Effects of Large-Scale Twin Tunnel Excavation on an Existing Pile Group: Three-Dimensional Centrifuge Modeling

Soil Mechanics and Foundation Engineering - Existing piles are commonly encountered during tunnel construction in congested underground areas. Tunnel-soil-pile interaction has recently attracted...     

遮帘桩工作性状影响因素分析

遮帘桩作为挡土桩在深水建港、深基坑开挖及护岸工程中应用越来越广泛.为了研究开挖过程中遮帘桩的工作性状,运用大型有限元软件建立三维有限元的遮帘桩结构模型,模拟某板桩码头港池开挖.分析港池开挖后遮帘桩的刚度、桩长、桩间距及遮帘桩与板桩墙距等对板桩墙结构的影响,从而提出控制板桩墙结构变形、保持港池开挖后稳定的遮帘桩布置方法.研究结果表明,增加遮帘桩桩长和刚度能有效减小板桩墙的变形、陆侧主动土压力和弯矩,而遮帘桩间距和墙桩距的变化对遮帘桩挡土效果的影响不明显.     

三峡水库蓄水后守护型工程对改善长江中游航道条件的作用

运用河流动力学理论,推求出整治水位下河槽在冲刷前、后航深变化值的表达式,对表达式的理论分析结果表明,在三峡水库下泄清水冲刷的条件下,通过守护关键可动洲滩,控制航槽不向两侧展宽,同时控制航槽内低矮的洲滩不被冲蚀,使清水冲刷只向纵向发展,就能达到增加航深的目的,这正是守护型控导工程对改善航道条件的积极作用所在。以长江中游荆江藕池口河段和太平口河段为例,计算了这两个河段守护关键可动洲滩后航深的变化值,模型计算值与实测断面概化后得到的航深变化值基本一致,进一步验证了守护型工程实现航道改善的作用。     

半直立式圆筒护岸地基现场加载试验及变形分析

半直立式圆筒护岸是一种新式港口工程结构,结合其在大连某水工护岸工程中的应用,进行了半直立式圆筒护岸地基的加载试验,通过实测土压力、沉降、水平位移及孔隙水压力,分析了半直立式圆筒护岸地基的沉降及水平位移变化特点,并进一步研究了其不均匀沉降的发展过程。试验结果表明：半直立式圆筒护岸沉降及水平位移对护岸荷载分级、每级荷载加载量、加载历时及两级荷载之间的间隔时间较为敏感,其中护岸后方最后一级不对称加载对圆筒结构的不均匀沉降影响最大,孔隙水压力变化主要受每级加载量、加载历时及潮汐作用影响,而圆筒安装及第一级荷载施加后,孔隙水压力产生较大的波动。     

Relationship between adjustment of low water level and utilization of water depth in Shashi Reach in middle Yangtze River

Hydrological, sediment, and bathymetric data of the Shashi Reach in the middle Yangtze River for the period of 1975–2018 were collected, and the characteristics of low water level changes and their impacts on utilization of water depth for navigation were investigated. The results showed that, during the study period, the Shashi Reach riverbed was significantly scoured and incised, with cross-sectional profiles showing overall narrowing and deepening. This indicated a strong potential to improve the water depth of the channel. The analysis of the temporal variation of in-channel topographical features showed that the Taipingkou diara underwent siltation and erosion, with its head gradually scoured and relocated downstream after 2008, and the Sanbatan diara continued to shrink and migrate leftwards. Low water levels with the same flow rate over the study period decreased. For instance, from 2003 to 2020, the water level at the Shashi hydrological station decreased to 1.37 m with a flow rate of 6 000 m³/s. Furthermore, the designed minimum navigable water level of the Shashi Reach was approximately 2.11 m lower than the recommended level. In terms of utilization of the channel water depth, continuous scouring of the river channel is expected to result in a reduction in discharge at the Taipingkou mouth, which will improve the water depth conditions of the channel during the dry season in the Shashi Reach. With several channel regulation projects, the 3.5-m depth of the Shashi Reach would basically be unobstructed. This promotes utilization of the shipping route from the Taipingkou south branch to the Sanbatan north branch as the main navigation channel during the dry season. Considering the factors of current water depth and the clear width limitation of the navigation hole at the Jingzhou Yangtze River Bridge, this route can still be favored as the main navigation channel with a 4.5-m depth during the dry season.     

Study on maximum power point tracking of photovoltaic array in irregular shadow

Traditional maximum power point tracking (MPPT) methods can hardly find global maximum power point (MPP) because output characteristics curve of photovoltaic (PV) array may have multi local maximum power points in irregular shadow, and thus easily fall into the local maximum power point. To address this drawback, Considering that sliding mode variable structure (SMVS) control strategy have such advantages as simple structure, fast response and strong robustness, and P&O method have the advantages of simple principle and convenient implementation, so a new algorithm combining SMVS control method and P&O method is proposed, besides, PI controller is applied to reduce system chattering caused by switching sliding surface. It is applied to MPPT control of PV array in irregular shadow to solve the problem of multi-peak optimization in partial shadow. In order to verity the rationality of the proposed algorithm, the experimental circuit is built, which achieves MPPT control by means of the proposed algorithm and P&O method. The experimental results show that compared with the traditional P&O algorithm, the proposed algorithm can fast track the global MPP, tracking speed increases by 60% and the relative error decreased by 20%. Moreover, the system becomes more stable near the MPP, the fluctuations of output power is greatly reduced, and thus make full use of solar energy.     

破碎波作用下粉沙悬移质浓度垂向分布的实验研究

通过水槽实验对破碎波作用下驴驹河粉沙和黄骅粉沙悬沙浓度的沿程分布和垂向分布进行了研究,并对实验现象进行了初步分析。实验中发现:在波浪破碎前近底有高浓度含沙水体层,而在波浪破碎后高浓度含沙水体层消失;断面平均悬沙浓度在破碎点附近达到最大,在破碎点前,断面平均悬沙浓度沿程增大,而在破碎点后,断面平均悬沙浓度沿程减小;在波浪破碎前附近,上层水体紊动较强,从而悬起比平坡情况下更多的泥沙,使悬沙浓度不但在下层水体高,而且在上层水体也较高,因此在计算泥沙输移时,应对此更加注重。     

温州浅滩二期围涂促淤方案数值模拟研究

利用数值模拟方法研究围涂促淤方案,能为工程的科学决策提供有力的技术支撑。本文采用了考虑波浪及其破碎作用的波浪辐射应力、波流底切应力、波流挟沙力、破波切应力描述泥沙运动机制,构建了多因素数学模型,对温州浅滩二期围涂促淤方案进行了数值模拟研究。研究表明：1）促淤方案实施后,不会大范围改变周边海域的潮流动力特征,仅在拟建促淤堤附近水域潮流变化明显,不会明显改变南、北口涨落潮流量而影响其分流比,对周边水域基本上没有影响;2）促淤区内流速普遍减小,流速减小有利于泥沙的落淤,促淤区普遍淤积,方案1、方案2平均淤积厚度分别为0.59m、0.51m,就泥沙的落淤环境与促淤效果而言,不留缺口的方案1略优于预留1km缺口的方案2。建议围涂开发先期启动促淤工程建设,以改变围涂水域的泥沙淤积环境,加快围涂区淤涨。     

瓯江口航道治理工程水沙环境问题研究

基于现场实测资料,对瓯江口的水沙特征、冲淤演变、航道的淤积特点及原因进行了分析。建立了波浪潮流泥沙数学模型和台风骤淤数学模型对瓯江口航道二期治理工程正常航道年泥沙淤积和台风泥沙骤淤进行了计算,对其对周围水沙环境的影响进行了分析。研究结果表明：1）瓯江口航道二期治理工程对周围水沙环境的影响很小;2）瓯江口航道的泥沙淤积主要是大风骤淤,瓯江口航道治理二期工程方案可以通过控制三角沙达到航道减淤的目的,采用北导堤和三角沙西堤作为整治方案有明显的减淤效果。     

适用于中小河流受损岸坡修复的楔形丁坝群水力特性初探

河道内流动控制结构物作为一种主动防护型的护岸型式,以其特有的生态效益,伴随着河流治理理念由渠化向河流再自然化的回归,日益成为新的研究热点。在归纳总结国内外常见河道内流动控制结构物分类和作用特性的基础上,选取逆水流方向布置的楔形丁坝为研究对象,采用三维数值模拟方法对布置楔形丁坝群前后193°强弯曲水槽内的三维水力特性进行对比分析,初步分析弯曲水槽内楔形丁坝群的作用机制和挑流效果。研究结果表明:楔形丁坝群主要通过调整弯道内的二次流结构,达到将高流速水流挑离凹岸、避免岸坡遭受冲蚀的目的;楔形丁坝群布置会造成弯道内水位雍高,高流速水流向凸岸一侧偏移,其雍水高度和偏移程度与楔形丁坝群的布置方式密切相关。研究成果对于河流生态修复领域生态水工结构物相关研究的开展与深化具有借鉴意义。