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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
slide6

Ro

ΔR, the same distance

R1

ΔR

R2

R1 at t1

R2 at t2 (t2 = t1 x 4)

ΔR = R2 – R1

slide7

Ro

R100

slide8

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
slide11

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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