FOUNDATION CONSIDERATIONS BASED ON SOIL TYPES

Soil type affects selection of types of foundations, foundation depth and foundation sizes.
Following are the considerations for foundation based on soil types:

Soil Type	Foundation		Trouble areas
	Types	Reason for use
Sand	Footings	Easy to construct and economical	Bearing capacity may be a problem but in most cases it is sufficientExcessive settlement in wet and loose deposits. Confining pressure is usually low.
	Retaining Structures	Must be used since sand cannot support themselves
	Deep foundations (Piles)	Uses friction resistance but low in bearing capacity
Clay	Footings	Economic but may have problem with bearing capacity in saturated clays	Low bearing capacity.Generally low shear strength when wet. High consolidation in soft clays Swelling is possible. Over-consolidated clays may contain cracks and fissures.
	Retaining Structures	Clays are self-supportive up to a certain height (critical). Must be used if height increases beyond the critical.
	Deep foundations (Piles)	If bearing capacity is low, piles may be driven to rock. May change formation of clay.

 

Following table shows solutions to some problems in foundations based on soil types:

Soil Type	Nature of problem	Possible solution
Sand	Settlement	Loose sands must be compacted
		Lowering water table may result in sand densification
	Bearing Capacity	Compaction increases cohesion and friction thus bearing capacity increases
		Use of deep foundation
Clay	Consolidation	Lowering water table
		Pre-loading
		Drive pile to rock
	Bearing capacity	Compaction
		Use of deep foundations
	Expansion or swelling	Treat or stabilize soil
		Maintain constant water table
		Alter soil nature (similar to stabilization)
		Include swell pressure in design