Abstract Binary soil mixtures are extensively used in the construction of geothermal-related earth structures such as geothermal energy piles (GEP), ground source heat pumps (GSHP) and earth air tunnel heat exchangers (EATHE). An evaluation of the binary soil’s thermal-mechanical properties is the key process in determining the final performance of geothermal-related projects. Therefore, the thermal-mechanical properties of binary soil mixtures were systematically investigated in this paper. A series of thermal and mechanical property tests was conducted on five sand-kaolin clay mixtures with sand contents ranging from 0% to 100% by dry weight. The experimental results indicated that the sand-clay mixtures achieved the theoretically densest state when the sand content reached the critical threshold. The further the binary mixture’s sand content was from the critical threshold, the lower the mixture’s density was. As the sand content increased, the shear stress-strain curves gradually shifted from strain-softening behavior to strain-hardening behavior due to the decrease in suction stress. The relationship between the sand content and the shear strength of the mixtures exhibited an “S” shape, which is attributed to the interaction between the sand and clay particles and varied with the sand contents. The shear wave velocity of the sand clay mixtures was found to decrease continuously with the increase in sand content until the sand skeleton had formed. In addition, the thermal conductivity of the binary mixed soil changed linearly with the sand content, and the upper bound of the critical threshold interval (77%) was found to separate the two different heat conduction modes. Finally, an elastic shear modulus (G0) model, which correlated to the tangent elastic modulus of the binary mixture (Em), and a more generalized thermal conductivity (K) model were formulated for the binary sand-clay mixtures, and the effectiveness and feasibility of the proposed models were validated by comparing the values predicted with the model and the experimental data.

中文翻译：

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二元土壤混合物热力学特性的实验室表征和建模

摘要 二元土壤混合物广泛用于地热相关地球结构的建设，如地热能桩（GEP）、地源热泵（GSHP）和地气隧道换热器（EATHE）。对二元土壤的热力学特性进行评估是确定地热相关项目最终性能的关键过程。因此，本文系统地研究了二元土壤混合物的热力学特性。对五种砂-高岭土混合物进行了一系列热性能和机械性能测试，砂含量按干重计从 0% 到 100% 不等。实验结果表明，当砂含量达到临界阈值时，砂粘土混合物达到了理论上的最密状态。二元混合物的含砂量离临界阈值越远，混合物的密度越低。随着砂含量的增加，由于吸入应力的降低，剪切应力-应变曲线逐渐从应变软化行为转变为应变硬化行为。混合料含砂量与剪切强度的关系呈“S”形，这是由于砂粒与黏土颗粒相互作用并随含砂量变化而变化的。发现砂粘土混合物的剪切波速度随着砂含量的增加而不断降低，直到形成砂骨架。此外，二元混合土的导热系数随含砂量线性变化，临界阈值区间的上限 (77%) 被发现将两种不同的热传导模式分开。最后，为二元砂粘土混合物制定了与二元混合物的切线弹性模量 (Em) 相关的弹性剪切模量 (G0) 模型和更广义的热导率 (K) 模型，以及有效性和通过比较模型预测值和实验数据，验证了所提出模型的可行性。