The most commonly used method for the design of flexible pavement is the CBR method, not the Benkelman beam deflection method.

So, statement 1 is false

Benkelman Beam deflection method:

• The Benkelman beam method is thus widely used for evaluation of the structural capacity of existing flexible pavements and also for estimation and design of flexible overlays for the strengthening of any weak pavement for highways.

• The Benkelman beam measures the deflection of a flexible pavement under a moving wheel load.

The non-destructive measure of pavement stiffness:

• Subgrade materials are typically characterized by their resistance to deformation under load, which can be either a measure of their strength (the stress needed to break or rupture a material) or stiffness (the relationship between stress and strain in the elastic range or how well a material is able to return to its original shape and size after being stressed). In general, the more resistant to deformation a subgrade is, the more load it can support before reaching a critical deformation value.

• The Falling Weigh Deflectometer t (FWD) testing can be a relatively quick and cost-effective method to determine pavement layers stiffness to compare the strength and the subgrade support condition along a project section.

Fatigue failure of the pavement:

• Fatigue or alligator cracking is the most common type of pavement distress, it is in fact the major one.

• This is the type of distress in which a series of interconnected cracks appears due to the fatigue failure of the Hot Mix Asphalt surface when the pavement experience repeated traffic loading.

Hence, S1 is false and S2 is true.