Brooks Hill to Bungendore

The line reaches its highest point of about 812m above sea level in the early part of this sector, and then descends the far side of the range down into Bungendore. This will be the first sector in which private landholdings will need to be acquired, as the line has now left the ACT. Vertical alignment must be carefully considered, as the crest of the line involves a vertical transition from maximum climb to maximum descent (a change of 6°) – this ideally requires a transition length of 2.5km for passenger comfort (but as little as 1km is allowable)

Alignment Design

Brooks Hill curves - click to enlarge

Brooks Hill curves – click to enlarge

BrooksHillSection

1 – The Nudist Club’s back fence

Section length is 1160m, sector start. Starts at the HQJOC overbridge and ends at the point where the existing alignment is rejoined. A medium depth cutting (~20m) straightens out a kink in the line near the southeast boundary of the ACT Nudist Club at Brooks Hill. Vertical alignment will be slightly different to existing, therefore all new track required.

  • Earthworks:
    • 550m long cut of average depth 8m
      • Volume 88,000m3, cost $2,728,000
    • 300m long fill of average depth 2.5m
      • Volume 11,813m3, cost $189,000
  • Whole length works:
    • Dual track @$2.25m/km = $2,610,000
    • Drainage @$200k/km = $232,000
    • Chainlink fencing (both sides) = $116,000
    • Signalling and Control @$127k/km = $147,000
  • Section cost = $6,022,000 ($5.19m/km)

2 – ACT Border Tunnel

Section length 650m, starting at 1160m. Comprises the section of existing or broadly similar alignment, but similarly to section 1, all-new rail will be assumed due to probably modifications to existing vertical alignment. The 300m tunnel at the ACT/NSW border is only 25-30m below grade, meaning that in all probability a cut would be more economical. However, similarly to the previous sector, we want to minimise the amount of fill produced, so we will specify a widening of the existing tunnel instead. It is within the tunnel that the line reaches its summit of 812m MSL. Also in this section, a vertical grade transition of 6% is initiated; it is possible to achieve this within 1.5km, which is within allowable limits.

  • Earthworks: Two approach cuts at either end of tunnel
    • Western approach
      • 300m, depth 7m, = 39,900m3
    • Eastern approach
      • 50m, depth 5m = 4250m3
    • Total volume = 41,150m3, cost $1,369,000
  • Ancillary works to above-ground section (length 350m)
    • Drainage: $70,000
    • Chainlink fencing (both sides): $35,000
  • Tunnel: Assume cost equal to new tunnel
    • OD = 12.4m, length = 300m, $62m/km
    • Cost = $18,600,000
    • Excavation volume = 36,229m3
  • Whole length works
    • New dual track $1,463,000
    • S&C $83,000
  • Section cost = $21,619,000 ($33.26m/km)
  • OPTION: Cut instead of tunnel
    • Compare this to an optional cut of average depth 20m
    • Excavation volume 192,000m3, and cost $5.95m
    • Dumping cost of additional spoil $1.09m

3 – Brooks Hill Curves

Section length 1950m, starting at 1810m. Straightens out the curves alongside Brooks Hill Reserve by traversing a pair of creeklines. Consists of a short but significant cut at the start of the section, then a large fill across private farmland. This is the first section in which we will have to consider land acquisition. Due to the small amount of farmland alienated by the new corridor, and the presence of the Brooks Hill Reserve adjacent, the area in green will be added to Brooks Hill Reserve.

  • Cut: 480m, average depth 10m, 1:1 slope
    • Volume 105,600m3, cost $3,274,000
  • Fill: 1.5:1 slope, 3 sections:
    • 500m @ 20m avg. height = 420,000m3
    • 500m @ 15m avg. height = 258,750m3
    • 470m @ 4m avg. height = 33,840m3
    • Total fill = 712,590m3, cost $11,401,000
  • Whole length works
    • New dual track $4,388,000
    • S&C $248,000
    • Drainage $390,000
    • Chainlink fencing (both sides) $195,000
  • Land acquisition – Approx. 32.5ha
    • Cost: assume a high farmland price of $5,000/ha
    • = $163,000
  • Section cost = $17,499,000 ($8.97m/km)

4 – Bungendore Plain

Section length 7040m starting at 3760m. This is a station section, so it will be somewhat more complex. Follows the existing almost-straight alignment right into the centre of Bungendore, to a renovated Bungendore Station. Existing curves are all of large radius, and no deviations are needed. There is one significant creek crossing – a 100m floodplain culvert at Halfway Creek. There are two grade separations at Ellendon St and Kings Hwy. Steel pallisade security fencing will be used within the township boundaries (ie, after the Ellendon St crossing).

  • Fills (all widening of existing)
    • 1500m x 4m high x 6m widening = 36,000m3
    • 4000m x 1.5m high x 6m widening = 36,000m3
    • Total = 72,000m3, cost $1,152,000
  • Bridge: Floodplain box-culverts @ $2.5m/track-km
    • =$500,000
  • Whole length works
    • Upgrade 1 track, add 1 track @$1.879m/km = $13,228,000
    • Drainage (assume all requires replacing) $1,408,000
  • Fencing
    • 4.8km chainlink (both sides) = $480,000
    • 2.24km steel pallisade (both sides) = $448,000
  • Grade separations
    • Ellendon St (minor, complex skew) = $2,500,000
    • Kings Highway major = $5,000,000
  • Signalling and Control
    • Cable and balises $894,000
    • Station approach crossover $4,000,000
  • Station costs
    • Renovate from partially operational state = $1m
    • 2x high-speed turnouts at station approach = $3m
  • Section cost = $38,076,000 ($5.41m/km)

Sector Summary

Component Cost ($m) Percentage
Tunnel 18.6 19.8%
Bridge 0.5 0.5%
Earthworks 20.1 21.4%
Track 25.8 27.5%
Civil Works 10.9 11.6%
Signalling & Communications 16.7 17.8%
Land 0.2 0.2%
TOTAL 93.8 100%

The total sector cost is $93,774 ($8.68m/km). Earthwork balance is -559,000m3, meaning this much fill must be imported from other sectors. The excess from the adjacent Kowen Forest sector can get us over half of the way there, with 295,000mavailable from a site only 5km away (close enough that the haulage is already priced in). The remaining ~260,000mcan be imported from the excess obtained at the Molonglo Gorge crossing (309,000m3 about 10km away). Given that both the cut and the fill have 5km haulage priced in, this is also close enough to not incur additional cost due to extra haulage distance.

Leave a Reply

Your email address will not be published.