Maximum Likelihood Estimation of Model Uncertainty in Predicting Soil Nail Loads Using Default and Modified FHWA Simplified Methods

Table 4

Design outcomes of nail length at different depths for pullout limit state.

Method	Nail number	Depth,	Nail length,
			Normal	Lognormal
Default FHWA simplified method	1	0.05	0.82	0.84
	2	0.20	0.85	0.87
	3	0.35	0.78	0.80
	4	0.50	0.70	0.72
	5	0.65	0.62	0.64
	6	0.80		0.50
	7	0.95		0.50
	Sum ()		4.78 (4.41)	4.88 (4.53)
Modified FHWA simplified method	1	0.05	0.80	0.80
	2	0.20	0.82	0.83
	3	0.35	0.74	0.75
	4	0.50	0.66	0.67
	5	0.65	0.58	0.59
	6	0.80
	7	0.95
	Sum ()		4.59 (4.18)	4.65 (4.25)

Note. Values in brackets are computed nail lengths that correspond to the target reliability index of 2.33; those nail lengths are increased to be 0.50 as per the requirement of FHWA soil nail wall design manual [1, 2], that is, / ≥ 0.50.