A Geotextile is a special fabric which have been designed for use for geological purposes, totally rot proof yet still permeable to water. Geotextile fabric is available in woven and non-woven forms and its main benefit in relation to block paving is the prevention of weed growth and stops the subsoil mixing with the hardcore.
Place the Geotextile layer on top of the subsoil across the entire area of the soon to be paved driveway. Hold the Geotextile layer down with some blocks to stop it moving until the hardcore is in place to stop it moving, remember to remove the blocks or whatever you used to hold it down before you compact the hardcore.
Next Step 3: Compacting the Hardcore > (coming soon)