House's backwall as retention wall 4

[ANgK]

We are brainstorming for the client project. The lot has limited buildable land with a big hill in the back. The client wants to explore the option of cutting down the back hill which resulting in 20-25 ft wall.

One option is building the house with the 20ft concrete back wall flush against the cut hill and also act as retaining wall. Is pour concrete wall or ICF wall suitable for this purpose? Is soil nailing also required to stabilize the slope in addition to the concrete wall?


The other option would be shotcrete/ soil nailing retaining wall and 5 feet space between the wall and the back of the house. The house will be smaller and the wall will be higher, about 25 ft

In your opinion, which option would be more feasible and economical?

 

[oldestguy]

While you are "playing" with various options, assume excavating a stable cut slope at 33 degrees to the horizontal (not allowing for possible cementing that may help), you need land extending up the hill about 60 feet for that cut starting at elevation 765 for rear of rear level place (lawn???).. Buy land back about 80 or 90 feet to be sure to allow for future unknowns. Might be cheaper than a tied back wall. A geotech might be able to recommend a less costly alternative.

 

[JoelTXCive]

I second the 'buy more land' option.

Being serious, If that is at all a viable option; then it very well might be cheaper than the wall options you are looking at.

 

[ANgK]

What would be a rough estimated cost of these options?

Land is not a problem. The back of the lot is more than 200ft uphill from the wall. If cutting the slope down to 33 degrees, do we still need some sort of erosion control or surface cover? The exposed dirt is hideous. Covering such large area is probably costly too.

 

[hokie66]

We don't know how much it would cost, especially in an area like that. Many of us would wonder why anybody would want to build a house there.

Your best source of cost might be the neighbor who has already done what you propose.

 

[JoelTXCive]

I'll look at the office tomorrow and see what I can find. The Texas department of transportation (TxDOT) publishes monthly what they pay for various types of retaining walls. It is called their low bid unit price report.

Their cost numbers are probably by cubic yard on something like that. It will not tell us how high the wall was though. I'll check at the office tomorrow and see if someone remembers what the cost was for the most recent large wall (cantilever and/or soil nail)

Here's a link to the TxDot website. Once you open the excel or text file, do a CTRL-F search for 'Retaining' to see all the wall types.

http://www.txdot.gov/business/letting-bids/average-low-bid-unit-prices.html

 

[Okiryu]

ANgK , Here are some costs information for soil nailing from

http://www.Geotechtools.org.

This website has tons of very good information.

Based on your photos, appears that you have sandy/silty soils and the face of that slope is prone to erosion. Recommend also to contact an specialized contractor in your area.

 

[ANgK]

Thanks!

What is the difference between Drilled/Grouted and Hollow Bar Soil Nailing vs Screw-in Soil Nailing?

Price seems to be so different between them

 

[Okiryu]

For Drilled/Grouted and Hollow Bar Soil Nailing, you drill a hole and then use cement grout to fix the nails into the ground.

For the Screw-in Soil Nailing, imaging a helical pile, no grouting. I think the name is self-explanatory.

 

[RSLC]

BEST RESULTS FOR THIS PLACE IN THE HILL
VETIVER GRASS PLANTING.
REGARDS
LOOK geotecniapro.00page.com

 

[ANgK]

Interesting idea but I don't think that grass would do well in colder climate.

Sasa veitchii, Sasa bamboo, is probably better.

 

[Okiryu]

What did you decide to do? Looks like a retaining wall with a proper slope (similar to what your neighbor did) is the way to go. I would add some erosion protection for the slope (vegetation and/or geosynthetic mat).