Building Movement

Question 1

What are some causes of building movement?

Answer 1

Settlement

Sub soil high in organic matter

Seasonal movement

Trees and shrubs

Differential settlement

Sub-surface drains

Landfill

Mining

Sulphate attack

Question 2

How does initial settlement affect building movement?

Answer 2

Buildings are compressed when built

Water in subsoil squeezed out

Clay soil particularly susceptible

Movement greatest in first years, should cease after 15-20 years

Question 3

How does organic matter in sub-soil affect buildings?

Answer 3

Organic matter can decompose creating gaps in soil

Question 4

How are organic matter issues prevented?

Answer 4

Removal of subsoil

Deep foundations

Question 5

How does seasonal movement affect buildings?

Answer 5

Frost heave

Clay shrinkage

Question 6

How do trees and shrubs affect building movement?

Answer 6

Foliage affects water content of soil

Roots can get under buildings applying upwards and outwards pressure

Removal of tree can also affect soil content and integrity

Question 7

What is differential settlement?

Answer 7

Desperate parts of a building subject to independent movement

Question 8

What can cause differential settlement?

Answer 8

Different construction materials (weaker, heavier etc)

Foundation formed at different depths

Foundation formed over different souls

Question 9

How can drains affect building stability?

Answer 9

Building weight can crush drains

Drains can leak

Water washes away sandy sub-soil

Increases water content of clay soil

Question 10

How can landfills affect structural movement?

Answer 10

Decomposition of landfill causes ground mass to shrink.

Is responsible for 50% of foundation failures in new houses

Question 11

How do mines affect structural movement?

Answer 11

Collapsing mines cause subsidence

Question 12

What is sulphate attack?

Answer 12

Occurs when subsoil contains calcium, magnesium and/or sodium sulphate

Sulphates in presence of moisture will attack cement

Question 13

What can cause wall movement?

Answer 13

Distortion of walls

Thermal movement

Moisture movement

Corrosion of steel and iron components

Lateral pressure on retaining walls

Question 14

What causes distortion of walls?

Answer 14

Poor building practice. E.g inadequate thickness

Question 15

What causes thermal wall movement?

Answer 15

Temp changes

Expansion and contractions causes cracking

Question 16

What causes moisture wall movement?

Answer 16

Expansion and cracking through moisture absorption and drying

Question 17

What causes corrosion of steel and iron joists?

Answer 17

Lack of protection from oxygen and water causing expansion and weakening