Gongcheng Kexue Yu Jishu/Advanced Engineering Science

Surface roughness of structures is a primary factor that affects the mechanical properties of soil-structure interface. To further study the effect of roughness on shear strength of interface, large-scale direct shear tests were performed on clay-concrete interface under different roughness conditions and the influence mechanism of roughness on peak shear strength of interface was revealed. The results showed that the shear stress-displacement curves of clay-concrete interface exhibited strain-softening under different roughness conditions, and the greater roughness, the more obvious peak point of curve. Increasing roughness could obviously increase the peak shear strength of interface and there existed a critical roughness in terms of its influence on peak shear strength of interface. Morphological characteristics of the shear failure plane of different rough interfaces indicated that the smooth interface mainly occurred shear slip failure during the shearing process, and the friction and occlusion between clay particles and concrete were strengthened with increasing roughness, which resulted in the internal shear failure of clay. The shear strength of interface can be approximately divided into two parts: the shear strength of smooth interface and the shear strength of soil in rough parts. A new peak shear strength model of interface considering roughness was established by introducing a roughness-related coefficient into Jewell’s model and proposing a function to describe the relationship between the coefficient and roughness. Finally, comparison results between calculated value and test value showed that maximum relative error was 11.01% and mean relative error was 4.74%, which verified the accuracy and rationality of the proposed model.

In order to improve the denitration performance of La-Mn perovskite catalyst, a series of Ce modified perovskite La-Mn composite oxide catalysts were synthesized by citric acid sol-gel method. The structure, morphology, composition and surface physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), N2 adsorption-desorption (BET) and temperature programmed technology (H2-TPR/NH3-TPD).The results of the activity test showed that the denitration performance of Ce modified perovskite type La-Mn composite oxide catalysts are improved. When the Ce/Mn molar ratio is 0.2, the catalyst has the best denitration activity. The NOx conversion rate could reach 90% at 135 ℃, and maintaining more than 90% NOx conversion in the temperature window range of 135～260℃. XRD results showed that the perovskite type La-Mn composite oxide modified by Ce has porous structure and could maintain the perovskite structure of LaMnO3.15. However, Ce ions do not completely enter the perovskite structure, and some of them cover the catalyst surface in the form of oxides. At the same time, part of Mn ions in the lattice overflow from the perovskite structure in the form of Mn3O4, thus maintaining the structural stability and charge balance. SEM and BET results showed that the specific surface area of the catalyst increases and more active sites are provided after the introduction of Ce, which promotes the denitration reaction. XPS results showed that Ce modified catalyst produces more Mn4+ and chemically adsorbed oxygen, which promotes the oxidation of NO. The results of temperature programmed technology showed that the catalyst modified by Ce has better redox performance and more acidic sites, which is conducive to the denitration reaction. Therefore, Ce modified La-Mn composite oxide could improve the denitration performance by promoting NO oxidation and NH3 adsorption.

Gas-containing coal is a two-phase dielectric composite material with porous characteristics and solid-gas coupling characteristics. In order to accurately simulate the physical and mechanical properties of gas-containing coal, based on similarity criteria and similarity scales of main control parameters, with more than 80 sets of material matching tests and mechanical parameter tests, a similar material for coal-gas two-phase medium was developed. The similarity between similar materials and raw coal was compared, and based on the new material, a three-dimensional simulation test of coal and gas outburst was performed. The main conclusions were as follows. 1) The elastoplastic parameters and adsorption parameters of new material prepared by pulverized coal and sodium humate aqueous solution as aggregate and binder is similar to raw coal. Similar materials with different elastic-plastic parameters can be prepared by adjusting the material ratio. The adsorption of similar materials is consistent with that of raw coal. 2) The expansion energy of the binary mixture of CO2 and N2 is between CO2 and N2. The proportional coefficient of expansion energy and CO2 volume fraction are quadratic functions. The expansion energy of the mixture with 45% CO2 volume fraction is consistent with that of CH4. The binary mixture of CO2 and N2 can be used as similar gas to CH4, and it is safer than CH4. 3) The new material is highly similar to the physical and mechanical parameters of raw coal containing gas, which realizes the simulation of gas-solid coupling characteristics. 4) A three-dimensional physical simulation experiment reproduces the phenomenon of outburst caused by uncovering coal, and the morphology of outburst holes and the quality of outburst pulverized coal that are close to the field are obtained, which verifies the rationality of similar materials, and also provides a scientific means for further study of the law of outburst and monitoring the precursor information of outburst.

The macro mechanical properties of slope are determined by the meso parameters of soil particles and their motion. Although the stress and deformation characteristics of slope at the macro level can basically be obtained by the finite element method based on continuum model, it is difficult to reveal the deformation and instability mechanism of slope in the micro scale, and there are obvious limitations. The three-dimensional DEM-CFD model of fluid solid interaction of coal measure soil slope was established by coupling DEM and CFD. The meso mechanism of coal measures soil slope failure under rainfall was analyzed. The results show that the failure mode of coal measure soil slope simulated by DEM-CFD is mainly of rain erosion, and the slope sliding surface is predicted to be of approximate straight-line section, which is very close to the range of rain erosion of slope in outdoor model test. This shows that the numerical method is suitable to analyze the stability of coal measure soil slope. Micro parameters such as force chain, coordination number and porosity of soil particles in slope will change during the rainfall. For example, the porosity of particles on the top of slope changed from 0.35 in initial state to 0.8 in unstable state. The change of these micro parameters is directly related to the macro mechanical performance of the slope soil. In this paper, the law of the failure evolution of the coal measure soil slope under the rainfall was explained through the analysis of the micro parameters change of the particles. The research results of this paper not only provides theoretical basis for the protection design and construction of the coal measure soil slope in this area, but also provides a new way of analyzing the macro mechanical laws in geotechnical engineering from the micro perspective.

With the development of computer technology, grid division technology is becoming more mature. Considering the frequent occurrence of floods due to climate change, the broad extents of calculation domains, the wide range of actual terrain, and the study area usually has narrow and long gullies and wide flooding areas, this paper proposes a structured non-uniform grid model with hierarchical topological relationships combined with a high-resolution model based on GPU acceleration to simulate the surface water flow process. High-quality grids affect the calculation accuracy and efficiency of the model. The principle of grid division is designed based on the gradient change of terrain elevation, and key terrain features are detected in the computational domain that requires high-resolution grids to reliably solve shallow water equations. Moreover, local area grids can be statically encrypted, so that the sensitive area of the water level calculation can be captured more accurately, while reducing the number of calculation grids and reducing the calculation cost. The numerical model adopts Godunov-type finite volume method for spatial discretization, uses the second-order TVD-MUSCL format to improve the temporal and spatial accuracy of the model, and uses GPU parallel technology to greatly increase the running speed of the model without reducing the calculation accuracy. The performance of high-resolution models on non-uniform grids is demonstrated by the more accurate simulation of flood inundation time and inundation area through ideal and practical cases. The results show that the numerical model based on the non-uniform grid has good stability, compared with the uniform grid, its running speed is about 2-3 times under the premise of ensuring the simulation accuracy and the efficiency is further improved on the basis of GPU acceleration. The new model is suitable for simulating large-scale flood evolution and urban inundation processes in complex areas, which has good potential in actual large-scale flood simulation.