Building Pathology - Cracking

Question 1

What sort of cracks would you expect to see on a brick building an what might of caused them?

Answer 1

SUBSIDENCE - vertical cracking in the middle of the building. Diagonal if in the corner. Cracks wider at top, thinner at bottom.

HEAVE - cracking distribution is the same as subsidence. However, Cracked wider at the bottom.

SETTLEMENT - Movement down due to increased load. Buildings often settle once first constructed.

DIFFERENTIAL SETTLEMENT - Two parts of the building on different foundations or soil make up is different. Cracking occurs between the two sections.

THERMAL MOVEMENT - characterised by vertical cracking which is consistent in width.

LINTEL FAILURE - section of brickwork above the window to drop down creating a triangular crack from the corner of the window to the centre

Question 2

What is Subsidence and why might it occur?

Answer 2

• Movement down in the ground caused when the soil loses moisture and shrinks.
• May occur in prolonged dry spells, or the growth large trees which removes water from the ground.

Question 3

What is Heave and why might it occur?

Answer 3

• Movement upward caused when soil moisture increases causing swelling. May occur in prolonged wet spells. Or where large trees are removed.

Question 4

What type of soil is susceptible to subsidence and heave?

Answer 4

Cohesive soils such as Clay and Silt.

Question 5

How did you assess the cracking found for Unit 15 Abbey Road.

Answer 5

• Firstly, I assessed the crack distribution which gave me an indication of the cause.
• Secondly, I assessed the cracking width against the BRE Digest 251 to give an indication of severity and recommend remedial actions.