Groundwater discharges in the Baltic Sea: survey and quantification using a schlieren technique application

Groundwater seeps are known to occur in Eckernförde Bay, Baltic Sea. Their discharge rate and dispersion were investigated with a new schlieren technique application, which is able to visualize heterogeneous water parcels with density anomalies down to Δσ_t = 0.049 on the scale of millimeters. With the use of an inverted funnel, discharged fluids can be captured and the outflow velocity can be determined. Overall, 46 stations could be categorized by three different cases: active vent sites, seep‐influenced sites, and non‐seep sites. New seep locations were discovered, even at shallow near‐shore sites, lacking prominent sediment depression, which indicate submarine springs. The detection of numerous seeps was possible and the groundwater‐influenced area was defined to be approximately 6.3 km². Flow rates of between 0.05 and 0.71 l m^?2 min^?1 were measured. A single focused fluid plume, which was not disturbed by the funnel was recorded and revealed a flux of 59.6 ± 20 ml cm^?2 min^?1 and it was calculated that this single focused plume would be strong enough to produce a flow rate through the funnel of 1.32 ± 0.44 l m^?2 min^?1. The effect of different seep‐meter funnel sizes is discussed.     

The geological methane budget at Continental Margins and its influence on climate change

Geological methane, generated by microbial decay and the thermogenic breakdown of organic matter, migrates towards the surface (seabed) to be trapped in reservoirs, sequestered by gas hydrates or escape through natural gas seeps or mud volcanoes (via ebullition). The total annual geological contribution to the atmosphere is estimated as 16–40 Terragrammes (Tg) methane; much of this natural flux is ‘fossil’ in origin. Emissions are affected by surface conditions (particularly the extent of ice sheets and permafrost), eustatic sea‐level and ocean bottom‐water temperatures. However, the different reservoirs and pathways are affected in different ways. Consequently, geological sources provide both positive and negative feedback to global warming and global cooling. Gas hydrates are not the only geological contributors to feedback. It is suggested that, together, these geological sources and reservoirs influence the direction and speed of global climate change, and constrain the extremes of climate.     

大型平原土体遗址主要地质病害及其保护治水工程技术研究

大量现场地质调查结果表明:大型平原土体遗址原地原样保护的主要环境地质病害是地下水形成的渗水对遗址及其文物造成的腐蚀和破坏,因而治水工程是这类遗址保护中最主要的岩土工程。结合该类遗址原地原样保护原则要求:①遗址围岩和文物的含水率要低于40%;②遗址区地下水位要长期保持在遗址底板高程减去土层毛细水上升的水平面上;③为遗址长期保护服务的地质工程要能长期保持稳定正常运行;④地质工程要与文物景观相容。提出了治水工程的基本技术思路;①查明遗址区水文、工程地质条件;②建立遗址区水文地质模型;③遗址区工程地质、环境地质问题评价;④遗址区治水工程方案论证;⑤工程优化设计;⑥工程施工。其中,治水工作的关键是查明遗址区水文地质条件和地下水渗流场的变化规律,而地下水数值模拟技术能够模拟计算地下水随时间的动态变化。本工作以抗州萧山独木舟遗址为例,分析了该遗址区的水文地质条件,采用地下水数值模拟技术模拟计算遗址区原始地下水位分布;根据遗址区工程地质条件和原始地下水位模拟结果,提出了暗沟疏干排水方案,并模拟预测疏干排水工程实施后地下水位随时间变化规律,模拟结果合理,能够用于指导治水工程设计施工。     

基于结构面网络模拟的龙门石窟擂鼓台渗水产生机理研究

渗水病害在龙门石窟擂鼓台中发育明显,为明晰擂鼓台区渗水机理,现场对石窟内外共149条裂隙开展了调查。基于此数据样本,运用Monte-Carlo随机模拟生成了擂鼓台斜坡区结构面三维网络图。模拟结果显示,擂鼓台三窟中主要连通途径是由倾向NNW的层面和倾向SW和SE的两组近直立结构面构成,在石窟中部和南部结构面连通率分别高达87.1%和83.6%。综合该模拟结果及窟内外裂隙发育特征,可将擂鼓台北、中、南三洞渗水机理归结为:北洞SW、NWW倾向裂隙J12、J4加速2号平台滞水进入石窟顶部,洞内大量发育的倾向SW、SE裂隙向上与J12、J4连通,方便地表水渗入至洞内;中洞渗水受裂隙J12及J35控制,洞内大量发育的SW、SE倾向裂隙与J12、J35相通构成窟内主要渗水通道,其中J12与JM1直接相连是中洞渗水关键;南洞因山体缺失不存在沿层面渗水,地表水主要沿砌体与山体间隙及SE、SW倾向的J11、J31、J30等构造裂隙渗入,后在洞内连通程度较高的SW倾向裂隙引导下流至窟内表。本研究所取得的经验可为同行在以后类似工程中所应用。     

南京包山式城墙典型病害及整体坍塌预警分析

南京城墙作为现存的世界第一城垣，对其安全性进行科学评估尤为重要。包山式城墙为南京城墙的主要形式之一，由于其与土体相连，受力特点不同于常规的自承重城墙。本研究整理了包山式城墙的6种典型病害，并提出了包山式城墙的数值建模方法，将其简化为城墙-粘结界面-土体的模型。利用ABAQUS软件，结合工程实例模拟土坡强度折减后包山式城墙的鼓胀。研究结果表明：随着土体的强度下降，包山式城墙的位移不断增大形成鼓胀现象，最终发生倾覆坍塌，可通过墙体底部拉应力-顶点位移曲线中的明显拐点确立监测变形预警值；在此基础上，讨论土坡高度对整体坍塌的影响，并给出放坡角度的合理取值；城墙底部的积水浸泡会导致底部强度折减进而发生相对错动，可通过底部墙体达到极限抗拉强度时的最大相对位移确立监测变形预警值。最后，提出了包山式城墙的修缮保护建议。