For ㄷ and ㅌ and other ㄷ batchim combined with 히 or any other ㅎ + Y vowel (e.g. 혀) produce a 치 like sound. E.g.
ㄷ + 히 = 치
ㅌ + 혀 = 쳐
It's called Palatalization. You can read more about it and other Batchim rules here: http://www.koreanwikiproject.com/wiki/Category:Consonant_assimilation