Liquefaction

Liquefaction

Mechanism of Liquefaction

Dry loose sand

Saturated loose sand

Water table

Compaction

PWP increase

in undrained condition (t_eq<t_diss)

Very loose sand:

Void s

Solid

1/2

1/2

Very Dense sand: _Void

s

Solid

1/3

Excess Pore Water Pressure Generation

Pore water

pressure, Δu

Time

I itial Effe tive over urde stress, σvo'

Step for Evaluation of Liquefaction (NSPT procedure)

1. Determine the (N₁)₆₀ value for

every depth of sand layer

N_m = measured NSPT

C_E = energy ratio correction factor C_B = borehole diameter corr. factor C_R = rod length corr. factor

Evaluation of Liquefaction (NSPT procedure)

2. Find Cyclic Stress Ratio (CSR)

τ y = cyclic shear stress

a max = acc. max at ground surface

σv = total overburden stress

σv‘ = effective overburden stress rd = stress reduction factor

Idriss (1999), Golesorkhi (1989):

depth in meter

Source: Kramer (1996)

Evaluation of Liquefaction (NSPT procedure)

3. Find Cyclic Resistance Ratio (CRR)

MSF = Magnitude scaling factor (N₁)_60cs = equiv. clean-sand SPT

Kσ = Overburden correction factor

Pa = at ≈ kPa

(Idriss, 1999)

(Boulanger and Idriss, 2004) (Boulanger and Idriss, 2004)

≤ 37

Evaluation of Liquefaction (NSPT procedure)

Magnitude Scaling Factor (MSF)

Source: Kramer (1996)

Spreadsheet (NSPT procedure)

Step for Evaluation of Liquefaction (CPT procedure)

1. Determine the (qc₁) value for every

depth of sand layer

q_c = measured cone resistance (kPa or Mpa) q_c1 = corr. cone resistance (kPa or Mpa)

q_c1N = normalized corr. Cone resistance

Pa = atmospheric pressure = 1 atm = 101 kPa

C_N = overburden corr. Factor (Liao and Whitman, 1986)

2. Find Cyclic Stress Ratio (CSR)

Evaluation of Liquefaction (CPT procedure)

3. Find Cyclic Resistance Ratio (CRR)

(Idriss, 1999)

(Boulanger and Idriss, 2004) (Boulanger and Idriss, 2004)

≤

211

Settlement

Liquefiable Soil

Data:

a max ground = 0.2g

γsa d = 8 kN/ 3

Home Work

From Das 1993:

10.2, 10.6, 10.8, 10.10

From Kramer: