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66 600 500 400 Load (kips) 300 Virgin Soil 200 Length = 3.0 ft Length = 4.0 ft Length = 5.0 ft 100 Length = 6.0 ft Length = 7.0 ft 0 0.0 0.5 1.0 1.5 2.0 Displacement (in) Figure 6-8. Results of parametric study on the length of the mass mix zone beside the pile cap on the computed load-displacement curve. increasing mass mix length will increase the cost. The optimal the lateral load direction (see Figure 6-10). FEM analyses are length requires a balance analysis between engineering capacity conducted for variable soilcrete depths. The top of the soilcrete and economic efficiency. is assumed to be at the ground surface and the bottom of the soilcrete is at depths of 2.5, 5.0, 7.5, 10.0, and 12.5 ft as shown in Figure 6-10. Other soil and pile parameters are the 6.4 Jet Grout Depth Effect (Beside same as those described in Section 5.5. the Cap) on Lateral Resistance The load-displacement curves computed by the FEM This parametric study is very similar to that conducted for model are presented in Figure 6-11. The depth of the jet grout the mass mix treatment except that the improved soil is now beside the cap has a significant effect on the lateral resistance soilcrete produced by jet grouting, which has a higher strength of the pile group. The increased lateral resistance (or improve- than that from the soil mixing. The jet grout soilcrete is ment ratio minus 1) at the cap lateral displacement of 1.5 in. assumed to be at the side of the pile cap and has a length of is 13%, 25%, 31%, 35%, and 40% for the mass mix depth of 4 ft in the direction of loading with a width of 9 ft transverse to 2.5, 5.0, 7.5, 10.0, and 12.5 ft, respectively. 2 1.8 Improvement Ratio 1.6 y = 0.0607x + 1.1746 2 R = 0.9976 1.4 1.2 1 0 1 2 3 4 5 6 7 8 Length of Mass Mix (ft) Figure 6-9. Improvement ratio as a function of mass mix length adjacent to the cap.
OCR for page 66
67 Figure 6-10. Jet grout soilcrete depth intervals beside cap for parametric study. 500 450 400 Lateral Force (kips) 350 300 250 Virgin Soil 200 Depth to 2.5 ft 150 Depth to 5.0 ft 100 Depth to 7.5 ft Depth to 10.0 ft 50 Depth to 12.5 ft 0 0.0 0.5 1.0 1.5 2.0 Displacement (in) Figure 6-11. Parametric study of jet grout depth adjacent to the cap on the computed load-displacement curve.