Abstract:Take Moya statue area of Shifosi cite in Chongqing as the engineering background, this paper proposes a research method for determination of the physicochemical properties of stone relics that cannot be moved through field survey as well as the application of cross-scale analysis method in immovable stone cultural relics. Laboratory tests were conducted by macro and micro tests, and the former include triaxial tests and direct shear tests, which were used to measure the basic mechanical parameters of samples. The micro tests include scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Through SEM, it can be seen that the sample is standard sandstone of large porosity, indicating that it is highly sensitive to water. In the long-term dry-wet cycle, its strength will decrease with time, namely, the typical water-rock interaction; XRD experiments show that the high content of clay minerals in sandstone leads to poor hydrologic properties and weak weathering resistance, which is also the main reason for weathering. Geological radar survey and auxiliary acoustic detection show that this method can be used to carry out macroscopic and microscopic cross-scale scientific analysis of cultural relics under the premise of effective protection of cultural relics.

Abstract:China's hydropower resources mainly concentrated in west China, which is also the meizoseismal area of China. The seismic safety of high earth rockfill dams in these areas is one of the most serious problems in China's hydropower development. Based on the relevant provisions of Code for seismic design of hydraulic structures of hydropower project (NB 35047—2015), the three-dimensional nonlinear seismic response analysis of Lianghekou super high core rockfill dam was carried out by using the ground motion time history generated by site related design response spectrum of the scenario earthquake. The research results show that the dam acceleration amplification effect was quite significant in the middle part of the valley which is exactly of 4/5 dam height above and within 1/3 dam axis length for Lianghekou super high core rockfill dam located in a V-shaped Valley. It showed obvious whiplash effect and three-dimensional valley effect. On this basis, the reinforcement range of Lianghekou super high core rockfill dam was proposed.

Abstract:In order to improve the accuracy of deformation prediction during construction of deep foundation pits, this paper proposes a support vector machine with genetic algorithm optimized parameters (GASVM) and autoregressive moving average (ARMA) model based on wavelet transform decomposition and reconstruction. This paper uses GASVM model to make one-step prediction and multi-step rolling prediction for trend items after wavelet decomposition, utilizing ARMA model to predict random items accordingly, and to sum the predicted values to get the final prediction result. Finally, taking a deep foundation pit of a subway station as a case, the prediction and analysis of the deep horizontal displacement of the supporting piles at the three monitoring points are obtained, and the short-term prediction value of one-step prediction and the medium- and long-term prediction value of multi-step rolling prediction are obtained. The predicted value of the GASVM model is used for comparison. The results show that the combined model in this paper effectively reduces the predictive error, and has achieved satisfactory results in both short-term and medium- and long-term estimations.

Abstract:In response to the problem of shields that underpass the existing buildings, the Nantong Metro Line 1 interval, from the East Huancheng Road Station to the Intermediate People's Court Station, which underpasses the old residential area of the Community Sendadi-Huayuan, was taken as the research case history. Based on the site settlement monitoring data, the impact of shield tunnel construction on the settlement of the adjacent buildings foundations was analyzed. Numerical simulations, taking into account the upper building load and the shield construction disturbance to the surrounding rock, were performed. The pattern of building foundation settlement was summarized. The results show that when the shield machine is tunneling in highly water-rich sandy soil and chalky soil, the head of the shield machine is prone to twisting due to soil disturbance and the dissipation of pore water, which causes instability in the excavation process and eventuallyresults in surface settlement. By setting a reasonable value of soil pressure, maintaining the balance of the digging surface, making the shield machine pass as smoothly as possible, while performing a grouting well, and filling the gap between the lining and the strata, the surface settlement caused by the shield can be effectively reduced.

Abstract:Coarse aggregate is an important proportion of concrete material, and the change of its size will affect the contribution of aggregate interlock behaviour in concrete beams to shear capacity. In order to consider the effect of the coarse aggregate size on the shear failure of Basalt Fiber Reinforced Polymer (BFRP) beams without stirrup systematically, the meso-scale simulation was selected and a numerical model of BFRP reinforced concrete beams without stirrup was established. The effects of member size and coarse aggregate size on the shear failure mode and shear strength of BFRP reinforced concrete beams were simulated and analyzed. The results show that the size effect exists in the shear strength of BFRP reinforced concrete beams without stirrup. Meanwhile, the increase of the maximum aggregate size improves the shear capacity of concrete beam, and weakens the size effect of shear strength. According to the influence mechanism and law of maximum coarse aggregate size, theoretical formula of size effect on the shear strength of BFRP reinforced concrete beams was established on the basis of Fracture-SEL, and its accuracy and rationality are verified via experimental data.

Abstract:The lower layer of magnesium crystal plate reinforced concrete composite floor is a prefabricated new fire-resistant magnesium crystal plate, and the upper layer is cast-in-situ reinforced concrete plate. In order to study the fire resistance and fire resistance rating of magnesium crystal plate reinforced concrete composite slab under different loading ratios, three composite slab specimens were tested subjected to ISO-834 standard temperature rise, and the fire time-temperature curve and fire time mid span-deflection curve at different positions of the composite slab were obtained. The test results show that the composite slab has good fire resistance up to more than 1.5 hours. The fire resistance of the specimens was analyzed by using the finite element software ABAQUS, and the reliability of the established model was verified by comparing with test results. The effects of loading ratio, thickness of magnesium crystal plate, thickness of concrete protective layer, strength of reinforcement and concrete on the fire resistance limit were investigated via the established model. The analysis shows that the load ratio and the thickness of magnesium crystal plate have great influence on the fire resistance of the composite slab. Based on parametric analysis, the fire resistance of composite slab is proposed for different loading ratios and thicknesses of magnesium crystal plate.

Abstract:To examine the seismic behavior of semi-rigid joint of the precast concrete frame, a type of beam-column joint connected by end-plate and bolts is proposed. The joints are designed and the quasi-static test is carried out, and compared with the test of cast-in-place concrete frame joint. The failure mode, bearing capacity, energy dissipation capacity and displacement ductility of the joints are investigated. The finite element program is used to simulate the mechanical performance of test joints, and the accuracy of the model is verified. The results show that the cast-in-place joints dissipate energy by the plastic hinge at the end of the beam, and the section at the end of the beam is damaged by bending and shearing. The cracks are found in both the column and the beam. The semi-rigid joint connected by end-plate and bolts mainly dissipates energy through the relative rotation between the beam and the column. Its failure is due to the insufficient strength of the concrete at the end of beam, but the column and its internal reinforcement remain intact. Consequently, the joint can be quickly repaired by replacing high-strength bolts and precast beam. The joint connected by end-plate and bolts can meet the requirements of energy dissipation and ductility of reinforced concrete structure. Whether the reinforcement and embedded end-plate in the beam can work together with concrete has great influence on the mechanical performance of the joint.

Abstract:In order to examine the flange local stability of T-rib stiffened plates under compression, considering the variation of flange width thickness ratio, T-rib stiffened plates with Q345 strength (5 pieces) and Q420 strength (4 pieces) were fabricated to carry out the local stability axial compression test, and the finite element (FE) models were established to compare with the test. The influence of different material constitutions, simplified welding residual stresses and local initial geometric imperfections on the mechanical properties of the flange were analyzed. The simplified calculation formula for the local stability of the flange was obtained. The results show that both the test and the FE model are subjected to the local buckling failure near the flange height of 1/2, and the larger the flange width-thickness ratio is, the earlier the specimen comes to local buckling failure. The FE models are simulated by an ideal elastic-plastic constitutive model. With increase of the relative flange width-thickness ratio, the axial stiffness of the component decrease because of the inclusion of residual stress. The coefficient of stability is smallest when local initial imperfections are included. The curve of the simplified formula for the flange local stability fitted by cubic polynomial is close to the trend of the Eurocode curve, while the curve fitted by Perry formula is close to the trend of the Chinese and American standard curves. The trend of formula curves fitted with different steel strengthes is basically the same, which can be calculated by Perry formula for a safer result.

Abstract:This paper investigates the vibration response of umbrella shaped tensioned membrane structure under the impact of natural disasters and other external loadings, and provides the basis for the damage analysis of actual membrane structures. Based on von Karman's large deflection theory and thin plate vibration theory, the nonlinear dynamic response control equation of umbrella shaped tensioned membrane structure under hail load is established. Bessel function and Euler equation are used to obtain the mode function, and KBM perturbation method and Galerkin method are used to solve the governing equation to obtain the approximate analytical solution of its dynamic response. The equations are solved by Mathematics software, and the data are sorted out. The time history displacement diagram of membrane surface after forced vibration is drawn by Origin drawing software. ANSYS software is used to establish the finite element model of umbrella shaped membrane structure; then, the dynamic process of hail impacting on the film surface is simulated by LS-DYNA display dynamics module, and the dynamic response of the film surface is obtained. In the same way, the displacement diagram is plotted, and the data results of the sorted theory and numerical analysis are compared and analyzed. The results show that the theoretical and numerical results are more consistent.

Abstract:Design method was proposed for self-centering concrete frame joints with energy-dissipation angle steel in this study. Finite element numerical model was established and its validity was verified by experiments. After the joints with different prestressed moment capacity ratios φdes were simulated, the energy dissipation capacity, self-centering performance and material damage under earthquake were studied. Changing the screw gauge distance of angle vertical leg, the measures to improve its energy-consumption capacity were further explored. The results show that the angle energy-consuming joints have perfect self-centering performance, but the energy consuming capacity is slightly insufficient. As the value of φdes decreases, the residual deformation increases and the self-centering ability decreases, but the energy dissipation capacity increases. Therefore, compared with the hybrid connection joint, the minimum φdes value of joint should be appropriately reduced to make up for its insufficient energy dissipation. The plastic deformation of the angle vertical leg is the main energy dissipation mode of the joint, concentrating on the height of the bolt hole and the turning of the vertical leg. If the distance between the vertical screws is reduced and the other material parameters keeps constant, it will lead to decrease in φdes values, increase of the bending capacity of the section and growth of the energy dissipation capacity of the joint.

Abstract:To deal with the high carbon emission and high cost of traditional backfilling materials, taking "green mine" as the concept, industrial solid wastes such as carbide slag, desulfurized gypsum and slag were used as cementitious components, and tailings were used as aggregates for backfilling materials. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to examine the hydration products and microstructure of the backfilling materials, and the working performance, mechanical properties and heavy metal solidification performance tests were carried out. The results show that the setting time and fluidity of the developed backfilling materials met the requirements of mine backfilling project. The maximum compressive strength of the backfilling body can reach up to 4.6 MPa and 7.9 MPa at 7 d and 28 d, respectively, and the concentrations of Pb and Zn in the leaching solution of the backfilling body were lower than the specified limits. Calcium hydroxide in carbide slag provided alkaline environment, and desulfurization gypsum provided sulfate ion. The aluminosilicate material in slag is activated by both, producing the hydration products that mainly consist of ettringites and C-A-S-H gels. A large number of needle like ettringite crystals and reticulated C-A-S-H gels interspersed with each other, and tightly bonded with tailings particles. With extension of age, the structure became more compact, and the backfilling would be of good mechanical properties.

Abstract:Traditional concrete crushing technology has the disadvantages such as large damage of coarse aggregates, serious mechanical wear and high energy consumption. These problems can be solved by microwave treatment of concrete before crushing. To evaluate industrial applicability of this technology, concrete specimens were heated by different microwave power, and compared with conventional heating method, the heating efficiency and macro-crack propagation mechanism of concrete were investigated. Then the uniaxial compressive strength test was carried out to obtain the strength weakening law of concrete under different heat treatment conditions. The results illustrate that compared with the conventional heating method, microwave heating technology can effectively promote the internal and surface crack propagation of concrete, thus reducing the strength of concrete, and has higher efficiency and less energy consumption under high microwave input power. Besides, the results show that the concrete which is not completely dried is easy to burst at low temperature under microwave heating, and the relationship between burst time and power level is a negative power function, and the relationship between burst time and drying time is a positive power function.

Abstract:The heterogeneity of hardfill is obvious, so it is of necessity to study its parameter’s statistical distribution. Take three hardfill projects with field tests’ data as research objects, the probability and statistical analysis have been done based on χ2 or K-S finite contrast method, and the recommended probability distribution models have been put forward：recommend normal distribution to fit the probability of density; recommend lognormal distribution to fit the probability of modulus of elasticity; recommend lognormal distribution to fit the probability of strength parameters; recommend β distribution to fit the probability of poisson ratio. Moreover, the correlation distance of hardfill dam is also discussed. Results are that the vertical correlation distance and the horizontal correlation distance are 0.5~2.0 m and 5~30 m, respectively.

Abstract:The infiltration air volume of platform screen doors (PSD) is an important factor affecting the cooling load of subway station. This paper proposes a calculation model of infiltration air volume of PSD. Based on the analysis of test wind speed, the single cycle PSD infiltration air volume is quantified, and the characteristics of infiltration air volume of PSD are studied in different positions and stages. Then, through the analysis of train operation factors, a calculation method of total infiltration air volume of PSD is established, in order to provide reference for the design and operation of subway station. The results show that: （1） the infiltration wind speed of PSD at different positions is different. Along the running direction of the train, the infiltration wind speed and air volume of PSD in a single cycle decrease with the change of door position. The single cycle infiltration air volume of PSD at the exit side is about 65% of that at the entrance side. （2） There are also differences in the infiltration air volume of PSD in different stages. The total infiltration air volume in a single cycle in the train stopping stage is the largest, which is about 10 times that in the train arrival stage. （3） The range of infiltration air volume of single cycle PSD is given, which provides a basis for the calculation of total infiltration air volume, and the corresponding calculation model is proposed, which can calculate the whole day air volume of PSD penetration of subway station.

Abstract:The large-scale use of plastic products has caused the increasing content of microplastics (MPs) in soils, which has attracted extensive attention. At present, the main factor that obstructs the assessment of soil environmental ecological risk is the lack of standardized testing and quantitative methods. However, the detection methods of MPs in complex soil media were still not homogeneous, which seriously affected the comparability and reliability of the previous studies. In this study, the microwave digestion method was used to extract MPs at once from complex soil media by optimizing the microwave digestion conditions (acid system, the heating procedure and the amount of acid added). The results showed that 0.1 g soil could be completely microwave digested by 15 mL HCl + 5 mL HNO₃ + 3 mL HF, and MPs could be completely extracted from the soil. Besides, the extraction efficiencies of polystyrene (PS), polyethylene (PE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA) and polypropylene (PP) in the scaling experiment were 126%, 146%, 51%, 85%, 96% and 162%, respectively. The weight of plastics (PS, PE and PP) was increased after digestion, possibly because the physical and chemical reaction between acids and MPs could change the surface properties of MPs, resulting in the higher porosity of MPs. The adsorption capacity of metals and organic matters were increased. However, the extraction efficiency of PMMA and PVC was above 80% under the condition. All plastic particles showed the degradation in the microwave digestion through the analysis of plastic surface morphology, but the results of Fourier infrared conversion spectroscopy (FTIR) showed that microwave digestion did not affect the identification of plastic types. However, the current method is only be applicable to qualitative and preliminary quantitative analysis, standardized quantitative analysis needs to be further explored.

Abstract:The comparative experiments of phytoremediation, microbial remediation and plant-microorganism combined remediation of outdoor dotted plant for different contents of diesel contaminated soil were carried by using mixed strains of petroleum hydrocarbon degrading bacteria and two kinds of plant (alfalfa and tall fescue). The germination rate of plant seeds and plant growth status in phytoremediation and plant-microorganism combined remediation experiments were studied, and the degradation effects on diesel contaminated of three remediation methods by ultrasonic extraction ultraviolet spectrophotometry were analyzed. The experimental results show that diesel oil delayed the germination time of plant seeds. The plant biomass and plant height of tall fescue are greater than that of alfalfa in the process of phytoremediation and plant-microorganism combined remediation. As a whole, the plant biomass and plant height of plant-microorganism combined remediation are significantly higher than that of phytoremediation. The sort of overall degradation effects of three remediation methods for diesel contaminated soil are as follows: plant-microorganism combined remediation, microbial remediation, phytoremediation. The remediation effect of tall fescue is better than that of alfalfa. The lower diesel concentration of diesel contaminated soil would make the remediation effect better.

Abstract:Organophosphorus flame retardants (OPFRs) are a category of emerging contaminates, which poses significant risks to human health and ecosystem. In this study, two typical OPFRs [tris (1-chloro-2-propyl) phosphate (TCPP) and tris (2-chloroethyl) phosphate (TCEP)] were selected as target pollutants. The removal efficiencies, concentration variations along the flow path and the accumulations of these two OPFRs in substrate and plant in integrated vertical-flow constructed wetland (IVCW) with intermittent inflow were investigated. The inflow and outflow mass, accumulation and transformation of TCPP and TCEP in IVCW based on mass balance were analyzed, and the possible transformation mechanisms were discussed. The results show that IVCW could effectively remove TCPP and TCEP, and the removal rate of TCPP and TCEP in stable stage after planting plants were 74.1%±5.3% and 49.3%±5.5%, respectively. Constructed wetland system was a converter of OPFRs, and the mass of TCPP and TCEP transformed in IVCW was far greater than that accumulated in substrate and plant (2.37% and 1.67%), which accounting for 59.72% and 44.6% of the total mass flow into the IVCW. Microbial degradation in substrate was an important process of OPFRs removal, and variations of TCPP and TCEP concentrations along the flow path were significantly correlated with the DO consumption rate and the concentration of degradable organic matter. Plant can enhance the removal performance, but due to the limitation of concentration in plant, it is not practical to significantly improve the removal rate by harvesting or increasing planting density.

Abstract:Sewage sludge was solidified with soda residue (SR), ground granulated blast furnace slag (GGBS), and quicklime, which was used as a temporary covering material for landfills. The effect of leachate concentration, soaking time and SR content on the long-term properties of solidified sludge was carried out. The micro mechanism of long-term performance was investigated. The results indicate that hydration products such as ettringite and calcium silicate hydrate are generated when the solidified sludge is soaked in the leachate. The strength of the sample increases with the increase in soaking time, indicating that the solidified sludge has good durability to the leachate. Nevertheless, a large amount of calcium carbonate and ettringite of different sizes are generated in the sample with 60% SR content after being soaked for 210 d. Then the structure becomes loose, cracks appear in the sample, the strength decreases significanty, and its long-term strength reduces to lower than the strength requirement for temporary cover. Too much SR content is not good for the long-term strength of solidified sludge. The strength of solidified sludge decreases as the leachate concentration increases due to the corrosive effects of leachate. The solidified sludge is structural, and the changes in the yield stress under leachate soaking are basically similar to the strength. During the long-term leachate soaking, SR-GGBS-quicklime can stabilize some pollutions such as chromium, copper, lead and arsenic in the sludge and leachate.

Abstract:In view of the difficulty of sludge dewatering and high operating cost in wastewater treatment plants, the effect of NaClO dosage, pH value of the sludge mixture, and the coupling of polymerized ferric sulfate (PFS)/ ferric chloride (FeCl₃) under the optimal dosage of NaClO and the optimum pH value of the sludge mixture on the dewatering performance of sludge were studied in depth, in order to obtain the influence mechanism of oxidation-flocculation conditioning on the dewatering performance of activated sludge. The results showed that when the dosage of NaClO was 40 mg/g DS and pH value of the sludge mixture was 3, the moisture content of mud cake and sludge specific resistance (SRF) after PFS coupled NaClO conditioning were reduced to 85.86% and 4.74×10¹¹ m/kg, respectively. The moisture content and sludge specific resistance of the mud cake after FeCl₃ coupling NaClO conditioning were reduced to 86.36% and 3.93×10¹¹ m/kg, respectively. The relationship of the conditioned sludge floc size D₅₀ is: NaClO+PFS>NaClO+FeCl₃>pH value >raw sludge>NaClO. Obviously, after oxidation-flocculation conditioning, the particle size of the sludge flocs increased significantly, and the organic matter content in the filtrate decreased. Oxidation-flocculation conditioning can significantly reduce SRF and improve the dewatering performance. NaClO coupled PFS and NaClO coupled FeCl₃ are expected to be novel sludge dewatering conditioners with high efficiency, environmental protection and low price.

Abstract:The growth status of Chlorella vulgaris, Chlorella proteinosa and Scenedesmus obliquus under different nitrogen levels and the efficiency of advanced nitrogen and phosphorus removal in sewage were compared, and the effect mechanism of nitrogen source level on nitrogen and phosphorus removal in microalgae was analyzed from the perspective of biomacromolecule accumulation, and a theoretical basis was provided for advanced nitrogen and phosphorus removal in wastewater and harvesting microalgae to produce energy to alleviate energy crisis.The results showed that when nitrate is the only nitrogen source, the growth of microalgae and the efficiency of nitrogen and phosphorus removal were significantly better than that of the experimental group with ammonia nitrogen as the only nitrogen source, and the content of chlorophyll was also higher than that of the ammonia nitrogen group, because nitrogen is an important element of chlorophyll synthesis. The higher the nitrate concentration in each experimental group, the more the number of algae cells, and the growth of chlorella cells was significantly higher than that of Scenedesmus obliquus. Within seven days, the nitrogen removal rate was above 98% when nitrate concentration ≤8 mg/L, but the chlorophyll-a content was low in the experimental group with low nitrogen concentration. Microalgae by adjusting the content of macromolecular substances in the cell to adapt to different living environment, under the condition of nutrition restricted consumes itself material to meet the needs of life activity, nitrogen limit conditions can lead to accumulation of lipid in cells, confirmed the possibility of nitrogen source level controlling on the depth of the wastewater biological nitrogen and phosphorus coupling feasibility of macromolecular accumulated.

Abstract:In the present study, three strains of high-efficiency phosphorus removal bacteria were screened and isolated from a stable anaerobic/aerobic/anoxic sequencing batch reactor (A/O/A-SBR). The species were identified by morphological observation, physiological and biochemical tests and 16S rRNA sequence analysis. The three strains of bacteria were identified as Acinetobacter, Klebsiella and Enterobacter.The NCBI preservation accession numbers were OL519151, OL519152 and OL519153, respectively. The effects of pH value, temperature and the carbon source on cell grow and phosphorus removal were explored. Meanwhile, the distribution and transformation of inorganic phosphorus and organic phosphorus in bacterial cells, soluble microbial products (SMP) and extracellular polymers (EPS) were also investigated. The results show that the highest phosphorus removal efficiency of Acinetobacter sp. PK01,Klebsiella sp. PK02 and Enterobacter sp. PK03 were 89.4%, 85.43% and 76.95%, respectively, based on the optimal condition. The removal of phosphorus from the environment by Acinetobacter mainly relied on the absorption of extracellular inorganic phosphorus and stored in the body as polyphosphate, removing 54.93% of phosphorus from the matrix. The removal of phosphorus by Klebsiella mainly relied on EPS synthesis and adsorption. This route removed 47.18% of phosphorus from the matrix. Enterobacter removed 48.32% of phosphorus, which mainly depend on the synthesis of polyphosphate and EPS.

Abstract:It is significant to realize the efficient recovery of phosphorus resource and resource utilization of agricultural wastes. Three kinds of modified rice straw biochar (PRSB-Fe, PRSB-FS and PRSB-Ca) were prepared by modifying rice straw biochar (RSB) with FeCl₃, Fe₂(SO₄)₃ and CaCl₂, respectively. SEM, XPS, FTIR and BET characterized the modified biochar. Its adsorption capacity for phosphate in simulated wastewater and feces and wastewater separation solution of septic tank was explored by batch experiments. The results of simulated wastewater test showed that the adsorption of phosphorous by three modified biochar was well fitted to the pseudo-second-order kinetic model (R²>0.99), which indicating chemical adsorption was the major. The adsorption isotherms were more consistent with Freundlich equation at 20 ℃, indicating that multilayer adsorption was dominant. In addition, the coexistence of Cl^- had little effect on the adsorption capacity of modified biochar. For the feces and wastewater separation solution of septic tank with initial phosphorus concentration of (12.94±1.51) mg/g, pH value of 7.4±0.2, the adsorption capacity of PRSB-Fe-5, PRSB-FS-5 and PRSB-Ca-5 for phosphorus was 10.77, 23.35 and 0.85 mg/g, respectively. PRSB-FS-5 had the best adsorption of phosphorus, with the removal rate as high as 97.31%, and the residual phosphorus concentration was only 0.37 mg/L, reaching the first level A standard of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002).