Refined mathematical model for the breaching of concrete-face sand-gravel dams due to overtopping failure

Overtopping is one of the main reasons for the breaching of concrete-face sand-gravel dams(CFSGDs).In this study,a refined mathematical model was established based on the characteristics of the overtopping breaching of CFSGDs.The model characteristics were as follows:(1)Based on the Renormailzation Group(RNG)k-εturbulence theory and volume of fluid(VOF)method,the turbulent characteristics of the dam-break flow were simulated,and the erosion surface of the water and soil was tracked;(2)In consideration of the influence of the change in the sediment content on the dam-break flow,the dam material transport equation,which could reflect the characteristics of particle settlement and entrainment motion,was used to simulate the erosion process of the sand gravels;(3)Based on the bending moment balance method,a failure equation of the concrete face slab under dead weight and water load was established.The proposed model was verified through a case study on the failure of the Gouhou CFSGD.The results showed that the proposed model could well simulate the erosion mode of the special vortex flow of the CFSGD scouring the support body of the concrete face slab inward and reflect the mutual coupling relationship between the dam-break flow,sand gravels,and concrete face slabs.Compared with the measured values,the relative errors of the peak discharge,final breach average width,dam breaching duration,and maximum failure length of the face slab calculated using the proposed model were all less than 12%,thus verifying the rationality of the model.The proposed model was demonstrated to perform better and provide more detailed results than three selected parametric models and three simplified mathematical models.The study results can aid in establishing the risk level and devising early warning strategies for CFSGDs.

Behaviour of large post-liquefaction deformation in saturated sand-gravel composites

The laboratory tests on the post-liquefaction deformation of saturated sand-gravel composites were performed to investigate the characteristics of stress-strain relation and the dissipation of pore water pressure by the hollow cylinder apparatus. It is found that the stress-strain response and the dissipation process of pore water pressure are composed of three stages, including the low intensive strength stage, the superlinear strength recovery stage and the sublinear strength recovery stage, and the demarcation points of the curve of pore water pressure are lag behind those of the stress-strain response. The comparison results of the behaviour of large post-liquefaction deformation between saturated sand-gravel composites and Nanjing fine sand show that the low intensive strength stage and the superlinear strength recovery stage of saturated sand-gravel composites are shorter while the sublinear strength recovery stage is longer. A stress-strain model and a dissipation model of excess pore water pressure of liquefied sand-gravel composites are established, in which the initial confining pressure and the relative density can be considered synthetically. And it is found that the predicted results by the two models are in good agreement with experimental data.

Construction parameters of graded sand-gravel foundation on seismic response law of nuclear safety grade underground corridor

The treatment of soft soil foundation under nuclear safety grade corridors with graded sand and gravel materials has a good development prospect.It is of great engineering value to explore the influence of construction parameters of graded sand and gravel foundation on the seismic response of gallery structures.Taking the safety grade underground corridor of a nuclear power plant as the engineering background,the equivalent linear method is used to consider the nonlinear dynamic characteristics of graded sand and gravel.The energy transfer boundary is applied at the truncation boundary to simulate the dissipation effect of scattered wave fluctuation energy and the ground motion input.The thicknessless contact element is introduced to consider the contact effect between the corridor structure and the graded sand and gravel foundation,so as to establish the calculation model of the dynamic interaction between the graded sand and gravel foundation and the corridor structure.Furthermore,the influence of the relative compactness and the foundation treatment depth on the seismic response of the corridor structure is studied,and the calculation results of the acceleration response spectrum and relative displacement of the corridor structure are analyzed.The calculation results show that the two construction parameters have different degrees of influence on the seismic response of corridor structure.The research results can provide reference for the engineering design and construction of underground corridors,and provide technical support for the application of graded gravel materials in soft soil foundation treatment.

The Hydrochemical Characteristics of a Stressed Sand-Gravel Aquifer: Kazan Plain, Ankara, Turkey

Over-exploitation and sand-gravel mining affect groundwater resources in terms of both quantity and quality. Groundwater level and well yields in and around the sand-gravel pits significantly decrease. Sand-gravel mining also changes the turbidity levels and temperature of groundwater. Reduction and destruction of valuable aquifers are significant issues. In this case, the natural state of the aquifer disappears. The Kazan Plain in central Turkey is a dramatic example of these kinds of results. The productive sand-gravel aquifer in the Kazan plain has been substantially damaged due to intensive sand-gravel mining since the 1980s. Additionally, over-exploitation has caused notable declines in groundwater levels, particularly in the 2000s. This study focuses on the hydrogeochemical situation of the Kazan Plain alluvium aquifer after intensive sand-gravel mining and over-exploitation. Groundwater samples were collected seasonally in 2015, five years after the over-exploitation and heavy sand-gravel mining. The decline reached 20 m (about half of the saturated thickness of the sand-gravel aquifer) in the region where the intensive groundwater abstraction lasted until 2010. Some quarries continued to operate until 2010, but after that mining activity continued only at a minimum level. Today, groundwater quality has been significantly degraded due to the over-exploitation of sand-gravel mining and also the cessation of recharge from fresh river water.

柴达木盆地卤水钾盐迁聚规律与找矿新突破

钾盐是我国大宗紧缺战略性“粮食”矿产,对保障国家粮食安全具有重要意义。我国钾盐资源具有需求量大、对外依存度高等特点,寻找新的钾盐矿床、形成新的大型钾盐资源基地刻不容缓。2023年,中国地质调查局组织开展青海柴达木盆地钾盐“增储保供”地质调查工作,在前期对柴达木盆地成盐聚钾规律性认识的基础上,于柴西北大浪滩—黑北凹地部署实施了“探采一体化”柴钾1井,钻获1021.95 m(井深111.54~1133.49 m)巨厚松散砂砾储卤层,全井段抽卤试验获日稳定涌水量8586 m^(3)/d、水位降深11.3 m、单位涌水量759.89 m^(3)/d·m、氯化钾平均含量为0.54%的高产工业品位“砂砾型”卤水钾矿,取得了柴达木盆地陆相深层卤水钾盐找矿新突破,为形成中国新的亿吨级大型钾盐基地夯实了资源基础。

砂卵石地层矿山法隧道长管棚支护机理及应用

研究目的:砂卵石地层由于卵石强度高且颗粒分布无序,因此长管棚施工地层扰动大且支护效果难以保证,已成为制约隧道实际应用的一大瓶颈。本文以某轨道交通暗挖法车站为依托工程,采用理论分析、现场测试与数值模拟相结合的方法,对不同直径、不同环向间距条件下长管棚的支护效果进行了深入研究,以期揭示砂卵石地层矿山法隧道长管棚支护机理,提出最佳支护参数。研究结论:(1)砂卵石地层,暗挖隧道管棚超前支护条件下,地层沉降变形在向地表传递过程中,沿高度方向的折减率约为0.91 mm/m;(2)管棚超前支护效果对矿山法隧道工程安全具有决定性作用,须采取措施减小管棚施工扰动及相应地层变形;(3)根据单因素敏感性分析结果,地表沉降随管棚支护长度的增加而增大,随管棚环向间距的增大而增加,且基本呈正相关;(4)为有效控制地表沉降并提高工程经济效益,建议直径127 mm管棚环向间距宜为35 cm,支护长度宜为40 m;直径159 mm管棚建议环向间距宜为40 cm,支护长度宜为40 m;直径209 mm管棚建议环向间距宜为45 cm,支护长度宜为50 m;管棚直径与其最佳打设长度正相关;(5)本研究结论可为砂卵石地层矿山法隧道支护措施提供借鉴与参考。

TRD工法在赣江尾闾围堰防渗工程中的应用

赣江下游尾闾综合整治工程4支枢纽采用TRD工法对防渗墙进行施工,并针对重难点区段调整了施工工艺,该做法克服了地质条件复杂、砂卵砾石地层厚度大、防渗墙深度大等不利因素的影响,施工效率高且安全环保,取得了良好的防渗效果。

基于BP神经网络的胶结砂砾石应力-应变关系预测

在前期宏观试验基础之上,采用离散元模拟和BP神经网络相结合的方法获取不同胶凝材料掺量和围压下胶结砂砾石的应力-应变关系。根据前期胶凝材料掺量分别为20、40、60、80、100 kg/m3的胶结砂砾石三轴排水剪切试验结果,开展离散元数值模拟。以试验数据为学习样本,开展BP神经网络模型训练,预测胶凝材料掺量分别为30、50、70、90 kg/m3的胶结砂砾石应力-应变关系,并将预测结果和离散元模拟结果进行对比。研究结果表明,BP神经网络能够实现胶结砂砾石应力-应变关系的预测,并在较低围压下具有较好的精度。

贵州省砂石矿山开采对生态环境的影响研究

正确认识砂石开采对生态环境的影响,对于调整砂石政策,保护矿区生态环境和制定矿区生态修复措施具有重要意义。以贵州省砂石矿山为例,通过分析砂石矿山开采对土地利用类型和生态系统服务功能的影响,揭示砂石矿山开采对生态环境的影响。研究结果表明:1)2010—2020年,贵州省砂石矿山开采占地共计11502.45 hm^(2),其中,占用农田4923.12 hm^(2),破坏森林面积4446.24 hm^(2);2)根据贵州省2020年砂石矿山开采现状,砂石矿区未来最适宜恢复的土地类型排序为森林>建设用地>农田;3)2010—2020年,贵州省因砂石开采损失的生态系统服务价值约6.34亿元,从生态系统服务功能看,对气候调节功能影响最大,对维持养分循环服务的影响最小。

小山口水电站砂砾石面板坝三维静、动力有限元计算分析

鉴于小山口水电站为软岩基础,坝体较长,且混合坝接头部位非常复杂。为了解决该坝体面临的变形控制难、坝体抗震等级高等设计难题,结合砂砾石面板坝结构、坝壳料设计,通过构建三维有限元模型,该模型包括坝体、泥岩和沙质泥岩基础组成。在静力本构分析中,采用了非线性邓肯E-B模型,而在动力本构分析中,则使用了等效线性粘弹性模型。通过这个模型,对坝体的应力和变形进行了全面系统的研究和分析,同时对坝体的抗震性能和抗震稳定性进行了验证。结果表明,在各种工况下坝体所表现出的变形规律合理。同时在混凝土面板最大拉应力和压应力都符合所采用混凝土材料的允许应力要求,坝体的抗震性能和抗震稳定性满足规范要求。

旱区连作砂田土壤质量和土地生产力演变与调控研究进展

砾石覆盖在改变旱区水文循环和物质转化方面有着至关重要的作用。然而,长期连作给砂田土壤质量及土地生产力带来危机和不确定性。以连作砂田为研究对象,归纳总结了连作年限对砂层质地结构、土壤物理结构、土壤水盐热效应、土壤养分状况、土壤酶活性、土壤微生物特性、作物生长发育以及产量品质的影响效应和可能机制,发现砂田土壤生态环境和土地生产力在人类活动及自然侵蚀的扰动和破坏下整体呈现退化态势,但对不同覆盖条件、施肥水平和种植结构等农田管理措施的响应过程表现出差异性。继而,基于土壤质量和土地生产力的协同和互作效应深入揭示了砂田性能逐年退化机理,并简述了生物、农业及工程调控措施在砂田退化阻控和修复方面的应用进展。在此基础上,提出了砂田退化进程中急需解决的关键科学问题和未来发展方向,主要包括土壤质量演变的基本过程及其发生机制、“砾石-土壤-微生物-植物”系统的叠加和互作效应及其分子机理、土壤改良与生物防治措施的定量化及其调控机制三个方面。在气候变化、植被演替和土地退化背景下,废弃风化砾石的劣化增肥机制及其环境效应将是今后研究的重点。

面板堆石坝含特细砂砂砾石填筑料碾压特性研究

阿尔塔什水利枢纽工程大坝主堆石区填筑料以砂砾石料为主,该地区河滩砂砾石料颗粒级配中的砂为特细砂,其在砂的级配中缺少中粗砂、级配不连续、保水性较差等特殊性级配料的特点导致其在施工过程中势必会影响到碾压的压实效果,给施工过程的质量控制带来很大难度。阐述了施工中通过对含特细砂砂砾石填筑料进行的不同加水量、不同厚度、不同碾压遍数及碾压机械等不同的碾压工艺参数进行试验检测、综合统计分析研究,探索出适合该工程的相关碾压施工参数标准,优化了施工碾压参数,提升了施工现场试验检测控制的时效性,为大坝填筑建设提供了稳定、可靠的施工参数,增强了坝体整体填筑的可靠性,为减小坝体沉降变形、提高大坝抗震安全储备和控制大坝施工质量等提供了有利条件。

复合过水围堰高效填筑技术

针对非洲的朱利叶斯·尼雷尔(Julius Nyerere)水电站大坝成功截流后,上游过水围堰建造期短、工程量大、施工要求高等难题,提出了一种复合过水围堰新型高效填筑技术,重点介绍了底部赶水混凝土浇筑、左岸堆石混凝土浇筑、下游预制挡块模板施工、上游黏土防渗层平起施工、主体胶凝砂砾石变态碾压施工5种高效填筑施工流程及关键技术。工程实践表明,该新型高效填筑技术大幅优化了施工组织与效率,最终在汛期来临之前安全、高效、优质地完成了过水围堰的修筑工作。

基于沙漠治理智能小车的创新实验教学系统设计

针对教育部提出的提高高校学生的创新和实践能力,该实践教学系统依托学科竞赛,设计了沙漠治理自动化装置,将智能小车和砾石铺设装置组合在一起,通过控制系统控制智能小车的行驶轨迹,同时控制砾石铺设装置,将砾石按田字形规律铺设,达到减轻人工铺设的劳动量,提高铺设效率。该实践教学系统激发了学生的兴趣和潜能,培养了学生的科研能力和创新精神。

南海岛礁珊瑚砂砾混合料动力特性试验研究

在南海岛礁实际建造工程中,上部吹填地基材料以大小砂砾共存、混杂无序的状态分布。地层中砂砾混合分布状态使地基在地震等动荷载下呈现出复杂的力学响应。通过开展一系列不同含砾量、密实度、围压和初始剪应力条件下的不排水循环三轴剪切试验,研究珊瑚砂砾混合料在不同工况下的动力特性。试验结果表明,无论是在松散还是密实状态,含有珊瑚砾的混合料试样在循环荷载下表现出更缓的轴向应变增长和孔隙水压上升的变化趋势。与单一珊瑚砂所构成的试样相比,珊瑚砂砾料试样具有更高的抗液化能力。珊瑚砂砾混合料抗液化强度随着含砾量、密实度和初始剪应力的增大而显著提高。密实珊瑚砂砾料的抗液化强度随围压的增大而减小,而针对松散试样没有发现明显规律,这可能是围压和密实度耦合影响引起的。试验结果表明含砾量对试样抗液化强度的影响主要受混合料骨架结构所控制,混合料骨架大致可分为粗颗粒(珊瑚砾)和细颗粒(珊瑚砂)结构主导两种状态。二元介质属性是开展砂砾混合料力学特性研究所必须考虑的影响因素。

胶凝砂砾石纳米压痕试验及系统聚类法界面过渡区的研究

针对胶凝砂砾石材料微观力学性能的研究成果较少的问题,以及胶凝砂砾石材料界面过渡区的存在性问题,提出了胶凝砂砾石不同相的确定方法以及界面过渡区尺寸的确定方法.结合纳米压痕试验,绘制微观力学性能图像,采用系统聚类法对测试矩阵内的测试点进行分类.在试验阶段,考虑到胶凝砂砾石的材料特性,完善了“30-2-30”测试制度,通过荷载-深度曲线结合Oliver-Pharr方法求出胶凝材料硬度H为0.18 GPa,折合模量Er为13.13 GPa,砂砾石材料硬度H为8.60 GPa,折合模量Er为84.56 GPa.在计算阶段,采用系统聚类法确定界面过渡区范围,确定其尺寸约为18μm.

砂卵石地层大直径盾构施工的关键技术

[目的]总结分析砂卵石地层大直径盾构施工中盾构机选型、盾构始发与接收、盾构掘进姿态控制等施工关键技术,并提出具体的施工控制参数与施工控制措施,以减轻刀盘刀具磨损、降低地层损失、减小地层沉降变形。[方法]针对砂卵石地层结构松散、颗粒无胶结或弱胶结、颗粒粒径大、透水性强的工程结构特性,采用理论分析、现场监测等方法,从盾构机选型、盾构始发接收、盾构掘进姿态控制、盾构刀盘刀具的检测维修等方面深入分析砂卵石地层大直径盾构施工关键技术。[结果及结论]大直径盾构的刀盘开口率、刀盘刀具类型、渣土改良方案等应根据地层结构特性进行特殊设计,且有利于盾构排渣和超前切割;盾构井端头宜采取地层注浆加固、大管棚支护、施工降水等综合加固措施以保证大盾构始发或接收时地层的稳定;大直径盾构的掘进施工应重点控制刀盘转速、出渣量、出渣温度等参数,并应适当增大注浆量,提高渣土改良效果,避免过大超挖,保证地层损失处于合理范围内。采用上述施工参数与施工措施后,盾构掘进风险可控,施工质量与施工效率明显提升,同时大大降低了施工成本。

抽水蓄能电站绿色施工技术

抽水蓄能电站建设发展迅猛,但在工程施工过程中存在高投入、高消耗、高污染、低效率等现象,迫切需采取措施推进绿色施工。为此,基于绿色施工的核心理念,介绍了近年来抽水蓄能电站绿色施工技术,包括抽水蓄能电站新坝型、绿色输水隧洞施工技术、绿色混凝土制备技术、绿色砂石加工技术、边坡生态修复技术、二氧化碳爆破技术及施工车辆电气化等,取得了良好效果。

根-土复合体抗剪强度影响因素研究

为比较根-土复合体组分及法向应力对其抗剪强度的影响程度,选取四川省喜德县冕山镇坡面(安宁河流域砾砂区)云南松根-土复合体和素土作为研究对象,通过室内直剪试验获得其抗剪强度,烘干试验获得各组分质量,利用根-土复合体的干土质量、水质量和干根质量进行Pearson相关分析,构建回归分析模型计算根-土复合体各组分质量与抗剪强度的标准化回归系数。结果表明:根-土复合体的干土质量与干根质量间存在显著负相关关系(P=0.002<0.01,r=-0.792),根-土复合体中水质量与干土质量和干根质量之间均无显著相关关系(P>0.05);云南松根-土复合体中干土质量、干根质量和水的质量与抗剪强度的标准化回归系数分别为0.06、0.03和0.03,表明干土质量对根-土复合体抗剪强度的影响程度较水的质量和干根质量的影响程度大;与素土的内摩擦角和黏聚力相比,云南松根-土复合体的内摩擦角增加了1.31%~1.97%,黏聚力增加了16.71%~34.74%。

中国西北旱区砂田表层土壤养分效应对连作响应的整合分析

为明确砂田表层土壤养分对连作的响应规律,深入揭示砂田性能逐年退化机理,文章基于国内外已发表的16篇相关文献的586组有效数据,借助Meta-analysis方法进行整合定量研究,定量分析覆砂1—3年农田与其他连作年限砂田(4—6年、7—9年、10—12年、13—15年、16—20年)在表层土壤水分状况(SWC)、养分特性(有机质SOM、全氮TN、全磷TP、全钾TK、碱解氮AN、速效磷AP、速效钾AK、全盐TSS)和酸碱环境(pH)方面的差异效应,系统阐释砂田表层土壤养分特性逐年变异的发生路径及驱动因素,进而综合评估其肥力水平。结果表明:伴随种植年限的增加,砂田表层土壤水分储量和养分强度整体呈现下降态势(P<0.05),4—20年的土壤SWC、SOM、TN、TP、TK、AN、AP、AK含量分别较1—3年减少39.06%、14.21%、14.96%、10.06%、8.20%、15.87%、37.01%、18.60%(P<0.05)。表层土壤SOM、TN、TP、TK、AN、AP、AK主要于10—12年开始大幅流失(P<0.05),而4—6年土壤SOM、TP、TK、AK含量的相对变化则不显著(P>0.05)。砂田在耕作12年内具有显著压盐效果,12年以后的表层土壤TSS含量则开始呈现逐年增加的发展趋向(P<0.05),其土壤pH整体增加1.29%(P<0.05)。连作年限是砂田表层土壤TN、TP和AK变异的关键因子;SWC则为土壤SOM、AP和TSS演化的主导要素。总体而言,砂田在连作10年左右即可出现明显的养分亏缺状态。因此,亟需提出科学合理的农田管理措施,以有效提升退化砂田的土壤肥力水平。