Prediction of Compression and Recompression …

1 Prediction of Compression andRecompression Indices of TexasOverconsolidated ClaysPresented By:Sayeed Javed, , Settlement Equationwhere H = consolidation settlement of the stratumCr = slope of the average rebound- Recompression lineCc = slope of the virgin Compression portion of the e-log p curveH = total thickness of the stratump o = effective overburden pressurep c = preconsoldation pressurep f = final pressure due to the loads in addition to the overburden pressureeo = original void ratiococfcocoocoorpppppeHCppppeHCH')''(' 'log1')''('log1!!+++!++=" A Typical Consolidation CurveCcCr Budget & Time Constraints A typical budget of $3,000 Field: $1,200 Lab: $800 Engineering: $1,000 Cost of a Consolidation Test rangesbetween $250 and $300 Consolidation test takes about a week Subsurface Stratigraphy Statistical Correlation Maximum use of index properties Lot of variables difficulty of memorizing lot of calculations Reduce number of variables such that theyare still representative of several other indexproperties Factors Influencing Cc and and Amount of clay Minerals PI2.

2 Physical State of Soil Moisture Content Density Stress History Presence of fissures, joints and cracks 1. Recompression Index versus Liquid LimitR2 = 2. Recompression Index versus Void RatioR2 = 020406080100120LL x 3. Recompression Index versus Product of Liquid Limit and Void RatioR2 = 020406080100120LL x Cr = + = 5. Compression Index versus Liquid LimitR2 = R2 = 020406080100120LL x 7. Compression Index versus Product of Liquid Limit and Void RatioR2 = 020406080100LL x 8.

3 Compression Index versus Product of Liquid Limit and Void Ratio After Removing OutliersCc = + = FIGURE 13 FIGURE 14 TABLE 2 Previous Published Equations for Recompression IndexNagaraj and Murthy (1985)Cr = , Krizek & Corotis (1976)Cr = (eo+ )6 Azzouz, Krizek & Corotis (1976)Cr = + + , Krizek & Corotis (1976)Cr = (eo wn1+ )4 Azzouz, Krizek & Corotis (1976)Cr = (eo + )3 SourceRecompression IndexEquation wn denotes natural moisture content2 Gs denotes specific gravity of solidsTABLE 3 Comparison Between Computed and Actual Cr Values 15 Figure 14 Figure 13 Figure 12 Figure 11 Figure 10 Figure 9 Computed CrEquation No.

4 1 Cr = + Summary of Comparison for Cr Azzouz et al equations overestimate by 2 times Nagaraj and Muthy s equationsoverestimate Cr values to 3 times TABLE 4 Previous Published Equations for Compression IndexNagaraj and Murthy (1985)Cc = LL Gs12 Koppula (1981)Cc = + LL11 Rendon-Herrero (1980)Cc = ((1 + eo)/Gs) , Krizek & Corotis (1976)Cc = (eo+ + )9 Azzouz, Krizek & Corotis (1976)Cc = + , Krizek & Corotis (1976)Cc = (eo+ )7 Azzouz, Krizek & Corotis (1976)Cc = (eo+ )6 SourceCompression Index Equation No. 2 Cc = + TABLE 5 Comparison Between Computed and Actual Cc 15 Figure 14 Figure 13 Figure 12 Figure 11 Figure 10 Figure 9 Computed CcEquation No.

5 Summary of Comparison for Cc Azzouz et al equations 6 and 9 work wellfor higher LL but underestimate at lower LL Rendon-Herrero s equation 10 generallyunderestimates, although close to the actualvalues Kopulla s equation 11 and Nagaraj andMuthy s equation 12 significantlyoverestimate Cc values Conclusions Significant overestimation was observed forCr values using the previous relationships For Cc, the difference using the author sequation and some previous correlations(Azzouz et al and Rendon-Herrero) was notsignificant. However, the author s equationappear to be in better agreement with theobserved values QUESTIONS ???