Retaining & slopes · Embedded walls & sheeting

Basal heave of an excavation in clay (Bjerrum–Eide) calculator

FS = Nc su/(γH + q) with Skempton's Nc for the excavation geometry.

Standard: Bjerrum & Eide (1956) · Skempton Nc

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Input	Value	Unit
Excavation depth	6	m
Width	10	m
Length	30	m
Undrained strength below base	30	kPa
Unit weight	17	kN/m³
Surface surcharge	10	kPa

Result	Value	Unit
Nc = 5(1 + 0.2H/B)(1 + 0.2B/L) (H/B ≤ 2.5)	5.97
FS	1.60

Diagram for the worked example

Nc = 5(1 + 0.2H/B)(1 + 0.2B/L) (H/B ≤ 2.5) = 5*(1+0.2*MIN(6/10,2.5))*(1+0.2*10/30) = 5.9733
FS = 5.9733*30/(17*6+10) = 1.6

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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.