Abstract:Parallel tunnels are generally constructed in urban subways to facilitate the movement of traffic in modern cities. Common solutions for predicting settlement induced by the excavation of two parallel tunnels are based on the single tunnel case and the simplified superposition method is utilized to generate the deformation profile without considering the interaction between the two tunnels. In this study, transparent soil model tests were performed to visualize the surface and subsurface settlement induced by the excavation of two parallel tunnels in sandy ground. Several key factors influencing the interaction of the parallel tunnels, as well as the surface and subsurface settlement, were investigated, including the spacing between the two tunnels, the volume of ground loss and the depth at which the tunnels were buried. Then the relationship between volume of the ground loss and the settlement was established. It is hoped that this study can provide guidelines for the design and construction of urban parallel tunnels excavations.

Abstract:We explored the failure mechanism of rock under ultra-high strain rates using 3D numerical modeling of the light gas gun test. Based on numerical results, it concluded that mesoscopic hydro-compressive failure rather than mesoscopic shear or tensile failure is the main mechanism of rock failure under the condition of shock compressive loading. The shock wave, indicated by the stress signals of two stress gauges in the rock specimen, can be well reproduced by numerical simulation with the quasi-static rather than the dynamic elastic parameters. The simulation results indicate that the compressive shock wave involves a compressive failure loading process similar to that shown in the conventional uniaxial compressive failure test rather than the ultrasonic test. A mesoscopic-rate-dependent failure model was developed to take the dynamic effect into account. Our results revealed that larger rock porosity could result in an decrease in dynamic strength and dynamic effect under shock compressive loading.

Abstract:The landslide, the evolution of which usually occurs under complex geological conditions, and which brings about great damage to human life and property, is a common geological disaster. Understanding the development of landslides is important for the prevention and control of these disasters. Using field time series data on cumulative landslide displacement, a landslide displacement prediction method based on the Genetic Simulated Annealing algorithm was proposed. The Genetic Simulated Annealing algorithm optimized BP neural network was used to analyze observation point Z118 in the Baishui River landslide warning area. The cumulative displacement data of the first 3 months was applied to predict the accumulated displacement of the 4 month. The results of the BP neural network model and the Elman neural network model were compared. At the same time, the prediction results of the Genetic Simulated Annealing algorithm and the Support Vector Machine model were compared. The results showed that the landslide displacement prediction model established in this article can improve the accuracy of the prediction, and provide a reference for landslide displacement prediction in engineering construction.

Abstract:Along the Karakorum Highway (KKH), the key route for the China-Pakistan Economic Corridor, there are many rockfalls and unstable slopes, usually caused by tectonic movement and rainfall on the fractured rocks and slopes. This paper presents a numerical investigation of the rockfall and slope stability along the Karakorum Highway in Jijal-Pattan, Northern Pakistan using DIPS, GeoRock 2D and SLIDE, focusing on rockfall and slope stability along the KKH to develop countermeasures. Along the KKH, two major sections susceptible to rockfalls were selected to investigate the mechanism of rockfall and slope instability. The stereographic projection analysis following four sets of joints indicates that both sections are prone to plane failure and wedge failure. Based on the limit equilibrium theory, under static loading, the slope for Section 1 showed a stability coefficient of 0.917, representing its instability, and the slope in Section 2 has a stability coefficient of 1.131 depicting its slight stability. However, under the seismic condition, the stability coefficients of the slopes were lower than 1 for both sections, which indicates their instability. The results by GeoRock 2D reveal that in Section 1 the fallen rock mass attained the bounce height of 33 m, and in Section 2 it attained a bounce height of 29 m. The fallen rocks in Section 1 have the total kinetic energy of 1 135.099 kJ with a velocity ranging from 0.5 m/s to 44 m/s, while in Section 2 the fallen rocks have a velocity ranging from 0.5 m/s to 40.901 m/s with a damage capacity of 973.012 kJ. This study showed the rockfalls and landslides along the KKH have great damage potential.

Abstract:The cone penetration test (CPT) is widely used to determine the mechanical properties of cohesionless soils. Most of the existing correlations were established in terms of silica sands, while the data for calcareous sands are limited. In comparison to silica sands, calcareous sands have a higher peak internal friction angle and the variation of the friction angle and the dilation angle with strain in calcareous sands is also different from silica sands. In this paper, the Arbitrary Lagrangian Eulerian method and a large deformation finite element approach, was used to study cone penetration in calcareous and silica sands. Frequent mesh generations were conducted to avoid the distortion of soil elements around the cone tip. A modified Mohr-Coulomb constitutive model was introduced to describe the mobilized strength varied with the plastic shear strain in calcareous and silica sands. The elastic and plastic parameters were determined by bender element tests and drained triaxial tests. Numerical results of cone tip resistance agree reasonably well with the existing data from centrifuge tests, showing that the established numerical model has the potential to simulate the cone penetration in calcareous sands.

Abstract:For braced excavations in deep deposits of soft clays or residual soils, the ground surface settlement behind the excavation is correlated with the extent of basal heave as well as the wall deflections and is also affected by the magnitude of the groundwater drawdown behind the retaining system. Reliability analysis based on a recently developed simplified logarithm regression model for estimation of the maximum ground surface settlement is presented. The first-order reliability method implemented with a variance reduction technique while considering soil spatial variability is employed to investigate the probability that certain ground surface settlement threshold is exceeded. This paper presents the effects of spatial averaging and the influence of several key design parameters including the stiffness of the wall system, the magnitude of the threshold ground surface settlement, the coefficient of variation of the soil properties, and the magnitude of the groundwater drawdown on the ground surface settlement. It is concluded that soil spatial variability results in a higher probability of failure (i.e., a lower reliability index), without considering it would result in an unreliable design. A larger characteristic length results in a lower probability of failure and a higher reliability index. When the spatial variability of both the c_u/σ'_v and E₅₀/c_u are considered, the influence on β is more significant.

Abstract:In this study, we investigated the post-welding behaviour of S690Q high strength steel butt joints experimentally. Three S690Q high strength steel butt joints were welded with 8 mm thickness plate by shield metal arc welding with different welding heat inputs. Microstructure observation and micro-hardness test of heat-affected zone were employed to reveal the welding influence on the joints at the micro level, and tensile test of S690Q high strength steel butt joints showed the welding impact at the macro level. The microstructure test indicated that the main microstructure of the S690Q high strength steel was tempered martensite and was transformed to granular bainite in the coarse-grained heat-affected zone and to ferrite and cementite in the fine-grained heat-affected zone after welding of the joints. In the tempering zone, some of the tempered martensite decomposed to ferrite. Based on the hardness test results, it can be observed there is a soft layer in the heat-affected zone with lower hardness compared with the base material. In addition, the width of the heat-affected zone increased in the joint welded with higher heat input. The subsequent tensile test showed that the formation of a soft layer directly impairs the tensile behaviour of S690Q high strength steel butt joints, and the strength deterioration becomes more serious with the increase of the welding heat input.

Abstract:The true stress-strain relationship and ductile fracture characteristics of Chinese Q690 high strength structural steel were investigated at different low strain rates. Sheet Q690 specimens with one unnotched and two different notch geometries were used for uniaxial tensile tests, and pure shear sheet specimens were also used for shear tests. These specimens were loaded to obtain a wide range of stress states. A hybrid experiment-simulation approach was used to determine the equivalent plastic strain to fracture, the stress triaxiality and the Lode parameter. The results showed that the stress triaxiality and the Lode parameter are the key factors controlling fracture, and that the strain is more sensitive to strain rate as compared to stress. It was observed that the equivalent plastic fracture strain increases with increasing strain rate. Further studies are required to design pure shear specimens since it is difficult to realize pure shear stress state on the fracture sections in most of the pure shear tests due to the obvious deformation and stress concentration before a fracture occurs at the gauge area.

Abstract:Local buckling refers to a failure pattern of a structural steel member. It is characterized by lower ability to withstand compressive stress than the stress that the steel material is designed to withstand. This paper highlights the effects of local buckling on the structural behavior of steel columns subjected to elevated temperatures with the aim of developing a suitable design method for the local buckling of the high-strength Q690 steel column at elevated temperatures. The local buckling of high-strength Q690 steel columns is numerically investigated by FE modeling using software ABAQUS. The developed FE models are validated against the experimental results of local buckling for high-strength Q460 steel columns under axial compression previously conducted by other researchers. Subsequently, a parametric study was carried out to evaluate the influence of several parameters affecting the design of steel members to resist local buckling such as the width-to-thickness ratio, temperature, initial imperfection, residual stress and interaction between the flange and web of the H-shaped cross-section. The results showed that local buckling is significantly affected by the width-to-thickness ratio; increasing the width-to-thickness ratio led to a reduction in the ultimate bearing capacity of the specimens. It also indicated that both initial imperfections and residual stress have a significant effect on local buckling stress. Furthermore, it was observed that the overall capacity of the specimens deteriorates significantly as the temperature increases. Based on the results, a simplified design method and new width-to-thickness ratio limits were proposed for the H-shaped high-strength Q690 steel compression members. The results data were also compared with the design rules provided by GB 50017-2017, Eurocode 3, and ANSI/AISC 360-10.

Abstract:The concrete filled double steel plate composite wall (CFDSPCW) with shear stud connectors is a new type of construction component for high-rise buildings that resist lateral force. In this paper, the in-plane shear resistance of CFDSPCWs is studied with nonlinear finite element analysis using ANSYS. To this end, some assumptions were made to simplify the numerical model. Based on the experimental results and the formula of shear-slip of stud connectors in the literature, a constitutive relationship explaining the shear-slip of shear stud connectors is proposed using curve fitting. Then, the finite element model of the experimental CFDSPCW is established and validated through experimental results. Thereafter, the study presents the effects of key parameters including the space of stud connectors, the thickness of both the steel plate and concrete core, the concrete strength, and the span-depth ratio of walls on the shear resistance of CFDSPCWs. The results indicate that the thickness of both the steel plate and the concrete core, and the strength of concrete are the most critical factors affecting the shear resistance of CFDSPCWs, and the spacing of stud connectors affects the failure mode of CFDSPCWs.

Abstract:Quasi-static cyclic tests were performed on one SRC column-RC beam frame after exposure to fire and an identical frame at ambient temperature to investigate the post-fire performance of the frame.The load bearing capacity, stiffness degeneration, ductility, and energy dissipation were evaluated, and the cumulative damage and the P-Δ effect were analyzed. Test results showed that after exposure to fire the SRC column-RC beam frame had a lower bearing capacity, less stiffness, lower ductility, increased cumulative damage and a more obvious P-Δ effect compared with its unexposed counterpart. Owing to the existence of core steel in the section of the frame column, after exposure to fire, the hysteresis loops of the SRC column-RC beam frame remained plump, and the load bearing capacity remained relatively high before destruction. Moreover, after exposure to fire, the SRC column-RC beam frame exhibited good energy consumption ability. The plastic limit rotation exceeded 0.04 rad, which could well meet the requirement of China's seismic design code.

Abstract:Through an experimental investigation of the seismic performance of diagonally braced cold-formed thin-walled steel composite walls subjected to vertical loads, the mechanical properties, failure modes, and hysteresis properties of the walls were elucidated. In addition, the influence of a sheathing panel on the hysteresis performance, ductility, and energy dissipation of the composite walls was analyzed. The experimental results show that the shear bearing capacity of the single-sided oriented strand board (OSB) panel wall was increased by 38.79% compared with the non-panel wall under the same vertical load. The shear bearing capacity, ductility coefficient, μ, and energy dissipation factor, E, of the single-sided OSB panel composite wall with an axial compression ratio of 0.24 were increased by 7.5%, 4.5%, and 4.1%, respectively, compared to the wall with an axial compression ratio of 0.16; however, the yield displacement was reduced by 8.1%. The cold-formed thin-walled steel composite wall with diagonal bracing exhibited good seismic performance. After verifying the reliability of the finite element model, the influence of the axial compression ratio of the wall stud and the yield strength of the steel components on the mechanical performance of the wall was investigated through a variable parameter analysis. The results showed that with the increasing axial compression ratio, the shear bearing capacity of the wall was improved. In addition, reducing the yield strength of the steel components significantly reduced the shear capacity of the composite wall. Finally, according to the Technical Specification for Low-rise Cold-formed Thin-walled Steel Buildings (JGJ 227-2011) and AISI S400-15, the resistance partial coefficient of the wall was derived, which determines the design value for the shear bearing capacity under a horizontal earthquake.

Abstract:In various areas of civil engineering, the artificial neural network (ANN) model is used to solve complex problems. In this study, ANN models were used to predict the shear bearing capacity of RC shear walls. Based on the results of 160 experiments, a database was constructed that included the performance of RC shear walls under cyclic loading. One hundred and forty samples were chosen to train the ANN models, and 20 were used for validation. There were fourteen inputs parameters: concrete compressive strength, aspect ratio, axial compression ratio, vertical bar yield strength, horizontal bar yield strength, web vertical reinforcement ratio, web horizontal reinforcement ratio, boundary region vertical reinforcement ratio, boundary region horizontal reinforcement ratio, sectional area ratio, sectional height thickness ratio, total section area, wall height, and section shape. ANN1 and ANN2 were normalized in intervals of [0, 1] and [0.1, 0.9], respectively. The shear force of the RC shear walls was the output data for both models. The predictions by the ANN models and the code methods from GB 50011 and ACI 318 were compared. The results reveal that the developed models exhibit better prediction and generalization capacity for RC shear walls than the code methods.

Abstract:A new flexibility-based nonlinear finite element model that considers shear deformation and coupled flexural-shear effects is proposed in this article. Cyclic loading tests of T-shaped and L-shaped shear wall specimens were conducted to verify the validity of the proposed model. All specimens exhibited a flexural failure mode characterized by the crushing of the concrete and the buckling of the reinforcement at the free web boundary. Closer stirrups and longer confined boundary elements should be used in the free web end to prevent premature failure when compressed. The seismic design of the boundary element at the web-flange junction could be relaxed, as no concrete spalling was observed at the web-flange junction. The ductility decreased as the shear span ratio decreased. The specimens exhibited higher strength and stiffness but lower ductility when the flange was in tension. Numerical simulation of the cyclic loading test of the RC flanged shear wall was conducted based on the proposed model, demonstrating that the model efficiently simulates the nonlinear response of RC flanged shear walls, as proved by satisfactory agreement between the analytical results and the test results.

Abstract:More than 8 000 grottoes and cliff statues are located in Sichuan and Chongqing. Most are made from sandstone. The sandstone has deteriorated due to long-term environmental effects, posing a threat to the cultural relics. Graphene sheets are added to the traditional mortar of the sandstone cultural relics to enhance the properties, which is defined as “CH@G mortar”. The mechanical properties and volume stability of the CH@G mortar are enhanced by the graphene sheets. The highest strength is obtained by the addition of 0.07% graphene sheets, and its values (increased proportion compared with CH mortar) of compressive strength, flexural strength and tensile strength at 56 d are 4.21 MPa (7.36 %), 2.21 MPa (19.46%) and 0.47 MPa (51.61%), respectively. The FT-IR and Raman spectra results show that the graphene sheets have little influence on the composition of the products, and could accelerate the hydration in the early days, according to the XRD results. The SEM images show that graphene sheets could form a uniform and compacted microstructure.

Abstract:The failure mechanism of the ancient pagoda under compression was analyzed, based on the total and partial deformation characteristics of the pagoda model structure, and the evolution of the damage was calculated. Taking the first story of a pagoda as the prototype, three model specimens were generated by the use of old bricks at different scales: the original brick, the 1/4 and 1/8 scaled model brick. Compression tests were then carried out. The characteristics of the structural cracks developed during the loading process were observed. Numerical simulation was carried out. structural load, displacements, and strains were determined, and the stresses and failure modes of the three models were compared. The compression failure mechanisms and characteristics of the damage variation of the models were analyzed. The results indicate that the masonry failure of pagodas under compression occurs in three stages, the initial cracking along the mortar joint, the expansion and extension of the cracks, and the running through of the cracks. The cracking of the pagoda starts at the top four corners, gradually extends downwards, and finally runs through the entire structure with the increase in loading. Small sections of brick columns deformed, leading to structural failure owing to instability. In addition, horizontal deformation occurred along both the inside and the outside of the pagoda wall, and some bricks were cracked. The initial damage and stiffness of the model structure varied due to the different sizes of bricks. The cracking load and ultimate strength decreased as the unit block size decreased, while the strain followed an inverse trend.

Abstract:Nutrient removal from digested piggery wastewater (DPW) using microalgae is of increasing interest as a secondary treatment prior to discharge to avoid environmental contamination. In this study, we investigated the main mechanisms involved in ammonium removal from DPW by Oedogonium sp. using the¹⁵N mass balance approach with a focus on the relationship between algal growth and ammonium removal and the dominant ammonium removal pathway. We noted 96.2% ammonium removal and 0.04~0.15 specific growth rate of Oedogonium sp. in the diluted autoclaved DPW during the incubation period and 94.1 % ammonium removal and -0.14~0.13 specific growth rate in the diluted raw DPW. Aeration provided a significant benefit to ammonium removal via the stripping effect, which was favored by the high pH in the experimental conditions. Isotope mass balance analysis indicated that bacteria present in the initial DPW had little effect on ammonium removal in the experiment. Algal uptake and gaseous loss were the dominant pathways for NH₄—N removal from the diluted DPW using Oedogonium sp. cultures and accounted for 40.97% and 32.59% of the total ¹⁵N amount, respectively. Regression and path analyses between NH₄—N removal and its main influencing factors indicated that to improve NH₄—N removal efficiency, the levels of Oedogonium sp. and dissolved oxygen (DO) should be increased under weakly alkaline conditions.

Abstract:To investigate the influences of free ammonia on nitrogen removal, the contents of extracellular polymeric substances and the chemical composition (proteins, polysaccharides, and DNA), four laboratory-scale sequencing batch reactors fed with synthetic wastewater were operated at free ammonia concentrations of 0.5, 5, 10 and 15 mg/L (R_0.5, R₅, R₁₀ and R₁₅, respectively). Results showed that high nitrogen removal efficiencies (97.6%~99.4%) were achieved under four free ammonia concentrations. Free ammonia had a significant impact on the three kinds of extracellular polymeric substance (loosely bound extracellular polymeric substance, tightly bound extracellular polymeric substance and total extracellular polymeric substance, respectively) and their composition. Results showed that with the increased of initial free ammonia concentrations from 0.5 to 10 mg/L, the production of three kinds of extracellular polymeric substance and their components were significantly increased. Further increased of free ammonia concentrations to 15 mg/L caused a decreased trend of them. Moreover, proteins were the main component of loosely bound extracellular polymeric substance, while polysaccharides dominated in tightly bound extracellular polymeric substance and total extracellular polymeric substance under different free ammonia concentrations. It was found that the contents of three kinds of extracellular polymeric substance and their components showed a similar variation tendency to the NO_x^-—N contents during the whole cycle under four free ammonia concentrations.

Abstract:Four parallel SBRs were established to treat synthetic wastewater with preset concentrations of free ammonia (FA) (0.5, 5, 10 and 15 mg/L), including S_0.5, S₅, S₁₀ and S₁₅. The four systems removed ammonia well throughout the experiment (average value of 98.7%). The inhibition of FA by nitrite-oxidizing bacteria (NOB) combined with process control was used to achieve a nitrite pathway in S₁₀ and S₁₅. During the initiation of the nitrite pathway, the accumulation rate (NAR) increased dramatically to 90.3% on day 79 in S₁₀ and to 90.5% on day 139 in S₁₅. For S₁₀ on day 80~250 and S₁₅ on day 140~250, the average NARs were steady at approximately 98.8% and 98.2%, respectively. High-throughput sequencing of the 16S rRNA gene played an ever-increasing role in analyzing the relative abundance and structure of the nitrifying bacteria in these samples. The results showed that the changes in the abundance of AOB and NOB were consistent with our experimental results. FA affected not only the relative abundance of AOB and NOB, but also the activity of NOB. Although AOB and NOB coexisted in the four systems, AOB was still the main nitrifying bacteria. We found that a lower abundance of AOB had a higher microbial utilization capacity of ammonia substrate at 15 mgFA/L.

Abstract:Zirconium oxide-loaded granular activated carbon (Zr-GAC) was prepared for the adsorption of sulfate ions in aqueous solution. The Zr-GAC was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelecton spectroscopy (XPS), and specific surface area measurement. The results showed that the Zr-GAC had a porous surface with many aggregates, composed of zirconium oxides. XPS analysis confirmed the massive presence of zirconium and hydroxyl groups in the adsorbent surface. The specific surface area of the activated carbon decreased after modification with zirconium oxides. Batch adsorption experiments were conducted to determine the effect of pH on sulfate adsorption, and it was found that better adsorption could be achieved at pH lower than 10. Modeling analysis of the adsorption isotherms showed that the Dubinin-Radushkevich (D-R) equation had better fittings than the Langmuir model, and the maximum adsorption capacity of the Zr-GAC determined by the D-R equation was 70.14 mg/g in neutral water solution, much higher than that of raw GAC (8.9 mg/g). The D-R equation may have a problem in determining the adsorption energy for a solution adsorption, which deserves more research. Kinetic studies show that the adsorption of sulfate on the Zr-GAC is relatively fast, and it follows the pseudo second-order kinetic equation. In addition, an increase of temperature may facilitate the sulfate adsorption, to some extent. The Zr-GAC showed good potential for the adsorption of sulfate ions in aqueous solution. It exhibited approximately twice the adsorption capacity and a much wider applicable range of pH compared with the zirconium-loaded biochar adsorbent.

Abstract:With the development of the social economy, people in the non-district heating zone have growing demands to deal with the harsh winter indoor environments and yearn for a comfortable indoor environment in the winter. Relevant studies on heating demand and behavior are based on questionnaire surveys whose options are subjectively made by researchers. That would lead to biased results for occupants who can only show complaints following the researcher's thinking. Apart from that, the options that researchers designed were also not abundant enough. The social listening method is applied in this study that reviews relevant discussions on heating issues based on the community social questions and answers. The method collects 21 653 pieces of data in the form of answers and comments expressed spontaneously by different users. It also focuses on the 3.19% dissatisfaction within the indoor environment of the five categories and found that complaints during winter are much more trivial than researchers had thought before. At the same time, online users tend to describe equipment service time as actions-activated. That will provide a reference for designing questions and options to the questionnaire in related research supplementing the traditional passive questionnaire survey.

Abstract:Natural ventilation can reduce the concentration of indoor pollutants, including that of biological aerosols. It does this mainly by cross ventilation. However, in closely built-up cities, the shielding effect between buildings will significantly reduce the ventilation effect. Previous studies rarely considered the effects of a building's characteristics on other buildings. This preliminary study takes two buildings and investigates the influence of the position and size of nine different windows on their cross ventilation potential. It focuses on only one direction of incoming flow where the distance between the two buildings is two times the width of the building, first, analyzing the reliability of the computational fluid dynamics(CFD) simulation based on steady Reynolds-Averaged Navier-Stokes equations. The results reveal that the reliability of the computational fluid dynamics simulation in some cases is insufficient and that with a simulation of 20% porosity it is difficult to reproduce the wind pressure on a downstream building by computational fluid dynamics in comparison to 10% or 5% porosity. The different simulation reliability may be caused by the instability of the airflow between the buildings. However, using data from the wind tunnel, we found that the cross ventilation potential of the downstream building decreases with the increase of the window area of the upstream building, which is contrary to general beliefs.