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85
estimating the undrained shear strength acting along the sides olation beyond the results investigated herein is not recom-
(assuming the shear strength profile varies with depth). If the mended. With any simplified approach, some discrepancy is
treatment block projected area contains a horizontal base, anticipated, and 15% would appear to be within the realm of
the adhesion acting on the base of the block also should be sufficient accuracy and precision for general design purposes.
included. If the treatment depth is deeper, a tension crack is The graph in Figure 7-15 provides a comparison of results
expected to develop behind the trapezoidal block beneath the including the FE parametric studies involving changes in the
bottom of the pile cap, thereby nullifying any base adhesion. treatment depth. The FE results and projected area dimensions
were presented in Figures 7-11 and 7-13, respectively. For all
cases, excellent agreement is obtained and further substanti-
Incorporation of the Lateral Resistance ates truncating the projected area depth at three times the
from the Treated Soil Mass into embedded pile cap depth.
the Analysis of the Pile Group
The proposed method decouples the limit equilibrium
7.5 Evaluation for Jet
analysis of the treated soil mass from the analysis of the pile
Grouting Cases
group. The magnitude of lateral resistance provided by the
projected area is computed in accordance with the methodol- Similar to the mass mix tests, jet grout ground improvement
ogy outlined previously. In order to incorporate this contri- techniques were performed in or around the pile groups and
bution into the analysis of the foundation response using tested to evaluate the benefit on performance of the group
available software (such as GROUP or similar), the magnitude under lateral loading. Jet grout ground improvement was con-
of the applied horizontal force acting on the pile group is structed adjacent to Pile Cap 1 and the leading row of piles in
reduced by the contribution of the treated soil mass. the group, as shown in Figure 7-16. It also was constructed
To illustrate the applicability of this simplified approach, beneath Pile Cap 2 around the piles in the group.
Figures 7-14 and 7-15 have been developed for comparison The plan dimensions provided in Figure 7-16 indicate a
purposes. The plots in Figure 7-14 provide a comparison of treatment area of 10 ft perpendicular to the direction of load-
results including the FE parametric studies involving changes ing and 15 ft parallel to the loading. The profile dimensions
in the treatment dimension parallel to the direction of loading. indicate ground improvement from the bottom of the pile cap
The FE results and projected area dimensions were presented to a depth of 12.5 ft below ground surface. All dimensions
in Figures 7-10 and 7-12, respectively. For all cases, the simpli- defining jet grout ground improvement must be considered as
fied approach is within 15% of the FE model. Less agreement estimates only. Neat lines do not exist considering the nature
is apparent for increasing dimensions of treatment, so extrap- of the jet grout process.
275
250
225
Passive + Adhesion (kips)
200
175
150
125
100
75
Simplified (Rankine + Adhesion)
50 Modeled (FE & GROUP)
Modeled + 15%
25
Modeled -15%
0
0 1 2 3 4 5 6 7 8
Mass Mix Treatment Dimension in Direction of Loading (ft)
Figure 7-14. Simplified and FE results with varying treatment width.

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86
180
160
140
Passive + Adhesion (kips)
120
100
80 Simplified (Rankine + Adhesion)
Modeled (FE & GROUP)
60
40
20
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Mass Mix Treatment Depth (ft)
Figure 7-15. Simplified and FE results with varying treatment depth.
Schematic plan view of Test 4.
Figure 7-16. Layout of test for pile group with jet grout treatment.

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The unconfined compressive strength of the jet grout The lateral resistance provided by the jet grout ground
improved soil at the time of the tests is estimated to be greater improvement is estimated using a limit equilibrium approach,
than 600 psi. Further discussion of the strength is provided and the contribution of the improved soil incorporated into the
in Chapter 4. However, the results of these analyses, as with analysis by reducing the magnitude of the applied force by the
the FE analyses, are not sensitive to the strength of the jet contribution to lateral resistance from the block of improved
grout improved soil since it is significantly stronger than ground. This reduced force is then used in GROUP (or
the in-situ soil. equivalent) to compute the response of the pile group separately
The first attempt at testing the two groups was not success- from the contribution of the improved ground.
ful. Because only one actuator was initially used, the load to The passive resistance is estimated using Rankine earth pres-
produce significant deflection was not available. Accordingly, sure theory and should be truncated at a depth equal to the
an additional actuator was used in series with the first to dou- width of the group from outside pile edge to outside pile edge
ble the horizontal load applied to Cap 2. However, additional perpendicular to the direction of loading. The adhesive resis-
loading capacity was not available for Cap 1. The measured tance along the sides of the treatment block, also truncated
load-displacement curves for Caps 1 and 2 are provided in with depth, is estimated using pass=0.9 times the undrained
Figures 3-26 and 3-27, respectively. The maximum loading shear strength. The undrained shear strength may be com-
magnitude applied to Caps 1 is about 450k, slightly more than puted using a weighted average over the surface of the block.
half the 800k maximum load applied to Cap 2. The 800k The adhesive resistance along the base should also be included
maximum load applied to Cap 2 appears to initiate an ulti- in a similar manner to that along the sides. This simplified pro-
mate, or limit state, condition with excessive deflection under cedure is shown graphically in Figures 7-17 and 7-18 for the
constant load. actual and simplified cases, respectively.
The simplified procedure described previously is compared Considering the jet grout ground improvement geometry
with the results of the jet grout ground improvement, based on beneath Cap 2 and the unit passive resistance and shear strength
the results measured at Cap 2 (jet grout beneath cap and versus depth data presented in Figure 7-9, the summation of
around piles). Insufficient load versus deflection data exist for passive and adhesive resistance can be estimated as follows for
Cap 1 to draw definitive conclusions. However, based on the the truncated depth:
similar load-deflection behavior observed at both caps at rela-
tively small displacements, and the applicability of the simpli- · Passive Resistance: 10 ft × 7.5 ft × 1.85ksf = 139k
fied procedure to mass mix or jet grout improved soils, it is where 10 ft is the treatment dimension perpendicular to
considered reasonable that the simplified procedure is appro- loading,
priate for conditions tested at Cap 1. where 7.5 ft is the truncated depth, and
1
0 Ground Surface
-1
-2
-3
-4
-5
Feet
-6
-7
-8
-9
-10 Jet Grout
-11
-12
-13
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Figure 7-17. Jet grout test as performed (Cap 2).

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2 Reduced Load
1
0
-1
-2
-3
Passive
Adhesion (2 Sides)
-4 Resistance
-5
Feet
-6
-7
-8
Adhesion (Base)
-9 Truncated Depth
-10
-11
-12
-13
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Figure 7-18. Forces on pile cap for simplified procedure for jet
grout test.
where 1.85 ksf is the average unit passive resistance over where 1.84ksf is the average unit passive resistance over
the truncated depth. the treatment depth.
· Adhesive Resistance (sides): 2 sides × 5 ft × 15 ft × 0.9 × · Adhesive Resistance (sides): 2 sides × 10 ft × 15 ft × 0.9 ×
0.58ksf = 78k 0.56ksf = 151k
where 5 ft is the truncated treatment depth beneath the where 10 ft is the truncated treatment depth beneath
cap (note the sides of the cap are not in contact with the the cap (note the sides of the cap are not in contact with
soil), the soil),
where 15 ft is the treatment dimension parallel to loading, where 15 ft is the treatment dimension parallel to loading,
where 0.9 is pass, and where 0.9 is pass, and
where 0.58 ksf is the average undrained shear strength where 0.56 ksf is the average undrained shear strength
over this depth. over this depth.
· Adhesive Resistance (base): 10ft × 15ft × 0.9 × 0.58ksf = 78k
· Adhesive Resistance (base): 10 ft × 15 ft × 0.9 × 0.50ksf = 68k
where 10 ft is the treatment dimension perpendicular to
where 10 ft is the treatment dimension perpendicular to
loading,
loading,
where 15 ft is the treatment dimension parallel to
where 15 ft is the treatment dimension parallel to
loading,
loading,
where 0.9 is pass, and
where 0.9 is pass, and where 0.58 ksf is the undrained shear strength at this
where 0.50 ksf is the undrained shear strength at this depth.
depth. · Therefore, reduce the applied load by: 230k + 151k + 78k =
· Therefore, reduce the applied load by: 139k + 78k + 68k = 459k.
285k.
If the magnitude of the applied load is reduced by the
Alternatively, if the depth were not truncated, the summa- amounts listed above (285k for truncated depth and 459k for
tion of passive and adhesive resistance would be estimated as full treatment depth), and applied considering the appropri-
follows for the entire treatment depth: ate effective cap depth (7.5 ft and 12.5 ft beneath ground sur-
face, respectively) using the GROUP model discussed above,
· Passive Resistance: 10 ft × 12.5 ft × 1.84ksf = 230k good agreement with measured performance is obtained. A
where 10 ft is the treatment dimension perpendicular to comparison of the results predicted using the aforementioned
loading, simplified procedure versus the measured data is provided in
where 12.5 ft is the treatment depth, and Figure 7-19.