Question

The construction process of subsurface pipe drainage system is in which sequence?
A. Outlet construction
B. Grade control
C. Setting out alignments and levels
D. Excavating the trenches
E. Placing the envelopes
F. Placing the drain pipes
Choose the correct sequence from the options given below:

• A. A, C, B, D, F, E
• B. A, B, C, D, E, F
• C. C, B, D, E, F, A
• D. C, B, D, F, E, A

Hint:

Always remember that in any drainage construction, the outlet must be built first to prevent water from ponding in the upstream trenches as they are excavated.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
A subsurface pipe drainage system is installed to control waterlogging and salinity by lowering the water table.
The installation of subsurface pipes requires a systematic, step-by-step engineering sequence.
This sequence ensures proper grade alignment, prevents trench collapse, and maintains the hydraulic integrity of the drainage network.

Step 2: Detailed Explanation:
Let us analyze the logical, field-recommended sequence of construction operations:
1. Outlet Construction (A):
The outlet is the point where the entire drainage network discharges its water.
It must be constructed first to ensure a free outfall and to allow any water entering the trenches during subsequent excavation to drain away immediately.
2. Setting out Alignments and Levels (C):
Before any excavation begins, the physical paths of the lateral and collector drains are marked on the ground.
Levels are taken using surveying instruments to establish the precise slope of the land.
3. Grade Control (B):
Grade control parameters are established to ensure that the excavated trenches maintain a constant downward slope toward the outlet, preventing siltation.
4. Excavating the Trenches (D):
Trenches are excavated to the designed depth along the established alignments and grades.
5. Placing the Drain Pipes (F):
Corrugated, perforated plastic pipes or clay tiles are laid along the bottom of the excavated trenches.
6. Placing the Envelopes (E):
Envelope material (such as gravel, geotextile, or organic fibers) is placed around the pipes to prevent soil particles from entering and clogging the drain perforations.
Therefore, the most logical and standard sequence of construction is A $\rightarrow$ C $\rightarrow$ B $\rightarrow$ D $\rightarrow$ F $\rightarrow$ E.

Step 3: Final Answer:
The correct sequential order of subsurface pipe drainage construction is A, C, B, D, F, E.
Hence, the correct option is (A).