Geoscience Reference
In-Depth Information
Fig. 15.45. Time history of excess pore water pressure withand without mitigation
of screen pipes (Harada et al., 2006)
Case 1 No drain
Case 2 Drain spacing = 100mm both inside and outside
Case 3 Spacing reduced to 60mm outside group pile
Case 4 Drain surrounding group pile (60mm spacing)
1000
Drain
installation
800
600
No drain
400
:case1
:case2
:case3
:case4
200
0
0
400
600
800
1000
200
Intensity of base acceleration (Gal)
Fig. 15.46. Amplification ofacceleration with and without screen pipes
(Harada et al.,2006)
grouppiledissipatedquicklywhenscreenpipeswereinstalled,whilethosewithoutpipes
lastedforalongtime.Itisalsoshownthatporepressureinthefreefield(farfromscreen
pipes) did not dissipatequickly.
It should be recalled, however, that the use of drains increases the response acceleration
atgroundsurfaceandthepilecap.Figure15.46comparestheaccelerationinthepilecap
infourcases:(1)withoutscreenpipedrain,(2)screenpipeswithspacingof100mmboth
inside and surrounding the group pile, (3) spacing was maintained at 100mm inside the
group pile, while reduced to 60mm outside, and (4) pipes were installed only outside
with spacing of 60mm as already illustrated in Figure15.43. Case 1 without drainage
indicates reduced acceleration in pile cap due to subsoil liquefaction and its insulation
