RETAINING WALL ON SLOPING SITE

[alumpkin]

I have a new home site that will be built on a 45 degree slope from the road above to the lake below. Approximately midway down the slope is the house. There will be two retaining walls...an upper one and then one out at the slope face to provide for a basement floor. It is in a red clay material. I am beginning to design the retaining wall and want to establish the allowable bearing capacity for footings on slopes. I have the Navfac manual and Bowles textbook for my references. Anybody have other suggestions or know of an Excel speadsheet that will perform this design? Also, will I need to do a trial wedge for slope stability or will the reduced bearing capacity established from NAVFAC account for the slope stability? Thanks.

 

[GeoPaveTraffic]

Before you can do anything with the wall design you must have the site investigated by a geotechncial engineer. Given that the existing slope is 45 degrees, I would assume that bedrock is very shallow. If this is the case then the wall should be designed to set on the bedrock and there should be few problems. However, if rock is not shallow, the bearing pressure of the retaining wall is the least of your problems. Global stability will be the biggest problem.

 

[Mccoy]

Alumpkin,
I would forget about using the slope inclination factor in the formula for bearing capacity. The theoretical model assumes no levelling of ground surface, which is pretty unrealistic since machinery and workers need some operating room. More models are available for the realistic case (even in Bowles's textbook). But, as GeoPavetraffic underlines, you should first work out the stratigraphy, sit the wall foundations on the bedrock and carry out all required calcs (global stability is most important).
If footing is far enough away from the slope edge then the correction factor for bearing capacity would amount to zero.

 

[dirtsqueezer]

Not to do any harping...lol I would definitely agree with Mccoy and GeoPaveTraffic. Assuming your structures were anchored on bedrock, your houses may still be in danger of slides from up-slope. I imagine homeowners are usually friendlier than their legal counterparts. Here's a page with a local problem area. It seems like you're always hearing about some slide or other in West Seattle!

http://www.tubbs.com/ic52/ic52.htm