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Monobox Maintenance Holes

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A rectangular monobox MH consists of a true monolithic top and bottom component. In the case of a monobase, the four walls and the base slab are poured together in one continuous concrete pour. Similarly, the monotop consists of the four walls and the top slab. The two halves are stacked to create a complete structure with only one joint. The geometry of these sections allows for much larger hole openings in the four walls to accommodate very large pipe and box units. The standard inside length and width dimensions of these chambers are available in 2400 x 1800mm, 3000 x 2400mm, 3900 x 2400mm and 3900 x 3000mm. Aside from these standard sizes, Concast also has the capability to manufacture specialty sized monobox manholes as well. The height of each monobase and monotop can be varied by 150mm increments. This precast structure is supplied with a shiplap joint that can be filled with a mastic joint treatment.


  • Quick installation since the entire structure only consists of a top half and a bottom half
  • Much larger pipe can be accommodated since all lift points are on the horizontal slabs
  • Most sections can be produced with large hole openings, eliminating any concrete pucks to be removed and disposed of on-site


Maintenance holes where pipe sizes are too large for a circular structure
Stormwater management structures
Underground storage tanks
Oil/grit separators and septic tanks
Watermain Chambers
Electrical Chambers



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Thank you for your interest.