Study on Geotechnical aspects related to rehabilitation of deteriorated sewer pipelines

在日本，许多安装在城市地区的旧下水道管道严重老化，降低了它们的功能，增加了地面凹陷的可能性。下水管道不是压力管道。因此，如果旧管道老化，土壤颗粒容易随水流入管道，容易在地面上形成空洞，造成地面凹陷。然而，目前对地下孔隙发育的机理和实际条件尚未明确。此外，由于在城市地区很难挖掘以新管道替换老化的管道，因此开发了使用塑料衬里的无挖掘修复方法，并在世界范围内越来越多地使用。塑料衬垫寿命长，但由于松弛作用，其刚度随时间的推移而降低。相反，管道周围回填土的刚度随时间的延长而增大。因此，受土-管相对刚度支配的埋地管道的力学性能会随着时间的流逝而发生变化。然而，到目前为止，这个问题还没有得到研究。本研究旨在阐明老化旧排水管道周围土体空隙发育的机理，探讨土-结构相互作用的长期变化规律。主要结论如下：1)土壤通过管道连接处的开口流入，形成了地面的空洞。孔洞的位置在管道的上部，而不是在管道的顶部。沿着管道长轴的裂缝不会在地面上产生空洞。2)车辆反复荷载使回填土表观刚度降低，导致塑料管挠度增大。随着时间的推移，塑料管的松弛作用显著地增强了塑料管的挠度。

In Japan, many old sewer pipelines installed in urban areas were severely deteriorated to decrease their functions and increase the possibility of ground depression. Sewer pipes are not pressure pipes. If the old pipes are deteriorated, therefore, soil particles tend to flow into the pipes with water, easily developing voids in the ground to cause ground depression. However, mechanism and actual condition of void development in the ground have not been clarified yet. Also, since excavation for replacing the deteriorated pipes by new pipes is difficult in urban areas, no-dig rehabilitation methods using plastic inner liners have been developed and are increasingly being used in the world. The plastic inner liners have long lives, but their rigidity decreases according to the elapsed time due to relaxation. On the contrary, the rigidity of backfill soils around the pipes increases according to the elapsed time. Therefore, mechanical behavior of buried pipes that is governed by relative rigidity between soil and pipe will be changed according to the elapsed time. However, this problem has not been studied hitherto.This study was carried out to clarify mechanism of void development in the ground around deteriorated old sewer pipelines and to investigate long-term change in soil-structure interaction. The main conclusions can be summarized as follows:1) Inflow of soil through opening at joints of the pipeline develop the voids in the ground. The location of the voids is at the upper part of the pipe, but not at the top of the pipe. Cracks along the long axis of the pipe do not produce the voids in the ground.2) Apparent rigidity of backfill soils decrease due to repeated vehicle loading, resulting in increase in deflection of plastic pipes. The relaxation of plastic pipes during the elapsed time remarkably strengthens the deflection of plastic pipes.