Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 57
57
400
Model, without Excavation
350 Model, with Excavation
Model, Passive Force
300
Lateral Force (kips)
Test, Passive Force
250
200
150
100
50
0
0.0 0.5 1.0 1.5 2.0
Displacement (in)
Figure 5-6. Simulated and tested pile cap passive
pressure.
about 140 psi after 63 days with a standard deviation of about
8 psi. Assuming that the soil-cement mixture cured at the same
Figure 5-5. Finite element mesh for model rate as concrete alone, the compressive strength of the mixture
of pile group with excavation adjacent at the time of testing would be approximately 126 psi.
to cap. Preliminary analyses suggested that the shear strength of
the mass mixed wall was sufficient to allow the wall to behave
steps with pile head lateral displacement of 0.03 in. per load- essentially as a rigid block. Based on this conclusion and the
ing step. fact that the mass mix has much higher strength than the clay,
The mesh of the FEM pile group model in virgin soil with the mass mix is modeled as elastic material. This assump-
excavation adjacent to the cap is shown in Figure 5-5. A total tion will introduce little error to the pile load-displacement
of 49,977 nodes and 44,666 elements were in the FEM mesh. response against a more complicated material model for the
The load-displacement curves computed using the FEM model mass mix. The Young's modulus of the mass mix zone is
with and without excavation adjacent to the cap were used to estimated as 6.4 × 105 psi from the compressive strength of
produce the passive force-displacement curve. The passive the mixture at the time of testing (126 psi) with the assump-
force on the pile cap was obtained by subtracting the load with tion that the Young's modulus can be estimated with the same
excavation from that without excavation. The simulated pas- formula as that for concrete [E = 57000(f c )0.5]. The Poisson's
sive force-displacement curve is compared with the measured ratio of the mass mix is assumed to be 0.2.
curve in Figure 5-6. The simulated force is greater than the A comparison of load-displacement curves from the test
measured force for displacements less than about 0.3 in., which data and the FEM model is provided in Figure 5-8. The FEM
is as expected for small displacement due to the residual dis- model provides very good agreement with the measured
placement. However, the agreement is satisfactory for displace- results. These results indicate that the linear elastic material
ments more than 0.3 in. model with the material properties described previously can
reasonably represent the lateral resistance of the pile group
after treatment with mass mixing. Furthermore, this result
5.4 FEM Model of Pile Group
provides confidence that additional parametric studies can be
with Mass Mixing
used as "virtual load tests" for the purpose of developing a
The mass mixing treatment zone in the FEM model is shown simplified model.
in Figure 5-7. The modeled zone is 10 ft deep, 4 ft long in the
direction of the lateral loading direction, and 11 ft wide trans-
5.5 Pile Group Model
verse to the loading direction. These dimensions are the same
with Jet Grouting
as in the field test.
Six 3-in. diameter core samples were extracted and tested Soil improvement using jet grouting was undertaken in
after 38 and 63 days of curing. The test results indicated an aver- Test 8. For Cap 1, improvement was limited to zones in the
age strength of 131 psi after 38 days and an average strength of front and back sides of the pile cap, while for Cap 2 the improve-
OCR for page 58
58
Figure 5-7. FEM model profile with mass mix treatment zone beside the cap--mass
mix zone is 10 ft deep, 4 ft long, and 11 ft wide transverse to loading.
600 ment extended underneath the entire pile cap as shown in Fig-
ure 5-9.
500 Figure 5-10 shows a schematic profile diagram of the
FEM model with the jet grout treatment zone. The model
400 shown in Figure 5-2 was used to model the pile with jet grout
Load (kips)
treatment after appropriate elements in the model were
300 assigned the properties corresponding to the soilcrete. Analy-
ses suggested that the shear strength of jet grouting soilcrete
200 was sufficient to allow the soilcrete zone to behave as a rigid
Model block. Based on this conclusion and the fact that the soilcrete
100 Test has a much higher strength than the clay, the soilcrete was
modeled as an elastic material. This assumption will introduce
0 little error into the pile load-displacement response relative to
0.0 0.5 1.0 1.5 2.0 2.5 a more complicated material model for jet grouting soilcrete.
Displacement (in) The Young's modulus of the soilcrete is estimated as 1.4 × 106
Figure 5-8. Comparison of load-displacement psi based on the compressive strength of the mixture at the
curves from FEM model and field test with mass time of testing, which would be approximately 600 psi. This
mix zone adjacent to the pile cap. modulus value is based on the assumption that the Young's
OCR for page 59
59
Figure 5-9. Layout of test using jet grouting under Cap 2.
Figure 5-10. Schematic profile drawing of FEM model with jet grouting beside
and/or underneath the cap.
OCR for page 60
60
1000 modulus can be reasonably well estimated based on the same
900 formula as that for concrete, E = 57000(f c )0.5. The Poisson's
ratio of the mass mix is assumed to be 0.2.
800
A comparison of the measured load-displacement curve
700
Lateral Force (kips)
with that computed with the FEM model is provided in Fig-
600 ure 5-11. Once again, the agreement between measured and
500 computed results is generally satisfactory especially for pile cap
Test
400 displacement more than 0.5 in. The researchers noted that
Model
300
for small displacements of the cap less than 0.5 in., the load-
displacement curve from the test is somewhat stiffer than
200
the curve obtained by the FEM model. This could be due to the
100 linkage between the pile cap and jet grouting soilcrete. Once
0 again, the relatively good agreement suggests that using the
0.0 0.5 1.0 1.5 2.0 2.5 3.0 linear elastic material model with the above-mentioned prop-
Displacement (in) erties can produce reliable estimates of the measured load-
Figure 5-11. Comparison of FEM computed and deflection curve obtained from the field tests with jet grout
measured load-displacement curve with jet treatment around the pile group. Therefore, the same model
grouting below and beside the cap. The jet can be used for parametric studies using the variations on
grouting soilcrete has a depth of 10 ft from the geometries to expand our understanding of the increased lat-
cap base, a length of 15 ft, and a width of 9 ft. eral resistance provided by jet grouting.
