Vibro compaction of granular soils 95
3.6.5 Liquefaction evaluation of CPT data after
vibro compaction and stone column treatment
The ground improvement program for a Southern California church building
was completed in late 2007 and addressed the liquefaction-induced settlement under the site design earthquake. To accomplish the site liquefaction
mitigation, the soils were densified, drained, and reinforced. In general,
procedures for the liquefaction mitigation with vibro stone columns were in
accordance with the methods presented by Baez and Martin (1993) and Baez
(1995). The stone column program consisted of a primary spacing of 19 ft
(5.8 m) center-to-center and secondary columns at the midpoint of the square
grid to achieve a replacement ratio of 14.1%. Figure 3.46 shows a typical
soil profile and the stone columns. Totally 416 primary stone columns and
380 secondary columns were installed at the site with an average column
diameter of 3 ft (0.9 m) and a maximum column length of 48 ft (14.6 m).
A liquefaction evaluation was performed on the posttreatment CPT data
for this project. The following outlines the analytical approach and compares CPTs before and after the stone column treatment.
Liquefaction-induced settlement analyses were based on Tokimatsu and
Seed (1987) procedures and NCEER (1997) for site liquefaction evaluation.
To be conservative, the soil thin layer connection was not used. The site is very
close to an active fault and has a design earthquake magnitude of 6.6 and a
peak ground surface acceleration of 0.69 g. The site design water table depth
Settlement (mm)
Load (kN/m
2 )
0
−5
−10
−15
−20
−25
200
0
50
100 150
300
250
400
350
500
450
600
550
Figure 3.45 Typical pressure–settlement curve for a 2 × 2 m footing on vibro
compacted sand. (Courtesy of Keller Group plc, London, UK.)
Table 3.11 Settlements and moduli as obtained from load tests
Load test
p = 250 kN/m 2
Kp = 500 kN/m 2
Settlement s (mm)
Modulus* E (MN/m 2 ) n
Settlement s (mm)
1
3.06
145
13.27
2
2.54
173
9.44
3
2.55
173
6.81
* E = 0.88·p·B/s with footing width B = 2 m.
3.6.5 Liquefaction evaluation of CPT data after
vibro compaction and stone column treatment
The ground improvement program for a Southern California church building
was completed in late 2007 and addressed the liquefaction-induced settlement under the site design earthquake. To accomplish the site liquefaction
mitigation, the soils were densified, drained, and reinforced. In general,
procedures for the liquefaction mitigation with vibro stone columns were in
accordance with the methods presented by Baez and Martin (1993) and Baez
(1995). The stone column program consisted of a primary spacing of 19 ft
(5.8 m) center-to-center and secondary columns at the midpoint of the square
grid to achieve a replacement ratio of 14.1%. Figure 3.46 shows a typical
soil profile and the stone columns. Totally 416 primary stone columns and
380 secondary columns were installed at the site with an average column
diameter of 3 ft (0.9 m) and a maximum column length of 48 ft (14.6 m).
A liquefaction evaluation was performed on the posttreatment CPT data
for this project. The following outlines the analytical approach and compares CPTs before and after the stone column treatment.
Liquefaction-induced settlement analyses were based on Tokimatsu and
Seed (1987) procedures and NCEER (1997) for site liquefaction evaluation.
To be conservative, the soil thin layer connection was not used. The site is very
close to an active fault and has a design earthquake magnitude of 6.6 and a
peak ground surface acceleration of 0.69 g. The site design water table depth
Settlement (mm)
Load (kN/m
2 )
0
−5
−10
−15
−20
−25
200
0
50
100 150
300
250
400
350
500
450
600
550
Figure 3.45 Typical pressure–settlement curve for a 2 × 2 m footing on vibro
compacted sand. (Courtesy of Keller Group plc, London, UK.)
Table 3.11 Settlements and moduli as obtained from load tests
Load test
p = 250 kN/m 2
Kp = 500 kN/m 2
Settlement s (mm)
Modulus* E (MN/m 2 ) n
Settlement s (mm)
1
3.06
145
13.27
2
2.54
173
9.44
3
2.55
173
6.81
* E = 0.88·p·B/s with footing width B = 2 m.