Geotextiles are extensively using in many civil engineering projects where soil improvement or slope stability is of great importance. In 1958, geotextiles were first applied as filters when traditional filters of designed graded coarse grained soil were replaced by it. Now-a-days geotextiles are using in many slope stabilization and erosion recovery problems.
As a filter, geotextiles should be properly designed to ensure adequate or designed retention of erodible materials to be retained and provide sufficient discharge capacity throughout designed life of structures. Now we will learn basic filter criteria that are considered in selecting geo-textile for filter purposes. These criteria are:
a. Retention requirement which considers the prevention requirements of migration of particles to be retained through geotextile.
b. Permeability requirement which ensures flow a liquid through the geotextile. Generally it is expected to establish a free flow condition. Our aim is to retain soil particles but provide a free passing out of liquid i.e. water in common cases.
c. Clogging prevention requirement, this requirement includes the performance of geotextile regarding above two criteria remain satisfactory throughout life cycle of structure i.e. the geotextile performs well with satisfying retention and permeability requirements.
But above three criteria of geotextile can be satisfied only by controlling distribution of pore sizes throughout the geotextile and largest openings of pore. Dear reader in united states the term AOS or O95 are used regarding geotextile opening size. AOS stand for apparent opening size. We will learn about AOS and O95 in our next post.