Ross Geddes (personal communication, 6 June 2006) suggests that there may be a primitive error here (the text is fully extant in 𝓞)—namely, the word about seems to be missing after were; that is, the text should read “as if it were about to divide asunder”. Usage elsewhere supports the occurrence of about in this expression:
Notice that the last two passages use the same basic language as here in 1 Nephi 17:45.
There isn’t much evidence for the omission of about in the history of the text. According to my original analysis (and in agreement with Joseph Smith’s editing for the 1837 edition), about was accidentally omitted in only one place:
However, subsequent information has led me to revise my analysis here and restore the earliest reading, namely, without the about (that is, “and I have digged it”). For discussion of this point, see the addendum under Jacob 5:47 (in this last part of volume 4).
Ultimately, there is nothing particularly wrong with the current reading here in 1 Nephi 17:45. Although about may be missing here, it is not necessary, and therefore the critical text will maintain the current reading in 1 Nephi 17:45.
Summary: Maintain in 1 Nephi 17:45 the reading without about (“as if it were to divide asunder”), although there is a possibility that the word was originally there.