Abstract:The analytical solution of the traditional two-dimensional dispersion test theoretical model cannot describe the tailing phenomenon. Therefore, this paper established an exponential decay model to simulate the C-t curve concentration drop in the two-dimensional dispersion test and verified it by the indoor two-dimensional dispersion test. It is found that the simulation effect is better. By changing the hydraulic gradient and concentration, the significance and change rules of the relevant parameters α, β of the exponential decay model are studied. The results show that α is the rate of change of pollutant concentration with time, and β is the ratio of the initial concentration of the source hole to the peak concentration of the measured hole. The greater the pollutant concentration, the smaller the α value, the slower the decay rate of pollutants, the longer the tail time; the greater the hydraulic gradient, the larger the α value, the faster the pollutant attenuation rate, and the shorter the tailing time, and the β value is independent of the flow rate; the farther away from the source hole, the smaller the α value, the pollutant attenuation, the slower the speed, the longer the tailing time, while the β value becomes larger and larger, and the peak concentration of the C-t curve becomes smaller and smaller.

Abstract:In order to explore the reinforcement mechanism of fiber to soil, a direct shear test was carried out by discrete element method to analyze the particle movement characteristics of texsol and plain soil in the shear process. A plain soil model and a texsol model with 0.6% fiber content were established. Besides, three typical displacement points were selected to analyze the movement characteristics of plain soil and texsol at the typical displacement points. Conclusions are as follows. The texsol has a larger displacement at the shear part and a smaller displacement at the upper part, showing greater integrity. Before the peak displacement, the large corner area of texsol is larger than that of plain soil. After the peak displacement, the large corner area of the plain soil is coarse, and there is basically no large corner area in the surrounding soil; the large corner area of the texsol is thin, and the large corner area is in the surrounding soil, distribured in strips. The large turning angle of texsol is mainly distributed at the shear and fiber. The shear zone of plain soil is larger than that of texsol. The relative sliding and relative rotation of the texsol in the shear zone are slightly larger than that of the plain soil. The relative sliding and relative rotation of the texsol and plain soil outside the shear zone are not much different. Both the relative sliding and the relative rotation of the soil inside and outside the shear zone increase with the development of shear.

Abstract:This thesis obtained the mechanical parameters of rock specimens through rock mechanics tests on a rock sample in a mining area in Jiangxi and applied the Hoek-Brown Criterion to estimate the rock mass mechanical parameters. Combining the fractal theory and the Monte Carlo method, a jointed rock mass network was generated, and jointed rock mass simulation specimens were taken by using the center of the jointed rock mass network as the base point. The discrete element software UDEC was used to stimulate the numerical experiment of the jointed rock mass compressive strength. The results show that controlling for the sampling angle and confining pressure, the increase in rock mass size correlates with the weakening of the anisotropy of the jointed rock mass. The compressive strength of the jointed rock mass shows a non-linear decrease trend and tends to a certain value, which can be fitted into a negative exponential change relationship; controlling for the confining pressure and size, the increase in the sampling angle will result in a slight fluctuation of the compressive strength of the jointed rock mass, which can be explained by the fractal characteristics of the joint distribution. The size effect and confining pressure effect of the jointed rock mass are more obvious when the sampling angle is at 60°, where the compressive strength value is slightly higher; when sampling angle and size are controlled for, as the confining pressure increases, the anisotropy of the rock mass weakens, demonstrating a linear increase in compressive strength.

Abstract:In order to study the anti-explosion effect of polyurea coating on H-section steel columns, the anti-explosion numerical analysis of sprayed polyurea elastomer H-section steel columns was carried out based on ANSYS/LS-DYNA finite element software. The dynamic response of H-section steel columns under explosion was studied. The protective effect of different polyurea thickness on H-section steel columns and its mechanism were analyzed. It is shown that when the shock wave propagates along the weak axis of the steel column, the maximum destructive effect of the shock wave on the steel column appears in the center of the web near the base of the steel column, and the polyure coating can effectively improve the overall stiffness and anti-explosion ability of the H-section steel columns, greatly reduce the overall and local deformation of the steel column, and reduce the absorbed internal energy of the steel column.

Abstract:The measured steel strut stress is often less than the design value of steel strut prestress in deep excavation engineering. The insufficient of steel strut prestress has an important effect of the steel strut reducing the large deformation of the retaining wall of excavation. A two-dimensional numerical calculation model as a subway station case in Nanjing was established by using Midas GTS software. The suitability of the calculation model and parameters was verified by the comparison of the field monitoring data and numerical calculation results. Then the influence of the strut prestress value on the horizontal displacement of the retaining structure and the final steel strut stress was analyzed. The results show that the steel strut prestress is an effective method to overcome the small compressive stiffness of steel strut in the theory and improve the actual compressive stiffness of steel strut supporting. Taking the design value of steel strut prestress as a reference, the prestress ratio has a negative linear relationship with the maximum horizontal displacement of the wall, and insignificant influence on the final value of strut stress. The economy is the best for 40% of the prestress ratio in the effect of strut prestress. The low and high bidirectional warning method and the corresponding strut prestress ratio are also proposed on basis of the strut stress particularity.

Abstract:Considering the influence of the type and content of anti-cracking admixture, the evolution of compressive strength of fly ash concrete under the conditions of curing and sulfate corrosion was studied. The test results show that the effect of UEA expansion agent is the same under different fly ash content, and the effect of HME-V high-efficiency anti-cracking agent is different. During the curing period, the compressive strength value of 30% fly ash mixed with UEA or HME-V is stable after 90 days. The best strength content is 5% and the loss of the specimen with 5% content is the lowest after sulfate corrosion. With the increase of fly ash content (10%~30%), the compressive strength at 28d of the two kinds of anti-cracking admixtures decreases. The strength of UEA specimens cured with 30% fly ash content is higher than that of HME-V specimens. After sulfate corrosion, the strength of HME-V specimens is higher than that of UEA. HME-V admixture can better delay the loss of mechanical properties caused by sulfate corrosion than UEA.

Abstract:In order to study the flexural behavior of external formwork with composite fireproof and self-insulation, six specimens were tested under loading. The failure modes, mechanical properties, flexural strength and the correlation between flexural strength and elastic modulus of specimens were analyzed. The test results show that the failure patterns of external formwork with composite fireproof and self-insulation are all manifested as cracks in the middle span mortar layer at the bottom, and the crack direction is perpendicular to the longitudinal axis of formwork and runs through the whole width. The load-displacement curves of the specimens were basically consistent, and the average values of the maximum load, flexural strength and elastic modulus are 846.34 N, 2.59 MPa and 5 125 MPa, respectively, which meets the requirements of the requirements of the corresponding specifications and have good flexural behavior. The flexural strength and the elastic modulus of the external formwork with composite fireproof and self-insulation are at the 0.01 level (R=0.972 5), showing a strong linear correlation.

Abstract:In order to evaluate the health status of prestressed concrete continuous rigid frame bridge accurately, a comprehensive evaluation method based on Analytic Hierarchy Process (AHP) and fuzzy theory was proposed. Firstly, the three-layer state evaluation index system (bottom-middle-top) of prestressed concrete continuous rigid frame bridge was established with the method of chromatography analysis, the grade division for index state of each layer and overall evaluation state was determined, and the quantitative index evaluation standard of each layer in the state evaluation system of prestressed concrete continuous rigid frame bridge was established. Secondly, the membership function of trapezoid and semi trapezoid was selected, the main steps of fuzzy comprehensive evaluation method of prestressed concrete continuous rigid frame bridge were established, and the calculation methods of constant weight, variable weight and evaluation vector of each index in the state evaluation system were proposed. Finally, the method was applied to the state evaluation of Qinjiang third bridge. The results show that the state evaluation method of prestressed concrete continuous rigid frame bridge proposed can evaluate the state of prestressed concrete continuous rigid frame bridge, the state of Qinjiang third bridge evaluated by this method presents "good", which is consistent with load test results. Feasibility and effectiveness of the proposed method are verified.

Abstract:The excavation of the tunnel will inevitably cause the lateral movement of the surrounding soil, which will cause horizontal deformation and additional bending moments of adjacent pile foundations. At present, the modeling and calculation process of finite element numerical simulation is relatively tedious. In order to solve the problem of pile-soil interaction under tunnel excavation, based on Winkler foundation model, a two-stage analysis method was used to establish a passive pile stress analysis under tunnel excavation conditions. The governing equation of pile-soil interaction was derived and the approximate solution is given based on the finite difference idea. Finally, the results combined with the engineering example shows that the approximate solution is in good agreement with the field monitoring data and can effectively analyze the influence of tunnel excavation on adjacent pile foundations.

Abstract:The accurate prediction of steel prices is helpful for construction companies to formulate reasonable material procurement strategies. For the current steel price prediction research, the long memory of its price changes is not considered, resulting in the loss of effective information in the modeling process and the increase of prediction errors. In this paper, the ARFIMA steel price prediction model considering long memory was established. The steel price prediction was carried out based on the price of rebar in Qingdao from January 2014 to June 2019. The predicted values of the ARFIMA model and ARIMA model were used for comparative analysis of the true value. The experimental results show that the accuracy of the steel price prediction of the ARFIMA model is 1.7% higher than that of the ARIMA model, and the prediction effect is more stable.

Abstract:In order to maximize the benefits of cascade reservoirs in the lower reaches of Jinsha River under different typical years and different operation periods, the optimal operation model of reservoir groups in the lower reaches of Jinsha River was designed to maximum power generation and minimum square sum of water shortage. NSGA-II method was used to solve it, which obtained the non-dominated solution set under different typical years and partial periods. The replacement ratio was introduced to analyze the competition between the two targets. In addition, the water level process under different preferences in dry years was analyzed. The results show that between power generation and water supply targets,the competition is mainly reflected in the reservoir impounding period and the water supply period. The coordination is between the flood season and the pre-flood ebb period. The replacement ratio of water-power generation target shows an increasing trend with power generation. According to the replacement ratio curve, the influence on water supply is obtained with increasing unit generating capacity under different cascade generating capacity. Setting reasonable generating capacity in actual dispatching can maximize the target benefit of power generation and water supply.

Abstract:This paper evaluated the ecological security of a typical composite ecological system with the case study of Lu An Wangzhuang mining area in Changzhi, Shanxi Province. Based on the pressure-state-response (PSR) model, the evaluation index system was assumed. According to the structural characteristics of the index system, the weights of the indicators were calculated by Analytic Network Process method (ANP), and weights sensitivity analysis was used to determine sensitive factors which affected the ecological security of the mining area. The evaluation results reveals that: (1) the ecological security integrated index of Wangzhuang mining area showed an increasing trend year by year, from 0.560 in 2006 to 0.712 in 2010. Ecological security became relatively safe in this area after 2009 and responsive actions in recent years played a key role to this change; (2) Due to greater weights and more changeable values, 9 indicators such as GDP increasing rate, Waste water recycling rate, Per capita green area shows relatively sensitivity to ecological security integrated index. More attentions should be paid to insensitive indicators in low level and sensitive indicators which have downward trend in order to further improve the ecological security of this mining area.

Abstract:Based on the analysis of 18 coal-measure source rock samples of Jurassic in Junggar basin, the results of rock pyrolysis, organic carbon test, vitrinite reflectance test and microscopic component identification show that the evaluation results of organic matter types obtained by pyrolysis method and microscopic type index method are contradictory.When pyrolysis method was used to determine the type of organic matter in source rocks of coal measures, the type of organic matter in coal measures is the best, followed by carbonaceous mudstone, and mudstone is the worst; while when organic micro type index method was used to determine the type of organic matter, the type of organic matter in mudstone is the best, followed by carbonaceous mudstone, and coal is the worst.It is found that the vitrinite, which is traditionally believed to be non hydrocarbon generating, has an important contribution to hydrocarbon generation.The recognition of hydrocarbon generating ability of vitrinite is the key to the contradiction between the two methods of organic matter type evaluation.For the source rocks of coal measures, the classification of organic matter types by pyrolysis method is more accurate and economical.

Abstract:The abandoned loess cave slope of Sipo Village, Chang'an District in southwest of Bailu Plateau was taken as the research object in this paper. And the characteristics of stress and strain of the cave slopes under different cave states were simulated with the help of MADIS GTS NX finite element software, thus further revealing the deformation and failure mechanism of the abandoned loess cave slope and put forward corresponding prevention measures. The analysis and summary of the MADIS numerical simulation results of the cave slopes in different states shows: as the cave is abandoned, the increase of the soil moisture content leads to the decrease of the mechanical properties of the soil and the loss of the local free surface soil. Furthermore, with the effect of rainfall, the mechanical properties of the soil are further reduced, and the arch structure of the cave is destroyed, which causes the collapse of the slope where the cave is located and other overall failure.

Abstract:Based on the project of "Geological Hazard Investigation and Special Research of Zhenba County in the Middle River of Hanjiang River", and combined with regional geological environment overview, remote sensing interpretation and fieldwork, the development regularity of geological hazards in Zhenba County were studied. According to the results, there are nine conditioning evaluation factors: slope height, slope, slope shape, rainfall, engineering geological rock group, distance from fault, distance from river, human engineering activity and disaster point density, which were extracted. Then the judgment matrix of conditioning factors and factor classes were conducted by analytic hierarchy process method,and geological hazard index was built. Finally the geological hazard of Zhenba County was assessed and the risk of geological hazard map was classified. The results are as follows: (1) the main types of geological disasters in Zhenba County are landslides, collapses, and debris flows, including 93 landslides, 6 collapses, and 4 debris flows;(2) Geological disasters are mostly developed in concave-convex slopes, slopes with angles of 0°~10°, slopes with undulations of 0~30 m, and are concentrated in low mountains with elevations of 500~800 m on both sides of the valley;(3) The risk of geological hazard map can be classified into three classes, including high, moderate, and low, with an area of 62.05 km², 143.43 km² and 224.57 km² respectively. High-risk areas are mainly distributed in the Jingyang River Basin, accounting for 14.4% of the total area.

Abstract:By using high-pressure thermal compression (HPTC), the blends of SmCo-based amorphous-nanocrystalline powders and the commercial Nd-Fe-B nanocrystalline powders were deformed, and the bulk anisotropic nanohybrid SmCo₇/Nd₂Fe₁₄B magnets were successfully prepared. The microstructure and magnetic properties of the obtained magnets were studied by XRD, TEM and VSM. The experimental results show that the obtained SmCo₇/Nd₂Fe₁₄B magnets are composed of SmCo₇ and Nd₂Fe₁₄ nanocrystalline regions, and the SmCo₇ and Nd₂Fe₁₄B nanocrystals possess a (00l)texture along the pressure direction (parallel to the pressure direction). Magnets exhibit an obvious magnetic anisotropy and a maximum energy product of 16 MGOe at room temperature (RT) along the pressure direction. Moreover, the obtained magnets have a good thermal stability with a low β_{(RT-250 ℃)}=-0.26% ℃^-1.These findings demonstrate that the bulk anisotropic nanohybrid SmCo₇/Nd₂Fe₁₄B magnets have high potential to be applied in national defense, military industry, rail transit and other scientific and technological fields.