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25 Prior to placing concrete in the test piles, a 1-in. diameter row piles were instrumented. The strain gauge depths were PVC pipe was installed to a depth of 30 ft in the middle pile in selected to provide the maximum negative and positive each row of each pile group. A shape accelerometer array could moments along the pile. For a fixed-head or restrained-head be inserted into this pipe at the beginning of the load tests so pile, the maximum negative moment is expected to occur that deflection versus depth profiles could be determined at at the pile-pile cap interface. Preliminary LPILE analyses various load increments. Using triaxial accelerometers embed- suggested that the maximum positive moment would likely ded into a flexible cable at 1-ft intervals, the shape arrays pro- occur between 11 and 13 ft below the top of the piles. Angle vided real-time displacement versus depth profiles throughout irons were welded on opposite sides of the instrumented piles the process of testing. To provide some check on the accuracy to a depth of 20 ft to protect the strain gauges during pile of the shape array measurements, inclinometer pipes were also driving. Data was recorded using two computer data acquisi- installed in the middle pile in the front and back rows of each tion systems. pile group. Inclinometer measurements were typically per- formed before testing and then again once the 1.5-in. or final 3.6 Pile Group Tests displacement increment had been reached. Bending moment in Untreated Clay along the length of the piles was evaluated using two comple- mentary procedures. First, the deflection versus depth curves Plan and profile drawings showing the layout of the pile obtained from the shape array data were used to determine group in untreated clay for Tests 1 and 2 are provided in Fig- bending moment versus depth profiles along the length of ure 3-14. Tests 1 and 2 were performed to provide a baseline of the pile. The moment, M, was computed using the following the lateral load behavior of the pile caps in virgin soil con- equation: ditions prior to any soil treatment. Test 1 was conducted by pulling the caps together using the actuator while the untreated EI ( y -1 - 2 y0 + y1 ) native soil was in place adjacent to the pile cap. At the comple- M= (5) h2 tion of Test 1, the pile cap was pulled back to zero deflection, but after the actuator load was released some residual deflec- where tion remained. Prior to Test 2, the soil immediately adjacent to E is the elastic modulus of the pile; the opposite face of the pile cap was excavated by hand to cre- I is the moment of inertia of the pile; ate roughly a 1-ft-wide gap between the pile cap face and the y-1, yo, and y1 are the horizontal pile deflections at locations adjacent soil as shown in Figure 3-14. This excavation elimi- 12 in. above, at the depth, and 12 in. below the depth of nated passive force against the pile cap for the subsequent test. interest; and After excavation was complete, which required less than an h is the vertical spacing between the deflection (12 in.). hour to accomplish, Test 2 was carried out by pushing the pile For the steel pipe pile with concrete fill, this required a cal- caps apart using the actuator. The testing was performed using culation of the composite properties. These calculations the same procedure described previously. Test 2 was designed indicated that EI was 1.415 107 kip-in2 using a compressive to define the passive force provided by the unsaturated clay soil strength of 5100 psi based on compression tests on concrete against the pile cap. cylinders at the time of testing. The moment computed using Equation 5 is very sensitive to minor variations or errors in the Load versus Displacement measured displacement versus depth curves. To reduce the influence of minor variances in the measured displacement Plots of the complete pile cap load versus displacement data on the computed moment, a 5th-order polynomial equa- curves for Cap 1 are provided in Figure 3-15. This plot provides tion was developed based on the measured data to smooth the the load path taken during loading, unloading, and reloading displacement versus depth curves. The displacements used for each cycle. At the end of each loading cycle it was necessary in Equation 5 were then based on values computed with the to apply a tensile force to bring the actuator deflection back to polynomial equation. Although the difference in the displace- zero. This does not appear to be a result of yielding in the pile ment values at any depth were generally very small, this pro- based on measured moments. The behavior could result from cedure produced moment versus depth curves with more a flow of weak soil into the gap behind the pile during loading realistic shapes. or lateral resistance due to side shear on the pile as it moves in Secondly, waterproof electrical resistance type strain gauges the opposite direction. During reloading, the load is typically were placed at depths of 2, 6, 11, and 13.5 ft below the top of less than that obtained during virgin loading and considerably two to three piles within each group. For Pile Cap 1, the mid- more linear, but after the load exceeds the maximum previ- dle piles within each row were instrumented with strain gauges ous load, the load increase and the load deflection transitions while for Pile Cap 2, the middle piles within the front and back into what appears to be the virgin curve.

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N Figure 3-14. Plan and profile drawings of Pile Caps 1 and 2 during Test 1 when the pile groups were pulled together by the actuator. (During Test 2, the soil adjacent to the pile cap was excavated to the base of the cap and the pile caps were pushed apart by the actuator.)

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27 350 300 250 200 150 Load (kips) 100 50 0 -50 -100 -150 -200 -0.5 0 0.5 1 1.5 2 Displacement (in) Figure 3-15. Complete pile cap load vs pile head deflection curve for Cap 1 during Test 1. The virgin pile head load versus displacement curves for erties across the site are sufficiently uniform for valid com- each pile group have been developed in Figure 3-16 by plotting parisons to be made between the pile caps with various soil the peak values and eliminating the unload and reload seg- improvement techniques relative to the untreated conditions. ments. The curve exhibits the conventional hyperbolic shape that would be expected for a pile in soft clay. Despite the fact Rotation versus Load that the two pile groups are 32 ft apart and have minor varia- tions in construction details, the two load-displacement curves Pile cap rotation versus load curves based on the string are nearly identical. These results suggest that the soil prop- potentiometer and shape arrays for Cap 1 are provided in 350 300 250 Load (kips) 200 150 T1 Cap 1 100 T1 Cap 2 50 0 0 0.5 1 1.5 2 Displacement (in) Figure 3-16. Peak pile cap load vs pile head deflection curves for Caps 1 and 2 during Test 1.

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28 Displacement versus Depth Curves Displacement versus depth curves obtained from the shape accelerometer arrays in the piles within Pile Cap 1 are provided in Figure 3-18. One of the shape arrays in each pile cap appeared to be providing unrealistic information, which was likely due to damage from previous field testing. As a result, profiles are only provided for two shape arrays in each cap. The location of the shape arrays relative to the piles in the group and the loading direction are shown by the legends in each fig- ure. The average displacements measured by the string poten- tiometers at the elevation of the load application for each load increment are also shown in these figures for comparison pur- poses. The displacements obtained from the shape arrays Figure 3-17. Peak pile cap rotation vs load for Caps 1 are generally quite consistent with those measured by the and 2 during Test 1. string potentiometers; however, in some cases, variations are observed. The discrepancies appear to be related to the difficulty of providing a tight fit between the shape array and Figure 3-17. The curves are fairly linear up to a load of about the surrounding PVC pipe in some cases. The deflected shape 170 kips after which the rotation begins to increase more curves are generally consistent with a restrained-head bound- rapidly with load. The measured rotations are fairly consis- ary condition. Some rotation is observed, but the rotation is tent for both caps, although the rotation of Cap 1 is some- small relative to a free-head pile subjected to the same load lev- what greater than that for Cap 2. Although pile cap rotation els (see single pile test results). It appears that the shape arrays is clearly observed, it is considerably lower than the rotation were long enough to extend below the depth where lateral dis- of the single pile under free-head conditions. placements dropped off to zero. Array 104 Test 1 Array 106 Test 1 Cap 1 Middle Pile Cap 1 North Pile Horizontal Displacement (in) Horizontal displacement (in) -0.5 0.0 0.5 1.0 1.5 2.0 -0.5 0.0 0.5 1.0 1.5 2.0 0 0 5 5 Depth From Top of Corbel (ft) Depth From Top of Corbel (ft) 10 10 Load Load 15 15 A-142 A-104 A-106 A-142 A-104 A-106 1-S 1-M 1-N 1-S 1-M 1-N 20 20 0.125 in 0.125 in 0.5 in 0.5 in 25 0.75 in 25 0.75 in 1.0 in 1.0 in 1.5 in 1.5 in Average String Pot Average String Pot 30 30 Figure 3-18. Deflection vs depth curves at several deflection increments for Pile Cap 1 during Test 1.

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29 Figure 3-18 provides comparisons between the displace- curves with little evidence of strong group interaction effects ment versus depth curves obtained from the shape arrays and for the displacement levels involved. The agreement between the two inclinometer pipes in Pile Cap 1. Since inclinometer the curves computed by the strain gauges and shape arrays soundings were only taken at the maximum displacement, varies. comparisons are only provided for one increment. Because the inclinometer soundings required 20 minutes to perform the Test 2 Results after Excavation displacement profiles from the shape arrays are sometimes dif- Adjacent to Pile Cap ferent than the values for the 1.5-in. displacement increments shown in Figure 3-19. The displacement profiles from the As previously indicated, the two pile caps were pulled back shape arrays are quite consistent with the profiles from the to zero displacement at the end of Test 1. However, when the inclinometers. These results provide increased confidence in load was released, the caps relaxed back toward the direction the accuracy of the profiles. It should be noted, however, that they had previously been pushed leaving a residual (negative) the inclinometer profiles, which extend deeper into the pile, displacement offset of about 0.3 in. at the start of Test 2. indicate that some negative displacement is occurring below Because the pile caps during Test 2 were pushed in the oppo- the base of the shape arrays. site direction to those from Test 1, the residual deflection is given a negative sign. Figure 3-22 provides a comparison between the load-displacement curves for Caps 1 and 2 during Maximum Moment versus Load Curves Tests 1 and 2. The load-displacement curves for Test 2 have Figures 3-20 and 3-21 provide plots of the maximum nega- been shifted right slightly (0.15 in.) to account for gap effects tive and positive bending moments versus applied pile cap so that the curve for Cap 2 matches the curves for Caps 1 and load, respectively, for Cap 2 during Test 1. Moment data come 2 during Test 1 at larger displacements than would be expected. from both shape array and strain gauge data when available. A comparison of load-displacement curves for Cap 1 with and Initially, the curves are relatively linear; however, the bending without passive force on the pile cap can then be made and the moment tends to increase more rapidly with load at the higher results indicate that the passive force is approximately 50 kips. load levels as soil resistance is overcome. The curves from the Based on the curves in Figure 3-22, the passive force versus strain gauges provide relatively consistent moment versus load displacement curve shown in Figure 3-23 has been developed, Array 104 Test 1 Array 106 Test 1 Cap1 Inclinometer Com p arison Cap 1 Inclinometer Com p arison Horizontal Displacement (in) Horizontal Displacement (in) -0.5 0.0 0.5 1.0 1.5 2.0 -0.5 0.0 0.5 1.0 1.5 2.0 0 0 5 5 10 10 Depth From Top of Corbel (ft) Depth From Top of Corbel (ft) 15 15 20 Load 20 Load A-142 A-104 A-106 A-142 A-104 A-106 25 25 1-S 1-M 1-N 1-S 1-M 1-N 30 30 35 Final Middle Array 35 Final North Array Final North Inclinometer Final North Inclinometer 40 Final South Inclinometer 40 45 45 Figure 3-19. Comparison of displacement vs depth curves measured by shape arrays and inclinometers for Cap 1 during Test 1.

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30 (a) Test 1 Maximum Negative Moments in Pile 1-N 80 70 Strain Gage Maximum Moment (kip-ft) 60 50 40 30 Load 20 A-142 A-104 A-106 10 1-S 1-M 1-N 0 0 50 100 150 200 250 300 Maximum Load (kips) (b) Test 1 Maximum Negative Moments in Pile 1-M 120 100 Maximum Moment (kip-ft) Strain Gage Array 104 80 60 Load 40 A-142 A-104 A-106 20 1-S 1-M 1-N 0 0 50 100 150 200 250 300 Maximum Load (kips) (c) Test 1 Maximum Negative Moments in Pile 1-S 80 70 Strain Gage Maximum Moment (kip-ft) 60 50 40 Load 30 20 A-142 A-104 A-106 1-S 1-M 1-N 10 0 0 50 100 150 200 250 300 Maximum Load (kips) Figure 3-20. Maximum negative moment vs total pile cap load for Piles (a) 1-N, (b) 1-M, and (c) 1-S in Cap 2 during Test 1.

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31 (a) Test 1 Maximum Positive Moments in Pile 2-N 80 70 Strain Gage Array 134 Maximum Moment (kip-ft) 60 50 40 Load 30 20 A-112 A-115 A-134 2-S 2-M 2-N 10 0 0 50 100 150 200 250 300 Maximum Load (kips) (b) Test 1 Maximum Positive Moments in Pile 2-M 80 70 Maximum Moment (kip-ft) 60 Array 115 50 40 30 Load 20 A-112 A-115 A-134 2-S 2-M 2-N 10 0 0 50 100 150 200 250 300 Maximum Load (kips) (c) Test 1 Maximum Positive Moments in Pile 2-S 120 100 Maximum Moment (kip-ft) 80 Strain Gage 60 Load 40 A-112 A-115 A-134 2-S 2-M 2-N 20 0 0 50 100 150 200 250 300 Maximum Load (kips) Figure 3-21. Maximum positive moment vs total pile cap load for piles (a) 2-N, (b) 2-M, and (c) 2-S in Cap 2 during Test 1.