Abstract Proper soil conditioning is critical for effective earth pressure balanced tunnel boring machine (EPBM) operation. Foam as a soil conditioner has been extensively used in EPBM tunneling to modify the excavated soil properties. A critical characteristic of foam-conditioned soil is stability, i.e., the ability to maintain the engineering properties throughout the residency time (30–90 min) in the mixing chamber. A comprehensive suite of experiments on foam-conditioned soil was conducted at both microscale and macroscale to investigate the fundamentals of foam-soil interaction and engineering properties of foam-conditioned soil. A foam-soil capture device and an optical microscope were used to capture bubble-grain images at a microscale under pressure. A pressurized testing chamber (PTC) was used to examine the stability of the mechanical properties of foam-conditioned soil. The compressibility, vane shear strength, pore pressure, and effective stress of foam-conditioned soil with elapsed time were obtained from the PTC test. The bubble-grain image analysis results reveal that foam is more stable when mixed with soil than by itself, indicating that soil particles help stabilize foam bubbles. Soil particles create a barrier to bubble coalescence and coarsening. The PTC test results show that the engineering properties of foam-conditioned soil remained constant over the 60-minute test duration. The results suggest that the accumulated “air bubble” at the top of the mixing chamber during EPBM tunneling is not due to the de-stabilization of foam bubbles when mixed with soil.

中文翻译：

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EPBM室压力下泡沫调理砂稳定性的实验研究

摘要 适当的土壤调理对于有效的土压平衡隧道掘进机 (EPBM) 操作至关重要。泡沫作为土壤改良剂已广泛用于 EPBM 隧道施工，以改善开挖土壤的性质。泡沫调节土壤的一个关键特征是稳定性，即在混合室中的整个驻留时间（30-90 分钟）内保持工程特性的能力。在微观尺度和宏观尺度上对泡沫调节土壤进行了一套综合实验，以研究泡沫-土壤相互作用的基本原理和泡沫调节土壤的工程特性。泡沫土壤捕获装置和光学显微镜用于在压力下捕获微观尺度的气泡颗粒图像。加压试验室 (PTC) 用于检查泡沫调节土壤机械性能的稳定性。从 PTC 测试中获得了泡沫调节土的压缩性、叶片剪切强度、孔隙压力和有效应力随时间的推移。气泡颗粒图像分析结果表明，泡沫与土壤混合时比单独使用时更稳定，表明土壤颗粒有助于稳定泡沫气泡。土壤颗粒形成了气泡聚结和粗化的障碍。PTC 测试结果表明，在 60 分钟的测试持续时间内，泡沫调节土壤的工程特性保持不变。结果表明，EPBM 隧道开挖过程中混合室顶部积聚的“气泡”不是由于与土壤混合时泡沫气泡的不稳定所致。