Highway cutting landslide investigation 1

[Looshus]

Can anyone advise me on what site investigation should be done in order to determine the cause of the failure?

The geology is is glacial clay deposits over lower coal measures.

The slip has lots of wet material, and there is a slow but continuous water flow through the slip.

 

[BigHarvey]

Terzaghi used to say that when you have a slope stability problem there are only three things to do :
the first one is drain
the second one is drain
the third one is drain

 

[cvg]

I don't think there is any way this can be scoped without an expert in the field. hire a geotechnical engineer experienced in slope stability analysis, ask him to visit the site and have him scope it?

 

[fattdad]

You need to drill, sample and do lab testing. From the results, you need to evaluate the driving forces and the resisting forces and determine the conditions that led to a safety factor of unity. From there you can look at solving the problem.

Sampling in a stiff fissured clay can be a problem if it's too hard for a Shelby tube.

You need to look at both peak strength and also residual strength. This may very well be a residual strength problem.

You need to fully evaluate secondary features in the clay, such as bedding, fissures and tension cracks.

If it's glacial terrain, you may find that the clay has failed in the past (the geologic past). It would be helpful to look for any bedding angles that may suggest rotational failures in the geologic past.

These are not simple problems and the geotechnical firm may outline a field program that ultimatly needs to be supplemented by additional data.

f-d

¡papá gordo ain’t no madre flaca!

 

[TDAA]

"the cause of the failure?"

"The slip has lots of wet material, and there is a slow but continuous water flow through the slip. "

Enough said.

Now trying to determine the best fix, how to complete the construction, or if the mass should be stable in the current state, is the tougher question.

 

[mudman54]

as an engineering geologist, i am curious to know where this is. in this situation, the slope has already failed and you know the geometry of the failure surface. don't forget to carefully investigate the water table in the area. i like the idea of looking for similar slope failures along the highway. please ask your consultant if it is possible to back-calculate the failure to determine the shear strength parameters. that would be a contribution to our profession.