The Use of Geosynthetics to Improve Geological Materials for Construction

Arthur Saldivar-Sali, MSc, DIC, FGS, PhD

CONSULTING GEOLOGICAL ENGINEER

Abstract

Throughout the history of construction involving earthworks, attempts have been made to enhance the properties of geological materials, particularly soils, in order to improve the stability of engineering structures built on them, thus the term ”engineered soil” in technical literature. Traditionally, “engineered” earth materials are those that are compacted at optimum moisture content to increase their density and strength.

Today human-made materials (geosynthetics) are now mixed with earth materials to create what is known as “reinforced earth”. Two earthwork projects where geosynthetics are used are presented in this paper. An earth dam in Itnayat, Batanes overcame problems in logistics and lack of adequate source of geologic materials for construction by using a composite geotextile/geonet as chimney gravity drain. In a mine tailings dam in Benguet, its state of stability precluded any digging at the toe to build a properly keyed rock toe dam. A geogrid-reinforced toe buttress design will be applied to avoid disturbing the old dam’s toe. These design innovations are made possible with the emergence of a new chapter in soil-, rock-, and groundwater-related activities in engineering construction. This is the adding of human-made or geosynthetic (polymer-based) products to improve the engineering properties of the geotechnical or earth materials.

Different types of geosynthetics are used for five major functions: reinforcement, separation, filtration, drainage and containment. Each of these functions is served by the geogrid, geotextile, geonet and geomembrane, respectively. The use of some of these materials in the construction of the zoned earth irrigation dam on the island of Itbayat in Batanes province and in the stabilization of an old tailings dam in Benguet are presented in this paper.

A geotextile is made of polymer fibers woven into flexible, permeable textile used as separator between dissimilar earth materials so that the integrity and functioning of both materials can remain intact or be improved. It also acts as a filter to retain the soil but allows liquid to flow through for long-term equilibrium.

A geogrid consists of parallel sets of tensile ribs. This can be included inside the base course of roads or with the pavement (bitumen or concrete) to increase their modulus and minimize rutting. It is also used to reinforce embankments/buildings on soft foundations and as well as stabilize steep soil slopes.

A geonet consists of integrally connected parallel sets of ribs overlying similar sets for biaxial or triaxial drainage of liquids or gases. These are used in the gravity drainage system of zoned dams.

A geomembrane is a low permeability synthetic material used as liner or barrier with geotechnical engineering-related materials to control fluid migration in landfill projects.

The two projects presented in this paper will be finished ahead of schedule despite constant work stoppage due to adverse weather conditions. Using geosynthetics under these adverse conditions made these projects economically through speedy construction, greater durability and longer life, thus reducing construction and maintenance costs.