A soil scientist with National Environment Management Authority (NEMA) says the cracks that developed on Karuma and Isimba hydro-power dams were caused by use of poor quality sand rather than poor workmanship.
The cracks with width varying from 0.2 to 1.48 millimetres were noticed in the spillway concrete. Some engineers blamed the cracks on Karuma dam on shoddy work by Chinese state-owned engineering and construction company, Sinohydro Corporation. But Dr Jerome Lugumira, a specialist in soils and land, blames the cracks on materials used especially locally-sourced sand.
"It was understood that sand was not the problem by people who specialise in materials science. Unfortunately, we have many who specialise in metals and not many in earth materials. They understood only the size of the grain - how rough it is would be the most appropriate. Little did they understand that, even when it is cleaned, you will have residues oxides that really escape with the grains. After all, the agreement is that you can’t clean it 100 percent. Unfortunately the syndicates that escape with the grain are oxides that allow expansion and contraction", he said.
Dr Lugumira suggests that the sand had elements of shrink and swell clay which is not recommended in the construction industry. Shrink and swell clay is said to contain vermiculite mineral. Vermiculate is highly porous and is prone to contractions when mixed with cement.
Cracks at Karuma hydro power dam were discovered after about 30 percent of the construction works had been done. Similar cracks were also reported at the construction of the 183MW Isimba dam.
The cracks at the over $2 billion projects reportedly angered President Yoweri Museveni leading to the sacking of some officials at the ministry of energy and mineral development.
President Museveni later appointed former Electoral Commission chairperson, Dr Badru Kiggundu, to head a project steering committee on the two projects. The committee was tasked with fixing the cracks.
Dr Lugumira suggests that the two projects could have been started without specifically identifying where the right sand for the projects would be obtained.
He explained that there are different grades of sand that can be used for different construction works. Lugumira says an initiative has not been taken in Uganda to determine what quality of sand is available in the country.
"Quite recently in Karuma the sand that was being used was got from Nakasongola. And this is sand that is not clean in a way and was used to construct part of the structure. Little did they know that it was sand that has elements that can expand the clay. So cracks emerged. We had not learnt what happens on Owen Falls Dam.
The three turbines which were constructed using materials from the UK up today have no single crack. The two turbines which were constructed using local materials developed cracks after 10 years and are non-functional", Lugumira said.
Lugumira says he is not shocked by the fact that poor sand is causing cracks in dams being constructed in Uganda. He says even some of the biggest dams in United States of America have developed cracks because of geological forces but mostly due to structural inefficiencies in materials.
Engineer Hillary Onek, the minister for relief and disaster preparedness, in a presentation at the Uganda Institute of Professional Engineers said incidences of cracks in dams most often occur due to hydration heat differential.
But Onek, who once headed the ministry of energy, ruled out tremors as the likely cause. He said there has not been a recorded tremor since construction of Karuma dam started.
There is another side to the cracks at Karuma. A study by Energy Infratech Pvt published by the International Academic Journals Network says the cracks revealed that they were thermal in nature due to heat of hydration.