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RE: Retaining Wall Design Methodology

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Method 3 (listed below) is similar to the method prescribed in the OHBDC
(Ontario Highway Bridge Design Code) except as noted:

Sizing of the footing, to avoid punching into the soil, is made at Ultimate
Limite States (ULS).  At ULS (similar philosophy to LRFD) a contact pressure
of uniform intensity is assumed.  For eccentrically loaded foundations, an
equivalent area having a contact pressure of uniform intensity is assumed
such that the centroid of the vertical component of the factored load
coincides with the vertical component of the bearing pressure (i.e. the 2e
exclusion noted below).

For structural design the more critical of the following two cases at ULS is
used .  Case 1 considers a uniform pressure distribution where the maximum
bearing pressure is not greater than the factored bearing resistance.  This
case corresponds to a contact pressure distribution due to a yielding soil.
Case 2 considers a linear pressure distribution where the maximum bearing
pressure may be greater than the factored bearing resistance.  This case
corresponds to to the contact pressure distribution due to an elastic but
non-yielding soil.

Also, at ULS the eccentricity of the resultant of the factored force, for a
rectangular footing, shall not exceed 30% per cent of the dimension of the
foundation in the direction of eccentricity being considered.

For settlement, deflection, rotation and other serviceabilty requirements,
design is carried out using Serviceability Limit States (SLS) is used.  SLS
design is a similar philosophy to allowable stress design and uses a linear
distribution of stress.

Concerning the design of the heel of the footing, I have always neglected
the upward soil pressure when using non-factored soil pressures.  I always
figured that to develop your safety factor against overturning that you
better make sure that the heel could support the total weight of itself and
the loads above it. Just my opinion.

Regards

Harry Olive, P.E., P.Eng.

   

> -----Original Message-----
> From:	Caldwell, Stan [SMTP:scaldwell(--nospam--at)halff.com]
> Sent:	Wednesday, July 12, 2000 1:22 PM
> To:	'SEAINT Listserv'
> Subject:	Retaining Wall Design Methodology
> Importance:	High
> 
> 
> 3)  For determining soil bearing pressure AND for designing the heal and
> toe
> footing, a uniform soil pressure distribution is applied over a portion of
> the footing, excluding a width of "2e" at the end of the heal, where "e"
> is
> the eccentricity between the center of the footing and the resultant
> vertical force.  This method is the newest, and appears to be strongly
> supported by the research of G. G. Meyerhof, and others.  This method is
> described in the 5th Edition (1996) of Foundation Analysis and Design by
> Bowles.  Although this method might well be the most logical of the three,
> it does not appear that it is currently supported by any commercial
> software.    
>           
> 

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