"a substantial bulk of" is correct and usable in written English.
This phrase is generally used to describe a large quantity of something. For example, you could say "A substantial bulk of the population voted in the election."
Any attempt to analyze folk art in terms of the established, sophisticated categories, though revealing in comparison, fails to take into account a substantial bulk of the art.
Distinguishing between these measures is important, because a substantial bulk of the monetary base in developing nations does not circulate within the formal banking sector.
There is a substantial bulk of evidence concerning the unfavorable prognostic value of EGFR both for disease stage and for outcome [ 61], even in Caucasian populations [ 62], the only exception being a recent Korean study [ 51].
In Drosophila, substantial bulk of transcribed mRNAs and translated proteins necessary for early embryonic patterning and development are maternally contributed to the oocyte at high levels.
A substantial majority of undergraduates participate.
In order to improve PV performance of this structure, therefore, a substantial decrease of bulk resistance is necessary.
He tried valiantly to exercise and diet, but even his own family couldn't help thinking of him, as we do, in terms of his substantial bulk.
Some companies offer packages for every type of service and most give substantial "bulk rate" price breaks.
They eat it to add to their substantial bulk.
To solve the problem, we studied plasma treatments on the polymer surface because there would not be a substantial risk of damaging the bulk properties of the polymer and the stent by plasma surface treatments.
