Abstract:To investigate the failure mechanisms of the geogrid-reinforced and pile-supported foundation in which the embedded piles and floating piles exist at the same time, the centrifuge model test with the similar constant of 1∶100 was performed based on a typical project of a high speed railway located in the coastal areas of Zhejiang Province. The deformation characteristics and failure modes of such foundation on soft soil with overlying sloping base were analyzed in detail. According to the centrifuge model test, the conclusions are drawn as follows: most vertical and horizontal displacement occurred during the construction phase and the standing time, and increased continuously in operating phase. Meanwhile, the differential settlement increased gradually with the operation time. The distribution of the composite foundation settlement was asymmetric, and a settlement basin appeared after the test. Under the upper load, the settlement of the composite foundation was mainly caused by the underlayer compaction, the upward and downward pricking destruction of the pile, and tilting or transversal displacement of the pile. The horizontal displacement of the pile head increased gradually along the downward direction of the overlying sloping base, and the soil flowed around the piles in varying degrees. The pile head vertical displacement distributed unevenly and presented an asymmetric shape of "V". The embedded piles suffered bending tensile failure or bending-shear failure; piles on the overlying sloping base suffered bending-shear failure or tilting failure; and floating piles suffered tilting failure and transversal displacement failure. Test results indicate that it is unreasonable that this kind of foundation is reinforced by equilong piles, and the effective reinforcement measures for this kind of high speed railway foundations still need further research.

Abstract:Deep-water pipeline system is an important structure that transports oil and gas in offshore engineering. To ensure the fluidity of oil, pipelines are usually applied with high temperature during operation. The asymmetric expansion and shrink can make the pipeline move axially and globally toward one direction. The phenomenon is called pipeline walking, which is a severe challenge for the safety of pipeline systems. The working period of pipeline lasts for a long time, starting from heating up and ending in cooling down. Therefore, the soil resistance on pipeline in the cooling down process may be larger than that in the heating process due to soil consolidation, and the soil resistance of the overall working period is not a constant value. Through theoretical analysis, the effective axial force along the pipeline considering soil resistance increment within one loading cycle was investigated, and a walking-rate prediction method was proposed. In addition, an engineering case was analyzed based on the obtained analytical solution.

Abstract:This paper aims to solve the negative effects of the large unfrozen water content and high compression of high warm and frozen soil on the stability of roadbed. In this study, by taking the silty clay in the permafrost regions of Qinghai-Tibet Plateau as the research object, 15% ordinary Portland cement, high-performance Sulphoaluminate cement, and (ordinary Portland cement+high-performance Sulphoaluminate cement) were prepared as samples at negative temperature. The oven drying method, TDR (time domain reflectometry) technique, X-ray diffraction, scanning electron microscopy (SEM), and thawing compression test were adopted to analyze changes of the total water content, changes of unfrozen water content, and the phase composition of the soil with the addition of soil stabilizers, as well as to compare the solidification effects of different soil stabilizers. MATLAB was used to develop CURVEEXTRACT image analysis system to deal with SEM image, which was then imported to the Image-ProPlus6.0 (IPP) software to analyze the characteristics of micro pore distribution, morphology, and directivity of high warm and frozen soil before and after solidification. The relationship between macroscopical and microcosmic before and after solidification was established based on the relationship between compression property and pore orientation fractal dimension. Results show that adding soil stabilizer could reduce the total water content and increase the unfrozen water content in the soil samples. After solidification, soil particles became closer, the pore area of the soil decreased, and the pore transformed from narrow to equiaxial. There was a good linear relationship between the pore directional fractal dimension (D_f) and the coefficient of thaw compression (a_v). The better the curing effect was, the smaller the D_f was, and the smaller the corresponding a_v was.

Abstract:To describe the creep characteristics of frozen sand along the Qinghai-Tibet Railway, a creep constitutive model considering the coupling of stress and time was proposed. First, the tri-axial creep tests under different negative temperatures and dry density conditions were carried out. Then, based on the Nishihara model, considering the coupling influences of time and stress on the model elements, the coefficient of viscosity in viscoelastic part was modified under the effect of time and stress, and the viscoplastic element was improved. By introducing the damage variable, an improved Nishihara model for frozen sand was proposed. Finally, the new creep model was verified based on the test results. It was found that the creep curves predicted by this model agreed well with the corresponding experimental results from low stress to high stress, and the model could describe the unsteady, steady, and accelerating creep characteristics accurately under different temperatures and stress levels. Besides, the coefficient of viscosity and shear modulus in viscoelastic part and the coefficient of viscosity in viscous plastic part decreased with the increase of temperature and shear stress, while the damage variable increased. This study could provide a new choice for the creep prediction of frozen sand, and accumulate data for the study of creep theory.

Abstract:During the vacuum preloading of hydraulic fill ultra-soft soil, "soil pile" is often formed around drainage plate, which hinders the consolidation of the surrounding soil and even leads to the failure of the foundation treatment, but the forming mechanism of "soil pile" is still unclear. To this end, a model test was carried out to implement non-intrusive measurement of the surrounding soil deformation during vacuum preloading using the transparent soil experimental technique and the PIV (particle image velocimetry) technique. The research showed that the surrounding soil deformation of drainage plate was related to drainage rate. During the quick and steady drainage period, the surrounding soil of the drainage plate had obvious horizontal displacement, and the range of the horizontal displacement expanded gradually with the increase of the vacuuming time. During the slow drainage period, the vertical displacement was obvious in the surrounding soil of the drainage plate, and there was almost no horizontal displacement. The formations of "soil pile" and "soft zone" were mainly due to the transportation and gathering of the soil particles around the drainage plate. Compared with the deep soil layer, the shallow soil layer had finer particle size and lower self-weight, which was easier to transport under the seepage force, thus leading to the decrease of the radius of the "soil pile" along the depth, and the maximum radius of the "soil pile" could reach 11 cm. The density of the "soil pile" was higher than that of the "soft zones", and the compression of the "soil pile" was smaller under self-weight and "vacuum load", resulting in the formation of the "pile head" on the foundation surface.

Abstract:To investigate the stability and failure mechanism of soil-rock mixture (SRM) slope, three-dimensional discrete element modeling method (3-D DEM) models for meso-structure of SRM slopes were constructed based on the basic principle of geotechnical centrifugal model test and the developed 3-D DEM for irregularly shaped rock blocks and SRM. Then, particle flow code strength reduction for slope stability analysis was introduced and a novel identification method for slope failure based on the energy evolution was developed. Finally, effects of rock block proportion, rock block shape, spatial structure, and spatial configuration on the stability and failure model of SRM slope were analyzed. Results show that the safety factor is increased with increasing rock block proportion. Multiple zigzag sliding surfaces by passing the rock blocks occurred in the SRM slope model, and some big rock blocks located in the slope toe caused an obvious shift of the shear outlet. The safety factor of the SRM slope is gradually increased when the rock blocks changed from spheres and pebbles to gravels. The failure mode of dual structural slope model with a thick overburden SRM and a low gradient or single SRM slope is mainly the cambered sliding that occurred within SRM, whereas the dual structural slope model with a thin overburden SRM and flat bedrock generally have wholly sliding along the bedrock surface. With the spatial configuration of SRM slope from strip type and outlet-open type to outlet-locked type, the safety factor is gradually increased, and the outlet-locked slope have significant arch-supporting effect, which is more obvious when the rock block proportion is larger.

Abstract:To quantify the stability of slope under earthquake action, the vector sum method was optimized and its dynamic safety factor was calculated. Based on the failure mode of slope under earthquake action, which is the combination of the slope top crack and the slope foot shear crack, the safety factor formula of the vector sum method under pull-shear failure was derived, the slope safety factor and the potential sliding surface curve were obtained by self-programming, and the method was verified by a case study. For a rocky slope with weathered layer, dynamic stability analysis was carried out by using old and new vector sum methods. Results show that the potential sliding surface of the slope would move towards the interior of the slope with the duration of the earthquake. The safety factors obtained by the two methods were consistent, but the decline trend angle of the tension-shear failure mode was larger. In the tension-shear failure mode, the safety factor of the slope decreased, and the comprehensive safety factor of the slope was reduced by 3%, indicating that the original method overestimated the stability of the slope. The optimized vector sum method could reflect the stability of slope more realistically during earthquake and provide more accurate theoretical guidance for seismic design.

Abstract:To study the dynamic mechanical properties of biotite granite under cyclic impact loading, four different stress amplitudes of incident wave were selected to cyclically strike the rock samples on a modified split Hopkinson pressure bar (SHPB). The related mechanism and experimental phenomenon were analyzed. Results showed that when the stress amplitudes of incident wave were 110.57 and 90.48 MPa, the peak stresses of the rock samples decreased gradually with an increase in the number of impacts, while the maximum strain, average strain rate, and damage value all increased. When the stress amplitude of incident wave was 70.82 MPa, the peak stress of the sample first increased and then decreased as the number of impacts increased, while the opposite law occurred for the maximum strain, average strain rate, and damage value. As the stress amplitude of incident wave dropped to 50.69 MPa, the mechanical properties of the rock sample were basically unchanged, and no obvious damage was detected inside the rock sample. Besides, it was found that the static crack initiation stress determined based on the static compressive stress-strain curve could be extended to the dynamic loading state by multiplying a strength increase factor, which could well explain the phenomenon observed in the cyclic impact test.

Abstract:To explore the dynamic characteristics of granite under different impact loading conditions, single and repeated impact tests of granite samples were carried out by the split Hopkinson pressure bar respectively. The stress-strain response, strain rate curve, energy dissipation characteristics, and the failure modes of the samples were analyzed. Results show that in the single impact test, the relationship between the dynamic compressive strength and the specific energy presented a logarithmic function. The damage degree of the granite sample aggravated gradually with the increase of the specific energy. With the increase of the incident peak stress, the curve of the strain rate showed a "double-peak" form, and the second peak gradually became larger than the first peak. The rebound phenomenon of the stress-strain curve in the post-peak phase tapered off. In the repeated impact test, when the sample did not fail, the stress-strain curve generally experienced three stages, i.e., elastic loading, damage evolution, and post-peak rebound. When the sample underwent the last impact, the post-peak shape of the stress-strain curve was related to the failure degree of the sample. In addition, it was found that as the accumulative specific energy increased, the damage degree of the granite samples increased, and the curve of the strain rate gradually transited from "single-peak" to "double-peak".

Abstract:To study the effect of loading rate on the characteristic stresses of brittle rocks, uniaxial compression tests were carried out using MTS815 test machine and acoustic emission (AE) test system. The volume strain method, AE method, and bonded particle model (BPM) method based on the development of micro-cracks were adopted to determine the characteristic stresses of samples and investigate the loading rate effect of characteristic stresses for marble. Results show that values of the normalized characteristic stress determined by the three methods are relatively close, and the BPM method based on the numbers of micro-crack is a reliable and effective method. Moreover, the normalized characteristic stresses decrease as loading rates increase in the range of medium and low. Numerical simulation results show that when the loading rates increased in a wide range, the normalized crack initial stress and crack damage stress both decrease. When the loading rates are in medium and low range, the normalized characteristic stresses decrease significantly. However, it tend to be stable when the loading rates are high, especially for the normalized crack damage stress. In comparison, the loading rate effect of normalized crack damage stress is more obvious than that of the normalized crack initial stress.

Abstract:The study of seismic deformation of ground is an effective and intuitive way to analyze the influence of earthquake. The Tawarayama tunnel subjected to the 2016 Kumamoto earthquake in Kumamoto City in Japan was taken as an example to investigate the correlation between the seismic deformation of ground and the seismic damages of underground structures. Data of the ground surface above the Tawarayama tunnel before and after the earthquake were collected by the technology of airborne light detection and ranging (LiDAR), and digital elevation models were obtained from the LiDAR data. Combination and Classification Iteratively Closest Point algorithm was introduced to detect the deformation field of the ground. Based on the detected results, spatial comparison of the ground deformation with the seismic damages of Tawarayama tunnel was analyzed to find their correlation. Results show that strong ground horizontal motion can reflect the damage conditions of underground structures to some extent (such as failure of tunnel lining, pavement, or construction joints) when subject to earthquake force. Moreover, the direction of the ground horizontal deformation can provide an insight into the propagation direction of the seismic wave, such as excluding the influence of some special geological conditions (e.g., fault). The finding can also be used to verify the failure mechanism of Tawarayama tunnel by seismic wave.

Abstract:When a tunnel is near a water-rich fault fracture zone, water and mud inrush disaster easily occurs, where the determination of the minimum safe thickness of water-resistant rock mass is a key issue. Based on the silo theory and the limit equilibrium method, models of water inrush in fault fracture zone were established under the conditions that the tunnel axis is orthogonal and parallel to the tunnel face respectively. The analytic formulas of the water-resistant rock mass influenced by ground stress were obtained. Then, the criterion of water inrush in fault fracture zone was established, and the influence of the width of the fault fracture zone on the minimum safe thickness of the water-resistant rock mass was analyzed. Finally, the research result was applied to the Yonglian tunnel and the Qilianshan tunnel. Results showed that the width of the fault fracture zone had a significant influence on the determination of the minimum safe thickness of the water-resistant rock mass when the width of the fault fracture zone was less than 200 m. The minimum safe thickness of the water-resistant rock mass of Yonglian tunnel was calculated as 7.34 m. Water inrush occurred in Yonglian tunnel due to the insufficient safe thickness. The minimum safe thickness of the water-resistant rock mass value of F6 and F7 faults in Qilianshan tunnel were 10.22 and 11.59 m respectively. In the construction of Qilianshan tunnel, it is safe to pass F6 and F7 faults with 12 m water-resistant rock mass, which indicates that the theoretically calculated value is relatively close to the actual value and has certain reliability.

Abstract:To investigate the variation of steel surface with corrosion age, specimens were obtained through rapid corrosion test under neutral salt spray environment and divided into 9 groups according to corrosion age. A PS50 3D profiler was employed to acquire the geometric characteristics and roughness of the test pieces surfaces. Multifractal theory was adopted to calculate the multifractal spectrum of the corroded surfaces, and the characteristic parameters (Δα and Δf) were adopted to study the influences of corrosion age on steel surfaces. Results show that as age grew, the average Δα showed an "increasing (424.34%)—decreasing (26.5%)—increasing (29.7%)" tendency, which was consistent with a fourth power function curve, while the average Δf exhibited a significant decline (53.2%) in a quadratic curve. The increase of corrosion age could result in 1) the style changes of the pits on the surfaces from deep-narrow to wide-shallow and finally a secondary pit, 2) a variation of "significantly increasing—slowing down—stabilizing" the altitude difference of the surface, and 3) a gradually smooth transition between different altitude areas.

Abstract:Considering the difference of the maximum amplitude and phase of the shearing angle of top and bottom flanges as well as the equilibrium of the internal force of the section, the two-parameter shear lag warpage displacement function of the stress balance was proposed. On this basis, the differential equations and boundary conditions of simply supported box girder were established based on the principle of minimum potential energy. Then, the self-equilibrating stress of the simply supported box girders at nonlinear temperature was calculated and compared with the finite element results. Numerical analysis show that results of the two-parameter method were consistent with those of the finite element analysis, and the calculation accuracy of the two-parameter function satisfying the axial force self-balance of section was higher than that of the direct method. The self-equilibrating stress of the simply supported box girder in the nonlinear temperature gradient led to the shear lag effect at the end. The influence range of the temperature shear lag effect was about 1.5 times of the width of the box girder, and the stress result was greater than the stress based on the plane cross-section assumption. For the cantilever box girder with symmetry section, the calculation results of the stress in the span considering the shear lag effect were the same with the results obtained based on the plane cross-section assumption. For the cantilever flanged box girder with asymmetric section, the plane section method neglected the modification of section curvature which was caused by shear force due to nonlinear temperature, so the calculation error of the mid-span stress by plane section method was still smaller than the exact solution. While the two-parameter method modified the influence of shear force on section curvature and improved the calculation precision.

Abstract:As a new structural material, bamboo scrimber has been widely adopted in construction engineering. However, considering that bamboo scrimber is a combustible material similar to timber, it is urgent to complement and improve the fire resistance design of bamboo scrimber structures. To study the charring properties of bamboo scrimber, a total of 16 specimens in 4 groups exposed to three-and four-side fire were tested to analyze effects of section size, exposure time, and exposure surface number on charring depth and charring with furnace temperatures following the requirements of ISO 834. Results show that the charring rate decreases as the exposure time increases due to the thermal resistance of char layer. The effective section decreases and the cross-section changes to corner rounding due to the double heating process. The difference of the charring depth between the corner and non-corner areas is significant. Comparing with the charring properties of bamboo scrimber exposed to one side fire, the charring depth in multi-side fire is larger than that in one side fire. The simulation model of charring depth is further revised by considering multi-side charring factor. To simplify the fire resistance design, the notional charring rate is suggested to be 0.7 mm/min based on the corner rounding effect. Therefore, the reliable data can be used in residual cross-section simulation of bamboo scrimber structures after fire.

Abstract:To study the vertical ground motion characteristics of Wenchuan earthquake, a vertical ground motion attenuation relationship was fitted. First, the site effect and hanging/foot wall effect on the vertical ground motion were investigated, and the characteristics of vertical pseudo-spectral acceleration (a_PS, damping ratio 0.05) were analyzed. Then, a simple vertical design response spectrum was proposed. The vertical-to-horizontal ratios (V/H) relationship was obtained by using vertical and horizontal ground motion attenuation formulas, and the characteristics of V/H were analyzed at different distances in different periods. Results showed that the vertical ground motion was affected by the site conditions and the hanging/foot wall. There were many differences between the vertical and the horizontal response spectra, including the excellent period, the characteristic period, the period span of oscillation of peak response spectrum, and the attenuation rate of the falling phase. V/H had great discreteness, which showed completely different characteristics with the variation of distances in different periods, whereas the site effect and the hanging/foot wall effect on V/H were caused by the difference between those on vertical and horizontal ground motions. The V/H of acceleration response spectrum exhibited a "saddle type", while it had different characteristics at different distances that the maximum value appeared in high frequency band (t<0.1 s) for near field and in low frequency band (t>1 s) for far field. Considering the process from research to application, the investigation of vertical ground motion in China in the future, on one hand, shall continuously improve the vertical design response spectrum, and on the other hand, shall consider estimating the key value of response spectrum by using the relationship of V/H.

Abstract:In order to realize in-situ utilization of weak current generated in microbial fuel cell (MFC), an MFC-EF coupling system was constructed by utilizing the advantages of electro-Fenton (EF) technology. To further improve the performance of the coupling system, a composite cathode of iron and manganese (FeMnO_x/CF composite electrode, CF refers to carbon fiber brush) was prepared, which introduced Fenton-like catalyst manganese on the basis of Fenton catalyst iron. The electrochemical performance of the MFC-EF coupling system and its degradation effect on Rhodamine B (RhB) were investigated by being compared with CF unloaded electrode and Fe&Fe₂O₃/CF composite electrode. Results showed that FeMnO_x/CF composite electrode was successfully loaded with the binary metal oxides of Fe and Mn. The maximum output power of the coupling system was improved (5.47 W/m³), the internal resistance of the MFC was reduced (109.00 Ω), and both the removal rate (91.60%) and mineralization rate (30.84%) of RhB were increased. Besides, the FeMnO_x/CF composite electrode was free from the strict restriction of catholyte pH in conventional Fenton system, and the pH range of catholyte in MFC-EF coupling system was expanded. The study can realize the regeneration and utilization of resources in the process of pollutant removal, which is expected to provide a new idea for practical dye wastewater treatment.

Abstract:The study investigated the recovery potential of phosphorus from supernatant enriched with phosphorus by aluminum and ferric salts, as well as the effects on the performance of mainstream biological phosphorus systems. Two parallel SBR reactors were designed, which used aluminum and ferric salts as flocculants to illustrate the influence on the performances of wastewater treatment, sludge, and phosphorus recovery. Results indicated that the maximum release rates of phosphorus in anaerobic stage of the two systems could be 2.58 and 2.63 times of the influent phosphorus, and the average recovery contents of the influent phosphorus resources by aluminum and ferric salts in a cycle were 1.57 times and 2.68 times. In addition, the COD removal efficiency was not significantly affected by the stripping treatment. Due to the stripping operation, the intracellular polyphosphate particle content in PAOs decreased, the ability of phosphorus release declined, and the phosphorus removal by microorganism was inhibited. Therefore, the removal rates of phosphorus in the two systems declined after stopping sidestream stripping. Owing to the lower removal rate, the aluminum salt system could be recovered in a shorter time, while the ferric salt need a longer time. In sidestream stripping period, a little residue of Al³⁺ and Fe³⁺ promoted the increase of extracellular polymeric substances produced by microorganism. The contents of EPS in the aluminum salt system and the ferric salt system increased by 62.93% and 94.52%, respectively. In summary, though the content of phosphorus recovery in aluminum salt system was smaller than that of the ferric salt system, the restoration capability was stronger, and the effect on the ability of biological phosphorus removal in mainstream system was less, which were more beneficial for the long-term recovery of phosphorus.

Abstract:To analyze the effect of Ca²⁺ ions on the membrane fouling behavior in the mixture of SiO₂ and bovine serum albumin (BSA), atomic force microscope (AFM) technique was used to measure the interaction between foulant-membrane and foulant-foulant under different Ca²⁺ ion contents. Combined with PVDF membrane fouling and cleaning experiments, effects of Ca²⁺ ions on the membrane fouling behavior in the mixed SiO₂-BSA system were investigated. Results showed that with the increase of Ca²⁺ ion content, the membrane fouling caused by SiO₂-BSA gradually decreased, owing to that the Ca²⁺ ions changed the interaction between the foulant-membrane and the foulant-foulant. The addition of the Ca²⁺ ions could effectively trigger the hydration repulsion between PVDF membrane and BSA or SiO₂, which weakened the adsorption rate of BSA on the surface of PVDF and ultimately reduced the membrane fouling rate at the initial stage of operation. As the Ca²⁺ ion content increased, the interaction force between SiO₂-SiO₂ and SiO₂-BSA increased, resulting in the formation of large aggregates and a loose porous fouling layer on the surface of the membrane, accompanied by minor membrane fouling.

Abstract:To identify the composition and properties of extracellular polymeric substances (EPS) in aerobic granular sludge (AGS), activated sludge from aerobic tank of a wastewater treatment plant was used as seed sludge in this study. AGS-LAB and AGS-WWTP were cultured from laboratory synthetic wastewater and wastewater treatment plant influent respectively, and the EPS in the two types of AGSs was compared and analyzed. Results showed that the EPS content increased from 84.36 mg/g MLVSS of seed sludge to 122.49 mg/g MLVSS of AGS-LAB and 128.23 mg/g MLVSS of AGS-WWTP, and the protein content in TB-EPS greatly increased while the polysaccharide content slightly changed. The contents of aromatic amino acids, tyrosine/ tryptophan proteins, and aspartic acid proteins in the AGSs were remarkably higher than those in seed sludge. The hydrophilic amino acids contents in three kinds of sludge were relatively lower, while the hydrophobic amino acids presented higher contents. In addition, the total amount of the amino acids in AGSs increased by 28.31% on average. Moreover, the carrier substance hexamethyl-cyclooctasiloxane and ethylene benzene with crosslinking role only existed in the EPS of two AGSs, indicating that they played potential roles in shortening the granulation process of seed sludge and improving the structural stability of AGS.

Abstract:To investigate the pollution status and migration and transformation rules of dissolved organic nitrogen (DON) in urban wastewater treatment plants (WWTPs) of Taihu Basin, several typical WWTPs were selected. Through long-term wastewater quality monitoring of the DON pollution level and seasonal variation, DON molecular weight, hydrophobicity, and fluorescence spectrum characteristics were studied by multiple methods. Experimental results showed that 97.66%-99.22% of effluent nitrogen were dissolved nitrogen compound, and the proportion of DON to soluble total nitrogen (STN) was 21.88%-26.15%, and the average DON concentration ranged from 2.7 to 3.4 mg/L. A significant decrease of DON was observed in anaerobic tank, and the DON with molecular weight higher than 30 ku was degraded to lower than 3 ku after moving bed biofilm reactor (MBBR) process. In the study, 42% of the DON with molecular weight lower than 1 ku was measured within effluent, and 79% of the effluent DON were hydrophilic compounds. Fluorescence spectrum showed that tyrosine-like proteins and soluble microbial metabolites were the main influent DON components, and the total fluorescence response percentage (P_i,n, %) reached 76.5%. However, the removal rates of tyrosine protein and soluble microbial metabolite were 77.0% and 23.7% respectively, which further indicated that the activated sludge process was not suitable to the effective removal of low molecular weight organic nitrogen.

Abstract:Due to the randomness and complexity of the actual operating environment, the parameters of water distribution network (WDN) hydraulic model are uncertain. Based on the Monte Carlo stochastic simulation method, this paper proposes an uncertainty analysis method for WDN hydraulic model considering the correlation of parameters. Correlated parameters were regarded as random variables with specified correlation coefficients. In the Monte Carlo random sampling, independent normal random number sampling was performed, and then the independent normal random number was converted into the correlated random number by inverse-Orthogonal transformation and inverse-Nataf transformation. The correlated random number was used as the model parameter value for hydraulic calculation. The effect of the correlation and uncertainty of pipe roughness on the uncertainty of the node pressure and the pipe flow in the WDN hydraulic model was studied. Case analysis showed that the correlation of pipe roughness had a significant impact on the uncertainty analysis results. The differences of the average fluctuation values of node pressure and pipe flow were more than 70% and 60% separately in correlated and independent conditions. Therefore, the correlation between model parameters should be considered in the uncertainty analysis of WDN.

Abstract:In order to evaluate the impact of rainfall input on the simulation results of BASINs/HSPF model in Qinglong River Watershed and improve its simulation accuracy, 200 sets of rainfall simulation series were obtained using random modeling procedures such as trend component modeling, periodic component modeling, dependent random component modeling, and independent random modeling (white noise) procedures, as well as the Monte Carlo simulation method. The Nash-Sutcliffe efficiency coefficient (E_NS) was taken as the evaluation criterion of the model simulation, and the following conclusions were drawn: 1) Using trend component, periodic component, ARMA modeling, and normal random simulation to obtain rainfall stochastic simulation series is a suitable method for the quantification of randomness of rainfall input. 2) Under the condition of model parameter optimization, the variation range of E_NS value of HSPF simulation was [71.09%, 74.96%], and the fluctuation range was 3.87%, suggesting that the randomness of rainfall input had a significant impact on the HSPF simulation results. 3) When considering the annual daily rainfall extremes, the variation range of E_NS value was [75.35%, 78.81%], the fluctuation range was 3.46%, and the results were better than those of the stochastic simulation series which ignored the daily rainfall extremes. It revealed that the extremes of rainfall time series had a significant impact on HSPF simulation results. 4) With the increasing number of extremes considered in the simulated rainfall time series, the HSPF simulation results showed a downward trend, indicating that more attention should be paid to the impact of some critical extremes. 5) The uncertainty of rainfall input is a crucial source of the uncertainty of HSPF simulation results, so randomness and extremes of rainfall time series should be taken into consideration to improve the simulation effects of HSPF. This study provides reference for quantifying the impact of rainfall input on HSPF model simulation and optimizing rainfall scenarios for HSPF simulation.

Abstract:The common problem with standard particle filters is weight degradation. Resampling can solve this problem, but it causes another noted hindrance—sample impoverishment. To overcome sample impoverishment, an improved particle filter algorithm based on krill herd optimization is proposed. The algorithm combines the solving process of particle filters and guides the particles to move to the high likelihood area by the induced motion, foraging motion, and physical diffusion of krill individuals. Firstly, the state values of particles were regarded as the individual positions of the krill herd. Thus the state estimation of particles was transformed into the optimization of krill herd. Secondly, according to the characteristics of the particle filter, parameters that can be improved in the krill herd algorithm were analyzed. A new dynamic updating strategy was designed for the weights of the individual induced motion and foraging motion to ensure fast global optimization in the early stage and accurate local optimization in the later stage. At the same time, to maintain the diversity of particles, the crossover operation in the genetic algorithm was carried out on krill individuals, and a new crossover probability updating formula was designed for krill individuals. Then, the convergence of the improved algorithm was analyzed based on the standard krill herd algorithm. A single static non-growth model was selected for simulation. The simulation results show that the proposed algorithm has a higher accuracy of state estimation, smaller root mean square error, and more reasonable particle distribution compared with standard particle filters, particle swarm optimization algorithm optimized particle filters (PSO-PF), and bat algorithm optimized particle filters (BA-PF).

Abstract:Soil organic contamination is a serious environmental issue that has attracted wide attention. As a low cost and environmental friendly method, the addition of soil amendments has great prospect in soil situ remediation. However, the efficiency of soil amendments on the biodegradation of organic pollutants depends on its impact on bioavailability. Soil amendments have multiple influences on the bioavailability of organic pollutants. On the one hand, organic pollutants are immobilized by soil amendments due to adsorption effect, thus decreasing the bioavailability of the organic pollutant. On the other hand, dissolved organic matter from soil amendments can facilitate the desorption of the organic pollutants and increase the bioavailability. Moreover, microbial activity can be enhanced by soil amendments, which is also beneficial for organic pollutants biodegradation. This paper investigates the impact of three common soil amendments (i.e., biochar, compost, and surfactants) on the bioavailability of organic pollutants from the perspectives of adsorption and desorption, mass transfer between organic pollutants and microorganism, as well as microbial abundance and activity. Results of this study will provide reference for finding soil amendments with high efficiency.