$**$Flexible Pavement for Civil Engineering Projects$**$

Flexible pavement is a type of road construction that uses layers of materials to provide a durable and flexible surface for vehicles. It is commonly used in civil engineering projects such as highways, roads, and parking lots. Unlike rigid pavement, which is made of concrete, flexible pavement is designed to distribute the load from vehicles over a wider area, reducing stress on the underlying layers and increasing the overall lifespan of the road.

The construction of a flexible pavement typically involves several layers, each serving a specific purpose. The layers are as follows:

$1.$ Subgrade: The subgrade is the natural soil or improved soil on which the pavement is built. It provides the foundation for the road and must be properly prepared to ensure stability and prevent settlement.

$2.$ Subbase: The subbase layer is placed on top of the subgrade and consists of a coarser material such as crushed stone or gravel. It helps to distribute the load from the traffic and provides additional support to the pavement structure.

$3.$ Base Course: The base course is the layer immediately above the subbase and is typically made of a stronger material such as crushed stone or asphalt. It serves as a transition layer between the subbase and the surface layer and provides additional strength and stability to the pavement.

$4.$ Surface Course: The surface course is the topmost layer of the pavement and is designed to withstand the wear and tear caused by traffic. It is usually made of asphalt or concrete and provides a smooth and skid$-$resistant surface for vehicles.

The design of a flexible pavement takes into account factors such as traffic volume, climate, and soil conditions. Engineers use various methods and calculations to determine the thickness and composition of each layer, ensuring that the pavement can withstand the expected traffic loads and environmental conditions.

Now, for the fill in the blank question:

In flexible pavement construction, the subbase layer is typically made of $\_\_\_\_\_\_\_\_\_\_\_.$

A$)$ Concrete B$)$ Crushed stone C$)$ Asphalt D$)$ Gravel