Limestone layer

[Rainbowtrout]

Hey all, I am a structural engineer. Recently I came across a geotechnical report where the elevation of limestone layer varies about 13 ft between two boring 150 ft apart. Is it normal? I would like to hear from other geotech engineers on this forum before I raise the question to our project geotech engineer. The project is located in Dallas Texas, and there is a small creek about 400 ft away from the borings.

(I didn't want to complicate the question. But there are other borings clustering around the two borings in question. In each "cluster", their elevation variations are within 5 ft.)

 

[fattdad]

if the rocks have inclined bedding, it's very likely.
if the small creak has incised through limestone during geologic time (and the incision infilled by alluvium) it's very likely.
if the limestone is prone to solutioning, it's very likely.

fortunatly there are no prior ice sheets/glaciers that made it down to Texas!

f-d

ípapß gordo ainÆt no madre flaca!

 

[Rainbowtrout]

@fattdad, thanks for your quick response. It sounds like I was over-worrying. All good!

 

[GeoPaveTraffic]

Actually, I might worry for your project. In addition to the items that fattdad indicated, limestone can also weather along joints. This can create all kinds of variations in bedrock elevation and can lead to Karst (sinkhole)formations. I recommend you talk with your geotechnical engineer and see what they think is going on. If you are planning a deep foundation bearing on limestone; you need either additional borings or geophysics to better define your top of rock.

Mike Lambert

 

[Rainbowtrout]

Thanks Geopavetraffic. I will send an email to our geotechnical engineer after all. FYI, the limestone layers in the borings are all unweathered.