Settlement Equation " H = CrH 1+ e o log p' o + ( p' p' c o! p' o ) CcH + 1+ e o log p' c + p' f! ( p' p' c c! p' o ) where ΔH = consolidation settlem

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1 Prediction of Compression and Recompression Indices of Texas Overconsolidated Clays Presented By: Sayeed Javed, Ph.D., P.E.

2 Settlement Equation " H = CrH 1+ e o log p' o + ( p' p' c o! p' o ) CcH + 1+ e o log p' c + p' f! ( p' p' c c! p' o ) where ΔH = consolidation settlement of the stratum C r = slope of the average rebound-recompression line C c = slope of the virgin compression portion of the e-log p curve H = total thickness of the stratum p o = effective overburden pressure p c = preconsoldation pressure p f = final pressure due to the loads in addition to the overburden pressure e o = original void ratio

5 A Typical Consolidation Curve C r C c

7 Budget & Time Constraints A typical budget of $3,000 Field: $1,200 Lab: $800 Engineering: $1,000 Cost of a Consolidation Test ranges between $250 and $300 Consolidation test takes about a week

8 Subsurface Stratigraphy

9 Statistical Correlation Maximum use of index properties Lot of variables difficulty of memorizing lot of calculations Reduce number of variables such that they are still representative of several other index properties

10 Factors Influencing C c and C r 1. Type and Amount of Clay Minerals PI 2. Physical State of Soil Moisture Content Density Stress History Presence of fissures, joints and cracks

11 Cr 0.04 R 2 = LL FIGURE 1. Recompression Index versus Liquid Limit

12 Cr 0.04 R 2 = e o FIGURE 2. Recompression Index versus Void Ratio

13 Cr 0.04 R 2 = LL x e o FIGURE 3. Recompression Index versus Product of Liquid Limit and Void Ratio

14 Cr 0.04 C r = LLe o R 2 = LL x e o

15 Cc R 2 = LL FIGURE 5. Compression Index versus Liquid Limit

16 Cc R 2 = e o

17 Cc R 2 = LL x e o FIGURE 7. Compression Index versus Product of Liquid Limit and Void Ratio

18 Cc C c = LLe o R 2 = LL x e o FIGURE 8. Compression Index versus Product of Liquid Limit and Void Ratio After Removing Outliers

23 FIGURE 13 FIGURE 14

25 Equation No. 1 C r = LLe o TABLE 2 Previous Published Equations for Recompression Index Equation No Recompression Index C r = (e o LL -0.06) C r = (e o w 1 n ) C r = 0.003w n LL C r = 0.135(e o +0.01LL-0.002w n -0.06) C r = LLGs 2 Source Azzouz, Krizek & Corotis (1976) Azzouz, Krizek & Corotis (1976) Azzouz, Krizek & Corotis (1976) Azzouz, Krizek & Corotis (1976) Nagaraj and Murthy (1985) 1 w n denotes natural moisture content 2 Gs denotes specific gravity of solids TABLE 3 Comparison Between Computed and Actual C r Values Equation No. Figure 9 Figure 10 Figure 11 Computed C r Figure 12 Figure 13 Figure 14 Figure Actual C r

26 Summary of Comparison for C r Azzouz et al equations overestimate by 2 to 4.5 times Nagaraj and Muthy s equations overestimate C r values 1.5 to 3 times

27 Equation No. 2 C c = LLe o TABLE 4 Previous Published Equations for Compression Index Equation No Compression Index C c = 0.37(e o LL-0.34) C c = 0.40(e o w n -0.25) C c = 0.009w n LL-0.1 C c = 0.37(e o LL w n -0.34) C c = 0.5((1 + e o )/Gs) 2.4 C c = 0.009w n LL C c = LL Gs Source Azzouz, Krizek & Corotis (1976) Azzouz, Krizek & Corotis (1976) Azzouz, Krizek & Corotis (1976) Azzouz, Krizek & Corotis (1976) Rendon-Herrero (1980) Koppula (1981) Nagaraj and Murthy (1985)

28 TABLE 5 Comparison Between Computed and Actual C c Values Equation No. Figure 9 Figure 10 Figure 11 Computed C c Figure 12 Figure 13 Figure 14 Figure Actual C c

29 Summary of Comparison for C c Azzouz et al equations 6 and 9 work well for higher LL but underestimate at lower LL Rendon-Herrero s equation 10 generally underestimates, although close to the actual values Kopulla s equation 11 and Nagaraj and Muthy s equation 12 significantly overestimate C c values

30 Conclusions Significant overestimation was observed for C r values using the previous relationships For C c, the difference using the author s equation and some previous correlations (Azzouz et al and Rendon-Herrero) was not significant. However, the author s equation appear to be in better agreement with the observed values

31 QUESTIONS???

土壤力學概論及第一章

土壤力學概論及第一章 87 11 1 (Soil Mechanics) (Geotechnical Engineering) (Soil Mechanics) (Foundation Engineering) (Engineering Geology) (Rock Mechanics) 1925 Karl Terzaghi Terzaghi (Rock Cycle) 2 (Specific Gravity, G s )