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Design Suction Envelope for Drilled Shafts in Expansive Soil
Robert L. Lytton
Professor, Fred J. Benson Endowed ChairZachry Department of Civil Engineering
Texas A&M UniversityTexas A&M University
Foundation Performance Association Houston, Texas
December 11, 2013
UPLIFT
OREINFORCING MOVEMENT ACTIVE ZONE
ANCHORZONE
2
Load
SHRINKAGESHRINKAGE
MOVEMENTMOVEMENT ACTIVE ZONE
ANCHORZONEZONE
BEARING
3
BEARING CAPACITY
Thornthwaite Moisture Index (TMI, 1948)Thornthwaite Moisture Index (TMI, 1948)
100 60R DEFTMIE
pE
R = runoff moisture depthDEF =deficit moisture depthpEp = evapotranspiration
4
Suction Distribution with DepthSuction Distribution with Depth(-) Suction Ground Surface
Wet Season
E ilib i
Dry Season
Equilibrium
Dep
th
Dry Season
5
0.00 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Soil Suction, pF
5.0
10.0
15.0
20.0
epth
, ft.
25.0
30.0
De
35.0
40.0
66
45.0Copyright John T. Bryant (2008)
Figure 1 - Total Soil Suction Histogram for 2006
1000
700
800
900
500
600
Freq
uenc
y
200
300
400
F
0
100
200
2 6 2 7 2 8 2 9 3 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 4 4 1 4 2 4 3 4 4 4 5 4 6 More
7
2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3 4.4 4.5 4.6 More
Total Soil Suction, pF
Field ConditionsField Conditions
pF Wilting point 4.5 pFField capacity Equilibrium
e 3.5633exp( 0.0051TMI)U
0
2
2.0 3.0 4.0 5.0
Root zone2
4
6ft 6
8
10
Dept
h (f
Moisture active zone
12
14
8
0( ) exp -e
nU Z U U Z
Suction Distribution with DepthSuction Distribution with Depth(-) Suction Ground SurfaceSoil Sample
Wet Season
E ilib i
Dry Season
Equilibrium
Dep
th
Dry Season
How do you find the envelope?envelope?
9
10
11
12
13
14
Thornthwaite Moisture Index (TMI, 1948)Thornthwaite Moisture Index (TMI, 1948)
100 60R DEFTMIE
pE
R = runoff moisture depthDEF =deficit moisture depthpEp = evapotranspiration
15
16
Mean Surface Suction, pF
4
5
, p
4.5
2
3
43.0 3.3
3.0
0
1
2
J F M A M J J A S O N D
0
Month
17
18
Surface suction variation with timeSuction variation with depth and timeare predicted with Fourier Series
19
Suction envelopes are also predicted with Fourier Series
20
21
Demonstration of suction envelope spreadsheet
22
Suction Distribution with DepthSuction Distribution with Depth(-) Suction Ground SurfaceSoil Sample
Wet Season
E ilib i
Dry Season
Equilibrium
Dep
th
Dry Season
How do you find the envelope?envelope?
23
Design Suction Envelope for Drilled Shafts in Expansive Soil
Robert L. Lytton
Professor, Fred J. Benson Endowed ChairZachry Department of Civil Engineering
Texas A&M UniversityTexas A&M University
Foundation Performance Association Houston, Texas
December 11, 2013
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