----- Original Message -----
From: "Wilfred Wrigley" <[log in to unmask]>
To: "Jitendrapal Sharma" <[log in to unmask]>
Sent: Thursday, May 12, 2005 11:23 PM
Subject: Re: Use of net bearing pressure for ultimate limit state design of
spread foundations
> Dear Jitendra
> Most soils have nonlinear stiffness that is dependent on the current mean
> effective stress. As the mean effective stress increases the stiffness
> increases so to assess the allowable bearing pressure for the
serviceability
> limit state the absolute initial mean effective stress is required.
> In addition many granular soils have an operational drained friction
angle
> that strongly depends on density state and current mean effective stress,
> either contracting or dilating towards the critical state. Selection of
the
> correct operational shear strength parameters in this case would depend on
> absolute mean effective stresses at failure. This feature of granular
soils
> and sensitivity of cohesive soils also complicates the selection of
partial
> factors on strength suggested by Brian as an alternative to lumped safety
> factors on ultimate loads.
> In most cases Qult/Qdesign is preferred assuming Qdesign is defined as the
> gross load including the weight of the foundation and any superimposed
soil
> load.
>
> Regards
>
> Wilf Wrigley
> Divisional Director (Geotechnics)
> Bullen Consultants Limited, Darlington, UK.
>
>
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