Sentence:  You need to excavate and remove the topsoil, line the subsoil with a geotextile, then lay and compact hardcore. Follow this with a layer of compacted "hoggin" – compacted clay, gravel and sand. This is then sprayed with hot <WSD>bitumen</WSD>, and has a layer of pea shingle rolled into it. 
Meaning of the word marked with <WSD> tags:  Mineral pitch; a black, tarry substance, burning with a bright flame. It occurs as an abundant natural product in many places, as on the shores of the Dead and Caspian Seas. It is used in cements, in the construction of pavements, etc.