Abstract:Aeration intensity is an important parameter to control intermittent aeration DO. To clarify the effects of same total aeration intensities and different aeration intensities on the intermittent aeration SBR nitrosation process, activated sludge with good nitration abilities was inoculated in reactors at 25-28 ℃. Effect of aeration intensity under intermittent aeration on the stability of nitrosation system was studied using response surface analysis in an intermittent aeration SBR reactor. Results show that the controlled aeration intensity of 1.2 L/(h·L) could inhibit the activity of NOB, where the nitrite nitrogen accumulation rate could reach 93%, while the ammonia nitrogen removal rate was only 80%. When the aeration intensity was increased to 1.58 L/(h·L), the nitrosation performance was deteriorated with the increase of the operating cycle. When the aeration intensity was 1.93 L/(h·L), and the ammonia oxidation rate and nitrite accumulation rate were 90% and 91.6%, higher ammonia oxygen removal and nitrite accumulation were achieved. Batch experiments and response surface analysis showed that aeration intensity and aeration time had significant effects on ammonia nitrogen removal and nitrite accumulation. The shorter the aeration time was, the higher the nitrite accumulation rate would be achieved, and the higher the aeration intensity was, the higher the ammonia nitrogen removal efficiencies would be achieved. However, the activity of AOB was suppressed under low aeration intensity, and the high ammonia nitrogen removal efficiency could not be maintained by prolonging the aeration time. Under high aeration intensity, the activity of AOB could not be enhanced accordingly. The ammonia nitrogen removal rate and the nitrite accumulation rate were only affected by the aeration time. Therefore, under the same total aeration intensities, higher aeration intensity should be adopted with the combination of short aeration time to achieve high ammonia nitrogen removal and nitrite accumulation.

Abstract:The process of starting AAOB granular sludge under low temperature substrate (NH+₄-N, NO-₂-N (40±10) mg/L) was investigated. In this study, SBR reactor was used to gradually shorten the experimental cycle to start AAOB granular sludge, and the nitrogen removal rate and nitrogen load of the system were analyzed for the kinetic characteristics of anaerobic ammonium oxidation process at each stage. Meanwhile, the granular sludge morphology, average particle size, EPS content, and three-dimensional fluorescence characteristics of EPS were analyzed. Results showed that the experimental period was shortened (24 h→12 h→10 h→8 h), and the nitrogen load increased from 0.074 g/(L·d) to 0.204 g/(L·d). The Grau second-orders model better characterized the process of starting AAOB granular sludge. The matrix removal rate constant k₂ increased from 0.15 to 0.22, and the denitrification performance was gradually improved. The MLSS and MLVSS of the sludge were finally stabilized from 2 989 and 2 348 mg/L to 2 460 and 1 776 mg/L. As the reaction went on, the anaerobic ammonium oxide sludge fully utilized the matrix, and the granular sludge was gradually stabilized. The average particle size of the particles reached 410 μm. The PN content and the PN/PS value first increased and then tended to be stable, and they became larger as the particle size increased. The three-dimensional fluorescence component in the sludge EPS was analyzed by the PARAFAC method, which was composed of NADH, riboflavin, and humic acid.

Abstract:To investigate the structural characteristics of microbial community in the anaerobic digestion system of straw and sludge, the Illumina HiSeq high-throughput sequencing technology was used to study the changes and diversity of microbial community structure under high and low substrate loading conditions, and monitor its gas production. Results show that the average daily gas production was about 4.1 L under high load conditions (20 g/(L·d)) and about 2.1 L under low load conditions (12 g/(L·d)). The relative abundance of bacteria under high load substrate conditions was 91.57%, and the relative abundance of methanogenic archaea was 8.43%; the relative abundance of bacteria under low load substrate conditions was 94.35%, and the relative abundance of methanogenic archaea was 5.65%. The relative abundance of methanogenic archaea under high load substrate conditions increased about 49.2% compared with that under low load substrate conditions, indicating that there was a positive correlation between the relative abundance of archaea and gas production. The first three dominant phyla under high load conditions were Bacteroidetes with a relative abundance of 51.06%, Firmicutes with that of 11.65%, and Euryarchaeota with that of 8.25%. The first three dominant phyla under low load conditions were Bacteroidetes with a relative abundance of 50.78%, Cloacimonetes with that of 7.67%, and Synergistetes with that of 6.46%. Twelve kinds of methanogens archaea were detected under the two substrate conditions, which belong to hydrogenotrophic, methylotrophic, and aciticlasitic, indicating that the metabolic pathway of the whole straw and sludge anaerobic digestion system was rich, the growth metabolism of various microbial communities was interdependent and balanced with certain anti-shock loading, and a relatively balanced buffer system was established.

Abstract:To clarify the pyrolysis characteristics of straw waste and the correlation with biochar yield in the preparation of biochar, and meanwhile explore the optimal condition for biochar preparation from straw waste, four different types of straw waste were selected to investigate the effects of straw waste type, final pyrolysis temperature, and heating rate on the pyrolysis characteristics and biochar yield of straw waste by thermogravimetric simulation combined with the component characteristics analysis of straw waste. Results show that the maximum weight loss and maximum weight loss rate both appeared at pyrolysis stage, and the order of maximum weight loss rate was: wheat straw>corn straw>rice straw>reed straw, relating to the cellulose content of the four types of straw. Statistical analysis shows that straw waste type, final pyrolysis temperature, heating rate, and retention time all had significant effects on biochar yield of straw waste. The higher the final pyrolysis temperature was, the faster the heating rate and the longer the retention time were, and the lower the biochar yield was. The effects of final pyrolysis temperature and heating rate on the biochar yield of straw were consistent with the thermogravimetric simulation results. According to the pyrolysis characteristics and statistical analysis of biochar yield and energy consumption, the optimal condition of biochar preparation was: heating to 500 ℃ at a rate of 10 ℃/min and keeping for 30 min.

Abstract:Raw water with natural organic matters produces a variety of halogenic organic compounds after liquid chlorine or sodium hypochlorite disinfection, known as disinfection by-products (DBPs). Among them, the generation of trichloromethane (TCM) has attracted extensive attention. Factors affecting its formation including the organic content, pH, water temperature, chlorine dosage, disinfection contact time, and so on. According to survey, the scale of the water treatment plants in many cities and counties in northeast China is mainly small with a daily production capacity of less than 50 000 t/d. Moreover, due to the problems of testing capability and cost, it is impossible to detect TCM continuously in effluent water, and once the raw water quality changes, the safety of the effluent water quality will not be guaranteed. Therefore, the establishment of the prediction model between TCM and conventional parameters will help water treatment plants with no TCM detection abilities to predict the generation of TCM. In this study, taking a large water treatment plant in northeast China as an example, the contents of each parameter were detected using national standard methods. With the method of multiple linear regression analysis, the parameters which concern with the characteristics of raw water and disinfection processes, such as water temperature, pH, turbidity, potassium permanganate index, and chlorine dose, were added to the establishment of the TCM generation model. The multiple regression model provides a good prediction method for the generation of TCM in small and medium-sized water treatment plants with similar raw water characteristics and disinfection processes.

Abstract:To explore the resource utilization of waste incineration fly ash, the incineration fly ash, coal-fired fly ash, and slag powder produced by fluidized bed incinerator were selected as main raw materials, and alkali-activated bricks were prepared by using sodium hydroxide and sodium silicate as alkali activators. When the ratio of the maximum addition of incineration fly ash was 40%, the 28-day compressive strength reached 28.69 MPa, which meets the requirements of GB/T21144—2007 concrete solid bricks. In terms of environmental compatibility, the HJ/T 300 test on the 28-day alkali-activated brick produced by waste incineration fly ash shows that heavy metals were stable in the brick. Long-term pH-related leaching test reveals that the leaching amount of heavy metal Ba in the brick increased with the decrease of pH value; leaching of heavy metal Zn could be detected in the environment with pH value less than 7, and heavy metals Cd, Cr, Cu, Ni, and Pb only appeared in the environment below pH 6. Results of tank and sink diffusion dissolution test show that the alkali-activated bricks produced by incineration fly ash had an environmentally stable pH value between 11.0 and 11.5 that only heavy metals Ba and Cr appeared, and analysis shows that the leaching amount was trace.

Abstract:To efficiently remove phthalates (PAEs) from liquid, di(2-ethyl)hexyl phthalate (DEHP) was used as template molecule, di-n-octyl phthalate (DNOP) as auxiliary template molecule, silicon dioxide modified magnetic nano-ferric tetroxide (Fe₃O₄@SiO₂) as carrier, alpha-methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as crosslinking agent, and azodiisobutyronitrile (AIBN) as lead in this experiment. The bulk thermal initiation polymerization method was used to prepare double template molecularly imprinted polymers (D-MIPs) which had better adsorption performance than traditional single template molecularly imprinted polymers and could adsorb both target substances simultaneously. The specific adsorption, selectivity, and regeneration of D-MIPs were studied in detail. Results show that the introduction of the DNOP auxiliary template molecule could optimize the adsorption performance of DEHP. The unit adsorption capacity of D-MIPs for 10 DEHPs with different concentrations ranged from 0.49 mg/g to 6.16 mg/g, and the unit adsorption capacity and adsorption rate of D-MIPs were both superior to those of DEHP-MIPs. There were multi-site synergies between the two template molecules and the selected monomer, and D-MIPs could reach the optimal adsorption equilibrium state in 30 min. The adsorption capacity at the fifth time was 84.02% more than that at the first time, and it had good regeneration performance. Static adsorption process fitting indicates that the polymer system was more consistent with the single layer specific adsorption Langmuir adsorption model. The adsorption of D-MIPs and DEHP-MIPs on the target molecules was in accordance with the pseudo-second-order kinetics process. FT-IR infrared spectroscopy on the imprinted polymer characterization of the functional groups confirmed that the polymerization effect was good.

Abstract:To understand the sources and pollution characteristics of black carbon (BC) aerosols in metropolitan areas, the mass concentration and meteorological parameters of BC, PM_2.5, and other pollutants in Shanghai urban areas in 2014 were experimentally studied. Relevant parameters were obtained to evaluate BC pollution characteristics, source distribution, and effects on atmospheric extinction in Shanghai urban area. Results show that the mass concentration of BC had typical diurnal double-peak variations, and the annual average value reached (3.11±2.40) μg/m³. The mass concentration of BC also showed an obvious seasonal variation trend that the value was high in winter ((3.82±3.32) μg/m³) and low in summer ((2.56±1.37) μg/m³). In addition, it had a good correlation with PM_2.5, and the ratio of BC/PM_2.5was the highest in autumn (7.37%). The value of BC absorption coefficient was (44.8±31.8) Mm^-1, and the ratio of absorption in extinction was 14.9%. Low wind speed, low rain frequency, and low temperature conditions were not conducive to the diffusion, transmission, and settlement of BC. Besides, it was found that the transmission in the north and northwest areas of Shanghai had a great influence on the mass concentration of BC, and the pollution trajectories of different air mass types accounted for the seasonal differences of BC concentration, indicating that the pollution of BC aerosols is the result of both local emission sources and external transmission.

Abstract:To obtain the analytical solution of cylindrical cavity unloading-contraction problem considering the effect of different degrees of intermediate principal stress, quantitative prediction of contraction and plastic deformation was conducted under a certain degree of unloading during cavity excavation. Based on the unified strength theory and by introducing the unloading factor and contraction coefficient, the dimensionless similarity solution of cylindrical cavity unloading-contraction was derived. Compared with the large strain solution without considering the influence of the intermediate principal stress, the effects of the influence coefficient of intermediate principal stress on the displacement and stress distribution of the borehole, and the effects of soil stiffness, cohesion, and friction angle on unloading-contraction were given. Results show that the larger the intermediate principal stress influence parameter b was, the smaller the borehole unloading-contraction effect was, and the essence was that the increase of b reduced the initial yield unloading pressure, delayed the appearance of the peripheral peak hoop stress, and helped to reduce the borehole wall plastic zone. The influence of b on the radial displacement and hoop stress of the borehole was not negligible, while the radial stress was less affected. Soil stiffness had a great influence on the relation between cavity unloading and contraction that the greater the stiffness was, the smaller the effect of b was. Based on the dimensionless unloading contraction solution of borehole, a more reasonable quantitative prediction of the radius variation of cavity at a specified unloading degree can be performed, which can be used in the practice of tunneling excavation and support, pile bearing capacity analysis after boring unloading, and stability analysis of well drilling.

Abstract:To study the compacting effect of post-grouting in clay under unloading effect, a compaction grouting model was constructed based on the spherical cavity expansion theory and the effect of different unloading degrees through the reduction of soil elastic modulus. The ultimate grouting pressure, expansion rate of grouting, expansion rate of plastic zone, and distributions of radial and circumferential stresses and radial displacement along radial directions were calculated under different unloading degrees. Results show that the ultimate grouting pressure of compaction grouting and the increase rate of plastic zone radius with the diffusion radius of the grout decreased nonlinearly with the increase of the unloading degree. Under the same grouting pressure, when the value of unloading ratio was less than 0.8, the unloading degree had no obvious effect on the distributions of radial and circumferential stresses and radial displacement along radial directions, whereas when the value of unloading ratio was larger than 0.8, the radial and circumferential stresses and radial displacement of the soil at the same position were obviously larger than those when the unloading ratio was less than 0.8. For the same grouting volume, the radial stress at the same position, the minimum circumferential stress, and the radial distance of the steady values of circumferential and radial stresses decreased with increasing unloading degree. However, the distribution of radial displacement was not affected by the unloading degree. With the same unloading ratio, the radial stress at the same position, the minimum circumferential stress, the steady values of circumferential and radial stresses, and the radial distance of the steady values of radial displacement increased with the increase of grouting volume. The magnitude of the minimum circumferential stress was not affected by the unloading degree and grouting volume.

Abstract:There are a great number of soil-structure interaction problems during construction, and the mechanical characteristics of the interfaces may have significant effects on the forced deformation and interactions of soil-structure systems. Hence, following the slip theory of plasticity, the macro deformation of soil-structure interfaces was decomposed into a macro normal deformation and a series of orientated micro shear deformations associated with virtual micro shear structures in the shear plane. Based on the principle of virtual work, a multi-shear bounding surface model for coarse granular soil-structure interfaces was established in consideration of the states of coarse granular soil and within the framework of bounding surface elasto-plastic theory. Each micro shear response contains a stress-strain relation and a stress-dilatancy relation at a micro level. By introducing a state parameter dependent on soil density and normal stress, the model was used for characterizing the deformation and strength characteristics of soil-structure interfaces in different states. The effectiveness of the model was confirmed by simulating the available published interface tests between coarse granular soil and structure interfaces subjected to monotonic and cyclic loadings for two- and three-dimensional stress paths.

Abstract:During subway operation period, the soft soil foundation is subjected to periodic vibration and intermittent loading, and changes of mechanical properties of soft soil during intermittency will affect its stiffness degradation, which has been ignored in most related previous researches. Hence, considering different dynamic stress ratios and unit intermittent and vibration durations, triaxial tests of undrained continuous and intermittent cyclic loading were designed, where samples were consolidated by real K₀, and the long-term stiffness softening rule of undisturbed soft clay under train discontinuous load was studied. Then by comparing the test results of continuous and intermittent loading, it was found that intermittent had a weakening effect on stiffness degradation, which can reduce the residual softening index under large cycle number and shorten the cycle number during rapid softening period. Finally, based on the test results, the influence mechanism of intermittent was analyzed. It was found that soft soil was affected by the excitation during initial loading, and the dynamic adjustment of the soil structure was retained to the intermittency period, which led to continuous pore water pressure generation, stiffness degradation of soft soil, and increase of the average softening rate. After a certain number of cycles, because of the structure adjustment of the soft soil under intermittent and vibration loading in the earlier stage, the soil structure entered the steady state in advance, partial pore water pressure was dissipated, and stiffness loss was restored, which led to the decrease of softening rate in the next vibration. The restored stiffness during the intermittencies was accumulated as the vibration times increased, and the final residual softening index was significantly increased. Under the same conditions, with longer intermittent duration, the initial softening rate was greater, and the attenuation of the softening rate was more significant with the increase of the vibration times, so the weakening of the overall softening degree was more obvious, and the vibration times required to enter the softening stationary phase was fewer.

Abstract:The chemical compatibility study between salt solution and sodium bentonite plays an important role in evaluating the service performance of the antifouling barrier. Effects of different concentrations of NaCl solution and CaCl₂ solution on the permeability, swelling characteristics, and plasticity of sodium bentonite were studied by hydraulic conductivity test, free swell test, and water ratio limit test. Experimental results show that as the concentration of the cations in the solution increased, the hydraulic conductivity of the sodium bentonite increased, the swell index first increased and then decreased, and the plasticity index decreased. At the same concentration, the hydraulic conductivity of the sodium bentonite in NaCl solution was lower than that in CaCl₂ solution, and the swell index and plasticity index were both higher than those in CaCl₂ solution. Within the consolidation pressure range of 12－800 kPa, the hydraulic conductivity had a strong correlation with the swell index and plasticity index in CaCl₂ solution; in NaCl solution, when the solution concentration exceeded the critical concentration (200 mmol/L), the hydraulic conductivity also had a strong correlation with the swell index and plasticity index. Therefore, it is feasible to replace the hydraulic conductivity test with water ratio limit test and free swell test.

Abstract:In view of the nonlinear rheological characteristics of saturated clayey soil, the secondary consolidation coefficient was assumed as a hyperbolic function of the logarithm of time, and a modified secondary consolidation equation was proposed. Based on this idea, the unified hardening (UH) constitutive model was modified. To verify the effectiveness of the modified UH constitutive model, by taking a kind of reconstituted clayey soil in Henan province as an example, a series of one-dimensional rheological oedometer tests with one-way drainage were carried out. Test results illustrate that there was still some pore water pressure to be dissipated in the soil sample, when the primary consolidation determined by the Cassagrande method was completed. Then, the modified UH constitutive model was applied to simulate the measured data obtained at different loading stages, and results show that the model could fit the data well. Finally, in order to further verify the applicability of the model, some oedometer test results reported in the literature were simulated.

Abstract:The construction of pipe pile will cause the inhomogeneity of the surrounding soil. By considering the influence of the radial inhomogeneity effect and the vertically layer characteristic on the vertical vibration dynamic impedance of pipe pile, a multi-circle plane strain model based on soil viscous damping was proposed, and a simplified model for vertical vibration analysis of pipe pile in radially and vertically layered soil was established. Based on the Laplace transformation and the transitivity of impedance function, the analytical solution of the dynamic impedance of the pile head was derived. Computational results show that the vertical soft and hard interlayer had a significant effect on the amplitude of the dynamic impedance curve in a certain low frequency range, where the softer (harder) the interlayer was, the higher (lower) the amplitude of the dynamic impedance curve at the resonance frequency became. The radial inhomogeneity caused by construction disturbance had a significant influence on the complex stiffness curve of the pile head. In the analysis of vertical vibration characteristics of pipe piles, the analytical solution derived by the proposed soil-pile interaction model was more reasonable.

Abstract:To assess the possibility of promotion of fresh medium to resuspend thallus (RF) in sand reinforcement and its mechanisms, a series of solution and sand column tests were conducted to analyze the abilities of four biological solutions with different compositions in urea hydrolysis, MICP, and sand reinforcement. Results show that the ability of the original bacterial solution (US) without any treatment after the completion of culture in urea hydrolysis and MICP mainly derived from the urease in thallus, and the other part came from the free urease released by lysis of bacteria. With high concentration of bacterial solution, the resuspension of thallus by fresh medium could promote the MICP ability of thallus of the biological solution to some extent, however, the removal of supernate (SS) in preparing RF led to urease loss, which resulted in the total MICP ability of RF basically the same with that of the original bacterial solution. The sand column reinforced by original bacterial solution had more calcium carbonate precipitation and higher shear strength, and the co-existence of SS and thallus led to more effective cementation contact. Compared with RF, US has the characteristics of simple, low cost, and high activity, which can be preferred selected in the application of MICP in solving the foundation problem that requires rapid reinforcement.

Abstract:To investigate the dynamic response of granite target plate under repeated penetration, the nonlinear dynamic software AUTODYN along with the FEM-SPH coupling algorithm was used to simulate granite penetration. First, JH-2 model parameters were preliminarily determined through theoretical analysis. Then, the parameters were adjusted and optimized according to the simulation results of single penetration experiment of granite. Finally, under the projectile velocity of 220 m/s≤V_s≤420 m/s, the repeated penetration of granite was simulated and analyzed by using the optimized parameters. Results show that the JH-2 model coupled with tensile fracture softening model could make up for the deficiency of the JH-2 model in describing the dynamic response of rocks in low stress zone due to the action of main tensile stress. The failure mode of “conical crater + tunnel” formed during the initial penetration of the granite target plate provided a prerequisite for the subsequent repeated and stable penetration. With increasing impact times, the absolute penetration depth gradually increased, while the relative penetration depth decreased. The higher the impact times or impact velocity was, the more stable the penetration process of the projectile was. In addition, the concept of relative penetration coefficient and the theoretical formula of repeated penetration depth based on impact times and projectile velocity were given, both of which have certain practical values.

Abstract:To study the strength characteristics and 3D fracture evolution law of granite under unloading confining pressure, 3 different stress paths tests including conventional triaxial compression, unloading confining pressure-loading axial pressure, and graded unloading confining pressure-loading axial pressure cyclic loading and unloading were carried out on granite, and corresponding axial and radial stress-strain curves were obtained. Meanwhile, 3D reconstruction technique of CT scanning was used to obtain 3D images of the distribution of internal fracture during and after rock unloading confining pressure process. Results show that: 1) Compared with the conventional triaxial compression test, the brittle failure characteristics of specimens under unloading confining pressure were more obvious, and graded unloading confining pressure-loading axial pressure cyclic loading and unloading test could enlarge the post peak ductility of the granite, as well as reduce the axial compression of instability and the fierce of failure. 2) Both unloading confining pressure schemes reduced the bearing capacity of the granite by about 30%. 3) The macro-fracture of the granite under loading was a combination of tension and shear, and the transition between tension and shear was not obvious. The apparent fracture was the result of the outward expansion of the internal fracture. 4) The amount of cracks of the granite generated before the peak under unloading was small, while a large number of cracks were generated after the peak, and the fracture was sudden and transient. When the confining pressure was low, the macroscopic cracks were firstly generated at the edge of the sample, and when the confining pressure was high, the macroscopic cracks were firstly generated in the middle of the sample.

Abstract:Brittleness evaluation is of great significance to the study of fracturing, excavation damage, and rock burst characteristics of rocks (especially deep rocks). The rock brittleness evaluation methods at home and abroad were summarized. Based on the limitation of the existing brittleness index in quantitatively characterizing the brittleness of rock, the statistical damage constitutive model which can simulate the whole process curve of rock stress-strain was considered, and the damage evolution characteristics of rock were analyzed. A new method for evaluating the brittleness characteristics of rock based on statistical damage constitutive relation was proposed. The brittleness index B_D was established to quantitatively characterize the brittleness of rock, and the rationality of the brittleness index was verified by model theory demonstration and laboratory triaxial compression test. Results show that the brittleness index B_D could well characterize the brittleness of rock, and the rock brittleness evaluation method based on statistical damage constitutive relation had good applicability. The correctness of the brittle index B_D and its superiority compared with other methods were verified by physical experiments of marble, granite, and Tamusu clay rocks under different confining pressures. Moreover, as confining pressure increased, Tamusu clay rocks showed obvious characteristics of transition from brittle failure to plastic failure.

Abstract:The stability of a landfill is a key issue for the safety of the landfill project. Thus, centrifuge test and numerical simulation were carried out to investigate the stability of vertically extended earth dams in landfill projects. The stability of a steep extended earth dam with or without reinforced by geotextile was studied through centrifuge test, and the rationality of the design was verified. Before using the finite element (FE) method for parametric study, the FE model was validated by comparing with centrifuge test data in terms of soil displacement. Then, numerical simulations were conducted to extend the centrifuge test data during construction and operation stages. For extended earth dam reinforced by geotexile, the safety factor of the dam and the position and shape of potential slip surface were investigated under different working conditions during construction and operation stages. Effects of parameters such as permeability of fill soil, reinforced methods, shear strength of fill soil, stiffness and arrangement of reinforcement were analyzed and compared. Results show that for vertically extended earth dam projects, the stability of the steep dam reinforced by geotextile was effectively improved and not constrained by site conditions, which meets the demand of safety for design purpose.

Abstract:To understand the repair effect of trenchless centrifugal spraying method on defective pipeline and reveal the failure mechanism of the repaired interface and “pipeline-lining” system, a composite curved beam model was established. Analytical formulae of the cross section stress and the interface stress of the composite curved beam with different materials were derived by using the method of variable cross section, and the accuracy of the formulae was verified through the Three Edge Bearing Test (TEBT) of the repaired pipeline under concentrated load. The criterion for judging the coordinated deformation of the “pipe-lining” system was given—when the resistance of the interface was greater than the load, a composite structure was formed; otherwise, a unitized structure was formed. Through the analysis of the parameter study, a simplified interface shear stress formula was obtained based on the ratio β of lining thickness to host wall thickness,the ratio η of elastic modulus, and the diameter of the existing pipe D. The accuracy error between the proposed model and the mechanical model was less than 1%. Finally, the design method of lining repair for existing pipelines with different failure modes was given.

Abstract:Most of the existing evaluation methods for the groutability of sand stratum are classification evaluation methods, and the classification standards are different, which is not conducive to practical engineering application. To solve this problem, particle swarm optimization (PSO) was used to optimize the least squares support vector machine (LSSVM), and a quantitative evaluation model of sand groutability was proposed. With water/cement ratio (R_WC), relative density D_r, fine sand content θ (diameter<0.075 mm), and sand characteristic particle size D₁₀ and D₁₅ as control variables, 129 groups of groutability tests were conducted, and grout diffusion distances of each group were measured and used as quantitative evaluation indexes. The relational model between groutability factors and the control variables was obtained by PSO-LSSVM method. Furthermore, the global sensitivity of groutability factors was analyzed by FAST method. Results show that the grout diffusion distance predicted by the PSO-LSSVM model in the test set was close to the test value, the goodness of fit R² was 0.982, and the prediction model had a high prediction accuracy. The sensitivity sequence of groutability factors was: D₁₀>D₁₅>D_r>θ>R_WC, where D₁₀ and D₁₅ were significantly more sensitive than D_r, θ, and R_WC.

Abstract:To investigate the stress-strain behavior and yield characteristics of marshy and lacustrine clay under the influences of soil structure and anisotropy, the effects of soil structure and stress path on stress-strain behavior of marshy and lacustrine clay were analyzed, and the yield characteristics of marshy and lacustrine clay were systemically studied by means of stress path tests. Results show that the stress-strain behavior of marshy and lacustrine clay was significantly affected by bonding and fabric of soil. When the soil was in a stress path under positive mean effective stress increments, bonding and fabric of soil bore the mean effective stress together, which improved the compressive strength of the soil and reduced the compressive deformation. When the soil was in a stress path under negative mean effective stress increments, fabric could not bear the tensile stress and only bonding bore the tensile stress, which improved the ability of soil to bear tensile stress and produced large expansion deformation. Due to the interaction between mean effective stress and deviatoric stress under different stress paths, there was a little difference between the orientations of strain and stress paths. However, since there was a good orthogonality between plastic strain increment and yield loci, the correlation flow rule could be used for marshy and lacustrine clay. Finally, the yield loci of marshy and lacustrine clay was a rotating and distorting ellipse, which intersected to the p′ axial on the left of the origin of q-p′ plane along with the critical state line, because of the effects of K₀ consolidation and bonding during sedimentation.

Abstract:On the basis of the results obtained by relevant literature at home and abroad, the quantified expressions for clay brick, mortar, and brick masonry were established, and some existing problems were summarized. Analysis shows that at high temperature, the compressive strength of clay brick decreased linearly with the increase of temperature, and the reduction coefficient of the compressive strength of clay brick was 0.53 at 1 000 ℃. When the temperature was lower than 600 ℃, the compressive strength of clay brick after high temperature decreased linearly with increasing temperature, and the compressive strength at 600 ℃ was about 56.2% of that at room temperature. The compressive strength of cement mortar after high temperature decreased with rising temperature. With temperature between 300 and 800 ℃, the reduction coefficient of the compressive strength of cement mortar after high temperature increased with the increase of water cement ratio when it was lower than 0.45, and it decreased when the water cement ratio was over 0.45. The compressive strength of clay brick masonry decreased with increasing temperature. Finally, formulas for calculating the compressive strength of clay brick, mortar, and clay brick masonry after high temperature were established.