Tracer experiments conducted in the laboratory on undisturbed core samples (<7.3‐cm‐diameter) have been a standard method for estimating hydraulic and transport properties of fractured till since the 1980s. This study assesses the relationship between visible fractures on the top and bottom of core samples and the resulting hydraulic and mass transport properties of the core. We hypothesized that more visible fractures would indicate the presence of a well‐connected fracture network, leading to greater hydraulic conductivity (K) values and earlier chemical breakthrough times. To test this hypothesis, water flow and bromide (Br‐) tracer experiments were performed on 10, 16‐cm diameter, 16‐cm‐tall samples of fractured Dows Formation till from central Iowa. Visually identifiable fractures were present on the top and bottom of every sample. Results indicate that the visual identification of fractures does not predict a connected fracture network, as some samples produced breakthrough curves showing rapid first arrival times and shapes characteristic of solute transport in a fractured medium, while others appeared similar to an unfractured medium. No correlation was found between the number of visible fractures and K (Pearson's r = 0.25), or Br‐ first arrival time (r = −0.33), but a strong negative correlation between K and first arrival time (r = −0.92). Results indicate that the sample volume was not large enough to reliably contain a connected fracture network. Thus, testing large volumes of till at the field scale coupled with fracture‐flow modeling likely represents the best approach for estimating hydraulic and mass transport properties for fractured till.

中文翻译：

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可见裂缝是否精确预测了裂缝中的流量和质量传输？

自1980年代以来，在实验室中对未扰动岩心样品（直径小于7.3 cm的直径）进行的示踪剂实验一直是估计裂缝的水力和输送特性的标准方法。这项研究评估了岩心样品顶部和底部的可见裂缝与岩心的水力和传质特性之间的关系。我们假设更多的可见裂缝将表明存在一个连接良好的裂缝网络，从而导致更大的水力传导率（K）值和更早的化学渗透时间。为了验证该假设，对直径10，直径16厘米，高16厘米的道氏岩层样品（从爱荷华州中部开始）进行了水流和溴化物（Br‐）示踪剂实验。每个样品的顶部和底部都存在视觉上可识别的骨折。结果表明，裂缝的视觉识别无法预测相连的裂缝网络，因为一些样品产生的突破曲线显示了快速的首次到达时间和溶质在裂隙介质中的运移特征，而其他样品则表现出与未裂隙介质相似的特征。在可见的骨折数量和K（Pearson'sr  = 0.25）或Br-初次到达时间（r  = -0.33），但K与初次到达时间之间存在很强的负相关性（r  = -0.92）。结果表明，样品量不足以可靠地包含连接的裂缝网络。因此，在现场规模下测试大量的耕作设备，并结合裂缝流动模型，可能是估算裂缝耕作设备的水力和传质特性的最佳方法。