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.

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.

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.

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。

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。

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。

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。

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。

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。

山东省建筑用灰岩资源潜力分析

建筑用灰岩是山东省砂石的主要矿种,因此本文重点研究山东省建筑用灰岩潜力情况,分析了建筑用灰岩赋存层位及其分布情况,圈定了9处建筑用灰岩资源潜力集中区,并采用地质体积法预测了各集中潜力区压占及未压占资源潜力情况。结合实际情况提出了山东省重点开发建筑用灰岩的区域等开发利用建议。

238m深古河槽帷幕灌浆试验结果分析

古河道两岸基岩出露,河道内沉积了深厚的砂卵砾石层,在托其里萨依河岸边呈直立的陡坎状,上部为第四系上更新统Q3砂卵砾石层,青灰色,厚34~40m;下部岩性为巨厚层的Q_(2)砂卵砾石层,泥质半胶结,呈土黄~棕黄色,厚度50~295m,底部岩性为下元古界蚀变辉绿岩。古河道最底部低于正常蓄水位,最深283m,蓄水后主要位于Q_(2)泥质半胶结的砂卵砾石层,该层存在渗漏的可能。用“孔口封闭灌浆法”进行生产性灌浆试验,取得了一定的成效。经帷幕灌浆处理后受灌地层渗透系数较灌前3.73×10^(-3)cm/s(中等透水地层)、1.0×10^(-2)cm/s(强透水地层)有较明显地减小,表明该地层经帷幕灌浆处理后,地层的防渗性能得到了较大幅度的提升,帷幕灌浆试验取得了一定的成效。

富水砂卵石地层深基坑降水特性及涌水量研究

以洛阳市周山大道下穿开元大道路口明挖深基坑工程为依托,分析各降水参数改变对渗流场分布与降水效率的影响。通过Midas GTS NX有限元软件,模拟分析不同降水参数下降水井抽排地下水情况,同时建立了标准状态下涌水量特征曲线,并针对非标准状态提出涌水量修正方法。结果表明:除地层渗透系数改变地下水流速外,其他参数均会导致流网形态发生改变,与阻隔效应耦合后将间接影响降水速率。另外,通过工程实例验证考虑止水帷幕阻隔作用后的深基坑涌水量预测公式及其修正函数具有合理性,可应用于砂卵石地层深基坑降水工程。

胶凝砂砾石筑坝材料特性研究

胶凝砂砾石是一种介于混凝土与堆石料之间的新型筑坝胶凝材料,具有节约资源、降低造价、保护环境等优点,对胶凝砂砾石材料的特性研究是坝体结构设计的关键,目前对于胶凝砂砾石材料的特性研究缺少较为全面的认识。为使胶凝砂砾石材料更好的应用于实际工程,因此通过文献查阅,本文总结了胶凝砂砾石材料的力学性能和冻融环境下的材料耐久性等方面试验研究,对胶凝砂砾石材料特性受胶材用量、单位用水量、水胶比、砂率、龄期等多种参数的影响规律进行综合分析,为胶凝砂砾石筑坝材料的进一步研究和应用提供理论基础。

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。

轴压荷载对胶凝砂砾石材料渗透性能的影响

胶凝砂砾石作为一种新型环保的建筑材料,在其实际服役状态下坝体承受各种荷载作用,为研究轴压荷载对于胶凝砂砾石渗透性能的影响,选用工程中常用的4种配合比,进行轴压加载试验、渗透试验、超声波速监测试验、核磁共振试验。针对试验数据分别分析了不同轴压荷载对胶凝砂砾石渗透性能的影响,得出以下结论:试件的渗透系数与孔隙率随轴压荷载水平呈正相关;渗透系数与孔隙率服从指数函数关系。采用孔径分布的回归模型能够较好的适用于胶凝砂砾石渗透系数的预测。

长江宜昌至大埠街段砂卵石河床疏浚对航槽动力影响研究

为研究长江宜昌至大埠街段砂卵石河床疏浚对航槽动力环境的影响,采用基于非结构网格的二维水流模型,充分考虑下游沙质河床水位下降溯源作用,分析出口水位下降与疏浚共同影响下的航槽内水流动力特征变化。结果表明,在河床保持稳定的前提下,下游沙质河段水位下降2 m,水位下降向上传递沿程递减,至陈二口处水位降幅降至0.004 m,至宜昌水位降幅降至0.001 m以内,比降的影响表现为局部比降增大,增大区域主要集中在姚港以下;疏浚能提升航道水深,缓解航槽内的坡陡现象,但也会降低沿程河段的水位控制强度,下游水位下降2 m结合疏浚后,水位下降0.004 m将上延至周家河,宜昌水位降幅将增大至0.002 m。研究成果可为长江干线砂卵石河段航道尺度提升、航道维护等提供技术支撑。