OCR and Preconsolidation Stress

OCR = \frac{σ _{p}^{'}}{σ _{v o}^{'}}, S_{c} = \frac{C _{r} H}{1 + e _{0}} lo g \frac{σ _{p}^{'}}{σ _{v o}^{'}} + \frac{C _{c} H}{1 + e _{0}} lo g \frac{σ _{v o}^{'} + Δ σ}{σ _{p}^{'}}

OCR>1 overconsolidated: use Cr (recompression) until σp', then Cc. NC clay OCR=1, only Cc. Casagrande construction finds σp' from the e–log σ' curve.

Step-by-step solved example

σvo'=80 kPa, σp'=160 kPa, Δσ=40 kPa. OCR and which indices?

e–log σ' with a break at σp'; OCR = σp'/σvo'.

1. OCR
160/80=2.0.
2. Path
Final 120 kPa < 160 so the increment stays on the recompression curve (Cr only).

Answer: OCR=2; use Cr only (final < σp')

0/10 correct

1.NC clay has OCR

2.If final σ' exceeds σp', settlement uses

3.Cc is the slope of

4.Cr is typically about

5.Glaciation / erosion often leaves

6.mv =

7.σvo'=50, σp'=200: OCR=

8.A surcharge fill is used to

9.e–log σ' plot: the sharp break is

10.H in the log formula is