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OCR for page 68
68 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-
OCR for page 69
69 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.
OCR for page 70
70 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.