Geotechnical Investigation Report - The City of San Antonio

Table 6-1 – Summary of Truck Data
Truck
Factor
Fuel Truck
Weight
%
Distribution
130,000 lbs 17.41 25%
102,240 lb 6.63 25%
86,790 lb 3.96 25%
98,950 lb 5.93 25%
Based on average of 80 fuel trucks per day and an estimated 4% annual growth, the resulting
Equivalent 18kip Single Axle Loads (ESALs) for this 20 year design is 3,420,449 ESALs.
6.4 Subgrade and Pavement Layer Strengths
Subgrade Strength. Subgrade design strength has been developed based on the results of the field
and laboratory tests. These soils were characteristically yellowish brown, and varied between fat and
lean clays and clayey gravels. Correlations were made to strength properties required for design as
seen in tables below. An elastic modulus of 2,300 psi for fat clay soil was selected for design.
Table 6-2 – Summary of PI and Correlated Modulus
Borehole
Number
Depth
(ft)
Plasticity
Index
(%)
Correlated
Elastic
Modulus,
psi
B-1 2-4 56 2,200
6-8 54 2,200
B-2 2-4 42 2,400
6-8 45 2,300
B-3
2-4 67 2,200
4-6 66 2,200
8-9.5 38 2,500
B-4 2-4 12 9,800
6-8 54 2,200
avg all 48 3,111
avg fat clay 53 2,275
The predominant subgrade soils on this project exhibit a potential for swell. Subgrade stabilization is
recommended for the entire length of the project for firm construction platform purposes. The
percentage of lime should be determined during construction based on testing of the actual subgrade
materials. Since high levels negatively affect the use of lime treatment for subgrade soils, HVJ testing
included sulfates. The resulting sulfate content is significantly less than 8,000 ppm per testing
procedure Tex-145-E and Tex-146-E; therefore it is recommended that the top 6 to 8 inches of the
subgrade be stabilized with lime.
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