Based on the temperature load on the wall slab of a large aqueduct when the temperature suddenly drops, the temperature self-confinement stress of the upper surface of the concrete slab was tested and analyzed. The temperature difference between upper and lower surfaces of concrete slabs at different cooling rates and the self-constrained principal stress of concrete slab surface temperature at 1 h at a cooling rate of 10 ℃/h were measured. The accuracy of finite element modeling was verified by comparing the numerical value of concrete transient temperature stress simulated by finite element method with the experimental test data. On this basis, the influence of cooling rate on transient temperature and stress field of aqueduct was analyzed. The impact of different insulation materials on surface temperature and stress field of aqueduct was discussed. The results show that the temperature tensile stress on the aqueduct surface will increase at a faster rate with the increase of the ambient temperature decreasing rate. Compared with the external surface temperature stress of the aqueduct without insulation measures, the tensile stress of the external surface temperature of the U-shaped aqueduct was reduced by 83%, 80% and 68%, respectively, when the polyurethane, polystyrene board and vitrified microbeads with 2mm thickness were adopted. Considering the cost and construction technology, vitrified microbead insulation materials are more suitable as thermal insulation materials on the outer surface of aqueducts.

During construction and operation, it is inevitable to have such engineering problems as cutoff wall defects. It is very important to accurately and systematically analyze the influence of defects in anti-seepage wall on seepage and deformation of cofferdam. The finite element model of an anti-seepage wall cofferdam project was established. By using the fluid-solid coupling analysis method, the material parameters of anti-seepage wall element in the finite element model were changed one by one to simulate different defects of anti-seepage wall. The influence of defect location of anti-seepage wall on saturation line, velocity vector field and deformation field of cofferdam was studied. The results show that the bottom defects of the anti-seepage wall have little influence on the saturation line, velocity vector field and deformation field of the cofferdam. With the upward movement of the anti-seepage wall defects, saturation line, pore water pressure and deformation value of the cofferdam behind the anti-seepage wall increase continuously, and the velocity of the cofferdam increases firstly and then tends to be stable. The research results can provide reference for the design and construction of anti-seepage wall and stability analysis of cofferdam.

Flexible Mattress is the main beach guarding structure in the middle and lower reaches of the Yangtze River. The water flow scouring is likely to cause the deformation of the flexible mattress, affecting the guarding effect. Aiming at its deformation monitoring difficulties, this paper explores the feasibility of using optical fiber sensing to monitor the deformation of the flexible mattress through the indoor experiment. The results of the study show that at the initial stage of tensile deformation (less than 20 mm), the measured strain value deviates less from the actual value. When the tensile length is greater than 20 mm, the error rate of each measurement point is exponentially increasing, and the fixing effect of the optical fiber cable and the flexible mattress at the fixed point determines the monitoring accuracy of tensile deformation. The positioning accuracy of optical fiber sensing to measure bending deformation is 3 times fixed-points interval. For the concentrated stress areas (such as the edge of scour pits), positive strain is mainly generated. Optical fiber sensing has the feasibility of monitoring the tensile deformation of flexible beach protection structures. When applying this technology, it is necessary to consider the coupling of the sensing fiber and the deformation of the flexible structure, the destruction of sinking the mattress and the complexity of the construction process. The results can be reference for the research and development of monitoring and assessment technology of the in-service condition of the flexible mattress.

In view of the influence of the analysis method of geosynthetics axial tensile test results on the authenticity of mechanical properties, the mechanical properties of PVC geomembrane and HDPE geomembrane materials were studied respectively, and the relationship curves of the two materials under different analysis methods were obtained. Then the error of material tensile index under the two analysis methods was compared. The results indicate that the experimental curves obtained by the true stress-strain analysis method considering thickness changes can more accurately reflect the tensile deformation process of materials. When the materials are different, the modulus errors of the materials under the two analysis methods are also completely different. However, the variation law of the true stress-strain curve is more consistent compared to standard methods for processing, which can more accurately evaluate the material's ability to adapt to load deformation.

In order to study the mechanical characteristics such as fracture mode, crack propagation characteristics, and strength characteristics of intersecting multi-fractured rock masses in uniaxial compression tests, the particle flow program was used to simulate the mechanical characteristics of intersecting multi-fractured rock masses in uniaxial compression tests. The impact of the angle between intersecting cracks on the strength characteristics, failure mode, microcrack development and evolution law of multi-fractured samples during uniaxial compression was analyzed. The experimental results show that the failure strength of the cross multi-crack specimen exhibits a slow bottom "U" shaped characteristic with the increase of crack angle; The failure mode of intersecting multi-crack specimens is mainly tensile shear failure, with some specimens exhibiting shear failure; The failure process of intersecting multi-crack specimens first involves the generation and intersection of cracks between the tips inside the cracks, followed by the generation of cracks at the outer tips of the cracks and their transmission parallel to the loading direction to both ends of the rock mass, ultimately leading to macroscopic failure of the rock mass. The results of this study contribute to the understanding of the mechanical mechanism of cross fissured rock masses in compression failure, and are a supplement to the research on the mechanical properties of cross fissured rock masses.

To improve the added value utilization rate of reservoir sediment in the field of construction materials, the reservoir sediment was used as auxiliary cementitious material to prepare pervious concrete. The results show that with the increase of reservoir sediment content, the compressive strength of the specimens will decrease, and the permeability will increase. With the extension of mechanical activation time, the compressive strength of the specimen increases and the permeability decreases. When the water cement ratio is 0.3, the mechanical activation time is 45 min, the 28 d compressive strength of the prepared pervious concrete can reach 21.44 MPa, and the permeation coefficient is 0.56 mm/s. The results of this study can provide reference for the resource utilization of reservoir sediment in the field of building materials.

Early freezing of concrete is common in the construction of water conservancy projects in northern China. Early freezing damage induces the deterioration of mechanical properties of concrete structures, which seriously affects the safety, stability and service life of engineering structures. Through laboratory uniaxial compression test and CT scan test, the influence law of freezing time and freezing temperature on the mechanical properties of concrete was analyzed, the three-dimensional pore structure of concrete at different freezing time was reconstructed, the pore distribution and pore structure characteristic parameters of concrete at different freezing time were studied, and the correlation analysis between mechanical properties and pore structure of early frozen concrete was carried out. The results show that with the delay of freezing time, the porosity of concrete test blocks increases first and then decreases, the average pore surface area decreases first and then increases, the average pore diameter increases with the trend of quadratic parabola, and the average pore shape factor increases first and decreases then increases and decreases. The correlation between the average pore surface area and the compressive strength and elastic modulus of early frozen concrete is the best. It is suggested that the average pore surface area should be preferred to construct the mesoscopic damage index of early frozen concrete. Relevant research results provide support for revealing the macro and micro damage mechanism of early frozen concrete.

In order to explore the impact of moisture change on the pore structure of reshaped loess, different times of humidification-dehumidification cycle tests were carried out for remodeled loess with different dry densities, and the pore structure inside the soil under different cycles was tested by nuclear magnetic resonance technology. The results show that the NMR T₂ pattern of reshaped loess presents a bimodal structure, that is, the sample contains two pore structures; The dry and wet cycles have an impact on the change of the pore structure of the loess, and the pore structure shows different laws under different times of dry and wet cycles. Finally, based on the quantitative parameters extracted from the T₂ pattern, the permeability of reshaped loess under different cycles were calculated by SDR permeability model, and the permeability mechanism of loess was explained from the microscopic aspect.

In order to deal with the serious problem of siltation in the main channel of the Yellow River Diversion Irrigation Area in Zuncun Village, Shanxi Province, a field water and sediment test was carried out on the main channel. The distribution law of suspended sediment in the channel, the relationship between channel flow and sediment deposition, and the sediment carrying capacity of the channel flow were explored by using the vertical suspension index and the planning solution method, so that it could express the sediment carrying capacity of the flow within a certain range. The critical suspended flow corresponding to the channel particle size was put forward. It was beneficial to prevent siltation by adjusting the flow according to the working conditions and particle size. The sediment carrying capacity formula was optimized. The conclusions are as follows: When the diversion flow is 4.46-24.52 m³/s, the sediment content in the channel is between 0.9-4.0 kg/m³, and the sediment content is positively correlated with the flow velocity. The channel flow can be properly adjusted to more than 39.6 m³/s to effectively suspend the sediment with large particle size. The correlation between the optimized sediment carrying capacity formula and the measured value of the main channel sediment reaches 0.828, which indicates that this formula can reflect the current sediment concentration to a high degree, and provide support for the design and analysis of the balance of channel erosion and deposition in the later stage.

In order to improve the prediction accuracy of vibration signals of hydropower units, a prediction method based on variational mode decomposition (VMD), sample entropy (SE) reconstruction and particle swarm optimization (PSO) optimization of bi-directional gated circulation unit (BIGRU) was proposed. In the VMD-SE-PSO-BIGRU model, firstly, the vibration signal was decomposed into several subsequences by VMD, and the subsequences were reconstructed by SE. The trend, oscillation and noise components of the vibration signal were obtained. Then, parameter optimized BIGRU prediction models were established for the reconstructed components. Finally, the prediction results of each component were superimposed to achieve vibration prediction. Compared with other models, example analysis shows that the prediction error of the model is smaller and the prediction accuracy is higher, which can effectively predict the vibration signals of hydropower units.