Abstract:Rockburst is a common engineering geological disaster in deep rock excavation. In order to predict rockburst intensity grade accurately,this paper proposes a rockburst intensity prediction model based on KPCA-WOA-KELM. Firstly,rockburst evaluation indexes are determined according to the influencing factors of rockburst intensity,and the kernel principal component analysis (KPCA) is used to perform feature compression on rockburst data,so as to simplify the input data structure of the model and fully retain the data feature information. Secondly,the kernel-based extreme learning machine (KELM) was used to fit the nonlinear mapping relationship between the evaluation index and rockburst intensity,and the whale optimization algorithm (WOA) is used to optimize the parameters of KELM to reduce the impact of manual setting parameters on the model prediction effect. Then,the accuracy,precision,recall,F-measure and other indicators are used to evaluate the prediction performance of the model. Finally, the prediction of rock burst intensity of Zhongnanshan highway tunnel in Qinling Mountains is made to verify the feasibility and applicability of the model. The results show that KPCA-WOA-KELM can simplify the data structure more effectively,effectively avoid the local optimal solution,and improve the accuracy of rockburst intensity prediction.

Abstract:Experimental studies on the effects of the replacement rates of recycled coarse aggregate (RCA) and the initial stress levels on the sulfate corrosion resistance of recycled concrete were carried out. Results show that when the replacement rate of RCA (denoted as ρ_r) increases step by step, the corrosion depth and mass loss rate of recycled concrete increase, and the mechanical properties including compressive strength and dynamic elastic modulus gradually decrease. The influence of initial stress damage on concrete can be divided into two types. Firstly, the initial stress damage has a threshold effect on the corrosion depth and mass loss rate of recycled concrete. Only when the initial damage degree is greater than 0.2, the corrosion depth and mass loss rate of concrete increase obviously with the increase of damage degree. Secondly, for the mechanical properties of recycled concrete, both the compressive strength and dynamic elastic modulus will deteriorate with the increase of initial damage.

Abstract:Waste concrete coarse aggregate used as recycled coarse aggregate was applied to replace crushed pebble coarse aggregate. The replacement ratio r was 0%, 15%, 30% and 45%, respectively. Based on this, 36 cube and prism specimens of recycled concrete with broken pebbles were made respectively, and when the curing ages were 3 d, 14 d and 28 d, the compressive strength and flexural strength tests were implemented. The variation law of compressive and flexural strength of crushed pebbles recycled concrete with r at different ages and the influence on the compression ratio and class discount ratio of crushed pebbles recycled concrete with r were analyzed. The results indicate that: With r increasing, the trends of change of compressive strength and flexural strength increase at early stage and then decrease at different ages. When r=30%, it reaches maximizing compressive strength and flexural strength. At the age of 3 d, there is no uniform and significant change pattern in the compression ratio and the analogous compression ratio as r increases. At the age of 14 d and 28 d, with the increase of r, both the compression ratio and the similar compression ratio first increase and then decrease. At the age of 28 d, when r=30%, both the compression ratio and the similar compression ratio reached their maximum values. The calculation models of the compression ratio and the similar compression ratio based on the replacement rate r were established respectively.

Abstract:In order to study the influence of clay particles on the occurrence and development of pipe gushing and the mechanical properties after the failure of pipe gushing, soil samples with different clay content were arranged to simulate indoor pipe gushing test, and the damaged soil samples were taken for triaxial compression test. The results show that:(1) There is a negative correlation between the critical hydraulic gradient of clay soils and the hydraulic gradient at the beginning of piping failure and the clay content. The velocity of destruction was positively correlated with the clay content.(2) The deeper the soil layer is, the greater the loss of fine particles, the greater the strength loss, and the less obvious the strain softening trend of the soil is.(3) The clay content promotes the loss of fine particles in soil, making the strength loss of soil samples containing clay particles greater after pipe gushing.The greater the viscosity content, the more obvious the promotion effect and the greater the strength loss.

Abstract:The Conventional triaxial consolidation drainage shear tests under different confining pressures were carried out for three kinds of non-viscous coarse particles in the overburden of a dam, and the effects of different relative compactness on mechanical properties of coarse particles were studied. The results show that before reaching the peak strength, with the increase of relative density and confining pressure, the initial tangent modulus and peak strength increase correspondingly. The relationship between the initial tangent modulus and confining pressure is a power function under the same relative density. Under the same confining pressure, with the increase of relative density, the stress-strain curve shows a more obvious softening phenomenon. The dilatancy of the sample gradually increases, and the axial strain corresponding to the peak strength gradually decreases. The relative density has a great influence on the deviator stress of the sample during failure, but has little influence on the residual deviator stress. Meanwhile, the study found that the parameters R_f and n of the Duncan-Chang model are basically not affected by the density, and K has a positive correlation with the density. A new parameter λ is introduced to quantitatively analyze the relation of parameter λ with confining pressure and compactness. The relationship between the strength index and the relative density is linear, and the relationship between the shear strength index and the relative density is given.

Abstract:The indoor drying-wetting cycle tests of composite clayey soil with different concentrations of organic polymer were carried out. By recording the change of water content of the sample and obtaining the characteristic pictures of crack development, the influence of the change of polymer concentration and the number of drying-wetting cycles on the moisture change and desiccation cracking of clayey soil was studied. The results show that: (1) the drying and water loss process of clay can be divided into three stages, and the internal water loss mainly occurs in the constant rate evaporation stage. Because the elastic membrane formed by the reaction of curing agent and water will block the "hydrophobic channel" in the soil, the water holding capacity of the soil will be gradually improved with the increase of the concentration of the polymer, and the time of constant rate evaporation stage was prolonged to some extent. (2) With the increase of the number of drying-wetting cycles, the cracks on the surface of the samples will be "healed" in different degrees. However, with the increase of the concentration of polymer, the soil particles are wrapped and cemented by elastic membrane, and the surface crack morphology of the samples changes little, and the overall stability is improved.

Abstract:In order to study the damage evolution characteristics of sandstone with different moisture contents, uniaxial compression acoustic and electrical signal monitoring test was carried out for red sandstone under dry, natural and saturated conditions by using RMT-150C rock mechanics testing machine, AEwin-USB acoustic emission signal acquisition system and KBD5 electromagnetic radiation acquisition system. Based on the acoustic emission bell count, electromagnetic radiation pulse number and stress change during rock failure, the damage evolution model of sandstone is established. The results show that the characteristic curves of acoustic emission, electromagnetic radiation and damage variables are in good agreement with the stress-strain curves of rock. The damage evolution of sandstone can be divided into three stages: initial damage stage, continuous damage growth stage and rapid damage growth stage. As the damage degree deepens, the number of rings and pulses increases. In the stage of initial damage and continuous damage growth, the ratio of ringing count and pulse number in the saturated rock sample in this stage is the highest, followed by that in the natural state and the lowest in the dry state, while it is the opposite in the stage of rapid damage growth.

Abstract:A comparative study of the reinforcement effect of conventional vacuum preloading method, graded vacuum preloading method and optimized graded vacuum preloading method is carried out through indoor model test. Through the comparative analysis of the change law of soil settlement, drainage and vacuum degree during the reinforcement process, and the comparison of the soil moisture content and particle size distribution curve indicators before and after reinforcement, the vacuum degree transfer law is worked out and the mechanism of different vacuum negative pressure strengths are analyzed. The results show that the optimized vacuum preloading method is better than the other two, and directly applying a large vacuum suction force (-80 kPa) after the first stage (-20 kPa) will not cause further blockage of the drainage plate and can improve drainage efficiency.

Abstract:In order to study the stability of high-fill slopes, based on the continuous-discontinuous coupling analysis theory, a boundary wall coupling method was used to establish a continuous-discontinuous coupling analysis model for high-fill slopes, and the strength reduction method was used to simplify rainfall conditions. Based on the actual landslide engineering cases, the soil parameters should be reduced by 15%, and the stability analysis of the high-fill slope under the influence of rainfall was carried out; by reducing the mesoscopic parameters, the safety factor of slope was obtained as 1.60. The possible deformation and failure of the slope under extreme conditions were analyzed. Through this case, the feasibility of the continuous-discontinuous coupling method for slope stability analysis was explored. The results show that the continuous-discontinuous coupling method can quickly, efficiently and intuitively evaluate the stability of high-fill slopes. The research conclusions can provide references for the application of continuous-discontinuous numerical simulation in geotechnical engineering.

Abstract:Considering the serious bending of the vertical drainage plate in the soft soil treatment process, a method of combining flocculant technique with horizontal mesh drainage combination with vacuum pre-pressure treatment of bagged sludge was proposed. The water content, unconfined compressive strength and shear strength of the sludge treated by the straight drainage body and the new horizontal mesh drainage body were tested, and the influence of the added amount of flocculant on the consolidation effect was compared. The test results show that the new horizontal mesh drainage can effectively improve the permeability of the soil compared to the straight drainage. The addition of 0.3% flocculant is the best ratio to improve the consolidation effect. The feasibility and effectiveness were verified of the cofferdam construction technology of the new horizontal mesh drainage combination with vacuum pre-pressure treatment of bagged sludge.

Abstract:The clay was strengthened with natural xanthan gum, and the unconfined compressive strength characteristics of improved clay under different curing time and xanthan gum content were studied through a series of unconfined compressive strength tests. And the reinforcement mechanism was analyzed deeply. The test results show that xanthan gum as an additive can improve the unconfined compressive strength of clay to a great extent, and the compressive strength of improved clay samples increases with the increase of xanthan gum content and time, and finally tends to be stable. The optimum content of xanthan gum to improve clay is 1.5%, and the best curing time is 14 days. When the curing time is 14 days, the strength of the improved clay samples containing 0.5%, 1.0%, 1.5% and 2.0% xanthan gum increase by 13.43%, 20.85%, 29.87% and 34.70% respectively. Xanthan gum matrix enhances the integrity and cohesion of soil samples by enhancing the cohesion of clay particles, so as to enhance the compressive strength of clay samples. The research results can provide a certain reference basis for the practical engineering application of clay strengthened with xanthan gum.

Abstract:The effect of different concentration of PVAc binder on the strength of clay was studied by unconfined compressive strength test and direct shear test. The test results show that: PVAc binder can improve the strength of clay;the unconfined compressive strength and shear strength of clay improved by PVAc binder increase with the increase of curing time;When the curing time is fixed, the cohesion and unconfined compressive strength of clay increase with the increase of PVAc binder content. While the concentration increases to 3%, the unconfined compressive strength of clay decreases compared with 2% concentration.

Abstract:When all kinds of garbage are buried in the ground, the landfill leachate will gradually infiltrate into the soil from the aeration zone, causing a certain impact on the soil environment. In view of the significant physical property difference between the upper landfill layer and lower undisturbed soil layer, the high-density electrical method is of limited precision, and the drilling survey is time-consuming, labor-consuming and costly, so complementing the advantages and disadvantages of the two methods has practical application significance for comprehensively identifying the spatial distribution characteristics of landfill layer. In this study, a landfill was explored by the combination of high-density electrical method and drilling method, and the stratum structure of the site and the spatial distribution of the landfill layer were found out, and the three-dimensional stratum solid model was constructed, and the spatial distribution of the landfill layer was determined with the Volxer software drawing the rendering results of high-density electrical inversion and constructing the 3D solid visualization model of landfill by GMS software, and analyzing the application results of the two methods, which provided a theoretical basis for landfill pollution control and risk control.

Abstract:This thesis takes smoking room as research object. Based on the combination of CFD simulation and the stepping motor experiment, this paper carries out numerical simulation of the smoke diffusion in the smoking room. The model is verified by PIV experiment, and the relative error is less than 25%. In the end,the indoor smoke velocity and CO mass fraction distribution under different ventilation modes, different smoke source quantities, and different fresh air velocity were obtained. Results showed that the upper side exhaustion is a manner of purifying the indoor smoking effectively. The indoor smoke concentration in different heights is mainly decided by exhaust manners and pollution source location. To increase the smoke source quantity will enhance the indoor air convection, and accelerate the airflow speed with relatively high indoor smoke concentration. The smokers will suffer much more damage from the second hand smoking. To accelerate the speed of new ventilation system is an effective method to decrease the indoor smoking concentration.

Abstract:Al-Cu-Mg-Ag new-type heat-resisting aluminum alloy was aged by cyclic creep with a rectangle wave load. The effect of cyclic creep aging on the microstructure and properties of Al-Cu-Mg-Ag alloy was researched by mechanical performance test, corrosion resistant performance tests, and combined with electrochemical analysis, transmission electron microscopy analysis and metallographic microscopic analysis, etc.. The results show that cyclic creep aging can improve the mechanical properties and corrosion resistance of the alloy. Cyclic creep aging can refine the precipitations both in the grains and on the grain boundaries, and can also promote the precipitation of θ' phase. The width of the precipitation free zones (PFZ) is reduced and the grains are stretched along the creep direction. The sample cyclic creep aged with a load of 200 MPa has the best comprehensive performance.

Abstract:As an excellent energy storage device, lithium ion battery has been developed rapidly in recent years, and more and more materials have been applied to lithium ion battery. In this study, porous carbon material has been successfully synthesized by carbonization of ZIF-8 in the atmosphere protected by nitrogen. We analyzed the phase purity of the material by XRD, the pores size distribution and specific surface area were analyzed by nitrogen sorption isotherm techniques. At last, the electrochemical properties of porous carbon material in lithium-ion batteries were investigated. the Results show that the specific capacity measured at 0.1C is 284.61mAh/g with good cycling performance, and the cycling efficiency is more than 95%, which indicates that the obtained carbon material shows remarkable lithium storage performance.

Abstract:Aiming at the heterogeneity of operation costs around private enterprises in PPP projects, this study designs the incentive mechanism to restrain private enterprises from misreporting cost information. This study establishes a principal-agent model. Through designing of the optimal contract that takes price compensation as the incentive measure, the gain of private enterprises by claiming false cost information is not greater than that of reporting his true cost information, which can encourage private enterprises to show their true cost information. Then, we further analyze the influence of enterprise type distribution on the optimal incentive contract. Results show that the incentive mechanism can screen the cost information of private enterprises. In addition, the charge price of private enterprises and the price compensation of government departments are related to the distribution of enterprise types. And the promotion of competition among enterprises will inhibit private enterprises from seizing information rent.