Consolidation analysis stuff you should know to complete your lab assignment
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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


Ro

ΔR, the same distance

R1

ΔR

R2

R1 at t1

R2 at t2 (t2 = t1 x 4)

ΔR = R2 – R1


Ro

R100


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


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


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