Abstract:The test uses a ternary cementing system of ordinary Portland cement, sulphoaluminate cement and hemihydrate gypsum, and chooses machine-made sand as fine aggregate to prepare fully machine-made sand cement-based self-leveling mortar; chooses fly ash, stone powder and silica Ash as a mineral admixture to study the influence of mineral admixtures on the fluidity, compressive and flexural strength and dimensional change rate of cement-based self-leveling mortar made of fully machine-made sand. The pozzolanic effect of mineral admixtures has a positive impact on the development of the mechanical properties of self-leveling mortar, and the fluidity of self-leveling mortar decreases with the increase of silica fume content. The formula of self-leveling mortar is optimized through orthogonal experiments, and the best content of the excellent mineral admixture:fly ash 7%, limestone powder 4%, silica fume 1.0%.

Abstract:An index parameter called the maximum area shrinkage-cracking ratio (SCR) was proposed in this paper. It was defined as the ratio of the total area of shrinkage cracks of soil after drying to the initial surface area of the soil sample in a standardized mold. The effect of four factors namely, initial water content, initial sample thickness, mold surface roughness and test temperature were investigated using the soil samples from many different regions. After that, the reliability of using SCR to classify expansive soil was analyzed. Finally, the classification of expansive soil by SCR is proposed. The test results show that the initial water content and mold roughness have little influence on the identification and classification. When the sample initial thickness is limited to 8 mm, the influence can be ignored. The recommended drying temperature is 105℃. Besides, SCR is linearly correlated with the montmorillonite content and cation exchange capacity, which can reflect the nature of expansive soil; The linear correlations between SCR and standard moisture absorption water content and plasticity index indicate that it is highly reliable to identify and classify expansive soil using SCR. The maximum area shrinkage-cracking ratio test is simple and credible.

Abstract:In order to increase the strength of sand, water-soluble polymer was used to improve it. The direct shear test was carried out on the improved sand with different dry density, curing agent content and curing time, and the cohesion and internal friction Angle were analyzed. The results show that the shear strength of sand improved by water-soluble polymer is improved to a certain extent, which is due to the fact that water-soluble polymer strengthens sand samples and forms elastic mucosa wrapped with particles and connected with each other, thus increasing the strength of soil. When the curing time is constant, the shear strength of the improved sand increases with the increase of curing agent content. The maximum cohesion of the sample can reach 183.52 kPa. When the curing agent content is constant, the shear strength of the improved sand increases with the increase of curing time. The maximum cohesion of the sample can reach 200.19 kPa. The shear strength is positively correlated with curing agent content, curing time and dry density of the sample. Elastic mucosa formed by water-soluble polymer solution in sand wraps sand particles and fills sand voids, thus enhancing interaction between soil particles and improving engineering properties of sand.

Abstract:Phase transformation and volume expansion of pore water at low temperature are the main reasons of the frost heaving damage in rock. The tensile strength of rock after freeze-thaw cycles is worthier of attention than the compressive strength. To investigate the mechanics of rock under tensile stress, this work proposed an approach based on the concepts of pore water particle and volume expansion to simulate the processes of phase transformation and frost heave of pore water at low temperature. The equation for expressing the relationship between the volume of pore water particle, temperature, and unfrozen water content was derived. Then, the new proposed approach was used to carry out the simulation of freeze-thaw cycles on water rich rock samples. The feasibility and reliability of the new proposed approach were verified by comparing the simulated results with the laboratory test results. Simulated results indicate that cracks inside the disc formed during the process of freeze-thaw cycles tend to gather near the surface. When the number of freeze-thaw cycles is small, the cracks inside the disc formed during the splitting test are mainly concentrated near the center line of the disc, while a large number of cracks will be generated far from the center line of the disc when the number of freeze-thaw cycles is large. The tensile failure rate is much higher than the shear failure rate in both the processes of freeze-thaw and Brazil splitting test.

Abstract:The material parameters of glass fiber reinforced plastic (GFRP) bolt were defined by writing VUMAT subroutine. Orthotropic anisotropic modeling was carried out considering the non-uniformity and damage characteristics of the interface between GFRP bolt and mortar. The bond slip characteristics of the interface between GFRP bolt and mortar were simulated sectionally by ABAQUS. The distribution of axial force and interfacial shear stress of GFRP bolt were explored, and the interface mechanical properties of GFRP bolt-mortar with different diameters were analyzed. The results show that the piecewise finite element model can better reflect the bonding characteristics of GFRP bolt-mortar. With the increase of the applied load, the axial force of the GFRP bolt gradually increases, the load transfer depth gradually deepens. The anchoring effect gradually plays from top to bottom. The maximum pull force and interfacial failure displacement of GFRP bolt increase with the decrease of diameter. The critical diameter of slip failure and strength failure is 28 mm. The slip failure occurs when the diameter is larger than 28 mm and the strength failure occurs when the diameter is less than 28 mm. The anchorage coefficient K₁ of 28 mm diameter GFRP bolt is determined to be 0.155.

Abstract:In order to study the seismic performance of Engineered Cementitious Composites (ECC) double steel plate-concrete combined shear wall, a numerical simulation model of 3 double steel plate-concrete combined shear walls and 12 ECC double steel plate-concrete combined shear walls at different ECC heights was established.The best suitable shear height of the combined ECC wall was determined by comparing the shear performance of the ECC double steel plate-concrete combined shear wall with different shear span ratios.The results show that the peak load and yield load of ECC double steel sheet-concrete combined shear wall are improved.The addition of ECC greatly improves the ductility and energy consumption power of the whole structure, but ECC affects little stiffness degradation at moderate to high shear span ratio.At the shear span ratio of 1.0, ECC optimal height was 36 mm.At the shear span ratio of 1.5, the optimal height of ECC was 180 mm.When the shear span ratio is 2.0, the ECC best height of 72 mm, double steel plate-concrete combined shear wall has the best seismic performance.

Abstract:The silo-frame structure is characterized by high center of gravity, high loading, poor overall stability and local stability, which is easily damaged under earthquake. In order to mitigate the damage of the silo-frame structure under earthquake, based on the project of degasification and storage silo-frame structure of a petrochemical company, ANSYS software was used to establish the finite element models of single silo-frame structure and seismic isolation structure respectively, and the dynamic response of the original structure and seismic isolation structure was analyzed under two working conditions of empty and full silo. The data of stress, displacement and strain of the silo-frame isolated structure model under different working conditions were analyzed by using the vibration decomposition reaction spectrum method and time course analysis method. The data analysis shows that the use of vibration isolation bearings can significantly improve the seismic capacity of the structure and the time course analysis is more accurate than the vibro-decomposition reaction spectrum method. A few suggestions has been put forward for the design of future silo-frame structures.

Abstract:Relying on the Guangzhou Metro Line 8 shield tunnel side-crossing the Huanan Express Viaduct pile project, and considering the situation of bridge piles with and without isolation piles, the finite element numerical model was established to study the ground settlement before and after reinforcement, the changes in additional axial force and bending moment of bridge piles, and the pile displacement. Then reinforcement optimization design was carried out. The results show that the isolation piles can effectively reduce the pile top displacement of existing bridge piles perpendicular to the driving direction. Due to the traction effect of the isolation piles, there is basically no reduction in the displacement of the middle of the bridge piles, and even a very small increase in the horizontal displacement. The isolation piles, which have a certain shielding effect on existing bridge piles, basically eliminate the horizontal displacement of bridge piles parallel to the driving direction. The isolation piles greatly reduce the additional axial force of the bridge piles, greatly reduce the additional bending moment of the bridge piles in the vertical shield direction, and basically have no effect on the additional bending moment in the parallel shield direction. Properly increasing the diameter of the isolation pile and the distance between the isolation pile and the bridge pile can effectively reduce ground settlement. It is recommended to set the isolation piles within 6 to 8 m away from the tunnel, so as to meet the safety net distance required by the specification and to protect the existing bridge piles to a greater extent.

Abstract:In order to deeply study the variation of stress distribution of grouting anchor, taking the excavation of circular tunnel as an example, the grouting anchor and surrounding slurry are regarded as anchor solids, the stress characteristics of anchor solids are analyzed, and the expressions of axial stress and shear stress of anchor solids are derived. The rationality of theoretical analysis is proved by theoretical analysis and numerical simulation, and the variation of stress distribution of anchor solids under different influencing factors is analyzed. The feasibility of the analytical method is verified by numerical simulation and theoretical analysis. The axial stress at both ends of the anchor is close to 0, and the axial stress at the neutral point is the largest; The smaller the bolt diameter is, the closer the neutral point is to the center of the tunnel; The length L of anchor has the greatest influence on the stress distribution, and the diameter d_s of anchor, the cohesion c of surrounding rock and the distance X₁ from the working face during the initial support construction have the second influence on the stress distribution.

Abstract:For analysis of hollow ceramic beads insulation effect on the carbon fiber cable snowmelt pavement heating rate, comprehensively considering road surface and the external environment and heat transfer characteristics of carbon fiber heating cable, using infrared thermal imaging technology and numerical simulation, the influence of the thermal insulation layer on the heating rate of the snow-melting pavement is analyzed, and the thermal insulation mechanism of the hollow ceramic microspheres is revealed. The results show that the heating rate of snowmelt road surface can be increased by 23.4%~35.3% by adding the insulation layer. In the test section with cable spacing of 200 mm and buried depth of 5 cm, after 2 hours of heating test, the highest temperature of road surface reaches 1.8℃ from -5.2℃, and the average heating rate is 3.5℃/h. The anti-heat insulation layer formed by the combination of hollow ceramic microbeads can absorb and reflect waves well, reduce the thermal conductivity, reduce the downward transmission of heat, so that the heat is mostly concentrated on the upper surface of the road, and the temperature field is more uniform. The material cost can be saved 88.3%~91.7% by adding hollow ceramic bead insulation layer to reduce the cable spacing.

Abstract:As the "internal source" of pollutants in water, polluted sediment has become a serious hidden danger of water environment for the water that exogenous pollution has been controlled. As a technique to prevent the secondary contamination of sediment, in-situ covering technology is limited in its development due to its disturbance to sediments during the covering process. To solve this problem, a new method using patchy soil as in-situ covering material has been proposed, and the law of material settling in water has been studied. The settlement experiment was carried out by using the silt as the material, and the relationship between the settling velocity of the material, its tangential Angle and its own properties was mainly concerned. The results show that the tangential Angle of the material does not affect the settling velocity of the stable settlement. When the material settlement is stable, the speed is proportional to the thickness and density of the material.

Abstract:Based on cluster analysis and factor analysis, the hydrochemical characteristics and influencing factors of water samples from 27 lakes in southern Tibet Plateau were studied. The results of cluster analysis showed that the lake hydrochemical parameters were spatially different due to the zonality of climatic conditions and the diversity of lake supply sources. The 27 water samples could be divided into 2 clusters and 5 sub-clusters, and their hydrochemical types were consistent with the evolution process of the lake. The results of factor analysis showed that the hydrochemical characteristics and influencing factors of different types of lakes were different. The main chemical type of fresh water lake was Na-HCO₃. Two factors were extracted to reveal the influence of the dissolution of carbonate and silicate minerals, and the dissolution of sulfate minerals and salt. The main hydrochemical type of saltwater lake is Na-SO₄. Three factors were extracted, which revealed the dissolution of carbonate minerals, the dissolution of sulfate minerals and salt, and the influence of human activities on the hydrochemical characteristics of salt lake. The main hydrochemical type of saline is Na-Cl, and two factors were extracted, which revealed the influence of the dissolution of rock salt minerals and silicate minerals, and the dissolution of sulfate minerals and carbonate minerals on the hydrochemistry of saline.

Abstract:When the slope stability is calculated, it is usually simplified to two-dimensional plane strain problem. The limit equilibrium method is used to calculate the safety factor after two-dimensional slicing of the main section. Obviously, it is a simplified model of the reality of a slope, although the phenomenon of slope failure occurred in the three-dimensional space. Strictly, a three-dimensional slope stability analysis should be performed. The paper provides a three-dimensional micro-column method which has expanded the traditional two-dimensional slice method and built the three-dimensional slope model based on high-resolution DEM. In this method, the soil slices in two-dimensional slice method have accordingly transformed the soil columns. Lastly, through analyzing the force condition of every column, based on the limit equilibrium theory, three-dimensional Bishop method is imbedded into GIS software platform by secondary development mode, and the three-dimensional spherical sliding surface is constructed and the three-dimensional factor of safety is calculated. The method realizes the automation and integration of 3-D model construction and 3-D safety factor calculation process, and expands the application of high-resolution DEM in geotechnical engineering field.

Abstract:In order to explore the resistance characteristics of heat exchange unit in heat pipes and optimize the design of the whole air supply system for the Mine ventilation shaft, the resistance analysis model of single module of heat pipe was established, and the wind resistance characteristics of different parallel modules were analyzed. On this basis, the resistance balance calculation method of heat pipe was proposed. At the same time, the laws of air inlet volumes in different shafts under different working conditions were analyzed. The results show that by changing the number of pipe exhaust, the distribution of wind speed is more uniform than the original design, and the resistance is reduced. The maximum wind speed difference is reduced from 2.1 m/s to 1 m/s, and the wind speed imbalance rate of the system is reduced from 80% to less than 20%. During the operation of the total air supply system, the air tightness is the most important factor to determine the fresh air intake. When the auxiliary air duct is opened, the intake air volume can reach 2600 m³/min, accounting for 26.8% of the total intake air volume.

Abstract:With the increasing demand for nickel ore in China, the import volume of nickel ore is increasing day by day. The fluidization of nickel ore in the process of marine transportation needs to be studied urgently. By means of indoor small vibration table modeling tests, the fluidization evolution process and the criterion for nickel ore's fluidization is studied. Firstly, with the aid of digital image acquisition and analysis system, the macro-evolution of nickel ore in fluidization process is analyzed, and the change rules of water content in layers and pore water pressure are studied. Based on the fluidization mechanism of nickel ore and the discrimination method for liquefaction of fine-grained soil, a new method for fluidization discrimination of nickel ore based on plasticity index is proposed. The results show that the fluidization of nickel ores is mainly caused by vibration softening under high water content conditions, during which water hardly migrates and pore water pressure hardly develops. The moisture content calculated by the discriminant method in this paper is basically consistent with the result of the model test. Therefore, the new method is suitable for determining the critical water content of fluidization of nickel ores with high fine particle content.

Abstract:We apply the multi-scale theory of wavelet transform to determine the optimal step parameter. More specifically, we decompose the original image using wavelet transform and according to the specific texture image, select the appropriate wavelet sub-image (approximate image or its detailed sub-image) for texture analysis. The texture feature parameter (contrast) of the decomposed image is utilized to determine the optimal step parameter. When the step parameter is optimal, the texture feature parameter reaches the extreme value of the period which is beneficial to texture analysis. As the amount of data in the decomposed image is less than that in the original image, both the computation complexity and the time consumed in finding the optimal step parameter are reduced. Furthermore, experimental results show that the optimal step parameter of the wavelet decomposed image is accurate.