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ENGINEERING, CS 2024 HSC 21b

A geotextile used in the construction of a retaining wall is shown.
 

Why are geotextiles used in the construction of retaining walls?   (3 marks)

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Answers could include three of the following:

  • They facilitate drainage in water-prone areas while simultaneously distributing structural loads more evenly across the soil base.
  • Additionally, these materials create a stable foundation that prevents soil erosion by holding soil particles in place against water movement.
  • Geotextiles enhance soil stability, by preventing mixing of different soil layers and
    improving load-bearing capacity.
  • They reinforce the soil mass, by increasing the overall strength and longevity of the retaining wall system.

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Answers could include three of the following:

  • They facilitate drainage in water-prone areas while simultaneously distributing structural loads more evenly across the soil base.
  • Additionally, these materials create a stable foundation that prevents soil erosion by holding soil particles in place against water movement.
  • Geotextiles enhance soil stability, by preventing mixing of different soil layers and improving load-bearing capacity.
  • They reinforce the soil mass, by increasing the overall strength and longevity of the retaining wall system.
♦ Mean mark 50%.

ENGINEERING, CS 2016 HSC 23b

This diagram shows the cross-section of a highway pavement drawn using AS 1100 drawing standards.
 

  1. Outline the properties of asphalt that make it suitable for highway pavement surfaces.   (3 marks)
  1. Why are geotextiles used in the construction of highway pavements?   (3 marks)
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i.    Successful answers should include 3 of the following:

Asphalt suitability

  • More durable than gravel and easier to lay than concrete.
  • Easily shaped and moulded to the contour of the road.
  • Can be driven on minutes after laying.
  • Can be easily repaired.
  • A smooth surface can be produced by pressing aggregate into substrate.
  • Flexibility allows for earth movement.

ii.   Reasons for using geotextiles:

  • Geotextiles are used to prevent the blockage of underground drainage by filtering silt from drainage below the surface.
  • They can also be used to prevent silt from undermining the road base, which can lead to road collapse.
Show Worked Solution

i.    Successful answers should include 3 of the following:

Asphalt suitability

  • More durable than gravel and easier to lay than concrete.
  • Easily shaped and moulded to the contour of the road.
  • Can be driven on minutes after laying.
  • Can be easily repaired.
  • A smooth surface can be produced by pressing aggregate into substrate.
  • Flexibility allows for earth movement.

ii.   Reasons for using geotextiles:

  • Geotextiles are used to prevent the blockage of underground drainage by filtering silt from drainage below the surface.
  • They can also be used to prevent silt from undermining the road base, which can lead to road collapse.

♦♦ Mean mark (ii) 38%.

ENGINEERING, CS 2022 HSC 12 MC

A geotextile is to be used in a retaining wall for a public green space project.

When selecting a suitable geotextile, which set of material properties should be considered?

  1. Colour, opacity and filtration
  2. Colour, permeability and rigidity
  3. Tensile strength, opacity and rigidity
  4. Tensile strength, permeability and filtration
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`D`

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  • Both colour and opacity are not material properties that need to be considered.
  • Therefore the answer cannot be `A`, `B` or `C`

`=>D`