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32 350 300 250 Load (kips) 200 150 T2 Cap 1 100 T2 Cap 2 T1 Cap 1 50 T1 Cap 2 0 -0.5 0 0.5 1 1.5 2 Displacement (in) Figure 3-22. Comparison of peak pile cap load vs pile head deflection curves for Caps 1 and 2 during Tests 1 and 2. which indicates that the full passive force was essentially devel- the pile group. A single-hole double fluid jet grouting tech- oped with a displacement of about 0.75 in. Additional test nique was employed to form the grout columns and each of the results for Test 2 are provided in Adsero (2008, Appendix 2). columns was constructed with identical installation param- eters. The jet grout drill head was initially advanced to the base of the treatment zone using water jets and a drill bit located at 3.7 Pile Group Load Tests the bottom of the drill rod. Subsequently, the drill head was Involving Jet Grouting rotated and pulled upward at a constant rate, while cement Plan and profile views of the jet grout columns around Pile slurry was injected at a specified pressure and flow rate from Caps 1 and 2 are shown in Figure 3-24. Jet grouting treatment the inner orifice of the drill nozzle. Concurrently, compressed for Pile Cap 1 involved treatment adjacent to the pile group. air was injected from the outer orifice of the drill nozzle to Treatment for Pile Cap 2 involved treatment below and around form a protective shroud around the slurry jet to improve the 200 150 Passive Force (kips) 100 50 0 0 0.5 1 1.5 2 Displacement (in) Figure 3-23. Interpreted passive force vs deflection curves based on comparison of Tests 1 and 2 on Pile Cap 1.

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N Figure 3-24. Plan and profile views of Pile Groups 1 and 2 after treatment with jet grouting.

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34 erosive capacity of the cement slurry jet. The grout slurry mix Table 3-3. Jet grouting installation had a specific gravity of 1.52, which is equivalent to a 1:1 water parameters for columns installed to cement ratio by weight. adjacent to Pile Cap 1. Column Length 12 ft Jet Grout Treatment below Pile Cap 2 Estimated Column Diameter 4 ft Grout Pressure 6000 psi A total of eight 5-ft diameter soilcrete columns were installed Grout Flow Rate 90 gallons/min beneath and around Pile Cap 2 to a depth of 10 ft below the bot- Rotation Speed 8 revolutions/min tom of the pile cap. Four of the columns were installed at the Pull Rate 1 in./min periphery of the pile cap, and an additional four were installed through the cap itself. During construction of the pile cap, four 6-in. diameter PVC pipes were placed in the pile cap between the rebar to allow easy access to the jet grout pile after construc- shown in Figure 3-24. The target diameter of each of the tion. After constructing the cap, backfill soil was placed over columns was 4 ft and they were spaced 3-ft-on-center in a tri- the cap to allow the jet grout rig to move over the cap. Four angular pattern. This created an overlap between columns of PVC pipes were extended to the ground surface to provide the approximately 1 ft. Each jet grout column extended from jet grout drill rod with an unobstructed path through the fill the top of the pile cap to a depth of 12 ft below the top of the material and the pile cap. For retrofit projects these access holes pile cap. The centers of the first row of jet grout columns would have to be drilled through the pile cap. The jet grout were positioned so that the jet could cut underneath the pile columns were spaced at approximately 3 ft center-to-center in cap and produce a soilcrete wall that would intersect the front the north-south direction and 5 ft center-to-center in the east- row of piles. Based on the target column diameter, the soil- west direction. This likely produced a 2-ft overlap between crete columns likely extended about 1.5 ft under the pile cap, columns in the north-south direction, but there was little or no or about to the middle of the outside row of piles. overlap between columns in the east-west direction. The grout Each of the columns was constructed using identical con- treatment extended about 3 ft beyond the front and back struction parameters that are summarized in Table 3-3. One ends of the cap and somewhat beyond the cap on the top and rotation of the high-pressure nozzles occurred in a 0.14-in. lift. bottom sides. Based on the column diameter, flow rates, pull rates, and rota- Each of the columns was constructed with identical instal- tion rates, the cement content for each jet grout column would lation parameters. These parameters are summarized in be expected to be about 24 lbs/ft3 or about 20% cement by Table 3-2. One rotation of the high-pressure nozzles occurred weight. in a 0.11-in. lift. Based on the column diameter, flow rates, pull rates, and rotation rates, the cement content for the jet grout Compressive Strength Testing columns would be expected to be about 26 lbs/ft3 or about 20% of Jet Grout Columns by weight. Wet grab samples were taken from five completed columns below Cap 2 and two columns adjacent to Cap 1. The samples Jet Grout Treatment Below Cap 1 were taken from locations near the top, middle, and bottom of A total of seven soilcrete columns were installed in two rows the columns. In addition, core samples were taken from the top to create a wall along one edge of the foundation. Plan and pro- of two columns adjacent to Cap 1 a few weeks after treatment. file views of the jet grout columns adjacent to Pile Cap 1 are Prior to testing, the cored samples measured 4 in. in diameter with an approximate length to diameter ratio of 2.0. The unconfined compressive strength of the soilcrete pro- Table 3-2. Jet grouting installation duced by the jet grouting process was evaluated using the wet parameters for columns created grab samples as well as core samples. Figure 3-25 provides a beneath Pile Cap 2. summary of the compressive strength test results as a function Column Length 10 ft of time after treatment. Although there is significant scatter to the data, which is typical for soilcrete columns installed using Estimated Column Diameter 5 ft jet grouting, there is a trend of increasing strength with curing Grout Pressure 6000 lbs/in.2 time. Although the compressive strength of the untreated soil Grout Flow Rate 90 gallons/min prior to treatment was approximately 4 psi, the average com- Rotation Speed 7 revolutions/min pressive strength after jet grout treatment reached about 680 psi Pull Rate 0.79 in./min with mean 1 standard deviation bounds ranging from about

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35 1200 Column 1 Column 2 1000 Column 3 Column 6 Mean + Std Dev. Column 7 Column 10 800 Column 14 Cored Samples Strength (psi) 600 Mean Wet-Grab Sample Strengths 400 Mean - Std Dev. Core 200 Sample Design Strength Range 0 0 5 10 15 20 25 30 35 40 Curing Time (Days) Figure 3-25. Compressive strength of jet grout columns as a function of time after treatment along with design strength values typically employed by geotechnical specialty contractors. 500 to 800 psi. These strength gains are typical for jet grouting combined curve had a maximum load of 612 kips at a pile cap applications in similar soils (Burke, 2004). Ground improve- displacement of 0.72 in., which is 398 kips greater than the ment specialty contractors typically use a design value of 214 kip maximum load from the virgin curve for the same dis- about one-third the value measured from field test specimens placement. This represents an increase in lateral resistance of to account for variations in properties within the treated zone. 185% at the maximum measured deflection. Using this approach, the compressive strength of the jet grouted Tests were also performed on Pile Cap 1 after the soil adja- zone would be about 250 psi; however, even cored specimens cent to the pile cap had been excavated. Despite excavation of had strengths of 480 psi as shown in Figure 3-25. The average the soil, the load-displacement curve was essentially the same strength from two cored samples is about 30% lower than the after consideration of reloading effects (typically a 10% reduc- strength obtained from the wet grab samples. The strength tion). Although the soilcrete mass was not connected to the pile from the core samples is likely more representative of in-situ cap, it was connected to the piles below because jet grouting conditions and is attributable to the poorer mixing produced by extended under the cap. Therefore, lateral movement of the the jet grouting process relative to the hand mixing employed piles engaged the soilcrete mass and produced the same lateral with the wet grab samples. resistance. Test Results for Cap 1 Test Results for Pile Cap 2 (Jet Grouting Adjacent to Cap) (Jet Grouting below the Cap) Treating the soil adjacent to Pile Cap 1 with jet grouting Figure 3-27 presents a plot of the load-displacement curve increased the lateral resistance of the pile cap substantially. The for Pile Cap 2 after jet grouting in comparison with the virgin results from Test 3 and Test 6 were combined to create a com- load-displacement curves. Comparing the resistance at a dis- posite load-displacement curve for the pile cap following jet placement of 1.5 in., jet grouting increased the lateral pile cap grouting. The combined curve is presented in Figure 3-26. The resistance from 282 kips to nearly 782 kips. This increase of