Where tunnel rounds are based on the burn cut, faster advance could often be achieved by increasing blasthole diameter from (the conventional) <45mm to within the 55-70mm range._x000d_>
The use of these larger blastholes is considered for 1. burn cut rounds of normal length, 2. burn cut rounds of about twice the normal length using individually-delayed deck charges in cut and easer blastholes, 3. cratering rounds, and 4. double-cratering rounds using individually- delayed deck charges in all blastholes. Of these four suggested methods, the first two are expected to offer the greatest potential cost savings. For any blasthole containing two charges on different delays, the inner charge must not be axially compressed and desensitised by detonation of the outer, earlier-firing charge._x000D_
For this reason, the two proposed designs for considerably longer rounds could well necessitate the use of detonator-sensitive cast explosives (e.g., pentolite) for all inner charges.