Retaining Wall Type Selection: in_situ
Retaining wall type selection decision matrix — 14 wall types across 7 structural categories (gravity, cantilever, MSE, sheet pile, soldier pile, in-situ soil nail, in-situ secant/diaphragm). Each record gives: practical height range, foundation requirements, backfill requirements, typical batter, relative cost index (1=lowest to 6=highest), construction speed, right-of-way requirements, aesthetics rating, seismic performance, drainage requirements, and typical applications. Sources: FHWA-NHI-07-071, AASHTO LRFD 9th Ed Sec 11, NAVFAC DM-7.2, Coduto Foundation Design 3rd Ed Ch.17, USACE EM 1110-2-2504.
| wall category | wall type | aesthetics rating | backfill requirement | batter typical | construction speed | drainage requirement | foundation requirement | height max ft (ft) | height max m (m) | height min ft (ft) | height min m (m) | notes | relative cost index (dimensionless) | row requirement | seismic performance | typical applications |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| in_situ | diaphragm_slurry_wall | fair — can be cast with architectural concrete finish | in-situ soil; no backfill required | 0.00 | slow | impermeable concrete wall; dewatering inside excavation required | any soil; most suited to cohesionless below GWT or soft clay; crane + bentonite plant required | 100 | 30.5 | 15 | 4.6 | Bentonite slurry stabilizes trench as concrete is cast; 24–36 in panels; can be permanent structure; also called diaphragm wall or slurry wall; casing optional; reinforcement cage installed before casting; extremely stiff — lateral deflections <0.1% H | 6 | minimal — constructed on wall alignment | excellent — very stiff; used as permanent building walls in seismic zones | deepest urban excavations; high-rise foundations; subway stations; below GWT in congested areas; permanent basement walls |
| in_situ | secant_pile | poor to fair — exposed pile heads | in-situ soil; no backfill required | 0.00 | slow | impermeable wall; dewatering required during excavation if above water table | any soil including very soft clay and below groundwater; requires concrete pump access and crane | 60 | 18.3 | 10 | 3 | Alternating primary (unreinforced) and secondary (reinforced) bored piles that overlap; 24–48 in diameter; pile spacing = 0.8× diameter; very low deflections; used where settlements are critical; expensive | 5 | minimal — constructed on wall alignment only | good — rigid system with small deflections; seismic connections at cap beam provide good performance | deep urban excavations; adjacent to existing structures; underground parking; below-water-table construction; metro stations |
| in_situ | soil_nail | good — shotcrete face can be textured or formed | in-situ soil retained in place — no fill required | 0.00 to 0.05 | moderate | face drainage via geocomposite or weep holes in shotcrete required | stiff to medium stiff native cohesive or dense granular soil; NOT in soft clay or loose fill | 50 | 15.2 | 10 | 3 | Top-down construction; soil nails at 4–6 ft horizontal and 4–6 ft vertical spacing; nail length = 0.7–1.0H; shotcrete facing 4–8 in; design per FHWA NHI-14-007 and AASHTO LRFD Sec 11.8; FS = 1.5–2.0 on nail pullout | 2 | minimal — no anchor zone behind wall; top-down construction | good to excellent — flexible; proven excellent seismic performance; FHWA NHI-14-007 recommends for seismic design | highway cuts; urban deep excavations; slope stabilization; seismic retrofit of existing walls |
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