r I ,.90
<~m.,~ . &
A section i B section ~ B
I
Load cell
i ! ======i >g ~Q
."!
I
148 A
II
h II
II
il 9
I
[* L=35.5 ~ j 40
T I g I n I " ~ \ \ \ \ , z , N ' - , \ \ \ ' , l - ' - " ~ \ \ \ \ \ \ \ \ \ ' - I
P~pe_pSt gment ~ / ~ / / ~ Pi\pe_end
t=0.95 t'=l.3
Dummy part Load cell part Flexible-pipe
9 ,B A
/ 2
1--[ M ~ Deflection
~ ~ Load cell ~gauge
" "' ,, " Strain
o Ii
o' ,i li*gauge
|
A section i B section ~ ' 148 "r
Rigid-pipe and
i,-20
<=3 t'=5.25 Supporting beam
Rigid-pipe Medium-pipe
• b=4.2
~7 Prismatic bar .25 1-5 Medium-pipe FIG. 1--Model pipes and detail of load cells (unit: mm).
TABLE i--Dimensions of Model Pipes.
External Wall Young's Flexural stiffness 1 Weight diameter thickness modulus Poisson's Sf/a a of pipe
D t Ep ratio kgf.cma/cm gf/cm
Pipe cm cm kgf/cm = (GPa) Vp (kPa/cm) (N/cm)
Flexible-pipe 9 0.095 0,65 ( 64) 31 (0.30}
Medium-pipe 8.6 0.15 740 000 {72.6) 0.33 2.94 ( 288) 20 (0.20)
Rigid-pipe 9 0.35 32.6 (3 190) 35 {0.34}
1Sf=EpTa/12/(1-Vpa): a=D/2. Similarity law is (Sf/a a) in models=(Sf/a 3) in prototypes.
measure the vertical deflection of the pipe.
Fig. 2 shows 2-D models that simulate the following three types of pipe installations: ditch-type with sheet-piling (Ditch-S, the most common installation type in Japan), embankment-type (Embk.), and ditch- type without sheet-piling (Ditch-O). These models are constructed to be 1/30 of the test prototypes using Rigid-pipe and Flexible-pipe,and 1/31.4 of those using Medium-pipe. The table in Fig. 2 shows the dimensions of prototypes corresponding to standard models having a cover height H=D, a thickness of soil bedding Hb=4/9.D , a ditch width Ba=I3/9-D, and a width of the ground B=34/9-D. In the Ditch-S model, a pa~r of plain aluminum plates with a smooth surface is installed in a homogeneous model ground as model sheet-piles; their thicknesses were determined to be 15 cm in prototype scale considering the thickness of soil adhering to the concave parts of the extracted sheet-piles, which is usually observed in the actual construction. At both ends of the model ground in the Ditch-S and Embk. models, a pair of rigid steel plates with a smooth surface is installed as boundaries. The ditch in the Ditch-O model is formed by a
TOHDA ET AL. ON EARTH PRESSURE AND DEFORMATION 183
D i m e n s i o n s of p r o t o t y p e c o r r e - spo n di ng to s t a n d a r d m o d e l s (m)
_.---~:, , D H
e t - p i l e _ _
tuH-;L:!k)P:ILII-I r II pipe::R:li
(a) D i t c h - S (b) E m b a n k m e n t (Embk.)
H b B d B
1.2 3.9 10.2
(c) Ditch-O FIG. 2-- Mo d el s for t h e t h r e e t y p e s of pipe i n s t a l l a t i o n s .
pair of rigid steel plates with a rough surface, assuming that the natural ground does not deform during construction.
The models were put into a centrifugal acceleration field of 30 G or 31.4 G (G: gravitational acceleration) by using a centrifuge shown in Fig. 3. In the Embk. and Ditch-0 models, a load equivalent to the design load of a 20-ton vehicle was applied at the center of the ground surface by means of a strip loading plate 2 cm wide. In the Ditch-S models, a pair of the model sheet-piles was extracted simultaneously, and the surface load was applied afterwards. The simultaneous sheet-pile extraction method was adopted both to produce high earth pressure concentration on Rigid-pipe similar to that observed in the former field test [2], and to simplify the behavior of the model pipes.
Three kinds of soils: dry sand, decomposed granite and silty sand, whose properties are shown in Table 2, were used as ground materials.
The main difference among them is the content of the fine graded fraction with grain size under 0.075 mm. The decomposed granite is usually used as the backfill material in pipeline construction in Japan. Dense and loose grounds were prepared by pouring for the tests using the dry sand;
only loose ground was prepared by light compaction every 2 cm layers, for the tests using both the decomposed granite with a water content w=lO % and the silty sand with w=12 %. The pouring and compaction of the soils was performed in the direction of the longitudinal axes of the model pipes. The properties of the model grounds are shown in Table 3, together with the respective friction parameters against the pipe surface.
Table 4 shows the conditions and contents of the test s e r i e s ~ ~ a n d ~ The investigated factors, combined with the types of pipe installations, are: pipe flexibility and density of the dry sand in s e r i e s ~ ground material in s e r i e s ~ a n d three burial dimensions (H, H b and Bd) in s e r i e s ~ Since the standard models are common in all the test series, total number of the tests is counted as 36.
In flight ~ lff ~ , i
I
I i ~ "
256cm '
FIG. a - - C e n t r i f u g e .
184 BURIED PLASTIC PIPE TECHNOLOGY
TABLE 2--Properties of ground m a t e r i a l s . Grain size distribution
Soil Maximum ,75urn 75um, 5Bm-
{Classification) G s mm % % %
Pdmax Pdmin Wopt U c g/cm a g/cm a %
Dry sand (SP) 2.65 1.4 100 0 0
Decomposed (SF) 2.71 2.0 83.7 8.6 7.7
granite
Silty sand (SF) 2.67 2.0 69.6 16.9 13.5
2 1.58 1.32
70 1.92 1.37 11.4
115 1.86 1.18 13.5
TABLE 3--Properties of model grounds.
Soi I
Water Shear strength 2 Friction 3
content Pd Dc 1 Dr Cd ~d c ~p
w kgf/cm 2 kgf~cm 2
Density % g/cm a % % (kPa) degree (kPa) degree
Dry sand Dense 0 1.55 97 83 0 ( 0 ) 43 0 ( 0 ) 17
Loose 0 1.43 91 47 0 ( 0 ) 37 0 ( 0 ) 16
Decomposed
granite Loose 10 1.50 78 30 0.09 ( 8 . 8 ) 38 0.01(1.0) 24
Silty sand Loose 12 1.50 81 58 0.30(29.4) 32 0 ( 0 ) 25
1Dc=Pd/Pdmax, 2strength_under consolidated-drained condition obtained through direct shear test, and 3friction parameters against the smooth pipe surface obtained through direct shear apparatus.
TABLE 4--Conditions and contents of the tests.
Flexibi- Type of Cover Bedding Ditch
Test lity of Ground condition pipe in- height thickness width Number series pipe Soil Density stallation H (cm) H b (cm) B d (cm) of t e s t s
Flexible Ditch-S
(~) Medium Dry sand Dense Embk. 9 4 13
Loose
Rigid Ditch-0
Dry sand
Decomposed- Ditch-S
(~) Flexible granite Loose Embk. 9 4 13
Silty sand
Ditch-S 4.5
1~1 Flexible Dry sand Loose Embk. 9 4 13
Ditch-0 18 Ditch-S 1
( ~ ( ~ 2 Flexible Dry sand Loose Embk. 9 2 13
4 Ditch-S 13
( ~ 3 Flexible Dry sand Loose 9 4 17
Ditch-0 21
18
TOHDA ET AL. ON EARTH PRESSURE AND DEFORMATION 1 8 5