Abstract:In order to study the influences of steel fiber capacity rate and recycled rough aggregate replacement rate on the split tensile and flexural tensile strength of destroyed pebble concrete, 15 sets of specimens with different steel fiber capacity rates of 0%, 1%, and 2% and different recycled rough aggregate replacement rates of 0%, 10%, 20%, 30%, and 40% were designed for splitting tensile tests and four-point bending tests. The test results show that the splitting and bending strengths of steel fiber recycled concrete are greatly affected by the capacity ratio of steel fiber, and both increase with the increase of steel fiber capacity rate, and are less affected by the replacement rate of recycled rough aggregate. In addition, both of splitting and bending strengths show a tendency of primary increasing and then decreasing with the increase of the replacement rate of recycled rough aggregate, and reach their maximum when the replacement rate of recycled coarse aggregate is 30%. Based on the experimental results, the practical relationship between the split tensile intensity and the flexural tensile intensity of steel fiber recycled concrete is suggested.

Abstract:The influence of the properties of the sediment on the dynamic response of the large diameter bored pile embedded in layered visco-elastic soil is analyzed in this study. First, the sediment is considered as a fictitious soil pile and the Rayleigh-Love rod theory is introduced to establish the longitudinal dynamic governing equations for the pile and the fictitious soil pile to approximately consider the three-dimensional effect of the pile. Then, the dynamic governing equation for the surrounding soil is built based on the three-dimensional axisymmetric model. By means of Laplace transform, impedance function recursion and inverse Fourier transform, the dynamic governing equations for the soil-pile system are solved to derive the solutions for the dynamic response of the pile in the frequency and time domain. Based on the established solution, the three-dimensional effect of the large diameter bored pile is portrayed and the influence of the properties of the sediment on the dynamic response of the pile is investigated. Finally, the reliability of the proposed solution is verified by comparing with the measured results.

Abstract:In response to the development idea of construction saving, rice husk ash is filled into red clay. The effect of rice husk ash on the road performance and micro mechanism of red clay is studied through a series of experiments. The results showed that the liquid plastic limit of red clay changed little with the addition of rice husk ash, the maximum dry density decreased with the increase of rice husk ash, and the optimal moisture content increased. The compressive strength of red clay mixed with rice husk ash increased first and then decreased with the increase of the content, and reached the maximum when the content was 15% and the curing time was 28 days. SEM test showed that the structural compactness of solidified red clay was improved, and in this process cementitious materials were produced. Using rice husk ash to improve red clay could be cost-effective in respect to roadbed stability, and can be beneficial in protecting the environment and realizing sustainable use of resources.

Abstract:The composite of xanthan gum and clay mixed with sand was used to analyze the crack characteristics of soil surface through a series of dry cracking tests under different xanthan gums and sand contents, and to explore the influence of different xanthan gums and sand contents on the crack resistance performance of soil. In addition, the mechanism of crack resistance is analyzed in depth, and the relevant results have certain reference value for the prevention and control of clay cracks in practical engineering. The results show that both xanthan gum and sand as additives can inhibit the crack development to a certain extent, and the soil under the combined action of them shows better crack resistance. When the content of xanthan gum in clay increases from 0 to 0.25%, the crack intensity factor (CIF) decreases from 11.586% to 0. When the sand ratio is less than 30%, the cracking of soil is less affected. The CIF of the sample without xanthan gum is between 10% and 14%. When the sand rate increases to 70%, the CIF decreases to 1.412%. The composite of sand mixed soil sample containing 0.15% xanthan gum does not crack. Xanthan gum can enhance the cohesion between clay particles and solidify with sand particles to form a stable structure, so as to improve the ability of soil to resist fracture and enhance the crack resistance of clay.

Abstract:Fluidity tests and unconfined compressive strength tests were carried out to study the influence of mud content on the curing effect of sandy soil. Based on the response surface methodology, the relationship models of mud content with fluidity and unconfined compressive strength were established for mixed samples with a water cement ratio of 2:1, and the influential laws were analyzed. The results show that the mud content and other factors affect the fluidity and unconfined compressive strength. The model obtained by fitting the test results is significant, and there is a certain mud content, which makes the fluidity and strength both have peak values.

Abstract:The traditional loess constitutive model is mainly composed of elastic model and elastic-plastic model. However,the assumption of elastic model on soil is too simple,and the elastic-plastic model sometimes does not meet the law of thermodynamics. Therefore,the loess constitutive model for elastic-plastic deformation based on the principle of maximum energy dissipation rate is more rigorous. Based on the constitutive model,a laboratory test scheme was designed to obtain the parameters of the model. Taking Southern Jing-Yang plateau as the study area,the value range of constitutive parameters and the form of hardening function of Q₃ Malan loess under different water content were studied. The results show that:the hardening function of the plastic shear strain of Q₃ Malan loess in Southern Jing-Yang plateau is hyperbolic,the value of parameter a ranges from 0.002 to 0.02,and that of parameter b ranges from 0.01 to 0.05; the hardening function of the plastic body strain is cubic,and its parameters m₁、m₂、m₃ are between 0.001 and 1;the volume modulus K ranges from 40 MPa to130 MPa and the shear modulus G ranges from 20 MPa to 60 MPa; compared with the experimental data,the constitutive model can accurately describe the stress-strain relationship of Q₃ Malan loess in Southern Jing-Yang plateau by using the parameters obtained from the experimental scheme.

Abstract:Three-dimensional finite element simulations of medium triaxial consolidation and drainage shear tests were carried out for a compacted clay and a soft soil under two end restraint conditions, corresponding to fully restricted end radial displacement and radial unconstrained (no end restraint and no friction), respectively. The strength and stress-strain results of specimens under different conditions were compared and analyzed to quantify the effects of end restraint conditions on the strength and stress-strain properties of the two soil materials. The results showed that the end restraint increased the strength of the soil but did not change the overall trend of the relationship curve between the axial deviatoric stress and axial strain, and that the effects of end restraints on the strength and stress-strain show a limited decrease with the increase of the surrounding pressure. In the triaxial test, compared with the radial unconstrained condition, the restraint caused by friction at the end of the specimen significantly increased the volume strain and the degree of softness of the soil had a larger influence on the bulk strain of the test. The average volume strain ε_v at the shear failure of end confined specimens increased by 17.2% for compacted clay soil and increased by 5.2% for soft soil compared to the radial unconstrained condition, respectively.

Abstract:Soil deformation has a significant stress path correlation, and the loading along different stress paths will have different stress, strain and strength properties. Understanding the stress-strain relationship under special stress paths such as lateral unloading is of great significance to the in-depth study of soil constitutive models and engineering design of foundation pit excavation. A stress-controlled triaxial apparatus was used to carry out lateral unloading triaxial consolidation drainage shear tests on a remodeled sample of silty clay in a certain engineering in Nanjing under the condition of K₀ consolidation, and the effect of dry density under the lateral unloading path was studied. The influence laws of the stress, strain and strength characteristics of silty clay are established. An empirical formula for the change of the internal friction angle of the soil due to the change of dry density is established, and an empirical formula for the lateral strain of the soil under the condition of lateral unloading is proposed. A method for estimating the ultimate displacement of the retaining structure of a foundation pit based on the proposed formula is proposed.

Abstract:In this paper, a three-dimensional elastic-plastic model was established based on the finite element software. Relying on a tunnel slope project, the influence of "bolt + anti-slide pile" support parameters on the safety factor of slope stability and the maximum shear strain was discussed, and then the best support scheme was obtained. Through field monitoring and numerical simulation, the deformation characteristics of surrounding rock of slope and tunnel with or without this support scheme were compared. Using the distribution characteristics of anti-slide pile stress and bolt axial force, the support effect of this scheme is clarified again. The results show that the best support scheme was A (anti-slide pile 14 m, bolt 14 m), the safety factor of the slope after support is significantly improved, and the anti-slide pile has a greater impact on the safety factor of the slope than the anchor bolt. Compared with the condition without reinforcement, the horizontal displacement and vertical displacement of the slope under combined support are significantly reduced, and the range of soil deformation area is significantly reduced. The anti-slide pile mainly bears the compressive stress, and the maximum value appears in the middle of the pile, which generally presents the distribution mode of "large in the middle and small at the upper and lower ends". The axial force of bolt decreases linearly with the increase of anchorage depth. The measured data of tunnel deformation are basically consistent with the numerical simulation results, and the combined support scheme has a significant effect on controlling tunnel deformation.

Abstract:In view of the cracking of the fine stone concrete spray layer, it loses its function, especially the steel mesh in the spray layer loses its protection and corrodes. To this end, according to the monitoring data of about 10 years of cutting rocky high slopes with a depth of about 200 m in Zhongyuntai Mountain in Lianyungang, the analysis of the cracking of the fine stone concrete sprayed layer was carried out. The axial force of the steel mesh on the slope is positively correlated with the temperature. According to the principle of strain coordination, the fine-stone concrete has the problem of pulling cracks along the slope, which is one of the reasons for the cracking of the fine-stone concrete on the slope. The position of horizontal displacement leads to the phenomenon that the sprayed layer of the fine stone concrete on the slope surface is lifted, which is another reason for the damage of the fine stone concrete on the slope surface.

Abstract:In order to analyze the correlation between asphalt and asphalt mixture indexes before and after aging, this paper carried out a series of indoor experimental tests including:asphalt penetration, ductility and softening point tests at different aging stages, and the semi-circular bending tensile test of AC-13 asphalt mixture in different aging periods under the condition of medium and low temperature to analyze the evolution laws of the mechanical strength, the elastic modulus and the fracture energy of the mixture; The correlation regression analysis is carried out between the three indexes of asphalt before and after aging and the mechanical indexes of asphalt mixture. The test results show that the initial stage of aging has a great influence on the strength and elastic modulus of the mixture, and the aging is more sensitive to the elastic modulus; The mixture has an obvious effect on the low-temperature fracture energy, and the medium temperature fracture energy is significantly higher than the low-temperature fracture energy. The strength and the elastic modulus of mixture before and after aging have high a linear correlation with the three indexes of asphalt. Penetration can predict the mechanical properties of mixture at medium and low temperature.

Abstract:This paper compares and analyzes the advantages and disadvantages of various floating structure forms of floating photovoltaic power stations on the water surface, expounds the technical characteristics and development direction of floating photovoltaic power stations on the water surface, puts forward the corresponding anchoring system scheme for the problems of water level fluctuation and uneven tension of anchor cables faced by the anchoring system of floating photovoltaic power stations, and derives the calculation method of the anchoring force and the volume of counterweight or floating ball. Finally, some suggestions on the design and installation of the electrical system of the floating photovoltaic power station are given.

Abstract:Fouling in geothermal systems reduces the efficient exploitation of geothermal fluids. In this paper, a scaled geothermal well in Bono, Hebei is selected. The type of scaling is analyzed while the scale inhibitor filling device is developed and designed and the scale inhibitor filling test is carried out in the field under various working conditions, with which the scale inhibition rate is calculated and evaluated. The results showed that the scale components of the geothermal well were aragonite and calcite, and that the scale inhibition rates of the four selected scale inhibitors were all above 80%, among which the best one scale inhibitor reached 94.49% at a spiking concentration of 35.95 mg/L. The scale inhibition effect in one heating season shows that the chemical scale inhibitor can effectively solve the calcium carbonate scaling in wellbore and surface equipment.

Abstract:In order to realize the boundary delineation of small coal mines in Jingu Coal Mine, the ground airborne frequency domain electromagnetic system is used to carry out for the survey and test work of the small coal mine goafs. In the actual exploration, 124 survey lines in the north-south direction were designed, and the UAV equipped with the detection antenna was used to continuously collect the electromagnetic data. Through data processing and interpretation, the apparent resistivity structure drawing within the range of -50~-300 m underground in the survey area is obtained. According to the relatively low-resistance anomaly distribution, the suspected locations of the two coal mine goaf areas are demarcated. After comparing with the actual coal mining data, there is a goaf with high water filling under the two defined low resistance abnormal areas. The research results prove the feasibility and effectiveness of the ground airborne frequency domain electromagnetic system in the investigation of small coal mines.

Abstract:Aiming at the problem that water droplets interfere with each other when they impact aircraft surface, resulting in dynamic behaviors such as spreading and rebound of water droplets, which makes aircraft icing mechanism more complicated. Therefore, in this paper, the influence characteristics of water droplets hitting the wall under different conditions are studied. The relationship between the droplet diameter, the wall temperature, the wall material, the initial velocity and the droplet spreading and springback process is studied by combining experimental and numerical methods, and the correlation formula between the spreading coefficient and the influential parameters is obtained. The results show that increasing droplet diameter can promote the maximum spread. The higher the wall temperature is, the more favorable the droplet spreading is. However, when the wall temperature is relatively low, the droplet bottom freezes while the spreading and rebound are restricted. It is also shown that the wall material is plexiglass, which is the most favorable for spreading, and that the larger the initial droplet velocity is, the better the droplet spreading is.

Abstract:Aiming at the small world network characteristics of the public, a small world network model is constructed for behavior simulation. The simulation results show that under the three modes of random, cluster priority and distance priority, the risk perception of production links have a significant impact on the public food safety behavior choice. In the "low agglomeration" network, when the risk perception is not considered, the impacts of the distance first and agglomeration first on the public food safety behavior is higher than the impact of random mode. In the "high degree of agglomeration" network, considering the risk perception, the distance priority model has a higher impact on the public food safety behavior than the cluster priority model. The results provide a simulation basis for food safety decision-making.