Consolidation Parameters
Table 1 lists several equations, along with their sources, that might be used to make compression index estimates. These correlations have particular value in preliminary site studies before extensive soil exploration and testing is undertaken for a final design.
| Compression index, Cc | Comments | Source/Reference |
|---|---|---|
| Cc = 0.009(wL – 10) (±30% error) | Clays of moderate St | Terzaghi and Peck (1967) |
| Cc = 0.37(eo + 0.003wL + 0.0004wn – 0.34) | 678 data points | Azzouz et al. (1976) |
| Cc = 0.141Gs (γsat/γdry)2.4 | All clays | Rendon-Herrero (1983) |
| Cc = 0.0093wn | 109 data points | Koppula (1981) |
| Cc = –0.0997 + 0.009wL + 0.0014IP + 0.0036wn + 0.115eo + 0.0025CP | 109 data points | Koppula (1981) |
| Cc = 0.329wnGs – 0.027wP + 0.0133IP(1.192 + CP/IP) | All inorganic clays | Carrier (1985) |
| Cc = 0.046 + 0.0104IP | Best for IP < 50% | Nakase et al. (1988) |
| Cc = 0.00234wLGs | All inorganic clays | Nagaraj and Srinivasa Murthy (1985, 1986) |
| Cc = 1.15(eo – 0.35) | All clays | Nishida (1956) |
| Cc = 0.009wn + 0.005wL | All clays | Koppula (1986) |
| Cc = –0.156 + 0.411eo + 0.00058wL | 72 data points | Al-Khafaji and Andersland (1992) |
| Cc = exp[(wn - 75) / 30] | Coode Island Silt | Srithar (2010) |
| Recompression index, Cr | Comments | Source/Reference |
| Cr = 0.000463wLGs | Nagaraj and Srinivasa Murthy (1985) | |
| Cr = 0.00194(IP – 4.6) | Best for IP < 50% | Nakase et al. (1988) |
| Cr = 0.05 to 0.1Cc | In desperation | |
| Cr = 0.01 to 0.33Cc | Coode Island Silt | Ervin (1992) |
| Secondary compression index, Cα | Comments | Source/Reference |
| Cα = 0.00168 + 0.00033IP | Nakase et al. (1988) | |
| Cα = 0.0001wn | NAFAC DM7.1 p. 7.1–237 | |
| Cα = 0.032Cc | 0.025 < Cα < 0.1 | Mesri and Godlewski (1977) |
| Cα = 0.06 to 0.07Cc | Peats and organic soil | Mesri (1986) |
| Cα = 0.015 to 0.03Cc | Sandy clays | Mesri et al. (1990) |
Notes:
1. Use wL, wP, wn, IP as percent, not decimal.
2. One may compute the in situ void ratio as eo = wnGs if S → 100 percent.
3. CP = percent clay (usually material finer than 0.002 mm).
4. Equations that use eo, wn, and wL are for both normally and overconsolidated soils.
Figure - Void ratio - effective stress relationship