Soil Nail Wall Wall, Exteral Force Required...

[ohinthecomputer]

I have to build a permanent soil nail wall 6m high to retain soil sloping at an angle of 15 degrees from the top of the wall back.

I have analysed the wall using GeoSlope software SlopeW and have come up with a solution which gives an adequate FoS.

However, the soil nail anchors used encroach on a neighbouring property which is 2.8m from the retaining wall, and so i need to calculate the external force required to make the section stable. I have been told to treat the modelled section as a high strength soil.

How do i go about calculating the external force required?

I'm only new in the field of geotech and would appreciate any help or guidance.

thanks.

 

[PEinc]

2.8m long nails are too short for a 6m high wall, especially with an upward sloping ground surface behind the top of wall. 2.8 / 6 = 0.466H. Tieback anchors would be even longer than the 2.8m long nails. Even at a 20 degree angle, the maximum nail length would be about 2.98m or 0.496H, still too short.

Pick a new type of (more expensive) wall or get permanent soil nail easements into the neighbor's property.

http://www.PeirceEngineering.com

 

[PSlem]

I've done a similar wall with helical tiebacks at 45 degrees to get helices at least 5' beyond failure plane. Keep top tier at least 5' down here. Deeper toe for soldier beams needed due to vertical component of ties. Double up ties at each point to keep individual tie loads down if needed.

 

[PEinc]

PSlem, this is a soil nail wall, not a tiedback wall. A top nail needs to be closer to the surface than 5'.

http://www.PeirceEngineering.com

 

[PSlem]

Right, but soil nail won't work so I picked "a new type of wall"

 

[paulyshore]

The "Snailz" program, available free from Caltrans's website, has an option to 'apply external force' to a soil nail wall. Adjust the (user-input) force until the desired factor of safety is achieved.

[An upper limit of the force should be <=(FS)x(ka)x(gamma)x(H^2)/2, because the soil mass mobilized by the nails provides partial stability.]

...and then the physical device for applying this force will need to be designed and incorporated into the construction.

 

[PEinc]

If there is not enough room to install long enough nails or tieback anchors, how would an external force be provided and evenly distributed over the soil nail wall facing?

If an external force is provided, it would be important to check the intermediate construction stages to make sure the wall is stable as it is being built. It is not wise to just add a lot of force (or a much longer nail) at one location and then believe that the wall is stable. For example, an extra long bottom nail will raise the calculated safety factor on paper but, in reality, may not stabilize the upper portion of the wall.

http://www.PeirceEngineering.com