Soil Density - Standard vs Modified Proctor
2003 Keystone Retaining Wall Systems912/30/03Soil Density - Standard vs Modified ProctorReinforced soil structures routinely specify that all soils be compacted to 95% of the maximumdensity determined by ASTM D698 - Standard Proctor Densityfor conformance with thedesign. However, Standard Proctordensity criteria is typically utilized in the Eastern US where-asModified Proctordensity criteria is typically utilized in the Western US which can createsome conflicting specification has been done showing the relationship betweenStandardandModified Proctordensi-ty testing for different soils types as indicated below:140130120110100908070 , water content in %05101520253035A1B1C1A2B2C2A3B3C3A- Modified ProctorB- Standard ProctorC- 15 blow ProctorSoil 2(Sand)Soil 1(Silty Sand)So il 3(Clay) moisture - Density Relationships(Ref. Tschebotarioff - 1973)TypeSand SiltClayLLPISoil 1 - Silty Sand80% 15%5%171Soil 2 - Sand92%5%3%NPNPSoil 3 - Clay10% 28% 62%6847Characteristics of Three SoilsMax Dry Density ,pcfOptimum moisture ,%TypeABCABCSoil 1 - Silty Sand13212512381010Soil 2 - Sand113110108indindindSoil 3 - Clay1028883202831Summary of DataTypeStandard 95% Standard % of ModifiedSoil 1 - Silty Sand12511990%Soil 2 - Sand11010593%Soil 3 - Clay888482%95% Standard vs Modified Proctor ComparisonIt is obvious from this limited data that a simple conclusion can not be drawn but some generalguidelines can be established
Standard Proctor density except for fine grained soils (ie: clay) where the difference may be significantly larger. ∗ Modified Proctor testing typically requires a lower optimum moisture content for achieving maximum density which is desirable for Keystone retaining wall construction and performance especially with silts and silty soils.
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