A building site in Hawaii has been identified as having 'a'a lava rock substrate. What special consideration is required for foundation design?
Correct Answer
C) Increased excavation costs and rock anchoring systems
'A'a lava rock is extremely hard and requires specialized equipment for excavation, and foundations may need rock anchoring systems for proper attachment.
Why This Is the Correct Answer
'A'a lava has a rough, clinkery, extremely hard surface that is very difficult to excavate with standard equipment. Specialized rock-breaking equipment (hydraulic hammers, blasting in some cases) is required, significantly increasing excavation costs. Additionally, foundations set in 'a'a lava may need rock anchoring systems (epoxy-set rebar or mechanical anchors drilled into the rock) to achieve proper connection between the concrete foundation and the substrate.
Why the Other Options Are Wrong
Option A: No special requirements needed
No special requirements is incorrect. 'A'a lava presents unique construction challenges that must be addressed in the foundation design. Ignoring the substrate type would lead to inadequate excavation methods, potential foundation instability, and permit non-compliance.
Option B: Deeper foundations due to poor bearing capacity
Deeper foundations due to poor bearing capacity is incorrect. 'A'a lava actually has excellent bearing capacity — it is extremely hard rock. The issue is not bearing capacity or depth, but rather the difficulty of excavating the material and anchoring to it properly.
Option D: Special drainage for unstable soil
Special drainage for unstable soil confuses 'a'a lava with soft or clay soils. 'A'a lava is not unstable, nor does it require drainage in the same sense as expansive or waterlogged soils. Drainage may be a secondary consideration for surface water, but it is not the primary special requirement for 'a'a lava foundations.
Memory Technique
The name ''a'a' sounds like what you'd yell when you try to dig through it with a regular shovel — it's painfully hard! Remember: 'a'a = Agonizing excavation, Anchoring required.
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