Abstract:Sheet-pile retaining wall is a very common retaining structure is widely used in construction of mountain road. However, in order to resist the lateral load, conventional sheet-pile retaining wall is of relatively large size, which is less economical. Under this condition, a new pile-arching retaining wall, which is suitable for mountain road construction, is proposed in this study. Considering that the arch structure is of good compression performance, the arching plate is used to replace the conventional plate structure, and the arch plate is connected with the pile foundation. The whole structure could be prefabricated or constructed in the way of cast-in-place. Based on the theories of earth pressure and lateral loaded pile, computational models were proposed for the active earth pressure of arch plate and the anti-slide pile. Then, the theoretical model was validated by comparing the predictions with the numerical results. Subsequently, parametric studies were conducted to investigate the influence of the geometric parameters of pile, geometric parameters of arch plate and the soil parameters on the limit load of the new pile-arching retaining wall structure. The results show that increase of ratio of length to width of the rectangular pile cross section, the embedded depth of pile as well as the friction angle of soil could effectively improve the limit load of pile-arching retaining wall structure.

Abstract:Model tests are carried out on the jacked single piles of different diameters under model pile of different diameters in clayey soil, which aims to investigate the penetration mechanical mechanism. The results show that pile driving pressure of test pile shows linear increase. The load transfer performance of test piles will be affected by different diameters, and the axial force transfer capability of large diameter in the depth direction is better than that of small diameter since the compacting effect is more obvious. Unit skin friction of pile increases gradually as the depth increases, which is larger due to the lateral extrusion force increases as the diameter increases. At the same depth, unit skin friction of two different diameters pile demonstrates "friction fatigue", which also decreases obviously as the depth increases. At the same time, the "friction fatigue" is more obvious as the pile diameter increases. In homogeneous clays, the piling resistance mainly includes the end resistance. The end resistance of test pile accounts for 59.5% and 66.2% of the piling resistance when sinking pile ends. The end resistance and the shaft resistance are influenced by the pile diameter. For the confirmation of the jacked piling resistance, it is more rational to consider the actual value with the friction fatigue of clayey soil.

Abstract:When suction caissons are used as foundation of the manifold or pipe terminal in deep waters, they are subjected to a torsion except for the vertical force, horizontal force and moment applied. The torsion may reduce the vertical, horizontal and moment bearing capacities of caisson foundation. In this study, theoretical analyses and finite element simulations are conducted to study the interaction between normally consolidated clay and the typical caisson (with a length-to-diameter ratio between 1 and 2) subjected to combined loadings. The strength reduction of the soil around the caisson skirt induced by installation are considered in the theoretical and numerical analyses. For caissons under undrained conditions, the uniaxial torsion capacity and the influences of the torsion on the other capacities are obtained. The results show that when it is less than 20% of the torsional capacity, the torsion applied has slight effect on the vertical, horizontal or moment capacities. When torsion applied reaches 20%~80% of the torsional capacity, the other three capacity components can be reduced by as much as 20%. The torsion influence factors against three capacities are proposed for routine designs.

Abstract:The uplift of anchor plates is of anchor-soil interaction process. The investigation into soil deformation and failure mechanism around the anchor plate is important for uplift capacity prediction. In this paper, a series of anchor plate uplift tests based on particle image velocimetry (PIV) technique have been carried out. The deformation fields and failure modes of soil around anchor plates have been obtained under different soil densities and embedment depths of anchor plates. The results of PIV displacement fields show that for shallow anchor plates, the failure modes of the loose and the dense sand foundation are characterized by frictional cylinder and truncated cone, respectively. When the anchor plate is deeply embedded, a bulb-shaped influence zone formed above the inner anchor plate in the loose sand foundation, and the dense sand foundation develops curved failure surface. The results of PIV strain fields show that whatever the embedment depth of anchor plates, the failure plane in loose sand foundation is inclined at an angle 45°+φ/2 with respect to the horizontal, and the angle between the failure plane and the vertical plane in dense sand foundation is approximately φ/4. The conclusions provide references for developing prediction models of anchor uplift behavior.

Abstract:Microbial curing (MICP) can significantly improve the mechanical properties of sand. However, the curing effect is affected by many factors. In this study,the consolidated drained triaxial shear tests and electron microscope scanning tests were carried out to investigate the curing effect and the related mechanism of MICP. On this basis,the effects of cementation concentration, relative density and the proportion of cementation liquid's composition on the shear characteristics of bio-cemented sand were studied. The results show that with the increase of cementation level, the strength and brittleness of bio-cemented sand samples are increased. The increase of the strength of the bio-cemented sand is mainly due to the increase of the cohesive strength provided by the calcium carbonate crystal. The strength of the bio-cemented sand consists of the strength of the soil skeleton and the cementation strength of calcium carbonate.The former is influenced by the properties of sand and related parameters, while the latter mainly depends on the content of calcium carbonate crystals. The strength of the bio-cemented sand sample can be improved by using appropriate initial relative density of sand, increasing the concentration and the molar concentration ratio of urea in the cementation liquid.

Abstract:In order to explore a new method of foundation reinforcement and solve the environmental problems caused by waste rubber tire stacking, a new type of foundation with the waste rubber tire hooping granular material was proposed. The elastic modulus of discarded rubber tire was obtained by carrying out tensile testing on rubber tire strip. By using axial compression test on waste rubber tires-sand composite, the rules were discussed, including the influence of loading system and lateral conditions on the foundation bearing capacity, stress distribution of inner wall of tire, and soil stress inside the laminated body. The results show that, compared with fast and slow loading system, the sedimentation of the superposition is the smallest, and the self-recovery ability and bearing capacity are optimal when loading and unloading in one direction. The bearing capacity of the composite is higher when under confined condition, but the self-recovery ability of the composite is not affected by confined condition. Under the condition of no or no limitation, The stress distribution around the inner wall of the tire is quite different. In the same radial plane, the closer to the center of the superposition, the smaller the effect of rubber tire ring, and the greater the soil stress.

Abstract:Taking the intact loess in a certain area in Xining as the research object, they were designed the three direction's slow freezing test under the closed system, the constant temperature and humidity thawing test and the triaxial shear test. Based on the Mohr-Coulomb strength theory of soil, the cohesion and internal friction were solved by using the shear strength envelope, and the variation of shear strength indexes under different freezing thawing temperature gradients are studied.The results show that:with increase of temperature gradients, the cohesion decay rate is remarkable, and it is -15~15℃ for the most disadvantageous freeze-thaw temperature gradient when the cohesion is minimum;The cohesion of frozen-thawed loess is related to the cold end temperature and thawing temperature;Compared with cold end temperature, the thawing temperature is the dominant factor when the moisture content is lower and the temperature at the cold end is lower, or the temperature at the cold end is higher. With the increase of the cold end temperature, the cohesion of samples with different moisture contents decrease firstly and then increase, the most disadvantageous moisture content is 18.34%.The internal friction shows irregular fluctuations, and the extent of variation is about 0°~14°. The calculation formula of the cohesion with the cold end temperature and moisture content is fitted by the experimental data. The experimental formula can better describe the variation characteristics of cohesion.

Abstract:The Kelvin constitutive model is modified by the spring-pot element based on the Caputo fractional derivative to describe the mechanical behavior of one-dimensional consolidation of saturated soil. After introducing the continuous drainage boundary condition, the analytical solutions of the effective stress and the settlement under time-dependent loading are derived by performing Laplace transformation. The Laplace inverse transformation is used to obtain the theoretical solutions in time domain, and the influences of relevant parameters on the settlement under trapezoidal cyclic loading and construction loading are studied. The results show that the settlement of viscoelastic soil under cyclic loading increases in an oscillating manner, and the amplitude of the oscillation increases with the boundary permeability. A higher value of the fractional order α slows the development of settlement in the early stage of consolidation. However, in the later stage of consolidation, the effect of α on settlement is reversed. The oscillation amplitude of the settlement under cyclic loading decreases with increase of α. Furthermore, detailed analysis indicates that the development of one-dimensional consolidation settlement is also related to mechanical properties of soil and loading parameters. The larger the elastic modulus E is, the smaller the final settlement, and the greater the delay time of viscoelastic is, the slower the settlement occurs.

Abstract:Jet grouting technology is widely employed as a reinforcement of excavation base in soft soil area. In this study, based on the monitoring data, numerical analysis of a railway station is carried out using PLAXIS 2D software. Firstly, comparison between the reinforced and unreinforced excavation cases is evaluated based on the analysis of deformation, bending moment of diaphragm wall and ground settlement. The results show that the lateral deformation of diaphragm wall and the ground settlement can be effectively reduced by basal grouting reinforcement in soft soil. Then four parameters, namely, the thickness of reinforcement zone, the penetration depth, the stiffness of diaphragm wall and the thickness of soft soil layer, are analyzed and discussed. The reasonable thickness of reinforcement zone and depth of diaphragm wall, and the sensitivity of deformation to the stiffness of diaphragm wall and the thickness of soft soil layer are also investigated.

Abstract:Railway stations are a type of large public facility, featured with a complex structural system, high people flow and long service life. Failure of the structural system will cause a serious social impact. In order to effectively monitor the health condition of the station structures, and find out damages of the station structures timely, so as to ensure structural safety of the railway stations to the greatest extent, it is essential to perform health monitoring on the railway station structures. In this study, a case study of a large railway stations is presented, with an overview of structural components and features of stations and an introduction of the health monitoring system used in stations. The main monitoring objects included three levels (roof layer, canopy without platform columns, and rail bearing layer) of the station during construction and operation stages. Problems remaining to be solved are discussed on the application of health monitoring on the railway stations structures, in order to promote the development of health monitoring in large railway station structures.

Abstract:Most of the existing constitute models of stirrup-confined concrete do not consider the size effect. A few consider the size effect using a strength reduction coefficient. In order to investigate the mechanical properties and size effect behaviors of the large-sized stirrup-confined RC columns under axial compressive load, the influence of volume stirrup ratio, the arrangement of stirrups as well as the specimen size on stress-strain curves of confined RC columns were analyzed based on the experimental results of the circular and squared concrete columns. The size effect formula of peak strain for stirrup-confined RC columns was established considering the influence of volumetric stirrup ratio and stirrup type. Moreover, combined with the size effect formula of peak stress in the previous study, the stress-strain model considering the size effect for stirrup-confined RC columns was proposed. Through comparison with the experimental and simulation data, it is demonstrated that the size effect formula of peak stress and peak strain showed good consistency with the experimental results, and the stress-strain model provided satisfactory predictions in large-sized stirrup-confined RC columns.

Abstract:In order to study the improvement of high-strength self-compacting concrete(HSCC) slender column after adding basalt fiber, ten HSCC slender columns in a slenderness ratio of 6 were designed for eccentric compression test, based on the parameters of basalt fiber volume in 0.1% and 0.2%, length in 15mm and 30mm.The results show that the addition of basalt fiber can significantly improve the stress performance and ductility of HSCC columns under eccentric compression. The cracking load of large and small eccentric compression members is increased by 20.7% and 11.8% respectively, and the maximum increase in ultimate bearing capacity is 18.2% and 16.7% respectively. During the compression of large and small eccentric members, the addition of basalt fiber has a remarkable impact on the concrete strain corresponding to its stress peak. When the maximum ultimate bearing capacity is reached, the maximum tensile and compressive strains are reduced by 25.0% and 15.0%; when the large eccentric compression specimens reaches the ultimate bearing capacity under the action of basalt fiber, the maximum deflection in the mid-span increases by 7.6%, which improves the member's deform-ability while has no big deflection effect by the change of fiber length and volume content.

Abstract:Light gauge steel-concrete mixed structure is a novel structural system which not only suits the Chinese practice but also meets the industrialization and modularization of building construction. The light-gauge steel substructure of the mixed structure system will increase the lateral stiffness of the main concrete structure. When the simplified model with only the main structure is adopted in design analysis, this effect can be taken into account by the period reduction factor. The simplified formulas of both the lateral stiffness of 2 or 3 story light steel wall substructure and the period reduction factor of the mixed structure were derived in this paper. Based on the test results, the refined and the simplified model of the light steel-concrete mixed frame were established by using ABAQUS software. The numerical results agree well with the experimental ones. Finally, the proposed simplified formulas of substructure lateral stiffness and period reduction factor were verified using FEM stimulations.

Abstract:The temporal and spatial variation characteristic of the temperature and relative humidity of early-aged concrete are dominant for the shrinkage cracking of early-aged concrete. The temperature and relative humidity interaction analysis model of early-aged concrete is present by the application of unconditional stable backward finite differential method. In the proposed model, the coupling effects of hydration, chemical drying and the diffusion of temperature and relative humidity are taken into account. The temporal and spatial variation of the relative humidity of early-aged concrete are simulated. The rationality of the proposed model is verified by the comparison with the test results. The parameters analysis have shown that the influence of temperature and humidity diffusion on relative humidity decreases with the distance from the diffusion surface. The influence of water-cement ratio on relative humidity is independent of position. The environmental humidity and surface moisture exchange coefficients primarily affect the relative humidity field near the concrete diffusion surface.

Abstract:The theory and research methods of wind-sand two-phase flow have become mature, mainly focusing on the physical movement of wind-sand and wind-sand consolidation engineering. However, the study of wind-sand movement phenomenon and its effect on building structures is relatively rare. It is of great practical and engineering significance to continue the research on wind-sand resistance of engineering structures in wind-sand areas. In view of this, the wind field characteristics under the actual desert landform are simulated through wind tunnel test. The variation of sand consistency, wind velocity profile and turbulence intensity with height under the similar sandstorm environment is mainly studied through the falling sand on the top of the wind tunnel. By controlling the same wind speed and changing the sand transport rate, sand fall is carried out to form a variety of different types of wind-sand two-phase flow coupled flow field and compare with the non-sand-driving wind. The experimental results show that the distribution of sand consistency is related to the number of sand holes, the control of wind speed and height; the movement of sand particles in wind-sand flow field weakens the wind velocity profile, but enhances the turbulence intensity; the influence of the presence of sand particles in wind field on the wind speed at different heights is directly related to the vertical distribution characteristics of sand consistency, and the larger the sand consistency is, the weaker the wind speed is, and the stronger the turbulence intensity is.

Abstract:Urban wastewater treatment plants are oriented to the entire process control, while automatic control systems encounter many problems in parameter measurement and decision making because the wastewater treatment process is nonlinear, multivariable and time-varying. Thus most of control systems in practice are merely aimed at single parameter control or single rector control by now. Automatic control strategies are the brain of control systems, which could fulfill the potential of the hardware and software in the system and ensure the robustness of the system. Thus the mathematical models applied in the automatic control strategies of the urban wastewater treatment are introduced, and the characteristics of Activated Sludge Models (ASMs) and Benchmark Simulation Models (BSMs) are summarized. The automatic control strategies in terms of aeration, chemical phosphorus removal and multi-objective optimization control are described respectively, and the challenges and opportunities in the recent research are presented. Combining the theoretical research and the engineering practice is necessary for the automation process of the urban wastewater treatment plants.

Abstract:As one kind of emerging contaminants, high abundance of microplastics have been identified in ecosystems due to their small size, increasing plastic production, extensive usage, poor waste management, and minimal biological degradation. Therefore, microplastic pollution in the marine and freshwater environment has become a global hot issue in recent years. The most important problem while conducting research on microplastics is to distinguish pollutants from complex environmental media. At present, there are abundant strategies for detection and analysis of microplastics, however, in order to make results comparable, it is urgent to seek unified and standardized separation, extraction, identification and quantification methods for microplastics. Based on a systematic review of common and reliable separation and extraction procedures including density separation, screening, filtration and digestion, elaborating qualitative identification methods such as thermal analysis, spectral analysis and presenting statistical quantification methods such as visual inspection of statistical, fluorescence analysis and thermal analysis, the research prospects of microplastics detection and analysis methods are put forward. Staining fluorescence combined with spectral analysis has broad application prospects in quickly and accurately assessing microplastic contamination in the environment.

Abstract:In order to provide excellent strains for microbial remediation of gasoline-contaminated soil, the gasoline-degrading bacteria were isolated and identified from petroleum-contaminated soil using LB medium as the substrate, and the gasoline degradation rate was determined by using the oil-reducing medium as the substrate. Single factor test was carried out on five strains with excellent gasoline degradation performance at culture temperature, medium pH and culture time. Based on the single factor test results, three factors and three levels of orthogonal test were carried out to degrade with gasoline. Response surface analysis of test results with gasoline degradation rate response, screening of strains with excellent degradation performance and determining the optimal conditions for the degradation of gasoline by the strain. The results showed that nine strains with gasoline degradation properties were isolated from petroleum contaminated soil. Among which Pseudomonas aeruginosa, Pseudomonas, Pleurobacter, Bordetella and Goldenella had excellent degradation performance. The optimal conditions for determining the degradation of gasoline by these five kinds of bacteria as follows:The optimum culture temperature for Pseudomonas aeruginosa, Pseudomonas, Pleurobacter, Bordetella and Gordonia is 32℃,the pH of the medium is 7.0 and the culture time is 20 h. The degradation rates of gasoline in the oil-reducing medium are 70.12%, 76.42%, 75.66%, 77.50% and 73.22%, respectively.

Abstract:China has fully launched the classification of domestic waste. It is urgent to solve the contradiction between classification habit and treatment implementation, and the contradiction between the increasing production of municipal solid waste and the backward treatment methods in China. Eco-city index system is based on its own situation, which is a dynamic and open index system updated in time. By referring to the development process of the index system of eco-city from static system to dynamic system, the construction method of the index system of municipal solid waste treatment was analyzed. Based on the statistical data of China's current situation and referring to the advanced international experience, a dynamic index system for municipal solid waste classification and treatment is established, which allows dynamic updating.It includes the determination of indicators, implementation and evaluation of results. The summary of international experience shows that the system can provide a quantitative method for the decision-making, execution and supervision of municipal solid waste treatment, and provide a data basis for further implementation of municipal solid waste classification and treatment.

Abstract:Modification of tobacco powder by pyridine catalytic method obtained modified tobacco powder biomass adsorbent (MTPBA). This provides a technical basis for the comprehensive utilization of waste biomass resources and the management of NO₃^- contamination. Through the conditional experiments, taken MTPBA direct recover and NO₃^- adsorption rate of 2 mg/L as indicators, the influence of main parameter conditions in the preparation process of MTPBA was studied, and determined the suitable conditions for the preparation of MTPBA. The physicochemical characteristics of tobacco powder before and after modification were characterized by scanning electron microscopy, energy spectrum analyzer, Fourier transform infrared spectroscopy etc. The results show that the suitable conditions for preparing MTPBA are NaOH concentration of 1.5 mol/L during strong alkali pretreatment; the temperature of the crosslinking reaction is 80℃; the dosage of the crosslinking agent is 5 mL/g; the temperature of the quaternization reaction is 80℃. The formed MTPBA showed uniform morphology, increased crystallinity, formed a large number of fine pores on the surface, and successfully introduced tertiary amine groups and chloroalkyl groups. The results indicate that MTPBA has a better pore structure than the original tobacco powder, and the introduction of tertiary amine groups, chloroalkyl groups and surface zeta potential changes are favorable for adsorption of NO₃^-.

Abstract:Rapid urbanization and global warming aggravate the thermal discomfort of urban outdoor environment and increase the risk of thermal security. In order to find out the physiological parameters changes of human body in outdoor thermal environment, provide a basis for rapid urban thermal environment evaluation, an outdoor experiment was carried out to observe the thermal response of human body. Based on the measured data, the simulation precision analysis and coincidence test of the two-node model were carried out. It is found that human skin temperature and body core temperature show different trends under the influence of outdoor wind speed, MRT and self-regulation, in order to ensure the simulation accuracy, the two-node model of human body needs to be modified from the following four aspects:skin and core temperature, standard human model, temperature of regulation starting, convective heat transfer coefficient, relevant parameters and calculation process shall be written as assignable variables or mathematical expressions, the revised two-node model is universal and applicable to the prediction of outdoor human thermal response.

Abstract:Urban ventilation or wind environment focus on the air flow distribution and pollution dispersion which are studied by the tools of wind tunnel and computational fluid dynamics (CFD) simulation. The latter is easy to be employed, but its reliability is under suspicion due to the high uncertainty of air stream. In the city, the sheltering among buildings affects each other in air flow, and the basic element is the two-building model. Shade problem between the two buildings are divided into upstream building with a hole (such as drafts) with no hole two situations, Reynolds average model of using CFD (RANS) simulation of wind pressure on the surface of the building downstream, and compared with wind tunnel experiments are strictly, to discuss the CFD method in question the reliability of the basic unit. The analysis of grid sensitivity states that the smallest side length of the cell around 2% of building height is sufficient to obtain steady results. The comparison of five typical RANS model presents:the reliability of RANS model to the upstream with hole occlusion was significantly higher than that of simulation without hole occlusion; estimations on upper parts of building are more accurate than on lower parts; the SST k-ω model can acquire best results with error of 11% in porous interfering building, and with 16% in sealed one, in comparison of experimental data.