Abstract:In order to investigate the microscopic characteristics between the acid medium and the sandstone, based on the digital core model and the lattice Boltzmann equation, this paper carried out an simulation test of the acid corrosion process of the sandstone, and analyzed the seepage characteristics of the sandstone under different acidic environmental circumstances. Firstly, the structural changes of the internal mineral components of the acid-corroded sandstone were studied by CT scanning equipment. Then, the seepage model of the sandstone subjected to acid corrosion was constructed by combining the digital core of acid-corroded sandstone which is established by the visual image processing software Image J, Avizo and the lattice Boltzmann theoretical equation. The change rules of the internal pore structure and seepage characteristics of sandstone in the process of acid corrosion were analyzed. Results show that the mineral composition and pore distribution of sandstone and the corrosion degree of the sandstone by acidic solution could be revealed by CT scan tests. The penetration depth increases with the increase of porosity. The rate of increase is first fast and then slow when the porosity is large, and finally tends to be stable. It indicates that the seepage model based on Boltzmann equation has good applicability for simulating the acid corrosion process of sandstone.

Abstract:Pore water pressure is an important parameter to evaluate the deformation and stability of loess deep filled ground. In order to explore the law of pore water pressure increase and dissipation in the loess deep filled ground in the valley terrain, the pore water pressure monitoring and analysis were carried out during and after the construction period of a loess deep filled project in Northern Shaanxi. The results show that when analyzing the law of the increase and dissipation of the excess pore water pressure, the change of the hydrostatic pressure caused by compression of the soil layer and the change of the groundwater level must be deducted; the increase and dissipation of pore water pressure are mainly affected by groundwater level and filling load; when the filling speed of earthwork construction is fast, the pore water pressure increases fast. On the contrary, the pore water pressure increases slowly or even dissipates; The increase in pore water pressure during construction period has an approximately linear relationship with the increase in filling load. The pore water pressure coefficient of multistage load is less than 0.2, and the soil is always in a stable state; the dissipation of pore water pressure is slow in the following stage of construction, and it takes a long time for the settlement to reach complete stability.

Abstract:The dynamic resilient modulus of subgrade soil is an important parameter in design of asphalt pavement structure. Accurate acquisition of the dynamic resilient modulus of subgrade soil is always one of the important research subjects in the field of road engineering.In this paper, based on the investigation of the relevant results of domestic and foreign subgrade soil dynamic resilient modulus testing methods, a dynamic resilient modulus testing method for subgrade soil considering influence of the loading and unloading duration has been established through finite element numerical and exploratory tests. Two kinds of typical subgrade soils were selected to carry out dynamic resilient modulus tests considering the loading and unloading duration of the vehicle load. The experimental results show that the dynamic resilient modulus of the two kinds of soil increases with the increase of confining pressure, and decreases with the increase of cyclic deviatoric stress and loading time.With the increase of loading time, the dynamic resilient modulus of subgrade soil can be reduced by 34.6%, and the influence of loading time cannot be ignored.Under different loading time, the influence law of the dynamic resilient modulus of subgrade soil with confining pressure and cyclic deviatoric stress is basically same.

Abstract:The probabilistic analysis of face stability of shield tunnel at present mostly focuses on the variability of soil parameters. However, few researches consider the variability of support pressure. In this paper, based on the K-L expansion, three dimensional random fields of soil parameters are generated to analyze the impact of variability of soil parameters on the failure mechanism of the tunnel face and the critical support pressure.Otherwise, the influence of mean value and the coefficient of variation of the support pressure on the failure probability has been discussed for determining the characteristic mean value of the critical support pressure. The results show that the spatial variability of cohesion and internal friction angle has an important influence on the tunnel face stability, and the influence of variability of internal friction angle is more significant.The failure mechanism of the tunnel face is closely related to the local distribution of random field. When the local random field of the tunnel face is dispersed, the local failure may occurs. The failure probability of the tunnel face is relevant with the mean value and the coefficient of variation of the support pressure. The failure probability decreases with the mean value of support pressure increase or the coefficient of variation of support pressure decrease. The concept of characteristic mean value of the critical support pressure has been proposed, and the determination procedure is given in combination with the failure probability.

Abstract:The significance of numerical analysis of foundation pit excavation lies in the selection of soil constitution and reasonable input parameters.The hardening model(HS model) is one of the soil constitutive models that are widely used.In this paper, the GDS Hollow Torsion Shear Tester (SS-HCA) and consolidation apparatus were used to complete a series of laboratory tests.The parameters of the hardening model of the soft soil layer in Nanchang were obtained through the tests. The proportional relationship between the modulus of each layer of soil parameters has been discussed.The experimental results were compared with the result from literatures. Then, the PLAXIS finite element software was used to conduct numerical simulation of a certain basement deep foundation pit project in Nanchang. The soil constitutive model adopted the programmed HS model. The results show that the calculated value of the deep horizontal displacement of the retaining pile is basically consistent with the measured value. The HS model and the determination method for parameters have been proved to be applicable in numerical analysis of foundation pit excavation engineering in Nanchang area.

Abstract:In order to study the effect of particle shape on shear behaviors of interface between coarse-grained soil and geogrid, the gravel and glass beads with the same particle size distribution were selected as test materials.A series of monotonic direct shear tests, cyclic shear tests and post-cyclic direct shear tests were carried out on the gravel-geogrid interface and glass bead-geogrid interface using a dynamic direct shear apparatus. The monotonic direct shear characteristics of the interface between reinforced gravel and reinforced glass beads under normal stresses of 30, 60, 90 kPa were analyzed. Then, the cyclic shear characteristics of two reinforced interfaces under cyclic loading with displacement amplitudes of 1, 3, 6, 9, 12, 15 mm were studied.The similarities and differences of monotonic shear characteristics of the two reinforced interfaces before and after cyclic shear were compared and analyzed. The results show that in the monotonic shear tests, the shear strength and maximum dilation of gravel-geogrid interface under the three types of normal stresses are greater than the corresponding values of glass beads-geogrid interface. In the cyclic shear tests, the cyclic shear behaviors of gravel-geogrid and glass beads-geogrid interfaces under the cyclic loading with different shear amplitudes are not exactly the same. In the post-cyclic direct shear tests after cycling, the interface shear strength of gravel-geogrid interface after cycling is greater than that of the interface without cyclic loading, except for the interface with amplitude of 15 mm, while the corresponding value of glass beads-geogrid interface at all amplitudes is degraded.

Abstract:A series of directional shear tests on Qinghai remolded loess under different conditions of average principal stress were performed using the British GDS Hollow Cylindrical Torsion Shear Apparatus. The influence of the average principal stress on the stress-strain characteristics of the Qinghai remolded loess was studied. In the test, the principal stress coefficient b remained unchanged. Under different conditions of the average principal stress, the remolded loess samples were subjected to two kinds of shear failure stress paths in which the principal stress axis did not rotate and rotates 45°, respectively. The experimental results show that the average principal stress and the principal stress direction angle have a significant effect on the strength and deformation of the remodeled loess; The octahedral peak shear stress of the remodeled loess has a linear relationship with the average principal stress of the remodeled loess when the major principal stress direction angle is equal to 45° shear failure. The development trend of the octahedral shear strain generated by the remodeled loess failure is basically the same; during the shearing process, the major and minor principal strains of the remodeled loess develop symmetrically, and the major principal strains increase only slightly during failure. When there is no peak in the octahedral shear stress-strain curve, it is recommended to use the octahedral shear stress corresponding to 15% of the octahedral shear strain as the destructive criterion for remodeled loess.

Abstract:Based on the fictitious soil pile model, the effect of pile-end stress diffusion on the settlement of a single pile has been investigated theoretically. Firstly, a pile-end stress-bubble fictitious soil pile model considering the spread of the pile-end stress-bubble was proposed to simulate the supporting effect of the pile end soil on the pile body by combining the fictitious soil pile model and Boussinesq solution. Then, based on the load transfer method, an analytical solution of single pile settlement considering pile-end stress-bubble diffusion in layered foundation was derived by utilizing the double-broken-line model for the soil around the pile. Furthermore, the effects of parameters such as elastic limit displacement, elastic shear stiffness coefficient and additional stress value on the settlement of single pile were discussed based on the present solution. Finally, combining with the actual engineering data, the present method was validated by comparing with existing theoretical solution. The stress-bubble fictitious soil pile model is more meaningful for engineering applications on account of the obvious advantage that the stress diffusion boundary at pile end can be given more strictly.

Abstract:Through a series of model tests in laboratory, the horizontal bearing characteristics of the pile in the calcareous sand foundation were investigated. The influence of the pile length on the pile top displacement, the rotation of the pile head, bending moment of the pile body and the distribution of the pile side soil pressure were analyzed. In addition, it is compared with model piles in silica sand (Fujian standard sand). The test results show that the horizontal displacement-load curve of the model pile in the calcareous sand is abrupt, and the pile length has a significant influence on the horizontal bearing characteristics. Increasing the pile length can significantly increase the ultimate horizontal bearing capacity of model pile, and the pile deformation gradually changes from rigid rotation to bending deformation. The distribution range of the bending moment along the pile body is changed from the whole pile length to half. The soil pressure on the side of the pile is mainly distributed in the upper soil layer on the soil-facing side, and the soil pressure changes significantly with the increase of the horizontal load. Under low stress levels, the horizontal bearing capacity of a single pile in calcareous sand is greater than that in silica sand. The model test of calcareous sand under higher stress levels needs to be further explored.

Abstract:Based on Bayesian theory, the compressive strength of existing masonry structure was deduced.The compressive strength of masonry tested by the method of axial compression in situ was taken as a prior information. At the same time, the estimated value of strength of block and mortar detected by the rebound method was used to construct the likelihood function, according to the calculation formula of compressive strength of masonry in the "Code for Design of Masonry Structures" (GB 50003-2011).Combining the prior information and the likelihood function, the posterior distribution of compressive strength of existing building masonry was derived.The research results show that the reasonable inferred values of compressive strength of existing masonry structures containing various information can be obtained through the posterior distribution. Moreover, the established posterior distribution can be used as the prior information for subsequent compressive strength Bayesian reference, which can realize the dynamic long-term observation of compressive strength of existing masonry structure.Furthermore,it provides a basis for the regular maintenance and reinforcement of existing masonry structure, and provides a foundation for the sustainable development of existing masonry structure.

Abstract:In order to study the characteristics of creep performance of glass fiber reinforced concrete hollow columns under axial compression, the mechanical properties were analyzed according to the mechanical characteristics of the hollow column under axial compression in this paper.The creep formula of the GFRP tube reinforced concrete hollow column was established under axial compression.A creep analysis program under the axial compression load was developed to calculate the creep strain-time relationship curve. And the correctness of creep program was verified by existing tests. On this basis, the influence of the main design parameters, such as applied load, thickness of GFRP tube wall, strength grade of concrete and hollow ratio on axial compression creep performance was calculated and analyzed.The results show that the creep of hollow columns increases rapidly in 28 days (the early stage of load action), and the growth rate becomes slower after 28 days.The creep tends to be stable after about 6 months. The hollow ratio and concrete strength have little effect on the axial compressive creep of GFRP concrete hollow columns,followed by the thickness of GFRP tube wall. The applied load has a greater effect on the creep.

Abstract:The properties of CO₂-modified recycled aggregates with different qualities and particle sizes have not been investigated systematically and comprehensively. In the conditions of 20% CO₂ concentration and natural environmental pressure, considering the effect of recycled coarse aggregate (RCA) quality and particle size, the carbonization rate, CO₂ absorption, alkalinity, water absorption of CO₂-modified recycled coarse aggregate (CRCA) and residual CO₂ content in CRCA were investigated; the compressive strength and chloride penetration resistance of CO₂-modified recycled coarse aggregate concrete (CRAC) were also evaluated. The results show that the carbonization rate and CO₂ absorption of CRCA increase with the increase of CRCA water-cement ratio; the CO₂ modification significantly reduces the alkalinity of RCA; the smaller particle size and lower water-cement ratio of CRCA, the more CO₂ sequestrates in CRCA; the CO₂ modification remarkably reduces the water absorption of CRCA and significantly improves the compressive strengths and chloride penetration resistance of CRAC.

Abstract:Urban wind environment is an important index to evaluate the quality of human life. In recent years, with the rapid development of the economy, more and more new high-rise buildings have been built and greatly changed the existing residential wind environment. It leads a great trouble to the normal life of the residents in the community. However, the target researches focus on this problem are still very scarce. In this paper, the Tongyong Shidai community is chosen as the case study, and all-round and multi-condition experimental study on the residential wind environment influenced by high-rise building is analyzed by large scale wind tunnel (10 m×3 m×32 m). Meanwhile, exceeding probability method is used to quantitatively evaluate comfort degree and risk degree of the residential area with or without new high-rise buildings. The results show that the profile index values for average wind profiles and turbulence profiles are much higher than the values of standard, which indicates that urban area has greater surface roughness. The added high-rise buildings will significantly change the wind environment of the adjacent areas. When the high-rise building is added, the average wind speed in current community within 100, 200, 300 m is increased by 25%, 6% and 2%, respectively. The maximum value of the wind environment comfort and risk exceeding probability is increased by two times and six times, respectively.

Abstract:Antibiotics are widely used in various industries, but due to its refractory properties, antibiotic sareenriched in water system and do harm to human health.Many researchers focus on the removal performance of antibiotics in water systems.Bioelectrochemical system (BES) combined with organic substrate biodegradation and electrical signals stimulation effectively accelerates the removal of all kinds of antibiotics in wastewater. Based on previous studies, in this review, the removal performance of antibiotics in BES are summarized. When BES are applied for antibiotic removal, the electroactive bacteria composition and metabolic pathways of electroactive biofilm on electrode surface are expounded. The factors which affecting the removal performance of antibiotics in BES are summarized. And the antibiotic removal efficiency of BES coupled with traditional wastewater treatment technologies are analyzed. Finally, this manuscript summarizes the advantages and disadvantages of BES in antibiotic removal.

Abstract:Large amounts of wastewater containing refractory organics would be produced in chemical, pharmaceutical and other industries. This kind of wastewater has complex composition and high toxicity, which has become a puzzle in the field of industrial water treatment. Recent years, electro-Fenton(EF) technology has attracted much attention due to its efficient removal ability towards organic pollutants. However, traditional EF technology still has some shortcomings such as low solubility of iron ions at neutral condition, slow reduction rate of Fe³⁺ and insufficient hydrogen peroxide production. Fortunately, the problems mentioned above can be effectively fixed by different enhancing methods like adding organic or inorganic ligands, synergistic effects of transition metals, as well as heteroatom-modified carbon materials, enhancing the effect of electro-Fenton technology. This review briefly introduces some latest work focused on the enhancement of EF process via different co-catalysis methods and analyzes their main mechanism. The advantages and disadvantages of typical co-catalysts are compared and analyzed. The main development direction in preparation and application is prospected according to the problems like insufficient mechanism research, complex synthesis process and that single technology cannot give full play to its advantages. This article aims to provide a reference for enhancing the EF removal of refractory organics by co-catalyst.

Abstract:There are many ways of nitrogen transformation in wastewater treatment, among which dissimilatory nitrate reduction to ammonium (DNRA) convert NO₃^-/NO₂^- into NH₄⁺, which is an important part of nitrogen transformation.This paper reviews the two-step reaction mechanism of DNRA process and microorganisms involved. In addition, the potential factors affecting the DNRA process in wastewater treatment, such as dissolved oxygen, types of carbon or nitrogen sources, C/N ratio, temperature, pH and special substances contained in wastewater,are emphatically discussed to explore how to regulate the competition between DNRA and denitrification fornitrate, and this paper introduces two main analytical methods for DNRA process in wastewater treatment.This paper confirms the occurrence and contribution of DNRA process in wastewater treatment, and the in-depth study of DNRA is of great significance for the removal or recovery of nitrogen in wastewater.

Abstract:The pollutant removal efficiencies of the bacterial-algae symbiotic system supported by head aeration and membrane aeration under different operating conditions were compared to explore the removal mechanism. Results showed that, in the MABAR (based on membrane aeration), the removal rate of NH₄⁺-N, total nitrogen (TN), PO₄sup>3--P, and COD were soared by 1.44,21.22,3.08,52.09 kg/m²/m³, respectively, compared to HABAR (based on aeration head aeration).In terms of algae accumulation, the algae accumulation concentration of MABAR in 5 stages are higher than that of HABAR, with a highest increased concentration by 15.17 mg/cm². These phenomena not only due to no-stripping and high carbonization ability of membrane aeration to provide sufficient inorganic carbon for autotrophic algae, but membrane aeration also provides a good living environment for the bacteria which has the function to stimulate algae growth, such as Acidovorax, Rhodobacter and Acinetobacter. In summary, MABAR can not only promote the removal efficiency, but also help the photobioreactor to resist shock and maintain stability. This new reactor provides a new operating mode for the practical application of the photobioreactor in the future.

Abstract:Hydrolysis including the cell disintegration is the rate-limiting step of anaerobic digestion of waste activated sludge. Adding Fe(Ⅲ) oxides to enrich the Fe(Ⅲ)-reducing bacteria via the dissimilatory iron reduction can enhance the decomposition of complex organic compounds, which is considered as an effective method to promote the hydrolysis and cell disintegration of waste activated sludge. However, the continuous addition of Fe(Ⅲ) oxides is uneconomical in the practical engineering. Adding nitrite, the intermediates in the denitrification, has been reported to promote the hydrolysis and cell disintegration of waste activated sludge.In the meantime the Fe(Ⅱ)in the sludge can be chemically oxided to Fe(Ⅲ).However, there are few reports on the effects of nitrite induced Fe(Ⅱ) oxidation and Fe(Ⅲ) reduction processes on sludge hydrolysis and cell disintegration and subsequent anaerobic digestion.In this study, adding nitrite into the waste activated sludge caused the oxidation of Fe(Ⅱ) with an efficiency of 97.3%. The produced Fe(Ⅲ) further drove the dissimilatory iron reduction.Analysis of scanning electron microscope and three dimensional fluorescence spectrum indicated that the hydrolysis and cell disintegration of waste activated sludge were significantly enhanced in the nitrite-added group, accompanied by the release of large amounts of soluble organic compounds.Analysis of microbial community showed that,both denitrifying and Fe(Ⅲ)-reducing bacteria were significantly enriched in the nitrite-added group. After anaerobic digestion, the sludge reduction and accumulative methane production in the nitrite-added group were 21% and 86% higher than that in the control group without nitrite, respectively.

Abstract:Advanced oxidation processes (AOPs) are one of the important methods to remove emerging organic contaminants in water. In this study, we investigated the degradation kinetics of carbamazepine (CBZ) during the activation of sulfite by Fe(Ⅱ) (Fe(Ⅱ)/sulfite system) and the contribution of reactive oxidative species to the degradation of CBZ in this process. The research results showed that the removal of CBZ at 20 min in the Fe(Ⅱ)/sulfite system increased with the concentration of sulfite increasing from 0.20 mmol/L to 0.50 mmol/L, while the removal of carbamazepine did not further increase with further increasing the sulfite concentration. CBZ could be degraded in the Fe(Ⅱ)/sulfite system over the initial pH (pH_ini) range of 3.0~7.0. The removal of CBZ at pH_ini 5.0 was the highest and was 87.3% at equilibrium. In addition, SO₄^2- and Cl^- in the Fe(Ⅱ) salt had no influence on the degradation of CBZ in the Fe(Ⅱ)/sulfite system. The results of electron paramagnetic resonance and quenching experiments showed that the reactive oxidative species in the Fe(Ⅱ)/sulfite system included sulfate radical (SO₄^-·), hydroxyl radical (HO·) and peroxymonosulfate radical (SO₅^-·), contributing to the degradation of CBZ,and the degradation of CBZ was mainly contributed by SO₄^-· and HO·.

Abstract:Organophosphorus phosphate(OPEs)and hexavalent chromium (Cr(Ⅵ)) are common combined pollutants in electronic waste dismantling area.Simultaneous photooxidation of tris (2-chloroethyl) phosphate (TCEP) and photoreduction of Cr(Ⅵ) by ferric iron (Fe(Ⅲ)) in aqueous solution were studied under 300 W mercury lamp (λ=365 nm). The effects of the initial concentrations of Fe(Ⅲ), Cr(Ⅵ), and TCEP were investigated.The regeneration of Fe(Ⅲ)/Fe(Ⅱ) redox cycle in UV/Fe (Ⅲ) was studied. The applicability of UV/Fe(Ⅲ) to degradation of other OPEs was proved. The results showed that photocatalytic degradation of TCEP and reduction of Cr(Ⅵ) occurred simultaneously in UV/Fe(Ⅲ) system. The increased Fe(Ⅲ) initial concentration was beneficial to the photocatalytic reduction of Cr(Ⅵ) and the oxidation of TCEP.The reduction of Cr(Ⅵ) increased with the increasing TCEP initial concentration.However, the Cr(Ⅵ) concentrations had no significant effect on TCEP degradation.In UV/Fe(Ⅲ) system, TCEP can be degraded completely and Cr(Ⅵ) can be reduced in five cycles. Similar photocatalysis effects were observed for other OPEs. As a homogeneous photocatalytic method, UV/Fe(Ⅲ) can solve the combined pollution containing OPEs and Cr(Ⅵ) at the same time.

Abstract:With the development of industrial utilization of chromium, the problem of chromium pollution is becoming more and more serious. Based on the advantages of easy separation of metal mesh, Al/Cu bimetallic mesh materials were prepared by chemical deposition method to realize the rapid removal of Cr(Ⅵ). Thereaction temperature, solution pH, Al/Cu bimetallic dosing quantity and other conditions were optimized by static test system. The Al/Cu bimetallic mesh material was characterized. It was found that the loose coral-like particles of Cu coating grew on the surface of the Al mesh in situ. The static test of Cr(Ⅵ) removal showed that the removal rate of Cr(Ⅵ) by Al/Cu bimetallic network can reach more than 90% in a wide pH range of 3.0~9.0.When the dosage of Al/Cu bimetallic network was 3 pieces, the Cr(Ⅵ) initial concentration was 5 mg/L, and the reaction temperature was 40℃, the removal effect of Cr(Ⅵ) in water worked best.Mechanism analysis showed that a large number of galvanic cells were formed on the surface of Al/Cu bimetallic network to promote Al⁰ corrosion and release electrons to reduce Cr(Ⅵ) to Cr(Ⅲ).The formation of[H]_abs on the surface of bimetallic mesh further promoted the reduction of Cr(Ⅵ) to Cr(OH)₃ or deposits in the form of flocs on the surface of bimetallic network to remove Cr(Ⅵ) from aqueous solution.The easily separated Al/Cu bimetallic mesh is helpful for the rapid removal of Cr(Ⅵ) in groundwater and other water bodies, and has a good prospect of engineering application.

Abstract:In order to investigate the degradation law and characteristics of β-lactam antibiotics during ozone oxidation, four typical β-lactam antibiotics in water were treated by direct ozone oxidation. The degradation effect of ozone on typical β-lactam antibiotics under different pH values was studied. Quenching experiments were adopted to explore the degradation mechanism,analyze intermediates and speculate the degradation path. Results showed that the degradation of amoxicillin and cephalexin was not significantly affected by changing pH, penicillin sodium was inhibited in acidic condition, and ceftriaxone sodium was promoted in alkaline condition.The results of quenching experiments showed that TBA can promote the degradation of amoxicillin and cephalexin, indicating that the degradation of amoxicillin and cephalexin was dominated by direct oxidation of O₃.With the increase of TBA concentration, the inhibition effect to penicillin and ceftriaxone sodium was more and more significant, which indicated that penicillin and ceftriaxone sodium were indirectly oxidized by ·OH.Amoxicillin, cephalexin, penicillin sodium and ceftriaxone sodium produced 4, 6, 3 and 3 main intermediates during ozonation, respectively. The degradation pathways were composed of β-lactam ring breaking, demethylation, hydration and addition etc.