Allowable Soil pressure in New Mexico
Allowable Soil pressure in New Mexico
(OP)
Hi All,
I’m designing foundation (drilled pier) for some pipe supports in New Mexico. At this stage, we don’t have soil report yet. As I look at drawings done by other, there are soil bearing assumptions that I am not sure about:
1. Allowable end bearing pressure: 12.5 ksf.
2. Allowable downward skin friction: 250 psf.
3. allowable uplift: 200 psf.
Question: are these assumption reasonable (conservative) in New Mexico. On the detail of pier depth, they stated: “8’-0” or to refusal”. Does this mean that the bedrock this shallow?
Any advices or direction to web site in New Mexico would be appreciated. Please note that I am not familiar to this area.
Thanks
I’m designing foundation (drilled pier) for some pipe supports in New Mexico. At this stage, we don’t have soil report yet. As I look at drawings done by other, there are soil bearing assumptions that I am not sure about:
1. Allowable end bearing pressure: 12.5 ksf.
2. Allowable downward skin friction: 250 psf.
3. allowable uplift: 200 psf.
Question: are these assumption reasonable (conservative) in New Mexico. On the detail of pier depth, they stated: “8’-0” or to refusal”. Does this mean that the bedrock this shallow?
Any advices or direction to web site in New Mexico would be appreciated. Please note that I am not familiar to this area.
Thanks





RE: Allowable Soil pressure in New Mexico
I don't know what the presumptive soil strengths "officially" are in New Mexico, but based on the values you've quoted, the end-bearing pressure indicates an "equivalent" su of about 3500 psf (cohesive) or "equivalent" uncorrected SPT N value of about 25 to 30 (cohesionless).
The downward skin friction is 25% higher than uplift, which looks OK. "Equivalent" su for side friction is about 400 to 500 psf, assuming full development of ultimate capacity.
As for the detail dimension of 8 ft or refusal, it could be that bedrock does get that shallow. You should check with the NM Dept of Natural Resources or State Geological Survey, etc. to see if they have any freebie downloads for soil and bedrock data in your project area, if you're that concerned about it.
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
RE: Allowable Soil pressure in New Mexico
RE: Allowable Soil pressure in New Mexico
RE: Allowable Soil pressure in New Mexico
RE: Allowable Soil pressure in New Mexico
Jdonville: what's the su meaning? I couldn't find it in my soil book (Essentials of Soil Mechanics & Foundation by McCathy)
BigH: can you direct me to where I can find US Conservation Authority surficial soils map?
Thanks to everyone again.
Nqchan
RE: Allowable Soil pressure in New Mexico
RE: Allowable Soil pressure in New Mexico
RE: Allowable Soil pressure in New Mexico
"su" is undrained shear strength: su = qu/2
"qu" is unconfined compressive strength
"c" values are commonly taken to equal su
Note: " c' " is effective stress cohesive strength and is not necessarily equal to su.
The propoer name of the US Conservation Authority is the Natural Resorces Conservation Service. A link to state offices is here: http:/
To find contact information for local soil and water conservation agencies (usually by county) try here:
http://www.nacdnet.org/resources/NM.htm
Good Luck!
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
RE: Allowable Soil pressure in New Mexico
RE: Allowable Soil pressure in New Mexico
Best regards,
Nqchan
RE: Allowable Soil pressure in New Mexico
http://www.nm.nrcs.usda.gov/soils/
Another good source for geological information is the geological survey for the state. New Mexico's is called the New Mexico Bureau of Geology and Mineral Resources
http://geoinfo.nmt.edu/index.html
They seem to have extensive geological maps online. You may be able to find depth to bedrock on these maps.
RE: Allowable Soil pressure in New Mexico
As for the bearing values, those seem reasonable to me. Low skin friction, meaning the overburden soils above the auger refusal materials are weak and a fairly conservative end bearing pressure indicating fractured rock which is a reasonable assumption for Alb. Do you know if the geotech company has attempted coring the material? Also, where in town is the development?
RE: Allowable Soil pressure in New Mexico