why shutchou not shucchou

Why is business trip written shutchou and not shucchou in romaji. For instance we write shuppai not shutpai. Is it something to do with the kanji? 出張　(しゅっちょう in hiragana). How would you know how to pronounce it just looking at the kanji?

The "tch" is just a way some people write the "cch" in romaji, since they sound phonetically similar. To be able to read that kanji compound, you'd have to know the readings of both Kanji, and most likely need to know the pronunciation of the compound. Kanji have many different readings, and it's a case of learning them and which ones are used with which compounds.