Question

Which of the following is not an environmental factor to be considered for the design of pavements?

• A. Formation width
• B. Height of embankment
• C. Depth of cutting
• D. Depth of water table

Hint:

Environmental factors in pavement design primarily encompass climate (temperature, rainfall, frost/thaw cycles) and subgrade conditions (drainage, water table, soil type). These factors directly affect the material properties and structural integrity of the pavement over its lifespan. Geometric design parameters like formation width, lane width, and alignment are design choices, not inherent environmental conditions.

Answer 1

The Correct Option is A

Step 1: Understand "environmental factors" in pavement design.
Environmental factors refer to natural conditions and phenomena that can influence the performance and durability of a pavement. These include climatic conditions (temperature, precipitation), drainage, and subgrade characteristics influenced by the surrounding environment.
Step 2: Analyze each option to determine if it is an environmental factor.

• (1) Formation width: Formation width (or roadway width) refers to the total width of the roadbed, including carriageway, shoulders, and sometimes verges. This is a geometric design parameter determined by traffic volume, design speed, and functional classification of the road. It is a design choice made by engineers, not a natural environmental factor that influences pavement behavior due to natural phenomena.
• (2) Height of embankment: Embankments are constructed fills. Their height influences the stresses on the subgrade and the overall stability of the road structure, especially in areas with varying ground levels. While the decision to build an embankment is a design choice, the environmental conditions of the foundation soil and the interaction between the embankment and the surrounding natural ground are influenced by environmental factors (e.g., soil type, moisture content, stability), and the embankment itself interacts with the environment (e.g., drainage, erosion). However, the "height" itself is a design output, but the need for an embankment and its performance are linked to topography and environmental conditions. More directly, the height determines the stress distribution which is a structural concern.
• (3) Depth of cutting: Cuttings are excavations made to achieve the desired road level. The depth of cutting exposes different soil layers, affecting subgrade conditions (e.g., moisture, stability) and drainage. This is directly related to the natural topography and the influence of the environment on the exposed subgrade. Deep cuts can expose subgrades to different environmental conditions.
• (4) Depth of water table: The depth of the water table is a crucial environmental factor. A high water table can lead to a saturated subgrade, significantly reducing its strength (CBR value) and increasing the risk of pavement distresses like pumping, stripping, and frost heave (in cold climates). This is a direct environmental condition that impacts pavement performance.

Step 3: Identify the option that is not an environmental factor.
Formation width is a dimension chosen during the geometric design process based on functional requirements, rather than a natural environmental factor that the pavement has to withstand or adapt to. While it impacts overall construction, it doesn't directly influence pavement material behavior or structural integrity in the same way climate or water table does. The height of embankment and depth of cutting are consequences of adapting the alignment to the natural topography, and their stability and drainage aspects are heavily influenced by environmental factors (soil, water). Depth of water table is a direct environmental condition. Therefore, formation width is the parameter that is most distinctly not an environmental factor but rather a geometric design parameter. $$\boxed{\text{Formation width}}$$