Civil Engineering Fundamentals Flashcards

What is the purpose of a retaining wall in civil engineering?

Answer: To resist lateral earth pressure and retain soil at different elevations

Retaining walls resist lateral earth pressure to maintain a difference in ground elevation. The design must account for active and passive earth pressures, surcharge loads, and water pressure.

In structural analysis, what is the degree of static indeterminacy?

Answer: The number of redundant reactions or internal forces beyond those needed for equilibrium

Static indeterminacy = (number of unknown reactions + internal redundancies) - (number of equilibrium equations). Indeterminate structures require compatibility equations for complete analysis.

What is the active earth pressure coefficient (Ka) for a soil with friction angle φ = 30°?

Answer: Ka = 1/3 (0.333)

Using Rankine's theory, Ka = tan²(45° - φ/2) = tan²(30°) = 1/3. Active pressure develops when the wall moves away from the soil. This is the minimum lateral pressure condition.

What is the purpose of prestressing in concrete?

Answer: To introduce compressive stresses that counteract tensile stresses from loading

Prestressing introduces compressive stresses into concrete to offset the tensile stresses caused by service loads. This allows longer spans, thinner sections, and crack-free performance under service loads.

In water resources engineering, the rational method formula Q = CiA is used to estimate:

Answer: Peak runoff rate from a small catchment

The Rational Method estimates peak discharge Q (m³/s) using runoff coefficient C, rainfall intensity i (mm/hr), and catchment area A. It is suitable for small catchments (< 80 hectares) common in Saudi urban drainage design.

What is the significance of the plasticity index (PI) of soil?

Answer: It indicates the range of water content over which soil behaves plastically

PI = Liquid Limit - Plastic Limit. A high PI indicates highly plastic (clayey) soil prone to volume change, while low PI indicates silty or sandy soil. PI is used to classify soils and predict behavior.