Help - coefficient of earth pressure at rest 2

[Myoho]

This is a theoretical question but it is related to a potential problem with a deep outfall shaft which subject to large intermitant internal pressures.

If I drill a borehole say 30m deep in sands and gravels overlain by boulder clay. Install a packer at the base of the borehole and expand the packer, will the coefficient of earth pressure at rest (Ko)value increase or will it remain at Ko = 1-sin angle of friction.

My thinking is that it will increase until it reaches the Kp value just before shearing.

Put it another way - is there any way you can increase the Ko value of a granular material insitu.

 

[fndn]

For deep foundations in granular soils, k value ranges from 1.0 to 2.0. The Jaky equation is useful, but haven't seen it used for deep foundations. You may refer to this link on page 34.

http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-2-2906/basdoc.pdf

 

[Myoho]

THanks fndn. I have concluded from the USACE publication "Design of Piling Foundations" that the effect of driving a pile results in increasing the K value, which has confirmed my assumption.

It is now my intention to increase the K value of the Glacial sands and gravels by TaM grouting around the shaft from approx 20m to 30mbgl. The inrease in the K value of the soil and will reduce radial expansion of the shaft to an acceptable level.