Abstract:A large number of dredged slurry are produced in the coastal area. In order to study the treatment methods of dredged slurry, an indoor model test was conducted to improve dredged slurry in Wenzhou area by stepped vacuum preloading combined with intermittent electroosmosis, and the time of intermittent power-on and intermittent stepped voltage electroosmosis were examined. The vacuum pressure, current, drainage and surface settlement were monitored during the test. After the test, the moisture content, vane shear strength of soil and the corrosion quality of electrodes were measured. The test results showed that although the longer the time of intermittent power-on, the better the consolidation effect of soil, when the time of intermittent power-on exceeded 24 hours, the effect of soil improvement began to weaken; however, the corrosion quality of electrodes and the average energy consumption coefficient of intermittent electroosmosis were still positively correlated with the time of intermittent power-on. In addition, compared with the stepped vacuum preloading combined with intermittent electroosmosis method, the stepped vacuum preloading combined with intermittent stepped voltage electroosmosis method obtained better soil improvement, the corrosion quality of electrodes and the average energy consumption coefficient of intermittent electroosmosis of which were also significantly reduced.

Abstract:Flocculation-solidification combined (FSCM) is a reasonable choice for the treatment and recycling of dredged mud slurry at extra high water content (EHW-MS). However, FSCM tends to show some limitations when the treated EHW-MS is recycled as filling material with high requirement on mechanical properties. In order to improve the treatment efficiency of EHW-MS, a new method is proposed, i.e., vacuum preloading-flocculation-solidification combined method (VP-FSCM). A series of laboratory model tests are done to verify the advantages of the VP-FSCM, and to identify the variation of its treatment advantages with the equivalent initial water content. In addition, the internal mechanism and feasibility of VP-FSCM are analyzed and demonstrated by micro-tests (e.g. XRD and SEM). The results show that the undrained shear strength of the VP-FSCM treated EHW-MS can be increased to 1.65 times than that of FSCM, and the strength advantage is maintained at least 1.2 times. On the micro level, the advantage of VP-FSCM is that the quantity and development of hydration products such as C(A)SH gel and ettringite have been significantly improved, and the soil structure has been further filled and compacted.

Abstract:Under the increasingly tense situation of land resources, in some mineral resource-based cities, utilization of disused mining pit has been promoted to improve the urban landscape or promote commercial significance. This paper focuses on the rock slope stability problem with reference to a deep mining pit renovation project in Changsha. The development pattern of rock deformation in both natural state and disturbed by construction activities is summarized through finite element analysis. For the rock slope suffering circular point heavy loading, the collaborative interaction between the rock and its overlying structures constitutes the research focus of this study. The results show that the disused deep mining pit is basically in a stable state without engineering activity, the construction disturbance and structural operation loads leave no significance impact to the rock slope stability. However, when the rock wall suffers paroxysmal failure, the local collapse or large deformation seriously endanger the safety of the mining pit and its overlying structures. As for the accidental failure of the foundation pile, it shows less effect on the stability of the rock wall and the building due to the well-behaved annular point foundation distribution.

Abstract:The high energy dynamic compaction has been effective in a wide range of applications, effective reinforcement depth is an important indicator for evaluating the reinforcement effect and determining the dynamic consolidation plan. In this paper, taking a project of 10000kN·m high energy dynamic compaction for filled subgrade as a background, the finite difference software FLAC 3D was used to perform multiple dynamic compaction analysis. The stress after tamping was considered as a criterion to calculate the effective reinforcement depth. The results show that with the increase in the number of drops, the effective reinforcement depth first increases and then stabilizes. The growth rate of effective reinforcement depth after six drops is extremely small. The sensitivity ranking of soil parameters on the effective reinforcement depth is obtained by orthogonal test and extreme difference analysis. The drop distance and hammer weight are positively correlated with the effective reinforcement depth, while the hammer diameter is negatively correlated. The impact of hammer weight on the effective reinforcement depth is greater than the drop distance. The combination of heavy hammer and low drop distance has greater cumulative settlement and effective reinforcement depth under the same tamping energy. The formula for estimating the effective reinforcement depth of high energy dynamic compaction is proposed, and the uniformity of dimensions is achieved, which has a small deviation from the simulation results. It can provide reference for the same type of dynamic compaction project.

Abstract:In order to study the mechanical performance of screw anchor under vertical compression load in silty clay area, firstly, based on the static load test of screw anchor, the differences of methods for determining its ultimate bearing capacity at home and abroad are discussed respectively; secondly, a refined finite element model is established for screw anchor, in which the compression effect of screw anchor on surrounding soil is considered, and the numerical analysis results and test results are compared; finally, based on the verified finite element model, the change rule of anchor internal force and side friction resistance along the range of foundation depth under different load levels is analyzed, as well as the proportion relationship between side resistance and anchor end resistance bearing load. The results show that the lgP-s method is suitable to determine the ultimate bearing capacity of the screw anchor foundation with large anchor pieces; the friction between the screw anchor and the soil increases with the increase of the down-force displacement, and the friction near the anchor plate fluctuates greatly due to the deformation of the anchor plate; the proportion of load shared by anchor pieces accounts for more than 75% of the load of the screw anchor foundation, the maximum difference of load shared by each anchor piece is about 6%, and the end resistance of screw anchor foundation can be negligible.

Abstract:When the local scour hole is formed around the pile foundation, the effective buried depth of the pile foundation will be reduced, which increases the safety hazard of the engineering structure. The scour models in the current research are mostly symmetrical, but the scour holes in engineering practice are asymmetric, which makes the pile foundation in a more unfavorable state. How to calculate the stress change of the soil caused by scour reasonably is pivotal for evaluating the bearing capacity of the pile foundation. However, there is still no strict theoretical calculation method. This paper aims to propose a simplified three-dimensional asymmetric scour hole model based on the asymmetric scour hole shape measured in the experiment. Which is based on the application of Boussinesq's equation in a semi-infinite space and regard the soil above the depth of the scour hole as a load. The calculation method of the vertical and horizontal effective stress of the soil in the asymmetric scour hole is derived. The "active and deactive element" in the finite element method is used to simulate the formation of scour holes in the semi-infinite space foundation, and the FEM results are compared with those obtained from the theoretical calculation method, which verifies the correctness of the theoretical calculation method in this study. Subsequently, based on the theoretical calculation method, the influence of the pile foundation is considered, and compared with the FEM results. The comparison results indicate that the theoretical calculation method in this research is feasible. Based on this, the sensitivity analysis of the parameters in the simplified model of the three-dimensional asymmetric scour hole was carried out, and the changes of the vertical and horizontal effective stress difference of the soil around the pile under the condition of the asymmetric scour hole were obtained.

Abstract:A new method is presented to compute the Stress Intensity Factors(SIF) by combining analytical solutions with numerical solutions in previous studies based on numerical manifold method, which obtains optimal approximation at the crack tip but only for the type Ⅰ and typeⅡ cracks in planar. Following the idea of combined application, Williams series is introduced at the crack tip and 3D SIF for three-dimensional straight through cracks is completed via combining analytical covers with numerical covers, which obtains higher computational precision than other numerical methods. Meanwhile, the corresponding formulas of the stiffness matrix and the strain matrix are deduced，and numerical examples shows the validity of the method in solving the exact solution of 3D stress intensity factor.

Abstract:The two-stage method is used to analyze the pipeline shear deformation which caused by the underneath shield tunneling. In the first stage, the Loganathan formula is applied for studying the ground loss at the pipeline axis caused by the tunneling. The Timoshenko beam theory and superposition method are combined to simulate the pipeline deformation. Then, through comparison with the existing results and engineering monitoring and centrifuge test data, the proposed result was verified to be correct. The influence of ratio of elastic modulus of pipe to soil, the diameter of pipe and the shear stiffness of pipe on the pipe deformation has been further studied. The results show that the maximum vertical displacement of the pipe decreases with the increase of the tube-to-soil modulus ratio and the diameter of the pipe. The shear stiffness of the pipeline has a great influence on the displacement of the pipeline, and the decrease of the shear stiffness can lead to the increase of the maximum displacement of the pipeline.

Abstract:Municipal tunnel engineering has developed vigorously in recent years, but many urban highway tunnels’ development are limited by construction, pipeline and other factors. In order to save land and construction period, most of them are designed as neighborhood tunnels. The most significant difference between neighborhood tunnel and separated tunnel during the construction process is that the stress state of the mid-adjacent rock is complex and the it’s stability is difficult to control. By the theoretical derivation, the instability mechanism of the soil mid-adjacent rock in shallow neighborhood tunnel is studied. Based on the bearing model of the neighborhood tunnel’s mid-adjacent rock the overburden pressure of mid-adjacent is ascertained. Combining the ultimate stress formula of the soil, the instability and failure characteristics of mid-adjacent road under different construction conditions are analyzed. Increasing the cohesion, internal friction angle and support reaction force can increase the ultimate stress of the soil, what’s more, the effect of increasing the support reaction force is more significant. Provide theoretical support for the role of supporting structure.

Abstract:Cold-formed light gauge steel framing (LSF) structure is a new type of fabricated steel structure. Fire resisting performance of LSF structure is the key factor for promoting related practical application. However, for the LSF floor as one of the main load–bearing systems in LSF structures, the available fire testing data are limited. Most of the published numerical investigations of LSF floors are carried out by using two-dimensional heat transfer analysis to study the temperature rise and distribution, or simplified linear temperature distributions. The difference between the analysis results of two-dimension and three-dimension structural members could accumulate and evolve into the essential discrepancy in force transfer when the structural scale is large and the system is complex. To determine the mechanism of the fire resistance, the model describing a floor system consists of LSF, structural plywood, and fire-resistant panel such as gypsum board or rock wool was built up in this article. According to the ISO-834 standard, the nonlinear heat process and coupled thermo-mechanical analyses were carried out. Hence, the influence of the three-dimensional thermal field and the coupling mechanical behaviors were demonstrated. In addition, a simplified modeling approach was presented to accurately describe the contact relationship, force transfer, and the deformation coordination between self-tapping screws, structural plates, and light steel members. After comparing with two sets of fire testing data for the full-scale floor slab systems, the mechanism drawn from the numerical simulation above mentioned was verified. In general, this model based on three-dimensional heat conduction and thermal-mechanical coupling can effectively describe the LSF spatial mechanical behavior under fire conditions. The results about nonlinear temperature distribution, the deformation evolution of the joists, and the final destruction mode are consistent with those of fire testing. The proposed modeling strategy can be utilized to predict the fire resistance of LSF floor systems and evaluate the effective factors on structural high-temperature behaviors via parametric analysis.

Abstract:In order to study the bond-slip performance between concrete and steel rebar after different cooling ways, 39 pull-out tests of reinforced concrete specimens after exposure to high temperature and the splitting tensile strength tests of concrete under natural cooling way were carried out. The effect of high temperature and different cooling ways on peak bond stress and peak slip are discussed. The calculation equations between peak bond stress, peak slip and temperatures are established, and the full curve equation of bond slip considering initial temperature damage is also proposed. Based on the theoretical model, the theoretical bond strength after natural cooling is calculated. The results show that: with the increase of temperature, the peak bond stress decreases linearly, the maximum reduction for 500℃ reaches to 80.5%, and the peak slip first decreases and then increases after the same cooling way, and the cooling way has little effect on these parameters; the theoretical damage bond slip curves is consistent with the test curves; the bond strength calculated by the theoretical model well agree with the test value.

Abstract:The ribbed prestressed concrete composite wall panel changes the traditional composite wall panel layer into the ribbed layer, and optimizes the concrete configuration of the section to reduce the self-weight of the composite wall panel. Prestressed reinforcement is added to both sides of ribbed prestressed concrete composite wall panel, which can increase the crack resistance of composite wall panel. In order to study the bending performance of the ribbed prestressed concrete composite wall panels, the bending test of 3 specimens under uniform load was carried out, and the mechanical properties and deformation modes of the composite wall panel were analyzed. The calculation formula of flexural bearing capacity was derived through theoretical analysis. The comparative simulation and ribbed plate angle parameter analysis of the composite wall panels were conducted by the finite element software ABAQUS. The results showed that the ribbed prestressed composite wall panel had similar bending behavior to the traditional composite wall panel. The flexural capacity of the ribbed prestressed composite wall panels decreased, but its reduction was less than the self-weight reduction. The application of prestressing can significantly improve the bearing capacity and crack resistance of the composite wall panel. The proposed calculation formula of the bearing capacity and the finite element simulation results of the ribbed prestressed composite wall panels are in good agreement with the experimental results.

Abstract:In order to reliably evaluate the safety and stability of running train during operation, the distribution of maximum acceleration response of the running train under random track irregularity excitation is analyzed, based on the theory of multi-body dynamics and the theory of probability statistics. To this end, the train-track coupling model is established using the multi-body dynamics software Simpack. As the internal source excitation of the train-track coupling model, the track irregularity is simulated through trigonometric series method. In addition, the Monte-Carlo method is used to obtain multiple samples of the train’s acceleration response under random track irregularity. Subsequently, the maximum value of each sample (time history of train’s acceleration responses) is obtained and treated as a random variable for statistical analysis. The distribution of the train’s maximum acceleration response is fitted by the Gaussian Mixture Model, in which the fitting parameters are obtained through expected maximum algorithm and maximum likelihood estimation. Meanwhile, the reasonable number of samples to derive appropriate distribution model is also discussed. The results show that the Gaussian Mixture Model can accurately model the distribution of the train’s maximum acceleration response. Additionally, it is found that the variation of the train’s maximum acceleration response increases with higher vehicle speed.

Abstract:Basalt fiber reinforced polymer(BFRP) with silica-alumina component, is always used in the harsh environment such as moist or corrosive environment，and water molecules will lead to the decline of the bonding capacity between epoxy resin and basalt fiber，which will further affect the mechanical properties and durability of BFRP. An aluminum-doped silica substrate model of basalt fiber surface is established by partly replacing silicon atoms with aluminum atoms. The evolution of interfacial bonding properties between epoxy and aluminum-doped silica substrate in water environment are simulated based on molecular dynamic (MD). Simulation results show that the bonding force of aluminum-doped silica substrate with epoxy is weaker than that of pure silica substrate. The epoxy and fiber substrate are bonded in the manner of H-bonds formed by oxygen of epoxy-hydrogen of substrate-oxygen of substrate. Water molecular weakens the bonding capacity by occupying the reactive sites of atomic pairs in H-bond. The feasibility of the molecular model was verified by the 47.53% decreased bonding force at the interface between basalt fiber bundles and epoxy resin under the condition of water immersion for 28 days.

Abstract:Corrosion is one of the most typical form of durability degradation of steel bridge and the corrosion morphology takes significant effect on the strain distribution of the structural surface，which has evident effect on the ultra-low cycle fatigue performance of steel plate. In order to investigate the characteristics of steel corrosion morphology as well as the effect of the corrosion on the structural ultra-low cycle fatigue(ULCF) performance, this paper takes the steel kind of Q345 as the study case, conducting 2D and 3D profile measurements on four groups of steel plate samples in different accelerated corrosion conditions. Quantitative analysis on 2D profile data were performed with the methods of surface roughness, fractal dimension, and power spectrum density function, thus discusses the possibility to classify the corrosion morphology. Meanwhile, precise finite element models consisted by hexahedron elements of corroded specimens were established on the basis of 3D profile data, applied by the improved cyclic void growth model (CVGM), those finite element models were conducted to calculate the UCLF lives and discuss the influence of corroded surface morphology. The research results indicate that: the corrosion rates of the artificial acceleration corrosion tests are significantly affected by the thickness of the rust layers. However, the surface roughness, fractal dimension, and power spectrum density function are unable to differentiate the corrosion degree. According to the numerical calculation results, the unevenness of corroded surface is the very important factor on the UCLF performance degradation. Also, the reduction of the cross section, the position on the surface of specimens, and the dimension characters of the critical corruption pits, that contribute a coupling effect on the ULCF life of the corroded steel specimens.

Abstract:Concrete slurry waste, CSW is a unique unhardened construction waste which is rich in silicate minerals generated from concrete ready-mixing plant. However, its recycling has always been greatly restricted owing to its complex composition, high water to solid ratio, hazardous and corrosion. The large-scale recycling methods of CSW are comprehensively reported and commented in this paper, including recycling as aggregates, fillers, cementitious materials (wet grinding technology), additions in concrete and raw materials for cement clinker production; preparation of new type of concrete products and lightweight aggregates by carbonation and cold bonded pelletizing technique; the development in “one or two” part alkali-activated materials (AAMs). The promising research directions of CSW in the future are pointed out as follows: 1. Pre-treatment regeneration technology and active excitation technology with low energy consumption; 2. Carbonation technology; 3. Long term leaching behavior of heavy metals and durability.

Abstract:Considering the influence of coal gangue coarse aggregate replacement rate (0, 20%, 40%, 60%), this article conducts freeze-thaw cycle test, uniaxial compressive constitutive test and acoustic emission detection test to study the damage constitutive model of coal gangue concrete (CGC). The research result indicates that the relative peak strain of CGC with different substitution rates has a high correlation with the freeze-thaw damage value. The resulting equations of freeze-thaw damage value and relative peak strain provide effective parameters for the establishment of constitutive models. The acoustic emission characteristics of CGC are closely related to its load damage development, mechanical properties, and stress-strain curve. Therefore, based on the acoustic emission characteristics under axial compression, this paper uses parallel bar system (PBS) to establish the load damage model of gangue concrete without freeze-thaw cycle. Combined with the damage model of freeze-thaw, the freeze-thaw damage constitutive relationship of CGC is established, and the calculation results are in good agreement with the test data. This model can accurately reflect the overall process damage characteristics of CGC under freeze-thaw and load damage under axial compression.

Abstract:Building materials have requirements of high-strength and low-density, and it is necessary to establish evaluation indexes that are suitable for optimizing the mechanical properties of building materials. Under the background of density and strength evaluation, a method for comprehensive evaluation of the density and strength of building materials, density-strength method, is proposed. Based on the density-strength method, the optimization of different materials and the optimization of different parameters of the same material are carried out, and the distribution of the density and strength parameters of different building materials in the density-strength diagram is studied. The results show that the density and strength of different materials is different on the density-strength diagram, and when selecting materials, the density-strength diagram can be used to calculate the relative density improvement amount and the improvement angle of each material for comparison and selection; the density and strength of the same material under different parameters are different, and the factors affecting the properties of the material can be optimized by the density-strength diagram; density and strength can comprehensively reflect the properties of density and strength of building materials, which is an intuitive and understandable method to express the lightweight and high strength of materials.

Abstract:Microbially-mediated nitrate-reducing Fe(II) oxidation (NRFO) is ubiquitous under neutral anaerobic iron-rich environments. However, it is still unknown whether NRFO can be mediated by dissimilatory iron reducing bacteria. In this study, Klebsiella pneumoniae L17, Shewanella oneidensis MR-1, and Shewanella putrefaciens strain CN32 were used as the model iron reducing strains to study the process of anaerobic NRFO. The results show that nitrate reduction and Fe(II) oxidation occurred simultaneously. The intermediate product nitrite during nitrate reduction is considered the dominant contributor to the overall Fe(II) oxidation. The presence of Fe(Ⅱ) inhibited microbial nitrate reduction, and the inhibitory effect of Fe(Ⅱ) was more significant with the higher Fe(Ⅱ) concentration. The competition between chemical reduction of nitrite by Fe(Ⅱ) and biological nitrite reduction resulted in the decrease of ammonium production. Iron oxides precipitated on the cell surface and subsequently prevented nitrate uptake and microbial nitrate reduction. The cell toxicity of Fe(Ⅱ) and secondary minerals inhibited biological nitrate reduction by L17 with low Fe(Ⅱ) concentration. Nitrate reduction by CN32 was inhibited by the secondary minerals during Fe(II) oxidation while the inhibition of nitrate reduction by MR-1 was attributed to cell toxicity of Fe(Ⅱ). Under high Fe(Ⅱ) concentration, microbial nitrate reduction was inhibited by cell encrustation. This study emphasizes iron-reducing bacteria mediated nitrate-reducing Fe(Ⅱ) oxidation in the anaerobic iron-rich environment, and expands the scope of microbial species with the ability of nitrate-reducing Fe(Ⅱ) oxidation. Therefore, the findings would be helpful for understanding the function and relative contribution of various microorganisms in the process of nitrate-reducing Fe(Ⅱ) oxidation in anaerobic environment.

Abstract:In order to understand the adsorption behavior and evaluate the adsorption performance of Dibutyl phthalate (DBP) by different grain-sized suspended particulate matter (SPM), and identify the potential mechanism, the adsorption of DBP by different grain-sized SPM was studied by Batch equilibrium method. The in-situ SPM that collected from the Yulin River of the tributary of the Three Gorges Reservoir Area, was sorted into five grain-sized fractions (clay-very fine silt (<8 μm), fine silt (8~20 μm), medium silt (20~32 μm), coarse silt (32~63 μm) and sand (>63 μm)) via physical method of wet screening and natural settling in this study. The results showed that partition was the main mechanism of removal of DBP by SPM from the solution, and the adsorption capacity of different grain-sized SPM for DBP follows: clay-fine sand > fine sand > medium sand > coarse sand > sand. Total organic carbon (TOC) was the main factor affecting the partition of DBP by different grain-sized SPM. In addition, the difference of organic matter composition in clay-very fine silt SPM may be the reason for its high adsorption capacity for DBP. The specific surface area, pore volume and humification degree of organic matter affect its adsorption of DBP by silt-sand SPM.

Abstract:Solidification/stabilization was an effective means for the remediation of chromium (Cr)-contaminated soil. Different agents differ in their abilities of Cr-reduction, adsorption and stabilization. Screening agents that are low-cost and high-efficiency is vital to remediate Cr-contaminated soil. In the present study, seven reductants, ten adsorbents and six stabilizers in different doses were used as amendments to remediate Cr-contaminated soil, respectively. The main findings were as follows: (1) Calcium polysulfide (CPS), sodium sulfide (Na₂S), ferrous chloride (FeCl₂) and ferrous sulfate (FeSO₄) can be used as reducing materials of Cr-contaminated soil. CPS had the best Cr (VI)-stability efficiency exceeding 90% when it was added at the mole ratio of 0.8. (2) Calcium magnesium phosphate (CMP), weak-base anion-exchange resin (WAR), magnesium oxide (MgO) and diaspore (Al₂O₃·3nH₂O) can be used as absorbing materials of Cr-contaminated soil. CMP demonstrated the best adsorptivity with Cr (VI)-stability efficiency being above 90% and total Cr 80% when it was added at the mass ratio of 20%. (3) Furnace slag powder (FSP, bought from Chongqing and Henan) and sodium silicate (Na₂SiO₃·9H₂O) can be used as immobilizing materials of Cr-contaminated soil. FSP from Chongqing was the best in immobilizing Cr (VI) with stability efficiency reaching 98% and total Cr higher 70% when it was added at the mass ratio of 16%. In conclusion, the materials used in this study played important role in remediation of Cr-contaminated soil and achieved the high Cr (VI)-stability efficiency under laboratory conditions. Their potential value as Cr-immobilizers and their remediation efficacy deserve further studies in large-scale field trials.

Abstract:Chromium slag and chromium-containing wastewater produced by some industrial and mining enterprises in our country often cause serious chromium pollution in soil due to poor management. It is urgent to seek low-cost remediation technology for chromium-contaminated soil. A technology for eluting chromium-contaminated soil with an extract of Dissolved Organic Matter (DOM) in decomposing rice straw was proposed. Through laboratory simulation tests, two types of chromium contaminated soil (the total chromium content is 121.54 mg/kg and 941.90 mg/kg respectively, and the hexavalent chromium is 119.90 mg/kg and 856.90 mg/kg respectively) as the research goals. The effect of solid-liquid ratio, leaching time, leaching times and other factors on the elution effect of total chromium and hexavalent chromium in the soil was investigated by the oscillation leaching method. The chromium form changes before and after leaching and the continuous passivation ability of hexavalent chromium remaining in the soil after leaching were also discussed. The results showed that DOM extract from rice straw decomposed for 35 days had the best effect of eluting chromium in soil and was determined as the best eluent. The solid-liquid ratio is 1:15, leaching for 4 h/ time, and leaching for 2 times is the best leaching process condition. Under this condition, the total chromium content in soil is eluted by 47.79% and 85.92%, and the hexavalent chromium content is reduced by 51.76% and 95.09%, respectively. DOM extract is weakly alkaline and contains a large number of carboxyl, hydroxyl and phenolic substances. It has good elution effect on chromium in water soluble, weak acid extracted and residue state, effectively reduces the environmental risk of soil, and can continuously passivate the residual hexavalent chromium in the leached soil.