application of expansive soil geotechnical...
TRANSCRIPT
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© 2008 All Presentation Copyright Bryant Consultants, Inc. Some slides adapted from PTI and Mr. Dean Read. All rights reserved by respective copyright owner.
Application of Expansive Soil Geotechnical
Procedures
Application of Expansive Soil Geotechnical
Procedures
FPA PRESENTATIONJohn T. Bryant, Ph.D., P.G., P.E withRobert L. Lytton, Ph.D., PE. And Mr.
Dean ReadHOUSTON, TEXAS
WEDNESDAY DECEMBER 10, 2008WEDNESDAY DECEMBER 10, 2008
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The “Design of Post-Tensioned Slabs-On-Ground”, 3rd Edition manual was published by the Post-Tensioning Institute in December 2004.
PTI 3rd Edition ManualPTI 3PTI 3rdrd Edition ManualEdition Manual
Addendum #1–May 2007Addendum #2–May/June 2008 ?
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Issue: Complexity of the ProcedureURBAN MYTH 1: To use and understand the
PTIGDPE you must either:a. Be Albert Einstein?b. Be a Protégé of Albert Einstein?c. Know who Albert Einstein is?d. None of the above?
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Fact: Answer is d, none of the above!
The procedure is not difficult and is based simply on the relationship between stress and strain in material, which in this case is soil. Chart 1 helps to explain the relationships between the various known and unknown variables in the procedure.
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Chart 1. Relationship between PTI soil parameters and stress/strain curve
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Expansive Soil?Expansive Soil?Expansive Soil?
PTI 3.2.1 - Expansive Soil Design is applicable if:All three of the following are true
Weighted PI of soil profile >= 15Weighted Passing #200 Sieve > 10%Weighted Finer than 5 micron > 10%
Or EI > 20
Modified definition of an expansive site included in
Addendum #1
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Issue—Where did the Zone Chart Curves come from for ?Myth: The zone chart curves found in the PTI manual, Figures 3.8 to 3.13 (pp. 17 to 19 3rd Edition Manual) were developed by extra-terrestrial intelligence and actually model the topography of some mountains on Mars?
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Newest Fact:
We are currently reviewing the gamma values for application
across all soil types
Newest Fact:Newest Fact:
We are currently reviewing the We are currently reviewing the gamma values for application gamma values for application
across all soil types across all soil types
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Issue--New Equipment?
Urban Myth: In order to use the PTI 3.1/3.2 , we must buy expensive laboratory equipment and we must do more testing AND WE MUST DO SOIL SUCTION TESTING!
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Fact: Not true. In fact the same test data that were required for the 1st and 2nd edition procedures are all that is required for the 3rd
edition. No additional tests are required and suction testing is not even required.
BUT………
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©Copyright Post-Tensioning Institute. All rights reserved 12
Distribution of Expansive SoilsDistribution of Distribution of
Expansive SoilsExpansive Soils
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©Copyright Post-Tensioning Institute. All rights reserved 13
Soil Structure Interaction –Center Lift
Soil Structure Interaction Soil Structure Interaction ––Center LiftCenter Lift
CENTER LIFT (Also commonly referred to as Edge Drop)
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Soil Structure Interaction –Edge Lift
Soil Structure Interaction Soil Structure Interaction ––Edge LiftEdge Lift
EDGE LIFT
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Differential Soil Movement, ym
Differential Soil Movement, Differential Soil Movement, yymm
Differential Soil Movement - ymrepresents the change in soil surface elevation at two locations separated by a distance em.
ym can be determined using the Stress Change Factor (SCF) method or computer methods.
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Differential Soil Movement, ym
Differential Soil Movement, Differential Soil Movement, yymm
ym is NOT the expected differential deflection of the foundation. ym should always be greater than the actual differential deflection of the foundation due to foundation stiffness.ym would only equal the differential deflection for a “perfectly flexible”foundation with no externally applied loads.ym is NOT the same as Potential Vertical Rise (PVR). PVR is a commonly used swell predictor used in Texas.
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Edge Moisture Variation Distance, em
Edge Moisture Variation Edge Moisture Variation Distance, Distance, eemm
Edge Moisture Variation Distance - em represents the distance measured inwards from the edge of a shallow foundation within which moisture will change due to wetting or drying influences around the perimeter of the foundation.
em is a function of both climatic and soil properties.(2nd Edition only included the effect of climate on em)
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PTI 2nd Edition ManualPTI 2PTI 2ndnd Edition ManualEdition Manual
The “Design and Construction of Post-Tensioned Slabs-On-Ground”, 2nd Edition manual was published by the Post-Tensioning Institute in October 1996.
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PTI 2nd Edition ManualPTI 2PTI 2ndnd Edition ManualEdition Manual
Liquid Limit (LL) – 55Plastic Limit (PL) – 28% Passing #200 Sieve – 79% Finer than 2 micron – 26Geographic Location – near Sacramento, CA
Depth to Constant Suction – 9 feet
REQUIRED Inputs for determining em and ym
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PTI 2nd Edition ManualPTI 2PTI 2ndnd Edition ManualEdition Manual
Determine ymDetermine clay type from
L, PL, %-200 and #-2µ
Determine equilibrium suction from TMI
Determine % fine clay from #-200 and %-2m
Depth to constant suction
Estimate velocity from TMI
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PTI 2nd Edition ManualPTI 2PTI 2ndnd Edition ManualEdition Manual
Determine em
Determine TMI from geographic location
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PTI 2nd Edition ManualPTI 2nd Edition ManualPTI 3rd Edition ManualPTI 3rd Edition Manual
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Liquid Limit (LL) – 55Plastic Limit (PL) – 28% Passing #200 Sieve – 79% Finer than 2 micron – 26Geographic Location – near Sacramento, CA
Depth to Constant Suction – 9 feet
REQUIRED Inputs for determining em and ym
Fabric Factor (Ff) – 1.2Note: With the exception of the Fabric Factor, the inputs were all
required in the 2nd Edition procedure.
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Depth to Constant SuctionDepth to Constant SuctionDepth to Constant Suction
The Depth to Constant Suction can be estimated by several different methods:
Published analytical proceduresThe depth at which the suction changes less than 0.027 pF (difficult to measure to this accuracy)2 feet deeper than the deepest rootDepth of “moisture active zone” (difficult to determine, can vary on different sites)
While the Depth to Constant Suction is commonly assumed to be 9 feet it can be significantly deeper.
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Optional VariablesOptional Variables
% Passing #10 Sieve
Dry Unit Weight (at natural water content)
Wet Total Unit Weight (at approx. 2.5 pF)
Note: Variables only required for Coarse Grained Soil Correction.
Additional Optional Variables for determining em and ym
Additional Optional Variables for determining em and ym
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Example of ymCalculation
Example of ymCalculation
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ymyymm
ym, in simple terms, is a function of a change in suction AND how much the soil changes volume for a given suction change.
The change in suction is modeled using Design Suction Envelopes.
The Suction Compression Index is the change in soil volume for a change in suction.
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Steps to determine ymSteps to determine Steps to determine yymm
Step 1 – Calculate Plasticity Index (PI)
Step 2 – Calculate Percent fine clay (%fc)
Step 3 – Determine Zone from Mineral Classification chart
Step 4 – Calculate Activity Ratio (PI/%fc)
Step 5 – Calculate LL / %fc
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Steps to determine ymSteps to determine Steps to determine yymm
Step 6 – Determine suction compression index
6a – Determine (γo) from gamma charts6b – Correct for Percent Fine Clay (γh) 6c – Correct for Coarse Grained
Component (γh corr) 6d – Modify for shrinking and swelling
(γh shrinking and γh swelling)
6e – Calculate weighted suction compression index
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Steps to determine ymSteps to determine Steps to determine yymm
Step 7 – Determine ThornthwaiteMoisture Index (Im)
Step 8 – Develop Suction Envelopes
Step 9 – Determine Stress Change Factors
Step 10 – Calculate ym
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ym Steps 1 & 2 –Calculate PI and %fc
yymm Steps 1 & 2 Steps 1 & 2 ––Calculate PI and %Calculate PI and %fcfc
Step 1 – Calculate Plasticity Index (PI)PI = LL – PLPI = 55 – 28 = 27
Step 2 – Calculate Percent Fine Clay (%fc)
%fc = % finer than 2 micron% passing #200 sieve
%fc = (26 / 79) * 100 = 33%
Note: Percent Fine Clay is not the same as Percent Clay as published in other sources.
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Note: No soil should plot above U-Line
There is no Zone Chart
for this area. PTI 3.6.2 says to use γο =
0.01
ym Step 3 –Determine Zone from Mineral Classification Chart
yymm Step 3 Step 3 ––Determine Zone from Mineral Classification ChartDetermine Zone from Mineral Classification Chart
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55Zone III
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ym Steps 4 & 5 –Calculate Activity Ratio and LL/%fc
yymm Steps 4 & 5 Steps 4 & 5 ––Calculate Activity Ratio and LL/%Calculate Activity Ratio and LL/%fcfc
Step 4 – Calculate Activity Ratio (PI / %fc)
PI / %fcPI / %fc = 27 / 33 = 0.82
Step 5 – Calculate LL / %fcLL / %fcLL / %fc = 55 / 33 = 1.67
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ym Step 6 –Determine Suction Compression Index
yymm Step 6 Step 6 ––Determine Suction Compression IndexDetermine Suction Compression Index
The Suction Compression Index is the change of soil volume for a change in suction.
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ym Step 6 –Determine Suction Compression Index
yymm Step 6 Step 6 ––Determine Suction Compression IndexDetermine Suction Compression Index
γo is the suction compression index for a soil with 100% fine clay (all particles smaller than 2 micron).γh is the suction compression index corrected for the actual percentage of fine clay γh corr is the suction compression index corrected for the coarse grained component of the soil.
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Note: Method for determining γobased on laboratory data from the National Resources Conservation Service, USDA with analysis by Covar and Lytton. Data included over 7,000 samples from across the United States.
ym Step 6a –Determine Suction Compression Index (γo)
yymm Step 6a Step 6a ––Determine Suction Compression Index (Determine Suction Compression Index (γγoo))
0.82
γo = 0.16
1.67
Zone III
PTI 3.6.2 – Beyond extreme values of the contours, use the nearest values for γo.
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ym Step 6b –Correct for Percent Fine Clay (γh)
yymm Step 6b Step 6b ––Correct for Percent Fine Clay (Correct for Percent Fine Clay (γγhh))
γo is the suction compression index for a soil with 100 % fine clay (all particles smaller than 2 micron).γh is the suction compression index adjusted for the actual percentage of fine clay and coarse grained soils.
γh = γo (%fc)/100γh = 0.16(33)/100 = 0.053
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Coarse Grained Soil Correction
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ym Step 6c –Correct for Coarse Grained Component (γh corr)
yymm Step 6c Step 6c ––Correct for Coarse Grained Component (Correct for Coarse Grained Component (γγhh corrcorr))
Note: Should only be used in cases where the percentage retained on the #10 sieve is 10% or more.Clarification regarding use provided in Addendum #1.
Error exists in Equation 3-11 in 1st Printing of 3rd Edition.
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ym Step 6d –Modify for Shrinking and Swelling
yymm Step 6d Step 6d ––Modify for Shrinking and SwellingModify for Shrinking and Swelling
γo and γh determined with zone charts represent mean values.γh needs to be modified for shrinking and swelling.
γh shrinking = γhe-γh
γh shrinking = 0.053e-0.053 = 0.050γh swelling = γheγh
γh swelling = 0.053e0.053 = 0.056Note: Correction is different than in Technical Note #12.
Incorrect modification performed in Example problems.
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Alternate Procedures for Determining γh Swelling
Alternate Procedures for Alternate Procedures for Determining Determining γγhh SwellingSwelling
Expansion Index Procedure - use ASTM D 4829 to determine EI:
For comparison purposes:γh swelling = 101/1700 = 0.059
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Alternate Procedures for Determining γh Swelling
Alternate Procedures for Alternate Procedures for Determining Determining γγhh SwellingSwelling
Consolidation - Swell Pressure Test Procedure: use ASTM D4546 Method C
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Alternate Procedures for Determining γh Swelling
Alternate Procedures for Alternate Procedures for Determining Determining γγhh SwellingSwelling
Overburden Pressure Swell Test
is decimal change of specimen height divided by the initial height
Overburden Pressure
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Alternate Procedures for Determining γh Swelling
Alternate Procedures for Alternate Procedures for Determining Determining γγhh SwellingSwelling
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ym Step 6e –Calculate Weighted Suction Compression Index
yymm Step 6e Step 6e ––Calculate Weighted Suction Compression IndexCalculate Weighted Suction Compression Index
(γh)weighted = (Σ Fi x Di x γhi) / (Σ Fi x Di)
For layered soil profiles - (γh) weighted to be calculated per the following equation:
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©Copyright Post-Tensioning Institute. All rights reserved 44
ym Step 7 –Determine Thornthwaite Moisture Index (Im)
yymm Step 7 Step 7 ––Determine Determine ThornthwaiteThornthwaite Moisture Index (Moisture Index (IImm))
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ym Step 7 –Determine Thornthwaite Moisture Index (Im)
yymm Step 7 Step 7 ––Determine Determine ThornthwaiteThornthwaite Moisture Index (Moisture Index (IImm))
Sacramento, California
Im = -20
-20
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©Copyright Post-Tensioning Institute. All rights reserved 46
ym Step 8 –Develop Suction Envelopes
yymm Step 8 Step 8 ––Develop Suction EnvelopesDevelop Suction Envelopes
DRYWET
Initial Suction ProfileFinal
Suction Profile
A Suction Envelope consists of an Initial Suction Profile and a Final Suction Profile between which the actual field suction is expected to change.
The suction profiles do not represent the actual field suction but the boundary condition which the suction is not expected to go beyond.
A suction change from dry (higher suction) to wet (lower suction) results in swell (ym edge).
A suction change from wet (lower suction) to dry (higher suction) results in shrink (ym center).
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ym Step 8 –Develop Suction Envelopes
yymm Step 8 Step 8 ––Develop Suction EnvelopesDevelop Suction Envelopes
The Suction Profiles (initial or final) can model:Sites controlled by climate (precipitation, evaporation, etc.) – (typical profiles for design)Equilibrium condition (typical profile for design)Site modifications such as:
Moisture controlled fill padsMoisture injection
Vertical moisture barriersVegetation
TreesFlower Beds
Poor Drainage
A Suction Envelope can consist of a combination of profiles (one for the initial profile and one for the final profile).
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©Copyright Post-Tensioning Institute. All rights reserved 48
ym Step 8 -Develop Suction Envelopes
ym Step 8 -Develop Suction Envelopes
The suction profile for a site controlled by climate takes the form of a “trumpet” shape
based on Mitchell’s suction distribution.
Initial Suction
Profile for a site
controlled by climate
only
Typically used for
design cases.
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ym Step 8 -Develop Suction Envelopes
yymm Step 8 Step 8 --Develop Suction EnvelopesDevelop Suction Envelopes
Suction profile for “Bad Drainage”.
Final Suction Profile for a
site controlled by “Extremely
Bad Drainage“
Not typically used for
design cases. Used more for
analysis cases.
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©Copyright Post-Tensioning Institute. All rights reserved 50
ym Step 8 -Develop Suction Envelopes
yymm Step 8 Step 8 --Develop Suction EnvelopesDevelop Suction Envelopes
Combining the Initial Suction Profile and the Final Suction Profile results in the Suction Envelope.
Initial Suction Profile for a
site controlled by climate
Final Suction Profile for a
site controlled by “Extremely
Bad Drainage“
Note: Not a typical Suction
Envelope used for design
cases.
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ym Step 8 -Develop Suction Envelopes
yymm Step 8 Step 8 --Develop Suction EnvelopesDevelop Suction Envelopes
Typical Suctions Envelopes used for design
Post-Equilibrium Suction Envelopes start with an equilibrium initial suction profile and changes to either a wet or dry climate controlled final suction profile.
Post-Construction Suction Envelopes start with either a wet or dry climate controlled initial suction profile and changes to the opposite climate controlled suction profile.
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©Copyright Post-Tensioning Institute. All rights reserved 52
ym Step 8 -Develop Suction Envelopes
yymm Step 8 Step 8 --Develop Suction EnvelopesDevelop Suction Envelopes
Post–Equilibrium Post–Construction
Swell Case – Both envelopes start dry and end wet.
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©Copyright Post-Tensioning Institute. All rights reserved 53
ym Step 8 -Develop Suction Envelopes
yymm Step 8 Step 8 --Develop Suction EnvelopesDevelop Suction Envelopes
Post–Equilibrium Post–Construction
Shrink Case – Both envelopes start wet and end dry.
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©Copyright Post-Tensioning Institute. All rights reserved 54
ym Step 8 -Develop Suction Envelopes
yymm Step 8 Step 8 --Develop Suction EnvelopesDevelop Suction Envelopes
For the same soil the envelope on the right will produce significantly more shrink.
Note the right envelope is for illustration purposes only and is NOT representative of an envelope that should be used for design purposes.
The magnitude of shrink and swell is a function of the area between the two profiles.
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ym Step 8 –Develop Suction Envelopes
yymm Step 8 Step 8 ––Develop Suction EnvelopesDevelop Suction Envelopes
4.5 Typical dry limit suction value
3.0 Typical wet limit suction value
What values of the surface suction should be used for “typical” design?
Changed to 3.0 from 2.5 in Addendum #1.
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©Copyright Post-Tensioning Institute. All rights reserved 56
ym Step 8 -Develop Suction Envelopes
yymm Step 8 Step 8 --Develop Suction EnvelopesDevelop Suction Envelopes
The magnitude of shrink and swell is a function of the area between the two profiles.
For the same soil, the Post-Construction Envelope (on the right) will produce significantly more shrink
than the Post-Equilibrium Envelope on the left.
Post-Equilibrium Post-Construction
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ym Step 8 –Develop Suction Envelopes
yymm Step 8 Step 8 ––Develop Suction EnvelopesDevelop Suction Envelopes
When to use Post-Equilibrium Envelopes versus Post-Construction Envelopes?
(Addendum #1)
-40 -30 -20 -10 0 +10 +20 +30 +40
Post-Equilibrium
Post-Equilibrium
Post-Construction
Thornthwaite Moisture Index (TMI)
<-15 >+15
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ym Step 8 –Develop Suction Envelopes
yymm Step 8 Step 8 ––Develop Suction EnvelopesDevelop Suction Envelopes
When to use Post-Equilibrium Model versus Post-Construction Model?
(Addendum #1)
-40 -30 -20 -10 0 +10 +20 +30 +40
Post-Equilibrium
Thornthwaite Moisture Index (TMI)
Houston, Texas (Im = +15)
USE POST-EQUILIBRIUM MODEL
<-15
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©Copyright Post-Tensioning Institute. All rights reserved 59
ym Step 8 -Develop Suction Envelopes
yymm Step 8 Step 8 --Develop Suction EnvelopesDevelop Suction Envelopes
Note: Also referred to as constant suction or measured suction at depth. This figure has changed from 2nd Edition.
-20
3.9
Equilibrium Suction may be estimated from the correlation below in the absence of local observations:
What value do I use for the Equilibrium Suction?
3.4
+20
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©Copyright Post-Tensioning Institute. All rights reserved 60
ym Step 8 –Develop Suction Envelopes
yymm Step 8 Step 8 ––Develop Suction EnvelopesDevelop Suction Envelopes
Shrinking Swelling
Initial Profile
Final Profile
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ym Step 9 -Determine Stress Change Factors
yymm Step 9 Step 9 --Determine Stress Change FactorsDetermine Stress Change Factors
For Post-Equilibrium or Post-Construction envelopes use Stress Change Factor (SCF) procedure included in 3rd Edition manual. (Post-Construction SCF table added in Addendum #1).The PTI Manual includes SCF tables to use other profiles (tree, moisture barrier, flowerbed) with the equilibrium as the initial suction profile.Other envelopes (including those above) can be modeled using VOLFLO or other computer methods.
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Post-Equilibrium Envelope Stress Change Factor Method
PostPost--Equilibrium Envelope Equilibrium Envelope Stress Change Factor MethodStress Change Factor Method
Assumes initial suction is at equilibrium.
Assumes final suction profile is climate controlled and typical “trumpet shape”.
Assumes Depth to Constant Suction is 9ft.
Possibly Over- or Under- conservative for soil profiles with multiple layers where γhvaries significantly (See PTI 3.6.3).
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Post-Construction Envelope Stress Change Factor Method
Post-Construction Envelope Stress Change Factor Method
Added in Addendum #1.
Assumes initial and final suction profiles are climate controlled and typical “trumpet shape”.
Assumes Depth to Constant Suction is 9ft.
Possibly Over- or Under- conservative for soil profiles with multiple layers where γhvaries significantly (See PTI 3.6.3).
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ym Step 9 -Determine Stress Change Factors
yymm Step 9 Step 9 --Determine Stress Change FactorsDetermine Stress Change Factors
SCFshrinking= -9.4
SCFswelling= +20.7
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ym Step 10 –Calculate ym
yymm Step 10 Step 10 ––Calculate Calculate yymm
ym Center = γh shrinking x SCFshrinking
ym Center = 0.050 x 9.4
ym Center = 0.47 inches (Use 0.5 inches)
ym Edge = γh swelling x SCFswelling
ym Edge = 0.056 x 20.7
ym Edge = 1.16 inches (Use 1.2 inches)
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Recommended Suction Change Range for Design
Recommended Suction Change Recommended Suction Change Range for DesignRange for Design
Addendum 1 Section 3.6.3, typical range is 1.5 pF for most conditionsTypical versus Extreme Values
Suction in pF units Wet Dry
Typical (well drained)
3.0 4.5
Extreme 2.5 6.0
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Reasonable SuctionChange Range
Reasonable SuctionReasonable SuctionChange RangeChange Range
2003 TOTAL SOIL SUCTION DATA (4776 OBSERVATIONS)
0
200
400
600
800
1000
1200
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Empirically Measured SuctionsBCI 2002 to 2008 = 26,000+ Data
Points
Empirically Measured SuctionsBCI 2002 to 2008 = 26,000+ Data
Points
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
0.000 1.000 2.000 3.000 4.000 5.000
Soil Suction, pF
Dep
th, f
t.
Copyright John T. Bryant (2008)
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Global vs. Incremental Suction Change ym Analysis
Global vs. Incremental Suction Change ym Analysis
Depth
Increment 2 Increment 1
Higher Suction
Slab on grade
Global InitialSuction Envelope
Global Final Suction Envelope
pF=4.5
pF=3.0
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Typical Suction EnvelopeTypical Suction EnvelopeTypical Suction Envelope
Initial Profile
Equilibrium Profile
Final Profile
Typical “Trumpet”shape based on Mitchell and Lytton.
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Post EquilibriumPost EquilibriumPost Equilibrium
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Post EquilibriumPost Equilibrium
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Post ConstructionPost ConstructionPost Construction
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Suction EnvelopeSuction EnvelopeSuction Envelope
Actual Field Measured Suction should stay within the “envelope”.
Dry limit of envelope
Wet limit of envelope
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Field Suction Envelopes
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Anomalous Suction Envelopes
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Anomalous Suction Envelopes
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Removed Tree EnvelopeRemoved Tree EnvelopeRemoved Tree Envelope
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Flower Bed EnvelopeFlower Bed EnvelopeFlower Bed Envelope
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Flower Bed EnvelopeFlower Bed Envelope
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Ym values as a function of PI YmYm values as a function of PI values as a function of PI
my
Ym Based on:1. Homogeneous Soil 15 feet deep.
2. Effective PI per 3rd Edition3. Volflo 1.5 using trumpet shapted curves
at surface with maximum suction change at surface
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
0 10 20 30 40 50 60 70 80
PI, %
Ym, i
nche
s
2.0 Decade
1.5 Decade
1.25 Decade1.15 Decade1.0 Decade
Edge
Lift
Cen
ter L
Ift
my
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Example of emDeterminationExample of emDetermination
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Steps to determine emSteps to determine Steps to determine eemm
Step 1 – Calculate Ss
Step 2 – Calculate Unsaturated Diffusion Coefficient (α)
2a – Calculate Modified Unsaturated Diffusion Coefficient (α’)
2b – Calculate Weighted Modified Unsaturated Diffusion Coefficient (weighted α’)
Step 3 – Determine em
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em Step 1 –Calculate Ss
eemm Step 1 Step 1 ––Calculate SCalculate Sss
Ss is the slope of the suction vs. gravimetric water content curve.
Can be determined from soil-water characteristic curve or be estimated with the following equation. Ss =-20.29 + 0.1555 LL – 0.117 PI + 0.0684 (%-#200)
Ss = -20.29 + 0.1555(55) – 0.117(27) + 0.0684(79)
Ss = -9.5
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em Step 2 –Calculate Unsaturated Diffusion Coefficient
eemm Step 2 Step 2 ––Calculate Unsaturated Diffusion CoefficientCalculate Unsaturated Diffusion Coefficient
The Unsaturated Diffusion Coefficient (α) for shrinking and swelling can be estimated with the following equations (based on field observations):
α shrinking = 0.0029-0.000162(Ss) – 0.0122(γh shrinking)
α shrinking = 0.0029-0.000162(-9.5) – 0.0122(0.050)
α shrinking = 0.0038
α swelling = 0.0029-0.000162(Ss) – 0.0122(γh swelling)
α swelling = 0.0029-0.000162(-9.5) – 0.0122(0.056)
α swelling = 0.0038
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eemm Step 2a Step 2a ––Calculate Modified Unsaturated Diffusion CoefficientCalculate Modified Unsaturated Diffusion Coefficient
α’ = α (Ff)Condition Ff
Non CH Soils 1.0
CH Soils
Profiles with 1 root, crack, sand/silt seam all less than or equal to 1/8” width/dimension in any combination 1.0
Profile with 2 to 4 roots, cracks, sand/silt seams all larger than 1/8” width/dimension in any combination 1.1
Profile with more than 4 roots, cracks, sand/silt seams all larger than 1/8” width/dimension in any combination 1.2
Modified Ff values included in Addendum #2.
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Reason for Fabric FactorReason for Fabric Factor
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Reason for Fabric FactorReason for Fabric Factor
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eemm Step 2a Step 2a ––Calculate Modified Unsaturated Diffusion CoefficientCalculate Modified Unsaturated Diffusion Coefficient
Since soil is a CH clay and number of cracks, roots, etc unknown – Use 1.2.
Condition FfNon CH Soils 1.0
CH Soils
Profiles with 1 root, crack, sand/silt seam all less than or equal to 1/8” width/dimension in any combination 1.0
Profile with 2 to 4 roots, cracks, sand/silt seams all larger than 1/8” width/dimension in any combination 1.1
Profile with more than 4 roots, cracks, sand/silt seams all larger than 1/8” width/dimension in any combination 1.2
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eemm Step 2a Step 2a ––Calculate Modified Unsaturated Diffusion CoefficientCalculate Modified Unsaturated Diffusion Coefficient
α’ shrinking = α shrinking (Ff)α’ shrinking = 0.0038 (1.2)= 0.0046
α’ swelling = α swelling (Ff)α’ swelling = 0.0038 (1.2) = 0.0046
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em Step 2b –Calculate Weighted Modified Unsaturated Diffusion Coefficient
eemm Step 2b Step 2b ––Calculate Weighted Modified Unsaturated Diffusion CoefficientCalculate Weighted Modified Unsaturated Diffusion Coefficient
(α’)weighted = (Σ Fi x Di x αi) / (Σ Fi x Di)
For layered soil profiles (α’) weighted to be calculated per the following equation:
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em Step 3 –Determine em
eemm Step 3 Step 3 ––Determine Determine eemm
2.5
5.3
9.0
4.6
Represents the middle of the 2nd
Edition bands
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Summary of Soil Support Parameters (SCF)
Summary of Soil Support Summary of Soil Support Parameters (SCF)Parameters (SCF)
near Sacramento, CA
em Center = 9.0 feetem Edge = 4.6 feet
ym Center = 0.5 inchesym Edge = 1.2 inches
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VOLFLO 1.5 - ShrinkingVOLFLO 1.5 VOLFLO 1.5 -- ShrinkingShrinking
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VOLFLO 1.5 - ShrinkingVOLFLO 1.5 VOLFLO 1.5 -- ShrinkingShrinking
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VOLFLO 1.5 - ShrinkingVOLFLO 1.5 VOLFLO 1.5 -- ShrinkingShrinking
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VOLFLO 1.5 - SwellingVOLFLO 1.5 VOLFLO 1.5 -- SwellingSwelling
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VOLFLO 1.5 - SwellingVOLFLO 1.5 VOLFLO 1.5 -- SwellingSwelling
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Comparison of Soil Support Parameters
Comparison of Comparison of Soil Support ParametersSoil Support Parameters
em ymCenter Edge Center Edge
SCF 7.8 4.0 0.66 0.97
VOLFLO 1.5 7.8 4.0 0.58 0.73
% Difference 0% 0% 14% 33%
Mesquite, TX Layered Soil Profile
Post-Equilibrium Suction Envelopes
The SCF method should only be attempted for layered profiles if “ γhdoes not vary by more than 10%. Otherwise, this procedure may not
be accurate or conservative.”
Layer 1 :γh = 0.028
Layer 2 :γh = 0.065
Layer 3 :γh = 0.052
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Simplified ApproachSoil Design Parameters and Soil
Data
Simplified ApproachSimplified ApproachSoil Design Parameters and Soil Soil Design Parameters and Soil
DataData
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Simplified ApproachPI = 40
Simplified ApproachSimplified ApproachPI = 40PI = 40
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Variation of PI on ReliabilityVariation of PI on ReliabilityVariation of PI on Reliability
PI = 10 PI = 20 PI = 30
PI = 40 PI = 50 PI = 60
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Simplified ApproachSoil Design Parameters and Soil
Data
Simplified ApproachSimplified ApproachSoil Design Parameters and Soil Soil Design Parameters and Soil
DataData
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Variation of PI on ReliabilityVariation of PI on ReliabilityVariation of PI on Reliability
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Finite Element Modeling
2D/3D Stress/Strain DeformationSaturated/Unsaturated Flow2D/3D Slope StabilitySettlement Study
Retaining Wall
Select FillPier
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Animation Reconstruction