I'm not sure what is your question. Here is Korean standard pronunciation rules 제10항 겹받침 'ㄳ', 'ㄵ', 'ㄼ', 'ㄽ', 'ㄾ', 'ㅄ'은 어말 또는 자음 앞에서 각각 [ㄱ, ㄴ, ㄹ, ㅂ]으로 발음한다. 넋[넉] 넋과[넉꽈] 앉다[안따] 여덟[여덜] 넓다[널따] 외곬[외골] 핥다[할따] 값[갑] 없다[업:다] 다만, '밟-'은 자음 앞에서 [밥]으로 발음하고, '넓-'은 다음과 같은 경우에 [넙]으로 발음한다. (1) 밟다[밥:따] 밟소[밥:쏘] 밟지[밥:찌] 밟는[밥:는→밤:는] 밟게[밥:께] 밟고[밥:꼬] (2) 넓-죽하다[넙쭈카다] 넓-둥글다[넙뚱글다] ㄼ is pronounced as ㄹ in front of consonant or end of word as the rule. 밟- is an exception which is always pronounced as ㅂ. 넓- in 넓죽하다 and 넓둥글다 is an exception which is always pronounced as ㅂ. ㄼ in 여덟 is pronounced as ㄹ in front of consonant or end of word as the rule. 여덟[여덜] 여덟시[여덜시] 여덟에[여덜베]

It's difference of the next word. 여덟 doesn't have after word. But 밟다, 밟지, 밟고 has words start with ㄷ, ㅈ, ㄱ after ㄹㅂ 받침. When ㄹㅂ 받침 meets ㄱ, ㄷ, ㅂ sounds it changes.

French pronunciation rules can be very helpful with this. Please keep studying!