回填软土中管道上拔试验及上浮承载力研究

Uplift tests and uplift resistance analysis of pipe segment in soft backfill clay

研发了一套足尺浅埋管道上拔试验装置,针对不同软土强度、管道埋深和加载方式的情况,较系统地研究了上拔过程中管-土相互作用、管周软土破坏模式、上浮承载力及其影响因素。试验结果表明:在管道上拔过程中,回填软土的变形主要由土块相对位置调整及块间间隙水的排出产生,这与均质软土中变形主要由固结导致明显不同;埋深管径比H/D(28)1时,回填软土的破坏模式接近流动破坏,远小于规范建议的H/D≥3;H/D≥1时,建议采用Palmer方法计算长期荷载作用下回填软土的极限上浮承载力;H/D越大,则回填软土中管道的上浮承载力也越大;在其他条件一定时,回填软土中管道的上浮承载力基本随抗剪强度呈线性增长,由于地基固结速度明显较均质软土快,设计时可适当考虑土体强度恢复的影响。

A set of test devices were developed, and a series of full-scale uplift tests were carried out on a pipe segment buried in lumpy soft clay backfill. Focusing on the influence of shear strength of soil, depth-diameter ratio and loading mode, the pile-soil interaction, the failure mode and the uplift resistance were studied. The test results show that the deformation properties of lumpy soft clay backfill are different from uniform soft clay during uplifting. For the former, deformation is due to the position shift of soft clay blocks and the outflow of water in gaps between the blocks. For the latter, it is due to consolidation. When the depth-diameter ratio is equal to 1, the failure mode of lumpy soft clay backfill is more closed to ＇local＇ flow-round. It is much less than DNV＇s suggestion which is H / D ≥ 3. It was suitable to use Palrner＇s approach to calculate the uplift resistance of lumpy soft clay under long-term load if H / D ≥1. The uplift resistance of pipeline in lumpy soft clay increases as the increase of H / D and it is mainly linear increase with the increase of the shear strength. The consolidation rate of lumpy soft clay is much larger than uniform soft clay, so it may be taken into account of the effect of strength restoration of clay to the uplift resistance during design.