Abstract:On the basis of analyzing the erosion characteristics of muddy coast in Jiangsu Province, the development process of coastal protection engineering in Jiangsu Province is summarized. With the southward shift of the erosion and siltation transition node, the range of eroded coast is expanding, with significant undercutting of tidal flats and large-scale disappearance of coastal salt marshes. Traditional localized coastal protection method have become passive. There is an urgent need for a sustainable erosive coastal management strategy that integrates both local and macro approaches, as well as natural and engineering solutions. It is suggested that the coast along the abandoned Yellow River Delta should be treated as a whole, and a comprehensive coastal protection system that combines large groynes and offshore submerged breakwaters should be established. Longitudinally, a headland-bay alternating coastline should be built using artificial headlands as nodes. Transversely, the restoration and reconstruction of salt marsh ecosystems should be carried out through offshore submerged embankments to dissipate waves and promote sedimentation.

Abstract:By reviewing the types and scales of termite nests in different periods of earth-rock dams, the structural characteristics and disaster modes of termite nests are expounded, and the physical properties based on the geophysical exploration of termite nests are summarized. The application status of methods such as the direct current resistivity method, ground penetrating radar technology and seismic exploration method in termite nest exploration is emphatically introduced. The application conditions of the methods are discussed from the perspectives of achievement dimension, detection efficiency, work intensity and detection accuracy. It is pointed out that the existing geophysical exploration technologies are still insufficient to support high-precision, high-efficiency, and three-dimensional detection of termite nests. Therefore, a comprehensive geophysical exploration service framework for termite nest detection is proposed, including survey, detailed investigation, management, and monitoring. Based on the objective needs of termite nest detection technology, it is proposed that future geophysical detection technology should focus on the development of 1∶1 physical simulation device for disease and hidden danger map of termite nest development stages, the development of termite nest detection equipment and forward and inverse algorithms adapted to dam terrain, and the construction of a regular inspection system for dam termite damage and time-lapse resistivity monitoring system.

Abstract:In order to understand the variations and causes of water and sediment in major rivers in southern China, the variation characteristics of runoff and sediment load at representative stations are analyzed and main influencing factors are investigated using the Mann-Kendall test method and the hydrological accumulation curve method. The results show that the annual runoff at representative stations of the main southern rivers such as the Yangtze River, the Pearl River, the Qiantang River and the Minjiang River has no significant change trend. The annual sediment load at representative stations in the southern rivers has a significant decreasing trend except for the Qiantang River. The Qiantang River experienced a normal runoff and sediment load period from 2016 to 2020, and a normal runoff and high sediment load period from 2011 to 2020. However, the other rivers experienced a normal runoff and low sediment load period from 2016 to 2020 and from 2011 to 2020. The main factors affecting runoff and sediment load include reservoir sediment retention, water and soil conservation measures, sand mining from rivers, and excessive construction. Among them, reservoir sediment retention is the main measure responsible for sediment reduction in southern rivers, water and soil conservation measures play an important role, and sand mining from rivers also plays a certain role in river sediment reduction.

Abstract:In order to clarify the spatiotemporal differentiation characteristics of water conservancy modernization, an evaluation index system for water conservancy modernization was constructed, including four major goals of demand guarantee for resource, environment, ecology, and security, and 14 criteria. A comprehensive evaluation method for water conservancy modernization was proposed, integrating the goal consistency method, coefficient of variation method, and hierarchical weighting method. The level of water conservancy modernization in China and its provinces (autonomous regions and municipalities) was evaluated, and the spatiotemporal differentiation characteristics were analyzed. The evaluation results show that China’s water conservancy modernization has gone through an initiation period, an acceleration period, and a speed-up period, with a generally high level of achievement. The levels of achievement in resource and security demand guarantees are high, but those for environmental and ecological demand guarantees are relatively low. Provinces (autonomous regions and municipalities) are accelerating the process of water conservancy modernization, with the eastern and central regions progressing significantly faster than the western and northeastern regions. Resource and security demand guarantees have been well achieved, while environmental demand guarantee lags behind, and ecological demand guarantee is poorly met. At present, provinces (autonomous regions and municipalities) in China urgently need to accelerate the construction of water ecological environment, improve the guarantee levels for environmental and ecological demands, and accelerate the promotion of high-quality development in water conservancy to advance the process of water conservancy modernization in China.

Abstract:Based on the monthly temperature and precipitation data from 1976 to 2020 in the Taohe River Basin, the standardized precipitation evapotranspiration index (SPEI) values at seasonal and annual scales were calculated. The time series stationariness test method and drought frequency method were used to quantitatively analyze the variation pattern and spatial distribution characteristics of different levels of meteorological drought frequency at seasonal and annual scales. The randomness and stability of the spatiotemporal distribution of meteorological drought at the annual scale were analyzed using the cloud model. The results show that the frequencies of drought in all four seasons are about 30%, with droughts mainly occurring in spring and winter. At the annual scale, the basin is dominated by mild and moderate droughts, which have a high occurrence frequency, while severe and extreme droughts occur less frequently, indicating an overall dry tendency. In terms of spatial distribution, droughts occur mainly in the middle and lower reaches of the basin. During the period from 1976 to 2020, the degree of drought in the basin weakened, with a stable trend and small fluctuations in drought severity.

Abstract:In response to the spatiotemporal similarity of multiple measuring points in gravity dams and the uncertainty of statistical model structure, a hierarchical clustering method was used to spatially cluster all deformation measuring points. Principal component analysis was use to extract the comprehensive displacement of multiple measuring points in each zone. A statistical model for the comprehensive displacement of multiple measuring points was established using the Bayesian model averaging (BMA) method. Using the second zone along the vertical monitoring line of the gravity dam of Ankang Hydropower Station as an example, the optimization results of the complex BMA model and the simplified BMA model for comprehensive displacement were discussed, and the optimal factors of the models were given based on the quantitative analysis of the weighted average model. The analysis results indicate that the fluctuations in reservoir water level have no significant lag effect on dam displacement. The impact of downstream water level on dam displacement is very small, and relevant factors can be ignored in the modeling process. The impact of temperature rise and fall on the displacement of the dam shows a significant lag, and it is necessary to maintain high or low temperatures for more than 15 days before significant changes in the displacement of the dam body occur.

Abstract:In order to make full use of the data information of all the measuring points on the landslide surface and to eliminate the misjudgment of the landslide stability state due to different evaluation methods based on displacement trend analysis, a fuzzy comprehensive evaluation method for landslide stability state was proposed, integrating the displacement information from multiple measurement points and the evaluation results of multiple indices. The validation results from case studies show that this method avoids the shortcomings of evaluating landslide stability based on the displacement trend of a single measuring point. Additionally, by considering the results from multiple evaluation methods, it also avoids the limitations of using a single evaluation method for assessing the actual landslide stability state, making the evaluation results more reasonable.

Abstract:Based on a self-developed high-permeability water pressure loading test system, the moisture content change law of three different strength grades of concrete under four different high-permeability water pressure environments after continuous exposure for 3, 10, 24, 72, and 240 hours was studied. The pore structure characteristics of concrete under high-permeability water pressure environments were measured using the mercury intrusion porosimetry, revealing the microscopic mechanism of water content evolution in concrete under different water pressures. A prediction equation for concrete moisture content under different water pressure was constructed. The results show that the concrete moisture content increases rapidly with the extension of the exposure time under the high-permeability water pressure. The higher the permeable water pressure and the lower the concrete strength grade, the shorter the time required for the concrete to reach saturation and the higher the saturation moisture content. The saturation moisture contents of C15 concrete under 1, 2, and 3 MPa permeable water pressures are 1.12, 1.13 and 1.19 times that under 0 MPa, respectively.

Abstract:In order to promote the application of MgO concrete, the microstructure of MgO cement-based materials (cement mortar and one-grade concrete mortar) of small-size autoclave-treated specimens was investigated using mercury intrusion porosimetry and scanning electron microscopy. The results show that with the change in specimen size, the average pore diameter of MgO cement-based materials of micro specimens is the largest, followed by small specimens and standard specimens. The proportion of harmless and less harmful pores of standard specimens is the largest, followed by small specimens and micro specimens. With the same amount of MgO, as the amount of fly ash increases, the standard specimens have the smallest average pore diameter and the highest proportion of harmless and less harmful pores compared to small and micro specimens.

Abstract:The problem of groundwater overexploitation is prominent in the Huaihe River Basin and Shandong Peninsula region. This paper analyzes the situation of groundwater overexploitation in this region from aspects such as groundwater development and utilization trend, dynamic change of water level, and ecological and environmental geological problems. The causes of groundwater overexploitation are analyzed from aspects such as water resources endowment conditions, water resources carrying capacity, urban water demand changes, and groundwater supervision ability. In view of the existing problems in groundwater dual control index system, monitoring and measurement, information supervision and other aspects, this paper puts forward relevant countermeasures and suggestions from the perspective of strengthening the unified management of groundwater resources in the basin.

Abstract:In view of the dynamic characteristics of planar vertical-lift gates with large aspect ratio under the influence of pulsating pressure from water flow, the natural vibration frequency of the middle hole gate of the Jinhui Harbour South Gate was obtained through the analysis of natural vibration characteristics.The pulsating pressure on the gate model under different conditions was measured through physical model tests. The power spectrum functions of pulsating pressure at various measurement points were obtained through spectral analysis using the fast Fourier transform technique. These results were compared with the natural vibration characteristics to determine whether resonance would occur. The measured pulsating pressure was converted into nodal loads for finite element calculations, and random vibration methods were employed for numerical simulations to analyze the flow-induced vibration response of the gate, yielding results for dynamic displacement, dynamic stress, and other response factors under different gate opening conditions. The research results show that the dominant frequency of the pulsating pressure is below 1 Hz, with a large offset from the first-order natural frequency of the gate, which is 1.42 Hz, making resonance unlikely. The dynamic displacement response of the gate is less than 0.25 mm, and the maximum total stress is 8.15 MPa. Under various gate opening conditions, the dynamic response of the gate remains within the allowable structural range, indicating a high level of safety.

Abstract:To address the issues of low denoising accuracy and the misclassification of useful high-frequency information as noise in existing methods for dam deformation monitoring data, a denoising method combining the adaptive noise complete ensemble empirical mode decomposition (CEEMDAN) and improved wavelet threshold was proposed. This method decomposes the original data using CEEMDAN and performs feature analysis on the intrinsic mode function (IMF) components obtained from the decomposition through t -tests, screening out noisy components. These components were verified using the Pearson correlation coefficient and variance contribution rate. Finally, the identified noise-containing components are finely denoised using an improved wavelet thresholding method, and the denoised IMF components are reconstructed to obtain the denoised data. Simulation tests and engineering case verification results show that this method outperforms three comparative methods across various indicators, while effectively preserving useful high-frequency information, improving accuracy and smoothness, and can be used for denoising nonlinear deformation data in dams.

Abstract:The construction timing of concrete cut-off walls in the old reservoir dam heightening project has a great influence on its own stress and deformation, which may cause potential safety hazards to the anti-seepage system of the dam body. Taking a heightening project of an earth-rockfill dam as an example, the three-dimensional finite element method was used to simulate the heightening process of the dam, analyze and compare the stress and deformation characteristics of the cut-off wall under different construction schemes, and discuss the optimal construction timing of the cut-off wall. The calculation results show that under the conditions that the cut-off wall of the old dam is built when or before the heightened dam is filled to 215 m, the stress and deformation of the cut-off wall are lower, and during the completion period and the water storage period, the displacements of the cut-off wall along the river are about -1.56 cm and 4.91 cm, the maximum principal stresses are about 1.01 MPa and 1.67 MPa, and the minimum principal stresses are about -0.41 MPa and -0.66 MPa, respectively. The extreme values of the tangential displacement and relative settlement of the joint between the cut-off wall and the connecting plate are 4.84 mm and 8.11 mm, respectively, which can meet the requirements of safe operation. Compared with the cut-off wall constructed in the late stage of heightening dam filling, completing the construction of the cut-off wall before the filling of the heightening dam starts or before the filling reaches the same height as the old dam can improve the stress and deformation state of the cut-off wall and reduce the tangential displacement and relative settlement of the joint between the cut-off wall and the connecting plate.

Abstract:In order to analyze the mechanical properties of white sandstone in northern Xinjiang, the direct shear, compression, permeability and SEM tests of white sandstone under different factors were carried out to analyze the mechanical properties from the macro and micro perspectives and reveal its microscopic mechanism. The test results show that in the direct shear test, the cohesion changes parabolically with the increase of moisture content, reaching a peak near the optimal moisture content, the internal friction angle decreases linearly with the increase of moisture content, and the cohesion and internal friction angle both show a linear upward trend with the increase of dry density. In the compression test, the compression index gradually increases and the rebound index fluctuates with the increase of moisture content, the compression index and rebound index decrease exponentially with the increase of dry density, the particle size increases and the roundness, pore size and microscopic porosity decrease with the increase of vertical pressure, the particles and pores have obvious orientation, and the microscopic porosity is the main factor affecting the compression index. In the permeability test, the permeability coefficient decreases exponentially with the increase of dry density, the magnitude of permeability coefficient decreases from 10^-4 to 10^-6 when the dry density increases from 1.60 g/cm³to 1.84 g/cm³, the trellis pore and permeability decrease with the increase of dry density, there is a significant correlation between the average pore size and permeability coefficient, and the average pore size is the key factor influencing the permeability of white sandstone.