Shielding effect by a metallic pipe against electromagnetic interference with ELF from high speed railway system

An experiment has been practised to demonstrate that a metallic pipe could have a shielding effect to electromagnetic interference by an ELF source generated from a traction system. There are two major variables in this experiment. They are the separate distances between a pipeline and a telecommunication line and also between the terminal grounds of them. It has been seen that the shielding effect increases when the two variables mentioned above decrease. A metallic pipe can have a shielding effect. From this result of experiment, it is assuemd that an urban area might have an environmental shielding effect by many buried facilities like gas/water provisions.