Neco 2023 Geography Question 28

Practice objective / multiple choice question 28 from the 2023 Neco Geography examination.

Neco 2023 Geography Objective / Multiple Choice Hard Difficulty
Question 28 NECO • 2023 • GEOGRAPHY • objective

A slope of height 30 m has an inclination angle of \(35^{\circ}\). The soil has cohesion \(c = 15\) kPa, unit weight \(\gamma = 18\) kN/m³, and internal friction angle \(\phi = 20^{\circ}\). The water table lies 10 m below the crest, giving a pore‑water pressure \(u = \gamma_{w} \; z = 9.81 \times 10 = 98.1\) kPa. Using the infinite‑slope model, (a) calculate the factor of safety \(F_{S}\). (b) State whether the slope is stable. (c) Assuming all other parameters remain unchanged, determine the required increase in cohesion (in kPa) to achieve a factor of safety of 1.

Answer Options

A. Factor of safety ≈0.75 (unstable); required cohesion ≈45.2 kPa (increase of ≈30.2 kPa)
B. Factor of safety ≈0.55 (unstable); required cohesion ≈55.0 kPa (increase of ≈40.0 kPa)
C. Factor of safety ≈1.10 (stable); required cohesion ≈20.0 kPa (increase of ≈5.0 kPa)
Correct Answer D. Factor of safety ≈0.41 (unstable); required cohesion ≈64.6 kPa (increase of ≈49.6 kPa)
Correct Answer
D
Correct Option:
Factor of safety ≈0.41 (unstable); required cohesion ≈64.6 kPa (increase of ≈49.6 kPa)

About This Question

This is Neco 2023 Geography Question 28. It is one of the objective questions from the 2023 Neco Geography examination.

Difficulty level: Hard .

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