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Uses and Advantages of Bentonite Slurry Walls



Ratay listed five main uses and subsequent advantages that diaphragm walls have that contribute to their regular use in basement construction today:

•   They are rigid

•   They can be made watertight

•   They have the ability to support substantial vertical and lateral loads

•   They are installed virtually without any vibration

•   They can be constructed in low head-room areas

While the above factors may be advantageous there is one main differential factor that sets the diaphragm wall apart from other earth retaining structures, and that is that the diaphragm wall forms part of the permanent structure which contributes to its overall efficiency.

Most common places where one would find reinforced diaphragm walls like the one outlined in this report would be; subways, basements and other underground major construction. Alternatively un-reinforced diaphragm walls can be used as impermeable cut-off walls where necessary e.g.in dams or other hydraulic structures.

Bentonite Slurry Farm

The Bentonite slurry farm consists of a number of aspects and parts and in some cases a number of intricate pipe systems carrying slurry to the desired destination. The main cause for concern for most contractors is the amount of space in which the farm takes up on a site.

The farm consists of a number of silos in which to store the slurry after it has been mixed, another aspect is a storage area for the dry bentonite powder as well as an allocated area for the mixing of the system.

The pipework in some cases may become complicated, depending on the layout of the slurry farm. There are usually three separate storage areas for the slurry, namely: a used slurry pond, a recycled slurry pond, a fresh slurry pond and a waste pond. The slurry displaced from the trench is pumped into the used slurry pond with some of the slurry going to the waste pond. The slurry in the used slurry pond is then pumped into the desander, this process is essential to remove the excavated material from the bentonite slurry so that it may be re-used in another panel excavation. This ‘desanded’ used slurry is then placed in the recycled slurry pond and is then pumped together with some slurry from the fresh slurry pond for use.

 

List of Applicable Equipment

The construction of diaphragm walls is complex, and in addition requires a number a large plant for the execution of the work, without which the process would be near impossible.

Some of the major plant and equipment used on a majority of the diaphragm wall construction sites are listed below:

•   Free hanging clam-shell

•   Excavating bucket

•   Percussion chisels (to break up boulders and penetrate rock)

•   Hydromill cutters

•   Crane (for placement of reinforcement cage)

•   Tractor

•   Welding Machine (if reinforcement is assembled on site)

•   Stop-end pipes

•   Generators

•   Desander

•   Silos/storage tanks

•   All Necessary Pipework (for bentonite flushing as well as for concrete introduction)

•   Vertical pump

•   Water pump

•   Mixers

•   Trucks for transporting the concrete

Maintenance and regular supervision of a majority of these plant and equipment is essential to the projects efficiency and ultimately its success.

 

Conslusion

After extensive research on the construction process of diaphragm walls it is clear to see that the development of the bentonite slurry method has greatly impacted how basement construction is performed. It is clear why it is the most commonly used method for basement construction, and is the most profitable and efficient today.

There are however a number of concerns that have been discovered after a look into a number of previous projects. The bentonite slurry farm, especially on smaller projects poses a major threat and could lead to major changes being done to accommodate for the farm, ultimately decreasing profitability and efficiency of the whole project.

Another possible short coming that could be encountered during the construction of a diaphragm wall could be the limited space directly above the trench for the manoeuvring of the heavy plant and machinery needed throughout the construction process.

Both concerns highlighted above refer to the possibility of limited space around site. This could therefore form a major issue for contractors in developed areas such as the CBD. In developed urban areas it is essential for the contracting team to do a large amount of research on the surrounding buildings and roads to fully understand the limitations.

As highlighted in the introduction of this report one of the most common reasons for basement construction is the limitation of above ground space, this is why it is essential to be well aware of the surrounding buildings. The contractor should only go ahead with plans if he is confident that he is able to overcome these possible threats.

Taking into account all the above information I believe that diaphragm slurry walls will continue to be used for years to come and even increase in the frequency of use due to the increased over population in some areas around the world.


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