(土の締固め) - 北海道大学 · 2017-11-28 · how to obtain compaction curves –...
TRANSCRIPT
Lecture No.7
Compaction of soils (土の締固め)
■ What is compaction? (締固めとは?) 1
Construction of embankments, river dykes, earth fill dams, etc
(盛土・堤防・アースダム)
Earth fill dam
Sumo mound
Compaction:
To densify (密実化) and stabilize (安定化) soil by applying
static or dynamic load
■ Changes in state by compaction (締固めによる状態の変化) 2
• Air
• Water
• Soil particles
rd
e
Air
Water
Soil
Compaction
vV
sV
V
Void ratio (間隙比)
Dry density (乾燥密度)
rd
e
■ Compaction curve (締固め曲線) 3
Water content, w (%)
Dry density, rd (kg/m3)
Zero air void curve
(Saturation curve)
(ゼロ空気間隙曲線) Sand
Clay
wopt wopt
rd,max
rd,max
Proctor (1933)
When a given soil is compacted at a given energy with varying water
content, the dry density – water content relationship shows;
•
•
w = 10%
w = 30%
■ How to obtain compaction curves – Compaction test 4
① Prepare soil at a given w ② Add soil to mould ③ Compact with rammer
④ Complete each layer ⑤ Trim the surface and weigh
➡ Total density, rt
Add water and repeat for a different w.
Adjust water content
and make it uniform Use a collar for the top layer
2.5 kg or
4.5 kg
Drop from
30cm or 45cm
Repeat ②~④.
Fill with 3 or 5 layers
Typically, 25 blows
per layer
⑥ Measure w
➡ Calculate rd from w and rt
■ Reference curves in compaction diagram 5
Water content, w (%)
Dry density, rd (kg/m3)
Sr =100% 80%
60%
■ Equations for reference curves 6
Saturation curve Constant degree of
saturation curve
Constant air content
curve
Air
Water
Soil
vV
sV
V wV
aVDegree of saturation (飽和度)
[%] 100V
Vv a
a
vwr VVS / [%] 100s
w
W
Ww
s
wsG
r
re
wGS s
r w
ssG
r
r
Water content (含水比)
Air content (空気間隙率)
Specific gravity (比重)
■ Optimum water content (最適含水比) 7
Water content, w (%)
Dry density, rd (kg/m3)
wopt
rd,max
Increasing w:
rd bound by zero air void curve
Decreasing w:
Increase of suction
Increase of stiffness
➡ harder to deform
(harder to be compacted)
wopt: Important parameter in controlling soil compaction
■ Characteristics of compaction curve (締固め曲線の特性) 8
Effect of compaction energy
WR: Rammer weight [kN]
H: Fall height [m]
NB: Blow number per layer
NC: Number of layers
V : Mould volume [m3]
Compaction energy (締固めエネルギー)
= Work done to soil (土に対する仕事量)
Expected field compaction energy
Compaction energy in laboratory test
[kJ/m3]
■ Characteristics of compaction curve (締固め曲線の特性) 9
Effect of compaction energy
Greater energy: (i.e. Larger rammer weight or
more blows)
wopt ➡
rd,max ➡
However… Over-compaction (過転圧、オーバーコンパクション) Decrease of strength due to too much compaction energy in some soils
Water content, w (%)
Dry density, rd (kg/m3)
wopt
rd,max
■ Characteristics of compaction curve (締固め曲線の特性) 10
Effect of soil type
Location & shape of compaction curves depends on soil types
Particle size (mm)
Perc
ent finer
(%)
Water content, w (%)
Dry
density,
rd (
g/c
m3)
■ Engineering properties of compacted soils 11
Strength
After compaction
After wetting
wopt
Max
w < wopt
Large
decrease w > wopt
No significant change
Dry
de
nsity,
rd (
kg
/m3)
Water content, w (%)
Water content, w (%)
Un
co
nfin
ed
co
mp
ressio
n
str
en
gth
, q
u (
kN
/m2)
Maximum when compacted
at slightly dry states
(Unconfined compression test)
■ Engineering properties of compacted soils 12
Permeability
wopt
Dry
de
nsity,
rd (
kg
/m3)
Water content, w (%)
Min
Co
effic
ien
t o
f p
erm
ea
bili
ty
aft
er
sa
tura
tion
, k
(m/s
ec)
Water content, w (%)
(at compaction)
Saturated permeability
And unsaturated permeability:
To be distinguished
■ Compaction in field 13
For given soil, the thinner each layer is,
the denser it gets compacted.
1-unit energy for 15-cm lift
2-unit energy for 30-cm lift
3-unit energy for 30-cm lift Which is best?
Roller
Depth
Energy
Control variables
• Compaction machine (weight, mechanism)
• Layer thickness (“lift”)
• Number of load application
Compaction of earth fill dam
Tamping roller
Vibration roller
Vibrating plate
compactor
■ Quality control of compacted soils 14
Degree of compaction, Dc(締固め度)
and air content, va(空気間隙率), as common indices
Dry
de
nsity,
rd
Dry
density,
rd
Water content, w Water content, w
Generally …
• Embankment: Dc≧85~95%
➡
• Subgrade (路床): Dc≧90~95%
■ Quality control of compacted soils 15
Example: River dyke building with wet sand – clay mixed soil
0 10 20 30 -10 -20 -30 (m)
2015年築堤
2016年築堤
1.0
1.1
1.2
1.3
1.4
1.5
10 15 20 25 30 35 40 45
乾燥密度
ρd(g/
cm
3)
含水比 w(%)
SP2210 2層目
SP2210 4層目
SP2210 6層目
SP2275 2層目
SP2275 4層目
SP2275 6層目
Sr100% ρ s=2.611g/cm3
Sr90%Sr80% 1次盛土(H27施工)
最大乾燥密度の90%= 1.27g/cm3
Water content, w (%)
Dry
de
nsity,
rd (
g/c
m3)