Purpose: To understand how incremental load consolidation test data is processed to yield consolidation parameters needed for assessment of stress history and engineering design.

Test Procedure: One-dimensional consolidation testing is performed in general accordance with ASTM Standard D2435 Standard Test Method for One-Dimensional Consolidation Properties of Soils. A load increment ratio (LIR) of 1 was used. Test data are given in the Excel data file. A copy of the ASTM standard is available in the CIE365 FirstClass folder. 22 load increments are given in the file, along with initial conditions for the specimen.

Test Specimen: An undisturbed sample of Boston blue clay (BBC) was obtained from Newbury, Massachusetts. The sample depth was 6.1 m and the soil has a specific gravity of 2.80. Initial void ratio, water content, and dry and total density were determined based on actual specimen properties. These are given in the Excel file.

Assignment: For the specimen, determine the following. Choose to either work in terms of void ratio (e) or strain (e):

• Consolidation curve based on strain or void ratio from the end of the increment (EOI).
• Consolidation curve based on strain or void ratio from the end of primary (EOP) consolidation. EOP is when 100% of pore pressure has dissipated and can be found to be "tp" from Figure 9.7; Holtz & Kovacs (1981).
• Recompression ratio Cr (e) or CR (e)
• Compression ratio Cc (e) or CC (e)
• Swelling (or unloading) ratio Cs (e) or CS (e)
• Preconsolidation stress (s'p) using Casagrande construction. (Figure 8.6; Holtz & Kovacs 1981)
• Overconsolidation ratio (OCR)
  
  

• Read Holtz & Kovacs (1981) §9.3. Determine:

1. Coefficient of consolidation (cv) using the Taylor method for increments in the normally consolidated (NC) stress region (s'v > s'p) that where EOP can be determined. (Holtz & Kovacs §9.4b)
2. Coefficient of consolidation (cv) using the Casagrande method for for increments in the normally consolidated (NC) stress region (s'v > s'p) that where EOP can be determined. (Holtz & Kovacs §9.4a)
3. Hydraulic conductivity using cv determined either from the Taylor and Casagrande method. Use Equ.8-5a and Equ.9-14 in Holtz & Kovacs 1981).

• Determine secondary compression index, Ca (e) or Cae (e) for NC increments according to Holtz & Kovacs §9.7.

Report:
Typical laboratory report that includes soil and specimen information, basic testing procedures (given above) and purpose for testing. Present results determined above. Present a range of values where necessary and the complementing range of stresses. Compare the differences between the Casagrande and Taylor analysis methods. Submit your Excel file on FC along with your report.

Excel data file: IL_consolidation.xlsx