Abstract:Fiber content is an important parameter affecting reinforced soil. In existing research, the range of fiber content values is generally small, and the physical and mechanical properties of reinforced soil with higher fiber content are not well understood. In order to study the impact of higher fiber content on rice straw fiber-reinforced soil, this study sets up 10 fiber mass fractions and uses direct shear tests for research, exploring the effect of fiber content on the strength characteristics of reinforced soil. Additionally, scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) tests are used to analyze the microstructure features of fiber-reinforced soil. The results show that adding fibers can effectively improve the shear strength of the soil. The reinforcement mechanism of fiber-reinforced soil is related to fiber content. A small fiber content has little effect on the porosity of the soil, and the reinforced soil is based on the soil skeleton. When the fiber content is high, the porosity increases significantly, and the main structure of the reinforced soil would be composed of both the soil skeleton and the fiber skeleton.

Abstract:In order to solve the issue of high energy consumption and significant potential loss at the soil-electrode interface during electroosmotic consolidation, this study investigates the impact of electrode reactions on interface resistance from an electrochemical perspective. By using a self-designed one-dimensional electro-osmotic consolidation device, indoor experiments were conducted to explore the trend of the clay-electrode interface resistance under different electrode materials and different power supply modes. The trend of interfacial resistance of four different electrode materials, electric geosynthetics (EKG), iron, aluminum and copper, under continuous power supply was investigated through laboratory electroosmotic tests. Further, the electrochemical mechanism of action of two optimized power supply modes, intermittent current and polarity reversal, were investigated. Results show that electrode reactions alter the interface electrochemical properties, affecting interface resistance and thus the electroosmotic drainage rate. The rapid growth of the interfacial resistance is one of the reasons for the high energy consumption of electro-osmosis The anode interface resistance is significantly affected by electrode reactions, with a smaller anode interface resistance observed in the EKG electrode under long-term electrification, while the metal electrode exhibits a larger anode interface resistance due to the combined effects of concentration polarization and surface membrane resistance. Using an optimized power supply strategy could help alleviate interface polarization and inhibit interface resistance growth.

Abstract:Bottom-bearing steel pipe concrete inclined support technique is a promising method for foundation pit excavation. While its effectiveness is evident in various engineering cases, its underlying mechanism requires further investigation. This study establishes a numerical model using finite element simulation, validated against monitoring data from specific projects. It explores the deformation of the inclined support during excavation, revealing insights into its performance under different soil conditions and tilt angles. Findings indicate significant control over soil and support deformation, especially in soft soil areas. Increasing the tilt angle enhances lateral force resistance but raises project costs. Thus, selecting the appropriate angle is crucial based on specific project needs and soil conditions.

Abstract:Water injection and underwater excavation is a new method of foundation excavation. It is used to solve the problem that traditional methods of off-pit precipitation and in-pit drainage cannot be implemented when there is a stable connection between groundwater in the foundation pit and river water. The design calculation method of deep foundation pit injection and underwater excavation is proposed. Combined with the deep foundation pit project of steel sheet pile cofferdam, a water injection and underwater excavation scheme was developed, and a corresponding numerical model was established to study the force and deformation pattern of the support structure corresponding to the deep foundation pit firstly precipitated to form dryland working conditions for excavation, then injected water for underwater excavation, and then precipitated after underwater pouring of sealing concrete. The water injection height has also been optimized. The conclusions are as follows: First precipitation to form dryland when the maximum depth of precipitation depends on the stability of the soil at the bottom of the pit against flowing sand and pipe surges. When the excavation depth increases from 2 m to 7 m, horizontal displacement of support structure increased by 53.6%, the maximum value of plastic uplift at the bottom of the pit gradually increases to 59.0 mm. When re-injecting water for underwater excavation, increasing the height of water injection can effectively reduce the uplift deformation of the soil at the bottom of the pit and the horizontal displacement of the support pile, the critical height of water injection is 9 m. When the water injection height exceeds the critical value, the effect of inhibiting the deformation of pit bottom and support piles would be weakened. The thickness of the sealing concrete depends on its floating stability and strength. The embedded depth of steel sheet piles depends on the overall stability of the support structure under the precipitation conditions after the concrete is placed underwater.

Abstract:Due to the long-term action of natural forces, the cultural heritages of grotto temples and rock carving are extremely vulnerable to tectonic stress, crack expansion, rainwater erosion, etc., resulting in serious rock mass instability. Taking the Cliff Statues of Shizhuan Mountain in Dazu Rock Carvings as an example, through field surveys and laboratory tests, the engineering geological conditions of the carving area and the macro mechanical properties of regional rock are obtained, and the stability of the dangerous rock mass under the two main failure modes of dumping and sliding are respectively evaluated by combining qualitative and quantitative methods, and reinforcement schemes are formulated. The calculation results show that the stability safety factors of dangerous rock masses of dumping and sliding are 1.39 and 1.20 respectively under the influence of seismic factors. Considering the particularity of preservation status of cultural relics and the tourist visit services in the grotto area, a comprehensive treatment of "bolt reinforcement + stone masonry + crack grouting + old treatment" is adopted. By monitoring the displacement and stress, the deformation of dangerous rock masses of dumping and sliding are controlled within the range of 3 mm and 6 mm after reinforcement, which verifies the effectiveness of the reinforcement scheme and minimizes the major danger of Shizhuan Mountain cliff statues in time to ensure the safety of tourists and cultural relics.

Abstract:The embankment fills are typically of an unsaturated state. Rainfall infiltration results in deformations of unsaturated fills due to wetting, leading to deformations of embankment slope. Geosynthetics have high tensile strength, which can effectively reduce the deformations of embankment and improve the stability. A constitutive model that considers the hydro-mechanical coupled behavior of unsaturated soils was introduced and implemented in the finite difference program FLAC. Triaxial testing data involving loading and wetting paths were used to validate the constitutive model implemented in FLAC. Using the validated constitutive model to simulate the embankment fill, the deformation behavior of unsaturated reinforced embankments subjected to rainfall infiltration was investigated. The influence of geosynthetic reinforcement on the wetting-induced deformations of embankments was investigated. The results show that the reinforcements have negligible impact in the unreinforced zone. However, the reinforcements could effectively reduce the volumetric strains and shear strains of the soil elements in the reinforced zone. The reinforcements have a negligible effect on surface settlement in the unreinforced zone near the centerline of embankment but are effective in reducing surface settlement at the shoulder and lateral displacements of embankment slope under rainfall. The longer reinforcements are more efficient in reducing surface settlements of embankment and lateral displacements of slope and could also increase the distance between the slope surface and the potential failure surface.

Abstract:The prestressed RC-UHPC composite box girder with high tensile strength and corrosion-resistant ultra-high performance concrete (UHPC) as the web and bottom plate and reinforced concrete (RC) as the top plate was proposed, and a specimen was fabricated. The flexural test was carried out to analyse the crack development pattern and damage mode of the specimen; the finite element software was used to simulate the test, and the calculation accuracy was verified by comparing the finite element calculation results with the testing data, on the basis of which 19 finite element analysis models were established to analyse the influence of various parameters on the cracking moment; relevant codes and existing literature were used to investigate the cracking moment of the prestressed RC-UHPC composite box girder. The results show that: the first crack appeared when the specimen was loaded to about 33.3% of ultimate load; the cracking moment was influenced by the prestressing bar tension factor, the prestressing bar reinforcement ratio and the tensile strength of UHPC; the cracking moment calculation method based on the conversion section and the crack width calculation formulas in DBJ 43/T 325—2017 were used to calculate the cracking moment and crack width of the prestressed RC-UHPC composite box girder, respectively, and the calculated values agreed well with the testing and FE results.

Abstract:In order to study the plate width-thickness ratio limits of steel palte based on section classification for Steel-Concrete Composite Beam with U-section (SCBU), monotonic static loading tests were conducted on five TSCU specimens. The damage modes, load-displacement curves and plastic deformation capacities of SCBU with different combinations of height-thickness ratios of outer steel-encased web in compression area and width-thickness ratios of compressed flange were analyzed. The testing results show that the width-thickness ratio of the steel plate has a direct influence on the buckling deformation and plastic deformation capacity of the SCBU. All the specimens suffered local buckling before reaching the peak bearing capacity, the failure mode was bending plastic damage. Meanwhile, the finite element analysis results show that the nonlinear behavior between the steel plate web and compressed flange interacts with each other, the buckling moment of the plate advances with the increase of width-thickness ratio of the adjacent plate, and the degree of plastic development of the SCBU decreases with the increase of width-thickness ratio of steel plate. Based on the results of the test and finite element parametric analysis, the recommended limit value of width-thickness ratio for class Ⅱ section (Class 2) steel palte of SCBU is proposed, and the proposed limit is compared and analyzed with the code limit, and the results show that this limit value is more consistent with the real force performance of the SCBU and could give fuller play to its structural advantages to a certain extent.

Abstract:Weathering steel is suitable for bridge construction in harsh environmental areas such as high-altitude cold areas, but the current corrosion resistance mechanism of weathering steel in high-altitude cold areas is unclear. To reveal it, typical bridge weathering steel and ordinary steel were used as research objects. In-situ corrosion tests of bridge steel were carried out in typical high-altitude cold areas to explore the feasibility of applying weathering steel in high-altitude cold areas. Firstly, 20 in-situ corrosion specimens were designed according to the specifications, and in-situ corrosion tests with corrosion cycles of 2, 4, 10, 18 and 24 months were carried out; combined with corrosion weight loss data, rust layer macromorphology and micromorphology, the distribution of elements along the rust layer, the corrosion resistance mechanism of weathering steel in high-altitude cold areas was analyzed. The research results show that the corrosion loss of the two specimens in Kangding atmospheric environment is basically the same before the corrosion cycle is 10 months; when the corrosion cycle is 24 months, the corrosion loss of weathering steel is about 10% lower than that of ordinary carbon steel; the goethite formed in the rust products of weathering steel hinders the accumulation of oxygen, moisture, etc. in the rust layer, further preventing its corrosion; during the corrosion process, Cr is enriched in the inner rust layer of weathering steel, causing the inner rust layer to become denser in subsequent corrosion, further enhancing the corrosion resistance.

Abstract:The combined effects of repeated load and corrosion could cause fatigue damage of prestressed concrete (PC) beams, which would reduce their service life. The fatigue crack growth size of strand and cumulative residual strain of concrete were taken as damage parameters in the present study, a quantitative method of uncoordinated deformation in bond-slip zone considering the residual strain of strands and steel bars and a fatigue life prediction method of corroded PC beams were proposed. The methods comprehensively consider the influence of fatigue crack growth of steel strand, interface corrosion fatigue bond degradation and fatigue damage of concrete. Then the rationality of the fatigue life prediction method was verified by experimental data, and the interfacial fatigue bond-slip of corroded PC beams under different prestresses, corrosion degrees and stress levels were discussed. Results show that the proposed methods can effectively predict the interface slip and the fatigue life of corroded PC beams. The prestress is an important parameter that affects the fatigue bond-slip of corroded PC beams. With the increase of corrosion loss and stress level, the specimen is prone to occur the fatigue bond-slip, and the increase of prestress force can effectively reduce the interfacial fatigue bond-slip. At the high stress levels, the more serious strain incompatibility would lead to more residual slip, the slip curve and its slope would rise and steepen as the stress level increases.

Abstract:Two joint models with a scale of 1∶3 were fabricated and fatigue tests were carried out to investigate the fatigue performance of steel truss web-concrete composite external joints and verify the reliability of the new structure applied to high-speed railway bridges. The fatigue damage mode, load-displacement relationship, and load-strain curve of the composite external joints were investigated, the fatigue force characteristics of the external joints under different stress amplitudes were examined and the experimental results showed that the fatigue life of the composite external joint exceeds 2.51 million loading cycles under the design stress amplitude, the joint is not damaged, the stiffness is not reduced, and the fatigue resistance performance meets the requirements. Under the action of 1.4 times design stress amplitude, the measured fatigue life of the external joint is 1.4 million times. The fatigue damage mode of the external joint is the cracking of the exposed gusset plate on the tensile side, and the critical detail of composite external joint is the welding detail which connecting the exposed gusset plate and the stiffening plate. The fatigue crack causes the stress redistribution in the gusset plate, the strain in the gusset plate above and below the crack is reduced by 81% at most, and the strain in the gusset plate near the crack is increased by 33% at most. According to the S-N curve obtained by the one-point method, the fatigue life of the composite external joint corresponding to the design stress amplitude of 53.2 MPa is 4.36 million times, which is 2.18 times of the design value.

Abstract:In order to promote the application of bolt fasteners with diameters of up to 10 mm in steel-wood composite structures, the effects of the number of transverse rows of bolts, bolt diameters and longitudinal spacing of bolts on the bending performance of steel-wood composite beams were investigated. By designing a composite beam with a I-steel beam at the lower part and wooden board at the upper part, the upper and lower parts connected by bolts. A three-point bending load test was carried out on 8 test beams, to observe the failure mode, mid-span deflection variation, mid-span section strain and slip effect at the steel-wood intersection at the end of the beam respectively, to investigate the effect of different bolt parameters on the flexural mechanical properties of the steel-wood composite beam. The test results showed that the main damage mode of the steel-wood combination beam is the mid-span deflection up to 1/27 of the calculated span, resulting in deformation damage; Composite beams had high flexural capacity and ductility coefficient. The maximum relative slip at the steel-wood interface of each specimen was 2-6 mm; Among the parameters of bolt arrangement, the longitudinal spacing of bolts had greater influence on the strain difference at the steel-wood interface in the span of the composite beam, while the bolt diameter had less influence. The concept of bolt area ratio of steel-wood composite beam was proposed, i.e. the ratio of total bolt area to compressive area of wood board. With the increase of the bolt area ratio, the flexural load capacity of the specimen increases significantly and the maximum slip at the intersection decreases gradually, although the displacement ductility coefficient decreases. The range of bolt could be quickly calculated by optimum the reasonable range of bolt area ratio, which provides design reference for practical application of such steel-wood composite beam.

Abstract:Floating shelf is a typical structural form of column base in traditional timber construction, and the timber column is prone to swinging under horizontal load. The rocking behaviour of timber columns shows that the floating column base joints have semi-rigid characteristics, which plays an important role in resisting the lateral load and maintaining the overall stability of timber structures. In this paper, a modelling method of rocking wood column base joints is proposed. A row of axial springs is arranged at the column base to simulate the stress state of the contact interface between the column base and the foundation stone. The corresponding numerical model is established based on the OpenSees platform. The validity of themodelling method is verified by comparing with the refined finite element model and the experimental data in a large number of related literatures. At the same time, some factors affecting themodelling method are analyzed, including the contact stiffness, distribution mode, spring number and constitutive material of the column spring. The results show that the modelling method is relatively insensitive to the contact stiffness. It is suggested that the calculated compression depth of the timber column is the radius of the timber column to determine the contact stiffness of each spring element. The three distribution modes are applicable to the modelling method, and the number of spring units should not be less than 10. For wooden columns with a high axial compression ratio, the ElasticPP material constitutive considering the spring element entering plasticity should be adopted in the modeling process.

Abstract:A novel two-stage buckling-restrained brace (TS-BRB) has been proposed to enhance the performance of conventional buckling-restrained braces (BRB), in particular to address the problem that conventional BRB cannot provide lateral resistance and energy dissipation capacity to the structure after failure under the action of major-after shocks. The energy dissipation unit of the TS-BRB consists of three Q235 steel plates in series with a tapered cross-section along the longitudinal axis. The energy dissipation section in the middle plays the role of energy dissipation first during the earthquake, and if this section breaks, the limiting slot in the restraint unit ensures that the rest of the energy dissipation section keeps working, giving the TS-BRB a higher energy dissipation capacity than conventional BRB. The slip distance of the TS-BRB is limited by varying the length of the limit slot, enabling the brace to meet the requirements of structural damping design. Test results demonstrate that the hysteresis curve of the TS-BRB is saturated and the shape of the hysteresis curve is consistent with theoretical expectations. The TS-BRB exhibits an obvious two-stage energy dissipation characteristic, with the end energy dissipation section continuing to operate after the middle energy dissipation section breaks. The additional accumulated energy dissipation after fracture is 138.41% of that before the fracture. The TS-BRB provides a solution to the problem of conventional BRBs losing load-bearing and energy-dissipation capacity immediately after fracture and offers greater energy dissipation reserves for the structure. Finally,a numerical model was established in ABAQUS,which demonstrates that the hysteretic curve of the numerical simulation agrees well with that of the experiment.

Abstract:In order to investigate the degradation law of the durability of damaged concrete beams, by introducing the fatigue damage factor and the creep damage factor, the calculation model of the corrosion depth of the steel bar after corrosion cracking of the protective layer of the concrete beam with fatigue and creep damage was established. According to the durability design standard of concrete structure, the durability limit state equation controlled by the rust crack width was established. The Monte-Carlo numerical simulation method was used to calculate the reliability of six concrete test beams within the crack width limit. The sensitivity of the four parameters,including corrosion current density, concrete compressive strength, protective layer thickness and steel bar diameter, was calculated using the checkpoint method. The research results show that the reliability decreases from 0.9 to 0.1 with the increase of corrosion time and the increase of holding time for three months has little effect on the reliability of the beam after cyclic loading of 60% of the fatigue life times. The increase of the protective layer thickness and the decrease of the diameter of the steel bar can both improve the reliability of the beam and slow down the decline rate of the structural reliability at the early stage of corrosion of the steel bar. The steel bar diameter of 8 mm can be used as a reference value for the durability design of damaged concrete beams. The sensitivity of the three parameters of corrosion current density, protective layer thickness and steel bar diameter is so relatively large that three parameters are the main influencing factors of durability limit state reliability.

Abstract:Some major key structures will face extreme events during their service life, which may be ignored due to their extremely low probability, but will result in serious losses if they occur. In order to accurately estimate the minimum probability of failure of complex structures, this paper presents a method that can balance the accuracy and cost of calculating the probability of extreme events. Using an active learning strategy based on a Gaussian surrogate metamodel, a search function is constructed that can effectively concentrate the training points on one side of the tail, and the function is better at finding the maximum error region weighted by the distribution function and re-investing the new training points. To verify the effectiveness of the algorithm, the nonlinear analysis of a structural crack is taken as an example. The relative error of the proposed algorithm is about 10% compared to MCS. The mean relative error of the estimated random variables is about 10%, indicating that this method can obtain acceptable statistical results. Compared to the results of AL-GP, the error expectation of the estimated random variables is reduced by 20%, indicating that the uncertainty in the tail can be reduced faster. The example proves that the algorithm is more sensitive to the tail and is suitable for the distribution calculation with potential tail risk.

Abstract:To meet the challenge of mismatches between power supply and demand, modern buildings must schedule flexible energy loads in order to improve the efficiency of power grids. Furthermore, it is essential to understand the effectiveness of flexibility management strategies under different climate conditions and extreme weather events. Using both typical and extreme weather data from cities in five major climate zones of China, this study investigates the energy flexibility potential of an office building under three short-term HVAC management strategies in the context of different climates. The results show that the peak load flexibility and overall energy performance of the three short-term strategies were affected by the surrounding climate conditions. The peak load reduction rate of the pre-cooling and zone temperature reset strategies declined linearly as outdoor temperature increased. Under extreme climate conditions, the daily peak-load time was found to be over two hours earlier than under typical conditions, and the intensive solar radiation found in the extreme conditions can weaken the correlation between peak load reduction and outdoor temperature, risking the ability of a building’s HVAC system to maintain a comfortable indoor environment.

Abstract:Carbon emissions from construction sites exhibit distinct traits of spatial concentration and temporal intensity, which underscores the pressing need for effective monitoring and regulation of their environmental impacts. However, many construction site carbon assessments are carried out before or after project completion, with little attention paid to monitoring environmental performance during the construction process. This paper develops a performance assessment model called Earned Carbon Value Management (ECVM) based on construction quota theory, internet of things technology and earned value theory to assess the performance of carbon emissions during construction and improve the accuracy and efficiency of the carbon emissions management at construction sites.The model links construction carbon emissions with project completion volume and resource consumption, proposing three key parameters and four key indicators.The development model was applied to a construction project of a building in Shanghai, and the evaluation revealed that at the 20-day mark of construction, the project had an emission variance (EV) of -105.46 kgCO₂e, while the schedule variance (SV) was -215 kgCO₂e. This indicates significant delays in the current construction progress, with carbon emissions exceeding the allocated limit. However,when construction progressed to 30 days, the EV and SV of the project were -2 603.18 kgCO₂e and 555.39 kgCO₂e, respectively. This demonstrates the positive impact of a moderate progress adjustment, resulting in effective control of the construction schedule. Nevertheless, the carbon emissions still exceeded the allotted limit, necessitating further measures to mitigate carbon emissions.The case demonstrates that ECVM can analyze the relationship between construction progress and carbon emissions during the construction process analyze the causes of deviations and propose targeted corrective measures based on carbon emission performance indicators. The model presented in this paper is generic and can be used for any construction project that aims to reduce carbon emissions.

Abstract:In recent years, the burden of health risks caused by dust particles generated by industrial operations has gradually increased. A large number of studies have shown that long-term exposure to productive dust particles is closely related to workers, respiratory occupational diseases, and the relationship between indoor exposure to dust particles in industrial buildings and adverse health effects in workers has been clarified. This is of great importance for the scientific evaluation of environmental safety and guarantee of workers, health. At present, research on the toxicity and biological effects of dust particles has gradually shifted the focus of research on dust particle exposure from environmental assessment to individual health effects. However, the correlation between exposure to industrial dust particles and health effects is not fully clarified, and the impact of exposure to different types and levels of dust particles on health effects in industrial settings remains to be clarified. This paper reviews the progress of research on the health effects of industrial dust particles at home and abroad from three aspects: the possible damage caused by dust particles to respiratory system health, the correlation of health effects of dust exposure and health risk assessment, and clarifies the effects of exposure on health and the current theoretical deficiencies in quantifying the mechanism of action of dust particles based on exposure effect models. And the urgency of effective biomarker selection, to provide reference information for future scientific protection of workers, health, different types of industrial environmental monitoring guidelines and development of control and improvement means.

Abstract:Algal blooms in drinking water sources produce a large amount of algal organic matter (AOM), and AOM can react with chlorine to produce disinfection by-products (DBPs), significantly endangering the water quality. Thus, the vacuum ultraviolet/persulfate (VUV/PS) process was employed to remove AOM and reduce the disinfection by-products (DBPs) formation. The VUV/PS process demonstrated superior efficiency in AOM removal compared to UV/PS, VUV, UV, and PS processes, achieving removal rates of dissolved organic carbon (DOC) and UV₂₅₄ of 74.7% and 70.7%, respectively. Additionally, the removal rate of fluorescent organic matter surpasses 82.2%. PS dose and initial pH impacted AOM removal by influencing the transformation and concentration of reactive oxygen species (ROS). The primary ROS in the VUV/PS process were hydroxyl radicals (HO^?) and sulfate radicals (SO₄^?-), with steady-state concentrations of 4.78×10^-13 and 1.51×10^-11 mol/L, respectively. AOM was effectively eliminated by VUV photolysis and ROS oxidation, with VUV enhancing the efficiency of AOM removal by facilitating the generation and conversion of ROS. Additionally, during subsequent chlorination, the VUV/PS process significantly reduced the yield of DBPs and theoretical toxicity. In conclusion, the VUV/PS process exhibited significant potential for application in treating AOM-rich water.

Abstract:The annual output of waste cooking oil (WCO) in China exceeds 5 million tons, and its main component is fatty acid glycerides. Through appropriate chemical conversion, it can be prepared into second-generation biodiesel with fatty hydrocarbons as the main component. Compared with traditional biodiesel (main components: fatty acid methyl esters or fatty acid ethyl esters), second-generation biodiesel can be blended with petrochemical diesel in any ratio for better combustion performance. Currently, research on preparing second-generation biodiesel from WCO mainly includes the hydrogenation catalytic process and the hydrothermal catalytic process. This article compares the reaction mechanisms and reaction parameters of the two processes, and focuses on the research and development of catalyst and carrier selection, temperature, gas and other reaction conditions. It summarizes the applicable scope of each process and provides a basis for selecting suitable processes. At the same time, it also looks forward to the future development direction of the two processes: hydrogenation catalytic process is relatively mature in commercial use, and the focus of future research is to improve the stability of catalysts and process economics; hydrothermal catalytic process, as an emerging technology capable of in-situ hydrogen production, should focus on in-depth research on green and efficient hydrothermal catalysts and continuous flow hydrothermal reactions in the future, so as to promote the industrial application of hydrothermal catalytic process.

Abstract:The presence of large quantities of sediments in urban drainage systems can lead to pipeline blockage and overflow contamination on rainy days. Ultrasound, as a clean physical treatment method, can destabilize sediment aggregates, and thus remove sediment during the dry season to maintain sewer function. To investigate the feasibility and optimal treatment conditions of ultrasonic technology for actual dredging, orthogonal experiments were designed to explore the effectiveness of ultrasonic dredging and the impact of five key factors on ultrasonic dredging. The results showed that the ultrasonic treatment exhibited good effects on improving the pipe siltation, with the shear resistance of sediments (EPS) reduced to 26.4%-91.5% of the control group after ultrasonic action, and a large number of EPS associated with adhesion were decomposed in the pipe sediments. Correlation analysis showed that the damage of EPS was an important reason for the decrease in the scour resistance of the sediments. The order of the impact of five key factors on ultrasonic dredging is: ultrasonic power>probe distance from mud surface>action time>sediment thickness>ultrasonic frequency. The optimal working conditions of ultrasonic dredging are: power 220 W, frequency 50 kHz, processing time 200 s, distance from the sediment surface of 3 cm. Explored the variation of dredging effect with sediment thickness, and found that ultrasonic dredging has a good effect on sediment with a thickness of ≤7 cm, and obviously decayed beyond this range. Based on this, further exploration was conducted on the changes in the properties of sediment along the depth direction after ultrasonic action.

Abstract:Water-sewage diversion of tunnel construction drainage is an important engineering technique to reduce tunnel construction sewage discharge. However, the leaching substances of unstable tunnel shotcrete can affect the drainage water quality. Therefore, the study of the influence of leaching substances on the water quality during the stabilization process of shotcrete is of great significance for the precise implementation of wastewater separation technology. The static and dynamic experimental methods have been applied to the systematic study of the pollution indicators and leaching laws of shotcrete. The static experimental results show that when water comes into contact with newly poured concrete, the large release of alkaline substances can lead to a rapid increase in the pH of the water, becoming an important pollution factor affecting the water quality. The dynamic experimental results show that the curing time of concrete, the ratio of water to concrete (the volume-to-volume ratio of water sample to concrete， L/S), and the contact area between concrete and water all affect the water quality. When the curing time of the concrete is less than three days, the calcium hydroxide crystal inside the concrete is not solidified by the C-S-H gel, which is easy to continue to precipitate, leading to the pH of the contact water sample exceeding the standard. With the increase of curing time, the leaching alkaline substances decrease significantly. When the maintenance time reaches 28 days, the pH of the leaching solution drops below 9, which can meet the requirements of comprehensive wastewater discharge. When the L/S ratio is low, the leaching substance has a significant impact on the pH and alkalinity of the water sample. When the L/S ratio exceeds 40∶1, the leaching substance has no significant impact on the water quality of the water sample. The larger the contact area between the concrete and water samples, the easier it is for alkalis in the concrete to dissolve and precipitate, and the more significant the impact on the pH and alkalinity of the water quality.

Abstract:In engineering construction, waste mud often contains an extremely high water content that can significantly impact the environment. Addressing the issue of dehydration is therefore a primary concern. To address the problem of high water content mud water separation, this study selected three types of flocculants CaCl₂, anionic polyacrylamide (APAM) and poly aluminum chloride (PAC), and then designed a 3-factor and 4-level orthogonal experiment using the comprehensive balance method. Indicators such as the 48-hour dehydration amount and pH value of the supernatant were selected, and range analysis and variance analysis were conducted to find the optimal combination of composite flocculants. The flocculation mechanism was also discussed through orthogonal test results and SEM microanalysis. The experimental results showed that dividing the dehydration rate curve over time into high, medium, and low dehydration zones, as well as fast and slow dehydration stages, led to a decrease in the overall mud dehydration rate. However, the high dehydration zone group had a higher dehydration rate at 12 h, which met the requirements for fast dehydration. Additionally, the three flocculants showed some synergistic effect. Through range analysis of variance analysis orthogonal tests, the optimal combination of composite flocculants was found to be 0.25 g CaCl₂ + 0.12 g APAM + 0.17 g PAC per 100 g total mass of slurry. Based on the mechanism analysis, the flocculation process of composite flocculants was divided into five stages: charge neutralization stage, bridging stage, adsorption agglomeration stage, network sedimentation stage, and solidification enhancement stage.

Abstract: