CPCS Ground Conditions & Stability 2 — Questions and Answers
Question 1: What effect does rain have on ground conditions for plant operation?
- Rain saturates soil, reducing bearing capacity and increasing the risk of plant sinking or overturning (Correct answer)
- Rain only affects surface traction on tyres
- Rain has no effect on ground bearing capacity
- Rain only matters for wheeled plant, not tracked machines
Correct answer: Rain saturates soil, reducing bearing capacity and increasing the risk of plant sinking or overturning
Rain saturates soil, reducing its bearing capacity significantly. Ground that appeared firm before rain may now be unable to support plant loads, increasing the risk of sinking, tilting, and overturning.
Question 2: Why is it important to position plant away from excavation edges?
- The surcharge load from plant near an excavation edge can cause the edge to collapse, burying workers below (Correct answer)
- Only relevant for tower cranes
- Excavation edges only affect plant if they are over 2 metres deep
- Plant positioned near excavations only risks the plant itself
Correct answer: The surcharge load from plant near an excavation edge can cause the edge to collapse, burying workers below
Plant near an excavation edge exerts a surcharge load that can destabilise the edge and cause collapse, potentially burying workers in the excavation below. Safe standoff distances must be established and enforced.
Question 3: On a construction site, who is responsible for assessing whether ground conditions are suitable for plant to operate?
- A competent person — typically a geotechnical engineer or experienced site manager — before the plant is positioned (Correct answer)
- The plant operator, who must assess conditions personally each morning
- The plant hire company, whose responsibility it is to check the ground
- Only the HSE inspector on their scheduled visit
Correct answer: A competent person — typically a geotechnical engineer or experienced site manager — before the plant is positioned
A competent person with appropriate knowledge — such as a geotechnical engineer or experienced site manager — must assess and confirm ground conditions before plant is positioned for operation.
Question 4: What is a 'crane mat' and when is it used?
- A large, heavy timber or steel mat placed under crane outriggers to spread the load on weak ground (Correct answer)
- A rubber mat placed in the crane cab for operator comfort
- A mat used to protect the ground surface from oil contamination
- A safety mat placed around the crane's perimeter
Correct answer: A large, heavy timber or steel mat placed under crane outriggers to spread the load on weak ground
Crane mats are large timber or steel platforms placed under crane outriggers to spread the point load over a larger area, reducing ground pressure to within the site's bearing capacity.
Question 5: What precaution should be taken when operating plant on made ground (filled ground)?
- Assess the fill material and compaction level, and assume reduced bearing capacity compared to natural ground (Correct answer)
- Made ground is always stronger than natural ground
- No special precautions are needed if the fill appears solid
- Made ground only requires precaution if it contains rubble
Correct answer: Assess the fill material and compaction level, and assume reduced bearing capacity compared to natural ground
Made ground has variable and often lower bearing capacity than natural ground, depending on fill material and compaction. It must be assessed by a competent person, as it is prone to differential settlement and sudden collapse.
Question 6: How does frost affect ground conditions for construction plant operation?
- Frost temporarily strengthens the surface but thawing rapidly reduces bearing capacity — creating dangerous conditions (Correct answer)
- Frost permanently improves ground bearing capacity
- Frost only affects surface grip and not bearing capacity
- Frozen ground is always suitable for heavy plant operations
Correct answer: Frost temporarily strengthens the surface but thawing rapidly reduces bearing capacity — creating dangerous conditions
Frost can temporarily harden the surface, giving a false impression of strength. When thawing occurs — often rapidly — the ground can lose bearing capacity suddenly, creating dangerous conditions for plant operations.
CPCS Ground Conditions & Stability 2
What effect does rain have on ground conditions for plant operation?