Complex sentence: Geotextiles are used as separation between two different types of soils to prevent contamination of the lower layer by the upper layer.2 Also, geotextiles act a cushion to protect synthetic layers against puncture from underlying and overlaying rocks.
Split into simpler sentences: Geotextiles are used as separation between two different types of soils to prevent contamination of the lower layer by the upper layer. Geotextiles also act as a cushion to protect synthetic layers against puncture from underlying and overlaying rocks.