Trying to grow a lawn in South Korea

i also have clay for soil at my house. i found this out when digging my pond out...it seems as if there is about 6 inchs of topsoil on top of the clay ground. not sure if topsoil is available to you or not but u might try acquiring some making it 6 or more inchs thick on top of your existing clay.then use your barrel to roll it flat.you could also grade your new dirt so that is will drain properly and possibly avoid making a drain although a drain may still be necessary for your property.when choosing your topsoil find one that has the right nutrients for your grass seed to better aid the growth.