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STONE RETAINING WALL SYSTEMS Soil Density - Standard vs Modified Proctor Reinforced soil structures routinely specify that all soils be compacted to 95%of the maximum density determined by ASTM D698 -Standard Proctor Density for conformance with the design. However,Standard Proctor density criteria is typically utilized in the Eastern US where- as Modified Proctor density criteria is typically utilized in the Western US which can create some conflicting specification problems. Research has been done showing the relationship between Standard and Modified Proctor densi- ty testing for different soils types as indicated below: Characteristics of Three Soils 140 T A-Modified Proctor Type Sand I Sift Clay LL PI B-Standard Proctor 130 C-1 blow Proctor Soil 1-Silty Sand 80% 15% 5% 17 1 Soil 1 Soil 2-Sand 92% 5% 3% NP NP (Silty Sand) u 120 Soil 3-Clay 10% 28% 62% 68 47 a 110 ;4S oil 28 (Sand) Summary of Data a tint is re% Type A B C A B C 0 100 A3+ Soil 3 Soil 1-Silty Sand 132 125 123 8 10 10 90 (Clay) Soil 2-Sand 113 110 108 ind ind ind Soil 3-Clay 102 88 83 20 28 31 80 - 95%Standard vs Modified Proctor Comparison 700 5 10 15 20 25 30 35 Type Standard 95%Standard ' %of Modified no,water content in% Soil 1-Silty Sand 125 119 90% Moisture-Density Relationships Soil 2-Sand 110 105 93% (Ref.Tschebotarioff-1973) Soil 3-Clay 88 84 82 It is obvious from this limited data that a simple conclusion can not be drawn but some general guidelines can be established when using Modified Proctor density testing in lieu of Standard Proctor testing for quality assurance testing of reinforced soil structures: * 90% - 92%of Modified Proctor density is roughly equivalent to the specified 95% 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. * The density difference between Modified Proctor and Standard Proctor density testing appears to increase with the percentage of fines in the soil matrix while the optimum moisture content decreases . It may be prudent to utilize 90%of Modified Proctor density and optimum moisture content when working with fine grained soils such as clays for best results. 12/30/03 9 0 2003 Keystone Retaining Wall Systems