ESTEIO has performed GPR survey in the cities of Campo Grande and Três Lagoas, both located in the state of Mato Grosso do Sul. Such surveys were carried out with the aim of locating interference in pipes of gas pipeline from MSGás – Companhia de Gás do Estado de Mato Grosso do Sul.
As the interference cadaster had been carried out before, this work was a complementary form, that is, to confirm interference already registered and to identify those that had not been verified yet.
The GPR survey lines were performed according the orientation of MSGás engineers. The points of measuring, as well as its respective depths, are detached in the network drawing sheet. These lines were divided in segments which are referred to streets where the studies had been performed. Every segment was subdivided in profiles corresponding to the original file generated in the field.
Methodology
Firs of all, it was done a bibliographical revision about the geological characteristics of the areas to be worked in order to foresee the difficulties to apply the GPR method, besides deciding what the best antennas would be used, as a result of the substratum kind and depth of interest. 200 and 400 MHz antennas were used in this work.
After that, it was done a reconnaissance and a preliminary planning of the segments. This stage was supported by MSGás engineers and by PROSUL Co. surveyor, who indicated which sites must have GPR soundings.
The survey consists on dragging an antenna very slowly (a transmitter and a receptor) along the gas pipeline. This antenna is connected to a control unit through a coaxial cable responsible for controlling all acquisition parameters and data storage.
Interferences
Due to limitations of GPR method, the described interference had not been specified as for their composition and size, except those that were visualized afield and allowed detailed description.
To obtain the exact determination of composition of each interference size, a bore hole or a digging would be necessary, which is a slow and expensive process. So, this work has a complementary form and basically all the interference that could generate problems related to the work execution have already been described in the Descriptive Memorandum of Interference, carried out by PROSUL.