Empolean really isn't weak against anyother types but it doesn't have a wide move pool like Torterra has. In a battle Empolean would win.
Ground, Electric, and Fighting ftl.
It does have alot of resistances but those aren't the best ones to be weak against.
I'll do a comparison between the two.
Base Stats
Empoleon
Hp - 84
Atk - 86
Def - 88
Sp. Atk - 111
Sp. Def - 101
Spd - 60
Torterra
Hp - 95
Atk - 109
Def - 105
Sp.Atk - 75
Sp. Def - 85
Spd - 56
Empoleon wins in Sp. Atk, Sp. Def, and Speed.
Torterra wins in HP, Atk, and Def.
The speed win of 4 is negligible. Neither are going to be extremely fast on their own.
Empoleon looks like a bulky water at first glance, but it doesn't have a good defensive stat, has bad weaknesses for a defensive pokemon, and doesn't really have the movepool to pull it off. So, its best option is a special sweeper with its good Sp. Atk stat. However, its speed sucks and using agility makes it vulnerable to incoming Earthquakes, Thunderbolts, and Close Combats from much faster pokemon.
Torterra on the otherhand, can be a good solid wall. Its movepool grants it many supporting and stat raising moves. (Ex. Leech Seed, Curse, Synthesis, Amnesia, Growth, etc.) Its weaknesses are easier to handle; Earthquake for fire types, Rock Slide / Stone Edge for flying, ice, and rock types. With only two moves it covers its weaknesses. It may need some EV's in Sp.Def to withstand those Ice attacks.
Infernape> Torterra > Empoleon