Abstract:Soil arching between anti-sliding piles is the interaction of horizontal soil arch and vertical friction arch, with distinct three-dimensional characteristics. Numerical model by the particle flow code PFC^3D was developed and a series of measurement balls to numerically monitor stress variations at different positions behind the anti-slide piles were set. Combined with the displacement of numerical model balls, we analyzed the formation process and evolution pattern of the soil arching effect were analyzed. Also the thickness of soil arch had been studied and finally we proposed a new method to determine the its thickness was proposed. The study shows that the soil arch initiates s from the free face near the bottom of pile and develops to the inner and upper part of the soil, and the failure process of arch expands from the bottom of pile to the top; The thickness of soil arch varies with depth, increasing first and then decreasing along the bottom of pile to the top; The thickness of soil arch varies with time. As the loading stage proceeds, the thickness of soil arch increases first and then decreases until the soil arch is destroyed.

Abstract:In order to study the effect of skirt soil reinforcement on the deformation and stress of foundation pit, model tests were carried out for cases without bottom reinforcement and skirt reinforcement respectively. To realize the reinforcement of bottom soil, the method of reinforcing soil by pre-pouring in the process of filling was adopted. The ground subsidence,the lateral displacement of top beam,the bending moment of piles and the earth pressure are measured during excavation. Extensive FE parametric studies indicate that the skirt reinforcement can effectively reduce the lateral displacement of the supporting structure. Although surrounding settlements decreased, the effect is less obvious. The bending moment of the pile is slightly less than that of the pile without reinforcement. With the excavation, the earth pressure in the upper part of the pile decreases and pressure at the bottom increases as the pile rotates at a certain point under the pit. The depth of skirt reinforcement has greater influence on the deformation of foundation pit than the width of reinforcement. When the depth and width of soil reinforcement exceed a certain range, the effect of controlling the deformation of foundation pit is marginaly improved. The reinforcement depth should be 0.3~`0.4 times of the excavation depth and the width should be 0.35~0.45 times of the excavation depth.

Abstract:A vehicle-track-subgrade coupling dynamics vertical model was applied to study the probability distribution characteristics of dynamic influence coefficients φ_i of ballast track subgrade with vertical profile irregularity. According to the relationship between cumulative deformation state characteristics and loading levels revealed by model test of typical coarse-grained soil filler of subgrade under cyclic loading, it is found that the embankment below subgrade is in a time-independent deformation state, and subgrade filler is in weak-time effect state. Using the dynamic strength of subgrade structure, long-term dynamic stability and cyclic deformation as design control indicators, the technical conditions of the high-speed railway ballast track subgrade structure were analyzed. The study shows that:lg φ_i which characterize the degree of subgrade bearing the dynamic effect of the train along the line longitudinal direction, obeys the normal distribution; the cumulative deformation state of each structural layer of the subgrade under train load is closely related to the nature of the filler; the subgrade structure's long-term dynamic stability is the main design control factor. Accordingly the technical standards for 350km/h high-speed rail double-layer subgrade structure of ballast track was proposed.

Abstract:The attenuation law of ground vibration of viaduct rail transit under sloping bedrock condition is studied by model test and finite element method. The effects of inclination angle, load frequency, pile length on ground vibration were analyzed. The results indicated that under the condition of inclined bedrock, the attenuation of ground vibration is different in directions. Generally, the attenuation is the slowest along the downward slope of bedrock, while the fastest along the upward slope. The attenuation is gradually faster from the downward to the upward; The greater the inclination angle of bedrock layer, the lower the ground vibration response. The change of bedrock angle has a significant influence on the directional differentiation of ground vibration response. With increase of load frequency, the vibration response of the ground increases linearly first then decreases gradually. When the frequency is 13 Hz, the differentiation of vibration response on the ground is the greatest in all directions at the same distance to the pile. The surface velocity response decreases linearly with the increase of pile length. The nearer the pile, the faster the decrease. The influence of the change of pile length on the vibration response in all directions with the same distance to the pile is insignificant.

Abstract:The compression behavior of river sediments is an important factor affecting the design and disposal of environmental dredging of river sediments. To investigate the compressibility of four river sediments, the consolidation tests of four kinds of river raw sediments and river sediments with hydrogen peroxide treated were performed in adapted odometers. The compression behavior of river sediments was studied and the effect of organic matter content on compression of sediments was discussed. The results show that the contents of organic matter in river sediments varies widely, and the compression behavior of river sediments is closely related to the physical properties of sediments. It is found that the main factors of influencing the compression behavior of reconstituted river sediments are initial void ratio and void ratio at liquid limit. The effect of organic matter on the compression behavior of river sediments can be attributed to the change of the liquid limit void ratio. The organic matter content affects the liquid limit and specific gravity of the river sediments, which leads to the change of remoulded yielding stress and compression behavior of river sediments. With increase of organic matter content, void ratio at liquid limit and compression index of river sediments increases, and the compressibility of river sediments is higher.

Abstract:China is one of the countries most seriously affected by the tropical typhoon disasters. Root pull-out and toppling damage caused by severe storms and rains occur frequently. Secondary disasters such as traffic disruption, vehicle damage and casualties are increasing. In order to investigate the effect of soil physical properties on the anti-overturning performance of trees, the pulling test of Ginkgo biloba seedlings under constant lateral loading rate was carried out through a self-designed lateral root loading test system to simulate the dumping process of roots under external load. Five sets of gradient water content and four buried depths were set to analyze the influence of soil moisture content and the root depth on the pull-out resistance during the pull-out process. The research indicates that in silty sand, the change of the anti-overturning force in the root displacement-drawing force curve can be summarized as three stages:gentle rise, steep rise and slowly rising to reach the peak. The anti-overturning force with the increase of moisture content showed the first rise. The overall trend of the post-fall is the same as the overall trend of the change of soil cohesion. When the moisture content approximates the saturated moisture content, the maximum anti-overturning force is significantly reduced. When the moisture content is constant, the maximum anti-overturning force of the root system increases linearly with the depth of the root system in the buried depth range set by the test.

Abstract:In order to study the load transfer pattern and the bearing capacity difference between the open test pile and the closed test pile in the static pile sinking process in the cohesive soil, the method of pre-embedded sensitized micro-fiber grating sensor is adopted in this paper. In the foundation soil, a comparison test of the bearing capacity of the test piles in different pile end models was carried out. The variation of pile force, pile end resistance, pile side friction resistance and pile axial force was measured. The testing results show that the fiber Bragg grating sensor can monitor the pile body stress state in the pile sinking process in real time; the pile bearing capacity and pile end resistance of the open and closed model pipe piles all increase with pile depth, with differentmagnitudes. The axial force of the pile under the depth is gradually decreasing; the ratio of the pile end resistance of the open pipe pile and the closed pipe pile is more than 50%; the double-walled open-ended model pipe pile is used for the pile side friction resistance, of which the outer tube is 3 times as much as the inner tube.. When the penetration depth of the open pipe pile reaches a maximum of 90 cm, the height of the soil plug is stable at 33 cm. Consequently, the distribution of the side frictional resistance of the pile side increase from the top to the bottom.

Abstract:The ultimate flexural bearing capacity test was carried out through a total of 27 root specimen of the heart reinforcement pile, the steel pipe + heart reinforcement pile, the steel pipe + H section steel pile. It wasfound that the heart reinforcement pile ultimate flexural bearing capacity is low and that the failure was of brittle type, while the steel pipe + heart reinforcement pile and the steel pipe + H section steel pile show a higher bearing capacity and was of better ductility performance. Through the load-displacement curve, the heart reinforcement ile under loading is divided into specimen bite stage, elastic stage, elastic-plastic stage and failure stage, while the steel pipe + heart reinforcement pile and the steel pipe + H section steel pile can be divided into specimen bite stage, elastic stage, elastic-plastic stage and strengthening stage. The ultimate flexural bearing capacity for steel pipe + heart reinforcement pile can be regarded as that of steel pipe concrete pile multiplied by an increase coefficient of 1.2.

Abstract:Based on Python and Abaqus platform, a stochastic finite element algorithm program was developed. The program can automatically discretize the non-stationary random field and calculate the failure probability when the geometric parameters of the slope and the mean, correlation distance and variation coefficient of the soil shear strength parameters are provided. The algorithm is used to calculate the benckmark slope examples, and the results verify the reliability of the proposed method. Moreover, the program can also effectively solve the complex problems of multiple software interaction and subroutine compilation. The program is then redeveloped on Abaqus platform, which is a widely applicable finite element software. It was beneficial to the popularization of the program in practical engineering applications.

Abstract:Cyclic tests were carried out on a conventionally reinforced concrete shear wall and three sandwich shear walls with concrete filled steel tubes (SW-CFT). The vertical compression forces on the experimental specimens were varied. The failure mode and hysteretic behavior of each experimental specimen under the combined vertical compression and lateral cyclic loading were evaluated. The equations to calculate the wall lateral resistances associated with the yielding states were derived. The experimental specimens were also simulated by the computer program-XTRACT. Comparisons revealed that the derived equations and the computer model both provide reasonable predictions for the wall resistances. The result show that the SW-CFTs exhibited high horizontal bearing capacity and energy consumption. In addition, the axial compression ratio is proportional to the strength exaltation and has only marginal effects on the seismic behavior of the SW-CFTs within the test range in this study.

Abstract:Most equivalent damping ratio (EDR) models available to date for RC framed system are generally difficult to describe the structural hysteretic characteristic effectively since they are derived on the bases of equivalent single degree of freedom system. In this paper, 66 RC framed structures with various parameters and configurations are established based on the current seismic design code and monotonic pushover analyses are implemented. Then, 51 structures that have ductility deformation mechanism are selected to perform cyclic pushover analyses for establishing a global EDR model based on the principle of equating energy dissipation. Considering that this EDR model may underestimate the displacements demand, nonlinear dynamic analyses (NDA) are implemented and this EDR model is modified. It is found that the results obtained by nonlinear static analysis using the proposed modified EDR are consistent with those obtained by NDA. The proposed EDR model is of wide applicability and can reflect the global energy dissipation characteristics of RC framed structures.

Abstract:Four lightweight aggregate concrete beams with plastic steel fiber content of 0kg/m³, 3kg/m³, 6kg/m³, 9kg/m³ were produced, to study the effect of plastic steel fiber on the flexural properties of lightweight aggregate concrete beams. The results show that plastic steel fiber effectively delay the development of beam cracks and reduce the maximum crack width and make the cracks much denser. The cracking moment and the ultimate moment increase with the proportion of plastic steel fiber, the cracking moment and ultimate moment of the LC-9 beam are increased by 72% and 8.43%, respectively, compared with the LC-0 beam. With the fiber content increases, the yield deflection of the beam increases and the ultimate deflection increases. Meanwhile the deflection ductility coefficient μ_f increases, with a maximum increase of 92.23%. The plastic steel fiber reduces the height of the relative compression zone of the beam, the load-holding capacity is improved, and the strain of steel bar is reduced, and the yield time of the steel bar is delayed.

Abstract:Fast-growing poplar has been widely planted in China. For the poor mechanical properties and large deformation of the timber, its application is greatly restricted. Modified fast growing poplar specimens with different plate thicknesses of 5, 10, 15, 20 mm, radial direction and chord direction), under different parameters were tested in this paper. The tests indicate that the failure gradually began by the single oblique section,then the horizontal crinkling failure occurs, finally to the double curvature failure and the single plate bending failure with gradual decrease of the plate thickness. In the compressive test of the modified specimens with different thicknesses, the mechanical properties of the modified specimens are improved greatly compared with the control specimens, the compressive strength, the peak compressive strain and the elastic modulus of the specimens increase significantly with decrease of the plate thickness. In the compression test of different texture combination modified specimens, the mechanical properties of chord and chord texture combination specimens are the best, followed by radial and radial texture combination specimens, and the lowest is chord and radial texture combination specimens. At the same time, the compressive strength, peak compressive strain and modulus of elasticity are significantly higher than those of the control specimens, and the compressive strength and modulus of elasticity of the modified specimens are lower than those of the control specimens.

Abstract:In order to solve the two-dimensional dynamic coupled thermoelasticity problem more effectively, a novel numerical method based on the meshless natural neighbour Petrov-Galerkin method is proposed in this study. Only a group of scattered nodes are required in this method, to construct approximation function and therefore complex meshing and disadvantage of mesh distortion are effectively eliminated. In comparison with the moving least-squares (MLS) approximation used widely in meshless methods, the natural neighbour interpolation requires no complex matrix inversions and no artificial intermediate parameters. The equations of motion and transient heat conduction equations of the coupled thermoelasticity interaction on each other and therefore these equations must be solved simultaneously. After spatially discretization, a series of second-order ordinary differential algebraic equations is obtained, which is solved by the Newmark method to obtain the numerical temperature and displacement field directly.

Abstract:Neutralization process and mechanism of long highway tunnel shotcrete lining structure in general atmospheric environment which is contacted with nitrogen dioxide in automobile exhaust was analyzed. The neutralization experiment was carried out by nitric acid solution (pH=2) immersion method. Neutralization process of shotcrete was examined via physical and mechanical properties, damage depth and pH value and nitrate ion content of shotcrete. Afterwards, the mineral phases composition and microscopic morphology of neutralization zone were characterized using XRD, TG-DSC and SEM, which investigated the neutralization mechanism of shotcrete. The durability deterioration process of nitric acid exposed shotcrete included three steps of neutralization reaction, hydration products decomposition, and aggregate spalling. The pH value of shotcrete decreased while nitrate ion content increased. With increase of experiment aging, hydration products (calcium silicate hydrate and Ca(OH)₂) content decreased while corrosion products (Ca(NO₃)₂, calcium aluminate nitrogen hydrate and kaolinite) increased. Microstructure of neutralization zone was damaged, which results in a rapid decrase of the physical and mechanical properties.

Abstract:imestone powder (LP) actually has hydration activity and can reacts with aluminate minerals, such as C₃A in Portland cement, and CA and CA₂ in aluminate cement (AC). The hydration product is calcium carboaluminate hydrate. In this paper, in order to study the hydration reaction, composite systems, which consist of limestone powder and aluminate cement, were analyzed by micro calorimeter, strength test and XRD. The results show that, LP could accelerate the hydration process of the system, and lead to a shorter induction period, an earlier and lower hydration heat peak in the hydration of aluminate cement. The more LP in the composite system, the faster the early hydration, but the lower the hydration heat of the composite system. 20% replacement of limestone powder is the most reactive and contributes significantly to the strength of the composite system. The more limestone powder in the composite system, the less hydration products of the aluminate cement. When the limestone powder content is 20%~40%, the XRD peak of calcium carboaluminate hydrate is relatively obvious. Accordingly, there is a optimal range of AC:LP in the composite system. It is concluded that a significant hydration reaction occurs between limestone powder and aluminate cement. The composite of limestone powder and aluminate cement is expected to produce a new type of cementitious material.

Abstract:An experiment was conducted to evaluate the effect of natural and rapid decay of Microcystis aeruginosa bloom on the production of CH₄, and the variations of water environmental factors as well as the release fluxes of CH₄ and CO₂ were also explored. The results indicated that the dynamics of water environmental factors and gas production during the decay of dense Microcystis aeruginosa followed a similar temporal pattern, and algal decay significantly promoted the production of CH₄ and CO₂. The CH₄ cumulative release of natural decay and rapid decay were 22.80 and 37.72 times that of control group respectively, and the CO₂ cumulative release of natural decay and rapid decay were 5.36 and 4.03 times that of control group respectively. There was little difference in total carbon (C) release between natural decay and rapid decay. However, the proportion of CH₄ in the gas released from rapid decay was 1.86 times that of natural decay. The correlation analysis revealed that dissolved organic carbon (DOC) was the dominant environmental factor affecting the release of CH₄ and CO₂. Moreover, the aromatic protein and soluble microbial metabolites of DOC were the main substrates for CH₄ and CO₂ production.

Abstract:Agricultural non-point source nitrogen has become the main source of environmental safety in the Three Gorges Reservoir. However, investigation on agricultural non-point source nitrogen pollution has not been studied in depth which agricultural land was the main source, and how to enter Three Gorges Reservoir. Purple soil sloping ploughland in Three Gorges Reservoir was taken as the studied object to explore the effect of ammonia volatilization on nitrogen pollution. The ammonia volatilization characteristics of ammonium bicarbonate, urea and compound fertilizer in typical farming modes, and the nitrogen budget in a small watershed were investigated. The study was conducted by using a paradigm of controlled experiments in situ. The results show that the ammonia volatilization flux of compound fertilizer is the lowest and the change is the most gradual. Meanwhile, the peak value of ammonia volatilization flux of urea lags behind and decreases slowly, while that of ammonium bicarbonate appears earlier and decreases faster. The ammonia volatilization loss ratio of urea, ammonium bicarbonate and compound fertilizer in the watershed are 8.82%~18.37%, 17.86%~30.70% and 2.56%~3.86%, respectively. Besides, the ammonia volatilization loss ratio is in order:ammonium bicarbonate > urea > compound fertilizer, and the ammonia volatilization loss ratio between typical land use is in order:paddy field > fruit forest > dry land. Moreover, it is found that chemical fertilizer and ammonia volatilization are the most important nitrogen inputs and outputs in the watershed, and soil nitrogen residues are serious, which increases the risk of nitrogen loss. From the perspective of environmental friendliness, reducing the frequency of ammonium bicarbonate use, reducing the amount of fertilizer applied to dry land and fruit forest, and optimizing the application structure of nitrogen fertilizer in the Three Gorges Reservoir are effective ways to reduce ammonia volatilization. The reduction of ammonia volatilization is of great significance for the prevention and control of nitrogen pollution in the Three Gorges Reservoir.

Abstract:Wastewater treatment is a complex process with high energy consumption and low efficiency. Different from the traditional concept of wastewater treatment, the pollutants contained of wastewater can be regarded as energy materials or as the raw materials of other products to be havested to reduce the energy consumption. The forms of the pollutants' embodied energy in wastewater were examined by employing two calculation methods and taking sewage and coking wastewater as examples. Moreover, two possible path ways for the utilization and maximization of the recovery of embodied energy during the wastewater treatment were discussed. The different forms of energy consumption and their causes in wastewater treatment process were analyzed based on thermodynamic laws and quality characteristics of the wastewater, with reasonable assumptions. The laws of energy transfer and distribution of two specific cases are expressed by the energy flow diagram. Some possible energy-saving approaches and wastewater treatment methods in the future are predicted by comparing different energy saving technologies. Based on in-depth understanding of the embodied energy in wastewaters, valuable elements such as nutrients (nitrogen, phosphorus) and heavy metals can be separated and recovered, and water resources can be reused by combining with related industries and technologies. Therefore, the goal of energy saving can be achieved by the indirect compensation of energy consumption in the wastewater treatment process.

Abstract:Room air conditioner (RAC) is the important facilitly to improve the indoor thermal environment in the Yangtze River Basin in China. However, the current study couldn't get an in-depth stady of the set temperature behavior of the RAC due to the limitation of the data acquisition method. In order to get the set temperature behavior of the RAC in the Yangtze River Basin, the distribution of the set temperature, the adjustment behavior of the set temperature, the relationship between the set temperature and the time of a day and the relationship between the set temperature and outdoor air temperature were statistically analyzed based on the big monitoring data platform. After the data processing, tens of thousands of times of RAC running data in summer and in winter from a total of 575 room air conditioners in Chongqing, a total of 430 room air conditioners in Wuhan, a total of 540 room air conditioners in Shanghai was obtained, which was aimed at three typical cities in the Yangtze River Basin. The results show that there are some differences between the set temperature behavior and its adjustment behavior in three typical cities. Besides, the short time requirement of the lower set temperature (below 26℃) exists in once running period in summer and the set temperature is also related with the time of a day and the outdoor air temperature.

Abstract:Naturally ventilated sports buildings in Guangzhou were taken as studied object in this study, and the parameters of indoor thermal environment and the thermal sensation votes of exercising people and spectators were collected by field measurement and questionnaires respectively. The adaptive thermal comfort models and comfort ranges of these two groups of people were initially established and then compared. The results showed that the thermal sensitivity of exercising people in the natural ventilation sports building is 0.326 6, which is lower than that of spectators (0.379 9). The neutral temperature of exercising people and spectators increases with the increasing of outdoor air temperature, which of the former is 0.80℃ to 1.48℃higher than that of the latter. And the upper and lower limits of thermal comfort range of exercising people and spectators increase with the increasing of outdoor air temperature, and the lower limits of thermal comfort range of the former is similar as that of the latter, while the upper limits of thermal comfort range of the former is 1.86℃ to 2.48℃ higher than that of the latter.

Abstract:The severe cold climate zone in China has a wide distribution range with complex climate conditions, which was divided into 3 subzones according to heating degree days based on 18℃ (HDD18). In order to investigate the rationality of the current second level index for dividing climate region for building thermal design, the annual cumulative heating loads of typical buildings in 61 cities in severe cold climate zone were simulated by EnergyPlus software. The climatic characteristics of several cities were compared and the relationship between HDD18 and annual cumulative building heating load were explored. The results show that the annual cumulative building heating load in low-altitude region is much higher than that in high-altitude region with similar HDD18. The annual cumulative building heating load is linearly correlated with HDD18 only in the regions with small differences in solar radiation intensity and summer temperature. Therefore, HDD18 is suitable for zoning in areas with small differences in solar radiation and summer temperature, which should be combined with the solar radiation to divide climate region in severe cold climate zone.