CLA CLA Hardscape & Materials 1 — Questions and Answers
Question 1: What is the recommended minimum thickness for a concrete pedestrian walkway slab in a residential landscape setting?
- 2 inches
- 4 inches (Correct answer)
- 8 inches
- 12 inches
Correct answer: 4 inches
A 4-inch thick concrete slab is standard for residential pedestrian areas; vehicular areas typically require 6 inches or more.
Question 2: Which paving pattern for rectangular brick or concrete pavers provides the greatest interlocking structural strength for vehicular areas?
- Running bond
- Stack bond
- Herringbone (45° or 90°) (Correct answer)
- Basketweave
Correct answer: Herringbone (45° or 90°)
A herringbone pattern creates maximum interlock between pavers, distributing loads laterally and resisting creep under vehicular traffic.
Question 3: What material is a 'geo-grid' used for in landscape and hardscape construction?
- Drainage filtration under gravel
- Soil reinforcement in retaining walls and base courses (Correct answer)
- Weed suppression under mulch
- Pipe protection in utility trenches
Correct answer: Soil reinforcement in retaining walls and base courses
Geogrid is a polymer mesh embedded in soil or aggregate base layers to reinforce retaining walls and stabilize road or pavement base courses.
Question 4: Which type of retaining wall system uses interlocking concrete blocks with no mortar and relies on mass and batter for stability?
- Poured concrete cantilever wall
- Segmental retaining wall (SRW) (Correct answer)
- Gravity stone wall with mortar
- Sheet pile wall
Correct answer: Segmental retaining wall (SRW)
Segmental retaining walls (SRWs) use dry-stacked interlocking concrete units that rely on mass, batter (backward lean), and often geogrid reinforcement for stability.
Question 5: What is 'batter' in the context of retaining wall design?
- The mix ratio of concrete in the footing
- The inward lean of a wall face from vertical to improve stability (Correct answer)
- The drainage aggregate placed behind a wall
- The texture of a wall's exposed face
Correct answer: The inward lean of a wall face from vertical to improve stability
Batter is the intentional backward lean of a retaining wall face toward the retained soil, which shifts the wall's center of gravity and improves overturning resistance.
Question 6: What is the function of a 'weep hole' or drainage aggregate in a retaining wall?
- Anchor the wall to bedrock below
- Relieve hydrostatic pressure by allowing water to drain through or around the wall (Correct answer)
- Support the wall cap during construction
- Provide aeration to plant roots behind the wall
Correct answer: Relieve hydrostatic pressure by allowing water to drain through or around the wall
Without drainage relief, water pressure behind a retaining wall can cause catastrophic failure; weep holes and drainage aggregate reduce this hydrostatic pressure.
CLA CLA Hardscape & Materials 1
What is the recommended minimum thickness for a concrete pedestrian walkway slab in a residential landscape setting?