Abstract:Foamed concrete is a porous material widely used in buildings, but its performance is directly affected by the internal pore structure. The property of cement slurry is an important factor affecting the stability of foam. In order to explore the influence of water/cement ratio on the performance of foamed concrete, three kinds of cement slurry with different water/cement ratio (w/c) were prepared to fabricate the foamed concrete in this paper, and their dry density, compressive strength, thermal conductivity and water absorption were measured to explore the relationship between their properties and w/c. The results show that as the w/c decreases, the cement content and cement slurry viscosity increase while the density of foam concrete, concrete strength, and thermal conductivity increase gradually. However, the water absorption decreases gradually. Under an appropriate w/c, the foam concrete has the largest decrease in density compared with the pure cement slurry, reaching 41.76%. The decrease of the strength is the smallest and the compressive strength reaches 9.8 MPa. The thermal conductivity decreases the most, reaching 0.212 W/m·K, and the water absorption rate reaches 21.5%.

Abstract:In order to study the effect of elastic support stiffness on the stability performance of rectangular steel tube concrete flange I-shaped beams, stability performance tests were conducted on three rectangular steel tube concrete flange I-shaped beams with different elastic support stiffnesses under concentrated load. The displacement and strain changes of the test beams were studied, and the instability form and stable bearing capacity of the beams were obtained. The experimental results show that the entire loading failure process is divided into three stages, namely the elastic stage, the elastic-plastic stage, and the failure stage. All three test beams experience overall bending torsional buckling instability. As the stiffness of the elastic support increases, the stable bearing capacity of the beam increases, which verifies that setting elastic support can effectively improve the stable bearing capacity of the beam. On the basis of the experimental results, nonlinear buckling analysis was conducted on the beam using ANSYS finite element software. The obtained stable bearing capacity is compared with the experimental results, and the error is less than 5%, thus verifying the correctness of the finite element analysis method. Finally, the influences of parameters such as concrete strength, upper flange steel content, and web thickness ratio on the stability performance of this type of beam are studied. The results show that increasing the steel content of the upper flange steel pipe and reducing the height to thickness ratio of the web can significantly improve the stable bearing capacity of the beam, while enhancing the concrete strength has a relatively small effect on the stable bearing capacity of the beam.

Abstract:To study the wind-induced vibration response characteristics of large-span photovoltaic tracking brackets, a flat single axis tracking photovoltaic bracket was taken as the research object, and its dynamic characteristics were analyzed. The harmonic superposition method was used to simulate the fluctuating wind speed time history. The wind-induced vibration response of the bracket was studied using the time history analysis method, and the effects of the average wind speed, photovoltaic panel inclination angle, and wind direction angle on the wind-induced vibration response of the photovoltaic tracking bracket structure were investigated. The results indicate that the natural frequency of photovoltaic tracking brackets is low and distributed centrally. Among all supporting components, the wind induced displacement response of purlins is the highest, while the displacement response of main beams and columns is relatively small. The displacement response of purlins along the windward direction has asymmetry, while the displacement response of the main beam along the windward direction is consistent with the symmetry of its own structure. The wind-induced displacement response of the structure increases with the increase of average wind speed, photovoltaic panel inclination angle, and wind direction angle. Under negative wind loads, the wind vibration response of photovoltaic tracking brackets is more severe. When the inclination angle of the photovoltaic panel increases from 25° to 35°, the stiffness of the bracket will rapidly decrease. The lateral pulsating wind has a significant impact on the displacement response of the main beam and columns.

Abstract:A model for analyzing the interaction characteristics between long piles and soil in layered soil is established based on test pile data to address the bearing problem of long piles in layered soil. Based on the analysis model, the influence of sand to clay ratio on the vertical load displacement curve of long piles is studied. The lateral and end resistance bearing ratios of long piles in layered soil are analyzed, and the excitation laws of lateral and end resistance of pile foundations in layered soil are revealed when the ultimate bearing capacity is reached. It is shown that the lateral resistance of the clay layer can be fully excited, the lateral resistance of the sand layer is not fully excited, and the resistance at the bottom of the pile is fully excited. The results provide a basis for selecting reasonable parameters for calculating the bearing capacity of long piles in practical engineering.

Abstract:To study the influence of particle size range and substitution rate of recycled coarse aggregate on the compressive performance of recycled concrete under uniaxial compression, recycled concrete prism specimens were designed and manufactured with particle size ranges of 5~10, 10~20, and 20~31.5 mm, as well as substitution rates of 0%, 10%, 30%, and 50%, respectively. Uniaxial compre-ssive performance tests were conducted on them. The results show that the compressive strength and peak strain of recycled concrete in the particle size range of 5~10 mm are higher than those in the particle size range of 10~20 mm and 20~31.5 mm when the substitution rate is the same. Under the same particle size range, as the substitution rate increases, the compressive strength of recycled concrete shows a gradually decreasing trend, while the peak strain shows a gradually increasing trend. Based on the experimental data, a functional relationship between the compressive strength and peak strain of recycled concrete was obtained.

Abstract:In order to accurately characterize the various stages of the rock creep curve, the viscous coefficient of the viscous pot element in the Kelvin model is defined as a time-dependent function and a damage viscoelastic body is constructed by considering the deterioration of creep parameters over time according to the creep damage theory. Then, the elastomers, nonlinear Kelvin body, viscous body and damage viscoelastic body are connected in series, and a nonlinear viscoelastic plastic damage creep model that can describe the entire process of rock creep is proposed. The one-dimensional and three-dimensional creep equations of the model under constant stress are reasonably derived. Finally, a parameter identification is performed based on relevant creep test data to verify the effectiveness of the damage creep model. A comparative analysis is conducted on the correlation between the theoretical model and experimental data, and the results show that the model can well describe the entire process of rock creep, with correlation coefficients above 0.92.

Abstract:In order to study the effect of locust bean gum to improve the strength of clay, unconfined compressive strength tests and tensile tests were conducted on improved clay with different curing ages and locust bean gum contents. The results indicate that the addition of locust bean gum can significantly improve the compressive and tensile properties of clay. When the curing age is fixed, with the increase of the locust bean gum content, the compressive and tensile strengths of the improved clay show an increasing trend. Through comparison, it can be seen that the optimal content of locust bean gum is 2%, and the maximum compressive and tensile strengths of the sample are increased to 425.74 and 234.61 kPa, respectively, which are about 1.8 times higher than those of the plain soil; When the dosage of locust bean gum is constant, the curing age also has a certain impact on the compressive and tensile strengths of the improved clay. Under the same dosage of locust bean gum, when the curing age is 7 days, the specimen compressive and tensile strength enhancement is the largest, the maximum enhancement is 68.12 and 34.39 kPa, respectively. Robinia pseudoacacia bean gum forms a layer of gum film on the surface of soil, and uses its own ductility to fill the pores between soil particles, improving the particle structure of the soil and its stability, and thus the strength characteristics of clay. As the curing age increases, the gum film gradually shrinks, making the arrangement of soil particles more compact, thereby improving the unconfined compressive strength and tensile strength of the improved cohesive soil.

Abstract:Shield load is an important parameter of shield machine, and accurate prediction of shield load is very important to ensure the safe construction of shield tunnel. In this paper, a new load prediction model (CGA), combining convolutional neural network (CNN), gate recurrent unit neural network (GRU) and attention mechanism (Attention), is proposed based on the shield machine cross existing station at close range. The CNN-Attention model is first used to extract the high-dimensional spatial features of the data and distinguish the importance of different features. Then the GRU model is used to extract the temporal characteristics of the data, followed by the attention mechanism to extract the important time node information. Finally, the prediction results are obtained. To verify the prediction performance of the proposed model, four existing algorithms are selected for comparison. The results show that the proposed model in this paper outperforms other models in three evaluation metrics, and the proposed model can also provide reference for predicting researches on shield tunneling tool wear, surface and structural deformation, etc.

Abstract:In order to study the influence of the combined advanced support parameters of shallow buried bias and small clear distance tunnel pipe shed plus advanced small conduit on the tunnel support effect, relying on the Yiliang tunnel entrance section project, the three-dimensional model working conditions under different parameters such as thickness, length, diameter, hoop spacing and extrapolation angle of the grouting reinforcement area of the pipe shed were established through FLAC^3D, and the control effect of each pipe shed parameter on the displacement of the surrounding rock was analyzed. The results show that the displacement of the surrounding rock can be reduced by increasing the thickness, diameter and length of the grouting reinforcement area. A grouting reinforcement zone with a thickness of 3 meters, a pipe shed diameter of 100 mm, and a length of 40 meters are preferred. With the increase of the interpolation angle and hoop spacing of the pipe shed, the displacement of the surrounding rock gradually increases. The interpolation angle of the pipe of 2° and the hoop spacing of 0.3 m are preferred. Based on the selection of reasonable support parameters for the pipe shed, the simulated values are compared with the on-site monitoring measurements to verify the rationality and reliability of the selected support parameters.

Abstract:Based on the construction collapse case of a hidden excavation tunnel near the ground fissure area of Xi'an Metro Line 3, the hydrogeological and construction behavior factors causing the collapse are analyzed. By further simulating the process of tunnel collapse using discrete element software, it is found that the initial support structure in the upper part of the tunnel accelerates the formation of the "force chain". In the collapse case, a series of treatment measures are taken to ensure the safety of the soil layer structure, without causing secondary disasters. The on-site monitoring data effectively verifies the effectiveness of the risk management plan. The research results indicate that surface precipitation is an important cause of collapse, and when excavating tunnels in weak strata, it is necessary to ensure that the tunnel structure forms a ring as soon as possible and ensure the stability of the bottom soil.

Abstract:In order to study the carbon emissions during the operation phase of buildings, this article establishes a carbon emission calculation model for building operations based on the energy balance table splitting method on the basis of the carbon emission factor method, and analyzes the characteristics of carbon emission changes through the carbon emission data of building operation in Hebei Province from 2005 to 2020. Secondly, the STIRPAT model is introduced to empirically analyze the factors affecting carbon emissions from building operations. The results show that during the research period, carbon emissions during the operation phase of buildings in Hebei Province increases by 1.24 times, with indirect carbon emissions dominating the operation phase. Residents accounts for the largest proportion of carbon emissions in the construction operation industry structure, and the number of permanent residents is the main driving factor for carbon emissions during construction operations in Hebei Province.

Abstract:In order to explore the issue of environmental vibration in the water transmission pipeline area of pumped storage power stations, combined with actual engineering environmental vibration monitoring data, Midas GTS software is used to analyze the vibration impact of the water transmission pipeline area environment of pumped storage power stations under different working conditions, and reasonable vibration reduction measures are proposed. The results indicate that the decibel values of environmental vibration in the upstream area near the unit are higher than those in the downstream area, and the decibel values of environmental vibration in the downstream area near the residential area are higher than the standard values of environmental vibration in the residential area, which seriously affects the normal life of residents. Owing to the complex environmental vibration sources in the pumped storage power station area, the filling ditch isolation measures have significant effects and are easy to construct, which has certain reference significance for similar pumped storage power station projects.

Abstract:In order to further prevent and control the risk of piping, a theoretical model for piping prediction is established using the flood control embankment of Poyang Lake as the research object. The GeoStudio 2018 software is used to simulate and analyze the flood control embankment, setting three key factors of rainfall intensity, rainfall type, and rainfall time, as well as four working conditions. The damage calculation of the flood control embankment is carried out using the See/W module and Sigma/W module, respectively. The results show that only under the fixed reservoir water level, different rainfall will occur. The phenomenon of pipe surge, and the pipe surge will be damaged by the fixed reservoir water level of 23 m+rainfall time 20~30 d+rainfall intensity 0. 06 m/d, the pipe gushing point is located at the foot of the downstream slope 0. at 2 m; A reverse filtration covering scheme was proposed, and the corresponding numerical simulation model was established. The solution has been verified to meet the requirements of the relevant specifications.

Abstract:Taking the Hebei section of the Taihang Mountains as the research object, the Remote Sensing Ecological Index (RSEI) is calculated to identify the ecological source area. Multiple spatial data sources such as the land use type, normalized vegetation index, elevation, and slope are selected for comprehensive resistance evaluation. The circuit theory model is used to extract ecological corridors and pinch points, and a long-term regional ecological security pattern of "source area corridor node" is constructed. The results show that: (1) The average RSEI of the study area in 2002, 2007, 2012, 2017, and 2021 are 0.507, 0.538, 0.554, 0.493, and 0.541, respectively, and the RSEI shows a trend of "rising-falling-rising" over the past 20 years; (2) The total area of the source area in the research area increases gradually, with an increase of 5705 km² from the initial stage to the final stage. The proportion of area increases from 2.66% to 18.56%, and the average RSEI of the source patches increases from 0.774 to 0.834; (3) The main ecological corridors in the research area are distributed vertically from north to south. At the end of the study, 16 ecological source areas, 21 ecological corridors, and 5 ecological pinch points are identified.