Analysis according to NEN (Buismann, Ladd)

This method computes both the primary and secondary settlement. When computing the method accounts for overconsolidated soils and differentiates between two possible cases:

(1) sum of the current vertical effective stress in the soil and stress due to external surcharge is less than the preconsolidation pressure so that only additional surcharge is considered

(2) sum of the current vertical effective stress in the soil and stress due to external surcharge is greater than the preconsolidation pressure so that the primary consolidation is set on again. The primary settlement is then larger when compared to the first case

Primary settlement

Primary settlement of the i^th layer of overconsolidated soil (OCR > 1) is provided by:

for: σ_or + σ_z ≤ σ_p  (sum of the current vertical stress and its increment is less than the preconsolidation pressure)

for: σ_or + σ_z > σ_p  (sum of the current vertical stress and its increment is greater than the preconsolidation pressure)

where:	σor,i	-	vertical component of geostatic stress in the middle of ith layer
	σz,i	-	vertical component of incremental stress (e.g. stress due to structure surcharge) inducing layer compression
	σp,i	-	preconsolidation pressure in the ith layer
	eo	-	initial void ratio
	hi	-	thickness of the ith layer
	Cc,i	-	compression index in the ith layer
	Cr,i	-	recompression index in the ith layer

Primary settlement of the i^th layer of normally consolidated soil (OCR = 1) reads:

where:	σor,i	-	vertical component of geostatic stress in the middle of ith layer
	σz,i	-	vertical component of incremental stress (e.g. stress due to structure surcharge) inducing layer compression
	eo	-	initial void ratio
	hi	-	thickness of the ith layer
	Cc,i	-	compression index the ith layer

Secondary settlement

Secondary settlement of the i–th layer assumes the form:

for: σ_or + σ_z  ≤ σ_p  (sum of the current vertical stress and its increment is less than the preconsolidation pressure)

for: σ_or + σ_z > σ_p  (sum of the current vertical stress and its increment is greater than the preconsolidation pressure)

where:	hi	-	thickness of the ith layer
	Cαr,i	-	secondary compression index below preconsolidation pressure in the ith layer
	Cα	-	index of secondary compression in the ith layer
	tp	-	time to terminate primary consolidation
	ts	-	time required for secondary settlement

If we specify the value of preconsolidation index of secondary compression the same as for the index of secondary compression, the program does not take into account in the computation of secondary settlement the effect of preconsolidation pressure.

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Literature:

Netherlandish standard NEN6740, 1991, Geotechniek TGB1990 Basisen en belastingen, Nederlands normalisatie-Institut