Laboratorial Prototype for Detection of Defects on Geomembranes - The Geophysical Approach

Abstract

Although there are some test methods do detect and locate defects in geomembrane liners after the placement of the primary leachate collection system, namely the soil-covered geomembrane method (mobile probe) and the grid method (permanent), the existing methods present some disadvantages. They are labor and time consuming and, so, very expensive. These conditions lead us to the development of a quick and low-cost, but also accurate, test prototype to check the geomembranes integrity after the placement of the granular layer. The methodology consists in the development of a prototype combining the mobile probe method with the multicables resistivity equipments presently used for geophysical surveys. This prototype is endowed with ways that allow to the semi-automatic data acquisition (detection location of the defects) and its processing in real time. The functionality of the prototype is presently being verified in a pilot plant, at one of ISEL's (Instituto Superior de Engenharia de Lisboa) laboratory. The experimental work under way includes different types of lining systems and defects. A bigger scale pilot plant is being constructed at LNEC's (Laboratório Nacional de Engenharia Civil) campus, to verify, at real scale, its functionality. Afterwards, the prototype will be checked in situ, at a true landfill.

Semi-automatic Mobile Equipment Test for Detecting Holes in Geomembranes – the Prototypes Evolution

“…As mentioned, validation tests of each prototype were performed under controlled conditions (in laboratory). Figure 4 illustrates the results obtained with the final mesh of electrodes both at the laboratory, in a confined space (1.8 × 1.8 m (Mota et al 2011)), where the electrical output of the source was limited to 60 V and the GM defect was a 4 cm cut, and at the large scale pilot plant (8.5 × 8.5 m) built at LNEC's campus with a 2 mm hole diameter and an output source of 200 V. The higher values of the electrical potential field at laboratory when compared to those obtained at LNEC's pilot plant is a result of the combined effect of the confined pilot plant at the laboratory and the dimension of the cut. With a hole of 2 mm at the laboratory the maximum absolute values were around 4 mV with the same output voltage and without the covering sand layer (Mota et al 2011).…”

“…An equipment was developed based on the manual mobile reading dipole described in ASTM D7007. In the first phase of the equipment development, several prototypes were built (Figure 1), which consisted primarily of bars where the electrical potential reading electrodes were installed with fixed distances (Mota et al 2011).…”

Electrical Flow Paths and the Application of the Resistivity Method to the Evaluation of Landfill’s Lining Systems

“…Landfills are engineering facilities, composed by one or more cells, designed and constructed with a barrier system (lining system) which objective is to assure the protection of the environment. This system includes active and passive barriers (Mota et al 2011). The active barrier includes, among other materials, a geomembrane.…”