Cyclic Simple Shear

Experimental Setup:

• Shear Load Cell
  
• Horizontal LVDT
  
• Vertical Load Cell
  
• Axial LVDT
  
• Axial LVDT (Long Range)

Cyclic Simple Shear Setup

Solid cylindrical specimen surrounded by rings

Testing procedure (ASTM D 6528-07):

• The test can be performed on both the intact and reconstituted specimens
  
• Intact specimens should be trimmed to the lateral dimension of confinement device (70 mm)
  
• Reconstituted specimens prepared at the required density can be tested both at unsaturated and saturated conditions
  
• Saturation of the specimens can be achieved by pushing water through the bottom of the specimen under a hydrostatic head of up to 1 m
  
• Anisotropic consolidation of the specimens is achieved under a desired vertical stress by creating Advanced Shear Box stage in GDSLAB Device Module and the change in height is measured by the axial LVDTs
  
• Consolidated specimens are then subjected to
  • Strain Control
  • Stress Control
    Under
  • Constant consolidated height
  • Constant vertical stress

At a desired loading frequency (0.0001 to5 Hz) and loading amplitude (± 8mm fort strain control and 5 kN for stress control)

•  The test stops itself as per the inputs given during creation of various stages (max. test time, Mac. Vertical stress, Number of cycles, Max. shear strain)

Strain Control Cyclic Simple Shear Testing

Input Loading

Horizontal displacement= 0.12 mm
??v = 100 kPa
Frequency= 0.1 Hz

Output Loading

Analysis

Stress Control Cyclic Simple Shear Testing

Input loading

CSR = 0.15
??v = 100 kPa
Frequency = 0.1 Hz

Output Loading

Analysis

Cyclic Simple Shear

Data Analysis:

Observation Sheet for controlled Cyclic Simple Shear Test (Constant volume):

Weight of Sample: ………………………. In-situ Density: ……………………….
Initial Water Content: ……………………….
Diameter: ………………………. Area (A): ……………………….
Volume: ……………………….
Axial Displacement during consolidation: ……………………….
Height after consolidation: 

Frequency of cyclic loading (Hz): ……………………….
Amplitude of cyclic loading for strain/stress control: …..mm/ ….kN
Normal Stress = ………………………

Calculation of Dynamic Properties

Cyclic Simple Shear

Result

Graphs:

Input data:

For Strain controlled cyclic simple shear test
Horizontal displacement versus Time

Output data:

For Strain controlled cyclic simple shear test
Horizontal load versus horizontal displacement

Analysis of the cyclic simple shear test data:

Shear stress versus Shear strain curve (Hysteresis loop)

Equivalent excess pore pressure versus Number of Cycles

Example:

A cyclic simple shear test was performed on silty-sand. The in-situ density and in-situ water content was 1.6 gm/cc and 8 % respectively. The shear strength parameters was c=0 kPa & F = 29 deg. The strain controlled cyclic simple shear test was performed on specimens at 0.1 Hz frequency and 0.12 mm displacement amplitude. The size of the specimen was 70 mm diameter and 20 mm height. The specimen was consolidated at vertical pressure of 100 kPa and

Input curve: Horizontal displacement versus Time

Output curve: Horizontal load vs horizontal displacement

Analysis of cyclic simple shear test data

i. Shear stress versus Shear strain (Hysteresis loop)

ii. Equivalent excess pore pressure versus Number of cycles
(pore pressure ratio = equivalent excess pore pressure/initial vertical stress;

At 20th cycle, pore pressure ratio is 1, which indicates that soil has liquefied.)

Cyclic Simple Shear

Result

Theory:

The first five cycles are usually considered for calculating shear modulus and damping ratio. The values for the first cycle are:
G = 2385 kPa
D = 35 %

The specimen exhibited cyclic liquefaction in 20 cycles. The pore water pressure reached the vertical normal stress of 100 kPa indicating a state of zero effective stress. The soil showed liquefaction in 20 cycles for cyclic simple shear loading of 0.12 mm horizontal displacement amplitude at 0.1 Hz frequency. Shear strain corresponding to 0.12 mm horizontal displacement is 0.6 %.

• CRR can only be evaluated from Stress-Controlled CSS Data
• Cyclic Stress Ratio, CSR = 𝝉/𝝈_𝒗

τ = Amplitude of Stress-controlled loading (Shear stress in kPa)

𝜎_𝑣 = Applied effective vertical overburden pressure

• Minimum 3 tests should be performed at different CSR to determine the CRR of the soil

• Input loading for Stress-Controlled Cyclic Loading:

• Output loading for Stress-Controlled Cyclic Loading:

• Liquefaction Criteria:

Number of cycles required to liquefy the specimen (N_L) can be determined using following criteria:

• Criterion 1: r_{u, max} ≥ 0.95
• Criterion 2: γ_DA ≥ 7.5%

r_{u, max} = Maximum excess pore water pressure ratio

γ_DA = Double amplitude shear strain

• Liquefaction Resistance:

Cyclic resistance ratio (CRR) is evaluated as the Cyclic stress ratio required to initiate liquefaction in 15 cycles (M_w = 7.5).

Special Note:

Same procedure can be followed for Stress-controlled Cyclic Triaxial (CTX) tests with the following changes:

1. CSR= (σ_d= Amplitude of cyclic deviatoric stress, σ_c= Effective confining pressure)
2. Criterion 1: r_{u, max} ≥ 0.95 (Same as CSS test)

Criterion 2: Double amplitude axial strain, ε_DA ≥ 5%