HELP NEEDED. Garden was covered in gravel and membrane sheet for years and heavy clay soil underneath which has now been compacted over the years.HELP NEEDED. Garden was covered in gravel and membrane sheet for years and heavy clay soil underneath which has now been compacted over the years. Following online advice the plan is to turn over the top 10-15cm of clay soil, add gypsum and compost and then top soil, compact and have a lawn. Ground is horrendous and digging by hand. Lumps are the size of footballs in places. Any advice, knowledge or anyone with a rotavator?