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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. 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

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
Coefficient of Consolidation (cv)

  • For every load increment

    • 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.


Coefficient of consolidation c v1
Coefficient of Consolidation (cv)

  • 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 c v casagrande log time method
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 c v casagrande log time method r 50
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%

      • this is NOT your first reading

    • determine R100, when U = 100%

    • then average to find R50,

    • which then graphically corresponds to t50


Consolidation analysis stuff you should know to complete your lab assignment

Ro

ΔR, the same distance

R1

ΔR

R2

R1 at t1

R2 at t2 (t2 = t1 x 4)

ΔR = R2 – R1


Consolidation analysis stuff you should know to complete your lab assignment

Ro

R100


Consolidation analysis stuff you should know to complete your lab assignment

Ro

R50 = (R100-Ro) / 2

R100


Void ratio e versus log stress
Void Ratio (e) versus Log Stress (σ)

  • 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 the void ratio e versus log stress plot
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


Consolidation analysis stuff you should know to complete your lab assignment

Minimum Possible

Most Probable

eo

5

2

1

4

Maximum Possible

3


On paper determine values from the void ratio e versus log stress plot1
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)

    • Slope of the unloading/reloading part of curve

    • Holtz and Kovacs Figure 8.9 pg 316


Details details details
Details, Details, Details

  • 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