In situ vane shear test 6

[pelelo]

Hello,

I am trying to become familiar with this in situ test since a client is requesting this for a project.

After doing some research, I noticed that the stores that sale the apparatus (blades + rods + etc), they only sale a total rod length of 3 meters (6 pieces of 0.5 m).

Is this test meant to be performed in the top 3 meters (10 ft) below surface?. I have watched few videos and usually they run the test in the top 2 to 3 m.

In this project, I foresee soft clays at 15 and 20 mt below surface. Is there any special way to perform this test at these depths?. I am not sure if by adding more rods will be enough to run the test at these depths. I noticed the rods are too thin and at these depths they might buckle.

Please advise.

Thanks.

 

[BigH]

We had vanes that were quite larger than the miniature vanes of which you seem to be describing. The vanes were fit onto the end of an A-Rod and the pushed into the ground, We went quite deep with them - 15 m doesn't seem unreasonable. I've used the Sprague and Henwood vane table and also fish-scales - yep, fish scale.

 

[pelelo]

So I can get a sub to connect the vane to my AWJ rods I guess.

At 15 m, how did you measure torque?, I ask that because 15 m is a long AWJ rod length, so i am not sure if applying torque from surface will require a special correction to whatever torque value you read at surface.

 

[BigH]

As I noted, when I worked with a few Cdn Geo firms - we used fish scales - with a t-bar across the top of the A-rod . . a fish scale each side - one person and then you move up together the pull . . . not pretty but it worked okay - the Sprague and Henwood (spelling?) was actually a table that sat on the A-rod coming out of the hole and then you turned gears to twist the vane - Gawd - that was a long time ago (1977 in Guyana). You can drop in your A-rod and "measure" the friction when turning the rod - then subtract this off your vane test results. See Hunt's Geo Investigation Book.

 

[coneboy]

You can buy a vane unit from a geotechnical supplier as you are pondering.
Yes, sometimes they can only reach to 5 or 10 feet in depth.
Sometimes the soft clay is located at 20 feet in depth which renders your equipment null and void.
Bear in min the cost comes out of your pocket and you may only use it 5 times.

Why not just ask the drillers if they have a vane?
I assume your going to hire a driller?
Many drill companies have vanes that can be put on the end of AW/AWJ/NWJ rods.
Vanes usually come in a variety of sizes for different soil stiffness.
Use some casing and then you can eliminate all the rod friction error issues.

As BigH noted - in the 70's and 80 we used a fish scale which was the best tool at the time.
Most drillers now have fancy calibrated torque wrench's that they carry on the drill that can be used to turn the rods and complete the test.
Check with your local drillers.

 

[EireChch]

In NZ we use to do hand auger boreholes. It was a 12inch auger bit on maybe 35mm dia hallow steel pipe, probably aluminum as it was light.

We had a pilcon shear vane that attached to the pipes also. We would do hand augers in SILT/CLAY down to 6m depth. The only reason we didnt do deeper was because it was difficult to pull 6m of pipe out of the hole, lay it down, take the soil out and put it back in the hole. Up to 4m generally 1 guy could manage but it was a 2man job after that.

 

[GeoEnvGuy]

Become familiar with ASTM D2573, and some drilling contractors are familiar with the field vane process, you can also find contractors which offer electronic vane testing. Depends on the quality of the data you require. In my practice we rent a setup and specify the length of rods we want and have our drilling subcontractor drill every 10 ft to push our vanes which come in metric 1 m length rods.

 

[geotechguy1]

There's one bloke in NZ who can do a 10m hand auger. I watched him do it. Roger Evans, you animal.

 

[EireChch]

10m is a slow process, you would need to disconnect the rods halfway to get them out. but fair play!

 

[geotechguy1]

In fairness, 2-3m is more common; 5 is really hard even with experience, and I've long suspected that lot hand augers reported as 5m here are in fact quite a bit short of that (as an example, at a previous employer, most staff seem to only go to site with 4m of rods but return with a 5m log...)

 

[Greenalleycat]

I've been doing hand augers for 12 years or so here in NZ. Typical length is 3m, done my share of 4m and only been to 5m once. Something I, and I assume everyone else does too, has glossed over is that the rod segments are 1m long but the overlap is 100mm...
So if you have 2 lengths it's 1.9m, 3 is 2.8, 4 is 3.7m, 5 is 4.6m, etc