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2.0 below the cap will dramatically increase the lateral capacity of
the pile group in virgin clay. A jet grouting soilcrete with the
1.8 height of 2.5 ft to 10 ft (2.4D to 9.4D) will increase the lateral
Improvement Ratio
capacity by approximately 40% to 85% for similar soil and pile
1.6 profiles. The slope of the trend line flattens somewhat as the
y = 1.0059x0.1291
R2 = 0.9953
soilcrete depth increases, which suggests that the upper layers
1.4 in the improved zone provide more lateral resistance than do
the lower layers.
1.2
It should be noted that the improvement ratio produced by
jet grout below the cap (1.40 to 1.85) is much higher than that
produced by jet grout beside the cap for the soilcrete with the
1.0
0 5 10 15 same depth. This result is likely a result of the larger cross sec-
Depth (ft)
tion (9 × 9 ft for the jet grouting soilcrete below the cap in this
section, 9 × 4 ft for jet grout beside the cap as in section 6.4)
Figure 6-12. Effect of jet grout depth beside the as well as the constraint of piles by the jet grouting. Again, the
cap on the improvement ratio for a lateral
improved soil below the cap will resist external load in any
displacement of 1.5 in.
direction.
It also is important to note that the increase in lateral resis-
Figure 6-12 plots the improvement ratio versus the depth of tance for the soilcrete produced by jet grouting was very sim-
the jet grout beside the cap. The equation for the best-fit trend ilar to that obtained for the soilcrete produced by mass mixing
is a power function. As was the case for the mass mix treatment, despite the lower compressive strength. This result suggests
the slope of the trend line flattens as the depth of the jet grout that lower strengths that can be produced by less expensive
soilcrete increases. This result suggests that the upper soilcrete treatment approaches might still be effective in improving the
zone carries more lateral resistance. Increasing the depth of the lateral resistance. This issue will be investigated further in a
jet grout zone beside the cap will increase the lateral capacity of subsequent parametric study.
the pile group; however, when the depth reaches a certain value
(roughly 10 times that of the pile diameter), increasing addi-
6.6 Jet Grout Length Effect (Beside
tional depth will only provide limited increases in lateral pile
the Cap) on Soil Improvement
group resistance relative to virgin clay.
This parametric investigation focuses on the block length
effect on the pile group lateral capacity for the jet grout mix
6.5 Jet Grout Depth Effect (Below
beside the cap. The jet grouting soilcrete has a fixed depth of
the Cap) on Soil Improvement
12.5 ft and a width of 9 ft (4.5 ft in the FEM model due to
For the numerical tests of the jet grout below the cap, the jet symmetry) perpendicular to the lateral load direction, and
grout soilcrete has the same cross section as the cap (length of has variable length from 3 ft to 7 ft along the lateral loading
9 ft in direction of loading and width of 9 ft perpendicular to direction (see Figure 6-16). Other soil and pile parameters are
the direction of loading). The bottom of the soilcrete block is kept the same as described in Section 5.5.
at depths of 5.0, 7.5, 10.0, and 12.5 ft below the ground surface The load-displacement curves calculated with the FEM
as shown in Figure 6-13. There is no linkage between the base model are presented in Figure 6-17 and the improvement ratio
of the cap and the top of the jet grouting block. Other soil and versus soilcrete length is provided in Figure 6-18. As the length
pile parameters remain the same as described in Section 5.5. increases, the load-displacement curves increase relatively con-
Figure 6-14 provides load-displacement curves computed sistently. The improvement ratios are 1.34, 1.40, 1.45, 1.51, and
by the FEM model. Again, the depth of the jet grout treatment 1.58 for the jet grouting soilcrete lengths of 3.0, 4.0 5.0, 6.0, and
below the cap is found to have a significant impact on the lat- 7.0 ft, respectively. The trend line in Figure 6-18 shows that the
eral resistance of the pile group. At a lateral pile cap displace- improvement ratio versus the jet grout soilcrete length is
ment of 1.5 in. the lateral capacity is increased by 40%, 59%, roughly linear, which is different from the nonlinear trend lines
74%, and 85% for the mass mix depths of 5.0, 7.5, 10.0, and associated with the jet grout depth as presented previously. The
12.5 ft, respectively. correlation equation shows that each additional foot of jet
Figure 6-15 provides a plot of the improvement ratio versus grouting soilcrete length will cause the improvement ratio to
the depth of the soilcrete below the cap. A best-fit curve and the increase by 0.06. This result is identical to that found for the
accompanying equation also are provided. These results sug- parametric study of soilcrete length with soil mixing. Since the
gest that the soil improvement method of jet grouting soilcrete passive pressure area is the same for various lengths of the soil-
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Figure 6-13. Jet grout depth intervals below cap for parametric study.
600
500
Lateral Force (kips)
400
300
Virgin Soil
200
Depth to 5.0 ft
Depth to 7.5 ft
100 Depth to 10.0 ft
Depth to 12.5 ft
0
0.0 0.5 1.0 1.5 2.0
Displacement (in)
Figure 6-14. Results of parametric study of the effect of
the mass mix depth below the cap on the computed
load-displacement curve.
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2.0
1.8
Improvement Ratio
1.6 0.3068
y = 0.8553x
2
R = 0.9987
1.4
1.2
1.0
0 5 10 15
Depth (ft)
Figure 6-15. Improvement ratio as a function of
jet grout treatment depth below the cap.
Figure 6-16. Jet grout treatment length intervals beside cap for parametric study.
