双河拱坝应力分析

介绍了双河拱坝的开裂情况和多种工况下拱坝拱梁分载法的应力分析成果,对双河拱坝的开裂原因和拱坝安全进行了初步分析和评价,并对拱坝的体形设计提出了建议。     

碾压沥青混凝土非常规施工方法的研究与应用

碾压沥青混凝土施工在很大程度上受制于天气,恶劣气候地区全年适应沥青混凝土施工的天数非常有限,如何增加其有效施工期非常重要;在四川省南桠河冶勒水电站大坝工程,进行了沥青混合料摊铺层厚30cm、环境气温-6℃以上、日铺筑2层的研究和应用。这些非常规施工方法经过冶勒大坝沥青混凝土防渗心墙施工的实践,证实和验证了其施工质量的可靠性。本文对碾压沥青混凝土的非常规施工进行了介绍。     

水电站大坝应有完善的险情预计和应急处理预案

水电站大坝失事会给下游人民的生命、财产和环境带来巨大的灾难。因此,大坝安全管理应在坚持防止或减少事故发生的同时,还必须对大坝可能的失事模式进行险情预计和编制应急处理预案,一旦事故发生,能最大限度地减小事故的损失。     

Towards online monitoring of concrete dam displacement subject to time-varying environments: An improved sequential learning approach

Data-based models are widely applied in concrete dam health monitoring. However, most existing models are restricted to offline modeling, which cannot continuously track the displacement behavior with dynamic evolution patterns, especially in time-varying environments. In this paper, sequential learning is introduced to establish an online monitoring model for dam displacement behavior. This approach starts by considering the timeliness difference between old and new data using the forgetting mechanism, and a novel adaptive forgetting extreme learning machine (AF-ELM) is presented. A primary predictor based on AF-ELM is then formulated, which aims to sequentially learn the complex nonlinear relationship between dam displacement and main environmental factors. Considering the chaotic characteristics contained in the residual sequence of the primary predictor, a multi-scale residual-error correction (REC) strategy is devised based on divide-and-conquer scheme. Specifically, time-varying filter-based empirical mode decomposition is adopted to decompose the raw chaotic residual-error series into a set of subseries with more stationarity, which are further aggregated and reconstructed by fuzzy entropy theory and suitable approximation criterion. Finally, the corrected residual sequence is superimposed with the preliminary predictions from AF-ELM to generate the required modeling results. The effectiveness of the proposed model is verified and assessed by taking a real concrete dam as an example and comparing prediction performance with state-of-the-art models. The results show that AF-ELM performs better in displacement prediction compared with benchmark models, and the multi-scale REC can effectively identify the valuable information within the residual sequence. The proposed online monitoring model can more closely track the dynamic variations of displacement data, which provides a fire-new solution for dam behavior prediction and analysis.     

Morphological response of the upper Yangtze Estuary to changes in natural and anthropogenic factors

Globally, over the past few decades, extreme river channel deformation has been observed downstream of dams. Specially, estuarine channel deformation and its response to natural and anthropogenic factors are key issues influencing channel regulation and prediction of long-term stability in large estuarine deltas. Herein, bathymetry data for the upper reaches of the Yangtze Estuary (YE), China was collected for the years 1995, 2003, 2008, 2013, and 2019 to analyze the channel deformation process. Our findings show that the total erosion volume was approximately 11.22 × 10⁸ m³, an equivalent of 15.7 × 10⁸ t of sediment assuming a bulk density of 1.4 t/m³ for the riverbed material during 1995–2019. Meanwhile, the annual erosion rate is 0.63 Mt/year in 1995–2019, and the annual erosion rate is 0.90, 0.12, 0.40 Mt/year in 1995–2003, 2008–2013 and 2013–2019, respectively. Meanwhile, the annual deposition rate is 0.7 Mt/year during 2003–2008. Further analysis indicated that continuous reduction of the sediment load due to the construction of dams (e.g., the Three Gorges Dam) in the basin was a key factor influencing channel erosion over the past 24 years. The channel deformation process was characterized by severe erosion during 1995–2003, a deposition period during 2003–2008, a dynamic equilibrium period from 2008–2013, and an erosion period after 2013. Due to floods with maximum peak discharge lower than 70,000 m³/s, despite the annual sediment load is reduced, the channel deposition phenomenon occurred in 2003–2008. The channel changed from a depositional system to an erosion system during 2008–2013. After 2013, the channel was dominated by extensive erosion, severe local deposition, or severe local erosion as a response to anthropogenic interventions. These findings are of great significance to river management and regulation, as well as to the navigational safety.     

冲击作用下铀尾矿坝损伤与氡析出规律北大核心

冲击损伤会破坏铀尾矿坝体结构,给周边及下游人身财产安全带来潜在危害。通过自研水平冲击试验台开展铀尾矿库坝体冲击模拟试验,研究冲击速度逐级加载下坝体损伤特征及其坝体损伤氡析出规律。结果表明,冲击对坝体的损伤主要表现为表面单主裂隙发育和穿透破坏,穿透深度随冲击速度的增加而增加,红土层穿透破坏后的穿透深度的变化速度增大;红土层穿透前的氡浓度累积增长速率快于穿透后,穿透深度与整体氡析出率的规律呈现为缓慢上升(OA)-快速上升(AB)-趋于平稳(BC);穿透深度与降氡系数之间呈现快速下降到趋于平稳的规律,在红土层穿透后的3~7 cm穿透区间内降氡系数变化仅为2.94%。其结果可为铀尾矿库坝体安全稳定性研究提供参考。     

坝基老化的反向水文地球化学模拟

根据不同化学组分在坝基岩水系统中的相互转化规律,建立了坝基老化的反向水文地球化学模型,利用Barrodale-Roberts算法对模型进行求解,计算给定随机误差极限范围内不同坝基渗漏量条件下的坝基岩土体与地下水溶液间的物质交换量及其变化范围。将该模型应用到新安江大坝右坝段坝基老化分析中,结果表明所建立的模型可靠实用,求解速度较快。     

特高土心墙堆石坝坝基防渗体渗流-溶蚀特征研究

针对渗透溶蚀效应下特高土心墙堆石坝的渗流与溶蚀问题，构建了以孔隙水压力、固相钙浓度与钙离子浓度为自由度的水泥基材料渗流-溶蚀耦合模型。以长河坝工程为背景，研究了特高土心墙堆石坝的渗流溶蚀特征，探讨了渗透溶蚀效应下特高土心墙堆石坝的失效标准，预测了坝体的服役年限。渗透溶蚀效应降低了坝体的防渗能力，服役100 a后坝体浸润线逸出点将较初始时刻抬升1.95 m;随着服役年限的增加，覆盖层、副防渗墙的渗透坡降增加，心墙、主防渗墙和防渗帷幕的渗透坡降降低;水泥基材料固相钙溶蚀相对严重的区域集中在两道防渗墙中下部、固结灌浆靠下游侧及防渗帷幕，靠近复合土工膜和高塑性黏土的坝基防渗体溶蚀程度较低。从固相钙的分解率、渗透系数、渗流量、渗透坡降和边坡稳定等角度分析，认为考虑渗透溶蚀效应时长河坝的服役年限约为68.3 a，降低主防渗帷幕的初始渗透性可较为有效地延长坝体服役年限。特高土心墙堆石坝坝基水泥基结构渗透溶蚀效应不可忽视，其设计、运行及维护应充分考虑水泥基材料的渗透溶蚀效应。