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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 ). For every load increment 10 increments -- 10 plots

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

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  1. 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

  2. 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.

  3. 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

  4. 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

  5. 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

  6. Ro ΔR, the same distance R1 ΔR R2 R1 at t1 R2 at t2 (t2 = t1 x 4) ΔR = R2 – R1

  7. Ro R100

  8. Ro R50 = (R100-Ro) / 2 R100

  9. 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

  10. 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

  11. Minimum Possible Most Probable eo 5 2 1 4 Maximum Possible 3

  12. 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

  13. 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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