Sunday, September 2, 2018
Operations in Embankment Dam Construction
Operations in Embankment Dam Construction
Construction of Embankment Dam
The construction operation of embankment dams is divided into four major groups of construction activities which include:
- Material source development activities
- Foundation preparation activities
- Fill construction operation
- Ancillary works construction activities
Fig.1: Embankment Dam Construction
Material Source Development Activities
The material source development activities include opening out quarries from which necessary materials are obtained, installation of fixed plants for instance crushers, and conveyor which is employed to transfer crushed materials to a specified location.
Construction of roads between various areas of quarries and the embankment dam is another material source development activity. These roads are commonly utilized to haul and transport materials to the embankment dam, in addition to move transportation and haulage plant between various parts of the quarry.
Fig.2: Installation of plants and conveyor and road construction to haul materials
Foundation Preparation Activities
One of the first works needs to be tackled properly is drying up the foundation area. This usually can be done through the construction of temporary diversion tunnel at the sides of the embankment dam.
Fig.3: Inlet portal of diversion tunnel used in the construction of hoover dam in the united states
Such tunnel may host outlet works as well. Sometimes, the outlet culvert through or under the embankment dam is built instead of diversion tunnel and this outlet culvert would be used for river diversion.
Earth fill source development is another construction activity at this stage. This can be carried out along with river diversion works. After the previous works finished, weathered materials, which migrated due to water and weak soil at the top surface would be removed at the project site.
There are cases in which soil foundation strength needs improvement. In addition to consolidate the area in advance and install sand drains. Necessary instruments and tools are also installed at this phase.
Not only do these devices used to measure pore water pressure but also observe the performance of cutoff point. Finally, the foundation construction stage is finished with the drainage blanket placement beneath downstream shoulder.
Fig.4: Drainage blanket placement in embankment dam
Fill Construction Operation
It is another dam construction activity that could be easily carried out. The material used should be conformed to the requirements of applicable code. As far as fill placement is concerned, it could be affected by weather conditions in addition to possible variations in material characteristics.
Fig.5: Placement of earth fill material
The quality of the construction is governed by number of factors for instance water content, thickness of soil layer being compacted, and compaction effort.
So, fill placement cannot be carried out properly unless the works is supervised and monitored adequately. The quality and uniformity of compacted core fill is considerably significant and need to be taken into consideration.
Then, the placement of horizontal drain layer in both shoulders at a vertical distance of 3-6m is proceeded. This construction activity is required to control construction pore water pressure and increase speed of consolidation in cohesive materials of low permeability.
While fill material are placed, devices and instruments needed to be placed in the core and shoulders are installed. The final activity of this stage is the construction of protection measures for instance placement of armoring layer at the upstream of the embankment dam.
Ancillary Works Construction Activities
It may involve the construction of spillway, stilling basin, tunnel or culvert for outlet works, valve towers, drainage works, wave wall, road way, and grassing of downstream face of embankment dam in the locations where weather condition would not spoil it.
Fig.6: Spillway of Darbandikhan Dam In Kurdistan Region-Iraq
Fig.7: Removing excess water using spillway of Darbandikhan dam in Kurdistan region-Iraq
Fig.8: Grassing downstream of an embankment dam
Cost of Reinforced Concrete FRP Strengthening System and other Methods
Cost of Reinforced Concrete FRP Strengthening System and other Methods
There are various techniques which are used to enhance both ultimate load capacity and serviceability of reinforced concrete structures. Strengthening reinforced concrete beams with FRP composite is the most novel method which has been developed. This method is widely accepted and has proven to be effective in improving capacity of reinforced concrete elements.
In this article, the economy of FRP strengthening systems in comparison with the cost of other conventional methods based on the conducted studies and projects will be discussed.
Fig.1: Reinforced concrete member strengthening using FRP composite (left side) versus strength using traditional methods (right side)
The economy of strengthening systems will be discussed in two stages which include:
- Cost of Installation of FRP systems
- Cost of Entire life service of strengthening systems installation of FRP systems
Cost of Installation of FRP Systems
The economy of FRP composite strengthening system at installation stage is based on the working conditions and factors that may involve the task.
Moreover, it is required to take the time frame allocated for completing the project and the available space at site when the cost of the work is evaluated. This is because these factors could have a substantial influence on the cost.
Furthermore, it is claimed that the cost of strengthening using FRP composite is around 70% of the total cost using other methods for strengthening. This claim is based on the study that conducted on the strengthening of rail track structure.
Installation cost estimation and studies on strengthening technique using FRP composite compare with other conventional methods
In certain projects such as high ways, closing of the structure for traffics would lead to penalty and hence increase the cost.
For instance, when main high way in New York City in the United States had to be upgraded, it was needed to do the work at night only because the high way needed to be open during the day otherwise a penalty of around thirty thousand US dollars would have been imposed for hour of high way closure in day.
There are number of projects for cost estimation has been carried out and all of them showed the superiority of strengthening technique using FRP over other ordinary or traditional methods.
For example a beam to column joint of parking garage structure enhanced by bonding carbine fiber sheet. It is found that, the use of such method needed around 35% of ordinary techniques which may involve the installation of additional reinforcement bars and pouring concrete as well.
In another project which located in Canada, the cost of shear strengthening of the entire bridge was estimated FRP sheet and steel stirrup. It was demonstrated that the cost of using FRP sheet was cheaper by about 30%.
As far as the installation time frame is concerned, there are cases in which the time needed to complete the strengthening project using FRP composite is substantially lesser that that needed when conventional method is employed.
For instance, the duration needed to strengthen a chimney in Japan was a month whereas the conventional method required six months. Finally, from the above examples, it can be concluded that, the cost of installation of FRP composite is considerable smaller than other traditional methods.
Cost of Strengthening Systems Installation of FRP Systems
The entire life service cost of strengthening technique is a major factor that plays significant role while a decision is made on how and when strengthens reinforced concrete structure.
Commonly, the enter life service cost of any strengthen system is composed of installation cost and maintenance cost that may be required during the life span of the structure.
However, since the installation cost has been discussed and accounted for, so the maintenance cost will be explored in this section.
When the entire life cost of strengthened structure is evaluated, it is necessary to take number of factors into account. For example, durability of strengthening technique, costs due to loss of service, requirements of the owner for serviceability and life service of the structure, and maintenance cost.
It is proven that, the cost of maintenance of reinforced concrete elements strengthened with FRP composite is smaller than that of reinforce concrete members strengthened with conventional methods.
Finally, it can be claimed that, the economy of using FRP composite systems to strengthen reinforced concrete structure is superior to other conventional method.
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