instrument and CCD high-speed industrial camera were used to continuously capture the scattered field generated by the pile peri-pile soil under the linear laser during the pile loading process, and the velocity and displacement field of the soil mass were obtained. Ordinary conical piles and bionic root piles were subjected to immersion tests, with the results indicating that the bearing capacity of bionic root piles on vertical loads was greater than double that of ordinary conical piles, and that the dragging effect of the pile body and the displacement of vertical soil at the bottom of the pile were more pronounced. Furthermore, when the concave at the pile's center was not excessively large, the transverse displacement of the soil was minimal.

Abstract:Porous eco-concrete is an alternative for the conventional concrete materials for slope protection, which could effectively protect the ecological environment of the slope in the service area during the field applications, with significant ecological and social benefits. In this paper, the key control methods of alkaline environment in porous eco-concrete for slope protection were studied by means of biogenic energy, durability test and microscopic mechanism analysis. The results demonstrate that the composite alkali-reduction method can achieve a good alkali reduction effect; the porous eco-concrete for slope protection after alkali reduction treatment has a good match with ryegrass and tall fescue and meets the growth requirements of vegetation; after plants’ growth, the compressive strength and porosity of specimens are not significantly changed. In summary, the proposed alkaline environment-modification method and vegetation matching technique could contribute to the performance improvement of porous eco-concrete, which will promote the engineering applications of “green-sustainable” eco-concrete in projects for slope protection.

Abstract:Soil strength anisotropy and seepage are important factors affecting the stability of slopes. In order to make the anisotropy of slope soil strength more practical in stability calculation, a method of graded loading and zoning of layered slope soil considering strength anisotropy is proposed. Firstly, the initial zoning is established according to the size distribution of the maximum principal stress direction angle of the slope soil and the intersection area of layered soil, and then, combined with the finite element calculation results, the formula for determining the anisotropy strength parameter of each layered soil is derived and the strength parameter of each zoning is calculated instantly. Secondly, in the process of applying load step by step, the initial partition is further adjusted according to the calculated soil strength parameters, the partition and the corresponding strength parameters of the coupling calculation are determined through three-level control of initial partition, subdivision and fine partition. On this basis, a flow-solid coupling model considering three working conditions: zoned anisotropy, unzoned anisotropy and unzoned isotropy of the soil body is established, and the change laws and characteristics of the stress field, displacement field and seepage field of the slope body are analyzed, and the stability of the slope is calculated using the strength reduction method. The results show that the average stress maximum value of zoned anisotropy is lower than that of unzoned anisotropy, but greater than that of unzoned isotropy, the seepage and flow velocities are lower than those of the other two cases; the calculated slope stability coefficient of zoned anisotropy is 1.109, which is 2.8% and 21.3% lower than those of the other two cases respectively.

Abstract:The previous data interpretation equation for medium and low stress is no longer applicable when in-situ tests are carried out in deeply seated soils. In order to explore the mechanical properties of sand under high stress conditions, in this paper, the cone penetration test in silica sand with different relative densities and confining pressure levels was performed in a self-developed high-pressure calibration chamber, and the Arbitrary Lagrangian-Eulerian method, a large deformation finite element approach, was used to study cone penetration in silica sands. Frequent mesh generations were conducted to avoid the distortion of soil elements around the cone tip. A modified Mohr-Coulomb constitutive model was introduced to describe the internal friction and dilatancy angle varied with the plastic shear strain in silica sands. A method for determining shear modulus by correcting the bending element tests was proposed. Numerical results of cone tip resistance agree reasonably well with calibration chamber tests. An empirical equation for cone tip resistance varied with different relative densities was established under high stress condition, and the comparison with the existing low stress test results show that the established equation can predict well the relative density of sand by the cone tip resistance.

Abstract:The foundations of islands in the South China Sea are constructed by hydraulic filling method. There are widely discontinuous gradation states in which large and small particles coexist in the hydraulic fill formation of island. The discontinuous conditions of particle gradation have a significant influence on the mechanical properties of the foundation material of coral sand. In this study, a series of drained triaxial shear tests under different effective confining pressures, relative densities, and coral gravel contents were carried out on coral sand-gravel mixtures, to investigate the strength and deformation characteristics of the gap-graded coral sand under static load. Also, the feature of particle breakage in the tested gap-graded soil has been studied. The results show that the stress-strain relationship curve of the coral sand sample is significantly affected by the confining pressure and relative density. The peak friction angle and dilatancy angle of coral sand-gravel mixtures decrease with the increase of the effective confining pressure, and increase with the increase of relative density. Under the same effective confining pressure, the strength of coral sand-gravel mixtures at different relative densities exhibited different growing patterns with increasing gravel content, which may be related to the contact state and composition ratio of the coarse and fine particles in coral sand-gravel mixtures. In addition, this study explored the correlation between the plastic work with relative breakage index for different gravel contents of coral sand-gravel mixtures and established the correlation function between the relative breakage index B_r and the plastic work W_p on this basis.

Abstract:The thermal conductivity of calcareous sand affects the heat transfer process of the surrounding soil and causes the change of engineering mechanical properties and disaster effects of calcareous sand at different ambient temperatures. The variation law of thermal conductivity of cemented calcareous sand with five different cement contents (P_s=5%, 7.5%, 10%, 12.5%, 15%) was analyzed based on hot needle method. SEM, MIP and NMR were used to comprehensively reveal the essential characteristics of micro-pore structure changes of cemented calcareous sand during the process above. On this basis, the microcosmic mechanism of the evolution of the thermal characteristics above was explained. The results show that the thermal conductivity (λ) of cemented calcareous sand increases with the increase of cement content (P_s). When P_s is less than 10%, λ increases linearly, and when P_s is more than 10%, λ increases slowly. With the increase of cement content (P_s), the number of pores in the cemented calcareous sand becomes less, and the proportion of pores decreases obviously. However, when P_s increases up to 10%, the change of micro-pore structure parameters such as total pore area, pore number and porosity stabilizes. The thermal conductivity (λ) of cemented calcareous sand with different cement contents is negatively correlated with the changes of their microscopic pore structure. The reason lies in that the gel-like cement hydration products continuously fill the pores of cemented calcareous sand, reducing its porosity and improving the heat transfer inside the sand sample. The macroscopic performance is that its thermal conductivity (λ) increases with the increase of cement content (P_s).

Abstract:When constructing tunnels in soft rocks with high ground stress, it should be considered that the soft rock has low strength and strong expansibility, and is extruded by high ground stress. Therefore, it is unavoidable to cause large deformation of soft rock if the construction measures are not appropriate, which brings great difficulties to the engineering construction. Based on the theory of surrounding rock loose circle, the unified strength criterion is adopted to analyze the stress state of surrounding rock with consideration of the influence of intermediate principal stress. Then the radius calculation formula of loose circle of surrounding rock of large deformation soft-rock tunnel is obtained. Based on the case of Xiejiapo tunnel of Anlan Expressway, it is found that the distribution of surrounding rock loose circle of large deformation soft-rock tunnel is not uniform along the cross section. And the loose circle tends to be large in the side wall and small in the vault, and increases with the increase of deformation grade and decrease of support reaction force. Combined with field test, it is found that the thickness of loose circle of grade Ⅱ large deformation is 6.5-7.0 m at vault and 7.0-7.5 m at side wall; the thickness of loose circle of grade Ⅲ large deformation is 7.5-8.0 m at vault and 8.0-8.5 m at side wall. Therefore, the length of the system bolt should be optimized based on the thickness of the loose circle. By monitoring the optimized section, it can be seen that the deformation of surrounding rock is reduced significantly and the stability is improved effectively.

Abstract:With the intensification of global climate warming, the probabilities and load intensities of extreme weather phenomenon are gradually increasing, which could threaten the safety of coastal and offshore infrastructures. The present study presents a joint probability distribution model of wind speed, wave height, wave period, wind direction and wave direction with Vine Copula function based on monitoring data from Lianyungang Ocean Station in the East China Sea. Firstly, the marginal probability distributions of wind and wave data are determined, in which the AIC criteria and RMSE index are employed to select the optimal probability distribution model and the maximum likelihood method is used to determine the model parameters. Subsequently, the optimal two-dimensional Copula function for wind and wave data is determined via the AIC criteria, and the model parameters are fitted with a Bayesian framework with a residual-based Gaussian likelihood function. To illustrate the goodness of fit, the binary frequency histogram of the original wind and wave data is compared with the proposed two-dimensional Copula function. Finally, the multi-dimensional joint probability distribution model of wind and wave data is established with the Vine Copula function based on the AIC criteria. The results show that the proposed Vine Copula model is able to describe the joint probability distribution between the wind speed, wave height, wave period, wind direction and wave direction.

Abstract:For the service transmission tower with long operation time or expansion and reconstruction requirements, the insufficient bearing capacity of certain components leads to the transmission tower unable to meet the higher design requirements. Therefore, it is necessary to study the reinforcement measures of angle steel components to effectively improve the bearing performance of transmission towers. Taking the typical angle steel in transmission tower as the research object, a non-destructive reinforcement method for transmission tower was proposed. In this method, bolts and fixtures are used to form a composite reinforcement component by combining the original component and the reinforcement component. The composite component does not cause damage to the original component, and the structure is simple while the application is wide. A more detailed numerical model of composite members was established to study the influence of slenderness ratio of original members, fixture spacing (number) and steel properties on the reinforcement effect of composite members, and the calculation method of compressive bearing capacity of composite members was deduced. The results show that the proposed reinforcement method has remarkable effect, and the reinforcement level is up to 56.34%. The slenderness ratio of the original component has obvious influence on the lifting level of the composite component, and the lifting effect of the composite component is gradually obvious with the increase of the slenderness ratio of the original component. When the number of fixtures is odd and the spacing of fixtures is less than 750 mm, the reinforcement effect of composite members is optimal. Steel properties of reinforced members have marginal effect on compressive bearing capacity and ductility of composite members. The proposed calculation method of compression bearing capacity of composite members is in good agreement with finite element simulation.

Abstract:Aiming at the problems of complicated beam-column connection structure and low construction efficiency in prefabricated concrete structures. Designed and developed a new type of prefabricated steel-reinforced concrete column to steel beam composite joint, and the influence of different beam end connection methods on the seismic performance of the new joint was studied by the pseudo-static test. The results show that the specimens with different beam end connections are all flexural failure, and the failure location is at the flange connecting plate, which realizes the effect of the plastic hinge moving out near the joint region. The strain of the flange connection plate and concrete is greatly affected by beam end connection mode, while the effect to strain of the steel beam web, H-shaped steel skeleton, and longitudinal reinforcement are relatively small. The bolt-weld hybrid joint and bolt joint belong to semi-rigid connections, while the weld joint belongs to rigid connections. The hysteretic behavior of each specimen is good, and the degradation performance of bearing capacity and stiffness is stable. The ductility coefficient is 4.03-11.84, and the equivalent viscous damping coefficient is 0.24-0.36. This type of joint has good bearing capacity and seismic performance, which can meet the existing seismic design requirements.

Abstract:In order to study the bond slip behavior of round steel tube concrete column after freeze-thaw cycle, a total of 21 specimens were designed to carry out the push test, taking the number of freeze-thaw cycles, steel tube wall thickness and strength of concrete as variables. The variation laws of bond strength, load-slip and strain of round steel tube concrete column under freeze-thaw damage were analyzed. The test results show that the load-slip curves of the circular steel tube concrete columns subjected to freeze-thaw cycles are similar to those of the specimens without freeze-thaw cycles, which can be divided into ascending section, descending section and residual section. Under the influence of freeze-thaw cycles, the interfacial bond performance of concrete column with round steel tube decreases, the bond strength is inversely proportional to the number of freeze-thaw cycles, and the interfacial slip generally increases. The increase of the hoop coefficient can increase the interfacial bond strength and improve the frost resistance of the concrete column of round steel tube. According to the test results, a formula for calculating the bond strength of concrete column with round steel tube considering the number of freeze-thaw cycles and the hoop coefficient is proposed, and the calculated results are in good agreement with the test results.

Abstract:In this work, the axial compression tests of circular concrete-filled double skin steel tube (CFDST) stub columns and CFRP-confined CFDST (CFRP-CFDST) stub columns were carried out. The influences of concrete strength, the number of CFRP layers on the axial compression performance of CFRP-confined CFDST stub columns were investigated. The typical failure modes, the load-displacement curves and load-strain curves of CFDST stub columns and CFRP-confined CFDST stub columns were obtained. The test results show that the ultimate bearing capacity of CFRP-confined CFDST specimens is significantly improved compared with that of CFDST specimens. And the more layers of CFRP, the higher the ultimate bearing capacity of CFST stub columns. Finally, the calculation formula of the minimum wall thickness of the inner steel tube to avoid the buckling failure of the inner steel tube prior to that of the outer steel tube is given. And a calculation formula of the ultimate bearing capacity of CFRP-confined CFDST stub columns under axial compression is proposed. The prediction results of the presented calculation method agree well with the experimental results.

Abstract:In order to study the flexural performance of bamboo member, 40 groups of bamboo standard wood strips from 10 raw bamboos were tested to obtain their failure modes and flexural strength. Then, the 24 raw bamboo beams with diameters of 90 mm and 120 mm making the spans of 3 000 mm and 3 600 mm were subjected to bending collapse tests. And the load-displacement curves, initial bending stiffness, ultimate bearing capacity, deflection and failure modes were analyzed. The height of compressive zone and edge stress of tensile zone of the raw bamboo beams were deduced theoretically. The results show that the influence of span change on deflection of bamboo beam is greater than that of diameter at breast height. The larger diameter at breast height and the smaller span, the greater the initial bending stiffness of the bamboo beams. According to the test data and the classical elastic theory, it is calculated that the compressive zone height of the bamboo beam is about 3R/2 height of the cross-section. Under the condition of small deflection, the bending of Phyllostachys pubescents beam conforms to the assumption of flat section, while under the condition of large deflection, the height of compression zone of section moves up, and the calculated tensile stress of failure edge is inconsistent with the calculated result of the assumption of flat section. It is suggested that the bending moment of Phyllostachys pubescents beam should be calculated according to the maximum compressive strength of the upper edge along the grain.

Abstract:Laminated bamboo lumber is a bamboo material that flat laminates are glued by adhesives and co MPacted into mould. Side-pressure laminated bamboo lumber has a good mechanical property. In order to explore its mechanical properties under axial compression, an experimental study was carried out in 6 groups of 18 specimens with different slenderness ratio. The relationships between various parameters (bearing capacity, strain, lateral displacement and axial displacement) and slenderness ratio were analyzed, and the failure modes of specimens under different slenderness ratios were discussed.The results indicate the mechanical process of side-pressure laminated bamboo lumber has experienced the stages of elasticity, elastic-plastic and failure. With the increase of slenderness ratio, the failure mode changes from material strength failure to buckling failure, and the material strength failure has obvious ductility property. The comparison between experimental results and various specifications was made to put forward the formula of bearing capacity under axial compression of side-pressure laminated bamboo lumber, and the calculated values agree well with the experimental values.

Abstract:Aggregate and interfacial transition zone (ITZ) have significant influence on the carbonation resistance of cementitious materials. Based on Fick's second law, a CO₂ diffusion model considering the influence of aggregates and ITZ is proposed in this paper, the diffusion coefficient of interfacial transition zone is introduced for the first time and the calculation method of corresponding parameters in this model is given. At the same time, a CO₂ reaction model is established based on the law of mass conservation, and the CO₂ concentration distribution in C30 and C50 concrete under load is studied by using this model. The results show that the diffusion coefficient and depth of carbonation of CO₂ in cementitious materials can be calculated more accurately by considering aggregate and ITZ effects. Finally, the reliability of the theoretical model is further verified by comparing with the experimental data in literature. Therefore, the model takes aggregate and ITZ as important factors to evaluate the durability of concrete, which provides foundation for the design and life prediction of reinforced concrete structures.

Abstract:At present, for the study of the thermal conductivity of building materials containing moisture, the prediction model generally assumes that the materials containing moisture are uniform, and the experimental measurement usually adopts the uniform humidification scheme. However, the indoor and outdoor humidity and meteorological conditions influence building materials in the process of actural use, causing the non-uniform distribution of moisture components in the process of moisture absorption and desorption, and the thermal conductivity of the materials is different under the same moisture content. In this paper, the moisture content of autoclaved aerated concrete (AAC), foam cement (FC) and red brick (RB) materials with different pore characteristics were tested by analyzing the changing trend of thermal conductivity in the whole process of moisture-increasing and moisture-reducing, the changing characteristics of thermal conductivity in non-uniform moisture-distributing materials were studied. The results show that the thermal conductivity of AAC, FC and RB in the humidification process increases by 279%, 266% and 106%, respectively, compared with that in the dry state. The difference value of thermal conductivity of ACC with the same moisture content in humidification process is about -20.2%~63.4%, the difference value of FC is about 14.5%~53.3%, and the difference vaule of RB is about -18.0%~37.4%.

Abstract:Pervious concrete has good permeability and moisture adjustment properties due to its rich pore structure. It can not only penetrate rainfall to reduce surface runoff, but also retain a certain amount of water inside then via evaporation to decrease surface temperature. In order to improve the water retention of pervious concrete and prolong its cooling effect, this study introduced a modified method of incorporating biochar produced by pyrolyzing agricultural wastes into pervious concrete as hygroscopic filler. The effects of biochar on the mechanical properties of pervious concrete were analyzed, then the thermophysical properties, water absorption properties and evaporative cooling performance of biochar-modified pervious concrete with the optimum replacement rate were studied. The results show that the carbonaceous particles after grinding could fully exert the filling and internal curing effects when the replacement rate was less than 5.0%, and effectively improve the mechanical strength of pervious concrete. It was found that the biochar addition had little impact on the emissivity of pervious concrete, while significantly reduced the reflectivity and thermal conductivity. Contributing to the abundant micro-pores and higher specific surface area of biochar particles, it could improve capillary water absorption and water storage ability of pervious concrete. During the evaporation process, the water absorption increment could effectively reduce surface temperature of 3-6 ℃ and maintain evaporation cooling effect for 14-18 h.

Abstract:Textile dyeing wastewater is one of the most difficult industrial wastewaters to treat because it contains a large amount of toxic and refractory pollutants such as dyes, heavy metals. The traditional biological treatment process has certain limitations, such as poor toxicity resistance, low treatment load, and being affected by the external environment, making it difficult to efficiently treat this type of wastewater. Aerobic granular sludge (AGS) has a high content of extracellular polymeric substances and contains a large number of functional groups such as amino groups and carboxyl groups. In addition, it has different redox microenvironments, which can effectively adsorb and degrade pollutants. However, there are still limitations in the removal of heavy metals from printing and dyeing wastewater by AGS, and there is still much room for improvement in the decolorization and mineralization efficiency of dyes. According to the pollutant characteristics of textile dyeing wastewater, the advantages of AGS technology and the removal mechanism of heavy metals and azo dyes in wastewater are summarized and discussed. The research progress of AGS treatment simulated and actual textile dyeing wastewater is reviewed, and the operation mode is summarized and analyzed. Based on the limitations of heavy metal ion removal, insufficient dye degradation, and the complexity of actual wastewater, the development direction is prospected, in order to provide a reference for the future research on the efficient treatment of textile dyeing wastewater by AGS.

Abstract:In order to reduce the energy consumption of sewage treatment, this study uses zeolite particles as biological fillers to build a fixed-bed biofilm reactor, and the biofilm on the filler surface in the reactor is placed in an alternating anaerobic-aerobic environment through the sequential batch water-drainage method. It avoids the large amount of energy consumption required by the traditional sewage treatment aeration process, and effectively removes COD and denitrification at the same time. The main principle of the process is that in the anaerobic stage (influent), the sewage is in contact with the biofilm and zeolite particles, and the glycan bacteria (GAOs) convert the organic carbon source into intracellular polyhydroxyalkanoates (PHAs), and the zeolite absorbs NH₄⁺-N in the sewage. In the aerobic stage (drainage), the combined action of glycan bacteria, nitrifying bacteria and denitrifying bacteria converts the NH₄⁺-N adsorbed by the zeolite into nitrogen, so that the biofilm and zeolite particles can be regenerated. The zeolite particle fixed-bed biofilm reactor uses activated sludge as the inoculation sludge. Under the sequential batch anaerobic-aerobic alternate operation mode, it successfully started within 2 weeks; in the long-term operation, removal of COD, NH₄⁺-N and TN rate in sewage was 87%, 83% and 83%, respectively, and no nitrate nitrogen was detected in the effluent; after long-term operation, the biofilm flora in the reactor was dominated by Thaurea, Candidatus competitivebacter , and Nitrospira. They are the key microorganisms for COD removal and denitrification.

Abstract:The environmental behavior of heavy metals in acidic mine drainage (AMD) was restricted by schwertmannite. When environmental conditions change, dissolution and phase transformation of schwertmannite will occur, causing redistribution or even releasing of bound heavy metals. This study investigated the dissolution and phase transformation of rapid chemical synthetic schwertmannite which was prepared in the presence of different contents of chromium and molybdenum induced by reducibility S(-II) of acid mine drainage with flow column method combined with XRD, SEM and XPS characterization. The results show that the concentrations of heavy metals and sulfur ions in the leachates decreased with the prolongation of reaction time and the increase of Cr and Mo loading contents, also followed Sch>0.1Mo0.06Cr-Sch>0.2Mo0.09Cr-Sch. Zero-order kinetic was proved to be the best kinetic model for the release processes of Cr and Mo. In addition, according to the XRD and XPS characterization, goethite was the main products of the pure schwertmannite treatments, and the loading heavy metals can improve the stability of minerals to a certain extent and retard the phase transformation of schwertmannite.