Abstract:The influence of ammonia nitrogen and natural organic matter on the performance of filter column for iron and manganese removal was analyzed, and the thickness of filter layer required by the filter column was explored. A pilot-scale biofilter column was constructed to remove iron, manganese, ammonia nitrogen, and natural organic matter (TFe 4.7-5.4 mg/L, Mn(Ⅱ) 1.1-1.3 mg/L, NH+₄-N 1.4-1.8 mg/L, COD_Mn 5.9-7.4 mg/L) from simulated groundwater under the conditions of water temperature of 14-17 ℃. The filter column used in the test was a mature biofilter column for iron and manganese removal. The startup of purifying ammonia nitrogen and natural organic matter in the same layer by means of cyclic inoculation and natural membrane hanging lasted for 79 d. Results show that the presence of ammonia nitrogen caused the Mn(Ⅱ) removal section of the filter column to move down, but it had no significant effect on the removal of iron and manganese by filter column. Fe(Ⅱ), Mn(Ⅱ), and ammonia nitrogen could be removed simultaneously under the condition of sufficient dissolved oxygen (DO). The presence of natural organic matter reduced the ability of the filter layer to purify iron and manganese. The efficient removal section for iron and manganese moved down, and the required filter thickness increased significantly. Natural organic matter could promote the removal of ammonia nitrogen to some extent. Proper backwashing had no effect on the purification performance of mature filter layer.

Abstract:For the rapid granulation and enrichment of denitrifying phosphate accumulating organisms (DPAOs), taking flocculent activated sludge and granular sludge stored at low temperature as inoculated sludge and synthetic water as treatment object, four groups of SBR were operated under constant hydraulic retention time (HRT) mode and alternating long/short HRT mode with different ratios. The impact of starvation under the alternating long/short HRT mode on DPAOs enrichment and granulation was explored. Results showed that the granular sludge under alternating long/short HRT mode had higher DPAOs proportion, better nitrogen and phosphorus removal capacity, better sedimentation capacity, and dense structure. The pollutant removal capacity of simultaneous nitrification-denitrification and phosphorus removal (SNDPR) particles was the best when the ratio of alternating long/short HRT mode was 12 h/6 h. The removal rates of COD, TN, and TP reached 93%, 96%, and 98% in the long cycle, and 95%, 90%, and 93% in the short cycle, which was mainly due to the comprehensive effect of anoxic zone formed in large size particles, the secretion of EPS under starvation, and the utilization of soluble microbial products (SMP) by denitrifying bacteria. When the ratio of HRT increased to 13.5 h/4.5 h, too high a level of SMP accumulation and too short anaerobic time led the effluent COD and TP concentrations to exceed the standard; when the ratio of HRT decreased to 10.5 h/7.5 h, the proportion of DPAOs decreased by 18%, and the TN removal rate of effluent also reduced, which indicated that 12 h/6 h was a reference value for the operation of alternating long/short HRT mode.

Abstract:The effects of combined application of biochar (a new type of soil conditioner) and nitrogen fertilizers on soil nutrient conditioning were investigated. The incubation experiment based on stoichiometric method was carried out to analyze the additive effects of the combined application of corn straw biochar (SBC), chicken manure biochar (MBC), and nitrogen fertilizer (urea). Results show that biochar improved the contents of soil nutrients, but its conditioning effect was dose-dependent and heterogeneous among species. The nutrient content of the soil increased in parallel with the dosage of biochar. Treatment with SBC increased the contents of soil organic carbon (SOC) and total phosphorous (TP) by 101.754% and 34.592% respectively, while treatment with MBC increased the contents of SOC and TP by 23.684% and 84.396% respectively. SBC increased C/N (ratio of SOC to total nitrogen (TN)) and C/P (ratio of SOC to TP) by promoting SOC, while the MBC treatment decreased C/P and N/P (ratio of TN to TP) by the dose-diluting effect of phosphorus. There was not a single additive effect between the biochar and nitrogen fertilizer, and the interactive effect of nitrogen fertilizer and biochar should be fully considered in actual application.

Abstract:Due to the frequent detection of sulfonamides and quinolones in surface water, trimethoprim (TMP) and enrofloxacin (EFX) were selected as target compounds to compare the degradation efficiency and kinetics of TMP and RFX in UV, UV/peroxymonosulfate (UV/PMS), UV/persulfate (UV/PDS), and UV/hydrogen peroxide (UV/H₂O₂) under different water matrix backgrounds. The quantum yields of TMP and EFX photodegradation were calculated at different pH values. Results show that the pseudo first-order rate constant k₀ of TMP and EFX increased with the increase in pH, and the k₀ of EFX photodegradation was significantly greater than that of TMP. At pH 3.0,7.0, and 11.0, the quantum yields of TMP and EFX photodegradation (λ=254 nm) were calculated as 0.001 0,0.001 3,0.003 6, and 0.005 3,0.051 1,0.064 5, respectively. The coupling of peroxides with UV increased the degradation rate of TMP and EFX, and an obvious enhancement was observed for TMP degradation, which had a small k₀ of photodegradation. Under the background of ultrapure water, the k₀ of TMP and EFX degradation by UV/PDS was the largest at pH 3.0 and 7.0, while the k₀ of UV/PMS system was the largest at pH 11.0. In tap water, the degradation rates of TMP by UV/PMS and UV/PDS were close, which were greater than that of UV/H₂O₂ system, while for EFX degradation, the degradation efficiency of UV/PDS was the largest. In surface water, the efficiencies of TMP degradation by the three systems were close, among which UV/H₂O₂ was the best, while the degradation rate of UV/PDS for EFX was the highest.

Abstract:As critical components of urban infrastructure, water and power supply networks play important roles by supplying water and power for living and production to maintain daily operation in urban areas. In previous earthquakes, seismic damage to these facilities has severe impact on urban emergency rescue, firefighting, and health care. Therefore, it is of great significance to ensure the seismic resilience of water and power supply networks. A new methodology based on network flow theory was proposed for the seismic resilience analysis of water and power supply networks with highly functional interdependent characteristics. First, the optimal objective function of the collaborative recovery of water and power supply networks was established, and the constraint conditions of the post-earthquake functional recovery of water and power supply networks were presented according to the network flow method. On the basis of the Gurobi solver, the coupled model was solved by the mixed integer programming method. The proposed method could effectively evaluate the seismic performance of different parts of each network. Moreover, the repair tasks could be reasonably distributed according to the existing repair resources to realize the optimal recovery of the interdependent networks. Results show that due to the uncertainties of physical damage of the components of water and power supply networks, the recovery process of water and power supply networks exhibited significant discreteness, and the discreteness changed over time. On average, the recovery speed of power grids was faster than that of water supply networks.

Abstract:The properties of the soil around buried pipelines vary in longitudinal direction, which directly affects the seismic performance and reliability of the pipelines. On the basis of design response spectra, artificial ground motions with different seismic intensities were generated, and a simplified elastic foundation beam model was adopted to analyze the dynamic response of pipeline joints under the seismic wave passage effect. Considering the reduction in the tensile strength of ductile iron water pipeline joints caused by factors such as installation difference and pipeline aging, the effects of four uncertain parameters (soil weight, internal friction angle, cohesion, and yield displacement of soil spring) on the seismic response of buried pipelines were investigated, and the uncertainties of soil parameters under different seismic intensities and weak joint ratios were analyzed. Results show that compared with the calculation results of the model with parameter certainties, and the influences of the four uncertain parameters on the peak dynamic response of joints from large to small were cohesion, internal friction angle, soil weight, and soil spring yield displacement. The model containing four uncertain parameters had the greatest influence on the results, and the variation coefficient of peak joint opening was up to 9.54%. The mean values of the conditions with parameter uncertainties were consistent with the results of certainty condition, and the most unfavorable values of uncertainty conditions were 1.1-1.3 of the results of certainty condition. Besides, the reduction in the tensile strength of the local joint had a significant effect on the response of the pipeline joint. On the basis of the numerical results, the prediction equations between the weak joint ratio and the peak joint opening under different seismic intensities were proposed.

Abstract:To study the effect and mechanism of cohesive sediment gradation on cavitation and cavitation erosion in high velocity flow, we selected two cohesive sediment gradation curves and conducted research in a self-developed small looped water tunnel. Sediment-laden flows with different mass percentages of cohesive sediment smaller than a certain grain size were prepared, and the real-time pressure within cavitation and cavitation erosion zones in working section of water tunnel was measured by a dynamic pressure data acquisition system. Concrete specimens with different mix proportions were prepared. Tests of cavitation erosion on the concrete specimens under different mass percentages of cohesive sediment smaller than a certain grain size were carried out for 4 h. The mass loss of concrete specimen per hour was adopted to characterize the cavitation erosion amount . Results show that the time-averaged pressure and cavitation number at each measurement point in the cavitation erosion zone of the working section of water tunnel gradually increased with the decrease in the mass percentage of cohesive sediment smaller than a certain grain size. With the decrease in the mass percentage of cohesive sediment smaller than a certain grain size, the cavitation erosion amount of concrete specimens gradually increased. The anti-cavitation erosion capacity of concrete specimens with higher strength was significantly greater than that with lower strength at the same flow velocity. Cavitation zone was mainly located in the front of the specimen at lower velocity, while it was located in the rear at higher velocity. Under the same sediment concentration, the higher the percentage of cohesive fine grain used in the test, the greater the cavitation erosion amount was.

Abstract:High-lift siphon drainage can release a large number of bubbles. The pipe diameter d≤5 mm should be adopted to form slug flow, so as to prevent the accumulation of air in the siphon process from damaging the long-term performance of siphon drainage. Due to the small pipe diameter and gas-liquid two-phase flow, the existing siphon velocity calculation may have large errors, which affect the rationality of siphon drainage system design. In view of the problem of large error in velocity calculation of small-diameter siphon, the velocity calculation parameters were determined by analyzing the characteristics of siphon flow process. The Barr formula was introduced into the calculation of friction head loss, and full-scale physical model test was carried out. The formula of head loss coefficient suitable for the iterative calculation of siphon velocity was determined, and the calculation method of laminar flow velocity in circular pipe was proposed by using the average head loss of cross-section to reflect the influence of boundary layer. The reduction coefficient was introduced into the Barr formula to reduce the calculation error of velocity in the critical Reynolds number region. Test results of the physical model show that the modified calculation method improved the calculation accuracy of siphon velocity, which can provide reference for engineering application.

Abstract:In order to study the influence of longitudinal joints on the convergence deformation of shield tunnel lining, the ratio of the convergence deformation caused by longitudinal joint rotation to the overall convergence deformation was introduced as an index to quantify the impacts of longitudinal joints on convergence deformation. On the basis of the initial assembling angle of longitudinal joints and the geometric recurrence relationship between joints, a simple algorithm for calculating convergence deformation caused by longitudinal joints in shield tunnel lining was proposed. First, the effectiveness of the proposed simple algorithm was verified by comparing with the results of existing multi-scale hybrid analysis. Then, with the results of full-scale loading test and 3D numerical simulation, the simple algorithm was applied to analyze the changes in the influence of longitudinal joints considering factors such as persistent/staggered fabrication, joint position, lining longitudinal force, and alternating loading and unloading. Results show that for persistently fabricated lining, the convergence deformation caused by joint rotation played a dominant role in the overall deformation, while staggered fabrication significantly reduced the influence of longitudinal joint rotation on the convergence deformation. The closer the joint was located to the maximum bending moment area, the greater the influence of longitudinal joint on the convergence deformation was. The increase in the longitudinal force enhanced the integrity of the segment, so the joint rotation-induced convergence deformation decreased with increasing longitudinal force. During the unloading process after loading, the influence of the longitudinal joint increased as the elastic self-deformation of segments could be recovered but the joint rotation-induced deformation retained. The research findings can provide useful guidance on segment structure design and tunnel health status evaluation in practical engineering.

Abstract:To accurately calculate primary loads for an induced trench installation culvert, the study first described the soil arching effect of unsaturated backfills above an induced trench installation culvert by using the circular-arc trajectory of minor principal stress, so as to derive a theoretical formulation of the earth pressure coefficient at a sliding surface. Then, the frictional shear stress at a sliding surface was determined based on the strength equation of two stress state variables for unsaturated soils, and an analytical solution of vertical earth pressure at the culvert top in unsaturated soils was presented. Application steps of the proposed solution were provided along with height calculation of an equal settlement plane, and comparing validations against field measurements reported in the literature were performed. Finally, load reduction rate was defined to analyze the influences of different factors including matric suction and its distributions, suction angle, compressible material thickness, and deformation modulus of compressible materials. Results show that the obtained analytical solution of vertical earth pressure could reasonably account for the comprehensive influences of matric suction and its distributions, the soil arching effect, the performance of compressible materials, and the height of equal settlement planes. Consequently, the proposed solution could improve the structural design theory of an induced trench installation culvert. The frictional effect increased and the equal settlement plane decreased simultaneously with increasing unsaturated soil strength. Both matric suction and suction angle had dual-effects on the load reduction rate, reflected by the fact that the load reduction rate increased at the beginning and decreased afterwards, and the dual-effect was more obvious for uniform suction. With the increase in compressible material thickness, the load reduction rate increased nonlinearly and tended to be stable, whereas it decreased nonlinearly with increasing deformation modulus of compressible materials.

Abstract:In order to explore the erosion damage mechanism of polymer cement protective layer on concrete surface of water transfer project under the action of high-speed water flow, the erosion characteristics of protective layer were studied by using improved high-pressure water gun erosion test equipment. Four characteristic parameters including maximum length, maximum width, maximum depth, and volume of erosion area were extracted by 3D scanning. The erosion damage pattern, damage parameter evolution law, and damage mechanism of protective layer under different spray pressure, spray length, spray angle, and spray time were analyzed. Taking the maximum erosion depth of protective layer as the target value, a prediction model of protective layer erosion depth based on Logistic regression function was established. Results show that under the same working conditions, the four erosion damage characteristic parameters of protective layer all increased with the increase in spray pressure and erosion time. With the increase in spray length (from 0.5 cm to 6.6 cm), the erosion pattern of protective layer changed from "hourglass" to "strip". In this process, the damage effect of hydraulic fracturing on the interface between protective layer and concrete decreased. The proposed prediction model of erosion depth of protective layer achieved good accuracy, and the erosion damage degree of protective layer could be significantly reduced by increasing the spray length and spray angle, which provides a reference for the surface protection design of concrete engineering.

Abstract:To study the influences of roughness, gravel content, and normal stress on the shear mechanical properties of the interface between limestone spoil mixture and concrete, a series of interface shear tests were carried out on limestone spoil mixtures with four types of gravel content and concrete surfaces with five types of roughness under different normal stress conditions by using a new large-scale direct shear apparatus. The influences of roughness, gravel content, and normal stress on the shear strength of the interface were investigated, and the internal relationships between roughness, gravel content, normal stress, and the shear mechanical properties of the interface, as well as the mechanism of shear strength were revealed. Test results show that under the same normal stress condition, as the roughness increased, the shear strength of the interface increased and then decreased, and the rough interface significantly increased the degree of dilation of the interface, but with the increase in normal stress, the influence of roughness on the shear strength and normal deformation of the interface was weakened. Under the condition of same normal stress, with the increase in gravel content, the variation of the shear strength of the interface was closely related to the magnitude of the normal stress. Besides, the shear strength of the interface was highly consistent with the Mohr-Coulomb strength criterion, and the influence of roughness and gravel content on the apparent cohesion of the interface was more significant than that on the internal friction angle of the interface. To a great extent, rational roughness and gravel content can improve the shear strength of the interface between spoil mixture and concrete.

Abstract:There are overlying soft soil layers in most offshore sites of China, which is disadvantageous to the construction of offshore wind farms. To investigate the effect of overlying soft clay on the bearing characteristics of pile-bucket composite foundation for offshore wind turbines, we established numerical analysis models for pile-bucket composite foundation in the overlying soft clay with different thicknesses. The bearing characteristics were analyzed under unidirectional loading (V, H, M) and combined loading (H-M) by using finite element software ABAQUS. The influences of the thickness of overlying soft clay on the ultimate bearing capacity in all directions, the bearing capacity sharing ratio of different structures of pile-bucket composite foundation, and the initial stiffness k_init were studied. Results show that the ultimate bearing capacity of pile-bucket composite foundation in all directions gradually decreased with the increase in the thickness of overlying soft clay. When the thickness of overlying soft clay was 6 m (equal to the inserted depth of bucket penetration), the vertical ultimate bearing capacity of pile-bucket composite foundation was reduced by 12.86%, the horizontal ultimate bearing capacity was reduced by 46.55%, and the ultimate moment capacity was reduced by 34.86%. The initial stiffness k_init of pile-bucket composite foundation decreased with the increase in the thickness of the overlying soft clay. In summary, the effect of the overlying soft clay on the bearing characteristics of pile-bucket composite foundation should be taken into consideration in the design of foundations for offshore wind turbines.

Abstract:In the project of underground excavation beneath existing building supported by piles, there is a need to evaluate the vertical bearing capacity of the in-service piles under the condition of soil excavation. The influence of variation of soil stress and soil rebound on the bearing characteristics of soil around pile and at pile base was determined. Considering the effect of soil excavation, a hyperbolic model of load transfer along pile shaft and a bilinear model of load transfer at pile end were established. In view of the over-consolidation state of soil induced by the unloading effect of excavation, the calculation method was established to evaluate the ultimate unit skin friction of pile shaft under the condition of excavation. On the basis of the finite difference method and the load transfer method, the calculation method was proposed for predicting the vertical bearing characteristics of in-service pile under the condition of underground excavation beneath existing building. The validity of the proposed method was verified by comparing with the experimental results. Results show that the influence of soil rebound and the over-consolidation state of soil due to excavation on the pile shaft resistance and pile base resistance should be taken into account for the analysis of the pile behavior subject to underground excavation. If the calculated normalized soil rebound is relatively small (e.g.less than 1), the soil rebound can be neglected in the settlement analysis.

Abstract:The deformation characteristics of soil under lightning impulse were studied. The shock wave theory was used to describe the lightning impulse pressure, and the expression for the electromagnetic force generated by lightning in the soil was derived based on Maxwell′s equations. Using Drucker-Prager elastic-plastic criterion, the finite element model of dynamic deformation characteristics of soil under lightning impulse pressure and electromagnetic force was established. The transient computation was performed to investigate the deformation characteristics of soil during lightning strikes, and the dynamic analysis of the deformation was carried out by combining the stress distribution characteristics in the soil. With the orthogonal analysis method, the influence of soil mechanical parameters on the model results and the ranking of primary and secondary factors were studied, and the influence of critical factors and lightning current peak was analyzed. Results show that under the action of lightning impulse, the deformation of soil increased sharply at first, then slowed down gradually, and tended to be stable after partial springback. In this process, the stress distribution in the soil was similar to the stress wave propagation. The internal friction angle and elastic modulus within the soil had more significant effect on the deformation, and a smaller value could cause a significant increase in deformation. The change in internal friction angle also affected the distribution law of vertical deformation curve of surface soil. In addition, the influence of electromagnetic force on soil deformation increased significantly with the increase in the peak value of lightning current.

Abstract:There are various stress states of solid waste mass in landfills (e.g., compression, tension, loading, and unloading), which are difficult to be fully simulated by using conventional triaxial tests and direct shear tests. Triaxial tests on reconstituted municipal solid waste (MSW) specimens under nine stress paths were carried out by GDS triaxial apparatus to analyze the influence of stress path on the stress-strain behavior and yielding characteristics of MSW. A unified mathematical model was proposed to describe the stress-stain responses of MSW, and the yielding locus of MSW was obtained in p-q stress space. By comparing the stress-strain relationships of sand soil and MSW, the effects of stress path on the reinforcement of fiber materials in MSW were discussed. Results show that for compression stress path with σ₃≥0, the stress-strain curves of MSW exhibited an upward curvature without any peak or asymptotic values, and the reinforcing effect of fiber materials was the most significant. For compression stress path with σ₃<0, the deviatoric stress of MSW increased with increasing axial strain and it gradually tended to a certain value, while the fibrous reinforcement was weak. For extension stress path with Δq<0, the stress-strain relationships of MSW were almost the same as those of sand soil, and there was no fibrous reinforcing effect in MSW. In conclusion, the fibrous reinforcing effect in MSW is closely related to stress path, and the research data provides a basis for comprehensive and in-depth understanding of the mechanical properties of MSW.

Abstract:The one-dimensional consolidation process of nonlinear saturated soils affected by temperature was investigated. Based on the assumption that the change in void ratio is caused by effective stress and temperature, a one-dimensional nonlinear consolidation equation considering thermal effects was established according to the heat balance equation and the continuity equation. An analytical solution for the one-dimensional thermal consolidation problem considering soil nonlinearity under continuous drainage boundary was derived by utilizing separated variable method and Laplace transform, and the reasonableness of the present solution was assessed by comparing with two existing analytical solutions. On the basis of the present solution, the influences of the ratio of thermal diffusion coefficient to consolidation coefficient, as well as the temperature increment, interface parameter, and nonlinear parameter on the consolidation behavior of soil were analyzed in detail. Results show that the larger the temperature increment or the larger the interface parameter was, the faster the consolidation rate of soil was. The consolidation rate defined by settlement increased with the increase in nonlinear parameter, while that defined by pore pressure decreased with the increase in nonlinear parameter. When the ratio of thermal diffusion coefficient to consolidation coefficient was large, the early thermal consolidation rate was obviously faster than that without considering temperature. Therefore, it is necessary to first measure the thermal diffusion coefficient and consolidation coefficient to determine whether the thermal consolidation method is suitable for foundation treatment.