HomeMy WebLinkAbout11-110 TY Lin SR-178_Morning Drive Interchange Final GDR 120801 - Table 727
Earth Mechanics, Inc.
Geotechnical & Earthquake Engineering
Table 6. In-Situ Soil Infiltration Rates at Detention Basins
Basin
No. Boring No.
Approx.
Ground Surface
Elevation (ft)
Approx.
Ground Water
Elevation (ft)
USCS
Classification
Infiltration Rates
Test Well
(in/hr)
Site Average
(in/hr)
1 A-12-91 +821.0 NE SP-SM, SM 0.11 0.20 A-12-92 +824.0 NE SM, SP 0.28
2
A-12-95 +711.0 NE SC, SM 0.36
0.30 A-12-96 +704.0 NE SM, SP 0.12
A-12-98 +707.0 NE CL, ML, SM 0.41
3
A-12-93 +796.0 NE SM 0.24
0.16 A-12-94 +784.2 NE SM 0.16
A-12-97 +788.0 NE SM, SC 0.08
Notes: NE = Not Encountered
For the design of detention basins, the City of Bakersfield requires either a double-ring
infiltrometer test (ASTM D 3385) or a laboratory permeability test (ASTM D 2434 or D5084) to
determine the infiltration rate of site soils at basin locations. Since the invert of Basin 3 is
approximately 10-15 ft below existing grade, double-ring infiltrometer test at the invert of the
basin could not be performed; therefore, a constant head permeability test (ASTM D 2434) was
performed on remolded samples compacted to 90% relative compacted per CT 216. The results
of the laboratory permeability tests for Basin 3 are provided in Table 7 below.
Table 7. Laboratory Soil Infiltration Rates Conducted on Remolded Samples – Basin 3
Basin
No. Boring No. USCS
Classification
Max. Dry
Density per CT
216 (pcf)
Remolded
Density of
Sample
Tested (pcf)
Permeability
Test Result
(in/hr)
Average
(in/hr)
3 A-12-93 SP-SM 120.5 108.6 0.17 0.10 A-12-97 SM 115.5 104.3 0.03
Global Stability. The “global stability” of the detention basin embankments was evaluated using
the computer program Slide 5.0 (Rocscience, 2006) under both static and pseudo-static
conditions. One cross section was cut along each basin where the embankment was tallest.
Two additional conditions for the detention basin embankments were also considered as part of
the “global” stability analysis; the steady state maximum pool condition and the rapid drawdown
from the maximum pool condition. The maximum pool condition assumes that the detention
basin is completely full to the crest of the lowest surrounding embankment and the embankments
are fully saturated. The rapid drawdown from the maximum pool condition assumes that the
detention basin drains instantaneously from the maximum pool condition and the surrounding
embankments remain saturated. The phreatic surface for the rapid drawdown condition is at the
ground surface within the basin.
Analyses were performed using the design parameters in Section 8.1.1. The minimum required
factor of safety for a permanent slope is 1.5 for the static and maximum pool condition, 1.2 for
the rapid drawdown condition and 1.1 for the seismic condition per Caltrans Guidelines (2006a).
Global stability calculations are provided in Section 13.10.