On the loss of contact between driving element and soil during vibratory driving into saturated soil

振动打桩是一种行之有效的方法，可以快速经济地将桩打入地面。与其他方法相比，振动打桩代表了一种相对低振动和低噪音的打桩方法。目前的调查显示，与同事Cudmani的观察和解释不太一致。在向上移动过程中，桩尖下方可能会形成空腔。这种可能正在形成的空洞的性质还没有完全了解。此外，孔隙水和土壤颗粒之间的分离以及由于负压而导致的孔隙水到水蒸气的可能相变（空化）尚未得到充分探索。当孔隙水由于土壤的渗透性而不能足够快地流入空腔时，就达到了为此所需的空化压力。因此，该研究项目的主要目标是澄清振动桩向上运动过程中剖面底部的过程，并确定打桩过程对静态承载性能的影响。另一个目的是调查振动打桩过程中桩尖下的物理空化和假定空腔的影响。为此，进行了数值模拟，并通过模型试验进行了补充和验证。

Vibratory pile driving is a proven method of driving piles into the ground quickly and economically. Compared to other methods, vibratory pile driving represents a relatively low-vibration and low-noise method of driving piles. Current investigations show insufficient agreement with the observations and interpretations of colleague Cudmani. During upward movement, a cavity may form under the pile toe. The nature of this presumably developing cavity is not fully understood. Besides, the separation between pore water and soil particles and a possible phase transition of the pore water to water vapour (cavitation) due to negative pressure has not been adequately explored. The cavitation pressure required for this is achieved when the pore water cannot flow into the cavity sufficiently quickly due to the permeability of the soil. The main objective of the research project is therefore to clarify the processes at the base of the profile during the upward movement of the vibrated pile and determine the effect of the driving process on the static load-bearing behaviour. Another objective is to investigate the influence of physical cavitation and the presumed cavity under the pile toe during vibratory driving. For this purpose, numerical simulations are carried out, which are supplemented and validated by model tests.