Dear reader in last post we have learnt about subsidence of foundation soil due to extraction of underground water or oil and due to shrinkage of underlying saturated or wet clay deposits. These two causes are also secondary causes of foundation settlement.
Now why is term ‘secondary’ used? The answer to this question is –they do not include direct weight of structure or some fraction or full live load from occupancy or from other sources.
The settlement may be observed after long time of construction of structure and exterior influence the settlement of foundation. The secondary causes may include followings:
a. Foundation settlement due to infiltration of water into ground where sensitive soil like collapse susceptible soil (collapsible soil) becomes unstable gaining moisture increment or moistening.
b. Foundation may settle and sometimes lead to collapse of structure under yielding of excavation adjacent to them.
c. Tunnels and underground mines may also lead to settlement when the collapse.
d. Other than above causes is natural disasters which are in most case can not be mitigated by us which include:
1. Foundation settlement by seismic activity
2. Undermining of foundation during flood
Dear reader we have published many posts about collapsible soil, earthquake disaster including liquefaction- causes and mitigation and excavation requirement and safety for cohesive and cohesionless soil including dewatering techniques. You are invited to read these posts for more clarification.