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THE GEORGE WASHINGTON UNIVERSITY DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING CE XXXXXXXXXXGEOTECHNICAL ENGINEERING SPRING 2013 PROJECT NO. 1: INTERIOR BRIDGE PIER ON SPREAD FOOTING Date...

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THE GEORGE WASHINGTON UNIVERSITY DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING CE XXXXXXXXXXGEOTECHNICAL ENGINEERING SPRING 2013 PROJECT NO. 1: INTERIOR BRIDGE PIER ON SPREAD FOOTING Date Assigned: March 20, 2013 Date Due: April 3, 2013 Total Points = 100 You have been selected to assist the structural engineer for a bridge replacement project. Your task is to design the size of the footing for an interior bridge pier, based on the allowable stress design method. A soil test boring was drilled at the location of the bridge pier. The soil test boring log has shown that the soil is fairly uniform at the pier location and consists of a layer of clay overlying a three-layer system of silty sand, well graded sand, and uniform sand. Detailed information about each layer is given in Fig. 1. Groundwater table was encountered at the depth of 9.1 meters during subsurface exploration, but seasonal changes may raise the water table to a depth of 7.5 meters below ground surface. The following information was provided by the structural engineer: ? Scour is not an issue at the site. ? Frost penetration depth is 1.0 m. ? Tolerable settlement for the project is 38 mm. ? Factored Axial Load = 8500 kN ? Factored Shear Load = 225 kN ? Factored Moment in Z-direction = 600 kN-m ? Factored Moment in Y-direction = 950 kN-m ? Use Schmertmann’s XXXXXXXXXXand Kulhawy and Mayne XXXXXXXXXXcorrelation between SPT and f’, and round to nearest degree. ? The increase in stress in each layer may be estimated using the 2:1 method ? Settlement analysis should be based on the Hough Method Using the information provided above, design the size of the footing for the interior bridge pier, based on the allowable stress design method. You should consider both settlement and bearing capacity, and check for overturning and sliding. You should provide the structural engineer with a formal typed report that will include all of your analyses and final size of the footing. You should also include all of your design assumptions in your report. Figure 1: Subsurface Profile Lean Clay Uniform Sand Silty Sand Well Graded Sand (Saturated) Well Graded Sand ? = 18.5 kN/m3 ? = 19.6 kN/m3 ? = 19.6 kN/m3 ?sat = 20.5 kN/m3 ?sat = 20.5 kN/m3

005_aavajo-w43duhpf.pdf
Answered Same Day Dec 22, 2021

Solution

David answered on Dec 22 2021
144 Votes
Introduction:
Footings are designed to transfer load from a structure to the supporting soil. Their designs are
ased upon the nature of loading, properties of soil and the type of footing. It is seen that the
footing in this case is an interior footing of a
idge pier. From the subsurface exploration it is
observed that the soil profile consists of mostly sand and lean clay layer at the top. Scour is not
an issue and frost penetration depth is 1m. Let us assume that a shallow foundation placed above
the sand-silt layer is sufficient to ca
y the loads as well as counter the moments etc. Moreover as
water table is at sufficient depth it should not have a negative impact on the bearing capacity as
well as negate chances of liquefaction. We design the plan of the footing based on bearing
capacity and settlement as the primary criterions and proceed further to check whether depth of
footing is adequate for overturning, sliding, punching shear etc.
*
Given,
For the soil profile shown in the above figure
i) Groundwater depth = 9.1 meters and may rise up to 7.5 meters
ii) Scour is not an issue at the site
iii) Frost penetration depth = 1m
iv) Tolerable settlement for the project = 38 mm
v) Factored Axial Load = 8500 kN
vi) Factored Shear Load = 225 kN
vii) Factored Moment in Z-direction = 600 kN-m
viii) Factored Moment in Y-direction = 950 kN-m
ix) Use Schmertmann’s (1975) and Kulhawy and Mayne (1990) co
elation between SPT
and φ’, and round to nearest degree.
x) The increase in stress in each layer may be estimated using the 2:1 method
xi) Settlement analysis should be based on the Hough Method
1) Determination of average soil friction angle ϕ’

Using the relation given by Kulhawy and Mayne,

Let us assume atmospheric pressure pa = 100 kN/m
2
Field SPT(N60) Effective stress (σ
'
0 in
kN/m
2
)

in degrees
6 13.87 36
7 27.75 36
18 42.55 43
20 57.25 43
22 71.95 43
42 87.63 48
38 117.03 45
47 146.43 46
33 175.83 41
45 191.86 44
49 207.89 44
42 223.93 42
37...
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