考虑砂土渗透性变化的吸力锚沉贯及土塞特性研究

Installation of suction caissons and formation of soil plug considering variation of permeability of sand

吸力锚负压沉贯过程中锚内部常常产生土塞现象,这将阻碍锚体的进一步沉贯,影响吸力锚在海床土体中的安装深度,最终导致吸力锚承载力的降低,本研究通过1g条件下室内模型试验研究土塞的形成机理。通过试验模拟吸力锚水下砂土中吸力沉贯过程,借助高分辨率相机记录锚体整个沉贯过程,同时利用微型孔压传感器测量锚内外负压值随沉贯深度变化情况。试验过程中发现吸力锚内部土柱在向上渗流作用下发生细颗粒迁移现象,且随着沉贯深度的增大,土塞隆起的高度逐渐增加。提出土塞的形成是由于吸力锚内部土体膨胀引起的,进而引起渗透系数的增加。本研究分析了渗透系数在锚体沉贯过程中的变化情况,并对Houlsby和Byrne提出的吸力锚砂土中沉贯吸力计算模型进行了改进,从而获得更加准确的沉贯吸力随沉贯深度变化关系理论计算方法,为吸力锚的工程设计和施工提供理论依据。

During the installation of suction caissons, there exists the phenomenon of soil plug inside the anchor, which will hinder the further penetration of the anchor. This phenomenon hinders the installation to reach the predetermined depth, resulting in a great reduction in bearing capacity. In this study, a series of tests under 1g are carried out to analyze the formation mechanism of soil plug. The negative pressure installation of an anchor model is conducted in sand, and the whole process is recorded by a high-resolution camera. The pore pressure transducers are used to measure the internal and external pore pressures. During the penetration, the fine sand particles move upwards and reach the top surface due to upward seepage flow within the sand inside the anchor. With the increase of the penetration depth, the height of the soil plug increases progressively. It is found that the soil plug is caused by the swelling of the soil inside the suction anchor, and the permeability coefficient increases due to the swelling of the inside sand. The variation of the permeability coefficient in the process of penetration is investigated, and it is used to improve the Houlsby & Byrne’s model. The modified model can accurately predict the suction in the penetration process and provide a theoretical basis for the design and construction of suction caissons.