水下真空预压的加固机理及其密封铺膜施工工艺

Reinforcement mechanism and membrane laying and sealing construction process of underwater vacuum preloading

水下真空预压与真空联合膜上覆水预压在应力状态和加固机理方面有着本质区别。水下真空预压过程中总应力不变,真空联合膜上覆水预压过程中土体总应力随膜上覆水厚度的增大而增大。水下真空预压的加固机理与陆上真空预压相同,即总应力不变的情况下,抽真空减小孔隙水压力,从而增大有效应力。水下真空预压前后的有效应力增长幅值与水深无关,其理论最大值为100 kPa。水下真空预压的关键施工工艺主要包括铺膜及密封工艺、真空泵选型与布置。从加固效果好的角度,应该采用类似挪威现场试验的密封膜密封和射流泵抽真空的组合,但水下真空预压施工的现场影响因素复杂,须根据现场实际情况选择性价比最优的方案。水下真空预压密封膜铺设装置专利技术集密封、滤管、出膜装置等功能于一体,实现完全水下环境下的密封膜的铺设及密封,减少水下作业,尤其适用于海上风电领域吸力桶基础的小范围的海底软黏土加固。

Essential differences in stress state and reinforcement mechanism exist between underwater vacuum preloading and preloading combining vacuum with overlying water on the membrane. Specifically, the total stress does not change during underwater vacuum preloading. In contrast, the total stress in soil increases with the thickness of the overlying water on the membrane in preloading combining vacuum with overlying water on the membrane. The reinforcement mechanism of underwater vacuum preloading is the same as that of onshore vacuum preloading, namely that on the premise of the same total stress, vacuum pumping reduces the pore water pressure and further increases the effective stress. The increasing amplitude between the effective stress before and after underwater vacuum preloading is independent of the water depth, with a theoretical maximum value of 100 kPa. The key construction process of underwater vacuum preloading mainly includes membrane laying and sealing and the selection and layout of the vacuum pump. A combination of sealing with an overlying sealing membrane and vacuum pumping with a jet pump similar to that adopted in the field test in Norway is advisable for the sake of a favorable reinforcement effect. However, factors influencing the construction site of underwater vacuum preloading are complex,demanding the selection of the scheme with the optimal cost performance according to the actual situation on site.Integrating the functions of the sealing device,filter pipes,and membrane outlet device,the patented technology of the sealing membrane laying device for underwater vacuum preloading is available for the sealing membrane laying and sealing in a completely underwater environment,and it reduces underwater operation,It is especially suitable for small-scale seabed soft clay reinforcement for suction bucket foundations in the field of offshore wind power.