The effect of thermal-oxidative ageing on in-isolation and in-soil stiffness is investigated for two high-density polyethylene (HDPE) and two polyester (PET) geogrids when incubated in an oven at 90°C. It is shown that the in-isolation and in-soil stiffness of three out of the four geogrids decreased during the 4-month ageing time with a faster degradation of the two PET geogrids. In contrast, one of the HDPE geogrids examined with thicker rib showed slower degradation compared to the PET counterparts. It is also shown that a geogrid might have a higher unaged stiffness, but less aged stiffness compared to another geogrid made of the same polymer type. It is suggested that the ageing approach used in this study could be adopted for the selection of geogrids based on their long-term stiffness for structures such as reinforced embankments or mechanically stabilized earth walls that require a long service life. Moreover, results indicate that the stiffness improvement factor for PET geogrids decreases with ageing time. On the contrary, the stiffness improvement factor of the HDPE geogrid increases with time and hypothetically might keep increasing followed by a sudden drop to zero at full degradation of the geogrid.

中文翻译：

---

氧化老化对 HDPE 和 PET 土工格栅刚度改进系数的影响

研究了两种高密度聚乙烯 (HDPE) 和两种聚酯 (PET) 土工格栅在 90°C 烘箱中孵育时热氧化老化对隔离和土壤中刚度的影响。结果表明，在 4 个月的老化时间内，四分之三的土工格栅的隔离刚度和土内刚度有所下降，而两种 PET 土工格栅的降解速度更快。相比之下，与 PET 同类产品相比，一种具有较厚肋的 HDPE 土工格栅的降解速度较慢。还表明，与由相同聚合物类型制成的另一种土工格栅相比，土工格栅可能具有更高的未老化刚度，但老化刚度较低。建议对于需要较长使用寿命的加筋路堤或机械稳定土墙等结构，可以根据其长期刚度采用本研究中使用的老化方法来选择土工格栅。此外，结果表明，PET 土工格栅的刚度改进系数随着老化时间的增加而降低。相反，HDPE 土工格栅的刚度改进系数随着时间的推移而增加，并且假设可能会继续增加，然后在土工格栅完全降解时突然降至零。