Historical aerial photos and geological map

qhtony · Mar 16, 2009

Hi guys, I've got a desktop study of a land slip site (500m x500m) needs to be carried out but with very limited information available (Client acknowledged the limitations), not even a site inspection or any tests can be made. The info includes:

1. known landslides in the past 50 years
2. historical aerial photos every 10 years from 1950s to present
3. geological map
4. site is dominated by clay/sand mixtures, overlaying sandstone. Occasional outcrops can be seen.

Based on all the information, I think the report can focus on the geomorphology side of discussion. However, is there a way to know any potential scale of landslides and the types of failure (i.e. flow, slump etc)? And from the information available, is there any other conclusions I can make?

I hope I am not confusing you guys too much here...

fattdad · Mar 16, 2009

There's a chance that state DOT may have aerial photos for 10 year periods (in Virginia we do).

I'd look at topographic maps (50 meters square would be 3/4 in on a 1:24000 scale USGS topographic map) and I'd check out the overall region for tell-tale signs of slides.

I'd look at the slope gradient where the slide occurred and I'd see if the original grade (slope percentage) is greater than local slopes of similar scale.

I'd compare geomorphic findings to the geologic map of the area.

I'd consider going to the geologic reference library at the nearest State College (that is if there is a geology program) and see if there have been any geologic hazzard assessments for the underlying formation.

I'd do a site visit.

f-d

¡papá gordo ain’t no madre flaca!

theCorkster · Mar 25, 2009

Go visit with a local engineering geologist, familiar with the geologic formation (soil and rock). He'll like know typical failure mechanism (circular versus planar, depths, etc.) Fine-grained soils over sandstone can be problematic, especially where the sandstone conveys groundwater (which is likely).

Get stereo- aerial photographs for the site and vicinity as well. Experienced eyes can tell lots about the site and vicinity.

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Historical aerial photos and geological map

qhtony

Civil/Environmental

fattdad

Geotechnical

theCorkster

Geotechnical

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