Abstract:A series of hollow cylinder torsion shear tests were conducted for the silty soil in the Yellow River flood area, considering the effect of drainage shearing with major large principal stress direction. The shear stress-strain behavior as well as the anisotropic characteristics of silty soil were investigated. Under different intermediate principal stress coefficients b and major principal stress direction angles α, the stress-strain relationship and the corresponding shear stress ratio of silty soil were obtained. It was concluded that the values of α and b have a significant effect on the octahedral stress-strain and the shear stress-major principal strain. The obvious anisotropicic behavior was observed, especially under b=0.5 or 1.0. Compressed deformation generally occurred in the major principal strain direction. Under a fixed α, the smaller shear strength occurred under a larger b value. The peak shear strength and the corresponding axial strain were the greatest under the conditions of α=45° and b=0.5, relevant with to the highest peak shear stress ratio q_f/p₀.

Abstract:The development pattern and distribution characteristics of the shear zone of the particle direct shear test determine the strength of the particle body, but it is not easy to observe. The direct shear test of transparent polycarbonate particles was carried out using a homemade test device. Based on the principle of photoelastic method, the development process of force chain, the development pattern of main contact angle and shear slip surface of particles were studied by observing the shear mechanical properties, stress chain distribution and displacement field of particles, and the simulation analysis was carried out in PFC^2D. The tests show that: the stress shielding phenomenon exists in the force chain distribution of the particle system during the direct shear process; the strong force chain, contact angle and main stress direction of the particle system are deflected, and the deflection characteristics are basically the same; the particles form an arch-shaped shear slip surface during the shear process, and form an arch-shaped slip shear zone together with the horizontal shear surface. The arch slip zone forms at the beginning of shear and continues throughout the shear process. At peak shear stress, the height of the arch-slip zone is proportional to the initial normal force and is between (13-15) d₅₀ thick. The arch slip zone gradually decreases during the residual stress phase, and the arch slip zone gradually tends to a steady state, and the height of the arch slip zone under different initial normal forces does not differ significantly during the residual stress phase, while thickness varies between (8-9) d₅₀.

Abstract:Exploitation of the shallow geothermal energy has gradually become a key topic in geotechnical engineering worldwide with the rapid development of renewable energy and geothermal heat pump techniques. However, the theory of the shallow geothermal energy falls far behind its application. In particular, the mechanism of soil under the complex coupling of stress and temperature fields remains unclear. For a single soil such as sand, clay, and silt, some results have been found by carrying out the temperature-controlled experiments and proposing the related thermal constitutive models. To promote more comprehensive and in-depth thermal behavior of soil and contribute to more practical application of the thermal constitutive model in energy engineering, this paper firstly summarizes the experimental research on the thermomechanical properties of soil. Then, research progress and status quo of thermomechanical constitutive relations of soil, based on different theoretical frameworks, are reviewed in detail. Thereafter, the application of these thermomechanical constitutive relations in engineering practiceis introduced briefly. Finally, suggestions in further research are provided, and the development trend of the thermomechanical constitutive relationship of soil is discussed and prospected, in view of current existing problems.

Abstract:Sandy soil is a common geotechnical material. To satisfy the mechanical and environmental requirements in engineering, the granulated blast furnace powder (GGBS) as a solid waste discharged by steel industry could replace cement as a soil curing agent. In this study, GGBS was used as curing agent and magnesium oxide (MgO) was used as stimulating agent to reinforce the sand. The influence of curing durations (3, 7, 14, 28, 56 days) and the mixing amount of curing agents (8%, 10%, 12%) as well as the amounts of magnesium oxide (0%, 5%, 10%, 15%, 20%, 40%) on the strength development were analyzed. The results showed that under the same amount of curing agent, the unconfined compressive strength （USC） of cemented sand has no obvious relation with curing age less than 7 days. However, when the curing age was longer than 7 days, the longer the age period, the higher of the sand soil USC. Furthermore, the amount of curing agent is positively correlated with the unlimited compressive strength of sand. Finally, although magnesium oxide dosage could promote the improvement of the unlimited compressive strength, excessive magnesium oxide would inhibit the increase of the unlimited compressive strength in sand.

Abstract:In geotechnical engineering, the small-strain shear modulus of sand G_max is an important mechanical parameter. The isotropic consolidation tests were carried out on artificial glass sand, combined with multi-direction bender element tests. The effects of MICP reinforcement methods and bender element arrangement on G_max of glass sand were investigated. The test results show that the development pattern of shear wave velocity V_S, small strain stiffness G_max and stiffness anisotropy G_HH/G_HV of glass sands reinforced by different methods are different. After MICP reinforcement, the G_max of glass sand is increased. Among them, “low pH one-phase method + direct back pressure after injection of reaction solution” has the greatest G_max increase, and the small-strain stiffness ratio (Gmaxload /Gmaxunload) has the maximum decrease. Due to the nonuniformity reinforcement, the placement height of bender element on the side wall also has a certain influence. Based on the test results in this study, it is recommended to arrange the HH and HV bender elements at the same plane to further discuss the effect of MICP on small strain stiffness anisotropy. Otherwise, the test error caused by reinforcement inhomogeneity can not be avoided.

Abstract:With the development of marine industry, coastal sand and soil water retention has become an important technical link in the ecological recovery of islands and reefs. The effect of synergising xanthan gum (XG) with Microbially Induced Calcium Precipitation (MICP) on the water retention properties of silica sand-calcium carbonate mixed sand was investigated by treating the sand with both XG and MICP simultaneously. A series of experiments including water retention, volume change, shear wave velocity and microscopic analysis were carried out to evaluate the treated sand at different concentrations of XG and MICP. The results showed that the water storage characteristics of the cured soil improved significantly with increasing xanthan gum content and MICP concentration. Compared with the untreated sandy soil that produced a mass loss rate of 72.59% over 7 d, the mass loss rate of 5% 2.0 XG-MICP cured soil was only 13.1%, which was reduced by a factor of about 81.95%. The rate of change in volume of the XG-MICP cured soil over the 7 d test days was less than that of the XG cured soil, and the XG-MICP cured soil had a higher volumetric stability. With the increase of xanthan gum concentration, the shear wave transmission time of XG-cured soil was prolonged and the shear wave velocity decreased. Compared with XG-cured soil, XG-MICP-cured soil showed greater shear wave transmission time and smaller shear wave velocity as affected by moisture content. The pores of XG-MICP samples showed rhombic calcite precipitation. The experiment verified the feasibility of using xanthan gum combined with MICP technique to improve the water storage of mixed sandy soils, which is expected to provide a reference for improvement of sandy soils in coastal areas.

Abstract:Water content has a great influence on the mechanical properties of granite residual soil reinforced with geogrids. In order to study the cyclic shear characteristics of granite residual soil-geogrid interface under different water contents, a series of cyclic shear tests were carried out by large-scale indoor direct shear apparatus. The shear stress-shear displacement curves, shear strength, shear stiffness and volume of the soil-reinforced interface were analyzed under four values of water content (13%, 19%, 25%, 32%), three values of normal stress (50, 100, 150 kPa), four shear frequencies (0.2, 0.5, 1, 2 Hz) and four shear amplitudes (5, 10, 15, 20 mm). The test results show that: When the soil is saturated with water content of 32%, the peak shear stress and shear stiffness of the interface increase first and then decrease during the cyclic shearing process. The initial increase of the peak shear stress under the normal stress of 50, 100 and 150 kPa is 6.2%, 22.3% and 33.0%, respectively, indicating that the increase of the normal stress is greater than that of the interface at the initial stage. The interface of soil-reinforced unsaturated soil shows shear softening characteristics. Under different normal stresses, the cyclic shear strength of the interface is negatively correlated with the water content. When the water content is 13%, 19%, 25% and 32%, the final shear shrinkage of the interface is 4.6, 7.7, 8.6 and 7.2 mm, respectively, indicating that the shear shrinkage increases first and then decreases with water content. At each water content, the maximum shear stiffness of the interface decreases first and then increases with the increase of shear frequency, and decreases with the increase of shear amplitude. The shear frequency of 0.5 Hz has the strongest weakening effect on the interface shear stiffness of the interface.

Abstract:Subjected to various natural forces, the disease of grotto temple is serious. The damage degree of grotto temple is increasing with time, and the preventive protection for grotto temple is becoming more essential. The preventive protection measures mainly consists of the numerical evaluation and on-site monitoring. In order to ensure the accuracy of numerical calculation, this paper proposes the following methodology: First, the three-dimensional laser scanning cloud image of the grottoes temple is used to generate a fine geometric model of the grottoes temple to accurately reflect its complex geometric shape; Secondly, H-B criterion is used to fully consider the deterioration of rock mass mechanical properties caused by weathering, cracks, joints and other diseases, and to obtain reliable rock physical and mechanical parameter, and then establish a refined numerical calculation model that more truly reflects the boundary conditions, stress displacement and possible failure path. Finally, the current stability of the grotto temple is analyzed by strength reduction method, and the danger zone of the grotto after the deterioration of the rock mass is predicted by the longitudinal wave velocity of the rock mass, and an early warning system is established to realize the preventive protection of the grotto temple. Taking Grottoes No. 9 and 10 of Yungang Grottoes as an example, systematic modeling, force analysis and stability discussion are carried out by using the above research ideas. The results show that the grottoes maintain a stable state as a whole at present, and stress concentration exists in some areas. By simulating rock strength deterioration, the potential instability risk area of the cave is predicted, and an early warning system based on rock P-wave velocity is established.

Abstract:The Hariti Statue in Fowan of the Beishan Rock Carvings at Dazu has a very high cultural, historical and artistic value, however its weathering is serious, and the statue of the long-term preservation is facing a serious challenge. In order to study the weathering mechanism of the Hariti Statue, this paper made a detailed investigation on the diseases of statues. The samples of weathered dust were collected from the surface of the rock mass of the Hariti Statue for X-ray diffraction (XRD) and ion chromatography (IC) analysis, which tested the mineral composition and the content and composition of the soluble salts. The meteorological parameters such as air temperature, relative humidity, rainfall and the concentration of atmospheric pollutants such as sulfur dioxide (SO₂), nitrogen dioxide (NO₂), 2.5-micrometer Particulate Matter (PM_2.5), inhalable particles (PM₁₀) in the study area were monitored for a long time by the integrated meteorological and air quality monitoring station. The results of disease investigation showed that dust and chalking flaking were the most important diseases to the stone and painting of the statue. XRD test showed that the mineral composition was dominated by quartz, plagioclase feldspar and gypsum. These mineral components have a large degree of weathering, and some components such as gypsum are susceptible to the decomposition under chemical weathering by various acids. IC analysis showed high content of sulfate ion (SO₄^2-), nitrate Ion (NO^3-) and chloride ion (Cl^-), whose acidic corrosion and salinization accelerate the weathering and disintegration of the artifactual minerals. The results of environmental monitoring showed that the area was in the high humidity range of 70%-80%. The air temperature fluctuates greatly depending on the season, and the maximum temperature in the area of the statue is over 40 ℃ in summer. The hot and humid environment is apt to induce the weathering of rock cultural heritage, and when the temperature fluctuation is accompanied by the change of humidity, the risk of weathering would be increased. The air pollution in the statue area is serious, among which atmospheric particulate matters are the most important pollution factors. The chemicals in particulate matter along with acidic gaseous pollutants such as SO₂ and NO₂ will catalyze the erosion of minerals on rock surfaces.

Abstract:Current research on the thermodynamic characteristics of the energy pile group foundation under external load mainly focuses on the vertical load, however the study on impact of horizontal load is limited. To investigate the deformation characteristics of horizontally loaded energy pile groups under asymmetric heating or cooling conditions, a single pile within the 2×2 energy pile group was heated and cooled through the model tests, and a three-dimensional finite element model of the energy pile group was established. The measured data and numerical results were compared and validated, and parametric analysis was conducted to study the thermo-mechanical response of the pile during the operation of a single pile for the energy pile group. Results indicate that the findings of numerical model and model tests are generally consistent. The bending moment was mainly concentrated in the upper part of the pile, its peak bending moment and inflection point are located 0.23L₁ and 0.8L₁ below the soil surface, and the horizontal displacement of the pile also decreased with the increasing depth (L₁ is the effective buried depth of pile). The horizontal loading had a greater impact on the deformation characteristics of the pile, but the influence of temperature could not be ignored. As the temperature increased or decreased, the bending moment and displacement of the energy pile tended to increase. Compared with the only subjected to horizontal load, the increase in water temperature by 10 ℃ and 20 ℃ led to an increase in the M_max (peak bending moment) of the energy pile by about 23.36% and 25.46%, and an increase in the horizontal displacement of the pile top by about 20.59% and 21.93% when the horizontal load and temperature variation were applied simultaneously. The decrease in water temperature by 10 ℃ and 20 ℃ resulted in an increase of approximately 23.48% and 24.39% in the energy pile M_max (peak bending moment), and an increase of approximately 17.97% and 21.27% in the horizontal displacement of the pile top.

Abstract:The dynamic behavior and energy evolution of rockburst at the moment of sudden instability are the key to reveal rockburst formation mechanism. Based on the instability theory and stiffness theory, a combination model consists of rockburst body and its surrounding rock was established using the three-dimension discrete element method (DEM). With it the energy evolution process of the system is visualized through secondary development and the ejection phenomenon of rockburst is simulated successfully. Based on the numerical simulation, the tempo characteristics and energy evolution patterns of instability of the system are studied. The results show that the rockburst rock body reaches the peak stress slightly earlier than the surrounding rock body. The rupture and softening of the rockburst body after the peak stress results in the unloading of the surrounding rock body, and causes its stress change from increases to decreases. The surrounding rock mass then has a rapid rebound deformation to the rockburst body, and the elastic energy stored in the surrounding rock body converges to the rockburst body. In this process, the positive feedback regulation mechanism formed by the interaction of the two subsystems accelerates the fracture process and finally leads to dynamic instability. The research results can provide theoretical reference and technical support for further revealing the rockburst mechanism.

Abstract:In order to investigate the surface settlement pattern caused by construction of a twin parallel shield tunnels in an arbitrary arrangement, a relevant theoretical prediction model needs to be established. Considering the effects of ground soil loss rate and convergence pattern, the classical two-dimensional Peck model is improved by introducing equivalent soil loss parameters to find the actual burial depth after tunnel convergence, taking circular tunnel as an example. Based on this, a prediction model for surface settlement due to construction of the twin parallel shield tunnels in any arrangement is established by considering three main influencing factors, including the angle α between the tunnel axis and the horizontal plane, the radius of the two-lane tunnel (r₁,r₂) and the tunnel axis distance D. The applicability of the proposed model is verified by the field monitoring and numerical simulation results from engineering practice, and predictive model for surface settlement due to construction of the twin parallel shield tunnels in any arrangement is established. The main influencing factors of surface settlement caused by construction under arbitrary arrangement of the twin parallel shield tunnels are analyzed. The results show that the prediction model could be used to solve the surface settlement problem caused by the construction of a two-line parallel shield tunnel in any arrangement, and it meets the engineering accuracy requirement of 20%. The critical parameter values [α,r₂/r₁,D/H'] for the variation of the surface settlement curve from "V" to "W" are [60°,2.0,1.0], which can be used to make a preliminary judgment on the shape of the surface settlement curve and check the rationality of the surface settlement results. It provides reliable guidance for prediction and control of surface settlement deformation in similar tunnel construction.

Abstract:In order to find out the horizontal axis offset law of the tube sheet caused by small curvature radius shield tunnel construction, and to prevent the occurrence of undesirable phenomena such as tube sheet misplaced breakage. Based on the modified longitudinal equivalent continuity model, the ellipticized deformation of tunnel convergence and the influence of comprehensive factors of curved tunnels are considered. By constructing the deflection differential equation of the Winkel foundation beam under the condition of small curvature radius, the prediction model of horizontal axis offset of the tube sheet in the construction stage of small curvature radius shield is established. The engineering applicability of the prediction model is verified by relying on the shield tunnel project of Nanchang City Railway Line 3. The results show that: when the tube sheet is assembled within 6 rings, the maximum error between the theoretical value of the prediction model and the monitoring and simulation values is 13.36% and 25.68%, respectively. The maximum errors between the theoretical values and the monitored and simulated values are 4.91% and 8.95%, respectively, when the pipe pieces are assembled in the range of 7 to 22 rings. The theoretical, simulated and monitored values of the tube sheet assembled in the 30th ring are -20.562 mm, -22.370 mm and -20.949 mm respectively, and the error between the theoretical and monitored values is less than 5%, and the overall trend is basically the same, which can effectively solve the problem of calculating the horizontal axial deviation of the tube sheet in the construction of shield tunnel under the condition of small radius of curvature.

Abstract:In order to explore the influence of manufactured sand dosage on the flexural performance of self-compacting lightweight aggregate concrete beams (SCLC), five SCLC with 0%, 30%, 60%, 80% and 100% manufactured sand dosage for four-point bending tests. The deflection curve, mid-span deflection and crack distribution of SCLC beams with different manufactured sand dosages under load were studied, and the influence of manufactured sand dosage on its cracking moment and flexural capacity was explored. The results show that the average strain of each test beam section conforms to the plane section assumption, and the load-deflection curves are basically similar. With the increase of manufactured sand dosage, the SCLC beam has more secondary cracks and more uniform crack distribution. The maximum crack width decreases under the same load before yielding. The mid-span deflection and ultimate bearing capacity reach the maximum when the manufactured sand dosage was 80%, which were increased by 16.13% and 6.62% respectively compared with SCLC beams with all river sand. Utilising the deflection calculation formula of lightweight aggregate concrete, the deflection calculation value of each test beam differs from the test value. The cracking moment of the test beam was calculated using the standard formula, and the calculated value is quite different from the test value. Through the analysis of test results and calculation of flexural bearing capacity, it can be concluded that the optimal dosage of manufactured sand in SCLC is 60%-80%.

Abstract:Based on the massive applications of FRP-reinforced structure technology, the time-varying patterns of interfacial stresses of FRP-strengthened RC beams under sustained load are investigated in this study. A finite element (FE) model was developed to analyze the external FRP strains, and the correctness and usability of the FE method were verified by comparing the predicted results with the test results. For the FRP end area, both the FE method and the analytical method were applied to conduct investigations considering the spew fillet of adhesive and the secondary loading of the reinforced structures. For the area near the intermediate concrete crack, the analytical method was used to conduct calculations. The results show that the concrete creep leads to the increase of interfacial stresses with time, and the adhesive creep leads to the relief of stresses. This conclusion is applicable to both areas mentioned above and is not affected by the spew fillet of the adhesive and the secondary loading of the reinforced structures. In the FRP end region, the FE results and analytical results are in good agreement.

Abstract:The PHI2 method is commonly used to perform the time-varying structural reliability analysis, with the calculation of outcrossing rate being pivotal to its implementation. Achieving sufficient accuracy is often necessary to calculate the outcrossing rate at a large number of moments. However, for practical problems involving complex limit state surfaces, the calculation of the outcrossing rate at each moment can be very time-consuming. To further improve the efficiency of PHI2 method, three strategies are proposed to be introduced in this paper to improve the efficiency of calculating outcrossing rate. Firstly, the strategy without Cholesky decomposition is used to reduce the number of random variables, while the corresponding calculation of correlation coefficients is given. Secondly, the improved first-order reliability method based on the adaptive Kriging model （AK-FORM） is introduced to efficiently calculate the reliability index at each moment. Finally, the two-dimensional integral is converted into a one-dimensional integral by using the dimension reduction method. The three improvement strategies are combined with the PHI2 method, which forms an efficient time-varying reliability analysis method based on the AK-FORM method and the dimension reduction method, i.e., the K-PHI2 method. Meanwhile, only the strategy without Cholesky decomposition is combined with the PHI2 method to form the PHI2- method. The calculation results of numerical and engineering examples demonstrate that the PHI2- and K-PHI2 methods proposed in this paper have the same high accuracy as the PHI2 method, and both are better than the PHI2+ method （an improved method based on PHI2） in terms of accuracy; compared with the PHI2 and PHI2+ methods, the PHI2- method has a little improvement in efficiency, while the K-PHI2 method further greatly improves the efficiency of time-varying reliability analysis on this basis.

Abstract:To investigate the shear performance of composite shear connectors under biaxial load, a finite element model was established and verified by experimental tests. The failure modes of composite shear connectors under biaxial load and unidirectional push-out load were compared, and the relationship between biaxial load and shear strength ratio was also analyzed. The effects of concrete strength and through reinforcement diameter on the shear strength under biaxial load were clarified. The shear mechanism of the composite shear connector was revealed. A shear strength model of composite shear connector under biaxial load was established by multivariable regression analysis. The results show that lateral compression can effectively prevent the transverse expansion of concrete, and a longitudinal main crack and some transverse microcracks appear in the concrete slab. Under the action of unidirectional push-out load, the composite shear connector fails due to the penetration of splitting cracks in the concrete slab. Lateral compression increases the shear strength of composite shear connectors, but the biaxial load effect is small when the concrete strength is high and the diameter of the continuous reinforcement is large (shear strength ratio is 1.05). The shear strength of composite shear connector significantly increases with the increase of concrete strength and through reinforcement diameter under biaxial loading.

Abstract:The initial welding defect is the key factor that affects the fatigue performance of the structural details of the orthotropic steel bridge deck. In order to study the whole life cycle dynamic characteristics of crack initiation and propagation of the joint weld between the top plate and the longitudinal rib of the orthotropic steel bridge deck, based on the fracture mechanics theory and ABAQUS-FRANC3D interactive technology, the dynamic characteristics of the stress intensity factor in the whole process from the weld buried defect to the fatigue fracture were studied, the crack shape development law was revealed, and the influence of sensitive parameters on the crack growth rate and fatigue life was analyzed, the full-life propagation behaviour of fatigue crack is clarified, and the reliability of the research results is verified by the full-scale segmental fatigue test of steel bridge deck. The analysis results show that the fatigue crack growth behavior of steel bridge deck can be divided into three stages: burial stage, initiation stage, and propagation stage. The distribution of stress intensity factors in the buried initiation stage and the propagation stage along different crack paths are exactly opposite; buried cracks of any initial shape tend to be round with continuous expansion, and surface cracks of any shape gradually flatten, which reasonably explains the flat shape of surface cracks when they continue to extend to the roof; the crack propagation rate along the upper surface of the buried stage is 54% higher than that along the lower surface. The crack propagation rate from the buried initiation stage to the roof direction is larger; The crack shape ratio and the burial depth have a great influence on the initiation life, and the initiation life accounts for the majority of the total fatigue life.

Abstract:Affected by the randomness of track irregularity, the dynamic factor of the guideway beam caused by the maglev vehicle has obvious uncertainty. In order to accurately calculate the reliability of the dynamic factors of the guideway beam, a vertical coupling vibration model of the medium and low speed maglev train-bridge system was established, which was composed of the maglev vehicle, the simply supported girder and the suspension control system. Then, combined with the idea of orthogonal random function and the strategy of selecting points by the number theory method, the reduced-dimension simulation method of track irregularity was developed, which repaired only two random variables to simulate the representative samples of the track irregularity. Finally, based on the probability density evolution method and the equivalent extreme-value principle, a reliability evaluation method for the guideway beam was proposed, by which the probability density function, the cumulative distribution function of the dynamic system and the dynamic reliability of the guideway beam can be accurately obtained. The Changsha low-medium speed maglev line, as a case study, was numerically analyzed. The reliability of the calculation model was verified by comparing with the results of field measurement and Monte Carlo method. Furthermore, the effects of vehicle speed, vehicle weight and track irregularity roughness on the dynamic factors and the reliability of the guideway beam were discussed. The results indicate that the reliability of the guideway beam is 1 within the speed range of 60 to 140 km/h. The weight of vehicle has a small effect on the dynamic coefficient of the guideway beam, but the effect of the track irregularity roughness is significant. Overall, the Changsha low and medium speed maglev 25 m simply supported girder bridge has good dynamic performance and a large safety margin.

Abstract:Construction schemes for long-span floating suspension bridges based on tension leg platforms have high application prospects in high water depth and soft soil environments. Due to their low foundation stiffness, vehicle loads may induce significant vibrations in bridges. This phenomenon can be mitigated by adjusting the parameters of the tension leg platform. So, there is limited research on this novel long-span floating bridge under vehicle loads. However, the feasibility and applicability of such schemes need validation. This paper utilized finite element software to compute the response of a floating suspension bridge model under the vehicle load. The effect of changes in the submerged depth and cable inclination angle on the response was investigated using methods such as modal analysis. The study revealed that adjusting the parameters of the submerged depth and cable inclination angle primarily alters the first two vibrational modes, significantly affecting the lateral responses. Increasing the submerged depth of the platform and adding inclined tension leg cables effectively reduced vibrations under the vehicle load. Additionally, the optimal modification of the cable inclination angle requires specific analysis. Therefore, during the design phase, the relevant tension leg platform design parameters are crucial for finding the most suitable configuration, which can enhance the overall feasibility and applicability of floating bridges under the vehicle load.

Abstract:Geopolymer is a kind of green and low-carbon cementing material, and the study of the cementation process of geopolymer is essential for engineering application. In order to investigate the mechanism of geopolymer cementation, five groups of geopolymer mortars with different mixture proportions (slag：fly ash) were placed in a special device and monitored them in real time by three ultrasonic inspection methods. The initial and final setting times of the geopolymer mortars were characterized by energy reception ratios and verified with the results of the penetration resistance method. The results demonstrated that the setting rate of the geopolymer mortar slows down with the decrease of mixture proportion. The ultrasonic transmission method could realized the whole monitoring of mortar. The mean error of initial setting time and final setting time of ultrasonic transmission method was 7.9% and 6.6% respectively. The reflection method has high accuracy in determining the initial setting time of the mortar, and its mean error was 2.8%. The ultrasonic guided wave method could realise the whole monitoring of the mortar. The mean error of the initial setting time and final setting time of ultrasonic transmission method was 3.3% and 2.5% respectively. Among the three methods, ultrasonic guided wave method is more suitable for monitoring the coagulation process of geopolymer mortar.

Abstract:Eutrophication is a global issue that threatens drinking water safety and even the entire ecological balance. The excessive discharge of phosphorus (mainly in phosphate) in water is one of the important reasons for eutrophication. Therefore, controlling the concentration of phosphorus in water, especially phosphate concentration, is of great significance. Mn-based materials have good potential for phosphate removal, but existing reviews lack a systematic summary of them, making this metal-based material that has not received enough attention. ln fact, research on Mn-based materials in the field of phosphate removal has evolved from single manganese oxides to mixed metal oxides and hydroxides, metal-support composite materials, and layered double hydroxides (LDHs). Meanwhile, the emerging methods such as electro assisted adsorption and plasma further enhance the ability of Mn-based materials to remove phosphates. The present article reviews the effects and mechanisms of phosphate removal using different Mn-based materials, and evaluates the application prospect of phosphate removal using different Mn-based materials. Then, from the perspective of increasing pHpzc or enhancing electrostatic effects, several methods for enhancing phosphate removal in Mn-based materials are analyzed and summarized. Finally, based on the existing research, the current shortcomings and future development directions are proposed in order to provide a reference for future research on phosphate removal using Mn-based materials.

Abstract:In order to reduce the safety and health hazards of the enclosure, on the basis of the field sampling and the orthogonal experiment, the influence of the growth characteristics of the dominant bacteria in order to expand the database of the dominant mold in the building and provide reasonable support for predicting the growth risk of mold under fluctuating temperature and humidity. First, mildew samples were obtained in Lingnan typical farmhouses by scraping, and high-throughput sequencing was used to identify the dominant bacterial species; then 22 ℃, 26 ℃, 30 ℃ and 60%, 70%, 85% temperature and humidity combinations were used to study the growth characteristics of the dominant bacteria on Potato Dextrose Agar (PDA) and establish a kinetic model with time and temperature and humidity. Finally, 26 ℃, 30 ℃, 34 ℃ and 50%, 90% ambient temperature and humidity combinations in the artificial climate chamber to study the growth characteristics of the dominant bacteria on common building materials. The results show that in Lingnan area, the dominant fungus on the surface of rural residential envelope structure with large white ash as the interior surface material are Cladosporium, Neoderiesia and Acremonium; 26 ℃ is the environmental temperature for the spore to grow and reproduce; the higher the relative humidity, the faster the growth; Gompertz model and response surface model can show the growth characteristics of spores on the culture medium.

Abstract:CO₂ capture and sequestration (CCS) is an emission reduction measure with great potential. Porous biochar contains rich multi-scale pore structure, which makes it have excellent CO₂ adsorption performance. To address the shortcomings of traditional CO₂ adsorption prediction models built with experimental data, such as low accuracy and complicated calculation, this paper adopts machine learning methods such as gradient boosting decision tree (GBDT), extreme gradient enhancement algorithm (XGB) and light gradient booster algorithm (LGBM) to make model predictions of CO₂ adsorption by biochar, and conducts comparative analysis of the prediction results. The results showed that the three most important factors affecting CO₂ adsorption were the specific surface area, C content, and O content of biochar in order. All three algorithms could effectively predict the CO₂ adsorption performance of biochar. In comparison, LGBM has the highest prediction accuracy of 94%; GBDT has a significant advantage in processing anomalous sample data; and XGB has more stable prediction results for different test set variations. When designing the adsorption performance of biochar, excessive surface area should not be blindly pursued. It is recommended that the selection of biochar C content should preferably be between 83% and 88%, and O content should preferably be between 15% and 18%.