Building design and construction standards are tailored to suit the environmental, social and economic conditions of individual countries, these modifications are recommended by the Building regulatory bodies of individual countries after a series of research and experiments. In Nigeria, these modifications take place without the backing or recommendations of our building regulatory agencies, resulting in structures that fail to meet relevant building design and construction codes. One of these modified construction techniques is the construction of Raft foundation which I have termed the “Nigerian Raft Foundation”.
Raft foundations are used in soils with relatively low bearing capacity, where a pad foundation might result in uneconomical pad footings and differential settlement of the foundation. The raft foundation helps to spread the load of the building over the soil and ensures even settlement of the foundation. There are different types of raft foundations each suited to tackle the loading and soil configurations of a project. We have a flat slab raft, an upstand beam raft, a down stand beam raft and a cellular raft.
The Nigerian raft foundation like other modified construction techniques lacks the backing of relevant civil engineering literature and in extreme modifications differ completely from the standard raft foundation.
Below are three mistakes to avoid while constructing the “The Nigerian Raft Foundation”.

-A Geotechnical investigation (Soil Test) Must Be Carried Out
There is a tendency to avoid a geotechnical investigation (soil test) in most Nigerian building projects due to ignorance about the cost by prospective homeowners and incompetence by the builders. The deductions from a geotechnical test indicate the type of foundations to be employed, of which the results are used directly in the design of the foundations. In Nigeria, the values used in the design of common foundations like strip foundation and pad foundations are assumed based on the adopted values of a particular region but for a Raft foundation these values cannot be assumed and must be gotten from the results of a geotechnical test.
Constructing a Raft foundation without a soil test to reveal prerequisite information like the depth of foundation, bearing capacity and settlement rate of the soil is akin to wandering the desert without a compass. This soil test result is a prerequisite in the design process of the raft foundation.

-The Raft Foundation Must Be Structurally Designed
The Nigerian building construction industry is plagued with the construction of Storey buildings without structural drawings partly due to the inefficiency of the building approval agency to enforce building construction standards and ignorance of some builders.
Raft foundation like other structural members requires the attention of a structural engineer to estimates loads, sizing of structural members and provision of adequate reinforcements.

-Reinforcement Must Be Provided for The Raft Slab
Due to a lack of understanding of the literature governing the design and construction raft foundations, the Nigerian building construction industry is plagued with raft foundations without reinforced raft slabs.
In Nigeria, what is commonly termed as “DPC” in raft foundation construction is actually the Raft slab, of which it is the most important structural member of the raft foundation. For example, the flat slab raft consists of just the raft slab and the columns and does not have a raft beam. The raft slab is usually neglected and emphasis placed on the Raft beam resulting in extreme cases of the Nigerian raft foundation in which the raft slab is constructed without steel reinforcement.
A foundation without reinforced raft slab should be called a reinforced strip foundation and not a raft foundation or we can also term it a “Nigerian Raft Foundation “.
-Avoid sancrete blocks in your raft foundation
The most extreme case of the Nigerian raft foundation is the introduction of sancrete blocks in the raft foundation. The sancrete blocks are introduced between the raft beam and raft slab in an attempt to cut the cost of construction. This practice stems from ignorance of basic construction procedures and it is also very dangerous as it might lead to a fatal collapse of the structure. This is Nigerian raft foundation In its purest form.

Making any or all of the above-mentioned mistakes can result in building deformation or in extreme cases, building collapse. There is a need for the relevant building regulatory agencies to ensure strict compliance with standard building construction practices especially in the construction of Raft Foundations.
https://www.harneyprojects.com/single-post/2018/08/17/THE-NIGERIAN-RAFT-FOUNDATION-AND-THREE-MISTAKES-TO-AVOID

Very informative thread...thanks OP.