Hi Treasure_digger,
There are two ways, you can locate the edge of the concrete cement and dig it from the side or use a dynamite. Experience miners knows how to use it with out a loud noise. You will need a diamond bit to make a small hole about 10 to 12 inches
depending on how thick the cement, then insert the dynamite in the small hole and cover the small hole with clay. The clay must fill the small hole then cover the top of the small hole with 2 or 3 sacks of soil be sure that the fuse which is like a wire
is long enough so that you can detonate it outside your tunnel. If you have a problem in looking for a diamond bet and a dynamite you can leave your contact info here I will be welling to help. I will be in the Philippines next year March 2013. Anyway, I am from Northern Luzon.. Where are you from?
Regards Bro,