Seating embankment layer works 1

[phuduhudu]

We are doing an amphitheatre embankment and I have been looking around for design principles for the earth layer works but there doesn't seem to be much around. We are casting concrete steps on one side for the seating and leaving the backside to slope down at 1:3. The insitu soil is a fine silty sand with no plasticity and a fair CBR of around 25 at 95% compaction. This sand goes on for considerable depth and is loose down to about 2m where it starts to get a bit denser. Anyone have any experience with embankment layerworks?

Carl Bauer

http://www.bauerconsultbotswana.com

 

[oldestguy]

Apparently you are concerned about the stability of the area where the seating will go. The slopes can be checked for safety factor against failure by a stability analysis.

These days this generally is evaluated via computer run programs by entering the configuration of the slope and the soil density, shear strength (in the form of angle of friction and cohesion). Other data needed would include water table and in some areas figure for earthquake effects.

However, unless this type of analysis and the use of these parameters are something common in your practice, I would defer to a geotechnical engineer.

These types of analysis are well described in geotechnical texts and professional papers, such as those published by ASCE.

I'd also see if another term than "layer works" for those in other parts of the world, specifically USA. My assumption that it is the checking of slope stability, yet it may not be your question.

It may be that you are planning to reinforce the slope with layers of geotextile reinforcing. That also is evaluated with the programs mentioned. Suppliers of the geotextile sometimes have information to assist in such a design.

Perhaps some further explanation of your job would help.

 

[phuduhudu]

I am not really worried about slope failure, especially not on the seating side as the soil will be effectively retained by the concrete seating. What I am worried about is differential settlement of the seating. I think it must be much like the problem of specifying the earthworks for an embankment approach to a bridge such that you get an adequate stiffness for the roadwork layers.

Carl Bauer

http://www.bauerconsultbotswana.com

 

[oldestguy]

Sounds like this is a natural area and you will be excavating for the seating area.

In that case you will be unloading the site. The concrete and audience will be significantly less load, thus insignificant settlement, if any.

In instances where I suspect future settlement, such as adding a backfill to a structure wall, I have that area pre-loaded for a while with at least as munch earth load as expected later. Follow by excavation of that pre-load and building the job. Cost runs up a little, but customer is happy later.

Of course you will have control joints at recommended intervals and that saves a lot of noticeable concrete movement, such as shrinkage and temperature effects.