Structures Resisting Hydrostatic Pressure

Hydrostatic Pressure is the force resisted by structures against some hydraulic forces. Hydrostatic pressure plays a very important role in the field of Hydrology and Hydraulics and in most of the cases the stability and reliability of hydraulics structures depends upon the ability of the concerned structures to resist the externally applied hydrostatic pressure.

Following are the few examples of the structures resisting the hydrostatic pressure.

• Retaining wall
• Aqueducts
• Pressure tunnels
• Penstocks
• Pipes etc

Civil engineering projects often require the construction of systems that retain earth materials. An excavation support system for a cut-and-cover trench for utilities installation is an example of a temporary retaining structure. A reinforced concrete retaining wall utilized in a highway project to accommodate a change in elevation over a limited distance is an example of a permanent retaining structure. Numerous earth retention systems have been developed over the years and a few systems.

The design of retaining structures requires an evaluation of the loads likely to act on the system during its design life and the strength, load-deformation, and volume-change response of the materials to the imposed loads. Lateral pressures develop on retaining structures as a result of the adjacent earth mass, surcharge, water, and equipment. The development of lateral earth pressures and the transfer of these pressures to the retaining system are inherently governed by soil-structure interaction considerations.

Hence, the analytical procedure should consider the relative rigidity/flexibility of the earth retention system. In this chapter, retaining structures will be broadly classified as either rigid or flexible Before applicable design procedures are discussed, lateral earth pressure concepts will be reviewed.

1. Retaining Wall

A retaining wall is a structure designed and constructed to resist the lateral pressure of soil/water when there is a desired change in ground elevation that exceeds the angle of repose of the soil. The active pressure increases on the retaining wall proportionally from zero at the upper grade level to a maximum value at the lowest depth of the wall. The total pressure or thrust may be assumed to be acting through the centroid of the triangular distribution pattern, one-third above the base of the wall.

2. Aqueducts

Aqueducts are an artificial channel for conveying water, usually by gravitation. The term (from the Latin aqua, water; and ducere, to lead) is most commonly understood to mean a bridge of stone, iron, or wood, for allowing the passage of water across a valley. But a pipe, open channel, or a tunnel through a mountain is equally an aqueduct, if its purpose is to convey water from one place to another. All great aqueducts have been constructed for the purpose of conducting water from some more or less distant source to large towns or cities. The term is also applied to a bridge carrying a canal for the purposes of navigation.

Features

1. Aqueducts are man-made tunnels that carry water from one place to another. They are used so that dry areas can get water from areas that have more water.
2. Aqueducts have been used for water supply or for transportation from one place to another.
3. Aqueducts my be covered or uncovered form the top.

3. Pressure Tunnels.

Pressure tunnels work on the principal of Pressure flow and the water flows through the tunnel under the pressure.

Pressure tunnels can be used in a verities of situations such as

• In dams as penstock.
• In Irrigation for water supply
• In water tanks for supply of water to community.

Pressure tunnels can be made from different materials such as

• Concrete
• Steel etc

Depending upon the situations and the pressure demand but in most of the cases such as in the construction of powar house or dam pressure tunnels are made of concrete.

Pressure tunnels can be:

• Construction without pre stressing; and,
• Construction with pre stressing.

Construction without pre stressing

When the rock can respond elastically to all the loading conditions which occur and if, furthermore, it contains few fissures and is not very permeable, a carefully constructed un-reinforced concrete lining of medium thickness is sufficient for a pressure tunnel. It is essential, however, that the voids which always occur between the concrete and the rock in the roof region be sealed by grouting. Complete water tightness cannot be achieved with a simple concrete lining. Attempts to approach this ideal.

Construction with pre-stressing.

Basically, both unreinforced and reinforced concrete linings are quite unsuitable for one of the most important tasks, namely the prevention of water losses because of their low tensile strength. Recognition of this fact led soon to the development of forms of construction comprising a so called passive prestressing, where the pre-stressing is produced by support from the surrounding rock. The best known of these methods include the core ring lining by Kieser' and the gap injection method.

4. Penstocks.

A penstock is a sluice or gate or intake structure that controls water flow, or an enclosed pipe that delivers water to hydraulic turbines and sewerage systems.

The modern penstock is designed to cater for a wide variety of duties from low seating to high off-seating heads in sizes from 150mm to 5000mm square. Selection of the correct penstock to suit the duty is important to satisfy the design criteria and provide the most cost effective solution. Operation of the penstock is governed generally by factors outside the control of the penstock

manufacturer. However, the range of available operating equipment is extensive: from simple direct operation by handwheel to complex control systems for electrical, pneumatic or hydraulic actuation. The range of penstocks together with its associated operating equipment will cater for the most demanding specification and application.

Types

1. Stainless Steel Fabricated Penstock
2. Coplastix® Series 50 - 40
3. Cast Iron Weir Penstocks
4. Cast IronSeries 90 - 6 0

Stainless Steel Fabricated Penstock

The Fabricated Stainless Steel Penstock is a rectangular faced penstock designed to meet the ever changing fluid handling demands of customers, combining the latest in penstock design and parametrics software.The generic penstock design, which is tailored using parametrics software, develops and individualizes the penstock to suit specific duty and aperture requirements.

Coplastix® Series 50 - 40

The Coplastix® Series 50-40 is a rectangular faced pen stock designed and manufactured to suit modern industrial and domestic effluent environments. Utilization of the latest synthetic materials for both sealing mechanisms and door construction combined with the use of steel or stainless steel in the construction of the penstock frames ranges.

Cast Iron Weir Penstocks

Weir Penstocks are utilized in water and sewage plants for accurate regulation or measurement of flow. Operation of the Weir Pen-stock is opposite to that of a conventional pen-stock, with the door opening downwards.

Cast IronSeries 90 - 6 0

The Series 90-60 is a rectangular metal faced pen stock suitable for wall and thimble mounting, with on-seating heads up to 9 metres and off-seating heads up to 6 metres.