Determining critical gradient
Determining critical gradient
(OP)
Hello,
I am working on a project where we are looking to construct a dam with rockfill shell over normally consolidated silty clay material.
Preliminary seepage modeling indicates locations have hydraulic gradients up to 0.4-0.45, however we were looking to have all values below 0.3.
Is there any sort of standardized lab testing for this?
My first thought was to complete a series of constant head test and just adjust distance between the reservoir and sample, and observe and record if/when erosion/heave is observed.
Any advise?
I am working on a project where we are looking to construct a dam with rockfill shell over normally consolidated silty clay material.
Preliminary seepage modeling indicates locations have hydraulic gradients up to 0.4-0.45, however we were looking to have all values below 0.3.
Is there any sort of standardized lab testing for this?
My first thought was to complete a series of constant head test and just adjust distance between the reservoir and sample, and observe and record if/when erosion/heave is observed.
Any advise?





RE: Determining critical gradient
Dams are typically designed with cutoff trenches and/or other cutoff elements which can lower the gradients.
Mike Lambert
RE: Determining critical gradient
I've seen values typically as low as 0.15 used for determining exit gradients.
Also see:
http://ussdams.com/proceedings/2014Proc/363-378.pd...
RE: Determining critical gradient
RE: Determining critical gradient
GeoPaveTraffic - Agreed about no lab testing normally being performed, however for this scenario we are potentially dealing with a higher consequence structure and are aiming to have all gradients at or below 0.3. I was just wondering if there was lab testing to provide data at what gradient mobilization of material or heave would begin.
BigH - Thanks for the paper, will read through. For our scenario we do not have any issues with the exit gradient, it is just between the silty clay and the rockfill... I am thinking it might be partly due to the large difference in hydraulic conductivity (1e-8 m/s for the clay vs 1e-2 m/s)
oldestguy - Yup. The area of interest for me is vertical flow.
RE: Determining critical gradient