The temporary all round enclosure which keeps the water away from the working area by using vertical barriers is called-
Coffer dam
Understanding Temporary Water Enclosures in Construction
The question asks about a temporary structure used to keep water away from a work area. This is a common need in civil engineering projects, especially when constructing foundations, bridges, or other structures in or near bodies of water like rivers, lakes, or the sea.
Identifying the Correct Structure: Coffer Dam
A structure specifically designed for this purpose—creating a dry working environment by excluding water temporarily—is known as a coffer dam (sometimes spelled cofferdam). These are typically temporary structures built around the excavation site or work area within the water body. They act as barriers, allowing workers and machinery to operate in dry conditions.
Key characteristics of a coffer dam:
- It is temporary. It is removed after the construction work it facilitates is completed.
- Its primary function is to exclude water from a specific area.
- It creates a dry working space within a body of water.
- It is often an all-round enclosure, surrounding the entire work zone.
- It uses vertical barriers, which can be made of various materials like steel sheet piles, earth, rock, or even concrete, depending on the scale and conditions.
Why Other Options Are Incorrect
Let's look at the other options provided:
| Structure Type | Purpose | Temporary or Permanent? |
|---|---|---|
| Arch dam | A permanent dam type that curves upstream, using the water pressure against its arch to support the structure. Primarily for water storage or diversion. | Permanent |
| Gravity dam | A permanent dam type that relies on its sheer weight (gravity) to resist the horizontal pressure of the water. Primarily for water storage or diversion. | Permanent |
| Earthen dam | A permanent dam type constructed primarily from compacted natural soil or rock fill. Primarily for water storage or diversion. | Permanent |
| Coffer dam | A temporary structure built to enclose an area, diverting water to allow construction within a dry space. | Temporary |
As you can see, Arch dams, Gravity dams, and Earthen dams are all types of permanent dams. Their purpose is typically long-term water storage, hydroelectric power generation, or flood control by holding back large bodies of water permanently. They are not temporary enclosures built to create a dry spot for construction within a water body.
Therefore, the only structure among the options that fits the description of a temporary all-round enclosure to keep water away from a working area by using vertical barriers is a coffer dam.
Revision Table: Temporary vs. Permanent Water Control Structures
| Feature | Coffer Dam | Permanent Dam (Arch, Gravity, Earthen) |
|---|---|---|
| Purpose | Create dry work area temporarily | Water storage, diversion, power generation (permanent) |
| Duration | Temporary | Permanent |
| Removal | Removed after construction | Generally remains in place indefinitely |
| Location | Around a specific work site within water | Across a river or valley to impound water |
Additional Information: Types and Uses of Coffer Dams
Coffer dams are essential in many civil engineering and construction projects. They can be constructed in various ways depending on the depth of water, soil conditions, and the scale of the project. Some common types include:
- Sheet pile coffer dams: Made of interconnected steel sheet piles driven into the riverbed or seabed.
- Earthen coffer dams: Simple barriers made of compacted earth, often used in shallow water with low flow.
- Rockfill coffer dams: Similar to earthen, but use rock material.
- Cellular coffer dams: Large, interconnected cells often filled with soil or sand, used in deeper water or strong currents.
- Double-walled sheet pile coffer dams: Two parallel walls of sheet piles with the space between filled with earth or gravel.
Understanding the function of a coffer dam is crucial for students studying civil engineering and construction methods involving water.
Important Questions from Dams and Spillways
Which type of gate is generally used for low navigation dams?
The heading up of water above its normal level while passing under the bridge is known as
The discharge passing over an ogee spillway, per unit length of its apex line is proportional to (Where H is head over the apex of its crest):
A gravity dam means:
To dissipate energy a fall is provided in a canal. A fall which has gradual convex and concave curves for smooth transition of water and to reduce disturbance and impact is a:
