Abstract:In this experiment, the effects of different stirring methods on the rejuvenation and operation of anaerobic ammonium oxidation sludge under normal temperature (21±1) ℃ conditions were investigated. Three groups of reactors (R1, R2, and R3) were studied, and the stirring methods were continuous stirring for R1 and intermittent stirring with different rotation speeds for R2 and R3. The denitrification performance and the performance of granular sludge during system rejuvenation and operation process were analyzed. Results show that the removal rates of ammonia nitrogen and nitrite nitrogen of R1, R2, and R3 were close to 100% in 0,2 and 2 d, respectively. The anaerobic ammonium oxidation rates of R2 and R3 were higher, which were more suitable for the growth of anammox bacteria. According to the results of cycle test, the fluidization state of the water flow formed by the intermittent stirring method was weak, so that the reactor had lower dissolved oxygen for a longer period, and it was easier to inhibit the activity of AOB, thereby increasing the activity of the anammox bacteria. The R1 system provided strong shearing force and had continuous contact with the substrate solution, resulting in more EPS. At the end of the static operation phase, the average particle size of granular sludge in R1, R2, and R3 was 3,5 and 649 μm, respectively.

Abstract:In view of the problems of high energy consumption and serious secondary pollution during traditional electric regeneration of activated carbon, cathodic electric field was adopted to activate persulfate in situ for regenerating phenol saturated activated carbon fiber (ACF), and the regeneration efficiency of ACF and degradation efficiency of pollutants in the regeneration solution were investigated. The adsorption process of ACF was fitted by Langmuir and Freundlich adsorption isotherm models. The effects of current density, persulfate concentration, and regeneration time on the electric cathode/persulfate regeneration process were investigated. Besides, the application potential and regeneration mechanism were analyzed by multiple adsorption–regeneration cycles experiments. Results show that the adsorption of phenol by ACF was more consistent with the Freundlich adsorption isotherm model, indicating heterogeneous adsorption. The regeneration efficiency of the electric cathode/persulfate regeneration process was 62.71%, and the total amount of phenol in the regeneration solution was only 3.10% of the maximum adsorption capacity of ACF. The optimal operating conditions were current density of 57.14 mA/cm², persulfate concentration of 0.1 mol/L, and regeneration time of 6 h. During the multiple regeneration of the electric cathode/persulfate process, the persulfate and the resulting sulfate radical would damage the pore structure and surface morphology of ACF to some extent. After three times of regeneration, the regeneration efficiency could still reach about 40%, which indicates that the process has strong application potential.

Abstract:Pseudomonas putida can oxidize Mn²⁺ to produce biological manganese oxide. The formation process and the adsorption oxidation activity of biogenic manganese oxide are crucial to the control of organic/heavy metal combined pollution in water. In this paper, the interaction between acetaminophen (APAP) oxidation and Fe(III) adsorption by biological manganese oxides was studied. Results show that BioMnO_x were amorphous nanoparticles. During its aging process, its structure evolved, and the surface appearance changed from flat to dense and protruding granule. The boundary of the particles became clearer. The average particle size ranged from about 49.9 nm to 70 nm. The adsorption of Fe(III) by BioMnO_x during the formation process occurred before the oxidation of APAP, and the adsorption of Fe(III) did not affect the oxidation rate of APAP. The oxidation degradation of APAP and the oxidation rate of Mn²⁺ all fitted well with the first-order kinetic equation. The oxidative activity of BioMnO_x had certain effect on the degradation of APAP. The increased concentration of Mn²⁺ reduced the degradation time of APAP. GC-MC results show that the degradation pathway of APAP was that it was firstly oxidized to acetamide and phenolic substances such as hydroquinone and p-aminophenol, then converted into simpler substances such as oxalic acid and benzoquinone, and finally mineralized.

Abstract:In order to improve the adsorption capacity of chitosan and study the adsorption of diclofenac from aqueous solution by chitosan, magnetic chitosan beads were prepared by in-situ coprecipitation method and modified by ethylenediamine. The adsorption capacity of the modified magnetic chitosan (EMMCS-G) for removal of diclofenac in water was investigated with different dosages of cross-linking agents such as glutaraldehyde, epichlorohydrin, and ethylenediamine, and results show that the optimal adsorbent was EMMCS-G when the dosages of glutaraldehyde, epichlorohydrin, and ethylenediamine were 4,2 and 6 mL, respectively. EMMCS-G was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD). Effects of time, temperature, pH, adsorbent dosage, and regeneration cycles on the adsorption of diclofenac by EMMCS-G were investigated. Results show that Fe₃O₄ particles were successfully coated by chitosan. The number of amino groups of the adsorbent increased significantly after modification, and the modified adsorbent had strong magnetic capacity and reusability. The optimum pH was 6.5. When the initial concentration of diclofenac was 50 mg/L and the dosage of the adsorbent was 100 mg, the removal rate was above 76% after 12 hours of reaction. The adsorption process accorded with the pseudo second-order kinetic model, and the adsorption data fitted well with the Freundlich model. Based on the thermodynamic analysis and pH experimental results, it demonstrates that the adsorption process was endothermic and spontaneous, which was mostly controlled by physical and chemical interactions.

Abstract:Pig manure often carries antibiotics resistance bacteria (ARB) because antibiotics are usually added in feed. Composting is an effective way to reduce the environmental risk of pig manure returning to the field, but the characteristics of ARB in pig manure composting products are still unclear. The purpose of this study was to reveal the species, number, and distribution of ARB in pig manure composting products. In this study, the number, resistance, and species of resistant bacteria contained in the composting of pig manure and pig manure with additional chlortetracycline (CTC) were investigated through measures such as plate counting, minimum inhibitory concentration (MIC) of antibiotic, and 16S rRNA sequencing. Results show that the number of culturable bacteria in composting process first increased and then decreased, and the number of culturable bacteria in compost was far less than that in fresh manure samples. Antibiotics residues such as CTC, enrofloxacin (ENR), erythromycin (ERY), and sulfamerazine (SMZ) were detected in pig manure samples. At the end of composting, ENR resistant bacteria in the compost increased slightly, while SMZ, ERY, and CTC resistant bacteria were effectively reduced. A total of 25 strains of ARB were screened out, and the detection rate for multi-ARB was 20%. Aerobic composting is effective to reduce the number and types of ARB, but there are still a small number of multi-ARB, which poses a potential threat to the environment.

Abstract:As the main component of the loss quantity of urban water supply network, the leakage quantity can be used as an important reference index for pipe network loss control. The existing calculation method of leakage is not accurate and the calculation process is complicated, whereas the blind source separation method needs less data and can achieve more accurate analysis results. However, the constrained independent component analysis (CICA) algorithm in blind source separation has the problem of misconvergence in the estimation of leakage quantity, which limits the further application of the blind source separation method. To solve this problem, an improved ICA-R algorithm was proposed to estimate the leakage of water supply network. The selection of objective function and signal processing were analyzed. An example pipe network was designed and the leakage experimental platform was built to verify the separation effect of the algorithm, and results were compared with the treatment effect of fast independent component analysis (FastICA). Pearson correlation coefficient was adopted to evaluate the effect of leakage separation, and average relative error was used to evaluate the separation accuracy of the improved ICA-R. Results show that the improved ICA-R algorithm could maintain the correlation coefficient of separation leakage at around 90% and the average relative error was within 15%, which was better than the FastICA algorithm. Instead of adding a large number of meters, the proposed method reduces the cost of calculation, and can provide reference for the calculation of leakage, so as to facilitate the water department to take targeted measures to control loss.

Abstract:The existing research on the calculating methods for WDS partitioning is mainly based on single network cases, while it lacks comparison and applicability analysis for different network cases and various requirements. This paper compares the partitioning effects of depth-first search combined with partial closeness centrality algorithm (DFS-PCC), fast iterative modularity greedy algorithm (CNM), and spectral clustering optimized by genetics algorithm (GA-SC) in five benchmark cases. The comparative analysis was achieved by developing evaluation indicators such as normalized mutual information (NMI), modularity, the balance of nodes quantity, and the number of feed lines. The influences of network intrinsic properties including topology structures of the cases, the number and types of water sources, and control elements were considered. In addition, the selection of weights and the determination of partition numbers were studied. Results show that for the cases with obvious regional water supply and high tree-like characteristics, DFS-PCC had high modularity and a large number of feed lines, while CNM had high NMI and a few feed lines. In the five cases, GA-SC had high modularity, a balanced number of nodes, and a few feed lines, indicating better applicability. By utilizing the weights of 1/q, the pipes with large flow and flow fluctuation could be effectively selected as feed lines.

Abstract:To detect the potential risks of drainage pipelines and accurately grasp the pipeline conditions, a data-driven defect diagnosis model was established by combining optimized extreme learning machine (ELM) neural network and closed circuit television (CCTV) inspection. Genetic algorithm (GA) was adopted to optimize the input weight matrix and the hidden layer offset of ELM neural network, which helps to solve the problems of unstable output and low classification accuracy of ELM neural network caused by random generation of network parameters. Taking the drainage pipeline dataset from Yangshan Free Trade Port Area in Shanghai as an example, the proposed GA-ELM model was conducted to identify and diagnose major structural defects, such as pipe rupture, disconnect, and leakage. The results of the GA-ELM model were compared with those of ELM model on the same dataset. It shows that the GA-ELM model achieved better classification performance by utilizing same neuron nodes in the hidden layer, and the optimization of parameters improved the fitting capability and generalization ability of the ELM model. Therefore, the proposed method is applicable to defect diagnosis and evaluation of urban drainage pipes and can provide a technical basis for the formulation of drainage network maintenance plan and repair plan.

Abstract:To investigate the characteristics of the flow field of high solids in solid state fermentation reactor with mechanical agitators and optimize the design parameters of mechanical agitators, computational fluid dynamics (CFD) method was used to simulate the flow field of five types of mechanical agitators, and parameters such as ratio of impeller diameter and stirring speed were analyzed quantitatively through the indexes of stirring power, mixing time, mixing energy, and the percentage of dead zone. Simulation results show that the high solids had a small range of disturbance and a large percentage of dead zone, indicating that it cannot be effectively mixed through double blade and turbine agitator. The high solids had the largest range of disturbance, the smallest percentage of dead zone, and the biggest stirring power through double helical agitator. For the impeller diameter of the double helical agitator, the dead zone decreased with the increase of the ratio of impeller diameter, and when the ratio of impeller diameter increased to 0.75, it no longer decreased, while the stirring power increased with the increase of the ratio of impeller diameter all along. With regard to the stirring speed of the double helical agitator, the stirring power increased linearly with the increase of the stirring speed, the mixing time decreased along a parabolic curve, and the mixing energy gradually increased. Considering a balance of mixing performance and mixing power, the double helical agitator with a stirring speed of 20 r/min and the ratio of impeller diameter of 0.75 was the best agitator design in this reactor.

Abstract:With the development of urbanization, the urban impervious area has increased rapidly, leading to serious rainwater problems such as the increased risk of urban flooding and runoff pollution. Meanwhile, there has also been severe impact on water safety and water environment at watershed scale. Therefore, the urban stormwater management model based on watershed management has developed rapidly in recent years. By analyzing the changes in the peak flow rate and the pollution load of the stormwater runoff before and after the development of the urban land, a management and control method for sponge city construction was put forward at basin scale, which was constrained by the peak flow rate of the flooding way and the self-purification capacity of the water environment. A multi-level stormwater control approach was put forward based on water quantity and quality control, and the stormwater management model of land sustainable development was proposed at the watershed-urban scale. Taking a development area as an example, the construction approaches of regional total runoff volume control, peak flow rate reduction, and runoff pollution control were analyzed, aiming at providing support for the overall coordination of watershed management and sponge city construction in the future.

Abstract:In order to reveal the influence of gentrification of Chinese cities on urban form and the urban form characteristics of gentrification neighbourhoods, the urban fuzzy index (I_UF) was applied to coordinate the characteristic parameters of space intensity value and space structure value of urban form based on two typical gentrification neighbourhoods in Shanghai. Results showed that the quality of urban form of most gentrification blocks were scored more poorly than conserved blocks or partly gentrified blocks, which was mainly due to high floor area ratio, closure, and space isolation. The gentrification blocks with high I_UF were mainly characterized by good accessibility and mixed-use development. The fuzzy comprehensive assessment method can objectively reflect the urban form characteristics of the research area and supply an effective approach for the quantitative analysis of urban form. The research results will provide guidance for the formulation of urban reconstruction, design, and planning schemes.

Abstract:Due to the volume compaction induced by creep effect of soft clay, the strength of soft clay increases over time, which leads to the growth of the bearing capacity of the driven pile installed in soft clay, even though the excess pore water pressure has been fully dissipated. Considering the installation of pile and the primary consolidation of the surrounding soil, the hyperbolic load transfer curves were employed in this study to model the load transfer characteristics of pile shaft and pile base, and the stress state of the soil around the pile was deduced by load transfer method. On this basis, taking advantage of an advanced elastic-viscoplastic model, the creep behavior of soil adjacent to the pile was evaluated by the quasi-overconsolidation ratio. Then, the evolution of soil strength during creep was analyzed, and a theoretical method was proposed for the long-term bearing capacity of driven pile in soft clay. The proposed theoretical method was verified by static load test. The variation of long-term bearing capacity of driven pile in soft clay with time was investigated, and the effect of soil parameters on long-term bearing capacity of driven pile was further analyzed. Results show that the long-term bearing capacity of driven pile in soft clay was primarily attributed to the increase of shear stress on lower pile shaft. The bearing capacity increased rapidly and then gradually slowed down with service time of pile. It was found that the evolution of long-term bearing capacity of driven pile was more significant in soil with higher creep index and swelling index. The theorical method presented in this study is expected to provide guidance and suggestion for determining and reusing driven piles whose superstructures have been demolished.

Abstract:To study the effect of post-grouting on the mechanical properties of the interface between soil and structure, a total of 22 groups of direct shear tests were conducted on samples with post-grouting sand-concrete interface under three grouting pressures, three grouting volumes, and four loading conditions. The influence of grouting conditions and loading conditions on the mechanical properties, shear dilation, and strength parameters of the sand-concrete interface were analyzed by using self-developed grouting equipment and grouting method. Test results show that the interface peak shear stress increased with the increase of grouting volume when the grouting pressure and normal stress remained unchanged. When the normal stress of the interface increased, the improvement effect of the grouting on the mechanical properties of the interface gradually decreased with the increase of the grouting volume. When the grouting pressure was low, the change of the interface peak shear stress was not obvious with the grouting volume and normal stress remained unchanged. When the grouting pressure reached a certain value, the increase of the interface peak shear stress was obvious. The shear strength enhancement coefficient of the interface was between 1.1 and 2.0 under different grouting and loading conditions. The shear behavior of the post-grouting sand-concrete interface was mainly improved by increasing the equivalent cohesion of the interface. The equivalent internal friction angle was approximately the same as that of the non-grouting interface. The shear contraction of the interface occurred under non-grouting conditions, and the maximum value of shear contraction increased with the increase of normal stress. Post-grouting could change the interface shear dilation mode for low normal stress. Under the same normal stress, with the increase of grouting volume and grouting pressure, the maximum value of shear dilation increased whereas the maximum value of shear contraction decreased.

Abstract:To investigate the stress-strain characteristics and hydro-mechanical coupling behaviors of unsaturated cohesive soils under static and cyclic loading, an elastoplastic two-surface model for describing the hydro-mechanical coupling behaviors of unsaturated cohesive soils under constant matric suction was established in the framework of plastic incremental flow theory. Considering the typical soil-water characteristics of unsaturated soils, based on the Barcelona basic model (BBM) and the plastic hardening rule suggested by Li and Meissner, the stress-strain characteristics and hydro-mechanical coupling behaviors of unsaturated cohesive soils under cyclic loading were described through the evolution of bounding surface and loading surface in stress space. Taking into account of the influences of initial degree of saturation, initial pore ratio, matric suction, net confining pressure, and dynamic stress amplitude, the model was verified by utilizing the previous research results of isotropic compression and static and cyclic triaxial tests. Comparisons between simulation results and experimental data show that the proposed model performed well in simulation. In addition, in order to examine the rationality of the model, several typical hydro-mechanical coupling behaviors of unsaturated soils under cyclic loading were predicted based on the test data. Results show that the proposed model could properly simulate and predict the hydro-mechanical coupling behaviors of unsaturated cohesive soils under static and cyclic loading with constant suction.

Abstract:In order to further investigate the consolidation mechanism of saturated soft clay ground with sand drains, Hansbo’s flow equation was adopted to describe the nonlinear relation between flow velocity and hydraulic gradient, and the unified hardening (UH) constitutive model considering time effect was introduced to describe the elasto-viscoplastic deformation of soil. The consolidation equation of ideal sand-drained ground was modified, the discrete scheme of implicit finite difference method was given, and the corresponding Fortran program was designed. By comparing the numerical solution with the existing analytical solution of nonlinear consolidation of sand-drained ground, the effectiveness of the proposed method was verified. Then, the influences of the parameters of UH model and Hansbo’s flow on the elasto-viscoplastic consolidation process of ground with sand drains were discussed. Numerical results show that the coupling mechanism of primary and secondary consolidation was the main reason for the increase of excess pore water pressure at the early stage of consolidation. The viscosity of soil and the non-Darcy characteristics of flow both delayed the overall dissipation of pore water pressure in the sand-drained ground at the middle-late stage of consolidation. In addition, the consolidation process was accelerated with the increase of the permeability index at the later stage of consolidation.

Abstract:To investigate the stability mechanism of vegetations on sandy slope under rainfall, a comparative experiment between “exposed slope” and “vegetated slope” was conducted by indoor rainfall model tests. Then, three kinds of selected fast-growing vegetations (Chinese holly, Bermuda-grass, and festuca arundinacea) were planted on sandy slope to further analyze vegetation slope protection. It was found that the growth curves of the vegetations were nearly S-type during plant growth, and the root depths were about 1.7-2.1 times of the vegetation heights. Under the same rainfall condition, the steady state time of vegetated slope was two times more than that of exposed slope. The global failure of exposed sandy slope had the characteristics of suddenness and linearity. Root architectures of vegetations played an important role in slope stability. The rainfall model test results show that the overall stability of the sandy slope with Bermuda-grass was the best, followed by the Chinese holly, and then the festuca arundinacea, whose root architectures were inverted triangle, uniform, and cone, respectively. Meanwhile, the growing root could bind the surrounding fine sand particles by releasing viscose materials. Consequently, the roots of vegetations were intertwined together to form a root net, and a compacted root-soil composite protective layer structure of 22 cm in thickness was formed on the slope surface. Additionally, Chinese holly with uniform root architecture could effectively prevent the occurrence of the local flow-type failure near the slope toe in the case of ponding water at the slope base, which can help to explore new bionic support technologies.

Abstract:To reveal the shear mechanical characteristics of the interface between deep alluvium frozen/thawed soil and concrete structure, a series of direct shear tests were carried out under high normal stress and thawing condition by using an improved DRS-1 high pressure direct/residual shear test system. Basic shear mechanical characteristics of the interface between frozen/thawed soil and structure were summarized. Based on the test results, empirical equations of shear stress-strain relation of interface between frozen/thawed soil and structure under different high normal stress and thawing conditions were established, considering pre-peak stress and strain softening behavior, respectively. Effects of normal stress and thawing degree on the maximum shear stress and the initial shear modulus were discussed. Results show that the pattern of shear stress-strain curves transformed gradually from strain softening to strain hardening as the process of thawing. When the shear strain was small (pre-peak), the general hyperbolic model could reasonably describe the shear stress-strain relation of the frozen/thawed soil-structure interface. Furthermore, an improved hyperbolic model in consideration of strain softening behavior was proposed to describe the whole shearing process under different high normal stress and thawing conditions.

Abstract:The frost heaving and thawing characteristics of dispersive clay in seasonal frozen soil region of China were studied by freezing-thawing test with different initial moisture contents, dry densities, and multiple freezing-thawing cycles. Results show that the freezing-thawing characteristics of dispersive clay were significantly different from those of non-dispersive clay, and the frost heaving amount of dispersive clay was much larger than that of non-dispersive clay. After several cycles of freezing-thawing, the dispersive clay exhibited loose property after frost heaving, while the non-dispersive clay showed compaction property. The initial moisture content, dry density, and freezing-thawing times had great influence on the thawing settlement coefficient and frost heave rate. The larger the initial moisture content was, the larger the frost heaving amount and the thawing settlement were. After multiple freezing-thawing cycles, the internal moisture content of the dispersive clay was re-distributed, and the lower the initial moisture content was, the higher the percentage increase of moisture content was in the corresponding part. In the case of external water replenishment, the dispersive clay with higher initial moisture content exhibited strong frost heaving after more than two times of freezing-thawing. For dispersive clay with different dry densities, the thawing settlement coefficient increased with increasing numbers of freezing-thawing cycles, and then tended to be stable. The experiment results will provide guidance for the necessary measures to reduce freezing-thawing damages of dispersive clay in the construction of highways, railways, and water conservancy projects in the northern line of “Belt and Road” in Heilongjiang and Jilin provinces.

Abstract:To obtain a seismic design method for underground structures, which has simple model with higher accuracy and can better reflect the soil-structure interaction, this paper presents a modified response displacement method. The two-parameter foundation model was adopted to simplify the soil, which is closer to the soil properties than the traditional single-parameter foundation model. Based on the force and deformation properties, the two-parameter computational model was simplified, and the modified response displacement method was obtained, which considers soil-structure interaction. Compared with the traditional model, the proposed model only modifies the foundation bed coefficient of normal spring, making it still a simple computational model. In addition, a numerical model was established to verify the correctness of the modified method and compared with the traditional response displacement method based on the results of dynamic time-history calculation. Results show that the error of the modified method could be reduced by half compared with the traditional response displacement method. Therefore, the proposed method has simple model and high computational accuracy, which can be applied in the seismic design of underground structures.

Abstract:To study the influence of axial pressure on the dynamic mechanical properties of granite under cyclic impact loading, a modified dynamic and static combined SHPB system was adopted to perform equal-amplitude cyclic impact on granite samples under five axial pressures (σ_A=0,0, 0,0 and 120 MPa). Experimental results show that under the same cyclic impact loading, the total number of cyclic impacts of the samples first increased and then decreased with the increase in axial pressure, and it reached maximum when σ_A=60 MPa. The samples under five axial pressures all exhibited typical II-type stress-strain curves. The average strain rate and peak strain of the samples under σ_A=0,0, 90 and 120 MPa increased with the increase in the impact number, while the peak stress and elastic modulus were opposite. The dynamic mechanical parameters of the samples deteriorated faster under σ_A=0 and 120 MPa. The average strain rate and peak strain of the samples under σ_A=60 MPa showed a trend of decreasing and then increasing with the increase in the impact number, while it was opposite for peak stress and elastic modulus, and the dynamic mechanical parameters deteriorated slowly. Combined with the acoustic emission energy count in static compression, it can be found that when the axial pressure exceeded the crack initiation stress, the influence of axial pressure on the rock dynamic characteristics converted from strengthening to deterioration under cyclic impact loading.

Abstract:Aiming at reducing the dynamic disasters such as rock fall and rock burst caused by deep strong disturbance, high damping rubber material with good anti-scouring and energy absorbing characteristics was applied to a new type of small strain energy absorbing bolt. To systematically evaluate the influence of geometric dimensions on the buffering and energy absorption properties of high damping rubber materials, the drop hammer impact system and SHPB device were used to carry out impact tests on high damping rubber samples and “rubber-granite” composite samples with different thickness-diameter ratios. Results of drop hammer impact system test show that under the same impact condition, the dynamic response of the material decreased with the increase of the thickness-diameter ratio and it tended to be stable when the thickness-diameter ratio was greater than 0.6. In addition, the peak value of each dynamic response of the material was less than 15% compared with the first dynamic response in six repeated impacts with the same drop distance. SHPB impact test results show that the maximum energy absorption rate was 0.336 at the thickness-diameter ratio of 0.3. Under the same pressure impact, the fractal dimension (D) of granite decreased with the increase of thickness-diameter ratio. When the thickness-diameter ratio was greater than 0.3, the D value tended to change steadily with smaller amplitude.

Abstract:The storage capacity of sludge landfills in some places in China is seriously inadequate. To restore the storage capacity and reinforce the pit body, the experiment of vacuum preloading drainage reinforcement of landfill sludge conditioned by FeCl₃ was carried out. The accumulative drainage volume and accumulative settlement of the sludge were recorded, and moisture content test, vane shear test, and mercury intrusion porosimetry were carried out after the experiment. Results show that the effect of deep dewatering of the sludge by vacuum preloading method was limited. After chemical conditioning, the dewatering performance was improved, the drainage rate and drainage volume were increased, and the average moisture content was reduced from 75.8% to 66.6%. After vacuum preloading, the distributions of moisture content and shear strength were uneven, and the closer it was to the drainage board, the greater the change was. The moisture content increased gradually along the radial and depth directions, while the shear strength gradually decreased. The pore diameter of the conditioned sludge was mainly distributed in the range of 200-100 000 nm. The proportion of small holes was the highest, followed by that of the middle holes, and the closer it was to the drainage board, the more the large holes were, the fewer the micropores were. The moisture content and volume of the sludge decreased by 9.2% and 28.8% respectively, and the strength increased by ten times, indicating that the proposed method had better treatment effect. The dewatering and volume reduction effect can be further improved by optimizing agent combination and vacuum preloading process parameters.

Abstract:To investigate the interaction between shield cutter and concrete, laboratory cutting experiments were carried out, which verified that the essence of cutting is the cyclic process of collision, extrusion, cutting, and peeling between cutter and specimen. The influence of tool rake and clearance angles, tool shape, cutting depth, and specimen strength on the normal cutting force F_n and tangential cutting force F_t of the tool was obtained through the cutting force testing system, and the fluctuation range of F_n, F_t and cutting force F_c under the influence of each factor was obtained through analysis. The research shows that the essence of cutting concrete with cutters was the repeated cycle of collision, cutting, and peeling, and the cutting force was always in a fluctuating state. The rake face played a major role in the rock breaking task, and the required F_n and F_t and their fluctuation decreased with the increase of the rake angle. The cutter with larger rake angle had more obvious pulling and shearing effects on the concrete. The mean value of F_n and F_t had a linear relationship with specimen strength and cutting depth. The larger the specimen strength and cutting depth were, the larger F_n and F_t were, and the smaller the fluctuation in its direction was. The effect of cutting depth on the fluctuation of F_c was greater than that of the specimen strength. The particle size of the debris increased with increasing cutting depth, while the debris at cutter tip was in powder form.

Abstract:Static crushing technology is a method that the mixed static crushing agent is filled in the hole of rock or concrete and the pressure generated by the static crushing agent is utilized to make the rock or concrete loose and crisp “quietly”. For the development and application of the static crushing technology, this paper introduces the main expansion performance and test methods of static crushing agent, investigates the influence of hole diameter, hole spacing, hole row spacing, hole margin, and hole depth on crushing effect, and reviews the application of static crushing technology in building demolition and concrete and rock crushing. Results show that lime-based static crushing agent composed of calcium oxide, cement, gypsum, and water reducer is the most widely used in engineering. The volume expansion of the static crushing agent mainly originates from the increase of solid volume and pore volume in the reaction process. The expansion pressure increases with the increase of calcium oxide content. Static crushing occurs preferentially at the minimum distance between the hole edge and the free surface. The crushing effect can be improved with increasing hole diameter, hole depth, static crushing agent, and expansion pressure, while too much static crushing agent makes it easier to be ejected from the hole. Within a certain range, the stress generated by the crushing agent at a point near the hole is inversely proportional to the square of the distance from the point to the hole edge, so better crushing effect can be obtained by appropriately reducing the distance of the hole.