Table 5 Reduction values of strength parameters for three double strength reduction methods.

Double Strength Reduction Method 1

Fc = 1.21 Fφ = 1.1

c = 10.33kPa φ = 11.76°

c = 9.34kPa φ = 8.43°

c = 9.67kPa φ = 11.44°

c = 14.38kPa φ = 10.46°

Fc = 1.44 Fφ = 1.2

c = 8.68kPa φ = 10.81°

c = 7.85kPa φ = 7.74°

c = 8.13kPa φ = 10.51°

c = 12.08kPa φ = 9.61°

Fc = 1.69 Fφ = 1.3

c = 7.35kPa φ = 9.99°

c = 6.65kPa φ = 7.15°

c = 6.92kPa φ = 9.72°

c = 10.3kPa φ = 8.88°

Fc = 1.96 Fφ = 1.4

c = 6.29kPa φ = 9.29°

c = 5.65kPa φ = 6.64°

c = 5.85kPa φ = 9.03°

c = 8.7kPa φ = 8.25°

Double Strength Reduction Method 2

Fφ = 1.1

c = 10.16kPa φ = 11.76°

c = 9.23kPa φ = 8.43°

c = 9.52kPa φ = 11.44°

c = 14.17kPa φ = 10.46°

Fφ = 1.2

c = 8.21kPa φ = 10.81°

c = 7.51kPa φ = 7.74°

c = 7.69kPa φ = 10.51°

c = 11.49kPa φ = 9.61°

Fφ = 1.3

c = 6.52kPa φ = 9.99°

c = 6.03kPa φ = 7.15°

c = 6.14kPa φ = 9.72°

c = 9.18kPa φ = 8.88°

Fφ = 1.4

c = 5.09kPa φ = 9.29°

c = 4.76kPa φ = 6.64°

c = 4.78kPa φ = 9.03°

c = 7.18kPa φ = 8.25°

Double Strength Reduction Method 3

Global Zone

Fc = 1.21 Fφ = 1.1

c = 10.33kPa φ = 11.76°

c = 9.34kPa φ = 8.43°

c = 9.67kPa φ = 11.44°

c = 14.38kPa φ = 10.46°

Shear Zone

Fφ = 1.1

c = 8.02kPa φ = 10.72°

c = 7.33kPa φ = 7.67°

c = 7.51kPa φ = 10.42°

c = 11.23kPa φ = 9.53°

Global Zone

Fc = 1.44 Fφ = 1.2

c = 8.68kPa φ = 10.81°

c = 7.85kPa φ = 7.74°

c = 8.13kPa φ = 10.51°

c = 12.08kPa φ = 9.61°

Shear Zone

Fφ = 1.1

c = 6.52kPa φ = 9.85°

c = 5.92kPa φ = 7.04°

c = 6.11kPa φ = 9.57°

c = 9.13kPa φ = 8.75°

Global Zone

Fc = 1.69 Fφ = 1.3

c = 7.35kPa φ = 9.99°

c = 6.65kPa φ = 7.15°

c = 6.92kPa φ = 9.72°

c = 10.3kPa φ = 8.88°

Shear Zone

Fφ = 1.1

c = 5.08kPa φ = 9.1°

c = 4.75kPa φ = 6.51°

c = 4.77kPa φ = 8.85°

c = 7.15kPa φ = 8.08°