Symbolism, Imagery, Allegory
Workin' in the coal mine, goin' down, down, down… As you might have guessed, the always-unpleasant pit mines in Sons and Lovers seem to symbolize the world of hard labor. Lawrence drops a lot of not-so-subtle hints about the exploitation of the workers that happens in these mines throughout the book.
After all, Walter Morel makes "Seventeen pounds eleven and fivepence" (4.178) for his work, but has to give back "sixteen an' six" (4.179) for "stoppages for rent and tools" (4.178). That's more than 90% of his earnings that he has to pay back to the company.
How would you feel about "taxes" like that? The misery of working in the mines might actually be our main source of sympathy for Walter.
Lawrence also positions the mines as places where only the manliest of men go to work. He does this primarily through the eyes of Gertrude Morel, who "realized the life of the miners, hundreds of them toiling below earth and coming up at evening […] seemed to her noble" (1.103).
Lawrence really wanted manly men to exist in the world because he worried that modern technology would eventually make men "soft." (What would he think about the internet? Gasp.) So even though he's opposed to exploitative labor, he's still half-glad that the mines kept men good and tough. And drunk, we might add.