soil nails v. soil screws for retaining walls
soil nails v. soil screws for retaining walls
(OP)
Soil nails include a tendon that is enveloped by grout that develops shear along the grout-soil interface. Soil screws include a shaft with helicies (sp) at varying locations. Between the helicies there is limited shear capacity along the shaft-soil interface.
Consider the image below:

Consider potential failure modes:

I would think that the soil screw doesn't work quite the same.
Comments?
f-d
Consider the image below:

Consider potential failure modes:

I would think that the soil screw doesn't work quite the same.
Comments?
f-d
¡papá gordo ain't no madre flaca!





RE: soil nails v. soil screws for retaining walls
1) face failure seems to be a structural failure of the concrete facing, mostly un-related to the soil nail or screw. If you are able to successfully install the nail and facing, then face failure should not happen.
2) screws may have more uniform tension along nearly the entire length of the rod, as the anchoring helix is generally on the end.
3) screws do not impart as much stress into the looser surface zones, instead they only anchor in the competent material where the helices are.
RE: soil nails v. soil screws for retaining walls
RE: soil nails v. soil screws for retaining walls
f-d
¡papá gordo ain't no madre flaca!
RE: soil nails v. soil screws for retaining walls
RE: soil nails v. soil screws for retaining walls
1) Helical anchors usually develop their resistance through bearing, and essentially act like a compression anchor. Sometimes you can substitute tiebacks for helical anchors in a bulkhead type system. You could use Helical anchors in a soil-nail grid pattern, but you would have to have a bulkhead face and an anchor zone beyond the failure plan (for an appropriate soil slope stability FS for local and global). Helical anchors usually aren't grouted, so you wouldn't develop large skin friction along the rod (usually smooth steel along main shaft).
2) Soil Nails create a large stable block of earth and develop their resistance along the anchor (Thus the requirement to meet ASTM standard indentations like Rebar).
The way I usually use helicals are in "tendon" type applications.
Hope this helps.
RE: soil nails v. soil screws for retaining walls
No offense intended, but it seems to me that you steered this thread toward helical tieback anchors instead of the original topic of soil screws.
1. Soil screws are similar to helical tieback anchors except that soil screws have helices spaced along the entire length of the nail, not just in the lead section(s) beyond the failure plane. Therefore, you don't need skin friction along the length of the soil screw. Instead, there are multiple helices each with bearing capacity. A wall with soil screws, helical tieback anchors, soil nails, or tieback anchors still needs a "bulkhead face" and tendon length behind the failure plane.
2. Soil screws also create a large stable block of earth and develop resistance (in bearing) along the anchor.
3. Helical anchors are usually used in tendon type applications as tieback anchors or as helical piers (piles). Soil screws are used for soil nailing.
RE: soil nails v. soil screws for retaining walls
f-d
¡papá gordo ain't no madre flaca!
RE: soil nails v. soil screws for retaining walls
RE: soil nails v. soil screws for retaining walls
However, soil nails are "passive" in that only when the shored height deflects slightly, do the nails start to hold back. These need grouting and have to be stressed to a design and test load to check capacity.
RE: soil nails v. soil screws for retaining walls
RE: soil nails v. soil screws for retaining walls
RE: soil nails v. soil screws for retaining walls
it will clear somethings.
Soil nails transfer the stresses of the nail (usually #8 thru #10 rabar)to the soil by friction along the drill hole perimeter and length. After construction is completed, if the soil behind the soil nail wall does not move, no load exists on the nail, so there are no stresses and therefore we call the nail is "passive".
Take tiebacked walls for example, the soldier piles have to be stressed prior to moving downward too much of a depth. So the tiedback strands or threaded bars are "active" right form the beginning.
You can get more information from the SNAILZ PDF manual found here:
http://www.dot.ca.gov/hq/esc/geotech/request.htm
RE: soil nails v. soil screws for retaining walls
Thanks everybody for your thoughts so far!
f-d
¡papá gordo ain't no madre flaca!
RE: soil nails v. soil screws for retaining walls
Yes that manual and the software is only for soil nail walls (free program).
RE: soil nails v. soil screws for retaining walls
f-d
¡papá gordo ain't no madre flaca!
RE: soil nails v. soil screws for retaining walls
RE: soil nails v. soil screws for retaining walls
RE: soil nails v. soil screws for retaining walls
RE: soil nails v. soil screws for retaining walls
When helical anchors are installed there is a dial on the drill that measures the torque on the helical shaft as it is installed. There are tables that relate the torque to axial load capacity, so you know as you are installing the anchor the approximate holding capacity.
Is this true for soil nails? I would think you are unsure of their actual capacity until the grout has set up and you test a few - is this true?
RE: soil nails v. soil screws for retaining walls
RE: soil nails v. soil screws for retaining walls
I would question if a torque indicator really gives you the actul capacity or if a pull test is the only way to really confirm capacity for any type of anchor.
RE: soil nails v. soil screws for retaining walls
On small helical anchor jobs, I often use the torgue value to confirm the ultimate tension capacity. On larger or more critical jobs, I will require the helical anchors to be tested with a hydraulic jack.
I have not done a screw soil nail job and probably would not want to. If you have questions about soil screws, I recommend calling A.B. Chance for technical guidance.
RE: soil nails v. soil screws for retaining walls