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What is the purpose of providing service reservoirs?

Service reservoirs, other than normal reservoirs, are provided because of the following reasons:

(i) In case of the breakdown of pumping stations and water treatment plants, it provides a temporary storage of water in emergency situation like fire fighting.

(ii) Since the demand of water supply from customers varies with time, the provision of service reservoirs aims to balance the fluctuation rate of water demand.

(iii) It provides a constant head of water to the distribution system under the design pressure.

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(iv) In the event of the occurrence of water hammer or surge during the rapid closure and opening of pumping stations, the reservoir acts to attenuate the surge and performs like a surge tank.

(v) It leads to a reduction of the size of pumps and trunk mains connecting to the distribution system as the pumps are not required to directly cope with the peak rates of water demand by the introduction of service reservoirs. As such, there is substantial cost savings arising from the use of smaller pumping pipelines and smaller pumps.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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Should pipelines be completely embedded into thrust blocks?

For unreinforced concrete thrust blocks in bends and tees for pressurized pipelines, it is recommended that the contact surface between the pipelines and concrete thrust blocks should not exceed 45o from either side of the pipe in the direction of thrust force through the center of pipelines. The reason is to prevent the occurrence of potential cracking arising from the deformation of pipelines under loading condition. If it is necessary to embed the whole section of pipelines into concrete, it is suggested to coat the pipe with a flexible material

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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Is reinforcement necessary in thrust blocks?

In normal situation, reinforcement is not required for thrust blocks in pressurized pipelines. However, certain amount of reinforcement has to be added in thrust blocks in the following situations:

(i) The structure integrity of huge thrust block could be enhanced by the introduction of reinforcement.

(ii) At the anchorages for straps in thrust blocks, some reinforcement has to be designed to avoid the development of tensile stresses.

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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How can restrained joints resist thrust forces in pressurized pipelines?

The unbalanced thrust forces in pressurized pipelines cause the line to move and joints to separate unless the unbalanced force is counterbalanced by some means such as thrust blocks.

Restrained joints can be adopted to resist the thrust forces. The mechanism of restrain joint involves gripping and locking the pipe joints together to avoid axial movement and joint separation. For the unbalanced thrust forces, they are distributed to the surrounding soils in such as way that the bearing area is assumed to decrease linearly from the location of thrust forces to the end of restrained pipes. The soil bearing against the pipelines and soil friction provide resistance to movement of pipelines.

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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How can thrust blocks resist unbalanced force in horizontal bends in watermain?

Thrust block resists the unbalanced force in two common approaches. In the first approach, thrust block serves as gravity block which makes use of its own dead weight to resist the thrust forces. An example of this application is vertical down bends.’

The second approach of thrust block to resist unbalanced forces in watermain involves providing a larger bearing area so that the resulting pressure against the soils does not exceed the bearing capacity of soils. Therefore, the function of thrust block in this case is to make use of stiffness of concrete to spread the thrust force into larger area. An example of this application is horizontal bends in watermain.

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Filed under Hydraulics | 0 Comments