End chainage = starting chainage Β± actual advance (+ if chainage is increasing, β if decreasing). The support call and instruction sheet cover the drive from the starting chainage to the end chainage (e.g. start 0+117, advance 3 m, increasing: CH 0+117 β 0+120).
Methods Used for Governing Class
The most conservative (highest-numbered) class among the selected methods governs.
Opening Geometry
Tunnel shape sets the section drawn and the support perimeter. Enter the full height of the profile, floor to highest point of the crown. The wall height to the springline is derived from it: Hw = Ht β B/2 (D-shaped), Ht β B/4 (segmental arch), Ht (rectangular). For a circular tunnel Ht is set automatically to B.
ESR scales the equivalent dimension De = B / ESR used with Barton's support chart and the maximum unsupported span 2Β·ESRΒ·Q0.4.
Installation Specification (printed on instruction sheet)
These are placeholders only β replace them with your mine's / project's approved ground support standard before issuing the sheet.
Optional Extra Support (adds to the class minimum β never removes)
Whatever the class requires is always installed and marked REQUIRED on the sheet; these settings can only add support. Going below the class needs the geotechnical engineer, not a setting here. Optional work is quantified separately so it can be priced separately. Minimum optional shotcrete thickness is 50 mm; if the total entered is not above the class thickness, the class thickness applies.
Quantity Allowances (from your approved standard)
Left at 0 % the sheet shows net quantities only. Typical values depend on wet or dry mix and on rock surface, so set them from your own standard. Supply volume = placed volume Γ (1 + overbreak) Γ· (1 β rebound); mesh to order = net area Γ (1 + lap) Γ (1 + waste).
A. Qβ² / Q β Structure & Friction (visual)
Quick face estimate: RQD β 115 β 3.3Β·Jv (Jv = joints per mΒ³, PalmstrΓΆm). RQD < 10 is entered as 10 in Q (Barton).
Sector pre-assigned: water & stress
At the face, Qβ² = (RQD/Jn)(Jr/Ja) is mapped. Jw and SRF are normally pre-assigned per depth sector and hydrological zone by the geotechnical department β override only for an obvious change (e.g. flowing water, squeezing).
B. GSI β Visual Matrix
C. RMR-89 Field Matrix
Dropdowns use the RMR-89 rating bands: the strength grade follows ISRM (R0βR6) and the spacing rating follows Bieniawski's joint-spacing classes with a structural description.
1. Face Cross-Section & Standard Support Pattern (schematic)
