The unconnected piles–caisson foundation (UPCF) consists of gravity caisson, mattress, and pile group. This foundation has been an attractive design for the mattress as it can reduce the seismic loads applied on the superstructure. However, a lack of understanding regarding its seismic behavior has hindered the application of this type of foundation. This paper reports on a series of slow cyclic tests (SCTs) conducted to investigate the seismic behavior of the UPCF. Six tests were conducted on model foundations on dry sand with the variables of mattress material, mattress thickness, vertical safety factor, and ground improvement. The experimental schemes, including the model design, the instrumentation, and the loading scheme, are illustrated in detail. The test results show that a large amount of energy was dissipated through the mattress during dynamic loading. With increasing loading displacement, the shear stiffness of these models decreased to a stable value. An empirical equation for the stiffness and loading displacement is developed. Below a drift ratio of 0.6%, there is no evident difference in the dynamic behavior of the foundation. After that, the aseismic behavior of the foundation depends on the mattress material, the mattress thickness, and the vertical pressure and is affected by the earthquake intensity and frequency.

中文翻译：

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使用慢循环测试的非连接桩-沉箱基础的地震行为

非连接桩-沉箱基础（UPCF）由重力沉箱、垫层和桩组组成。这个基础对于床垫来说是一个有吸引力的设计，因为它可以减少施加在上部结构上的地震载荷。然而，对其抗震性能缺乏了解阻碍了此类地基的应用。本文报告了为研究 UPCF 的地震行为而进行的一系列慢循环试验 (SCT)。以床垫材料、床垫厚度、垂直安全系数和地面改良为变量，在干沙模型基础上进行了六次试验。详细说明了实验方案，包括模型设计、仪器和加载方案。测试结果表明，在动态加载过程中，大量能量通过床垫耗散。随着加载位移的增加，这些模型的剪切刚度下降到一个稳定的值。建立了刚度和载荷位移的经验方程。在 0.6% 的漂移率以下，地基的动态性能没有明显差异。之后，地基的抗震性能取决于垫层材料、垫层厚度和竖向压力，并受地震烈度和频率的影响。基础的动态行为没有明显差异。之后，地基的抗震性能取决于垫层材料、垫层厚度和竖向压力，并受地震烈度和频率的影响。基础的动态行为没有明显差异。之后，地基的抗震性能取决于垫层材料、垫层厚度和竖向压力，并受地震烈度和频率的影响。