Where to find Site Soil Classification?

[StructureMan44]

Is there a friendly online source for finding the Site Soil Classification of various sites? A hydrologist friend of mine suggested I try the NRCS but I haven't been able to find the classification (A-E) on this website.

 

[StructureMan44]

Cancel this, I found it!

 

[jimstructures]

StructureMan44 please post the url for the site you found.

Jim

 

[StructureMan44]

http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx

These are the steps I took:
1. Find your site (I used search by address on the left)
2. Use the AOI (area of interest) button to draw out the site.
3. Click the "Soil Data Explorer" tab at the top
4. Click the "Soil Reports" in the new set of tabs that appear below the prior set of tabs
5. Click "Soil Physical Properties" on the left
6. Click "Engineering Properties" below that tab
7. Click "View Soil Report" button
8. Scroll down and the site class(es) appears under the hydrologic group column

If you feel this incorrect please let me know

 

[JLNJ]

Is this for seismic site classification?

 

[JStephen]

As far as I can tell, you're looking at two completely different classifications.
The table on the website explains in the text below what those classifications are in the text below the chart, dealing with permeability of the soil.
I assumed you were looking for "Site Classification" as described in Chapter 20 of ASCE 7, dealing with elastic properties of the soil.
It looks to me like hard rock near the surface would be Class D on the hydrologic classification and Class A on the Site Classification, so they're not necessarily the same.

 

[CCox]

He is probably looking to determine the bearing pressure based on classification. I have used this site to justify a soil bearing pressure of 2000 psi.

 

[Lomarandil]

Wow, 2000 psi soil!

 

[CCox]

whoops! 2000psf. thanks for the catch Lomarandil

 

[Splitrings]

The designation you are looking at on Web Soil Survey is a hydrologic classification, NOT a seismic design classification as used in ASCE.

 

[StructureMan44]

Is there an online database that gives the seismic design classification as used in ASCE?

 

[Ingenuity]

Yes, go to USGS Link and choose your structure and code, then your geographic region.

 

[wannabeSE]

In many cases, ASCE 7 allows Site Class D to be assumed (§11.4.2). I don't think there is a website with Site Class. It is typically in the soils reports for the site. The structural engineers I know, don't know the difference between "rock" and "hard rock" or "soft rock" unless it is played on the radio.

 

[StructureMan44]

This USGS website lists the soil classification as one of the inputs:

http://earthquake.usgs.gov/hazards/designmaps/usdesign.php

Is the soil classification from the NRCS not the same thing as the soil classification the USGS is looking for?:

http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx

 

[Splitrings]

See page 2-2 for a description of the NRCS hydrologic classifications:

http://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=17541.wba

It is not the same as what USGS is looking for. The NRCS classification is a hydrologic/runoff classification. There are only four classifications.

USGS is looking for one of the 5 classifications used in seismic design as listed in ASCE 7 that is called a SITE classification. USGS incorrectly refers to it as a soil classification.

 

[StructureMan44]

Thank you Splitrings. Is there any online resource that has the ASCE site classification? If not, where do most of you folks find this for your projects?

 

[Brad805]

I find it in the project geotech report, but I am in Canada and this tends to be the standard practice.

 

[Splitrings]

Check with the state geological department. A bedrock and surficial geological map will be very useful. In Vermont our Geological Agency has seismic design studies, including site classes for certain areas. Its going to be pretty difficult to determine a site class without a geotechnical report. As was mentioned above, it is acceptable to select Site Class D if the soil/bedrock details are not known.