Page 200 - Buried Pipe Design

174 Chapter Three

because of the lack of support in the haunch area. Also, a comparison
between the homogeneous installation and the poor haunch installa-
tion (Figs. 3.53 and 3.55, respectively) shows noticeable differences in
the pipe-strain plots from soil-box tests.
Figures 3.53 and 3.55 show the FEA results for the poor haunch
condition without compaction simulation. The load-deflection plots
show similar behavior, yet the deformations are larger in the FEA
results. The pipe-strain plots show very similar peaks of large strain
at the 45° position and low strains from the spring line to crown.
Figures 3.56 and 3.57 show the FEA results for poor haunches with
compaction simulation. In the load-deflection plots, the FEA indicates
larger deflections. The pipe-strain plots show larger strains in the pipe
from the spring line to the crown. However, the strain at the invert of
the pipe with compaction simulation compared better with measured
results. That is, FEA with compaction simulation seems to give a more
accurate prediction of strain at the pipe invert as compared with FEA
without compaction simulation. The physical pipe data for Figs. 3.56
and 3.57 are as follows:

Curve
Parameter A B
Stiffness, lb/in 2 10 10
Thickness, in 0.285 0.300
Surface pressure, lb/in 2 35.5 30.0
Vertical deflection, percent 3.14 5.14
Horizontal deflection, percent 1.30 2.92

Homogeneous installation with 80 percent relative compaction. Figures 3.58
and 3.59 show the test results for an 80 percent relative compaction
homogeneous installation. The physical pipe data are as follows:

Curve
Parameter A B
Stiffness, lb/in 2 10 10
Thickness, in 0.285 0.300
Surface pressure, lb/in 2 14.6 15.0
Vertical deflection, % 8.78 3.85
Horizontal deflection, % 7.87 2.06

The vertical and horizontal deflections are very similar throughout
the test, which indicates elliptical deformation as shown in Fig. 3.58.