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# CONSOLIDATION ANALYSIS -stuff you should know to complete your lab assignment - PowerPoint PPT Presentation

CONSOLIDATION ANALYSIS -stuff you should know to complete your lab assignment. CIE 366: Soil Mechanics Laboratory Originally by Mike St. Pierre, 2007 Modified by Will Manion, 2008. Coefficient of Consolidation (c v ). For every load increment 10 increments -- 10 plots

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### CONSOLIDATION ANALYSIS-stuff you should know to complete your lab assignment

CIE 366: Soil Mechanics Laboratory

Originally by Mike St. Pierre, 2007

Modified by Will Manion, 2008

• 10 increments -- 10 plots

• Holtz and Kovacs(1981) section 9.4, pg 395

• Use the Casagrande logarithm of time curve fitting method.

• Fig. 9.7 on page 398 shows it nicely.

• cv (cm2/sec)

• T50 = time factor at U = 50%

• Hdr50 = height of drainage at

U = 50%

• t50 = time at U = 50%

• U = percent of primary consolidation

• From Table 9-1 pg 390

• If Uavg = 50%, T50 = 0.197

Coefficient of Consolidation (cv)Casagrande log time method

• Construct a plot of dial reading vs. log of time

• Figure 9.7, pg 398

• To determine

• Ho = Initial height of specimen

• Rstart = 0 (if you zeroed the dial at the beginning of the test)

• R50 you determine from the plot

Coefficient of Consolidation (cv)Casagrande log time method: R50

• May have to plot data points and complete construction on paper – see next slide

• determine Ro, when U = 0%

• determine R100, when U = 100%

• then average to find R50,

• which then graphically corresponds to t50

ΔR, the same distance

R1

ΔR

R2

R1 at t1

R2 at t2 (t2 = t1 x 4)

ΔR = R2 – R1

R100

R50 = (R100-Ro) / 2

R100

• Determine initial height and final height for load increment

• Calculate the void ratio for each load increment

• Plot e versus log effective stress

• You will have to print the plot and perform the construction on papershow all work

• Holtz and Kovacs (1981) Figure 8.6, pg 296

On paper, determine values from theVoid Ratio (e) versus Log Stress (σ) plot

• Using methodology from Figure 8.6

• Determine the (most probable) preconsolidation pressure (σ’p)

• Steps from Holtz and Kovacs pg 296

• Choose point of maximum curvature (point A)

• Draw horizontal line from point A

• Draw tangent to curve at point A

• Bisect angle made in Steps 2 and 3

• Extend straight line portion of virgin compression curve through bisector line

Most Probable

eo

5

2

1

4

Maximum Possible

3

On paper, determine values from theVoid Ratio (e) versus Log Stress (σ) plot

• Determine compression index (Cc)

• Slope of virgin compression curve aka the steep part of curve

• Holtz and Kovacs Figure 8.9 pg 316 graphically

• Holtz and Kovacs Figure 8.7 pg 313 analytically

• Determine recompression index (Cr)

• Holtz and Kovacs Figure 8.9 pg 316

• Consolidation Memo

• Due three weeks from today

• ONE PAPER COPY for the whole group

• Hand draw constructions (Make them neat)

• 11 plot attachments (label them appropriately)

• Each lab member responsible for ONE loading increment and cv plot

• Sign bottom right hand corner