Slope

AASHTO

AASHTO LRFD 2024 — Strength I, φ 0.75

AASHTO LRFD Bridge Design Specifications, 10th ed. (2024)Revision 2Required FoS ≥ 1

Use it in Slope

In a design, choose it under Analyze → Design factor set, and the PDF report runs it too.

Checked against the standard · Not yet validated

Known limitations

  • φ divides soil strength only, inside the solve.
  • A permanent surcharge is factored as earth surcharge (ES, 1.50); a structure load (DC) would take 1.25. An external load that helps stability is left out (Art. 3.4.1).
  • Soil nails are calibrated with a 1.35 load factor on the nail demand (C11.12.2), which a single slope run does not apply, and the nail force Slope reports is capacity, not demand; Slope says so beside the result.
  • Anchor pull-out ×1.0 assumes every production anchor is proof-tested (Table 11.5.7-1, note 2); Slope says so beside the result.
  • Reinforcement takes its own φ (C11.10.5.6, C11.6.3.7); alternatives to the values used need a custom copy: mild-steel tendon 0.90, preliminary anchor pull-out 0.65 / 0.70 / 0.50, Grade 75 nail bar 0.75, steel grid on a flexible facing 0.75.
  • A geosynthetic layer needs its product reduction factor RF = RFID·RFCR·RFD on the element; a metallic layer's capacity is its corroded section's, entered as characteristic.
  • Piles have no AASHTO slope-stability resistance factor and are unfactored. Reinforced soil slopes are outside AASHTO LRFD (FHWA GEC 11).

Scope

  • Soil nails: AASHTO calibrates its soil-nail resistance factors with a load factor of 1.35 on the nail force (C11.12.2, Eq. 11.12.5.2-1) — the nail force Slope reports is the factored capacity available, not the design demand Tmax: a separate nail design must establish each nail's Tmax (C11.12.2) and show that its factored resistance is at least 1.35 × Tmax.
  • Anchors: AASHTO's anchor pull-out resistance factor of 1.0 holds only when every production anchor is proof-tested (Table 11.5.7-1, note 2) — without that testing, use a custom copy with the preliminary-design factor: 0.65 in cohesionless soil, 0.70 in cohesive soil, 0.50 in rock (note 1).

Values

Actions

Soil weightγUnfavorable×1.00
Favorable×1.00
Permanent loadγGUnfavorable×1.50
Favorable×0.00
Variable loadγQUnfavorable×1.75
Favorable×0.00
Seismic coefficientγE×0.00

Resistance

Earth / global resistanceγRe×0.75

Materials

Effective cohesionγc′×1.00
Friction (tanφ′)γφ×1.00
Undrained strength (cu)γcu×1.00
Shear strength (other models)—×1.00

Reinforcement

Anchor — tendonγt×0.80
Anchor — pull-outγpo×1.00
Nail — barγt×0.65
Nail — head plateγp×0.90
Nail — pull-outγpo×0.65
Geosynthetic — ruptureγt×0.90
Geosynthetic — pull-outγpo×0.90
Steel strip — ruptureγt×0.75
Steel strip — pull-outγpo×0.90
Steel grid — ruptureγt×0.65
Steel grid — pull-outγpo×0.90

Sources

Document: AASHTO LRFD Bridge Design Specifications, 10th ed. (2024)

Actions

FactorValueSource
Soil weight — unfavorable×1.003.4.1, Table 3.4.1-2, EV overall and compound stability, PDF p83 · Not yet validated
Soil weight — favorable×1.003.4.1, Table 3.4.1-2, EV overall and compound stability, PDF p83 · Not yet validated
Permanent load — unfavorable×1.503.4.1, Table 3.4.1-2, ES, γp maximum, PDF p83 · Slope convention · Not yet validated — A permanent surcharge is treated as earth surcharge (ES 1.50, owner decision); a structure load (DC) would take 1.25.
Permanent load — favorable×0.003.4.1, an external load that contributes to stability is not included, PDF p79 · Not yet validated
Variable load — unfavorable×1.753.4.1, Table 3.4.1-1, Strength I, LL / LS, PDF p82 · Not yet validated
Variable load — favorable×0.003.4.1, an external load that contributes to stability is not included, PDF p79 · Not yet validated
Seismic coefficient×0.003.4.1, Table 3.4.1-1, Strength I: EQ not included, PDF p82 · Not yet validated

Materials

FactorValueSource
Effective cohesion×1.0011.6.3.7, PDF p1496 · Not yet validated
Friction (tanφ′)×1.0011.6.3.7, PDF p1496 · Not yet validated
Undrained strength (cu)×1.0011.6.3.7, PDF p1496 · Not yet validated
Shear strength (other models)×1.0011.6.3.7, PDF p1496 · Not yet validated

Resistance

FactorValueSource
Earth / global resistance×0.7511.6.3.7, parameters and stratigraphy well defined, PDF p1496 · Not yet validated

Reinforcement

FactorValueSource
Anchor — tendon×0.8011.5.7, Table 11.5.7-1, anchor tendon, high-strength steel (A722), PDF p1489–1490 · Slope convention · Not yet validated — The high-strength tendon value is used; a mild-steel (A615) tendon takes 0.90 in a custom copy.
Anchor — pull-out×1.0011.5.7, Table 11.5.7-1, anchor pull-out, note 2, PDF p1489–1490 · Slope convention · Not yet validated — Every production anchor is proof-tested in the final design (note 2); the presumptive preliminary-design values (0.65 / 0.70 / 0.50, note 1) need a custom copy.
Nail — bar×0.6511.5.7, Table 11.5.7-1, soil nail tendon, Grades 95 and 150, PDF p1489–1490 · Slope convention · Not yet validated — The conservative grade value is used; a Grade 75 bar takes 0.75 in a custom copy.
Nail — head plate×0.9011.5.7, Table 11.5.7-1, soil nail facing, flexure and punching shear, PDF p1489–1490 · Not yet validated
Nail — pull-out×0.6511.5.7, Table 11.5.7-1, soil nail pull-out, PDF p1489–1490 · Not yet validated
Geosynthetic — rupture×0.9011.5.7, Table 11.5.7-1, overall and compound stability, geosynthetic tensile, PDF p1489–1490 · Not yet validated
Geosynthetic — pull-out×0.9011.5.7, Table 11.5.7-1, overall and compound stability, pull-out, PDF p1489–1490 · Not yet validated
Steel strip — rupture×0.7511.5.7, Table 11.5.7-1, overall and compound stability, metallic strip tensile, PDF p1489–1490 · Not yet validated
Steel strip — pull-out×0.9011.5.7, Table 11.5.7-1, overall and compound stability, pull-out, PDF p1489–1490 · Not yet validated
Steel grid — rupture×0.6511.5.7, Table 11.5.7-1, overall and compound stability, metallic grid tensile, PDF p1489–1490 · Slope convention · Not yet validated — The rigid-facing value is used; a grid on a flexible facing takes the strip value 0.75 in a custom copy (note 5).
Steel grid — pull-out×0.9011.5.7, Table 11.5.7-1, overall and compound stability, pull-out, PDF p1489–1490 · Not yet validated