Abstract Thermomechanical behaviour of clay has been widely investigated by well-controlled laboratory experiments, while in-situ test of thermal effects on soil is rare. The piezocone penetration test (CPTU) is first used in this study to directly evaluate the temperature effects under in-situ stress condition. A full-scale precast high strength concrete (PHC) pile was utilized as the heat source and a series of CPTU were conducted in adjacent layered clays after monotonic heating and thermal cycle. The results show that unprecedented temperature elevation leads to an apparent reduction of soil strength in all soil layers; this degradation was alleviated after the thermal cycle. After exposure to a higher temperature, the normally consolidated soil was improved even when tested at a lower elevated temperature; whereas, the overconsolidated soil could nearly recovered to the pre-heated value. The measured pore pressure (u2) also decreased after heating indicating a more overconsolidated or dilatant behaviour during shearing. By comprehensively considering the in-situ responses, the in-situ soils were believed to be unloaded by the thermally induced pore fluid pressurization and densified after cyclic thermal loading. Finally, a hypothesis is proposed to qualitatively explain the thermomechanical responses of in-situ soil in the framework of critical state soil mechanics theory.

中文翻译：

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CPTU 评估的能量桩周围粘土原位力学响应的温度效应

摘要 粘土的热力学行为已被控制良好的实验室实验广泛研究，而对土壤热效应的原位试验很少见。本研究首先使用压电锥体穿透试验 (CPTU) 来直接评估原位应力条件下的温度影响。采用全尺寸预制高强混凝土（PHC）桩作为热源，经过单调加热和热循环后，在相邻的层状粘土中进行一系列CPTU。结果表明，前所未有的温度升高导致所有土层的土壤强度明显降低；这种降解在热循环后得到缓解。暴露于较高温度后，即使在较低的高温下测试，正常固结的土壤也会得到改善；然而，过度固结的土壤几乎可以恢复到预热值。加热后测得的孔隙压力 (u2) 也降低，表明剪切过程中出现更多的过度固结或膨胀行为。综合考虑原位响应，认为原位土壤在热致孔隙流体加压的作用下卸载，并在循环热加载后致密。最后，提出了一个假设，在临界状态土力学理论的框架内定性地解释了原位土的热力学响应。原位土壤被认为通过热致孔隙流体加压卸载并在循环热加载后致密。最后，提出了一个假设，在临界状态土力学理论的框架内定性地解释了原位土的热力学响应。原位土壤被认为通过热致孔隙流体加压卸载并在循环热加载后致密。最后，提出了一个假设，在临界状态土力学理论的框架内定性地解释了原位土的热力学响应。