Water jetting can be utilized as an effective aid to impact pile driving when hard strata are encountered above the designated pile tip elevation. During jetting, the immediate
neighborhood of the pile is first liquefied due to high pore pressure induced by the water jet and subsequently densified with its dissipation. In addition, the percolating water also creates a filtration zone further away from the pile. Hence, jetting invariably causes substantial disturbance to the surrounding soil, which results in a notable change in the lateral load behavior. Tsinker (1988) and Hameed et al. (2000) investigated the lateral load performance of driven and jetted-driven model piles installed under the samein situsoil conditions, by comparing the normalizedp−ycurves of driven piles to those of jetted-driven piles (Figure 8.28). They also explored the effect of jet water pressure, soil unit weight, and groundwater conditions on thep−ycharacteristics. Based on the above study, Hameed et al. (2000)
developed approximate guidelines for predicting the lateral load behavior of jettedpiles based on that of piles impact drivenunder similar soil conditions.
FIGURE 8.28
Comparison ofp–ycurves of driven (UD1) and jetted (UJ2) piles. Hameed, R.A., 1998, Lateral Load Behavior of Jetted and Preformed Piles, Ph.D. dissertation, University of South Florida, Tampa, FL. With permission.)
In the Hameed et al. (2000) study,Kmaxratios(Kjet/Kdriven)and puratios(pu,jet/Pu,driven)obtained from the model testing program were plotted against the nondimensional jetting pressure (π3=P0/k2γ) (k=permeability coefficient of the foundation soil) and are shown inFigure 8.29 and Figure 8.30, respectively. Each data point represents the mean of five ratio values. TheK- ratio and pu-ratio can be related to nondimensional jetting pressure by Equations (8.53a) and (8.53b). The foundation soil was a sand contaminated by bentonite clay.
FIGURE 8.29
Effect of pile jetting onKmax. (From Hameed, R.A., Gunaratne, M., Putcha, S., Kuo, C, and Johnson, S., 2000,ASTM Geotech. Testing J.,23(3). With permission.)
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FIGURE 8.30
Effect of pile jetting onpu. (From Hameed, R.A., Gunaratne, M., Putcha, S., Kuo, C., and Johnson, S., 2000,ASTM Geotech. Testing J.,23(3). With permission.)
(8.53a)
(8.53b) where, α1,α2,β1,and β2are soil type dependent parameters which can be determined by the respective intercepts and slopes. Equations (8.53) and (8.54) produce on a log-log scale. The fitted values are shown in Table 8.2(a)and (b).
TABLE. 8.2
Parameters for Equations (8.53a) and (8.53b) Constant γ=16.2 kN/m3
Unsaturated Saturated γ=14.8 kN/m3
Unsaturated Saturated (a) Equation
(8.53a)
α1 165.32 748.82 110.8 237.42
β1 −0.323 −0.323 −0.323 −0.323
(b) Equation (8.53b)
α2 3509.67 797.02
β2 −0.4 −0.4
The values for β1andβ2seem to be independent of the unit weight of the foundation medium and the groundwater condition. On the other hand, the values ofα1andα2seem to increase with the foundation medium unit weight. Hence, one can assume the variation of α1
and α2to be linear proportional to the unit weight of the foundation medium.
Example 8.6
If a fieldp-ycurve of adriven pilein a clayey sand similar to the soil tested by Hameed et al. (2000) is available based on either (1) experimental data, (2) Reese et al. (1974) method (Figure 8.25), or (3) Murchison and O’Neill’s (1984) method (Figure 8.26), and if one neglects the possible errors due to scale effects, then one can generate thep-ycharacteristics for a pile to bejettedin the same soil type using the following procedure.
Solution
In order to illustrate this, assume that ap-ycurve based on Murchison and O’Neill’s (1984) method is available for a driven pile in a clayey sand site (with k=1.592×10−3cm/sec and γd=15.76 kN/m3above the groundwater table) and that the relevant Murchison and O’Neill parameters at a 3D depth are Ad=1,pu,d=900.00 kPa, and Kmax,d=30000.00 kN/m3(Figure 8.27). The subscript “d” indicates a driven pile. Using these values, the correspondingp-y curve can be plotted inFigure 8.30.
Also assume that one is interested in synthesizing ap-ycurve at a depth of 3Dfor a field jetting pressure of 861.88kPa (125 psi). The equivalent nondimensional jetting pressures corresponding to the above soil properties must be determined by the nondimensional jetting pressure,(P0/k2γ)(Table 8.3). The constants α1,α2,β1,andβ2can be obtained by linear interpolation based on the values given inTable 8.2(a)and (b).Table 8.3shows the interpolated values for a 15.76 kN/m3unit weight. It has beenassumedthat the range of valuesshown inTable 8.2is generally valid for any combination of unit weight and permeability for soils similar to the one tested by Hameed et al. (2000).
Using Equations (8.53a) and (8.53b), andTable 8.3, theK-ratio andpu-ratio can be determined as 0.14 and 0.43, respectively. Thus, the correspondingp-yparameters at a 3D depth, for the pile to be jetted at 861.88 kPa are,Aj=1.0, Kmax,j=4200.00 kN/m3, and pu,j=387 kPa. The correspondingp-ycurve is also plotted inFigure 8.31. This example shows how one can use Equation (8.53) to generatep-ycurves for a pile to be jetted at any desired pressure in the field. It must be noted that the same procedure can be extended to p-ycurves fordriven piles also available in terms of the Reese et al. (1974) method or experimental data.
TABLE 8.3
Interpolated Parameters for Use in Equations (8.53a) and (8.53b)
Unit weight (kN/m3) P0/k2γ α1 α2 β1 β2
15.76 2.11×109 147.90 2322.96 −0.323 −0.4
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FIGURE 8.31
Synthesizedp–ycurve for the jetted pile. (From Hameed, R.A., Gunaratne, M., Putcha, S., Kuo, C, and Johnson, S., 2000,ASTM Geotech. Testing J.,23(3). With per-mission.)