checklist and guidelines for review of geotechnical

8/6/2019 Checklist and Guidelines for Review of Geotechnical

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Checklist and Guidelines for Review of GeotechnicalReports and Preliminary Plans and Specifications

Table 3 - Required Geotechnical Engineering Analysis

Soil Classification Embankment and Cut Slopes Structure Foundations(Bridges and Retaining Structures)

Retaining Structures(Conventional, Crib and MSE)

Unified AASHTO1 Soil Type Slope Stability2 Analysis SettlementAnalysis

Bearing CapacityAnalysis

Settlement Analysis Lateral EarthPressure

Stability Analysis

GW A-1-a GRAVELWell-graded

Generally notrequired if cut or fillslope is 1.5H to 1V or flatter, andunderdrains are usedto draw down thewater table in a cut

slope.Erosion of slopesmay be a problem for SW or SM soils.

Generally notrequired exceptpossibly for SCsoils.

Required for spreadfootings, pile or drilledshaft foundations.

Spread footingsgenerallyadequateexcept possibly

for SC soils

Generally not neededexcept for SC soils or for large, heavy structures.

Empiricalcorrelations withSPT values usuallyused to estimate

settlement

GW, SP, SW & SPsoils generally suitablefor backfill behind or inretaining or reinforcedsoil walls.

GM, GC, SM &SC soils

generallysuitable if haveless than 15%fines.Lateral earthpressureanalysisrequired usingsoil angle of internal friction.

All walls should bedesigned to provideminimum F.S. = 2 againstoverturning & F.S. = 1.5against sliding alongbase.

External slope

stabilityconsiderationssame as previouslygiven for cut slopes& embankments.

GP A-1-a GRAVELPoorly-graded

GM A-1-b GRAVELSilty

GC A-2-6A-2-7

GRAVELClayey

SW A-1-b SANDWell-graded

SP A-3 SANDPoorly-graded

SM A-2-4A-2-5

SANDSilty

SC A-2-6A-2-7

SANDClayey

ML A-4 SILTInorganicsilt

Required unless non-plastic.

Erosion of slopes

Requiredunless non-plastic.

Required.Spread footinggenerally

Required.Can use SPTvalues if non-

These soils are notrecommended for usedirectly behind or in

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8/6/2019 Checklist and Guidelines for Review of Geotechnical

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Sandy may be a problem. adequate. plastic. retaining or reinforcedsoil walls.

CL A-6 CLAYInorganicLeanClay

Required Required

OL A-4 SILT

Organic

Required Required

MH A-5 SILTInorganic

Required.Erosion of slopesmay be a problem.

Required. Required.Deep foundationgenerallyrequired unlesssoil has beenpreloaded.

Required.Consolidation testdata needed toestimate settlementamount and time.

These soils are notrecommended for usedirectly behind or inretaining walls.

All walls should bedesigned to provideminimum F.S. = 2 againstoverturning & F.S. = 1.5against sliding alongbase.

External slopestabilityconsiderationssame as previouslygiven for cut slopes

& embankments

CH A-7 CLAYInorganicFat Clay

Required. Required.

OH A-7 CLAYOrganic

Required. Required.

PT ---- PEAT

Muck

Required. Required.

Longtermsettlement can besignificant

Deep foundation

required unless peatexcavated andreplaced.

Highly compressible and

not suitable for foundation support

Rock Fills - not required for slopes 1.5H to 1V or flatter.

Cuts - required but depends onspacing, orientation and strength of discontinuities and durability of rock

Required for spreadfootings or drilledshafts.

Empiricallyrelated to RQD3

Required where rock isbadly weathered or closely fractured (lowRQD).

May require in situtest such aspressuremeter.

Required.Use rock backfillangle of internalfriction.

Remarks:Soils - temporary ground water control may be needed for foundation excavations in GW through SM soils.Backfill specifications for reinforced soil walls using metal reinforcements should meet the following requirements in insure use of non-corrosive backfill:pH range = 5 to 10; Resistivity > 3000 ohm-cm; Chlorides < 100 ppm; Sulfates < 200 ppm; Organic content 1% maximumRock - Durability of shales (siltstone, claystone, mudstone, etc.) to be used in fills should be checked. Non-durable shales should be embanked as soils, i.e., placed inmaximum 0.3 m (1 ft) loose lifts and compacted with heavy sheepsfoot or grid rollers.1 This is an approximate correlation to Unified (Unified Soil Classification system is preferred for geotechnical engineering usage, AASHTO system was developed for rating pavement subgrades).

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2 These are general guidelines, detailed slope stability analysis may not be required where past experience in area is similar or rock gives required slope angles.3 RQD (Rock Quality Designation) = sum of pieces of rock core 4" or greater in length divided by the total length of core run.

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