Abstract:To explore the mechanism of the influence of calcium dissolution on the micro properties of self-compacting recycled concrete (SCRC), considering the effects of the replacement rate of recycled coarse aggregate (RCA) and the dosage of fly ash (FA), an experimental study was conducted on the micro properties of SCRC under accelerated calcium dissolution conditions using ammonium chloride solution. The experimental results show that as the dissolution age increases, the ultrasonic velocity of SCRC decreases, and the proportion of most probable and large capillary pores increases. The porosity of ordinary SCRC continues to increase, while the porosity of SCRC mixed with FA first decreases and then increases. Within the same dissolution age, as the replacement rate of RCA increases, the ultrasonic velocity of SCRC, and the internal pH value and size of the dissolution transition zone decrease; With the increase of FA content, the ultrasonic velocity of SCRC first increases and then decreases, and the internal pH value and the size of the dissolution transition zone increase. During the dissolution process, when the FA content is 10% or 20%, the pore structure of SCRC is refined and its resistance to dissolution is improved. However, when the FA content is 30%, the pore structure of SCRC deteriorates and its resistance to dissolution decreases.

Abstract:In order to deeply explore the effect of coal rock mass elastic-plastic deformation on structu-ral weak planes, fracturing experiments were conducted according to the combination relationship of crack initiation position, fracturing direction, and bedding direction. Non-metallic ultrasonic detectors and acoustic emission were used to monitor the fracturing process, and the fracturing effect was comprehensively evaluated from the aspects of crack propagation morphology, crack width, and permeability flow rate. Corresponding explanations were given from the perspective of energy. The experimental results show that the fracturing of the overlying strata is better than that of the coal seam, and vertical bed-ding fracturing is better than parallel bedding fracturing. The fracturing effect is best in the vertical bedding direction, and the crack propagation morphology is more complex, forming an "O" shape. Its ave-rage permeability coefficient is 6.6 mm/s, which is 1.10 times that of parallel bedding. The cracks propagate from the overlying rock of the roof to the coal block, and under the same initiation energy, 3.08 to 338 times equivalent length cracks can be formed in the coal block.

Abstract:Taking the highly weathered mudstone cutting slope of Longquanhu Expressway in Jianyang City as the research object, a slope scaling model based on the principle of similarity was used to conduct slope tests under different rainfall intensities and durations. By monitoring the entire process of slope rainfall, the influence of different rainfall conditions on slope stability was analyzed. The research results indicate that the large porosity and hydrophilicity of strongly weathered mudstone are the material basis for slope instability, and the rapid dissipation of slope matrix suction after rainfall is the essential reason for instability. In the early stage of rainfall, heavy rainfall causes a sharp increase in the volumetric moisture content and pore water pressure of the slope, and a sudden drop in matric suction, which is inversely proportional to the intensity of rainfall. Early heavy rainfall will accelerate slope fai-lure and shorten the time for slope failure, and the duration of rainfall directly determines whether slope failure will occur. The surface deformation of the slope is mainly caused by tension cracks at the top of the slope, which develop to the surface and internal depth of the uphill slope. The distribution of volumetric water content and pore water pressure at the top of the slope changes more than that of the uphill slope, leading to the first failure of the top of the slope and gradually developing to the uphill slope.

Abstract:To study the effect of basalt fiber on the piping restraint of cohesionless gap-graded soils, indoor tests were conducted on discontinuous graded soil containing basalt fibers to investigate the inhibi-tory effects of fiber content, fiber length, and soil prevention location on the occurrence and development of subsurface erosion. The results indicate that the addition of basalt fibers makes the migration channels inside the soil more tortuous and narrower, thereby suppressing the growth of soil piping; When the fiber content is low, the control effect of the entire soil is better than that of only the overlying soil. As the fiber content increases, the control effect of the overlying soil is close to that of the entire soil control; When the fiber length is 15 mm, the containment effect of all soil prevention is better than that of overlying soil prevention by the greatest extent. When the fiber length is 10 mm, the difference between the two is not significant.

Abstract:To study the feasibility of applying cement-silica fume-stabilized un-aged steel slag-crushed stone materials for base layer paving, the volume expansibility of steel slag was treated with silica fume. The experimental results showed that the minimum silica fume content for suppressing the expansion rate of steel slag was 2%. Based on this premise, the orthogonal test design method was adopted to explore the mechanical properties and frost resistance of cement-silica fume-stabilized un-aged steel slag-crushed stone base layer materials. The test results indicated that the main influencing factors on the 7-day unconfined compressive strength and splitting strength of the cement-silica fume-stabilized un-aged steel slag-crushed stone base layer materials were the cement content, while the main influencing factors on the 28-day unconfined compressive strength, compressive resilient modulus, and frost resistance were the steel slag content.

Abstract:In order to study the influence of recycled fine aggregate substitution on the compressive elastic modulus of regenerated concrete, as well as the quantitative relationship between the cubic compressive strength and static elastic modulus, and to determine the function calculation formula of the dynamic elastic modulus of regenerated concrete based on ultrasonic detection, six groups of prismatic specimens and cubic specimens with different amounts of recycled fine aggregate were made, and the specimens were tested using traditional static test methods and ultrasonic detection methods. The regres-sion equations of the static elastic modulus and compressive strength, as well as the static elastic modulus and dynamic elastic modulus, were obtained by fitting the measured data using the least squares method. A calculation formula for the static elastic modulus of regenerated concrete considering the ad-dition of recycled fine aggregate was established based on ultrasonic parameters. A function relationship formula between the static elastic modulus and compressive strength was also developed. The research results show that the addition of recycled fine aggregate has a significant influence on the dynamic elastic modulus, compressive strength, and static elastic modulus of regenerated concrete, and all of them decrease as the amount of recycled fine aggregate increases.

Abstract:To study the mechanism of using nickel-iron slag powder as a solidification material for cement soil, the microscopic properties of nickel-iron slag powder cement soil were deeply studied to more accurately reveal the physical and chemical changes during the solidification process. The size distribution of nickel-iron slag powder and cement was analyzed by laser particle size test, and it was found that the dispersion and average particle size of nickel-iron slag powder were slightly smaller than that of cement. The internal structure of nickel-iron slag powder cement soil was studied by synchronous thermal analysis experiment, which showed that nickel-iron slag powder filled the pores of cement soil, improved the degree of intergranular bonding, and thus improved its compressive strength. The microscopic experiment by scanning electron microscope (SEM) showed that a moderate amount of nickel-iron slag powder was beneficial to enhance the dynamic and static strength of cement soil, and the strength of cement soil also increased further with the increase of curing age.

Abstract:Based on the Lianyungang Refining and Chemical Xuwei Cable Tunnel Project, considering the unsaturated hard shell layer that occurs during the vacuum preloading process, indoor model tests were conducted to study the water transport mechanism during the vacuum preloading process, combined with relevant theories of unsaturated soil. The results showed that the groundwater level continuously decreased during the vacuum pumping process, the upper soil became unsaturated, and the pore water pressure showed negative values; The transport of water in the saturated zone is a process of continuously merging and converging towards the drainage plate, while the water in the unsaturated zone converges towards the drainage plate and vaporizes. Under the cycle of water vaporization and increased matric suction, the pore water pressure further decreases, and the soil can continue to consolidate.

Abstract:To enhance the bearing capacity of permeable pavers, cement hardening measures are often used below the brick, resulting in a decline in permeability. To solve this problem, permeable pavers with stone infiltration wells were added. The stone infiltration wells have a decreased permeability due to the retention of particulate matter from the external environment. The influence of different types of blockages on the clogging of stone infiltration wells was studied, and the structure of the stone infiltration wells was optimized by changing the grain size of the stone. The results show that the grain size of the stone affects its resistance to clogging. When the grain size is from 20 mm to 30 mm, the stone infiltration well can maintain good permeability under the influence of clogging.

Abstract:To study the mechanical properties of rocks under different water content conditions, sandstone was taken as the research object, and uniaxial compression tests were conducted to analyze the influence of water content on the mechanical properties and macroscopic failure characteristics of sandstone. Based on the 3D laser technology and fractal theory, the structural characteristics of macroscopic fracture surfaces in sandstone were quantified, the degree of deterioration of internal structure was determined, and the relationship between macroscopic fracture surface characteristics and mechanical parameters was established. The results show that the uniaxial compressive strength and elastic modulus of sandstone exhibit a non-linear decreasing trend with increasing the water content. The degradation of sandstone structures induced by water can be divided into three stages: intense growth stage, stable growth stage, and growth stage. It is found that the macroscopic failure mode of sandstone shifts from single shear failure to axial splitting failure. The fractal dimension variation characteristics of macroscopic fracture surfaces can be used to quantitatively evaluate the degree of deterioration inside sandstone and reflect its mechanical properties.

Abstract:To investigate the effect of grouting defects on the connection performance of prefabricated grout anchor lap joints, 39 grout anchor connection specimens with different positions and lengths of defects were tested using uniaxial tensile tests. The influence of grouting defect types and degrees on the stress performance of grout anchor connections was studied. The results show that when the defect level does not exceed 40%, the distribution type of defects has little effect on the stress performance of the grout anchor connection. For various types of defect specimens with defect levels of 50% and 60%, the peak load from large to small is the discrete defect, end defect, and middle defect. The most important thing to avoid in practical engineering is the defect in the middle of the grouting material, followed by the discrete defect of the grouting material, and finally the defect at the end of the grouting hole. The turning point of the comprehensive displacement ratio trend reflects that as the degree of defect increases, the failure modes of the specimens change from steel bar failure to bar pull-out.

Abstract:In response to the phenomenon of bending and torsional coupling of the upper structure of a curved bridge under vehicle load, the displacement and stress responses of the cross-section at the midspan of the curved bridge under the combined action of the vehicle and the bridge were analyzed and studied using ANSYS finite element software and UM dynamic software The results show that the displacement and stress responses reach their peak values when the vehicle travels to the midspan of the span, and reach the opposite peak values when it travels to the midspan of the adjacent span. The radial displacement is proportional to the vehicle speed, and the trend of other displacements and stress responses other than the radial displacement remains unchanged, while the peak values of the responses are not proportional to the speed. The lateral load causes the radial displacement at the midspan to shift in the opposite direction of the load, and the overall trend of the other displacements and stress responses is basically unaffected by the lateral load. The increase in the roughness grade of the road surface causes an increase in the amplitude of the fluctuations of the upper structure response.

Abstract:To investigate the mechanical properties of segments in sand and cobble strata and their influencing factors, based on a subway tunnel project, numerical simulations were conducted using FLAC^3D software and combined with field construction monitoring data to systematically analyze the surface displacement, stratum deformation, and segment internal force changes during shield tunneling. The influence of different water head heights on the tunnel structure and surrounding stratum was stu-died. The results show that, compared with the case without considering the fluid-solid coupling effect, the final settlement of the surface increased by 49%, the crown settlement of the segment increased by 61.3%, the lateral convergence increased by 51.45%, the maximum stress of the segment increased by about 37%, and the numerical simulation results considering the coupling effect were closer to the actual engineering than the results when the coupling effect was ignored. The water head height is positively correlated with the crown settlement and lateral convergence and negatively correlated with the crown bulge. The bending moment of the segment is positively correlated with the water head height, and the maximum positive bending moment occurs at the crown waist. The axial force distribution is symmetrical, with the axial force at the crown waist being greater than that at the crown shoulder, crown foot, crown top, and crown base. The fluid-solid coupling effect has a significant impact on the deformation of the stratum and the bearing capacity of the tunnel structure when a shield tunnel passes through a water-rich sandy pebble stratum.

Abstract:To investigate the mechanical properties of reinforced steel corrugated plate arch culverts, based on the Yangquan Ring Road realignment project, circumferential reinforcement and bidirectional reinforcement measures were selected. Numerical simulation methods were used to compare and analyze the stress and deformation of steel corrugated plate arch culverts, and to analyze their reinforcement effects. The results show that the arch culvert is under overall compression, with stresses and deformations symmetrically distributed. Under the influence of bolt connection, the stress is highest at the arch foot, followed by the arch waist, and the stress at the arch crown is the smallest. The maximum vertical deformation is located at the arch crown, and the deformation at the peak and valley is consistent, with a difference in stresses. The stress at the peak and valley of the arch waist is 4.83% greater than that at the peak, and the stress at the peak and valley of the arch crown is 18.78% greater than that at the valley. After strengthening, the stress and deformation of the arch culvert are significantly reduced, and the stress concentration at the arch foot decreases. However, stress concentration occurs at the strengthening point, and compared to the valley, the peak strengthening effect is more obvious. By increasing the number of circumferential reinforcement pipes, the structural rigidity also increases, and the reinforcement effect becomes more pronounced. The maximum reduction in the stress is 68.38% and the maximum reduction in the vertical deformation is 10.29%, while the axial reinforcement effect is not very significant.

Abstract:To perceive the physical and mechanical properties of the rock mass to be blasted in real-time through intelligent perception technology, a drilling system was independently developed to obtain real-time drilling information of the blasting hole. Through in-depth mining and analysis of collected data, an analysis method was proposed to characterize the integrity of rock mass and mechanical indicators such as the uniaxial compressive strength of rock blocks. A value map of rock coefficient A based on digital drilling while drilling information was constructed. On this basis, the rock coefficient calculated based on blasting fragmentation will be used as prior data, and Bayes theory will be used to continuously fuse the rock coefficient data determined by on-site blasting construction into the prior distribution, obtaining the posterior distribution of rock coefficients. Compared with traditional methods, the proposed rock coefficient determination method is more intelligent and accurate and can optimize the design of rock blasting parameters for the next stage.

Abstract:Taking the Xishuangbanna region as the research object, based on the GlobeLand30 land use data from 2000, 2010, and 2020, the dynamic changes in land use in the region over the past two decades were analyzed. The study area was divided into several evaluation units using the GIS grid method, and a landscape ecological risk assessment model was further constructed to comprehensively evaluate the landscape ecological risk in the Xishuangbanna region; Using spatial autocorrelation metho-ds to analyze and study the spatial differentiation characteristics of regional landscape ecological risks. The results show that the land use types in the Xishuangbanna region are mainly forest land, accounting for more than 60% of the total area, followed by arable land, accounting for more than 25% of the total area. In the past two decades, there have been significant changes in land use, mainly manifested as the transformation of forest land into arable land and artificial surface; The spatial distribution of the landscape ecological risk index shows a positive spatial correlation, with spatial clustering characteristics mainly manifested as high-high clustering and low-low clustering; The proportion of low-risk areas in landscape ecology has significantly decreased from 2000 to 2020, while the proportion of high-risk areas has shown a significant upward trend, and spatially, high-risk areas continue to expand towards the southeast. High-risk and higher-risk areas are mainly located in Menghai County and Jinghong County.