Abstract:Miscellaneous fill, steel slag, and slag powder were mixed to prepare steel slag-miscellaneous fill base material by soil solidification. Firstly, coupling influence test of main materials including steel slag, concrete crushed material and plain soil on the strength of base materials were conducted, regression model was established to obtain optimal mixing ratio. Experimental verification shows that the prediction error was within 2%. Secondly, the orthogonal test was carried out with steel slag, concrete crushing material, cement as well as curing agent as the factors, and the optimal results obtained were basically consistent with the strength coupling influence test. Thus, the optimal mix ratio of steel slag and miscellaneous fill was determined. The test results of the optimal sample showed that the strength increased significantly with age, which presented expansion rate of 1.03% after treatment 30 d high temperature water bath. X-ray diffraction analysis (XRD) and scanning electron microscope (SEM) test results show that SiO₂ in slag powder reacted with f-CaO in steel slag to form hydrated calcium silicate gel (C-S-H). It was also confirmed that the modification of the soil solidification agent to the soil can effectively prevent the expansion of steel slag; C-S-H gel is filled in the space of the broken concrete, steel slag as well as soil particles to increase the compactness of the steel slag-miscellaneous fill base material and thus enhance its strength.

Abstract:Jiangxi Shuanggang Shipping & Navigation Project attempted to use the saturated silty clay with soft clay dredged from the open diversion channel to build the cofferdam. During construction, the dredged saturated silty clay was dumped by boats above the water, resulting in disturbed and non-homogenous silty clay with soft clay. This results in the difficulties to form the cofferdam with the desired gradients and failure of the cofferdam during operation. To assess the cofferdam stability during construction and operation with water level fluctuations, extensive numerical modelling using the finite element program PLAXIS was carried out. Further considering the non-uniformity of the dumped saturated silty clay and the variation of its strength with rainfall and evaporation, sensitivity analyses on the soil strength parameters were carried out. Based on the maximum lateral deformation curve of the cofferdam with the factor of safety close to 1.0, the yellow and red alarm levels were proposed for the remote real-time monitoring. The results indicate: the cofferdam with a slope of 1:4-1:5 and berms is stable at normal water levels; the reduction in strength of the dumped soil would induce instability of the downstream cofferdam slope from the toe to the top; due to the non-uniformity and low strength of the dumped saturated silty clay, remote real-time monitoring shall be carried out on the cofferdam lateral deformation, seepage pressure, and rainfall; based on the deformation curve with the factor of safety, the red and yellow alarm levels are 1.5-2.0 mm/d and 1.1-1.5 mm/d respectively.

Abstract:In order to explore the cumulative plastic strain of weathered soft rock at the base of metro tunnels under long-term cyclic loading of trains, this paper focuses on the weathered argillaceous siltstone at the base of Nanchang Metro and develops laboratory dynamic triaxial tests of working conditions considering dynamic stress ratio, static deviator stress ratio, confining pressure and loading frequency, the dynamic deformation characteristics of saturated weathered argillaceous siltstone under different influential factors are studied. The results show that the cumulative plastic strain of fully weathered argillaceous siltstone and moderately weathered argillaceous siltstone become stable after 1 000 and 100 cycles, respectively, and the critical dynamic stress ratio of fully weathered argillaceous siltstone is between 0.3 and 0.4; compared with different dynamic stress ratios and static deviator stress ratios, confining pressure and frequency have marginal effect on the cumulative strain of the two weathered argillaceous siltstones; by analyzing the test result data, a mathematical model of cumulative plastic strain considering the loading times, dynamic stress ratio and other factors is proposed.

Abstract:Strength composite pile is a new type of pile formed by inserting a precast concrete pipe pile into soil-cement column. A series of shaking table model tests and finite difference analysis using FLAC3D were carried out to examine the seismic response of strength composite pile in a liquefiable ground. The accuracy and reliability of the numerical model were verified by the model testing results, and the effect law of diameter, length and modulus of soil-cement columns on the seismic response of sand-composite pile-superstructure were clarified. In addition, the anti-liquefaction performance of liquefiable ground and the bending failure of composite piles were evaluated. Results show that increasing the diameter and length of soil-cement column can effectively improve the seismic performance of composite pile. Increasing the shear modulus of soil-cement column to improve the seismic performance of composite piles is limited. A large moment response may occur in the pile near pile head or at the interface of cement-improved soil and liquefiable sand, so necessary seismic structural measures should be considered at the part. Based on the evaluation results, the key points of seismic design for composite piles in liquefiable soil were proposed.

Abstract:In order to further improve the measurement accuracy of 3D laser scanning technology, this paper studies the optimization method of point cloud grid filtering from the perspective of optimization filtering algorithm and improved algorithm based on Kriging, considering the space-related properties of description objects and aiming at the filtering processing problem of point cloud data. Based on engineering practice, grid processing and analysis of 3D laser point cloud data are carried out through field monitoring and comparison test, and the deformation data obtained from the test is compared with the measured data by traditional methods. The results show that the improved algorithm based on Kriging filtering can identify and extract the tunnel contour cross-section's visual data efficiently and obtain the deformation of the tunnel efficiently and accurately. The experimental data of vault subsidence is close to the traditional measurement data, while the peripheral convergence data has some differences. Therefore, tunnel deformation monitoring under 3D laser scanning can better reflect tunnel deformation's real condition under certain environmental conditions and provide a sufficient safety warning for tunnel construction.

Abstract:As a common soil reinforcement method, artificial ground freezing method is widely used in underground structure engineering such as coal mine and subway. The sandy cobble stratum in Chengdu has rich water content and high permeability coefficient, where is difficult for freezing method. In this paper, the construction of cross passage by artificial freezing method in sandy cobble stratum was examined based on a tunnel section of Chengdu Metro Line 10. Firstly, the field monitoring of freezing engineering is carried out. Secondly, a nonlinear three-dimensional elastic-plastic thermal-stress coupled numerical model considering ice water phase transformation was established according to the actual layout of freezing pipes. The development and distribution of temperature field and displacement field in active freezing period were studied by field monitoring and numerical simulation. The research result shows that the numerical simulation results were in good agreement with the field monitoring data, and the established numerical model was reliable; the time of closure of freezing wall is critical for rapid growth of frost heave deformation, and the time is about 25 days; the thickness of frozen wall reached 2 m for freezing of 43.7 days, and the average temperature in the frozen wall reaches -10 ℃ in 37.8 days, which meets the requirements of subsequent excavation construction.

Abstract:In order to study the dynamic responses and influential mechanism of 40-metre simply supported beams with different types under the action of low-to-medium speed maglev train, based on the beam rail integration and beam on beam scheme, considering PID active suspension control and adopting modal synthesis theory, a precise dynamic interaction theoretical model of low-to-medium speed maglev train and simply supported beam system is established, and the reliability is verified based on Changsha maglev test. The dynamic response of 40-metre simply supported beams with two different types under the action of low-to-medium speed maglev train is analyzed and compared, and the influential mechanism of bridge types on the coupling vibration of the system is also discussed. The results show that compared with the beam on beam scheme, the vertical dynamic deflection of the beam rail integration scheme is greater, and the acceleration is smaller. The vertical displacement of the car body is more significant, and the acceleration is similar. Comprehensively， the beam rail integration scheme is better. The influence of bridge types on active suspension control system is marginal; in the beam on beam scheme, there are abundant high frequency local vibration modes of simply supported beams, which increases the bridge deformation and the vibration dominant frequency of bridge and vehicle body; type difference can affect the coupling vibration of maglev train-track-bridge system via wavelength effect and local vibration.

Abstract:The weigh-in-motion system is one of the important part of the bridge structure health system, which can provide abundant vehicle load monitoring data. On this basis, establishment of vehicle load model that can reflect the actual traffic conditions is of great significance for safety assessment and vehicle-induced fatigue analysis of bridge structures. This paper proposes a random traffic flow simulation method and process that considering different traffic states. In the process of vehicle load statistical analysis, the traffic states are divided by the vehicle flow intensity in each period. For different traffic states, the common single-peak probability distribution models and the multi-peak one are introduced to carry out probability fitting for vehicle weight, vehicle speed and vehicle spacing, and the optimal probability distribution of vehicle load parameters can be obtained by K-S test. The Monte-Carlo method is used to simulate random traffic flow, and then decomposed into random loading flow. Finally, the rationality of the vehicle load simulation method is verified based on the vehicle load monitoring data of an actual bridge. The results show that when the different traffic states are considered for random traffic flow simulation, the stress amplitudes and stress cycle times of the steel box girder lower flange at mid-span are close to the results induced by the actual traffic flow. By contrast, when the different traffic states are not distinguished for traffic flow simulation, the stress amplitude and the number of cycles obtained are significantly smaller than the actual, which would lead to risky results for the vehicle-induced fatigue analysis of the bridge structure.

Abstract:The response of continuous curved box girder with corrugated steel webs is rather complicated due to the coupling effect of bending and torsion. In order to study the mechanical properties of continuous curved box girder with corrugated steel webs, considering the effect of shear lag and shear deformation, the restrained torsion differential equation of simply supported statically indeterminate curved box girder with corrugated steel webs (CCBG(CSWs)) are derived based on the energy method, and then analyzed and verified by combining CCBG(CSWS) simply-supported structure, using the differential equation combined with the three-bending moment method to solve the internal force of a three-span continuous curved box girder with corrugated steel webs, and the results are compared with those of the curved bar structure mechanics method and of the finite element analysis. The results show that: considering the effect of shear lag and shear deformation, the internal force results obtained by the method proposed in this paper are in good agreement with those obtained by finite element method, which verifies the correctness of the method proposed. The shear lag effect and shear deformation have a certain influence on the internal forces of CCBG(CSWS), and the influence on the internal forces of multi-span CCBG(CSWS) structure is more obvious.

Abstract:In order to realize the goal of load-bearing and thermal insulation integration of prefabricated steel residential buildings, a new type of load-bearing and thermal insulation integration wall with concealed bracing was proposed. The interior of the wall is steel braced frame, filled with foamed cement and other thermal insulation materials, and the exterior is provided with bidirectional steel mesh and mortar layer. The filling of foamed cement in the frame has great influence on the horizontal bearing capacity and lateral stiffness of the structure. Taking the height-width ratio of the walls and the existence of concealed bracing in the walls as the variable parameters, six one-bay and one-story integrated walls were tested under low-cycle reversed loads, and the horizontal bearing capacity, lateral stiffness and hysteresis characteristics of each specimen were obtained. The results show that the setting of concealed bracing can obviously improve the horizontal bearing capacity and lateral stiffness of the load-bearing and thermal insulation integration wall. Compared with steel braced frame, the new type of load-bearing and thermal insulation integration wall has higher horizontal bearing capacity and lateral stiffness, and its energy dissipation capacity and deformation characteristics are also better. The height-width ratio has a significant impact on the lateral resistance of load-bearing and thermal insulation integration wall. The larger the height-width ratio is, the smaller the horizontal bearing capacity, and lateral stiffness and energy dissipation capacity of the wall will also be. The calculation formula of the horizontal bearing capacity of the new type of load-bearing and thermal insulation integration wall was provided, and the calculation results are in good agreement with the experiment.

Abstract:Generally, the failure modes of FRP(Fiber Reinforced Polymer)-concrete composite structures are the interface peeling between FRP and concrete as well as the shear failure caused by insufficient shear bearing capacity of its own cross section. In this study, in order to improve the shear capacity of FRP-concrete composite structure, we tested five GFRP (Glass Fiber Reinforced Polymer)-Self-compacting RPC(Reactive Powder Concrete) stirrup composite specimens with GFRP shaped from multi-T-rib grooves. Discussion with the effects of interface treatment, stirrup configuration, and shear span ratio on composite specimens' mechanical properties. Measured the deflection and strain, respectively, and observed the formation and development process of cracks and their failure state. The results show that the interface sand adhesion treatment of GFRP plate and the arrangement of transverse penetrating reinforcement can enhance the interface shear strength between GFRP plate and concrete, obviously improve the cooperative performance of the two, and enhance the ultimate deformation capacity of composite specimens; the interface sand adhesion and stirrup arrangement can improve the shear bearing capacity of composite slabs and improve the failure mode to a certain extent; the higher the cross section of the specimen, the higher the bearing capacity, but the utilization of GFRP material will be reduced.

Abstract:In order to study the flexural properties of the fast-growing poplar glued timber beams reinforced by carbon fiber, the influence of factors was considered，such as different fiber distribution ratios and different fiber distribution positions. A four-point bending static load test of the beam was carried out, and the theoretical calculation formula of the ultimate bending moment of the beam was deduced. The results show that, compared with the pure glulam beam, the number and width of cracks of reinforced specimens decrease, and the elastic modulus, ultimate bearing capacity and initial bending stiffness increase significantly. The elastic modulus of the beam reinforced by carbon fiber increased by 28.02%~57.93%; the ultimate load increased by 16.47%~50.72%; the initial bending stiffness of poplar beam increased by 11.58%~23.37%. The ultimate bearing capacity and initial bending stiffness of beams with carbon fiber in tension zone can be effectively improved. Compared with the specimen only with carbon fiber in the tensile zone, the load-bearing capacity of the specimen is reduced when the carbon fiber is added in the tensile zone and the compression zone, but the deflection in failure is reduced. The fiber distribution rate in the tensile zone of the specimen should be between 0.060 6% and 1.031 1%, which can give full play to the plastic compressive properties of wood. The bending calculation formula of the beam was obtained. The calculation results of the ultimate bending moment of the specimen are consistent with the test results, and the calculation results can predict the ultimate bending moment of this kind of specimen under bending.

Abstract:To study the effect of corrosion on the axial compression performance of the upright tube of steel tubular scaffold with couplers, the surface morphology of steel tubes with different corrosion ages was tested to analyze the influence of corrosion on the surface morphology of the inner and outer walls of steel tubes, and the degradation law of mechanical properties of corroded steel was discussed through the monotonic tensile test of corroded steel tube. The calculated formula for the stability of the corroded steel tube was proposed through the results of the axial compression tests. The results show that the distribution of pit corrosion on the surface of steel tube develops from independent pits to ulcer-like pit groups with an increase of the quality loss rate of steel tube. The pit corrosion ratio, the average arithmetic height, and the root mean square height of the outer wall are higher than those of the inner wall in varying degrees. Randomly distributed and different sizes of pits will cause the decrease of the strength and plastic deformation ability of the steel. Compared with the decrease in strength, corrosion has a more severe impact on the plastic deformation ability of steel. The axial compression failure mode of steel tubes with different corrosion degrees is the overall bending instability. As the mass loss rate increases, the ultimate load decreases linearly, and the axial displacement value corresponding to the peak load point decreases gradually.

Abstract:The damage of aqueduct structures caused by earthquake disaster is influenced and restricted by various factors. The randomness in concrete mechanical properties and seismic excitations are two of the significant factors that may alter the failure modes of aqueduct structures. To this end, this paper carried out systematically the random dynamic response analysis of aqueducts subjected to the above two coupled randomness condition. Further, the anti-seismic reliability analysis method for aqueducts considering the coupled randomness from both structural parameters and excitations is developed taking a large aqueduct structure as an example. The basic research principles and application approaches of the developed framework were illustrated in detail based on the probability density evolution theory. The results show that the displacement response of the aqueduct structure under the coupled randomness condition intensifies obviously, and the residual deformation and displacement variability of the displacement response are larger than that caused by the single randomness earthquake condition. With the decrease of threshold value, the gap between the reliability of aqueduct structure under coupled randomness condition and that under single randomness earthquake condition is increasing, and the reliability of aqueduct structure under the above two conditions is decreasing continuously.

Abstract:In order to comprehensively and accurately evaluate reinforced-concrete-beam fire-damage state, with combination of various information from fire hazard tests and numerical simulations, MTOPSIS-GRA model for comprehensive assessment of RC-beam fire-damage state was successfully proposed. Firstly, through a series of fire high-temperature tests, vibration tests and static-load tests upon totally 10 T-shape beams, corresponding key data, such as thermodynamic-decay characteristics, was further achieved. And based on that, the above information was better compared with the results achieved by ANSYS numerical simulations and calculations. Secondly, one set of assessment-index systems for RC-beam fire-damage state, composed of post-disaster apparent characteristics, maximum surface temperature, fire duration, bearing capacity reduction, stiffness reduction and fundamental frequency reduction and other indexes, was constructed. Besides that, a comprehensive quantitative-classification standard targeting to the said assessment-index system was preliminarily determined. And by means of further optimizing assessment-index weights achieved by Analytic Hierarchy Process and Entropy-weight Method with combination forms, as well as introducing and improving Modified Technique for Order Preference by Similarity to Ideal Solution (MTOPSIS) and Grey Relational Analysis (GRA), one MTOPSIS-GRA model applicable to comprehensive assessment of RC-beam fire-damage state has been determined. Finally, by applying this way into practical post-disaster RC-beam fire-damage assessments and conducting necessary comparative analyses between the current post-disaster building-structure appraisal standard method and actual results achieved by a large number of experiments, it turns out that the assessment results achieved therein are basically consistent with the standardized assessment ones. However, the former can more comprehensively and accurately assess whole-structure fire-damage state.

Abstract:Polymer modification is an important way to improve the high temperature performance of asphalt. In this work, PU-SBS composite modified asphalt was prepared by PU and SBS， and the effect of PU-SBS on high temperature performance of asphalt and modification mechanism were studied. The results show that PU-SBS composite modification can significantly reduce the penetration of asphalt and improve the softening point. PU-SBS modified asphalt can effectively improve the viscosity and high temperature rheological properties of asphalt, and the modification effect is obviously better than that of single polymer modification. PU-SBS modified asphalt has good permanent deformation resistance and elastic recovery at high temperature. The rutting resistance factor G*/sin δ at 64 °C reaches 18.35 kPa, which is 2.6 times and 1.6 times of SBS modified asphalt and PU modified asphalt under the same conditions, respectively. In addition, PU-SBS composite modification combines physical and chemical modification to improve the high temperature performance of asphalt: physical adsorption swelling of SBS in asphalt and chemical reaction of PU with asphalt components.

Abstract:Engineering cementitious composites (ECC) have excellent toughness and crack control ability, which can be used in underground and hydraulic engineering solving the problems of concrete cracking and leakage. ECC with high water-cement ratio (w/c=1.03) has excellent fluidity, but its impermeability is poor. Meanwhile, the high water-cement ratio also induces large slump and poor cohesiveness, leading poor sprayable abilities. In order to solve the above problems, silica fume (SF) was then introduced into ECC (w/c=1.03) with different SF/cement mass ratios to improve its workability, impermeability, microstructure and mechanical behavior. The results indicate that when SF/cement ratio was 15%, the workability of ECC with high water-cement ratio was greatly improved, which could be pumped and sprayed. At the same time, the impermeability of ECC with high water-cement ratio is improved to above P8. The scanning electron microscope （SEM） and energy dispersive spectrometer (EDS) observations confirmed that adding SF made ECC microstructures denser, but also could reduce the alkaline substances to inhibit alkali-aggregate reaction and improve durability. Through the study of toughness, impermeability and workability (pumpable and sprayable) of ECC, the mix proportion of ECC with high toughness, high impermeability, spraying and pumping was obtained, which laid a foundation for the popularization and application in practical engineering.

Abstract:The magnetic coagulant/flocculant has attracted wide attention in the water treatment field due to its good coagulation effect, strong magnetic responsiveness and high solid-liquid separation efficiency. The purpose of the review is to summarize the application progress of the magnetic coagulant/flocculant in recent years, including the treatment of turbidity, heavy metals wastewater, dye wastewater, algae wastewater, oily wastewater and other types of wastewater. Magnetic coagulant/flocculant has shown great application potential in various water treatment. The analysis and prospect of the future research trend of magnetic coagulants/flocculants has been put forward with regard to the current bottlenecks in the application field, including the material selection, property analysis, adaptability, floc analysis and safety risk of the magnetic coagulant/flocculant.

Abstract:In order to understand the source and spatial distribution regularities of PAEs and the main environmental factors affecting their distribution in the tributary of the Three Gorges Reservoir, Five sections in Yulin River, the first level tributa at the end of the Three Gorges Reservoir, were selected: the Estuary, the backwater area (Paihua, Shujia, Meixi) and the upsteam inflow area (Donghe), which was not affected by the operation of the Three Gorges Reservoir, to conduct an in-situ investigation on PAEs. Based on Pearson correlation analysis and principal component analysis, the sources of six PAEs in Yulin River and the relationship between the main PAEs and environmental factors were identified. The results of in-situ investigations of 6 kinds of PAEs (DEP, DMP, DBP, BBP, DEHP and DnOP, according to US EPA) in five monitoring section of the Yulin River revealed that the total concentration of PAEs was in the range of 0.42~0.77 μg/L. The average total concentrations of PAEs in the five monitoring sections were: Estuary (0.771 μg/L) > Paihua (0.638 μg/L) > Meixi (0.613 μg/L) > Donghe (0.566 μg/L) > Shujia (0.421 μg/L), with DMP, DBP and DEHP being the primary monomers. Based on the correlation analysis and principal component analysis, it was found that there was a significant positive correlation between DBP and DEHP, which may be related to industrial and agricultural production activities and the “three wastes” generated in the process. The moderate correlation between DMP and DEP indicated that these pollutants may be attributed from the anthropogenic activities of local residents.

Abstract:In order to improve the removal efficiency of 17β-estradiol （E2） in wastewater, the predominant microorganisms that degrade E2 in the Erhai Lake sediment were screened, and the biosorption and biodegradation of E2 in different environment were studied in this study. The results showed that Escherichia coli (E. coli) is the dominant strain of E2 degradation, and its biological removal process of E2 is a combined process of rapid adsorption and continuous degradation. The removal rate of E2 with an initial concentration of 1.00 mg/L was about 70.42% after being degraded by E. coli for 3 days. Biosorption is mainly limited by pH value and biomass, and the highest adsorption efficiency was obtained in a weakly alkaline environment (pH=8). Electron donors, hydrogen peroxide, humus and heavy metals can effectively promote the biodegradation of E2 at appropriate concentrations. When the concentrations of glucose, sodium formate, H₂O₂, humus, Zn²⁺ and Cu²⁺ was 40 mg/L, 10 mg/L, 3 mmol/L, 2-15 mg/L, 0.5 mg/L and 0.5 mg/L, respectively, the biodegradation efficiency of E2 increased by 12.41%-57.47%. Draw a conclusion from the above results, the E. coli screened from the Erhai Lake sediment exhibits excellent E2 removal ability, but this process is affected by many environmental factors, and the removal efficiency of E2 can be greatly promoted by adjusting appropriate environmental conditions.

Abstract:One of the main substance that contributes to climate warming is CO₂, and the construction industry accounts for about 25% of the world's total CO₂ emissions. During the life cycle of a building, the stage with the largest average annual CO₂ emissions is the embodied stage. Therefore, it is important to study CO₂ emissions from the embodied stage of buildings. At the same time, the uncertainty analysis method was used because of the partial variability of data such as emission inventories due to human factors and the limitations of the technology level. In this paper, we decompose the building by sub-projects, quantify the CO₂ emissions of the embodied stage by combining specific unit processes, and then give the unit processes that need the most attention in emission reduction. Through the case study, it is found that the focus of carbon emission reduction in the embodied stage of the building is the material production phase, which accounts for 93% of CO₂ emissions. Next, among the different processes, the focus of emission reduction is civil engineering, whose carbon emissions account for 85% of the overall. Two types of uncertainties, data and scenario, are also calculated in the carbon emission quantification process. According to the results of data uncertainty, it can be seen that the coefficient of variation of the total CO₂ emissions in the embodied stage is 0.3%, and the confidence of the result data is high. According to the results of the scenario uncertainty, it is known that changing the distance and type of diesel fuel in the transportation stage can reduce carbon emissions by 39%, and changing the type of electricity used in the construction stage can reduce emissions by 27%.

Abstract: