The first crack appeared in the body of dam in September, 2008. In the two recent constructed cracks, the longest trace is high 31.5 meters, the deepest bathos is 6 meters. Talking on February 12th, Prof.Dr.Sc. Pham Hong Giang, the chairman's Association of Vietnam Large Dam and Water Resource Development has shared some information.
What causes concrete crack?
(The interview about the problem of crack at Son La hydroelectric dam)
Spillway construction at Son La Hydropower
BBT. The press has recently reported on some cracks at Son La hydroelectric dam. Reporters have contacted with the Office and met directly VNCOLD experts to ask for further information. On the morning of February 12th, 2009, the reporter of "Science and Life" magazine interviewed Prof.Dr.Sc. Pham Hong Giang, the chairman of VNCOLD. www.cncold.vn would like to recommend readers the interview content.
The first crack appeared in the body of dam in September, 2008. In the two recent constructed cracks, the longest trace is high 31.5 meters, the deepest bathos is 6 meters.
Talking on February 12th, Prof.Dr.Sc Pham Hong Giang, the chairman's Association of Vietnam Large Dam and Water Resource Development has shared some information.
Has the information about the cracks surprised you?
There are many reasons for concrete cracks which are unavoidable, so it has not brought any surprise. However, in this case there has been a bit surprise to me because it is not only the national key hydro-electric but also Southeast Asia largest-scaled project which is carefully prepared, strictly checked about technology, consulted by experts from famous foreign companies.
So what are the reasons for these cracks in your opinion?
There are many causes of concrete cracks because its physical and mechanical characteristics is much changeable due to time. These cracks may be caused in the process of concrete cure. To large concrete blocks, heat stress here causes crack. Another reason is the fault of concrete maintenance. Additionally, cracks may be affected by kinds of load, sunk foundation, etc. To determine the exact cause of cracked concrete, there is need of very specific surveys.
Dear sir, cracks in such large scale project like Son La hydro-electric dam normal or not?
Some reinforced concrete structures allow cracks to a certain extent. However, to work structures that require waterproof, leak proof such as water dams, water must be absolutely ensured not to penetrate. If it is a concrete structure, it is not allowed to crack, also there must comply strictly technical regulations in the construction process.
In the history of dam construction over the world, have alike incidents happened yet?
As I mentioned above, concrete cracks are quite common phenomenon which are caused by many reasons. In the world, such incidents are the same. However, most of them are detected and processed. Son La hydro-electric dam is built with rolling concrete which is recently used for block structure, mainly large dams. Due to used for block structure, the heat control in the rolling conpaction concrete should be specially paid attention not to crack.
Can you tell the advantages and disadvantages of the rolling compaction concrete technology?
In 2008, it has been solemnly celebrated 30 years of using the rolling compaction concrete. This kind of concrete has many advantages, for example it economizes cement, it is fast in building process. However, technical requirements are also strict to control heat in concrete and ensure the tightness in rolling compaction process. Currently in the world, all the big concrete dams use the type of rolling compaction concrete. The large dam of rolling compaction concrete with tens of millions m3 volume can be constructed in just three years.
To such large scaled project like Son La hydro power, are cracks because of consultancy and construction supervision matter?
I cannot affirm this reason because there has not been specific information about this incidents.
Is the technology for fixing cracks expensive or not?
Expenses for fixing cracks depend on the scope of cracks and treatment required. It is usual to fullfill the cracks. Additionally, it is advisable to consider solutions to creat waterproofing roof membrane at the upstream dam.
Is it necessary to stop constructing to treat three cracks?
If the construction is continuous with the new block, it must draw experience and make up fully to avoid similar cracks. To the constructed concrete blocks, they must be carefully checked to thoroughly resolve the current cracks.
Thanh you very much!