鋪設地工合成物在公路底層下方可做為隔離材，以防止底層碎石粒料與基層土壤之混合，而降低底層之力學效用。另一方面，可牽制土壤及碎石粒料之側向變形，提高路面之承載能力。
本研究對於加勁與不加勁之無鋪面道路模型進行反覆加載試驗，探討使用織布或地工格網做為隔離材與加勁材時，對於延緩道路車轍發生、延長道路壽命之效果。本研究之結果可提供一有效措施，以改善道路系統之服務年限與經濟效益。並可提供未來公路設計法改良之參考。
試驗結果顯示，採用地工格網為加勁材與隔離材時路面之表現，較使用織布時為佳。一般而言，若同時使用二層地工合成物一層為加勁材，另一層為隔離層，則可減少車轍深度，並減少基層土壤入侵底層級配之現象，大大提升無鋪面道路之壽命。

The purpose of a geosynthetic layer or separator beneath the base course of a road
pavement is to provide extra resistance and support capacity, as well as prevent the
aggregate and the subgrade from intermixing or contamination, which in turn causes the
weakening of the pavement structure. However, it is hypothesized that the absence of a
geosynthetic layer, in this case a geotextile or a geogrid, will allow the generally tough
aggregate of the base course and the generally soft subgrade to intermix.
Some cyclic loading tests on unpaved road structures were performed to
investigate and understand the performance of the design parameters currently in use.
With these tests, a better and more comprehensive approach could be sought to improve
the life span and economic impact of the road network, so as to aid in the overall
highway design criteria.
The test results demonstrated that a geogrid-reinforced ground outperformed the
woven-geotextile-reinforced one. In general, the use of two layers of geosynthetics, one
layer as a reinforcement and the other as a separator greatly enhances the roadway’s life
span; in the sense that a smaller rutting, a smaller degree of intermixing can be achieved
through correct placement of reinforcement and separation layers

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