Building onto this innovation of HICU Hollow pots, it is possible to apply the same to the ground floor slab.
This would mean the ground floor slab would be suspended and would be carried by the beams which in turn transmit the load to the columns and column basis. This would be cost effective for small to medium structures especially in black cotton soils and in areas prone to flooding.
The present method of building substructure by excavating in cotton soil in mass, carting away to spoil the excavated materials and then filling the excavated area with hardcore besides constructing strip foundation and masonry footing is not only slow and tedious but costly and wasteful.
The ground is stripped of top soil (300mm) before excavating the column bases. The normal method of blinding, bar bending and placement of bars for column basis is followed before concreting. The same applies to columns, while the beam can be partially concreted (slab thickness part can be done with the slab) in order to allow for re-use of timber formwork.
Where the difference in level between the existing ground level and the bottom of the slab is big (in flood prone areas and crawling space is achieved) it is better to use timber formwork which can be removed once the slab is fully cured.
For the small difference of 200- 400mm (between excavated ground and bottom of slab) we recommend use of HICU Wall blocks to carry the HICU Hollow pot. Dust blinding is laid first before placing of blocks for leveling purposes. Incase, double courses of blocks are required (400mm difference) the first course is laid with small gaps between the blocks with the second course laid back to back. The Hollow pots span 340mm unsupported width which is open at the bottom which translates to 63% of cotton sub grade being unrestricted. The hollow blocks are about 20% voids at the bottom which is about 9% of the restricted balance of the cotton area. The total unrestricted area for cotton sub grade is 72% besides the HICU hollow blocks only serve as temporary support and once the slab sets it carries its own weight and other imposed loads.
The voids for the top HICU block can be filled at the top (or the top can blinded with concrete when in upside position) with small hardcore before laying the polyethylene paper and placement of HICU hollow pots.
The speed for laying the blocks is much faster than timber form work (the termites will not be a problem thereafter due to decaying timber) and they lock better and are very stable.
This is a great milestone since most of precast/prefabricated building still rely on traditional strip foundation and quarry masonry stone to build the substructure which is often slow, tedious and expensive. This means that the last existing barrier to automating house construction has been overcome.
This will lead to durable houses being constructed at a lower cost due to the efficiency realized from this technology.
We have used this Substructure construction for 12 no. Domestic servant quarter for our project in Kitengela and the savings in cost were enormous. The structural design for the substructure was done by a consulting Engineer.
We have attached cost comparison of HICU wall block to machine dressed stone, HICU hollow pot slab to solid slab and HICU suspended ground floor slab to traditional substructure for 1 no. domestic servant quarter.