A Twenty-first Century Vision for a New Secondary School

Serving the Madras Catchment Area
 

Estimations of excavation costs at Pipeland Farm


The figures quoted below are computer-estimates of the volume of earth (soil/rock) that would need to be excavated in order to level the terrain at the Pipeland Farm for five Level Playing Field Pitches.

Presumptions
  • Pitch Size of 60m x 120m (36,000 sq.m for the 5 pitches) plus 1m separation between pitches.
    (Using 2m separations would increase the 5-pitch width by 5m, and the total volume and cost by approximately 2 percent.).
     
  • Foundations depth = 0.5m.
     
  • Estimated cost of excavation = 20 per cubic metre.
     
  • The cost of extensive drainage, catchment and connection to the main rainwater sewers, plus fair-surfacing and grassing, all to acceptable standards, plus stabilising the exposed "earth walls/slopes/revetments", could be at least 10 per square metre.

Cross-sections

The following data has been prepared from ordnance survey maps.

  • There are seven cross-sections running from south (at left) to north (at right), X3, X4, X5, X6, X7, X8, X9.  They are 100 metres apart (so X3 = EASTING Coordinate 300 on the Ordnance Survey [OS] map, etc.). X3 is the most westerly one, at the Hospital boundary, X9 is the most easterly one.
     
  • The vertical heights are in metres above sea-level. (these were interpolated from the contour lines on the OS map).
     
  • The horizontal distances are marked from 1000 (at left) to 1400 (at right) at the boundary of the Scooniehill Road houses. These are the NORTHING Coordinates on the OS map.
     
  • The vertical scale is six times bigger than the horizontal scale.

Results

DEEP-Excavation-to-Lowest-Point

Volumes

The Minimum Volume = 33,594 cubic metres. This occurred right at the eastern end of the site, about halfway between the N and S boundaries (where the field is more level just before it falls down rapidly to the North at the housing edge).
 
The nett average depth of excavation for the 5 contiguous Level Pitches is 0.747m.
 
This is the depth to reduce the earth to its Lowest Point within the 5 Pitch block.
The gross average + drains + foundations depth (0.5m more) is 1.247m. (Incidentally, the Maximum Volume comes out at 60,156 cubic metres. It occurred at the western part of the site. Its eastern end is just above Pipelands Farm Steading, its western edge coming close to the road-path by the Hospital. Compared with the Minimum location, the terrain falls more uniformly steeply here over the whole area. The area actually excludes the even steeper part where it tilts rapidly down to the North at the housing edge outside the Pitch Areas).
 
The nett average depth of excavation for the 5 contiguous Level Pitches is 1.337m.
 
(This is the depth to reduce the earth to its Lowest Point within the 5 Pitch block).
The gross average + drains + foundations depth (0.5m more) is 1.837m.  

Costs

The Excavation Costs based on the above volumes would lie between 671,880 and 1,203,120.
 
Minimum 33594 cubic metres x 20 per cubic metre = 671,880

Maximum 60156 cubic metres x 20 per cubic metre = 1,203,120
 

The cost of extensive drainage, catchment and connection to the Main Rainwater Sewers, plus fair-surfacing and grassing, all to acceptable standards, plus stabilising the exposed "earth walls/slopes/revetments" would add another 360,000 to the costs of the Playing Fields. 36000 square metres x 10 per square metre = 360,000

 

The CUT+FILL alternative

This means excavating only the uphill (southern) half of the long block, and placing that on the un-excavated lower (northern) half of the long block so as to create the level playing-field area (at a slightly higher height above sea-level).
Uphill embankments and downhill revetments would still be required. However, the downhill revetments would have to extend **further** downhill to get a safe and stable non-mud-slide edge, because the height of the levelled playing-field-site stands higher up than it would in the deep excavation. (The northern edge has been artificially built up).

That extra earth has to be dug from **somewhere else**, and rammed and consolidated, etc...
But again, in favour of CUT+FILL, the shallower dig may not meet as much rock as a DEEP dig.

So although CUT+FILL needs less immediate excavation than a DEEP excavation, the extra need for larger revetments to stabilise the northern downhill edge adds to the overall digging and consolidating - and hence to the CUT+FILL costs.

A reasonable estimate suggests that the cost of CUT+FILL may still come out somewhere between 65 and 75% of that of DEEP excavation.


Summary

  • The overall Pipeland playing field bill could come out between 1,000,000 and 1,500,000 if the safer DEEP excavation is used.
     
  • Such an excess would go a long way to cancelling out any short-fall between Fife Council's upper-bracket and the earlier University's sale-offer price.
     
  • All this without the dreadful disruption, to the hospital and the local residents, caused by the excavation, and the shipment of the spoil off-site in huge HGVs, jamming up the Community Hospital narrow carriageway and the southern roundabout.
     
  • Excavating the playing fields area down to the lowest practical level is the safest and more desirable plan for a site with such significant slopes.
     
  • The alternative of a shallower CUT+FILL method requires much more detailed engineering and constructional procedures. It could reduce the estimated initial excavation costs by perhaps 35 percent, and might at first seem to be the cheaper and more attractive option. But it could turn out to be the more dangerous solution, and in the end as expensive as the much safer "Lowest Depth" option. This is because of the much larger land-slip-prone revetments, drainage, etc. needed to shore-up and stabilise the higher FILL portions of the playing field area where the land slopes are greatest, leading to a sort of "Hanging Playing Fields of Pipeland" effect.
     
  • Moreover, the CUT+FILL work would also be saddled with the need for future regular inspection and maintenance work to safeguard the residential property, just over the Pipeland site fence, from land-slide and excessively steep water-run-off. The latter is already a well-documented and persistent problem troubling the houses in the Scooniehill Road area that back-up to the Pipeland fields. Any change from significantly sloping farm fields to a major school site would only make these existing problems far worse.
     
  • The cross-sections seem to reveal that the original natural falls of the Pipeland Farm fields appear to have already been cut-back into when the building site for the Scooniehill Road houses was being prepared, back in the 1950s. That housing site would have had to be levelled to grab as much useful building land from Pipelands Farm as could be done economically at the time.
    The sudden sharp increases in gradient can be clearly seen in the intermediate cross-sections (on the right).
    These increased slopes could be part of the cause of the run-off-water flooding problems that the residents frequently have to report and be helped with.
    That problem won't be helped by further excavation work for the playing fields.

     

Prepared by Dr John Amson, BSc, PhD(Cantab), FRAS