Retaining Wall Help!

[AKCivil]

I'm designing a 14.5 ft retaining wall on a site with poor soils and allowable bearing capacity of 1000 psf. I've gone through all the calcs for a cantilevered CIP wall and cannot meet bearing pressure requirements without a huge foundation. I'm now looking into MSE wall. Is the MSE wall bearing pressure looked at differently than for a cantilevered wall?

My overturning moment includes active pressure, traffic and nearby foundation surcharge which brings me to about 32 kft.

I'm looking at it as a block with structural fill wt of 130 pcf, wall height 14.5 ft, and starting with reinforcement width of 15 ft and am not even close to 1000 psf... any thoughts or tips would be greatly appreciated.

 

[youngmotivatedengineer]

Have you looked into doing helical piles under the wall?

 

[AKCivil]

I have not. Was told to try to avoid pile foundations but that may be the only option...

 

[PowerStroke79_PE]

Have you looked into doing helical piles under the wall?

Hi, why Helical?

I'm designing a 14.5 ft retaining wall on a site with poor soils and allowable bearing capacity of 1000 psf. I've gone through all the calcs for a cantilevered CIP wall and cannot meet bearing pressure requirements without a huge foundation. I'm now looking into MSE wall. Is the MSE wall bearing pressure looked at differently than for a cantilevered wall?

My overturning moment includes active pressure, traffic and nearby foundation surcharge which brings me to about 32 kft.

I'm looking at it as a block with structural fill wt of 130 pcf, wall height 14.5 ft, and starting with reinforcement width of 15 ft and am not even close to 1000 psf... any thoughts or tips would be greatly appreciated.

1. I dont see why bearing pressure would be different for and MSE wall, but look into what Geogrid does for you. 

2. My first thought would be to get with geotech firm and inquire about strenghening your load bearing soils with lime or cement. 1000 psf is really low. Try to find a mid point between a wide footing and strengthening existing soils. 

3. Deep foundations may be necessesary, with caps and continuous footing. Look for an on center reasonable spacing for drilled shafts. 

What do you mean by traffic in calculating overturning moment?

 

[youngmotivatedengineer]

@Hemi79 I was suggesting helical piles under the wall to increase bearing pressure. This is similar to your comment number 3, except it may be easier if site conditions don't allow for the installation of traditional pile (i.e limited access for equipment).

 

[AKCivil]

Hi, why Helical?

1. I dont see why bearing pressure would be different for and MSE wall, but look into what Geogrid does for you. 

2. My first thought would be to get with geotech firm and inquire about strenghening your load bearing soils with lime or cement. 1000 psf is really low. Try to find a mid point between a wide footing and strengthening existing soils. 

3. Deep foundations may be necessesary, with caps and continuous footing. Look for an on center reasonable spacing for drilled shafts. 

What do you mean by traffic in calculating overturning moment?

Traffic surcharge load of 250 psf