TM 5-818-1 / AFM 88-3, Chap. 7
Table 3-2. Estimating Degree of Preconsolidation
Method
Remarks
Surface topography
Soil below alluvial valley filling should generally have a preconsolidation stress at
least corresponding to elevation of abutments. In wide river valleys with
terraces at several elevations, an elevation corresponding to previous surface
elevation in the river valley may be several miles distant
Geological evidence
Ask geologist for estimate of maximum preconsolidation stress. Erosion may
have removed hundreds of feet of material even in abutment area
Water content
If natural water content is near PL or below it, anticipate high preconsolidation
stress. A high natural water content is not, itself, a suitable indicator of
absence of overconsolidation
Standard penetration resistance
If blow counts are high, anticipate high preconsolidation stress. From blow
counts, estimate undrained shear strength, su , in tons per square foot as
approximately 1/15 of blow count. If estimated value is substantially more
than corresponds to a su/po ratio of about 0.25,
anticipate high
preconsolidation stresses
Undisturbed sampling
If soil was too hard to sample with piston sampler, and a Denison or similar
sampler was required, suspect high preconsolidation stress
If higher than those corresponding to a su/po ratio of about 0.3, anticipate high
Laboratory shear strengths
preconsolidation stress
Compression index from consoli-
If compression index appears low for Atterberg limits of soil, suspect that test
dations tests
loads were not carried high enough to determine virgin compression curve
and correct preconsolidation stress. Expected values for compression index
can be estimated from correlations with water content and Atterberg limits
(table 3-3)
Estimate preconsolidation stress from figures 3-8 and 3-9 (pc values may be low)
Liquidity index and sensitivity
U. S. Army Corps of Engineers
3-11
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