subgrade improvement options - performance study …. cole... · 2017-01-24 · subgrade...
TRANSCRIPT
Subgrade Improvement Options -
Performance Study and Cost Comparison
• Remove-and-Replace
• Lime Treatment
Larry Cole, P.E.
Carmeuse Lime and Stone
Pittsburgh, PA
2
Subgrade Soil on Gateway Project (Detroit, MI)
3
Cut-and-Fill
4
Lime Treatment
5
Lime’s Effect on Soil
Drying up wet soil: –Drying
Modification: –Plasticity and swell reduction
–Improved stability & compaction
–Solid working platform
Stabilization: –Permanent strength increase
–Long-term strength gains
–Less moisture absorption
–Freeze-thaw durability
Em
ba
nk
me
nts
an
d F
ill
Wo
rkin
g P
latf
orm
Lim
e s
tab
iliz
ati
on
(p
ave
me
nt
de
sig
n)
6
Lime Reacts Chemically with Clays
to Alter Particle Interactions
Clay Particle Water Layer
7
• Increased Strength
• Reduced Plasticity
Lime Modified Soil:
• Reduced Expansion
8
Soil Before And After Lime Treatment
9
CBR Increases with Lime Modification
Soil Classification
State
Untreated
CBR
Treated CBR
(Immediate)
Treated
CBR
(Cured) AASHTO UCS
A6 CL MI 4 40 68
A-7- 6 CH MI 3 40 80
A-7- 6 CL MI 4 22 40
A-2- 6 SC MI 4 40 85
A6 CL VA 6 30 140
A-7- 6 CH GA 3 28 66
A-7- 6 CH TN 5 34 84
A-7- 6 CH TN 8 25 74
A6 CH TN 2 26 109
A6 CL OH 4 21 62
A-2-6 SC IL 9 27 100
10
Lime Treatment or Cut-and Fill?
Which technique:
• Works better for construction loads?
• Cost less?
11
The decision depends on a number of factors, including:
• Cost
• Project size
• Contractor capabilities and preferences
• Material availability
• Disposal options (for remove and replace)
• Equipment access or operating constraints
• Existing soil types and soil conditions
and should be evaluated on a case-by-case basis by a
competent geotechnical engineer, site work contractor and
soil stabilization specialty contractor.
Neither solution is always best in all situations.
Lime Treatment or Cut-and Fill?
12
North Carolina State University Study
13
NCSU Subgrade Testing Apparatus
14
Subgrade Installation
15
Unsoaked CBR of Subgrade Soil
16
Subgrade Test Sections
Subgrade -
CL Soil
% Passing #200 = 58
PI = 16
OMC = 15.6%
Agg Base Course - GW
(12” - 20”)
or Select Fill - SW
(17” - 36”)
Subgrade -
CL Soil
% Passing #200 = 58
PI = 16
OMC = 15.6%
Lime Treated Soil
(3% lime) (9” )
4” - 5” Agg Base Course
17
Subgrade Load Plate
18
Construction Load (Cat 631 Scraper)
80 psi
25-30 mph
19
Displacement After 200 Loading Cycles
0
0.25
0.5
0.75
1
1.25
1.5
1.75
2
9" LSS
with 4"
ABC
20" ABC 36" Select
Fill & 3"
ABC
16" ABC
with
Geogrid
14" ABC 12" ABC
with
Geotextile
Inch
es
20
Displacement After 10,000 Loading Cycles
0
0.5
1
1.5
2
2.5
3
9" LSS
with 4"
ABC
20" ABC 36" Select
Fill & 3"
ABC
16" ABC
with
Geogrid
14" ABC 12" ABC
with
Geotextile
200 Cycles
10,000 Cycles
Inch
es
21
Number of Loading Cycles to 0.5” Displacement
0
100
200
300
400
500
600
700
800
900
1000
9" LSS
with 4"
ABC
20" ABC 36" Select
Fill & 3"
ABC
16" ABC
with
Geogrid
14" ABC 12" ABC
with
Geotextile
Lo
ad
ing
s
Over
10,0
00
22
Unit Costs for Subgrade Improvement Options
Item Avg Cost ($) Units
Undercut Excavation $10.04 /yd3
Select Granular Fill $24.59 /yd3
Aggregate Base Course $24.12 /ton
Lime Treated Subgrade $2.54 /yd2
Lime $195.36 /ton
NCDOT Statewide Averages - 2008
23
Unit Costs for Subgrade Improvement Options
Item Small Quantities Large Quantities
Geotextile $4.57
Geogrid A $4.50 $3.04
Geogrid B $2.25 $1.28
Manufacturer Cost Estimates ($/SY)
24
Cost Comparison Subgrade Improvement Options
Test Configuration Unit Cost
($/SY)
9” Lime Stabilized Soil with 4” ABC $10.44
14” Agg Base Course $20.18
12” Agg Base Course with Geotextile $22.59
16” Agg Base Course with Geogrid $24.34
20” Agg Base Course $28.82
36” Select Fill and 3” ABC $38.95
12” of Lime Stabilized Soil: $5.40 /SY
$5.40 will buy < 4” of cut and fill with ABC
or
< 2” of cut and fill with ABC and geogrid (based on NCDOT State-wide average bid costs)
25
Performance and Cost
Low Displacement
Low Cost Low Displacement
High Cost
High Displacement
Low Cost
High Displacement
High Cost
1¾
40 Cost ($/SY)
Dis
pla
cem
en
t (i
n)
12” ABC w/Geotextile
14” ABC
20” ABC
18” ABC
16” ABC
w/ Geogrid
9” LSS
w/ 4” ABC 12”
LSS
19” ABC
with
Geotextile
26
Comparison Subgrade Improvement Options
NCDOT Comparative Costs (2008/2010) Unit Cost ($/SY)
12” Lime Stabilized Soil $5.44 / $5.00
14” Agg Base Course $20.18 / $15.43
12” Agg Base Course with Geotextile $22.59 / $18.54
16” Agg Base Course with Geogrid $24.34 / $19.43
20” Agg Base Course $28.82 / $22.04
36” Select Fill and 3” ABC $38.95 / $18.55
Compared to Cut-and Fill –
Lime-treated soil gives better results
at less than 1/3 the cost
27
Unit Costs for Subgrade Improvement Options
Item Avg Cost ($) Units
Excavation $7.46 /yd3
Geotextile (Subgrade Stab) $1.19 /yd2
Aggregate Base $37.46 /yd3
Lime Treated Subgrade,
12 inches deep $2.30 /yd2
Lime $128.82 /ton
ODOT Statewide Averages
2011
28
Comparison Subgrade Improvement Options
ODOT Comparative Costs - 2011 Unit Cost
($/SY)
12” Lime Treated Soil $4.26
14” Agg Base Course $17.46
12” Agg Base Course with Geotextile $16.17
16” Agg Base Course with Geotextile $21.16
20” Agg Base Course $24.97
Compared to Cut-and-Fill with ABC–
Lime-treatment is less than 1/3 of the
cost of remove-and-replace with
aggregate base course
29
Comparison Subgrade Improvement Options
GDOT - Comparative Costs Unit Cost
($/SY)
8” Lime Stabilized Soil $4.43
8” Agg Base Course $10.61
8” Agg Base Course with Geogrid $13.26
Compared to Cut-and-Fill with ABC–
Lime-treatment is less than 1/3 of the
cost of remove-and-replace with
aggregate base course & geogrid
31
Unit Costs for Subgrade Improvement Options
Item Avg Cost ($) Units
Regular Excavation $10.69 /yd3
Geotextile (Subgrade Stab) $1.61 /yd2
Agg Material 21B $24.70 /ton
Lime Treated Subgrade
Manipulation $2.90 /yd2
Lime $202.65 /ton
VDOT Statewide Averages
July 2009 to Aug 2011
32
Comparison Subgrade Improvement Options
VDOT - Comparative Costs Unit Cost
($/SY)
12” Lime Stabilized Soil $6.00
14” Agg Base Course $21.96
12” Agg Base Course with Geotextile $20.43
16” Agg Base Course with Geotextile $26.74
20” Agg Base Course $28.82
Compared to Cut-and-Fill with ABC–
Lime-treatment is less than 1/3 of the
cost of remove-and-replace with
aggregate base course
33
Unit Costs for Subgrade Improvement Options
Item Avg Cost ($) Units
Regular Excavation $3.47 /yd3
Geogrid $2.10 /yd2
Class 2 Base (rock or PCC) $25.23 yd2, 12” deep
Lime Treatment $315 ton
LADOTD Statewide Averages
Q4 - 2012
34
Comparison Subgrade Improvement Options
LADODT - Comparative Costs Unit Cost
($/SY)
12” Lime Treated Soil $7.10
12” Class 2 Base (rock) with geogrid $28.40
12” Sand $15.65
Compared to Cut-and-Fill with Rock or Sand –
Lime-treatment is less than ¼ - ½
of the cost
35
Lime Treatment or Cut-and Fill?
Which technique:
• Works better for construction loads?
• Cost less?
Subgrade Improvement Options -
Performance Study and Cost Comparison
• Remove-and-Replace
• Lime Treatment
Larry Cole, P.E.
Carmeuse Lime and Stone
Pittsburgh, PA